arXiv subjects

Wei-Wei Yang

Publications and source records attributed to Wei-Wei Yang.

13 recordsLinked to original sources

arXiv2026

Altermagnetism in exactly solvable model: the Ising-Kondo lattice model

Altermagnet (AM), a recently identified class of collinear magnet, has garnered significant attention due to its unique combination of zero net magnetization and spin-split energy bands, leading to a variety of novel physical phenomena. Using numerically exact lattice Monte Carlo simulations, we investigate AM-like phases within the Ising-Kondo lattice model which is commonly employed to describe heavy-fermion materials. By incorporating an alternating next-nearest-neighbor hopping (NNNH) term, which arises from the influence of non-magnetic atoms in altermagnetic candidate materials, our results reveal key signatures of AM-like states, including spin-splitting quasiparticle bands and spectral functions, and demonstrate that d-wave AM remains stable across a broad range of interaction strengths, doping levels, NNNH amplitudes and temperatures, highlighting its robustness. Furthermore, through an analysis of non-magnetic impurity effects, we further confirm the d-wave symmetry of the AM phase. These findings establish a solid theoretical foundation for exploring AM-like phases in f-electron compounds, paving the way for future investigations into their exotic magnetic and electronic properties.

cond-mat.str-el↗

arXiv2026

Spin-Lattice Relaxation in Two-Dimensional Superconducting BKT Transition

Two-dimensional superconductors undergo a Berezinskii-Kosterlitz-Thouless transition driven by vortex-antivortex unbinding, yet experimental signatures beyond transport remain limited. Here, we show that the spin-lattice relaxation rate provides a direct probe of this transition. In a 2-dimensional $s$-wave superconductor, $1/T_1T$ develops a Hebel-Slichter-like peak around $T_{\rm{BKT}}$, originating from the emergence of coherence peaks in the density of states, while no peak appears at the pair formation scale $T_{\rm{BCS}}$. We further extend our analysis to the $d$-wave superconductor. Our results highlight spin-lattice relaxation rate as a sensitive tool to detect the superconducting BKT transition and open routes to exploring its manifestation in unconventional pairing states.

cond-mat.supr-con↗

arXiv2025

Altermagnetism in Heavy Fermion Systems: Mean-Field study on Kondo Lattice

Recently, a novel collinear magnet, i.e. the altermagnet (AM), with spin-splitting energy band and zero net magnetization have attracted great interest due to its potential spintronic applications. Here, we demonstrate AM-like phases in a microscopic Kondo lattice (KL) model with an alternating next-nearest-neighbor-hopping (NNNH). Such alternating NNNH take nonmagnetic atoms, neglected in usual antiferromagnetism study, into account when encountering real-life candidate AM materials. With the framework of fermionic parton mean-field theory, we find three different ground-states for the half-filling KL: 1) a $d$-wave AM state; 2) a coexistent phase with both $d$-wave AM and intrinsic Kondo screening effect; 3) a Kondo insulator. The AM-like states are characterized by their spin-splitting quasiparticle bands, Fermi surface, spin-resolved distribution function and conductivity. It is suggested that the magnetic quantum oscillation, scanning tunneling microscopy and charge transport measurement can detect those AM-like phases. We hope the present work may be useful for exploring AM-like phases in $f$-electron compounds such as CeNiAsO and Ce$_{4}$X$_{3}$(X=As,Sb,Bi).

cond-mat.str-el↗

arXiv2024

Topic Review: Hatsugai-Kohmoto models: Exactly solvable playground for Mottness and Non-Fermi Liquid

This pedagogic review aims to give a gentle introduction to an exactly solvable model, the Hatsugai-Kohmoto (HK) model, which has infinite-ranged interaction but conserves the center of mass. Although this model is invented in 1992, intensive studies on its properties ranging from unconventional superconductivity, topological ordered states to non-Fermi liquid behaviors are made since 2020. We focus on its emergent non-Fermi liquid behavior and provide discussion on its thermodynamics, single-particle and two-particle correlation functions. Perturbation around solvable limit has also been explored with the help of perturbation theory, renormalization group and exact diagonalization calculation. We hope the present review will be helpful for graduate students or researchers interested in HK-like models or more generic strongly correlated electron systems.

