arXiv subjects

Dao-Xin Yao

Publications and source records attributed to Dao-Xin Yao.

At least 73 records · Page 4Linked to original sources

arXiv2024

The possible coexistence of superconductivity and topological electronic states in 1T-RhSeTe

Transition metal dichalcogenides (TMDs), exhibit a range of crystal structures and topological quantum states. The 1$T$ phase, in particular, shows promise for superconductivity driven by electron-phonon coupling, strain, pressure, and chemical doping. In this theoretical investigation, we explore 1$T$-RhSeTe as a novel type of TMD superconductor with topological electronic states. The optimal doping structure and atomic arrangement of 1$T$-RhSeTe are constructed. Phonon calculations validate the integrity of the constructed doping structure. The analysis of the electron-phonon coupling (EPC) using the Electron-phonon Wannier (EPW) method has confirmed the existence of a robust electron-phonon interaction in 1$T$-RhSeTe, resulting in total EPC constant $λ$ = 2.02, the logarithmic average frequency $ω_{\text{log}}$ = 3.15 meV and $T_c$ = 4.61 K, consistent with experimental measurements and indicative of its classification as a BCS superconductor. The band structure analysis revealed the presence of Dirac-like band crossing points. The topological non-trivial electronic structures of the 1$T$-RhSeTe are confirmed via the evolution of Wannier charge centers (WCCs). Collectively, these distinctive properties underscore 1$T$-RhSeTe as a possible candidate for a topological superconductor, warranting further investigation into its potential implications and applications.

cond-mat.supr-con↗

arXiv2024

Observation of in-gap states in a two-dimensional CrI2/NbSe2 heterostructure

Low-dimensional magnetic structures coupled with superconductors are promising platforms for realizing Majorana zero modes, which have potential applications in topological quantum computing. Here, we report a two-dimensional (2D) magnetic-superconducting heterostructure consisting of single-layer chromium diiodide (CrI2) on a niobium diselenide (NbSe2) superconductor. Single-layer CrI2 nanosheets, which hold antiferromagnetic (AFM) ground states by our first-principles calculations, were epitaxially grown on the layered NbSe2 substrate. Using scanning tunneling microscopy/spectroscopy, we observed robust in-gap states spatially located at the edge of the nanosheets and defect-induced zero-energy peaks inside the CrI2 nanosheets. Magnetic-flux vortices induced by an external field exhibit broken threefold rotational symmetry of pristine NbSe2 superconductor, implying the efficient modulation of the interfacial superconducting states by the epitaxial CrI2 layer. A phenomenological model suggests the existence of chiral edge states in a 2D AFM-superconducting hybrid system with an even Chern number, providing a qualitatively plausible understanding for our experimental observation.

cond-mat.supr-con↗

arXiv2024

Modulation of the Octahedral Structure and Potential Superconductivity of La$_3$Ni$_2$O$_7$ through Strain Engineering

The recent transport measurement of La$_3$Ni$_2$O$_7$ uncover a "right-triangle" shape of the superconducting dome in the pressure-temperature (P-T) phase diagram. Motivated by this, we perform theoretical first-principles studies of La$_3$Ni$_2$O$_7$ with the pressure ranging from 0 to 100 GPa. Notably, we reveal a pressure dependence of the Ni-$d_{z^2}$ electron density at the Fermi energy ($n_z^{EF}$) that highly coincides with such shape. On this basis, we further explore the electronic structure under uniaxial stress. By tracking the stress response of $n_z^{EF}$, we propose that superconductivity can be achieved by applying only about 2 GPa of compression along the c axis. The idea is further exemplified from the perspectives of lattice distortion, band structure, Fermi surface and superconducting phase coherence. We also discuss the possible charge modulation under the stress and provide an insight to the relation between n_z^EF and the superconducting Tc in La$_3$Ni$_2$O$_7$ system. Our study provides a helpful guide to the future experiment.

