arXiv subjects

L. Miao

Publications and source records attributed to L. Miao.

9 recordsLinked to original sources

arXiv2023

Spontaneous supercrystal formation during a strain-engineered metal-insulator transition

Mott metal-insulator transitions possess electronic, magnetic, and structural degrees of freedom promising next generation energy-efficient electronics. We report a previously unknown, hierarchically ordered state during a Mott transition and demonstrate correlated switching of functional electronic properties. We elucidate in-situ formation of an intrinsic supercrystal in a Ca2RuO4 thin film. Machine learning-assisted X-ray nanodiffraction together with electron microscopy reveal multi-scale periodic domain formation at and below the film transition temperature (TFilm ~ 200-250 K) and a separate anisotropic spatial structure at and above TFilm. Local resistivity measurements imply an intrinsic coupling of the supercrystal orientation to the material's anisotropic conductivity. Our findings add an additional degree of complexity to the physical understanding of Mott transitions, opening opportunities for designing materials with tunable electronic properties.

cond-mat.mtrl-sci↗

arXiv2020

Spin-valley locking, bulk quantum Hall effect and chiral surface state in a noncentrosymmetric Dirac semimetal BaMnSb$_2$

Spin-valley locking in the band structure of monolayers of MoS$_2$ and other group-VI dichalcogenides has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic electronic state has sparsely been seen in bulk materials. Here, we report spin-valley locking in a bulk Dirac semimetal BaMnSb$_2$. We find valley and spin are inherently coupled for both valence and conduction bands in this material. This is revealed by comprehensive studies using first principle calculations, tight-binding and effective model analyses, angle-resolved photoemission spectroscopy and quantum transport measurements. Moreover, this material also exhibits a stacked quantum Hall effect. The spin-valley degeneracy extracted from the plateau height of quantized Hall resistivity is close to 2. This result, together with the observed Landau level spin splitting, further confirms the spin-valley locking picture. In the extreme quantum limit, we have also observed a two-dimensional chiral metal at the side surface, which represents a novel topological quantum liquid. These findings establish BaMnSb$_2$ as a rare platform for exploring coupled spin and valley physics in bulk single crystals and accessing 3D interacting topological states.

cond-mat.mtrl-sci↗

arXiv2020

Inhomogeneous ferromagnetism mimics signatures of the topological Hall effect in SrRuO$_3$ films

Topological transport phenomena in magnetic materials are a major topic of current condensed matter research. One of the most widely studied phenomena is the ``topological Hall effect'' (THE), which is generated via spin-orbit interactions between conduction electrons and topological spin textures such as skyrmions. We report a comprehensive set of Hall effect and magnetization measurements on epitaxial films of the prototypical ferromagnetic metal SrRuO$_3$ the magnetic and transport properties of which were systematically modulated by varying the concentration of Ru vacancies. We observe Hall effect anomalies that closely resemble signatures of the THE, but a quantitative analysis demonstrates that they result from inhomogeneities in the ferromagnetic magnetization caused by a non-random distribution of Ru vacancies. As such inhomogeneities are difficult to avoid and are rarely characterized independently, our results call into question the identification of topological spin textures in numerous prior transport studies of quantum materials, heterostructures, and devices. Firm conclusions regarding the presence of such textures must meet stringent conditions such as probes that couple directly to the non-collinear magnetization on the atomic scale.

cond-mat.str-el↗

arXiv2017

Antiferromagnetic order in epitaxial FeSe films on SrTiO3

Single monolayer FeSe film grown on Nb-doped SrTiO$_3$(001) substrate shows the highest superconducting transition temperature (T$_C$ $\sim$ 100 K) among the iron-based superconductors (iron-pnictide), while T$_C$ of bulk FeSe is only $\sim$ 8 K. Antiferromagnetic spin fluctuations were believed to be crucial in iron-pnictides, which has inspired several proposals to understand the FeSe/SrTiO$_3$ system. Although bulk FeSe does not show the antiferromagnetic order, calculations suggest that the parent FeSe/SrTiO$_3$ films are AFM. Experimentally, due to lacking of direct probe, the magnetic state of FeSe/SrTiO$_3$ films remains mysterious. Here, we report the direct evidences of the antiferromagnetic order in the parent FeSe/SrTiO$_3$ films by the magnetic exchange bias effect measurements. The phase transition temperature is $\geq$ 140 K for single monolayer film. The AFM order disappears after electron doping.

cond-mat.supr-con↗

arXiv2012

The electronic properties of graphene on metal modified SiO2 substrate

Based on first principles calculation, the electronic properties of graphene on metal (Ti, Ca, Ni, Mn, Co, Fe, Cr, K) modified SiO2 substrate have been studied. The results of binding energies supported graphene indicate that the metal atoms are adsorbed more stably on O surface than on Si surface of SiO2 substrate, and graphene is adsorbed very stably on metal modified substrate. The band structures of supported graphene are similar with that of suspending graphene when deposited on Co modified SiO2 surface, but change obviously with the effect of decorated Fe atoms. Interesting, a semi-metal band structure with a 1-2 eV gap in spin-up state will occur on the magnetic atoms decorated surface.

cond-mat.mes-hall↗

arXiv2012

Thermal properties of bended graphene nanoribbons from nonequilibrium molecular dynamics

We have studied the thermal properties of bended graphene nanoribbons (GNRs) using nonequilibrium molecular dynamics simulations. The thermal conductivity of bended GNRs shows a non-monotonous relationship with the bending angle, due to the influence of chirality and Kapitza conductance. When a constant heat flux is allowed to flow, sharp temperature jump is observed at the inside corner. On the basis of the magnitude of these jumps, we have computed the Kapitza conductance as a function of bending angles. Besides, modification of the inside corner is applied to change the ability of heat transfer at the bending place. Equations to obtain the thermal conductivity of the whole structure from the thermal conductivity of each part have been derived to guide us for GNR-interconnected circuits design.

cond-mat.mes-hall↗

arXiv2011

Half-Metallicity of Wurtzite NiO and ZnO/NiO (0001) Interface: First Principles Simulation

First principles calculations based on density functional theory are performed to investigate the structural, electronic and magnetic properties of wurtzite ZnO/NiO (0001) interface. By using DFT+U method we discover that the half-metallic behavior of wurtzite NiO (w-NiO) retains in the ZnO/NiO (0001) interface. Through analyses of density of state, charge population and magnetic moments, we find the half-metallicity is weakened around the interface but interface effect is quite localized. More over the interface system keeps a ferromagnetic ground state as bulk w-NiO does. Based on the simulations of epitaxial growth case, w-NiO is predicted to be a promising candidate of electrode for the injection of spin polarized currents.

cond-mat.mtrl-sci↗

arXiv2011

Electronic properties of edge-functionalized zigzag graphene nanoribbons on SiO2 substrate-v2

Based on first-principles calculations, electronic properties of edge-functionalized zigzag graphene nanoribbons (ZGNRs) on SiO2 substrate are presented. Metallic or semiconducting properties of ZGNRs are revealed due to various interactions between edge-hydrogenated ZGNRs and different SiO2 (0001) surfaces. Bivalent functional groups decorating ZGNRs serve as the bridge between active edges of ZGNRs and SiO2. These functional groups stabilize ZGNRs on substrate, as well as modify the edge states of ZGNRs and further affect their electronic properties. Band gaps are opened owing to edge states destruction and distorted lattice in ZGNRs.

cond-mat.mtrl-sci↗

arXiv2011

Electronic properties of edge-functionalized zigzag graphene nanoribbons on SiO2 substrate

cond-mat.mtrl-sci↗