Stochastic resonance is a phenomenon in which adding random noise to a system enhances the detection or transmission of a weak signal. It occurs when the noise interacts with the system's nonlinearity, thus improv...Stochastic resonance is a phenomenon in which adding random noise to a system enhances the detection or transmission of a weak signal. It occurs when the noise interacts with the system's nonlinearity, thus improving signal-to-noise ratio and increasing sensitivity. Although parametric resonances in an atomic spinor Bose-Einstein condensate have been investigated, the question of whether one can observe stochastic resonance in such a system persists. In this study we propose a scheme for generating stochastic resonance in a cavity-spinor Bose-Einstein condensate coupling system. We demonstrate stochastic resonance through numerical calculations using the mean-field theory and truncated Wigner approximation methods. Furthermore, the characteristics of the system's response to noise and periodic signals are studied in detail. This study unravels a new scheme for observing stochastic resonance via linking atomic many-body physics with cavity quantum electrodynamics.展开更多
Spontaneous time-reversal symmetry breaking plays an important role in studying strongly correlated unconventional superconductors.When two superconducting gap functions with different symmetries compete,the relative ...Spontaneous time-reversal symmetry breaking plays an important role in studying strongly correlated unconventional superconductors.When two superconducting gap functions with different symmetries compete,the relative phase channel(θ_(-)≡θ_(1)-θ_(2))exhibits an Ising-type Z_(2) symmetry due to the second order Josephson coupling,where θ_(1,2) are the phases of two gap functions.In contrast,the U(1) symmetry in the channel of θ_(+)≡(θ_(1)+θ_(2))/2 is intact.The phase locking,i.e.,ordering of θ_(-),can take place in the phase fluctuation regime before the onset of superconductivity,i.e.,when θ_(+) is disordered.If θ_(-) is pinned at ±π/2,then timereversal symmetry is broken in the normal state,otherwise,if θ_(-)=0,or,π,rotational symmetry is broken,leading to a nematic normal state.In both cases,the order parameters possess a 4-fermion structure beyond the scope of mean-field theory,which can be viewed as a high order symmetry breaking.We employ an effective two-component XY-model assisted by a renormalization group analysis to address this problem.As a natural by-product,we also find the other interesting intermediate phase corresponds to ordering of θ_+ but with θ_(-)disordered.This is the quartetting,or,charge-4e,superconductivity,which occurs above the low temperature Z_(2)-breaking charge-2e superconducting phase.Our results provide useful guidance for studying novel symmetry breaking phases in strongly correlated superconductors.展开更多
The near-Earth(within~100 pc)supernova explosions in the past several million years can cause the global deposition of radioactive elements(e.g.,60Fe)on Earth.The remnants of such supernovae are too old to be easily i...The near-Earth(within~100 pc)supernova explosions in the past several million years can cause the global deposition of radioactive elements(e.g.,60Fe)on Earth.The remnants of such supernovae are too old to be easily identified.It is therefore of great interest to search for million-year-old near-Earth neutron stars or black holes,the products of supernovae.However,neutron stars and black holes are challenging to find even in our Solar neighbourhood if they are not radio pulsars or X-ray/γ-ray emitters.Here we report the discovery of one of the nearest(127.7±0.3 pc)neutron star candidates in a detached single-lined spectroscopic binary LAMOST J235456.73+335625.9(hereafter J2354).Utilizing the time-resolved ground-based spectroscopy and space photometry,we find that J2354 hosts an unseen compact object with M_(inv)being 1.4-1.6 M_(⊙).The follow-up Swift ultraviolet(UV)and X-ray observations suggest that the UV and X-ray emission is produced by the visible star rather than the compact object.Hence,J2354 probably harbours a neutron star rather than a hot ultramassive white dwarf.Two-hour exceptionally sensitive radio follow-up observations with Five-hundred-meter Aperture Spherical radio Telescope fail to reveal any pulsating radio signals at the 6σflux upper limit of 12.5μJy.Therefore,the neutron star candidate in J2354 can only be revealed via our time-resolved observations.Interestingly,the distance between J2354 and our Earth can be as close as~50 pc around 2.5 million years(Myrs)ago,as revealed by the Gaia kinematics.Our discovery demonstrates a promising way to unveil the hidden near-Earth neutron stars in binaries by exploring the optical time domain,thereby facilitating understanding of the metal-enrichment history in our Solar neighbourhood.展开更多