cond-mat.supr-con↗

arXiv2024

Magnon, doublon and quarton excitations in 2D S=1/2 trimerized Heisenberg models

We investigate the magnetic excitations of the trimerized Heisenberg models with intra-trimer interaction $J_1$ and inter-trimer interaction $J_2$ on four different two-dimensional lattices using a combination of stochastic series expansion quantum Monte Carlo (SSE QMC) and stochastic analytic continuation methods (SAC), complemented by cluster perturbation theory (CPT). These models exhibit quasi-particle-like excitations when $g=J_2/J_1$ is small, characterized by low-energy magnons, intermediate-energy doublons, and high-energy quartons. The low-energy magnons are associated with the magnetic ground states. They can be described by the linear spin wave theory (LSWT) of the effective block spin model and the original spin model. Doublons and quartons emerge from the corresponding internal excitations of the trimers with distinct energy levels, which can be effectively analyzed using perturbation theory when the ratio of exchange interactions $g$ is small. In this small $g$ regime, we observe a clear separation between the magnon and higher-energy spectra. However, as $g$ increases, these three spectra gradually merge into the magnon modes or continua. Nevertheless, the LSWT fails to provide quantitative descriptions of the higher-energy excitation bands due to significant quantum fluctuations. Notably, in the Collinear II and trimerized hexagon lattice, a broad continuum emerges above the single-magnon spectrum, originating from the quasi-1D physics due to the dilute connections between chains. Our numerical analysis of these 2D trimers yields valuable theoretical predictions and explanations for the inelastic neutron scattering (INS) spectra of 2D magnetic materials featuring trimerized lattices.

cond-mat.str-el↗

arXiv2024

Phase diagram and critical behavior of Hubbard model on the square-hexagon-octagon lattice

Employing the projective formalism of determinant quantum Monte Carlo (DQMC) simulations, we meticulously explore the ground-state phase diagram and critical behavior of the half-filled Hubbard model on a square-hexagon-octagon (SHO) lattice. This lattice, a two-dimensional (2D) structure comprising squares, hexagons, and octagons, is representative of the biphenylene network (BPN). Our findings reveal an intriguing ground-state phase diagram, featuring an antiferromagnetic (AFM) Mott insulating phase enveloped by three valence-bond solid-like (VBS-like) insulating phases. Analyzing the single-particle gap, spin gap, and single-particle spectral function, we observe that the metallic state in the noninteracting case becomes unstable under the influence of Hubbard U. This interaction drives the system into a hexagon insulating phase before transitioning into an AFM Mott insulating phase. To quantify the critical exponents, we use finite-size scaling techniques. The critical exponents of quantum critical points between the AFM Mott insulating phase and two insulating phases, plaquette insulator and ethylene insulator, closely align with the 3D O(3) universality class. However, the critical exponents of quantum critical points between the hexagon insulating phase and the AFM Mott insulating phase deviate from the 3D O(3) universality class. This deviation is a finite-size effect and can be attributed to the coupling between the fluctuations of magnetic order parameter and very low-energy fermionic excitations. Our comprehensive study not only advances the understanding of correlation effects on the SHO lattice but also sheds light on the less-explored critical exponents in weakly insulating quantum critical point.

cond-mat.str-el↗

arXiv2024

Measuring the Boundary Gapless State and Criticality via Disorder Operator

The disorder operator is often designed to reveal the conformal field theory information in quantum many-body systems. By using large-scale quantum Monte Carlo simulation, we study the scaling behavior of disorder operators on the boundary in the two-dimensional Heisenberg model on the square-octagon lattice with gapless topological edge state. In the Affleck-Kennedy-Lieb-Tasaki phase, the disorder operator is shown to hold the perimeter scaling with a logarithmic term associated with the Luttinger liquid parameter K. This effective Luttinger liquid parameter K reflects the low-energy physics and CFT for (1+1)D boundary. At bulk critical point, the effective K is suppressed but keeps finite value, indicating the coupling between the gapless edge state and bulk fluctuation. The logarithmic term numerically captures this coupling picture, which reveals the (1+1)D SU(2)1 CFT and (2+1)D O(3) CFT at boundary criticality. Our Letter paves a new way to study the exotic boundary state and boundary criticality.

cond-mat.str-el↗

arXiv2024

Normal and superconducting properties of La$_3$Ni$_2$O$_7$

This review provides a comprehensive overview of current research on the structural, electronic, and magnetic characteristics of the recently discovered high-temperature superconductor La$_3$Ni$_2$O$_7$ under high pressures. We present the experimental results for synthesizing and characterizing this material, derived from measurements of transport, thermodynamics, and various spectroscopic techniques, and discuss their physical implications. We also explore theoretical models proposed to describe the electronic structures and superconducting pairing symmetry in La$_3$Ni$_2$O$_7$, highlighting the intricate interplay between electronic correlations and magnetic interactions. Despite these advances, challenges remain in growing high-quality samples free of extrinsic phases and oxygen deficiencies and in developing reliable measurement tools for determining diamagnetism and other physical quantities under high pressures. Further investigations in these areas are essential to deepening our understanding of the physical properties of La$_3$Ni$_2$O$_7$ and unlocking its superconducting pairing mechanism.