cond-mat.str-el↗

arXiv2023

Shubnikov-de Haas effect in the Falicov-Kimball model: strong correlation meets quantum oscillation

We present a comprehensive investigation of quantum oscillations (QOs) in the strongly-correlated Falicov-Kimball model (FKM). The FKM is a particularly suitable platform for probing the non-Fermi liquid state devoid of quasiparticles, affording exact Monte Carlo simulation across all parameter spaces. In the high-correlation regime, we report the presence of prominent QOs in magnetoresistance and electron density at low temperatures within the phase separation state. The frequency behavior of these oscillations uncovers a transition in the Fermi surface as electron density diminishes, switching from hole-like to electron-like. Both types of Fermi surfaces are found to conform to the Onsager relation, establishing a connection between QOs frequency and Fermi surface area. Upon exploring the temperature dependence of QOs amplitude, we discern a strong alignment with the Lifshitz-Kosevich (LK) theory, provided the effective mass is suitably renormalized. Notwithstanding, the substantial enhancement of the overall effective mass results in a notable suppression of the QOs amplitude within the examined temperature scope, a finding inconsistent with Fermi liquid predictions. For the most part, the effective mass diminishes as the temperature increases, but an unusual increase is observed at the proximity of the second-order phase transition instigated by thermal effects. As the transition ensues, the regular QOs disappear, replaced by irregular ones in the non-Fermi liquid state under a high magnetic field. We also uncover significant QOs in the insulating charge density wave state under weak interactions ($0 < U < 1$), a phenomenon we elucidate through analytical calculations. Our findings shed light on the critical role of quasiparticles in the manifestation of QOs, enabling further understanding of their function in this context.

cond-mat.str-el↗

arXiv2023

Bose metal in exactly solvable model with infinite-range Hatsugai-Kohmoto interaction

In a conventional boson system, the ground state can either be an insulator or a superfluid (SF) due to the duality between particle number and phase. This paper reveals that the long-sought Bose metal (BM) state can be realized in an exactly solvable interacting bosonic model, i.e. the Bose-Hatsugai-Kohmoto (BHK) model, which acts as the nontrivial extension of Bose-Hubbard (BH) model. By tuning the parameters such as bandwidth $W$, chemical potential $μ$, and interaction strength $U$, a BM state without any symmetry-breaking can be accessed for a generic $W/U$ ratio, while a Mott insulator (MI) with integer boson density is observed at small $W/U$. The quantum phase transition between the MI and BM states belongs to the universality class of the Lifshitz transition, which is further confirmed by analyzing the momentum-distribution function, the Drude weight, and the superfluid density. Additionally, our investigation at finite temperature reveals similarities between the BM state and the Fermi liquid, such as a linear-$T$ dependent heat capacity ($Cv\sim γT$) and a saturated charge susceptibility ($χ_{c} \sim $ constant) as $T$ approaches zero. Comparing the BM state with the SF state in the standard BH model, we find that the key feature of the BM state is a compressible total wavefunction accompanied by an incompressible zero-momentum component. Given that the BM state prevails over the SF state at any finite $U$ in the BHK model, our work suggests the possibility of realizing the BM state with on-site repulsion interactions in momentum space.

cond-mat.str-el↗

arXiv2023

Friedel oscillation in non-Fermi liquid: Lesson from exactly solvable Hatsugai-Kohmoto model

