arXiv subjects

Jia-Tao Sun

Publications and source records attributed to Jia-Tao Sun.

14 recordsLinked to original sources

arXiv2024

Enforced symmetry breaking for anomalous valley Hall effect in two-dimensional hexagonal lattices

The anomalous valley Hall effect (AVHE) is a pivotal phenomenon that allows for the exploitation of the valley degree of freedom in materials. A general strategy for its realization and manipulation is crucial for valleytronics. Here, by considering all possible symmetries, we propose general rules for the realization and manipulation of AVHE in two-dimensional hexagonal lattices. The realization of AVHE requires breaking the enforced symmetry that is associated with different valleys or reverses the sign of Berry curvature. Further manipulation of AVHE requires asymmetry operators connecting two states with opposite signs of Berry curvature. These rules for realizing and manipulating AVHE are extendable to generic points in momentum space. Combined with first-principles calculations, we realize the controllable AVHE in four representative systems, i.e., monolayer AgCrP2Se6, CrOBr, FeCl2 and bilayer TcGeSe3. Our work provides symmetry rules for designing valleytronic materials that could facilitate the experimental detection and realistic applications.

cond-mat.mtrl-sci↗

arXiv2024

Topological Woodward-Hoffmann classification for cycloadditions in polycyclic aromatic azomethine ylides

The study of cycloaddition mechanisms is central to the fabrication of extended sp2 carbon nanostructures. Reaction modeling in this context has focused mostly on putative, energetically preferred, exothermic products with limited consideration for symmetry allowed or forbidden mechanistic effects. Here, we introduce a scheme for classifying symmetry-forbidden reaction coordinates in Woodward-Hoffmann correlation diagrams. Topological classifiers grant access to the study of reaction pathways and correlation diagrams in the same footing, for the purpose of elucidating mechanisms and products of polycyclic aromatic azomethine ylide (PAMY) cycloadditions with pentacene-yielding polycyclic aromatic hydrocarbons with an isoindole core in the solid-state and on surfaces as characterized by mass spectrometry and scanning tunneling microscopy, respectively. By means of a tight-binding reaction model and density functional theory (DFT) we find topologically-allowed pathways if a product is endothermic, and topologically-forbidden if a product is exothermic. Our work unveils topological classification as a crucial element for reaction modeling for nanographene engineering, and highlights its fundamental role in the design of cycloadditions in on-surface and solid-state chemical reactions, while underscoring that exothermic pathways can be topologically-forbidden.

physics.chem-ph↗

arXiv2023

Hybrid nodal surface and nodal line phonons in solids

Phonons have provided an ideal platform for a variety of intriguing physical states, such as non-Abelian braiding and the Haldane model. It is promising that phonons will realize the complicated nodal states accompanying unusual quantum phenomena. Here, we propose the hybrid nodal surface and nodal line (NS+NL) phonons beyond the single-genre nodal phonons. We categorize the NS+NL phonons into two- and four-band situations based on symmetry analysis and compatibility relationships. Combining database screening with first-principles calculations, we identify the ideal candidate materials for realizing all categorized NS+NL phonons. Our calculations and tight-binding models further demonstrate that the interplay between NS and NL induces unique phenomena. In space group (SG) 113, the quadratic NL acts as a hub of the Berry curvature between two NSs, generating ribbonlike surface states (SSs). In SG 128, the NS serves as the counterpart of the Weyl NL, in which NS-NL mixed topological SSs are observed. Our findings extend the scope of hybrid nodal states and enrich the phononic states in realistic materials.