cond-mat.supr-con↗

arXiv2024

Orbital-Dependent Electron Correlation in Double-Layer Nickelate La3Ni2O7

The latest discovery of high temperature superconductivity near 80K in La3Ni2O7 under high pressure has attracted much attention. Many proposals are put forth to understand the origin of superconductivity.The determination of electronic structures is a prerequisite to establish theories to understand superconductivity in nickelates but is still lacking. Here we report our direct measurement of the electronic structures of La3Ni2O7 by high-resolution angle resolved photoemission spectroscopy. The Fermi surface and band structures of La3Ni2O7 are observed and compared with the band structure calculations. Strong electron correlations are revealed which are orbital- and momentum dependent. A flat band is formed from the Ni-3dz2 orbitals around the zone corner which is ~50meV below the Fermi level and exhibits the strongest electron correlation. In many theoretical proposals, this band is expected to play the dominant role in generating superconductivity in La3Ni2O7. Our observations provide key experimental information to understand the electronic structure and origin of high temperature superconductivity in La3Ni2O7.

cond-mat.supr-con↗

arXiv2024

Superconducting Klein and anti-Klein tunneling in Weyl junctions

Klein tunneling is an old topic in relativistic quantum physics, and has been observed recently in graphene where massless particles reside. Here, we propose a new heterostructure platform for Klein tunneling to occur, which consists of a Weyl-semimetal-based normal state/superconductor (NS) junction. By developing a Blonder-Tinkham-Klapwijk-like theory, we find that Klein tunneling occurs at normal incidence, which can lead to differential conductance doubling. If the (single) Weyl semimeltals are replaced by double Weyl semimetals, anti-Klein tunneling will take place of Klein tunneling. Our work provides a theoretical guide for the detection of (anti-)Klein tunneling in three-dimensional chiral NS junctions.

cond-mat.mes-hall↗

arXiv2024

Trilayer multi-orbital models of $\mathrm{La_{4}Ni_{3}O_{10}}$

Recently, the discovery of superconductivity in Ruddlesden-Popper (RP) $\mathrm{La_4Ni_3O_{10}}$ under pressure has further expanded the realm of nickelate-based superconductor family. In this paper, we performed a first-principle study of $\mathrm{La_4Ni_3O_{10}}$ for both $P2_1/a$ phase at ambient pressure and $I4/mmm$ phase at high pressure, with $U$=0, 3.5\ eV. Our results confirmed the characteristic upward shift of Ni-$d_{z^2}$ bonding band under pressure. Moreover, our analysis of electronic spectrum and orbital occupancy unveil the dynamic mechanism of electronic reconstructions under pressure, embedded in a critical dual effect. Based on our results, we further proposed a trilayer two-orbital model by performing Wannier downfolding on Ni-$e_g$ orbitals. Our model reveals four Fermi surface sheets with $α,β,β^\prime,γ$ pockets, bearing resemblance to that of bilayer $\mathrm{La_3Ni_2O_7}$. According to the model, our calculated spin susceptibility under random phase approximation shows that $d_{x^2-y^2}$ orbital is also important for the magnetic fluctuation in RP series. Finally, a high energy sixteen-orbital model with direct $dp,pp$ hoppings is proposed, which implies that $\mathrm{La_4Ni_3O_{10}}$ also lies in charge-transfer picture within Zaanen-Sawatzky-Allen scheme. Our exposition of electronic reconstructions and multi-orbital models shed light on theoretical electronic correlation study and experimental exploration of lower pressure superconductor in RP series.

cond-mat.supr-con↗

arXiv2024

Demonstrating the wormhole mechanism of the entanglement spectrum via a perturbed boundary

The Li-Haldane conjecture is one of the most famous conjectures in physics and opens a new research area in the quantum entanglement and topological phase. Although a lot of theoretical and numerical works have confirmed the conjecture in topological states with bulk-boundary correspondence, the cases with gapped boundary and the systems in high dimension are widely unknown. What is the valid scope of the Li-Haldane conjecture? Via the newly developed quantum Monte Carlo scheme, we are now able to extract the large-scale entanglement spectrum (ES) and study its relation with the edge energy spectrum generally. Taking the two-dimensional Affleck-Kennedy-Lieb-Tasaki model with a tunable boundary on the square-octagon lattice as an example, we find several counterexamples which cannot be explained by the Li-Haldane conjecture; e.g., the low-lying entanglement spectrum does not always show similar behaviors as the energy spectrum on the virtual boundary, and sometimes the ES resembles the energy spectrum of the edge even if it is gapped. Finally, we demonstrate that the newly proposed wormhole mechanism on the path integral of a reduced density matrix is the formation principle of the general ES. We find that the Li-Haldane conjecture is a particular case in some limit of the wormhole picture while all the examples of the conjecture we have studied can totally be explained within the wormhole mechanism framework. Our results provide important evidence for demonstrating that the wormhole mechanism is the fundamental principle to explain the ES.