When non-magnetic impurity immerses in Fermi sea, a regular modulation of charge density around impurity will appear and such phenomena is called Friedel oscillation (FO). Although both Luttinger liquid and Landau Fermi liquid show such characteristic oscillation, FO in generic non-Fermi liquid (NFL) phase is still largely unknown. Here, we show that FO indeed exists in NFL state of an exactly solvable model, i.e. the Hatsugai-Kohmoto model which has been intensively explored in recent years. Combining T-matrix approximation and linear-response-theory, an interesting picture emerges, if two interaction-induced quasi-particles bands in NFL are partially occupied, FO in this situation is determined by a novel structure in momentum space, i.e. the 'average Fermi surface' (average over two quasi-particle Fermi surface), which highlights the inter-band particle-hole excitation. We hope our study here provides a counterintuitive example in which FO with Fermi surface coexists with NFL quasi-particle, and it may be useful to detect hidden 'average Fermi surface' structure in other correlated electron systems.

cond-mat.str-el↗

arXiv2022

Violation of Luttinger's theorem in the simplest doped Mott insulator: Falicov-Kimball model in strong correlation limit

The Luttinger's theorem has long been taken as the key feature of Landau's Fermi liquid, which signals the presence of quasiparticles. Here, by the unbiased Monte Carlo method, violation of Luttinger's theorem is clearly revealed in the Falicov-Kimball (FK) model, indicating the robust correlation-driven non-Fermi liquid characteristic under any electron density. Introducing hole carriers to the half-filled FK leads to Mott insulator-metal transition, where the Mott quantum criticality manifests unconventional scaling behavior in transport properties. Further insight on the violation of the Luttinger's theorem is examined by combining Hubbard-I approximation with a composite fermion picture, which emphasizes the importance of a mixed excitation of the itinerant electron and the composite fermion. Interestingly, when compared FK model with a binary disorder system, it suggests that the two-peak band structure discovered by Monte Carlo and Hubbard-I approaches is underlying the violation of Luttinger's theorem.

cond-mat.str-el↗

arXiv2021

Demystifying strange metal and violation of Luttinger theorem in a doped Mott insulator

Metallic states coined strange metal (SM), with robust linear-$T$ resistivity, have been widely observed in many quantum materials under strong electron correlation, ranging from high-$T_{c}$ cuprate superconductor, organic superconductor to twisted multilayer graphene and MoTe$_{2}$/WSe$_{2}$ superlattice. Despite decades of intensive studies, the mystery of strange metal still defies any sensible theoretical explanation and has been the key puzzle in modern condensed matter physics. Here, we solve a doped Mott insulator model, which unambiguously exhibits SM phenomena accompanied with quantum critical scaling in observables, e.g. resistivity, susceptibility and specific heat. Closer look at SM reveals the breakdown of Landau's Fermi liquid without any symmetry-breaking, i.e. the violation of Luttinger theorem. Examining electron's self-energy extracted from numerical simulation provides the explanation on the origin of linear-$T$ resistivity and suggests that the long-overlooked static fluctuations in literature play an essential role in non-Fermi liquid behaviors in correlated electron systems.

cond-mat.str-el↗

arXiv2020

Hexagon Ising-Kondo lattice: An implication for intrinsic antiferromagnetic topological insulator

Recently, the MnBi$_2$Te$_4$ material has been proposed as the first intrinsic antiferromagnetic topological insulator (AFMTI), where the interplay between magnetism and topology induces several fascinating topological phases, such as the quantum anomalous Hall effect, Majorana fermions, and axion electrodynamics. However, an exactly solvable model being capable to capture the essential physics of the interplay between magnetism and topology is still absent. Here, inspired by the the Ising-like nature [B. Li \textit{et al.} Phys. Rev. Lett. \textbf{124}, 167204 (2020)] and the topological property of MnBi$_2$Te$_4$, we propose a topological Ising-Kondo lattice (TIKL) model to study its ground state property in an analytical way at zero temperature. The resultant phase diagram includes rich topological and magnetic states, which emerge in the model proposed in a natural and consistent way for the intrinsic magnetic topological insulator. With Monte Carlo simulation, we extend the AFMTI ground state to finite temperature. It reveals that topological properties do sustain at high temperature, which even can be restored by elevated temperature at suitable correlation strength. The results demonstrate that TIKL may offer an insight for future experimental research, with which magnetism and transport properties could be fine tuned to achieve more stable and exotic magnetic topological quantum states.

