arXiv subjects

Xiao-Tian Zhang

Publications and source records attributed to Xiao-Tian Zhang.

15 recordsLinked to original sources

arXiv2026

Non-Abelian chiral spin liquid in a spin-$1$ antiferromagnet on the square lattice

Non-Abelian chiral spin liquids (CSLs) host non-Abelian anyon excitations and are promising platforms for topological quantum computation. However, realizing non-Abelian CSLs in short-range interacting spin systems remains elusive. Here, we study a spin-$1$ square-lattice model with the first- and second-neighbor bilinear ($J_1,J_2$) and biquadratic interactions ($K_1,K_2$), as well as the three-spin scalar chiral coupling $J_χ$. Inspired by the evidence of the Moore-Read state in exact diagonalization and infinite Projected Entangled Pair States calculations, we fix $J_1=1.0$, $J_2/J_1=0.623$, $K_1/J_1=-0.176$, and obtain a quantum phase diagram for $0 \leq K_2/J_1 \leq 0.4$ and $0.3 \leq J_χ/J_1 \leq 0.6$ by using the density matrix renormalization group (DMRG) calculations. We identify a stripe antiferromagnetic phase, a Néel antiferromagnetic phase, a magnetically ordered chiral spin state phase, and a non-Abelian CSL phase emerging near the boundaries of the ordered phases. The unbiased DMRG results provide strong evidence for the Moore-Read state, including the three topological sectors, the quantized spin Chern number $C=1$, and the level counting of low-lying entanglement spectra which is consistent with the chiral SU(2)$_2$ conformal field theory. Our results may shed new light on searching for non-Abelian CSLs in other higher-spin ($S > 1/2$) systems with short-range couplings.

cond-mat.str-el↗

arXiv2026

Strange metal at the Lifshitz transition

Strange metal behavior is widely observed in cuprates, ruthenates, and twisted bilayer graphene. We study quantum critical transport at a two-dimensional Lifshitz transition, where the Fermi surface hosts a van Hove singularity and changes from convex to concave. Self-consistently solving the fermion-boson coupled system, we demonstrate a linear-in-$1/ω$ optical conductivity driven by the interplay between impurity and critical scattering. The resistivity exhibits a persistent linear-in-$T$ in the quantum critical regime down to $T\rightarrow 0$. Spatially fluctuating Yukawa interaction further extends the linear-in-$T$ regime, providing a unified mechanism for strange metallic transport at the Lifshitz transition.

cond-mat.str-el↗

arXiv2025

Spin pumping effect in non-Fermi liquid metals

Spin pumping effect is a sensitive and well-established experimental method in two-dimensional (2D) magnetic materials. We propose that spin pumping effect can be a valuable probe for non-Fermi liquid (NFL) behaviors at the 2D interface of magnetic heterostructures. We show that the modulations of ferromagnetic resonance exhibit power-law scalings in frequency and temperature for NFL metals induced near a quantum critical point (QCP). At the Ising nematic QCP, we demonstrate that the enhanced Gilbert damping coefficient $δα$ acquires negative power-law exponents in distinct frequency regimes. The exponents convey universal parameters inherited from the QCP and reflect the non-quasiparticle nature of the spin carriers in the NFL metal. At finite temperature, we show that the Gilbert damping mechanism is restored in the quantum critical regime and $δα$ measures the temperature dependence of the correlation length. Our theoretical proposal has the potential to stimulate the development of an interdisciplinary research domain where insights from non-equilibrium spin physics in spintronics are integrated into strongly correlated matter.

cond-mat.str-el↗

arXiv2024

Thermal Hall effects in quantum magnets

In the recent years, the thermal Hall transport has risen as an important diagnosis of the physical properties of the elementary excitations in various quantum materials, especially among the Mott insulating systems where the electronic transports are often featureless. Here we review the recent development of thermal Hall effects in quantum magnets where all the relevant excitations are charge-neutral. In addition to summarizing the existing experiments, we pay a special attention to the underlying mechanisms of the thermal Hall effects in various magnetic systems, and clarify the connection between the microscopic physical variables and the emergent degrees of freedom in different quantum phases. The external magnetic field is shown to modify the intrinsic Berry curvature properties of various emergent and/or exotic quasiparticle excitations in distinct fashions for different quantum systems and quantum phases, contributing to the thermal Hall transports. These include, for example, the conventional ones like the magnons in ordered magnets, the triplons in dimerized magnets, the exotic and fractionalized quasiparticles such as the spinons and the magnetic monopoles in quantum spin liquids. We review their contribution and discuss their presence in the thermal Hall conductivity in different physical contexts. We expect this review to provide a useful guidance for the physical mechanism of the thermal Hall transports in quantum magnets.