cond-mat.str-el↗

arXiv2024

A spin-rotation mechanism of Einstein-de Haas effect based on a ferromagnetic disk

Spin-rotation coupling (SRC) is a fundamental phenomenon that connects electronic spins with the rotational motion of a medium. We elucidate the Einstein-de Haas (EdH) effect and its inverse with SRC as the microscopic mechanism using the dynamic spin-lattice equations derived by elasticity theory and Lagrangian formalism. By applying the coupling equations to an iron disk in a magnetic field, we exhibit the transfer of angular momentum and energy between spins and lattice, with or without damping. The timescale of the angular momentum transfer from spins to the entire lattice is estimated by our theory to be on the order of 0.01 ns, for the disk with a radius of 100 nm. Moreover, we discover a linear relationship between the magnetic field strength and the rotation frequency, which is also enhanced by a higher ratio of Young's modulus to Poisson's coefficient. In the presence of damping, we notice that the spin-lattice relaxation time is nearly inversely proportional to the magnetic field. Our explorations will contribute to a better understanding of the EdH effect and provide valuable insights for magneto-mechanical manufacturing.

cond-mat.mes-hall↗

arXiv2024

Unraveling the Mn $L_3$-edge RIXS spectrum of lightly manganese doped Sr$_{3}$Ru$_{2}$O$_{7}$

Resonant inelastic x-ray scattering (RIXS) experiment was performed at the Mn $L_3$ edge. A 10 $\%$ Mn-doped Sr$_{3}$Ru$_{2}$O$_{7}$ compound, where the Mn$^{3+}$ ions are in the 3$d^4$ state, were probed for $dd$ excitations. The dilute doping concentration allows one to treat the dopant Mn$^{3+}$ ions as effectively free in the host ruthenium compound. The local nature of $dd$ RIXS spectroscopy permits one to use a single-site model to simulate the experimental spectra. The simulated spectra reproduces the in-plane [100] experimental RIXS spectrum. We also predict the intensity for the in-plane [110] direction and the out-of-plane spin orientation configuration [001]. Based on our single-ion model we were able to fit the experimental data to obtain the crystal field parameters, the 10Dq value, and the intra-orbital spin-flip energy 2$\mathcal{J}$(or $3J_{H}$, where $J_{H}$ is the Hund's energy) of the Mn$^{3+}$ ion. Utilizing our computed RIXS quantum transition amplitudes between the various $d$ orbitals of the Mn$^{3+}$ ion, the expression for the Kramers-Heisenberg cross section, and a self-consistent fitting procedure we also identify the energy boundaries of the non-spin-flip and spin-flip $dd$ excitations present in the experimental data. From our fitting procedure we obtain $2\mathcal{J} (3J_{H})=2.06$ eV, a value which is in excellent agreement with that computed from the free ion Racah parameters. We also identified the charge transfer boundary. In addition to predicting the microscopic parameters, we find a quantum spin-flip transition in the non-cross ($σ_{in}-σ_{out}$, $π_{in}-π_{out}$) x-ray polarization channels of the $dd$ RIXS spectra. A similar transition, was previously predicted to occur in the $π-π$ channel of the magnon spectrum in the non-collinear non-coplanar Kagome compound composed of Cu$^{2+}$ 3d$^{9}$ ion.

cond-mat.str-el↗

arXiv2024

Phonon and electronic properties of semiconducting silicon nitride bilayers

The two-dimensional (2D) IV-V semiconductors have attracted much attention due to their fascinating electronic and optical properties. In this work, we predicted three phases of silicon nitrides, denoted $α$-Si$_{2}$N$_{2}$, $β$-Si$_{2}$N$_{2}$, and $γ$-Si$_{4}$N$_{4}$, respectively. Both $α$-Si$_{2}$N$_{2}$ and $β$-Si$_{2}$N$_{2}$ consist of two buckled SiN sheets, and $γ$-Si$_{4}$N$_{4}$ consists of two puckered SiN sheets. It is challenging to transform between $α$-Si$_{2}$N$_{2}$ and $β$-Si$_{2}$N$_{2}$ because of the high energy barrier. The three dynamically stable bilayers are semiconductors with fundamental indirect band gaps from 0.25 eV to 2.92 eV. As expected, only the s and p orbitals contribute to the electronic states, and the pz orbitals dominate near the Fermi level. Furthermore, insulator-metal transitions occur in $α$-Si$_{2}$N$_{2}$ and $β$-Si$_{2}$N$_{2}$ under the biaxial strain of 16%. These materials perhaps have potential applications in microelectronics and spintronics.

