Anisotropy is an important feature of layered materials,and a large anisotropy is usually related to the two-dimensional charac teristics.We investigated the anisotropy of the layered transition metal dicalcogenide 2H...Anisotropy is an important feature of layered materials,and a large anisotropy is usually related to the two-dimensional charac teristics.We investigated the anisotropy of the layered transition metal dicalcogenide 2H-NbSe_(2)in the superconducting and charge density wave(CDW)states using magnetotransport measurements.In the superconducting state,the normalized H_(c2)^(‖c)/H_(p)is independent of the thickness of 2H-NbSe_(2),while H_(c2)^(‖ab)/H_p increases significantly with decreasing thickness,where H_p is the Pauli limiting magnetic field and H_(c2)^(‖c)anu H_(c2)^(‖ab)are the upper critical fields in the c and ab directions,respectively.It is found that the superconducting anisotropy parameterγH_(c2)=H_(c2)^(‖ab)/H_(c2)^(‖c)increases with reduction in the thickness of 2H-NbSe_(2).In the CDW state,the angular(θ)dependence of magnetoresistance,R(H,θ)scales with H(cos^(2)θ+γ_(CDW)^(-2)sin^(2)θ)^(1/2),which decreases with increasing temperature and disappears at about 40 K.It is found that the CDW anisotropy parameterγ_(CDW)is much larger than the effective mass anisotropy but does not change a lot for ultrathin and bulk samples.Our results suggest the existence of three-dimensional superconductivity and quasi-two dimensional CDWs in bulk 2H-NbSe_(2).展开更多
A new photon-in/photon-out endstation at beamline 02B02 of the Shanghai Synchrotron Radiation Facility for studying the electronic structure of energy materials has been constructed and fully opened to users.The endst...A new photon-in/photon-out endstation at beamline 02B02 of the Shanghai Synchrotron Radiation Facility for studying the electronic structure of energy materials has been constructed and fully opened to users.The endstation has the capability to perform soft x-ray absorption spectroscopy in total electron yield and total fluorescence yield modes simultaneously.The photon energy ranges from 40 eV to 2000 eV covering the K-edge of most low Z-elements and the L-edge of 3d transition-metals.The new self-designed channeltron detector allows us to achieve good fluorescence signals at the low photon flux.In addition,we synchronously collect the signals of a standard reference sample and a gold mesh on the upstream to calibrate the photon energy and monitor the beam fluctuation,respectively.In order to cross the pressure gap,in situ gas and liquid cells for soft x-ray absorption spectroscopy are developed to study the samples under realistic working conditions.展开更多
We demonstrate a photon-counting chirped amplitude modulation(CAM) light detection and ranging(lidar) system incorporating a superconducting nanowire single-photon detector(SNSPD) and operated at a wavelength of 1550 ...We demonstrate a photon-counting chirped amplitude modulation(CAM) light detection and ranging(lidar) system incorporating a superconducting nanowire single-photon detector(SNSPD) and operated at a wavelength of 1550 nm.The distance accuracy of the lidar system was determined by the CAM bandwidth and signal-to-noise ratio(SNR) of an intermediate frequency(IF) signal. Owing to a short dead time(10 ns) and negligible dark count rate(70 Hz) of the SNSPD, the obtained IF signal attained an SNR of 42 d B and the direct distance accuracy was improved to 3 mm when the modulation bandwidth of the CAM signal was 240 MHz and the modulation period was 1 ms.展开更多
Recently,by intercalating organic ions into bulk FeSe superconductors,two kinds of layered FeSe-based superconductors[(TBA)xFeSe and(CTA)xFeSe]with superconducting transition temperatures(Tc)above 40 K have been disco...Recently,by intercalating organic ions into bulk FeSe superconductors,two kinds of layered FeSe-based superconductors[(TBA)xFeSe and(CTA)xFeSe]with superconducting transition temperatures(Tc)above 40 K have been discovered.Due to the large interlayer distance(~15A),these new layered superconductors have a large resistivity anisotropy analogous to bismuth-based cuprate superconductors.Moreover,remarkable pseudogap behavior well above Tcis revealed by nuclear magnetic resonance(NMR)measurements on77Se nuclei,suggesting a preformed pairing scenario similar to that of cuprates.Here,we report another new kind of organic-ion-intercalated FeSe superconductor,(PY)xFeSe,with a reduced interlayer distance(~10A)compared to(TBA)xFeSe and(CTA)xFeSe.By performing77Se NMR and transport measurements,we observe a similar pseudogap behavior well above Tcof~40 K and a large resistivity anisotropy of~10~4 in(PY)xFeSe.All these facts strongly support a universal pseudogap behavior in these layered FeSe-based superconductors with quasi-two-dimensional electronic structures.展开更多
Superconducting nanowire single-photon detectors(SNSPDs) have attracted considerable attention owing to their excellent detection performance;however, the underlying physics of the detection process is still unclear.I...Superconducting nanowire single-photon detectors(SNSPDs) have attracted considerable attention owing to their excellent detection performance;however, the underlying physics of the detection process is still unclear.In this study, we investigate the wavelength dependence of the intrinsic detection efficiency(IDE) for NbN SNSPDs.We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm.Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510–1700 nm are obtained.From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted.The results exhibit clear nonlinear energy–current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs.Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.展开更多
