查看更多>>摘要：Based on the Gross-Pitaevskii equation,we theoretically investigate exciton Bose-Einstein condensation(BEC)in transition metal dichalcogenide monolayers(TMDC-MLs)under in-plane magnetic fields.We observe that the in-plane magnetic fields exert a strong influence on the exciton BEC wave functions in TMDC-MLs because of the mixing of the bright and dark exciton states via Zeeman effect.This leads to the brightening of the dark exciton BEC states.The competition between the dipole-dipole interactions caused by the long-range Coulomb interaction and the Zeeman effect induced by the in-plane magnetic fields can effectively regulate dark exciton BEC states.Our findings emphasize the utility of TMD-MLs as platforms for investigating collective phenomenon involving excited states.
查看更多>>摘要：Recently,high temperature(Tc～80 K)superconductivity(SC)has been discovered in La3Ni2O7(LNO)under pressure.This raises the question of whether the superconducting transition temperature Tc could be further enhanced under suitable conditions.One possible route for achieving higher Tc is element substitution.Similar SC could appear in the Fmmm phase of rare-earth(RE)R3Ni2O7(RNO,R=RE element)material series under suitable pressure.The electronic properties in the RNO materials are dominated by the Ni 3d orbitals in the bilayer NiO2 plane.In the strong coupling limit,the SC could be fully characterized by a bilayer single 3dx2-y2-orbital t-J||-J⊥ model.With RE element substitution from La to other RE element,the lattice constant of the Fmmm RNO material decreases,and the resultant electronic hopping integral increases,leading to stronger superexchanges between the 3dx2-y2 orbitals.Based on the slave-boson mean-field theory,we explore the pairing nature and the evolution of Tc in RNO materials under pressure.Consequently,it is found that the element substitution does not alter the pairing nature,i.e.,the inter-layer s-wave pairing is always favored in the superconducting RNO under pressure.However,the Tc increases from La to Sm,and a nearly doubled Tc could be realized in SmNO under pressure.This work provides evidence for possible higher Tc R3Ni2O7 materials,which may be realized in further experiments.
查看更多>>摘要：High-temperature superconductivity(HTSC)remains one of the most challenging and fascinating mysteries in condensed matter physics.Recently,superconductivity with transition temperature exceeding liquid-nitrogen temperature is discovered in La3Ni2O7 at high pressure,which provides a new platform to explore the uncon-ventional HTSC.In this work,using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation,we systematically investigate the electronic structures of La3Ni2O7 at ambient pressure.Our ex-periments are in nice agreement with ab initio calculations after considering an orbital-dependent band renor-malization effect.The strong electron correlation effect pushes a flat band of dz2 orbital component below the Fermi level(EF),which is predicted to locate right at EF under high pressure.Moreover,the dx2-y2 band shows pseudogap-like behavior with suppressed spectral weight and diminished quasiparticle peak near EF.Our findings provide important insights into the electronic structure of La3Ni2O7,which will shed light on understanding of the unconventional superconductivity in nickelates.
查看更多>>摘要：The discovery of ferroelectricity in HfO2-based materials with high dielectric constant has inspired tremendous research interest for next-generation electronic devices.Importantly,films structure and strain are key factors in exploration of ferroelectricity in fluorite-type oxide HfO2 films.Here we investigate the structures and strain-induced ferroelectric transition in different phases of few-layer HfO2 films(layer number N=1-5).It is found that HfO2 films for all phases are more stable with increasing films thickness.Among them,the Pmn21(110)-oriented film is most stable,and the films of N=4,5 occur with a P21 ferroelectric transition under tensile strain,resulting in polarization about 11.8μC/cm2 along in-plane a-axis.The ferroelectric transition is caused by the strain,which induces the displacement of Hf and O atoms on the surface to non-centrosymmetric positions away from the original paraelectric positions,accompanied by the change of surface Hf-O bond lengths.More importantly,three new stable HfO2 2D structures are discovered,together with analyses of computed electronic structures,mechanical,and dielectric properties.This work provides guidance for theoretical and experimental study of the new structures and strain-tuned ferroelectricity in freestanding HfO2 films.
查看更多>>摘要：The rapid advancement in electric vehicles and electrochemical energy storage technology has raised the demands placed on rechargeable batteries.It is essential to comprehend the operational principles and degradation mechanisms of batteries across multiple scales to propel the research on rechargeable batteries for the next generation forward.Microstructure,phase information,and lattice of energy materials in both two dimensions and three dimensions can be intuitively obtained through the utilization of x-ray imaging techniques.Additionally,x-ray imaging technology is increasingly gaining attention due to its non-destructive nature and high penetrative capability,enabling in situ experiments and multi-scale spatial resolution.In this review,we initially overview the basic principles and characteristics of several key x-ray imaging technologies.Each x-ray imaging technology is tailored to specific application scenarios.Furthermore,examples of multi-scale implementations of x-ray imaging technologies in the field of rechargeable batteries are discussed.This review is anticipated to augment the comprehension of readers for x-ray imaging techniques as well as to stimulate the development of novel concepts and approaches in rechargeable battery research.
查看更多>>摘要：About 2 percent of red clump stars are found to be the lithium-rich and thus the surface lithium increases obviously in some red clump stars.The physical mechanism of the lithium enrichment in these stars has not yet been explained satisfactorily by the evolutionary models of single stars.The flash induced internal gravity wave mixing(i.e.,IGW)could play a primary role in explaining the red clump star with lithium enrichment and it has a very significant impact on the internal structure and surface compositions of a star.Rotation can significantly increase the mixing efficiency of the internal gravity wave because the timescale for the enrichment event has been enlarged.Thermohaline mixing can explain the observed behavior of lithium on red giant stars that are more luminosity than the RGB bump.However,it has a very small effect on the diffusion of elements because its diffusion coefficient is much smaller than the one of IGW induced mixing after the core helium flash.
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