cond-mat.mtrl-sci↗

arXiv2024

Structural transition, electric transport, and electronic structures in the compressed trilayer nickelate La4Ni3O10

Atomic structure and electronic band structure are fundamental properties for understanding the mechanism of superconductivity. Motivated by the discovery of pressure-induced high-temperature superconductivity at 80 K in the bilayer Ruddlesden-Popper nickelate La3Ni2O7, the atomic structure and electronic band structure of the trilayer nickelate La4Ni3O10 under pressure up to 44.3 GPa are investigated. A structural transition from the monoclinic P21/a space group to the tetragonal I4/mmm around 12.6-13.4 GPa is identified, accompanying with a drop of resistance below 7 K. Density functional theory calculations suggest that the bonding state of Ni 3dz2 orbital rises and crosses the Fermi level at high pressures, which may give rise to possible superconductivity observed in resistance under pressure in La4Ni3O10. The trilayer nickelate La4Ni3O10 shows some similarities with the bilayer La3Ni2O7 and has unique properties, providing a new platform to investigate the underlying mechanism of superconductivity in nickelates.

cond-mat.supr-con↗

arXiv2024

Topological Superconducting States and Quasiparticle Transport on Kagome Lattice

The pairing symmetry of superconducting states is a critical topic in the realm of topological superconductivity. However, the pairing symmetry of the $A\mathrm{V_3Sb_5}$ family, wherein $A=\mathrm{K,Rb,Cs}$, remains indeterminate. To address this issue, we formulate an effective model on the kagome lattice to describe topological superconducting states featuring chiral charge density wave. Through this model, we explore the topological phase diagrams and thermal Hall conductivity under various parameters, with and without spin-orbit coupling. Our analysis reveals that the disparities in thermal Hall conductivity curves between different pairing symmetries are safeguarded by the topology resulting from the interplay of spin-orbital coupling and superconducting states. Remarkably, this theoretical prediction can potentially enable the differentiation of various superconducting pairing symmetries in materials via experimental measurements of thermal Hall conductivity curves.

cond-mat.supr-con↗

arXiv2024

Dynamical localization transition in the non-Hermitian lattice gauge theory

Local constraint in the lattice gauge theory provides an exotic mechanism that facilitates the disorder-free localization. However, the understanding of nonequilibrium dynamics in the non-Hermitian lattice gauge model remains limited. Here, we investigate the quench dynamics in a system of spinless fermions with nonreciprocal hopping in the $\mathbb{Z}_2$ gauge field. By employing a duality mapping, we systematically explore the non-Hermitian skin effect, localization-delocalization transition, and real-complex transition. Through the identification of diverse scaling behaviors of quantum mutual information for fermions and spins, we propose that the non-Hermitian quantum disentangled liquids exist both in the localized and delocalized phases, the former originates from the $\mathbb{Z}_2$ gauge field and the latter arises from the non-Hermitian skin effect. Furthermore, we demonstrate that the nonreciprocal dissipation causes the flow of quantum information. Our results provide valuable insights into the nonequilibrium dynamics in the gauge field, and may be experimentally validated using quantum simulators.

cond-mat.dis-nn↗

arXiv2024

Periodicity staircase in a Fe/Gd magnetic thin film

Presence of multiple competing periodicities may result in a system to go through states with modulated periodicities, an example of which is the self-similar staircase-like structure called the Devil's staircase. Herein we report on a novel staircase structure of domain periodicity in an amorphous and achiral Fe/Gd magnetic thin film wherein the reciprocal space wavevector \textbf{Q} due to the ordered stripe domains does not evolve continuously, rather exhibits a staircase structure. Resonant X-ray scattering experiments show jumps in the periodicity of the stripe domains as a function of an external magnetic field. When resolved in components, the step change along Q$_x$ was found to be an integral multiple of a minimum step height of 7 nm, which resembles closely to the exchange length of the system. Modeling the magnetic texture in the Fe/Gd thin film as an achiral spin arrangement, we have been able to reproduce the steps in the magnetization using a Landau-Lifshitz spin dynamics calculation. Our results indicate that anisotropy and not the dipolar interaction is the dominant cause for the staircase pattern, thereby revealing the effect of achiral magnetism.

cond-mat.mtrl-sci↗