The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging(ULF MRI)based on the superconducting quantum interference device(SQUID). The shielded room is effective to attenuate ...The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging(ULF MRI)based on the superconducting quantum interference device(SQUID). The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio(SNR) and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses(SE) of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m×1.5 m×2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance(NMR) signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields.展开更多
The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials.For layered superconductors,the vortex pinning can be enhanced...The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials.For layered superconductors,the vortex pinning can be enhanced by a strong interlayer interaction in accompany with a suppression of superconducting anisotropy,which remains to be investigated in iron based superconductors(FeSCs)with the layered structure.Here,based on the transport and magnetic torque measurements,we experimentally investigate the vortex pinning in two bilayer FeSCs,CaKFe_(4)As_(4)(Fe1144)and KCa_(2)Fe_(4)As4F_(2)(Fe12442),and compare their superconducting anisotropyγ.While the anisotropyγ≈3 for Fe1144 is much smaller thanγ≈15 in Fe12442 around Tc,a higher flux pinning energy as evidenced by a higher critical current density is found in Fe1144,as compared with the case of Fe12442.In combination with the literature data of Ba_(0.72)K_(0.28)Fe2As_(2) and Nd Fe As_(O0.82)F_(0.18),we reveal an anti-correlation between the pinning energy and the superconducting anisotropy in these Fe SCs.Our results thus suggest that the interlayer interaction can not be neglected when considering the vortex pinning in Fe SCs.展开更多
The maximum velocity of a mobile vortex in movement is generally limited by the phenomenon of flux-flow instability(FFI),which necessitates weak vortex pinning and fast heat removal from non-equilibrium electrons.We h...The maximum velocity of a mobile vortex in movement is generally limited by the phenomenon of flux-flow instability(FFI),which necessitates weak vortex pinning and fast heat removal from non-equilibrium electrons.We here demonstrate exfoliations and nano-fabrications of Bi_(2)Sr_(2)Ca_(2)Cu_(3)O_(10+δ) crystalline nanostrips,which possess a rather weak pinning volume of vortices,relatively low resistivity,and large normal electron diffusion coefficient.The deduced vortex velocity in Bi_(2)Sr_(2)Ca_(2)Cu_(3)O_(10+δ) crystalline nanostrips can be up to 300 km/s near the superconducting transition temperature,well above the speed of sound.The observed vortex velocity is an order of magnitude faster than that of conventional superconducting systems,representing a perfect platform for exploration of ultra-fast vortex matter and a good candidate for fabrications of superconducting nanowire single photon detectors or superconducting THz modulator.展开更多
The proximity effect to reduce the transition temperature of a superconducting film is frequently used in transitionedge sensors. Here, we develop these transition-edge sensors using Mo/Au/Au tri-layer films to detect...The proximity effect to reduce the transition temperature of a superconducting film is frequently used in transitionedge sensors. Here, we develop these transition-edge sensors using Mo/Au/Au tri-layer films to detect soft x-rays. They are equipped with an overhanging photon absorber. We reduce the fabrication complexity by integrating the sensor patterning with the tri-layer film formation. We determine the electro-thermal parameters of the sensors through a series of resistance vs. temperature and current vs. voltage measurements. We also demonstrate their energy-resolving capability by using a55Fe radioactive x-ray source. The best energy resolution was approximately 6.66 eV at 5.9 keV, with a theoretical count rate of 500 Hz.展开更多
Superconducting quantum interference devices(SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors(TESs). The linear flux range is an important parameter for SQUID amplifiers...Superconducting quantum interference devices(SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors(TESs). The linear flux range is an important parameter for SQUID amplifiers, especially those controlled by high-bandwidth digital flux-locked-loop circuits. A large linear flux range conduces to accurately measuring the input signal and also increasing the multiplexing factor in the time-division multiplexed(TDM) readout scheme of the TES array. In this work, we report that the linear flux range of an SQUID can be improved by using self-feedback effect. When the SQUID loop is designed to be asymmetric, a voltage-biased SQUID shows an asymmetric current–flux(I–Φ) response curve. The linear flux range is improved along the I–Φ curve with a shallow slope. The experimental results accord well with the numerical simulations. The asymmetric SQUID will be able to serve as a building block in the development of the TDM readout systems for large TES arrays.展开更多
Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolutio...Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism,with the combination of angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory calculations,we investigate how band dispersions change with the increase of lattice distortions.In particular,we focus on the electronic states around M point,where the van Hove singularities are expected to play crucial roles in the CDW transition.Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M point,which is associated with the 3D lattice modulations.Our studies reveal that this“splitting”can be connected to the two van Hove singularities at k_(z)=0 and k_(z)=π/c in the normal states.When the electronic system enters into the CDW state,both van Hove singularities move down.Such novel properties are important for understanding of the CDW transition.展开更多
In the last few years, charge order and its entanglement with superconductivity are under hot debate in high-Tc community due to the new progress on charge order in high-Tc cuprate superconductors YBa2Cu3O6+x. Here, w...In the last few years, charge order and its entanglement with superconductivity are under hot debate in high-Tc community due to the new progress on charge order in high-Tc cuprate superconductors YBa2Cu3O6+x. Here, we will briefly introduce the experimental status of this field and mainly focus on the experimental progress of high-field nuclear magnetic resonance(NMR) study on charge order in YBa2Cu3O6+x. The pioneering high-field NMR work in YBa2Cu3O6+x sets a new stage for studying charge order which has become a ubiquitous phenomenon in high-Tc cuprate superconductors.展开更多
Rapid single flux quantum(RSFQ)circuits are a kind of superconducting digital circuits,having properties of a natural gate-level pipelining synchronous sequential circuit,which demonstrates high energy efficiency and ...Rapid single flux quantum(RSFQ)circuits are a kind of superconducting digital circuits,having properties of a natural gate-level pipelining synchronous sequential circuit,which demonstrates high energy efficiency and high throughput advantage.We find that the high-throughput and high-speed performance of RSFQ circuits can take the advantage of a hardware implementation of the encryption algorithm,whereas these are rarely applied to this field.Among the available encryption algorithms,the advanced encryption standard(AES)algorithm is an advanced encryption standard algorithm.It is currently the most widely used symmetric cryptography algorithm.In this work,we aim to demonstrate the SubByte operation of an AES-128 algorithm using RSFQ circuits based on the SIMIT Nb0_(3) process.We design an AES S-box circuit in the RSFQ logic,and compare its operational frequency,power dissipation,and throughput with those of the CMOS-based circuit post-simulated in the same structure.The complete RSFQ S-box circuit costs a total of 42237 Josephson junctions with nearly 130 Gbps throughput under the maximum simulated frequency of 16.28 GHz.Our analysis shows that the frequency and throughput of the RSFQ-based S-box are about four times higher than those of the CMOS-based S-box.Further,we design and fabricate a few typical modules of the S-box.Subsequent measurements demonstrate the correct functioning of the modules in both low and high frequencies up to 28.8 GHz.展开更多
The performance of a superconducting quantum interference device(SQUID) gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupl...The performance of a superconducting quantum interference device(SQUID) gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupled flux threading a magnetometer obtained by Wikswo, we studied how the gradiometer performance parameters, including the current dipole sensitivity, spatial resolution and signal-to-noise ratio(SNR), are affected by its pick-up coil via Mat Lab simulation.Depending on the simulation results, the optimal pick-up coil design region for a certain gradiometer can be obtained.To verify the simulation results, we designed and fabricated several first-order gradiometers based on the weakly damped SQUID with different pick-up coils by applying superconducting connection. The experimental measurements were conducted on a simple current dipole in a magnetically shielding room. The measurement results are well in coincidence with the simulation ones, indicating that the simulation model is useful in specific pick-up coil design.展开更多
Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices.For epitaxially grown graphene,the pr...Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices.For epitaxially grown graphene,the process conditions and the microstructures are strongly dependent on various substrate materials with different lattice constants and interface energies.Utilizing angle-resolved photoemission spectroscopy,here we report an investigation of the electronic structure of single-crystalline graphene grown on Cu/Ni(111)alloy film by chemical vapor deposition.With a relatively low growth temperature,graphene on Cu/Ni(111)exhibits a Dirac cone-like dispersion comparable to that of graphene grown on Cu(111).The linear dispersions forming Dirac cone are as wide as 2 e V,with the Fermi velocity of approximately 1.1×10^6 m/s.Dirac cone opens a gap of approximately 152 meV at the binding energy of approximately 304 meV.Our findings would promote the study of engineering of graphene on different substrate materials.展开更多