The Hot Universe Baryon Surveyor(HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectr...The Hot Universe Baryon Surveyor(HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectroscopy and large field of view,the HUBS mission will be uniquely qualified to measure the physical and chemical properties of the hot gas in the interstellar medium, the circumgalactic medium, the intergalactic medium, and the intracluster medium. These measurements will be valuable for two key scientific goals of HUBS, namely to unravel the AGN and stellar feedback physics that governs the formation and evolution of galaxies, and to probe the baryon budget and multi-phase states from galactic to cosmological scales. In addition to these two goals, the HUBS mission will also help us solve some problems in the fields of galaxy clusters, AGNs, difuse X-ray backgrounds, supernova remnants, and compact objects. This paper discusses the perspective of advancing these fields using the HUBS telescope.展开更多
We present an ab-initio study of monolayer BaBiO_(3) focused on how to harness the insulator-metal transition through suppression of the charge density wave(CDW)phase in this material.After the determination of the mo...We present an ab-initio study of monolayer BaBiO_(3) focused on how to harness the insulator-metal transition through suppression of the charge density wave(CDW)phase in this material.After the determination of the most stable structure for the freestanding monolayer,we investigate the effects of an applied electric field and of charge doping on the electronic properties of the system.Our results show that external electric fields of the order of 0.1-0.3 V/A are able to stabilize the metallic phase,destroy the CDW phase and,in addition,lead to a metallic metastable phase.On this same footing,we show that hole doping could also suppress the CDW phase and drive the system toward a metallic phase with large electron-phonon coupling.To this end,we also study the dependence of the electron-phonon coupling on hole-doping concentration and show that this could drive the onset of superconductivity.Indeed,low-dimensional BaBiO3 is an extremely flexible material with electronic properties that could be tuned using different and possibly combined external tools such as electric fields and charge doping,paving the way to achieve effective control on the transition from the CDW,to the metallic and then superconducting phase.展开更多
Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity...Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity has been discovered in Nd_(0.8)Sr_(0.2)NiO_(2)films.Herein,we report structural,electronic transport,magnetic,and thermodynamic characterizations of single crystals of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6).La_(3)Ni_(2)O_(7)is metallic with mixed Ni^(2+)and Ni^(3+)valent states.Resistivity measurements yield two transition-like kinks at~110 and 153 K.The kink at 153 K is further revealed from magnetization and specific heat measurements,indicative of the formation of charge and spin density waves.La_(3)Ni_(2)O_(6)single crystals obtained from the topochemical reduction of La_(3)Ni_(2)O_(7)are insulating and show an anomaly at~176 K on magnetic susceptibility.The transition-like behaviors of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6)are analogous to those observed in La_(4)Ni_(3)O_(10) and La_(4)Ni_(3)O_(8),suggesting that charge and spin density waves are a common feature in the ternary La-Ni-O system with mixed-valent states of nickel.展开更多
Halide perovskites(ABX_(3)), as promising candidates for solar cell photovoltaic devices, have recently attracted increasing research interest [1-3], but many issues remain unsolved for their practical applications. O...Halide perovskites(ABX_(3)), as promising candidates for solar cell photovoltaic devices, have recently attracted increasing research interest [1-3], but many issues remain unsolved for their practical applications. One such issue is their poor stability, which largely reduces device lifetime and efficiency [4]. In recent decades, using inorganic ions or organic molecules for replacement or alloying the A-site atoms in halide perovskites has improved thermodynamic stability to some extent.展开更多
Time-reversal symmetry breaking has been intensively studied in condensed matter physics and photonics for non-reciprocal devices, signal routing and source protection [1]. The introduction of time-reversal asymmetry ...Time-reversal symmetry breaking has been intensively studied in condensed matter physics and photonics for non-reciprocal devices, signal routing and source protection [1]. The introduction of time-reversal asymmetry into quantum walks has led to new behaviors and applications of quantum walks.展开更多
Nonclassical states, with features impossible to be described via the classical theory, are important resources for many quantum technologies. For example, nonclassical optical states play a pivotal role in the develo...Nonclassical states, with features impossible to be described via the classical theory, are important resources for many quantum technologies. For example, nonclassical optical states play a pivotal role in the development of quantum metrology both theoretically and experimentally. Thus certifying the boundary between classical and nonclassical states has attracted a wide range of interest.展开更多