cond-mat.str-el↗

arXiv2024

Quantum criticality with emergent symmetry in the extended Shastry-Sutherland model

Motivated by the novel phenomena observed in the layered material $\rm SrCu_2(BO_3)_2$, the Shastry-Sutherland model (SSM) has been extensively studied as the minimal model for $\rm SrCu_2(BO_3)_2$. However, the nature of its quantum phase transition from the plaquette valence-bond solid (PVBS) to antiferromagnetic (AFM) phase is under fierce debate, posing a challenge to understand the underlying quantum criticality. Via the state-of-the-art tensor network simulations, we study the ground state of the SSM on large-scale size up to $20 \times 20$ sites. We identify the continuous transition nature accompanied by an emergent O(4) symmetry between the PVBS and AFM phase, which strongly suggests a deconfined quantum critical point (DQCP). Furthermore, we map out the phase diagram of an extended SSM that can be continuously tuned to the SSM, which demonstrates the same DQCP phenomena along a whole critical line. Our results indicate a compelling scenario for understanding the origin of the proposed proximate DQCP in recent experiments of $\rm SrCu_2(BO_3)_2$.

cond-mat.str-el↗

arXiv2024

Chiral spin liquid and quantum phase diagram of spin-$1/2$ $J_1$-$J_2$-$J_χ$ model on the square lattice

We study the spin-$1/2$ Heisenberg model on the square lattice with the first and second nearest-neighbor antiferromagnetic couplings $J_1$, $J_2$, as well as the three-spin scalar chiral coupling $J_χ$. Using density matrix renormalization group calculations, we obtain a quantum phase diagram of this system for $0 \leq J_2/J_1 \leq 1.0$ and $0 \leq J_χ/J_1 \leq 1.5$. We identify the Néel and stripe magnetic order phase at small $J_χ$ coupling. With growing $J_χ$, we identify the emergent chiral spin liquid (CSL) phase characterized by the quantized spin Chern number $C = 1/2$ and entanglement spectrum with the quasidegenerate group of levels agreeing with chiral SU(2)$_1$ conformal field theory, which is an analog of the $ν= 1/2$ Laughlin state in spin system. In the vicinity of the Néel and CSL phase boundary, our numerical results do not find evidence to support the phase coexistence of Néel order and topological order that was conjectured by mean-field calculations. In the larger $J_2$ and $J_χ$ coupling regime, the entanglement spectrum of the ground state also exhibits the chiral quasidegeneracy consistent with a CSL, but the adiabatic flux insertion simulations fail to obtain the quantized Chern number. By analyzing the finite-size scaling of magnetic order parameter, we find the vanished magnetic order suggesting a magnetic disorder phase, whose nature needs further studies. Different from the spin-$1$ $J_1$-$J_2$-$J_χ$ model, we do not find the coexistent stripe magnetic order and topological order. We also investigate the $J_χ$ dominant regime and find a strong tendency of the system to develop a dimer order rather than the chiral spin magnetic order observed in the spin-$1$ model.

cond-mat.str-el↗

arXiv2023

Infinite critical boson non-Fermi liquid on heterostructure interfaces

We study the emergence of non-Fermi liquid on heterostructure interfaces where there exists an infinite number of critical boson modes accounting for the magnetic fluctuations in two spatial dimensions. The interfacial Dzyaloshinskii-Moriya interaction naturally arises in magnetic interactions due to the absence of inversion symmetry, resulting in a degenerate contour for the low-energy bosonic modes in the momentum space which simultaneously becomes critical near the magnetic phase transition. The itinerant electrons are scattered by the critical boson contour via the Yukawa coupling. When the boson contour is much smaller than the Fermi surface, it is shown that, there exists a regime with a dynamic critical exponent z=3 while the boson contour still controls the low-energy magnetic fluctuations. Using a self-consistent renormalization calculation for this regime, we uncover a prominent non-Fermi liquid behavior in the resistivity with a characteristic temperature scaling power. These findings open up new avenues for understanding boson-fermion interactions and the novel fermionic quantum criticality.