Recently, 5d transition metal iridates have been reported as promising materials for the manufacture of exotic quantum states. Apart from the semimetallic ground states that have been observed, perovskite SrIrO_3 is a...Recently, 5d transition metal iridates have been reported as promising materials for the manufacture of exotic quantum states. Apart from the semimetallic ground states that have been observed, perovskite SrIrO_3 is also predicted to have a lattice-symmetrically protected topological state in the(110) plane due to its strong spin–orbit coupling and electron correlation. Compared with non-polar(001)-SrIrO_3, the especial polarity of(110)-SrIrO_3 undoubtedly adds the difficulty of fabrication and largely impedes the research on its surface states. Here, we have successfully synthesized high-quality(110)-SrIrO_3 thin films on(110)-SrTiO_3 substrates by reactive molecular beam epitaxy for the first time. Both reflection high-energy electron diffraction patterns and x-ray diffraction measurements suggest the expected orientation and outstanding crystallinity. A(1 × 2) surface reconstruction driven from the surface instability, the same as that reported in(110)-SrTiO_3, is observed. The electric transport measurements uncover that(110)-SrIrO_3 exhibits a more prominent semimetallic property in comparison to(001)-SrIrO_3.展开更多
A cold preamplifier based on superconducting quantum interference devices(SQUIDs)is currently the preferred readout technology for the low-noise transition edge sensor(TES).In this work,we have designed and fabricated...A cold preamplifier based on superconducting quantum interference devices(SQUIDs)is currently the preferred readout technology for the low-noise transition edge sensor(TES).In this work,we have designed and fabricated a series SQUID array(SSA)amplifier for the TES detector readout circuit.In this SSA amplifier,each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers,and an on-chip low pass filter(LPF)as a radiofrequency(RF)choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells.In addition,a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation.The measured results show smooth V-Φcharacteristics and a swing voltage that increases linearly with increasing SQUID cell number N.A white flux noise level as low as 0.28μφ;/Hz;is achieved at 0.1 K,corresponding to a low current noise level of 7 pA/Hz;.We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.展开更多
The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped i...The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.展开更多
Superconductivity at the 2D limit shows emergent novel quantum phenomena, including anomalously enhanced H_(c2),quantum metallic states and quantum Griffiths singularity, which has attracted much attention in the fiel...Superconductivity at the 2D limit shows emergent novel quantum phenomena, including anomalously enhanced H_(c2),quantum metallic states and quantum Griffiths singularity, which has attracted much attention in the field of condensed matter physics. In this article, we focus on new advances in quasi-2D superconductors in the bulk phase using an organic molecular electrochemical intercalation method. The enhanced superconductivity and emergent pseudogap behavior in these quasi-2D superconductors are summarized with a further prospect.展开更多
Characterization of Fermi surface of the BaSn3 superconductor(Tc~ 4.4K)by de Haas–van Alphen(dHvA)effect measurement reveals its non-trivial topological properties.Analysis of non-zero Berry phase is supported by the...Characterization of Fermi surface of the BaSn3 superconductor(Tc~ 4.4K)by de Haas–van Alphen(dHvA)effect measurement reveals its non-trivial topological properties.Analysis of non-zero Berry phase is supported by the ab initio calculations,which reveals a type-II Dirac point setting and tilting along the high symmetric K–H line of the Brillouin zone,about 0.13 eV above the Fermi level,and other two type-I Dirac points on the high symmetric Г–A direction,but slightly far below the Fermi level.The results demonstrate BaSn3 as an excellent example hosting multiple Dirac fermions and an outstanding platform for studying the interplay between nontrivial topological states and superconductivity.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574338 and 12074038)NSAF(Grant No.U1530402)。
文摘Anisotropy is an important feature of layered materials,and a large anisotropy is usually related to the two-dimensional charac teristics.We investigated the anisotropy of the layered transition metal dicalcogenide 2H-NbSe_(2)in the superconducting and charge density wave(CDW)states using magnetotransport measurements.In the superconducting state,the normalized H_(c2)^(‖c)/H_(p)is independent of the thickness of 2H-NbSe_(2),while H_(c2)^(‖ab)/H_p increases significantly with decreasing thickness,where H_p is the Pauli limiting magnetic field and H_(c2)^(‖c)anu H_(c2)^(‖ab)are the upper critical fields in the c and ab directions,respectively.It is found that the superconducting anisotropy parameterγH_(c2)=H_(c2)^(‖ab)/H_(c2)^(‖c)increases with reduction in the thickness of 2H-NbSe_(2).In the CDW state,the angular(θ)dependence of magnetoresistance,R(H,θ)scales with H(cos^(2)θ+γ_(CDW)^(-2)sin^(2)θ)^(1/2),which decreases with increasing temperature and disappears at about 40 K.It is found that the CDW anisotropy parameterγ_(CDW)is much larger than the effective mass anisotropy but does not change a lot for ultrathin and bulk samples.Our results suggest the existence of three-dimensional superconductivity and quasi-two dimensional CDWs in bulk 2H-NbSe_(2).