According to the Lorentz reciprocity theorem, an electromagnetic wave has the reciprocity of bi-directional transmission through ordinary time inversion invariant media. In some special systems(such as optical isolato...According to the Lorentz reciprocity theorem, an electromagnetic wave has the reciprocity of bi-directional transmission through ordinary time inversion invariant media. In some special systems(such as optical isolators and annular devices), however, a transmission can be nonreciprocal, and such transmission is typical so far. Despite the critical role of quantum nonreciprocal devices in chiral quantum technology and topological photonics [1], their physical realization remains challenging.展开更多
Hidden spin polarization refers to that doubly degenerate bands protected by combined inversion and time-reversal symmetry in nonmagnetic inversion-symmetric crystals could have opposite non-zero local spin polarizati...Hidden spin polarization refers to that doubly degenerate bands protected by combined inversion and time-reversal symmetry in nonmagnetic inversion-symmetric crystals could have opposite non-zero local spin polarizations, which are spatially separated in two real-space sectors paired by the inversion symmetry. Since its first prediction from ab initio calculation, hidden spin polarization has inspired tremendous interest and has been observed experimentally due to its intriguing fundamental properties as well as the great potential for applications. Moving forward, the search for moment-dependent spin splitting has also been extended to antiferromagnets even without considering spin-orbit coupling. This paper systematically reviews recent works in this field with a focus on basic concepts and material realization. It also details several remaining bottlenecks and suggests possible avenues for future research.展开更多
Spin-lattice (SL) coupling plays an important role in spintronic applications given its effects on magnetic,ferroelectric,optical,and thermodynamic properties.Experiments and theoretical calculations have revealed a l...Spin-lattice (SL) coupling plays an important role in spintronic applications given its effects on magnetic,ferroelectric,optical,and thermodynamic properties.Experiments and theoretical calculations have revealed a large SL coupling effect in CrGeTe_(3) and CrI_(3) monolayers.However,the microscopic origin of SL coupling in these systems is still unclear.In this work,we develop a systematic method to explore the atomistic mechanism of SL coupling based on the density functional theory.We find that the first-and second-order SL couplings in ternary system CrGeTe_(3) are considerably stronger than those in binary system CrI_(3).For the first-order SL coupling,the Cr ions of the magnetic pair and Ge ions positively contribute to the strain enhancement of ferromagnetism in CrGeTe_(3).However,the Cr ions provide a negative contribution in CrI_(3).Furthermore,our tight-binding analysis suggests that the p-d hopping in CrGeTe_(3) gradually decreases with the tensile strain,rapidly enhancing the ferromagnetism under the tensile strain.The large frequency shifts in CrGeTe_(3) are caused by the large second-order exchange derivatives (one type of second-order SL coupling) of the Cr ions of the magnetic pair.展开更多
We perform the first search for an isotropic non-tensorial gravitational-wave background(GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves(NANOGrav)...We perform the first search for an isotropic non-tensorial gravitational-wave background(GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse(ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is 107 ± 7, but no statistically significant evidence for the tensor transverse, vector longitudinal, and scalar longitudinal polarization modes. The median and the 90% equal-tail amplitudes of ST mode are ■ , or equivalently the energy density parameter per logarithm frequency is ■, at frequency of 1/year.展开更多
The interplay between quantum physics and machine learning may lead to unprecedented perspectives for both fields [1]. On the one hand, ideas and techniques from machine learning, or more broadly artificial intelligen...The interplay between quantum physics and machine learning may lead to unprecedented perspectives for both fields [1]. On the one hand, ideas and techniques from machine learning, or more broadly artificial intelligence, can be exploited to tackle challenging problems in the quantum domain.展开更多
The thermoelectric effect refers to the phenomenon in which an electric voltage is directly generated from a temperature difference or vice versa.The two primary such effects are the Seebeck and the Peltier effects di...The thermoelectric effect refers to the phenomenon in which an electric voltage is directly generated from a temperature difference or vice versa.The two primary such effects are the Seebeck and the Peltier effects discovered in the early nineteenth century[1].These two effects provide the basis for functional thermoelectric devices,and are used to harvest electrical energy from waste heat or as solid-state Peltier cooler,see Figure 1(a).Here,the most challenging issue is to increase the thermoelectric figure of merit zT,which is determined by several interrelated material parameters including the Seebeck coefficient,the electrical and thermal conductivities,as well as the working temperature.展开更多