cond-mat.str-el↗

arXiv2023

Infinite critical boson non-Fermi liquid

We study a distinct type of non-Fermi liquid where there exists an infinite number of critical bosonic modes instead of a finite number of bosonic modes for the conventional ones. We consider itinerant magnets with both conduction electrons and fluctuating magnetic moments in three dimensions. With the Dzyaloshinskii-Moriya interaction, the moments fluctuate near a boson surface in the reciprocal space at low energies when the system approaches an ordering transition. The infinite number of critical modes on the boson surface strongly scatter the gapless electrons on the Fermi surface and convert the metallic sector into a non-Fermi liquid. We explain the physical properties of this non-Fermi liquid. On the ordered side, a conventional non-Fermi liquid emerges due to the scattering by the gapless Goldstone mode from the spontaneous breaking of the global rotational symmetry. We discuss the general structure of the phase diagram in the vicinity of the quantum phase transition and clarify various crossover behaviors.

cond-mat.str-el↗

arXiv2022

Infinite critical boson induced non-Fermi liquid in $d=3-ε$ dimensions

We study the fermion-boson coupled system in $d=3-ε$ space dimensions near the quantum phase transition; infinite many boson modes located on a sphere become critical simultaneously, which is dubbed "critical boson sphere" (CBS). The fermions on the Fermi surface can be scattered to nearby points located on a boson ring in the low-energy limit. The number of boson scattering channel $N_{B}$ is also infinite, which renders the well-known Landau damping effect largely suppressed. The one-loop renormalization group analysis is performed with asymptotic $ε$-expansion. We find that the fermion self-energy and Yukawa interaction vertex are dressed with $ε$ poles; in addition, there emerges an enhancement due to the curvature effect of CBS. In certain perturbative regimes, we identify a marginal non-Fermi liquid (NFL) fixed point that exists intrinsically in the large-$N_B$ limit. The infinite critical bosons comprise a physical realization of the flavor degrees of freedom which has been proposed for matrix large-$N_B$ bosons.

cond-mat.str-el↗

arXiv2021

Fragility of the nematic spin liquid induced by diagonal couplings in the square-lattice SU(3) model

We present a large-scale density matrix renormalization group (DMRG) study of the spin-$1$ SU(3) bilinear-biquadratic model on the square lattice, which was suggested to host a nematic spin liquid state in recent DMRG calculations. We report that this spin liquid appears to strongly compete with a three-sublattice magnetic order. To further study the competition between the two states, and the reason of the emergent nematic spin liquid, we included an additional next-nearest-neighbor SU(3) symmetric interactions along one of the two plaquette diagonal directions. This allows to tune the square-lattice model to the triangular-lattice model. By computing spin correlation functions and various order parameters, we find that the three-sublattice order may develop at infinitesimal additional new coupling, at least within the precision of our study. Compared with the previous findings that the nematic spin liquid is stable in extended parameter regions with additional couplings that respect the lattice symmetries of the square lattice, we argue that here the diagonal couplings, which frustrate the bipartite-lattice structure, rapidly suppress the two-sublattice fluctuations and the three-sublattice order thus wins. This numerical result is consistent with the conjecture that the nematic spin liquid emerges from the competition between two- and three-sublattice fluctuations.

cond-mat.str-el↗

arXiv2020

Clusterization transition between cluster Mott insulators on a breathing Kagomé lattice

Motivated by recent experimental progress on various cluster Mott insulators, we study an extended Hubbard model on a breathing Kagomé lattice with a single electron orbital and $1/6$ electron filling. Two distinct types of cluster localization are found in the cluster Mott regime due to the presence of the electron repulsion between neighboring sites, rather than from the on-site Hubbard interaction in the conventional Mott insulators. We introduce a unified parton construction framework to accommodate both type of cluster Mott insulating phase as well as a trivial Ferm liquid metal and discuss the phase transitions in the phase diagram. It is shown that, in one of the cluster localization phases, the strong inter-site repulsion results into locally metallic behavior within one of two triangular clusters on the breathing Kagomé lattice. We further comment on experimental relevance to existing Mo-based cluster magnets.

cond-mat.str-el↗

arXiv2019

Topological thermal Hall effect of "magnetic monopoles" in pyrochlore U(1) spin liquid