cond-mat.mtrl-sci↗

arXiv2021

Database Construction for Two-Dimensional Material-Substrate Interfaces

The interfacial structures and interactions of two-dimensional (2D) materials on solid substrates are of fundamental importance for the fabrication and application of 2D materials. However, selection of a suitable solid substrate to grow 2D material, determination and control of the 2D material-substrate interface remain a big challenge due to the large diversity of possible configurations. Here, we propose a computational framework to select an appropriate substrate for epitaxial growth of 2D material and to predict possible 2D material-substrate interface structures and orientations using density functional theory calculations performed for all non-equivalent atomic structures satisfying the symmetry constraints. The approach was validated by the correct prediction of three experimentally reported 2D material-substrate interface systems with only the given information of two parent materials. Several possible interface configurations are also proposed based on this approach. We therefore construct a database that contains these interface systems and has been continuously expanding. This database serves as preliminary guidance for epitaxial growth and stabilization of new materials in experiments.

cond-mat.mtrl-sci↗

arXiv2021

Pressure-enhanced interlayer exciton in WS2/MoSe2 van der Waals heterostructure

The atomic-level vdW heterostructures have been one of the most interesting quantum material systems, due to their exotic physical properties. The interlayer coupling in these systems plays a critical role to realize novel physical observation and enrich interface functionality. However, there is still lack of investigation on the tuning of interlayer coupling in a quantitative way. A prospective strategy to tune the interlayer coupling is to change the electronic structure and interlayer distance by high pressure, which is a well-established method to tune the physical properties. Here, we construct a high-quality WS2/MoSe2 heterostructure in a DAC and successfully tuned the interlayer coupling through hydrostatic pressure. Typical photoluminescence spectra of the monolayer MoSe2 (ML-MoSe2), monolayer WS2 (ML-WS2) and WS2/MoSe2 heterostructure have been observed and it's intriguing that their photoluminescence peaks shift with respect to applied pressure in a quite different way. The intralayer exciton of ML-MoSe2 and ML-WS2 show blue shift under high pressure with a coefficient of 19.8 meV/GPa and 9.3 meV/GPa, respectively, while their interlayer exciton shows relative weak pressure dependence with a coefficient of 3.4 meV/GPa. Meanwhile, external pressure helps to drive stronger interlayer interaction and results in a higher ratio of interlayer/intralayer exciton intensity, indicating the enhanced interlayer exciton behavior. The first-principles calculation reveals the stronger interlayer interaction which leads to enhanced interlayer exciton behavior in WS2/MoSe2 heterostructure under external pressure and reveals the robust peak of interlayer exciton. This work provides an effective strategy to study the interlayer interaction in vdW heterostructures, which could be of great importance for the material and device design in various similar quantum systems.

cond-mat.str-el↗

arXiv2020

Manipulating Weyl quasiparticles by orbital-selective photoexcitation in WTe2

Optical control of structural and electronic properties of Weyl semimetals allows development of switchable and dissipationless topological devices at the ultrafast scale. An unexpected orbitial-selective photoexcitation in type-II Weyl material WTe2 is reported under linearly polarized light (LPL), inducing striking transitions among several topologically-distinct phases. The symmetry features of atomic orbitals comprising the Weyl bands result in asymmetric electronic transitions near the Weyl points, and in turn an anisotropic response of interlayer shear motion with respect to linear light polarization, when a near-infrared laser pulse is applied. Consequently, not only annihilation of Weyl quasiparticle pairs, but also increasing separation of Weyl points can be achieved, complementing existing experimental observations. Our results provide a new perspective on manipulating the singularity of Weyl nodes and coherent control of electron and lattice quantum dynamics simultaneously.

cond-mat.mtrl-sci↗

arXiv2019

Fermionic analogue of black hole radiation with a super high Hawking temperature

Measurement of gravitational Hawking radiation of black hole (BH) is prohibitive because of an extremely low Hawking temperature (TH). Here we demonstrate a fermionic analog of BH with a super high TH ~ 3 K, which is several orders of magnitude higher than previous works. We propose that Floquet-Dirac states, formed in a periodically laser driven two-dimensional black phosphorous thin film, can be designed with a spatial gradient to mimic the "gravity" felt by fermionic quasiparticles as that for a Schwarzschild BH (SBH). Quantum tunneling of electrons from a type-II Dirac cone (inside BH) to a type-I Dirac cone (outside) emits a SBH-like Hawking radiation spectrum.