Quantum secure direct communication(QSDC)is a unique technique,which supports the secure transmission of confidential information directly through a quantum channel without the need for a secret key and for ciphertext...Quantum secure direct communication(QSDC)is a unique technique,which supports the secure transmission of confidential information directly through a quantum channel without the need for a secret key and for ciphertext.Hence this secure communication protocol fundamentally differs from its conventional counterparts.In this article,we report the first measurement-deviceindependent(MDI)QSDC protocol relying on sequences of entangled photon pairs and single photons.Explicitly,it eliminates the security loopholes associated with the measurement device.Additionally,this MDI technique is capable of doubling the communication distance of its conventional counterpart operating without using our MDI technique.We also conceive a protocol associated with linear optical Bell-basis measurements,where only two of the four Bell-basis states could be measured.When the number of qubits in a sequence reduces to 1,the MDI-QSDC protocol degenerates to a deterministic MDI quantum key distribution protocol.展开更多
We study the steady state of two coupled two-level atoms interacting with a non-equilibrium environment that consists of two heat baths at different temperatures. Specifically, we analyze four cases with respect to th...We study the steady state of two coupled two-level atoms interacting with a non-equilibrium environment that consists of two heat baths at different temperatures. Specifically, we analyze four cases with respect to the configuration about the interactions between atoms and heat baths. Using secular approximation, the conventional master equation usually neglects steady-state coherence,even when the system is coupled with a non-equilibrium environment. When employing the master equation with no secular approximation, we find that the system coherence in our model, denoted by the off-diagonal terms in the reduced density matrix spanned by the eigenvectors of the system Hamiltonian, would survive after a long-time decoherence evolution. The absolute value of residual coherence in the system relies on different configurations of interaction channels between the system and the heat baths. We find that a large steady quantum coherence term can be achieved when the two atoms are resonant. The absolute value of quantum coherence decreases in the presence of additional atom-bath interaction channels. Our work sheds new light on the mechanism of steady-state coherence in microscopic quantum systems in non-equilibrium environments.展开更多
Both the LUNA(Laboratory for Underground Nuclear Astrophysics)collaboration in Europe and the JUNA(Jinping Underground Laboratory for Nuclear Astrophysics)collaboration in China are planning to study the key reactions...Both the LUNA(Laboratory for Underground Nuclear Astrophysics)collaboration in Europe and the JUNA(Jinping Underground Laboratory for Nuclear Astrophysics)collaboration in China are planning to study the key reactions during the stellar helium burning at or close to their stellar energies in deep underground laboratories[1-3].The success of such experiments relies on the ratio of the reaction展开更多
Hypersonic vehicles,which flight at Mach numbers greater than 5,will serve as a more convenient and efficient transport tool than present subsonic airplanes for long-distance journeys in future.Typically,it only takes...Hypersonic vehicles,which flight at Mach numbers greater than 5,will serve as a more convenient and efficient transport tool than present subsonic airplanes for long-distance journeys in future.Typically,it only takes a couple of hours from Beijing to New York at hypersonic speed.Recent interest展开更多
基金supported by the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0303200)the National Natural Science Foundation of China (Grant Nos. 12074120, 12234014, 11654005, 11964014, and 12364046)+4 种基金the Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX01)the National Key Research and Development Program of China (Grant No. 2016YFA0302001)the Innovation Program of the Shanghai Municipal Education Commision (Grant No. 202101070008E00099)the Major Discipline Academic and Technical Leader Training Program of Jiangxi Province (Grant No. 20204BCJ23026)the Fundamental Research Funds for the Central Universities。
文摘Stochastic resonance is a phenomenon in which adding random noise to a system enhances the detection or transmission of a weak signal. It occurs when the noise interacts with the system's nonlinearity, thus improving signal-to-noise ratio and increasing sensitivity. Although parametric resonances in an atomic spinor Bose-Einstein condensate have been investigated, the question of whether one can observe stochastic resonance in such a system persists. In this study we propose a scheme for generating stochastic resonance in a cavity-spinor Bose-Einstein condensate coupling system. We demonstrate stochastic resonance through numerical calculations using the mean-field theory and truncated Wigner approximation methods. Furthermore, the characteristics of the system's response to noise and periodic signals are studied in detail. This study unravels a new scheme for observing stochastic resonance via linking atomic many-body physics with cavity quantum electrodynamics.