基金Project supported by the National Natural Science Foundation of China(Grant No.11227902)as part of NSFC ME2 beamline project,Science and Technology Commission of Shanghai Municipality,China(Grant No.14520722100)the National Natural Science Foundation of China(Grant Nos.11905283 and U1632269)
文摘A new photon-in/photon-out endstation at beamline 02B02 of the Shanghai Synchrotron Radiation Facility for studying the electronic structure of energy materials has been constructed and fully opened to users.The endstation has the capability to perform soft x-ray absorption spectroscopy in total electron yield and total fluorescence yield modes simultaneously.The photon energy ranges from 40 eV to 2000 eV covering the K-edge of most low Z-elements and the L-edge of 3d transition-metals.The new self-designed channeltron detector allows us to achieve good fluorescence signals at the low photon flux.In addition,we synchronously collect the signals of a standard reference sample and a gold mesh on the upstream to calibrate the photon energy and monitor the beam fluctuation,respectively.In order to cross the pressure gap,in situ gas and liquid cells for soft x-ray absorption spectroscopy are developed to study the samples under realistic working conditions.
基金Project supported by National Key R&D Program of China(Grant No.2017YFA0304000)the National Natural Science Foundation of China(NSFC)(Grant Nos.61501442 and 61671438)the Joint Research Fund in Astronomy(U1631240)under Cooperative Agreement between the NSFC and Chinese Academy of Sciences(CAS)
文摘We demonstrate a photon-counting chirped amplitude modulation(CAM) light detection and ranging(lidar) system incorporating a superconducting nanowire single-photon detector(SNSPD) and operated at a wavelength of 1550 nm.The distance accuracy of the lidar system was determined by the CAM bandwidth and signal-to-noise ratio(SNR) of an intermediate frequency(IF) signal. Owing to a short dead time(10 ns) and negligible dark count rate(70 Hz) of the SNSPD, the obtained IF signal attained an SNR of 42 d B and the direct distance accuracy was improved to 3 mm when the modulation bandwidth of the CAM signal was 240 MHz and the modulation period was 1 ms.
基金supported by the National Natural Science Foundation of China(Grant Nos.11888101 and 12034004)the National Key R&D Program of China(Grant No.2017YFA0303000)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)。
文摘Recently,by intercalating organic ions into bulk FeSe superconductors,two kinds of layered FeSe-based superconductors[(TBA)xFeSe and(CTA)xFeSe]with superconducting transition temperatures(Tc)above 40 K have been discovered.Due to the large interlayer distance(~15A),these new layered superconductors have a large resistivity anisotropy analogous to bismuth-based cuprate superconductors.Moreover,remarkable pseudogap behavior well above Tcis revealed by nuclear magnetic resonance(NMR)measurements on77Se nuclei,suggesting a preformed pairing scenario similar to that of cuprates.Here,we report another new kind of organic-ion-intercalated FeSe superconductor,(PY)xFeSe,with a reduced interlayer distance(~10A)compared to(TBA)xFeSe and(CTA)xFeSe.By performing77Se NMR and transport measurements,we observe a similar pseudogap behavior well above Tcof~40 K and a large resistivity anisotropy of~10~4 in(PY)xFeSe.All these facts strongly support a universal pseudogap behavior in these layered FeSe-based superconductors with quasi-two-dimensional electronic structures.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFA0304000)the National Natural Science Foundation of China(Grant Nos.61671438 and 61827823)+2 种基金the Science and Technology Commission of Shanghai Municipality,China(Grant No.16JC1400402)Program of Shanghai Academic/Technology Research Leader,China(Grant No.18XD1404600)the Joint Research Fund in Astronomy(Grant No.U1631240)under Cooperative Agreement between the NSFC and the Chinese Academy of Sciences
文摘Superconducting nanowire single-photon detectors(SNSPDs) have attracted considerable attention owing to their excellent detection performance;however, the underlying physics of the detection process is still unclear.In this study, we investigate the wavelength dependence of the intrinsic detection efficiency(IDE) for NbN SNSPDs.We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm.Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510–1700 nm are obtained.From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted.The results exhibit clear nonlinear energy–current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs.Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.
基金Project supported in part by the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04020200)in part by the National Natural Science Foundation of China(Grant No.11204339)
文摘The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging(ULF MRI)based on the superconducting quantum interference device(SQUID). The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio(SNR) and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses(SE) of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m×1.5 m×2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance(NMR) signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields.