cond-mat.mes-hall↗

arXiv2019

Ideal type-II Weyl phonons in wurtzite CuI

Weyl semimetals exhibitinging the topologically nontrivial touching points in electronic band dispersion of solids pave the wave way to novel electronic devices and functionalities. Here, we demonstrate the signature of topologically nontrivial Weyl points (WPs) in phonon dispersion of solids through a first-principles investigations. ofT noncentrosymmetric wurtzite CuI (cuprous iodide at high temperature). These type-II phononic WP in phonon dispersion of wurtzite CuI is manifested in noncentrosymmetric wurtzite CuI by six pairs of the nontrivial touching points in the k_z=0.0 plane. The ideal WPs in phonon dispersion are completely isolated from bulk phonon continuum, are different distinct from many type-II WPs in electronic band dispersion of solids associated with the overlapping band states. The opposite chirality of Weyl phonon nodes with quantized Berry curvature are utilized forproduces Weyl phonon Hall effect, in analogous analogy towith valley Hall effect of electrons. Such ideal type-II Weyl phonons are phase is readily observable in experiment, and could provideing a unique platform to study novel thermal transport properties different distinct from that in type-I Weyl phonons phase.

cond-mat.mes-hall↗

arXiv2019

Orbital design of topological insulators from two-dimensional semiconductors

Two-dimensional (2D) materials have attracted much recent attention because they exhibit various distinct intrinsic properties/functionalities, which are, however, usually not interchangeable. Interestingly, here we propose a generic approach to convert 2D semiconductors, which are amply abundant, to 2D topological insulators (TIs), which are less available, via selective atomic adsorption and strain engineering. The approach is underlined by an orbital design principle that involves introducing an extrinsic s-orbital state into the intrinsic sp-bands of a 2D semiconductor, so as to induce s-p band inversion for a TI phase, as demonstrated by tight-binding model analyses. Remarkably, based on first-principles calculations, we apply this approach to convert the semiconducting monolayer CuS and CuTe into a TI by adsorbing Na and K respectively with a proper s-level energy, and CuSe into a TI by adsorbing a mixture of Na and K with a tuned s-level energy or by adsorbing either Na or K on a strained CuSe with a tuned p-level valence band edge. Our findings open a new door to the discovery of TIs by a predictive materials design, beyond finding a preexisting 2D TI.

cond-mat.mtrl-sci↗

arXiv2019

Spin-Orientation Dependent Topological States in Two-Dimensional Antiferromagnetic NiTl$_2$S$_4$ Monolayers

The topological states of matters arising from the nontrivial magnetic configuration provide a better understanding of physical properties and functionalities of solid materials. Such studies benefit from the active control of spin orientation in any solid, which is yet known to rarely take place in the two-dimensional (2D) limit. Here we demonstrate by the first-principles calculations that spin-orientation dependent topological states can appear in the geometrically frustrated monolayer antiferromagnet. Different topological states including quantum anomalous Hall (QAH) effect and time-reversal-symmetry (TRS) broken quantum spin Hall (QSH) effect can be obtained by changing spin orientation in the NiTl2S4 monolayer. Remarkably, the dilated nc-AFM NiTl2S4 monolayer gives birth to the QAH effect with hitherto reported largest number of quantized conducting channels (Chern number C = -4) in 2D materials. Interestingly, under tunable chemical potential, the nc-AFM NiTl2S4 monolayer hosts a novel state supporting the coexistence of QAH and TRS broken QSH effects with a Chern number C = 3 and spin Chern number C_s = 1. This work manifests a promising concept and material realization toward topological spintronics in 2D antiferromagnets by manipulating its spin degree of freedom.

cond-mat.mes-hall↗

arXiv2019

Engineering Dirac states in graphene: Coexisting type-I and type-II Floquet-Dirac fermions