基金supported by a startup funding of UCSD and the National Science Foundation (Grant No. DMR-2238360)supported by the National Natural Science Foundation of China (Grant Nos. 12234016, and 12174317)supported by the New Cornerstone Science Foundation。
文摘Spontaneous time-reversal symmetry breaking plays an important role in studying strongly correlated unconventional superconductors.When two superconducting gap functions with different symmetries compete,the relative phase channel(θ_(-)≡θ_(1)-θ_(2))exhibits an Ising-type Z_(2) symmetry due to the second order Josephson coupling,where θ_(1,2) are the phases of two gap functions.In contrast,the U(1) symmetry in the channel of θ_(+)≡(θ_(1)+θ_(2))/2 is intact.The phase locking,i.e.,ordering of θ_(-),can take place in the phase fluctuation regime before the onset of superconductivity,i.e.,when θ_(+) is disordered.If θ_(-) is pinned at ±π/2,then timereversal symmetry is broken in the normal state,otherwise,if θ_(-)=0,or,π,rotational symmetry is broken,leading to a nematic normal state.In both cases,the order parameters possess a 4-fermion structure beyond the scope of mean-field theory,which can be viewed as a high order symmetry breaking.We employ an effective two-component XY-model assisted by a renormalization group analysis to address this problem.As a natural by-product,we also find the other interesting intermediate phase corresponds to ordering of θ_+ but with θ_(-)disordered.This is the quartetting,or,charge-4e,superconductivity,which occurs above the low temperature Z_(2)-breaking charge-2e superconducting phase.Our results provide useful guidance for studying novel symmetry breaking phases in strongly correlated superconductors.
基金supported by the National Key R&D Program of China(Grant No.2021YFA1600401)the National Natural Science Foundation of China(NSFC)(Grant Nos.11925301+10 种基金12033006)supported by the NSFC(Grant Nos.11973002,and 12322303)supported by the NSFC(Grant No.12103041)supported by the NSFC(Grant Nos.11988101,and 11933004)supported by the NSFC(Grant No.U2031117)supported by the NSFC(Grant No.12033004)supported by the NSFC(Grant No.12273029)supported by the NSFC(Grant No.12221003)supported by the NSFC(Grant No.11933008)supported by the NSFC(Grant No.12090044)supported by the NSFC(Grant Nos.12041301,and 12121003)。
文摘The near-Earth(within~100 pc)supernova explosions in the past several million years can cause the global deposition of radioactive elements(e.g.,60Fe)on Earth.The remnants of such supernovae are too old to be easily identified.It is therefore of great interest to search for million-year-old near-Earth neutron stars or black holes,the products of supernovae.However,neutron stars and black holes are challenging to find even in our Solar neighbourhood if they are not radio pulsars or X-ray/γ-ray emitters.Here we report the discovery of one of the nearest(127.7±0.3 pc)neutron star candidates in a detached single-lined spectroscopic binary LAMOST J235456.73+335625.9(hereafter J2354).Utilizing the time-resolved ground-based spectroscopy and space photometry,we find that J2354 hosts an unseen compact object with M_(inv)being 1.4-1.6 M_(⊙).The follow-up Swift ultraviolet(UV)and X-ray observations suggest that the UV and X-ray emission is produced by the visible star rather than the compact object.Hence,J2354 probably harbours a neutron star rather than a hot ultramassive white dwarf.Two-hour exceptionally sensitive radio follow-up observations with Five-hundred-meter Aperture Spherical radio Telescope fail to reveal any pulsating radio signals at the 6σflux upper limit of 12.5μJy.Therefore,the neutron star candidate in J2354 can only be revealed via our time-resolved observations.Interestingly,the distance between J2354 and our Earth can be as close as~50 pc around 2.5 million years(Myrs)ago,as revealed by the Gaia kinematics.Our discovery demonstrates a promising way to unveil the hidden near-Earth neutron stars in binaries by exploring the optical time domain,thereby facilitating understanding of the metal-enrichment history in our Solar neighbourhood.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11721303, 11821303, 11825303, 11873029, 11890693, 11973033, 11991052, 12025303, 12033004, 12041301, 12121003, 12133008, 12173018, 12192220, 12192223, 12221003, 12233001, 12233005, 12273010, 12273030, 12273057, 12011540375, and U1931140)the China Manned Space Project (Grant Nos. CMS-CSST-2021-A04, CMS-CSST-2021-A06, CMS-CSST-2021-A10, and CMS-CSST-2021-B02)+5 种基金the Ministry of Science and Technology of China through its National Key R&D Program (Grant No. 2018YFA0404502)the National SKA Program of China (Grant No. 2020SKA0120300)the National Key Research and Development Program of China (Grant No. 2022YFA1602903)the Outstanding Young and Middle-aged Science and Technology Innovation Teams from Hubei colleges and universities (Grant No. T2021026)the Young Top-notch Talent Cultivation Program of Hubei Province, the National Science Foundation (Grant Nos. AST-2107735, and AST-2219686)NASA (Grant No. 80NSSC22K0668)。