基金Project supported by the National Natural Science Foundation of China(Grant No.11574338)the National Natural Science Foundation of China–China Academy of Engineering Physics NSAF Joint Fund(Grant No.U1530402)+4 种基金supported by the Superconducting Electronics Facility(SELF)of Shanghai Institute of Microsystem and Information Technology.The work at IOPCAS was supported by the National Key Research and Development Program of China(Grant No.2018YFA0704200)the National Natural Science Foundation of China(Grant Nos.11822411 and 11961160699)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(Grant No.XDB25000000)the Youth Innovation Promotion Association of CAS(Grant No.2016004)。
文摘The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials.For layered superconductors,the vortex pinning can be enhanced by a strong interlayer interaction in accompany with a suppression of superconducting anisotropy,which remains to be investigated in iron based superconductors(FeSCs)with the layered structure.Here,based on the transport and magnetic torque measurements,we experimentally investigate the vortex pinning in two bilayer FeSCs,CaKFe_(4)As_(4)(Fe1144)and KCa_(2)Fe_(4)As4F_(2)(Fe12442),and compare their superconducting anisotropyγ.While the anisotropyγ≈3 for Fe1144 is much smaller thanγ≈15 in Fe12442 around Tc,a higher flux pinning energy as evidenced by a higher critical current density is found in Fe1144,as compared with the case of Fe12442.In combination with the literature data of Ba_(0.72)K_(0.28)Fe2As_(2) and Nd Fe As_(O0.82)F_(0.18),we reveal an anti-correlation between the pinning energy and the superconducting anisotropy in these Fe SCs.Our results thus suggest that the interlayer interaction can not be neglected when considering the vortex pinning in Fe SCs.
基金supporting high quality of post growth treatment Bi_(2)Sr_(2)Ca_(2)Cu_(3)O_(10+δ)single crystalssupported by the National Key Research and Development Program of China(Grant No.2017YFA0304000)+4 种基金the National Natural Science Foundation of China(Grant Nos.61971408 and 61827823)Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)Shanghai Rising-Star Program(Grant No.20QA1410900)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant Nos.2020241 and 2021230)the Natural Science Foundation of Shanghai(Grant No.19ZR1467400)。
文摘The maximum velocity of a mobile vortex in movement is generally limited by the phenomenon of flux-flow instability(FFI),which necessitates weak vortex pinning and fast heat removal from non-equilibrium electrons.We here demonstrate exfoliations and nano-fabrications of Bi_(2)Sr_(2)Ca_(2)Cu_(3)O_(10+δ) crystalline nanostrips,which possess a rather weak pinning volume of vortices,relatively low resistivity,and large normal electron diffusion coefficient.The deduced vortex velocity in Bi_(2)Sr_(2)Ca_(2)Cu_(3)O_(10+δ) crystalline nanostrips can be up to 300 km/s near the superconducting transition temperature,well above the speed of sound.The observed vortex velocity is an order of magnitude faster than that of conventional superconducting systems,representing a perfect platform for exploration of ultra-fast vortex matter and a good candidate for fabrications of superconducting nanowire single photon detectors or superconducting THz modulator.
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFA0304000)the Shanghai Municipal Science and Technology Major Project (Grant No. 2017SHZDZX02)+2 种基金China National Space Administration (CNSA) (Grant No. D050104)the grant for low energy gamma-ray detection research based on SQUID techniquesupported by the Superconducting Electronics Facility (SELF) of Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences。
文摘The proximity effect to reduce the transition temperature of a superconducting film is frequently used in transitionedge sensors. Here, we develop these transition-edge sensors using Mo/Au/Au tri-layer films to detect soft x-rays. They are equipped with an overhanging photon absorber. We reduce the fabrication complexity by integrating the sensor patterning with the tri-layer film formation. We determine the electro-thermal parameters of the sensors through a series of resistance vs. temperature and current vs. voltage measurements. We also demonstrate their energy-resolving capability by using a55Fe radioactive x-ray source. The best energy resolution was approximately 6.66 eV at 5.9 keV, with a theoretical count rate of 500 Hz.
基金Project supported by the Fund from China National Space Administration (CNSA) (Grant No. D050104)the Fund for Low Energy Gamma Ray Detection Research Based on SQUID Techniquethe Superconducting Electronics Facility (SELF) of Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences。
文摘Superconducting quantum interference devices(SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors(TESs). The linear flux range is an important parameter for SQUID amplifiers, especially those controlled by high-bandwidth digital flux-locked-loop circuits. A large linear flux range conduces to accurately measuring the input signal and also increasing the multiplexing factor in the time-division multiplexed(TDM) readout scheme of the TES array. In this work, we report that the linear flux range of an SQUID can be improved by using self-feedback effect. When the SQUID loop is designed to be asymmetric, a voltage-biased SQUID shows an asymmetric current–flux(I–Φ) response curve. The linear flux range is improved along the I–Φ curve with a shallow slope. The experimental results accord well with the numerical simulations. The asymmetric SQUID will be able to serve as a building block in the development of the TDM readout systems for large TES arrays.