cond-mat.str-el↗

arXiv2020

Hidden Anderson Localization in Disorder-Free Ising-Kondo Lattice

Anderson localization (AL) phenomena usually exists in systems with random potential. However, disorder-free quantum many-body systems with local conservation can also exhibit AL or even many-body localization transition. In this work, we show that the AL phase exists in a modified Kondo lattice without external random potential. The density of state, inverse participation ratio and temperature-dependent resistance are computed by classical Monte Carlo simulation, which uncovers the AL phase from previously studied Fermi liquid and Mott insulator regime. The occurrence of AL roots from quenched disorder formed by conservative localized moments. Interestingly, a many-body wavefunction is found, which captures elements in all three paramagnetic phases and is used to compute their quantum entanglement. In light of these findings, we expect the disorder-free AL phenomena can exit in generic translation-invariant quantum many-body systems.

cond-mat.str-el↗

arXiv2020

Exactly Solvable Kondo Lattice Model in Anisotropic Limit

In this paper we introduce an exactly solvable Kondo lattice model without any fine-tuning local gauge symmetry. This model describes itinerant electrons interplaying with a localized magnetic moment via only longitudinal Kondo exchange. Its solvability results from conservation of the localized moment at each site, and is valid for arbitrary lattice geometry and electron filling. A case study on square lattice shows that the ground state is a Néel antiferromagnetic insulator at half-filling. At finite temperature, paramagnetic phases including a Mott insulator and correlated metal are found. The former is a melting antiferromagnetic insulator with a strong short-range magnetic fluctuation, while the latter corresponds to a Fermi liquid-like metal. Monte Carlo simulation and theoretical analysis demonstrate that the transition from paramagnetic phases into the antiferromagnetic insulator is a continuous $2D$ Ising transition. Away from half-filling, patterns of spin stripes (inhomogeneous magnetic order) at weak coupling, and phase separation at strong coupling are predicted. With established Ising antiferromagnetism and spin stripe orders, our model may be relevant to a heavy fermion compound CeCo(In$_{1-x}$Hg$_{x}$)$_{5}$ and novel quantum liquid-crystal order in a hidden order compound URu$_{2}$Si$_{2}$.

cond-mat.str-el↗

arXiv2018

Benchmarking the simplest slave-particle theory with Hubbard dimer

Slave-particle method is a powerful tool to tackle the correlation effect in quantum many-body physics. Although it has been successfully used to comprehend various intriguing problems, such as Mott metal-insulator transition and Kondo effect, there is still no convincing theory so far on the availability and limitation of this method. The abuse of slave-particle method may lead to wrong physics. As the simplest slave-particle method, $\mathbb{Z}_2$ slave spin, which is widely applied to many strongly correlated problems, is highly accessible and researchable. In this work, we will uncover the nature of $\mathbb{Z}_2$ slave-spin method by studying a two-site Hubbard model. After exploring some properties of this toy model, we make a comparative analysis of the results obtained by three methods: (i) slave-spin method on mean-field level, (ii) slave-spin method with gauge constraint and (iii) the exact solution as a benchmark. We find that, protected by particle-hole symmetry, the slave-spin mean-field method can recover the static properties of ground state exactly at half filling. Furthermore, in the parameter space where both $U$ and $T$ are small enough, slave-spin mean-field method is also reliable in calculating dynamic and thermal dynamic properties. However, when $U$ or $T$ is considerably large, the mean-field approximation gives ill-defined behavior, which results from the unphysical states in enlarged Hilbert space. These findings lead to our conclusion that the accuracy of slave particle can be guaranteed if we can exclude all unphysical states by enforcing gauge constraints.Our work demonstrates the promising prospect of slave-particle method in studying complex strongly correlated models with specific symmetry or in certain parameter space.

cond-mat.str-el↗