文摘The Hot Universe Baryon Surveyor(HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectroscopy and large field of view,the HUBS mission will be uniquely qualified to measure the physical and chemical properties of the hot gas in the interstellar medium, the circumgalactic medium, the intergalactic medium, and the intracluster medium. These measurements will be valuable for two key scientific goals of HUBS, namely to unravel the AGN and stellar feedback physics that governs the formation and evolution of galaxies, and to probe the baryon budget and multi-phase states from galactic to cosmological scales. In addition to these two goals, the HUBS mission will also help us solve some problems in the fields of galaxy clusters, AGNs, difuse X-ray backgrounds, supernova remnants, and compact objects. This paper discusses the perspective of advancing these fields using the HUBS telescope.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074241,11929401,52120204,and 62004043)the Science and Technology Commission of Shanghai Municipality(Grant Nos.22XD1400900,20501130600,21JC1402700,21JC1402600,and 20QA1401000)+1 种基金the Key Research Project of Zhejiang Laboratory(Grant No.2021PE0AC02)the High-Performance Computing Center,Shanghai Technical Service Center of Science and Engineering Computing,Shanghai University。
文摘We present an ab-initio study of monolayer BaBiO_(3) focused on how to harness the insulator-metal transition through suppression of the charge density wave(CDW)phase in this material.After the determination of the most stable structure for the freestanding monolayer,we investigate the effects of an applied electric field and of charge doping on the electronic properties of the system.Our results show that external electric fields of the order of 0.1-0.3 V/A are able to stabilize the metallic phase,destroy the CDW phase and,in addition,lead to a metallic metastable phase.On this same footing,we show that hole doping could also suppress the CDW phase and drive the system toward a metallic phase with large electron-phonon coupling.To this end,we also study the dependence of the electron-phonon coupling on hole-doping concentration and show that this could drive the onset of superconductivity.Indeed,low-dimensional BaBiO3 is an extremely flexible material with electronic properties that could be tuned using different and possibly combined external tools such as electric fields and charge doping,paving the way to achieve effective control on the transition from the CDW,to the metallic and then superconducting phase.
基金supported by the National Natural Science Foundation of China(Grant Nos.12174454,11904414,11904416,and U2130101)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011123)the National Key Research and Development Program of China(Grant Nos.2019YFA0705702,2020YFA0406003,2021YFA1400401,and 2021YFA0718900)。
文摘Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity has been discovered in Nd_(0.8)Sr_(0.2)NiO_(2)films.Herein,we report structural,electronic transport,magnetic,and thermodynamic characterizations of single crystals of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6).La_(3)Ni_(2)O_(7)is metallic with mixed Ni^(2+)and Ni^(3+)valent states.Resistivity measurements yield two transition-like kinks at~110 and 153 K.The kink at 153 K is further revealed from magnetization and specific heat measurements,indicative of the formation of charge and spin density waves.La_(3)Ni_(2)O_(6)single crystals obtained from the topochemical reduction of La_(3)Ni_(2)O_(7)are insulating and show an anomaly at~176 K on magnetic susceptibility.The transition-like behaviors of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6)are analogous to those observed in La_(4)Ni_(3)O_(10) and La_(4)Ni_(3)O_(8),suggesting that charge and spin density waves are a common feature in the ternary La-Ni-O system with mixed-valent states of nickel.
文摘Halide perovskites(ABX_(3)), as promising candidates for solar cell photovoltaic devices, have recently attracted increasing research interest [1-3], but many issues remain unsolved for their practical applications. One such issue is their poor stability, which largely reduces device lifetime and efficiency [4]. In recent decades, using inorganic ions or organic molecules for replacement or alloying the A-site atoms in halide perovskites has improved thermodynamic stability to some extent.