基金supported by the National Key R&D Program of China (Grant No.2017YFA0402901)the National Natural Science Foundation of China (Grant No.U2032153)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDB25000000)the Users with Excellence Program of Hefei Science Center of the Chinese Academy of Sciences (Grant No.2021HSC-UE004)。
文摘Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism,with the combination of angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory calculations,we investigate how band dispersions change with the increase of lattice distortions.In particular,we focus on the electronic states around M point,where the van Hove singularities are expected to play crucial roles in the CDW transition.Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M point,which is associated with the 3D lattice modulations.Our studies reveal that this“splitting”can be connected to the two van Hove singularities at k_(z)=0 and k_(z)=π/c in the normal states.When the electronic system enters into the CDW state,both van Hove singularities move down.Such novel properties are important for understanding of the CDW transition.
基金Project partially supported by the National Natural Science Foundation of China(Grant Nos.11522434 and U1532145)the Recruitment Program of Global Experts,Chinathe Chinese Academy of Sciences Hundred Talent Program
文摘In the last few years, charge order and its entanglement with superconductivity are under hot debate in high-Tc community due to the new progress on charge order in high-Tc cuprate superconductors YBa2Cu3O6+x. Here, we will briefly introduce the experimental status of this field and mainly focus on the experimental progress of high-field nuclear magnetic resonance(NMR) study on charge order in YBa2Cu3O6+x. The pioneering high-field NMR work in YBa2Cu3O6+x sets a new stage for studying charge order which has become a ubiquitous phenomenon in high-Tc cuprate superconductors.
基金This work was supported by the National Natural Science Foundation of China(Grant No.92164101)the National Natural Science Foundation of China(Grant No.62171437)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA18000000)Shanghai Science and Technology Committee(Grant No.21DZ1101000)the National Key R&D Program of China(Grant No.2021YFB0300400).
文摘Rapid single flux quantum(RSFQ)circuits are a kind of superconducting digital circuits,having properties of a natural gate-level pipelining synchronous sequential circuit,which demonstrates high energy efficiency and high throughput advantage.We find that the high-throughput and high-speed performance of RSFQ circuits can take the advantage of a hardware implementation of the encryption algorithm,whereas these are rarely applied to this field.Among the available encryption algorithms,the advanced encryption standard(AES)algorithm is an advanced encryption standard algorithm.It is currently the most widely used symmetric cryptography algorithm.In this work,we aim to demonstrate the SubByte operation of an AES-128 algorithm using RSFQ circuits based on the SIMIT Nb0_(3) process.We design an AES S-box circuit in the RSFQ logic,and compare its operational frequency,power dissipation,and throughput with those of the CMOS-based circuit post-simulated in the same structure.The complete RSFQ S-box circuit costs a total of 42237 Josephson junctions with nearly 130 Gbps throughput under the maximum simulated frequency of 16.28 GHz.Our analysis shows that the frequency and throughput of the RSFQ-based S-box are about four times higher than those of the CMOS-based S-box.Further,we design and fabricate a few typical modules of the S-box.Subsequent measurements demonstrate the correct functioning of the modules in both low and high frequencies up to 28.8 GHz.
基金Project supported by the Key Project of Shanghai Zhangjiang National Innovation Demonstration Zone of the Special Development Fund,China(Grant No.2015-JD-C104-060)the National Natural Science Foundation of China(Grant No.61741122)
文摘The performance of a superconducting quantum interference device(SQUID) gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupled flux threading a magnetometer obtained by Wikswo, we studied how the gradiometer performance parameters, including the current dipole sensitivity, spatial resolution and signal-to-noise ratio(SNR), are affected by its pick-up coil via Mat Lab simulation.Depending on the simulation results, the optimal pick-up coil design region for a certain gradiometer can be obtained.To verify the simulation results, we designed and fabricated several first-order gradiometers based on the weakly damped SQUID with different pick-up coils by applying superconducting connection. The experimental measurements were conducted on a simple current dipole in a magnetically shielding room. The measurement results are well in coincidence with the simulation ones, indicating that the simulation model is useful in specific pick-up coil design.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51772317,11604356,and 11704394)
文摘Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices.For epitaxially grown graphene,the process conditions and the microstructures are strongly dependent on various substrate materials with different lattice constants and interface energies.Utilizing angle-resolved photoemission spectroscopy,here we report an investigation of the electronic structure of single-crystalline graphene grown on Cu/Ni(111)alloy film by chemical vapor deposition.With a relatively low growth temperature,graphene on Cu/Ni(111)exhibits a Dirac cone-like dispersion comparable to that of graphene grown on Cu(111).The linear dispersions forming Dirac cone are as wide as 2 e V,with the Fermi velocity of approximately 1.1×10^6 m/s.Dirac cone opens a gap of approximately 152 meV at the binding energy of approximately 304 meV.Our findings would promote the study of engineering of graphene on different substrate materials.