The coupling of monochromatic light fields and solids introduces nonequilibrium Floquet states, offering opportunities to create and explore new topological phenomena. Using combined first-principles and Floquet analysis we show that one can freely engineer Floquet-Dirac fermions (FDFs) in graphene by tuning the frequency and intensity of linearly polarized light. Not only type-II FDFs are created, but they also coexist with type-I FDFs near the Fermi level. Intriguingly, novel topologically nontrivial edge states connecting type-I and type-II Floquet-Dirac points emerge in photodriven graphene, providing an ideal channel to realize electron transport between the two types of Dirac states. Simulating time- and angle-resolved photoelectron spectroscopy suggests that the new coexisting state of type-I and type-II fermions is experimentally accessible. This work implies that a rich FDF phenomenon can be engineered in atomically thin graphene, hinting for developments of novel optoelectronic and quantum computing devices.

cond-mat.str-el↗

arXiv2018

Screening magnetic two-dimensional atomic crystals with nontrivial electronic topology

To date only a few two-dimensional (2D) magnetic crystals were experimentally confirmed, such as CrI3 and CrGeTe3, all with very low Curie temperatures (TC). High-throughput first-principles screening over a large set of materials yields 89 magnetic monolayers including 56 ferromagnetic (FM) and 33 antiferromagnetic compounds. Among them, 24 FM monolayers are promising candidates possessing TC higher than that of CrI3. High TC monolayers with fascinating electronic phases are identified: (i) quantum anomalous and valley Hall effects coexist in a single material RuCl3 or VCl3, leading to a valley-polarized quantum anomalous Hall state; (ii) TiBr3, Co2NiO6 and V2H3O5 are revealed to be half-metals. More importantly, a new type of fermion dubbed type-II Weyl ring is discovered in ScCl. Our work provides a database of 2D magnetic materials, which could guide experimental realization of high-temperature magnetic monolayers with exotic electronic states for future spintronics and quantum computing applications.

cond-mat.mtrl-sci↗

arXiv2017

Photoinduced topological phase transitions in strained black phosphorus

Photoinduced topological phase transitions (TPTs) in black phosphorous (BP) under compressive strain were investigated by combining Floquet theory and first-principles calculations. Intriguing photo-dressed electronic states including Floquet-Dirac semimetals and Floquet topological insulators have been identified, which can be feasibly engineered by changing the direction, intensity and frequency of incident laser. Remarkably, tunable TPT from type-I to type-II Floquet-Dirac fermions can be realized by irradiating circularly polarized laser (CPL), with an origin rooted in optical Stark effect. Furthermore, the photoinduced Floquet-Dirac phases is shown to host topological surface states that exhibit nonequilibrium electron transport in a direction locked by the helicity of CPL. This work provides useful guidance for experimental observation of Floquet TPTs, and extends optoelectrionic applications of BP to nonequilibrium regime.

cond-mat.mtrl-sci↗

arXiv2016

Magnetic Dirac Fermions and Chern Insulator Supported on Pristine Silicon Surface

Emergence of ferromagnetism in non-magnetic semiconductors is strongly desirable, especially in topological materials thanks to the possibility to achieve quantum anomalous Hall effect. Based on first-principles calculations, we propose that for Si thin film grown on metal substrate, the pristine Si(111)-root3xroot3 surface with a spontaneous weak reconstruction has a strong tendency of ferromagnetism and nontrivial topological properties, characterized by spin polarized Dirac-fermion surface states. In contrast to conventional routes relying on introduction of alien charge carriers or specially patterned substrates, the spontaneous magnetic order and spin-orbit coupling on the pristine silicon surface together gives rise to quantized anomalous Hall effect with a finite Chern number C=-1. This work suggests exciting opportunities in silicon-based spintronics and quantum computing free from alien dopants or proximity effects.

cond-mat.mes-hall↗