Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition t...Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition to piezoelectricity,ferroelectricity,and flexoelectricity,this study reports the observation of ferroelasticity using piezoelectric force microscopy(PFM) and scanning transmission electron microscopy(STEM).The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field.Switching of the retentive domains is observed through repeated wake-up measurements.This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.展开更多
Twisted van der Waals bilayers provide an ideal platform to study the electron correlation in solids. Of particular interest is the 30° twisted bilayer honeycomb lattice system, which possesses an incommensurate ...Twisted van der Waals bilayers provide an ideal platform to study the electron correlation in solids. Of particular interest is the 30° twisted bilayer honeycomb lattice system, which possesses an incommensurate moiré pattern,and uncommon electronic behaviors may appear due to the absence of phase coherence. Such a system is extremely sensitive to further twist and many intriguing phenomena will occur. Based on first-principles calculations we show that, for further twist near 30°, there could induce dramatically different dielectric behaviors of electron between left and right-twisted cases. Specifically, it is found that the left and right twists show suppressed and amplified dielectric response under vertical electric field, respectively. Further analysis demonstrate that such an exotic dielectric property can be attributed to the stacking dependent charge redistribution due to twist,which forms twist-dependent pseudospin textures. We will show that such pseudospin textures are robust under small electric field. As a result, for the right-twisted case, there is almost no electric dipole formation exceeding the monolayer thickness when the electric field is applied. Whereas for the left case, the system could even demonstrate negative susceptibility, i.e., the induced polarization is opposite to the applied field, which is very rare in the nature. Such findings not only enrich our understanding on moiré systems but also open an appealing route toward functional 2D materials design for electronic, optical and even energy storage devices.展开更多
Multiferroics are materials where two or more ferroic orders coexist owing to the interplay between spin, charge, lattice and orbital degrees of freedom. The explosive expansion of multiferroics literature in recent y...Multiferroics are materials where two or more ferroic orders coexist owing to the interplay between spin, charge, lattice and orbital degrees of freedom. The explosive expansion of multiferroics literature in recent years demonstrates the fast growing interest in this field. In these studies, the first-principles calculation has played a pioneer role in the experiment explanation, mechanism discovery and prediction of novel multiferroics or magnetoelectric materials. In this review, we discuss, by no means comprehensively, the extensive applications and successful achievements of first-principles approach in the study of multiferroicity, magnetoelectric effect and tunnel junctions. In particular, we introduce some our recently developed methods, e.g., the orbital selective external potential method, which prove to be powerful tools in the finding of mechanisms responsible for the intriguing phenomena occurred in multiferroics or magnetoelectric materials. We also summarize first-principles studies on three types of electric control of magnetism, which is the common goal of both spintronics and multiferroics. Our review offers in depth understanding on the origin of ferroelectricity in transition metal oxides, and the coexistence of ferroelectricity and ordered magnetism, and might be helpful to explore novel multiferroic or magnetoelectric materials in the future.展开更多
基金Project supported by the the National Key Research and Development Program of China (Grant No. 2022YFA1402902)the National Natural Science Foundation of China (Grant Nos. 12074119, 12204171, 12134003, and 12374145)+1 种基金the Chenguang Program Foundation of Shanghai Education Development Foundation and Shanghai Municipal Education Commission, ECNU (East China Normal University) Multifunctional Platform for Innovation (006)the Fundamental Research Funds for the Central Universities。
文摘Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition to piezoelectricity,ferroelectricity,and flexoelectricity,this study reports the observation of ferroelasticity using piezoelectric force microscopy(PFM) and scanning transmission electron microscopy(STEM).The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field.Switching of the retentive domains is observed through repeated wake-up measurements.This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.
基金Supported by the National Key Research and Development Program of China(Grant No.2017YFA0303403)the Shanghai Science and Technology Innovation Action Plan(Grant No.19JC1416700)+1 种基金the National Natural Science Foundation of China(Grant No.11774092)the ECNU Multifunctional Platform for Innovation。
文摘Twisted van der Waals bilayers provide an ideal platform to study the electron correlation in solids. Of particular interest is the 30° twisted bilayer honeycomb lattice system, which possesses an incommensurate moiré pattern,and uncommon electronic behaviors may appear due to the absence of phase coherence. Such a system is extremely sensitive to further twist and many intriguing phenomena will occur. Based on first-principles calculations we show that, for further twist near 30°, there could induce dramatically different dielectric behaviors of electron between left and right-twisted cases. Specifically, it is found that the left and right twists show suppressed and amplified dielectric response under vertical electric field, respectively. Further analysis demonstrate that such an exotic dielectric property can be attributed to the stacking dependent charge redistribution due to twist,which forms twist-dependent pseudospin textures. We will show that such pseudospin textures are robust under small electric field. As a result, for the right-twisted case, there is almost no electric dipole formation exceeding the monolayer thickness when the electric field is applied. Whereas for the left case, the system could even demonstrate negative susceptibility, i.e., the induced polarization is opposite to the applied field, which is very rare in the nature. Such findings not only enrich our understanding on moiré systems but also open an appealing route toward functional 2D materials design for electronic, optical and even energy storage devices.
基金supported by the National Basic Research Program of China (2014CB921104, 2013CB922301)the National Natural Science Foundation of China (61125403)+2 种基金Program of Shanghai Subject Chief ScientistFundamental Research Funds for the central universities (ECNU)Hang-Chen Ding acknowledges the support from ECNU-PY2012001
文摘Multiferroics are materials where two or more ferroic orders coexist owing to the interplay between spin, charge, lattice and orbital degrees of freedom. The explosive expansion of multiferroics literature in recent years demonstrates the fast growing interest in this field. In these studies, the first-principles calculation has played a pioneer role in the experiment explanation, mechanism discovery and prediction of novel multiferroics or magnetoelectric materials. In this review, we discuss, by no means comprehensively, the extensive applications and successful achievements of first-principles approach in the study of multiferroicity, magnetoelectric effect and tunnel junctions. In particular, we introduce some our recently developed methods, e.g., the orbital selective external potential method, which prove to be powerful tools in the finding of mechanisms responsible for the intriguing phenomena occurred in multiferroics or magnetoelectric materials. We also summarize first-principles studies on three types of electric control of magnetism, which is the common goal of both spintronics and multiferroics. Our review offers in depth understanding on the origin of ferroelectricity in transition metal oxides, and the coexistence of ferroelectricity and ordered magnetism, and might be helpful to explore novel multiferroic or magnetoelectric materials in the future.