基金Project supported by the National Key Research and Development Program of the MOST of China(Grant No.2016YFA0300204)the National Key Basic Research Program of China(Grant No.2015CB654901)+2 种基金the National Natural Science Foundation of China(Grant Nos.11574337,11227902,11474147,and11704394)Shanghai Sailing Program(Grant No.17YF1422900)the Award for Outstanding Member in Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘Recently, 5d transition metal iridates have been reported as promising materials for the manufacture of exotic quantum states. Apart from the semimetallic ground states that have been observed, perovskite SrIrO_3 is also predicted to have a lattice-symmetrically protected topological state in the(110) plane due to its strong spin–orbit coupling and electron correlation. Compared with non-polar(001)-SrIrO_3, the especial polarity of(110)-SrIrO_3 undoubtedly adds the difficulty of fabrication and largely impedes the research on its surface states. Here, we have successfully synthesized high-quality(110)-SrIrO_3 thin films on(110)-SrTiO_3 substrates by reactive molecular beam epitaxy for the first time. Both reflection high-energy electron diffraction patterns and x-ray diffraction measurements suggest the expected orientation and outstanding crystallinity. A(1 × 2) surface reconstruction driven from the surface instability, the same as that reported in(110)-SrTiO_3, is observed. The electric transport measurements uncover that(110)-SrIrO_3 exhibits a more prominent semimetallic property in comparison to(001)-SrIrO_3.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFA0304003)。
文摘A cold preamplifier based on superconducting quantum interference devices(SQUIDs)is currently the preferred readout technology for the low-noise transition edge sensor(TES).In this work,we have designed and fabricated a series SQUID array(SSA)amplifier for the TES detector readout circuit.In this SSA amplifier,each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers,and an on-chip low pass filter(LPF)as a radiofrequency(RF)choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells.In addition,a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation.The measured results show smooth V-Φcharacteristics and a swing voltage that increases linearly with increasing SQUID cell number N.A white flux noise level as low as 0.28μφ;/Hz;is achieved at 0.1 K,corresponding to a low current noise level of 7 pA/Hz;.We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0303000 and 2016YFA0300201)the National Natural Science Foundation of China(Grant No.11888101)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000).
文摘The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB25000000)the National Natural Science Foundation of China (Grant No. 11888101)+2 种基金the National Key R&D Program of China (Grant No. 2017YFA0303001)the Anhui Initiative in Quantum Information Technologies, China (Grant No. AHY160000)the Key Research Program of Frontier Sciences, CAS (Grant No. QYZDYSSW-SLH021)。
文摘Superconductivity at the 2D limit shows emergent novel quantum phenomena, including anomalously enhanced H_(c2),quantum metallic states and quantum Griffiths singularity, which has attracted much attention in the field of condensed matter physics. In this article, we focus on new advances in quasi-2D superconductors in the bulk phase using an organic molecular electrochemical intercalation method. The enhanced superconductivity and emergent pseudogap behavior in these quasi-2D superconductors are summarized with a further prospect.
基金Supported by the National Natural Science Foundation of China(Grant No.11874264)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA18000000)+3 种基金the Starting Grant of Shanghai Tech University,the Shenzhen Peacock Team Plan(Grant No.KQTD20170809110344233)the Bureau of Industry and Information Technology of Shenzhen through the Graphene Manufacturing Innovation Center(Grant No.201901161514)the Key Scientific Research Projects of Higher Institutions in Henan Province(19A140018)Analytical Instrumentation Center,SPST,Shanghai Tech University(Grant No.SPST-AIC10112914).
文摘Characterization of Fermi surface of the BaSn3 superconductor(Tc~ 4.4K)by de Haas–van Alphen(dHvA)effect measurement reveals its non-trivial topological properties.Analysis of non-zero Berry phase is supported by the ab initio calculations,which reveals a type-II Dirac point setting and tilting along the high symmetric K–H line of the Brillouin zone,about 0.13 eV above the Fermi level,and other two type-I Dirac points on the high symmetric Г–A direction,but slightly far below the Fermi level.The results demonstrate BaSn3 as an excellent example hosting multiple Dirac fermions and an outstanding platform for studying the interplay between nontrivial topological states and superconductivity.