文摘Time-reversal symmetry breaking has been intensively studied in condensed matter physics and photonics for non-reciprocal devices, signal routing and source protection [1]. The introduction of time-reversal asymmetry into quantum walks has led to new behaviors and applications of quantum walks.
文摘Nonclassical states, with features impossible to be described via the classical theory, are important resources for many quantum technologies. For example, nonclassical optical states play a pivotal role in the development of quantum metrology both theoretically and experimentally. Thus certifying the boundary between classical and nonclassical states has attracted a wide range of interest.
文摘According to the Lorentz reciprocity theorem, an electromagnetic wave has the reciprocity of bi-directional transmission through ordinary time inversion invariant media. In some special systems(such as optical isolators and annular devices), however, a transmission can be nonreciprocal, and such transmission is typical so far. Despite the critical role of quantum nonreciprocal devices in chiral quantum technology and topological photonics [1], their physical realization remains challenging.
基金supported by the National Science Fund for Distinguished Young Scholars(Grant No.11925407)the National Natural Science Foundation of China(Grant No.11904359)+2 种基金the Basic Science Center Program of the National Natural Science Foundation of China(Grant No.61888102)the Key Research Program of Frontier Sciences,CAS(Grant No.ZDBSLY-JSC019)the National Key Research and Development Program of China(Grant No.2018YFB2202800)。
文摘Hidden spin polarization refers to that doubly degenerate bands protected by combined inversion and time-reversal symmetry in nonmagnetic inversion-symmetric crystals could have opposite non-zero local spin polarizations, which are spatially separated in two real-space sectors paired by the inversion symmetry. Since its first prediction from ab initio calculation, hidden spin polarization has inspired tremendous interest and has been observed experimentally due to its intriguing fundamental properties as well as the great potential for applications. Moving forward, the search for moment-dependent spin splitting has also been extended to antiferromagnets even without considering spin-orbit coupling. This paper systematically reviews recent works in this field with a focus on basic concepts and material realization. It also details several remaining bottlenecks and suggests possible avenues for future research.
基金supported by the National Natural Science Foundation of China(Grant Nos.11825403,and 11804138)the Program for Professor of Special Appointment(Eastern Scholar)+1 种基金supported by Anhui Provincial Natural Science Foundation(Grant No.1908085MA10)the Opening Foundation of State Key Laboratory of Surface Physics Fudan University(Grant No.KF2019_07)。
文摘Spin-lattice (SL) coupling plays an important role in spintronic applications given its effects on magnetic,ferroelectric,optical,and thermodynamic properties.Experiments and theoretical calculations have revealed a large SL coupling effect in CrGeTe_(3) and CrI_(3) monolayers.However,the microscopic origin of SL coupling in these systems is still unclear.In this work,we develop a systematic method to explore the atomistic mechanism of SL coupling based on the density functional theory.We find that the first-and second-order SL couplings in ternary system CrGeTe_(3) are considerably stronger than those in binary system CrI_(3).For the first-order SL coupling,the Cr ions of the magnetic pair and Ge ions positively contribute to the strain enhancement of ferromagnetism in CrGeTe_(3).However,the Cr ions provide a negative contribution in CrI_(3).Furthermore,our tight-binding analysis suggests that the p-d hopping in CrGeTe_(3) gradually decreases with the tensile strain,rapidly enhancing the ferromagnetism under the tensile strain.The large frequency shifts in CrGeTe_(3) are caused by the large second-order exchange derivatives (one type of second-order SL coupling) of the Cr ions of the magnetic pair.
基金supported by the National Key Research and Development Program of China (Grant No.2020YFC2201502)the National Natural Science Foundation of China (Grant Nos.11975019,11690021,11991052,and 12047503)+2 种基金the Key Research Program of Frontier Sciences,Chinese Academy of Sciences (Grant No.ZDBS-LY-7009)the Chinese Academy of Sciences Project for Young Scientists in Basic Research (Grant No.YSBR006)the Key Research Program of the Chinese Academy of Sciences (Grant No.XDPB15)。
文摘We perform the first search for an isotropic non-tensorial gravitational-wave background(GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse(ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is 107 ± 7, but no statistically significant evidence for the tensor transverse, vector longitudinal, and scalar longitudinal polarization modes. The median and the 90% equal-tail amplitudes of ST mode are ■ , or equivalently the energy density parameter per logarithm frequency is ■, at frequency of 1/year.