"Magnetic monopole" is an exotic quantum excitation in pyrochlore U(1) spin liquid, and its emergence is purely of quantum origin and has no classical analogue. We predict topological thermal Hall effect (TTHE) of "magnetic monopoles" and present this prediction through non-Kramers doublets. We observe that, when the external magnetic field polarizes the Ising component of the local moment, internally this corresponds to the induction of emergent dual U(1) gauge flux for the "magnetic monopoles". The motion of "magnetic monopoles" is then twisted by the induced dual gauge flux. This emergent Lorentz force on "magnetic monopoles" is the fundamental origin of TTHE. Therefore, TTHE would be a direct evidence of the "monopole"-gauge coupling and the emergent U(1) gauge structure in pyrochlore U(1) spin liquid. Our result does not depend strongly on our choice of non-Kramers doublets for our presentation, and can be well extended to Kramers doublets. Our prediction can be readily tested among the pyrochlore spin liquid candidate materials. We give a detailed discussion about the expectation for different pyrochlore magnets.

cond-mat.str-el↗

arXiv2018

Theory of metal-insulator transitions in graphite under high magnetic field

Graphite under high magnetic field exhibits consecutive metal-insulator (MI) transitions as well as re-entrant insulator-metal (IM) transition in the quasi-quantum limit at low temperature. In this paper, we identify the low-$T$ insulating phases as excitonic insulators with spin nematic orderings. We first point out that graphite under the relevant field regime is in the charge neutrality region, where electron and hole densities compensate each other. Based on this observation, we introduce interacting electron models with electron pocket(s) and hole pocket(s) and enumerate possible umklapp scattering processes allowed under the charge neutrality. Employing effective boson theories for the electron models and renormalization group (RG) analyses for the boson theories, we show that there exist critical interaction strengths above which the umklapp processes become relevant and the system enter excitonic insulator phases with long-range order of spin superconducting phase fields ("spin nematic excitonic insulator"). We argue that, when a pair of electron and hole pockets get smaller in size, a quantum fluctuation of the spin superconducting phase becomes larger and destabilizes the excitonic insulator phases, resulting in the re-entrant IM transitions. We also show that an odd-parity excitonic pairing between the electron and hole pockets reconstruct surface chiral Fermi arc states of electron and hole into a 2-dimensional helical surface state with a gapless Dirac cone. We discuss field- and temperature-dependences of in-plane resistance by surface transports via these surface states.

cond-mat.mes-hall↗

arXiv2017

Theory of transport property of density wave phases in three-dimensional metals and semimetals under high magnetic field

Three-dimensional (3D) metals/semimetals under magnetic field have an instability toward a density wave (DW) ordering which breaks a translational symmetry along the field direction. Effective boson models for the DW phases take forms of XY models with/without Potts terms. Longitudinal conductivity along the field direction is calculated in the DW phases with inclusion of effects of low-energy charge fluctuation (phason) and disorder. A single-particle imaginary-time Green function is identified with a partition function of 3D XY models in the presence of pairs of magnetic monopoles. In terms of the celebrated electromagnetic duality, electronic spectral function is calculated near the DW phase transition. The result shows that the single-particle spectral function acquires an additional low-energy feature due to the strong phason fluctuation. Relevance to an in-plane conductance due to surface chiral Fermi arc states are also discussed.

cond-mat.str-el↗

arXiv2015

Dirac fermions in Fe ultra-thin film

We show the existence of massive Dirac fermions in electronic band structures of a few Fe atomic layers with perpendicular magnetization. Based on a tight binding model fitted to ab-initio band structure, we observe four distinct massive Dirac fermions near the Fermi level, which result from atomic spin-orbit coupling of Fe and a band inversion between Fe $4s$-$3d_{x^2-y^2}$ hybrid orbital band and $3d_{xy}$ orbital band. These lead to a valence band with finite Chern integer (+2) and chiral edge modes near the Fermi level. When the chemical potential is set inside the Dirac gap by carrier doping, the Hall conductivity exhibits a plateau-like structure with quantized value $2\frac{e^2}{h}$, and orbital magnetization shows a prominent increase, latter of which is mostly due to chiral orbital motion of electrons along the edge modes. We discuss the stability of the Dirac fermions in Fe(001) monolayer on MgO(001) substrate and Fe(001) bilayer case.

cond-mat.mtrl-sci↗