文摘The interplay between quantum physics and machine learning may lead to unprecedented perspectives for both fields [1]. On the one hand, ideas and techniques from machine learning, or more broadly artificial intelligence, can be exploited to tackle challenging problems in the quantum domain.
文摘The thermoelectric effect refers to the phenomenon in which an electric voltage is directly generated from a temperature difference or vice versa.The two primary such effects are the Seebeck and the Peltier effects discovered in the early nineteenth century[1].These two effects provide the basis for functional thermoelectric devices,and are used to harvest electrical energy from waste heat or as solid-state Peltier cooler,see Figure 1(a).Here,the most challenging issue is to increase the thermoelectric figure of merit zT,which is determined by several interrelated material parameters including the Seebeck coefficient,the electrical and thermal conductivities,as well as the working temperature.
基金supported by the National Basic Research Program of China(Grant Nos.2017YFA0303700,and 2015CB921001)the National Natural Science Foundation of China(Grant Nos.61726801,11474168,11974189,and 11474181)。
文摘Quantum secure direct communication(QSDC)is a unique technique,which supports the secure transmission of confidential information directly through a quantum channel without the need for a secret key and for ciphertext.Hence this secure communication protocol fundamentally differs from its conventional counterparts.In this article,we report the first measurement-deviceindependent(MDI)QSDC protocol relying on sequences of entangled photon pairs and single photons.Explicitly,it eliminates the security loopholes associated with the measurement device.Additionally,this MDI technique is capable of doubling the communication distance of its conventional counterpart operating without using our MDI technique.We also conceive a protocol associated with linear optical Bell-basis measurements,where only two of the four Bell-basis states could be measured.When the number of qubits in a sequence reduces to 1,the MDI-QSDC protocol degenerates to a deterministic MDI quantum key distribution protocol.
基金supported by the National Natural Science Foundation of China(Grant No.11575071)
文摘We study the steady state of two coupled two-level atoms interacting with a non-equilibrium environment that consists of two heat baths at different temperatures. Specifically, we analyze four cases with respect to the configuration about the interactions between atoms and heat baths. Using secular approximation, the conventional master equation usually neglects steady-state coherence,even when the system is coupled with a non-equilibrium environment. When employing the master equation with no secular approximation, we find that the system coherence in our model, denoted by the off-diagonal terms in the reduced density matrix spanned by the eigenvectors of the system Hamiltonian, would survive after a long-time decoherence evolution. The absolute value of residual coherence in the system relies on different configurations of interaction channels between the system and the heat baths. We find that a large steady quantum coherence term can be achieved when the two atoms are resonant. The absolute value of quantum coherence decreases in the presence of additional atom-bath interaction channels. Our work sheds new light on the mechanism of steady-state coherence in microscopic quantum systems in non-equilibrium environments.
基金the equipment research and development project of Chinese Academy of Sciences(Grant No.28Y531040)support from the National Natural Science Foundation of China(Grants Nos.11021504,11321064,11475228,and 11490564)+2 种基金the National Key Basic Research Program of China(Grants No.2016YFA0400501)the 100 Talents Program of the Chinese Academy of Sciencessupport from the National Science Foundation for Young Scientists of China(Grant No.11405228)
文摘Both the LUNA(Laboratory for Underground Nuclear Astrophysics)collaboration in Europe and the JUNA(Jinping Underground Laboratory for Nuclear Astrophysics)collaboration in China are planning to study the key reactions during the stellar helium burning at or close to their stellar energies in deep underground laboratories[1-3].The success of such experiments relies on the ratio of the reaction
基金supported by the National Natural Science Foundation of China(Grant Nos.11372324,and 11572333)the State Key Laboratory of High Temperature Gas Dynamics,Institute of Mechanics,Chinese Academy of Sciences(Grant Nos.LHD2017TC01,LHD2017MS04,and LHD2017QN03)
文摘Hypersonic vehicles,which flight at Mach numbers greater than 5,will serve as a more convenient and efficient transport tool than present subsonic airplanes for long-distance journeys in future.Typically,it only takes a couple of hours from Beijing to New York at hypersonic speed.Recent interest
