arXiv subjects

Zenghui Fan

Publications and source records attributed to Zenghui Fan.

7 recordsLinked to original sources

arXiv2026

Stripe-Ordered Altermagnetism Emerging from Correlation-Driven Spin-Density-Wave Instability

Altermagnetism is conventionally identified within the paradigm of collinear antiferromagnets. Its potential realization within other spin instabilities, such as a spin-density wave (SDW), remains a fundamentally compelling open question. Here, we combine Hartree-Fock mean-field and unbiased determinant quantum Monte Carlo methods to investigate a minimal Hubbard model relevant to iron pnictides. We reveal a novel $d_{xy}$-wave stripe-ordered altermagnetic (SOAM) insulating phase driven fundamentally by the correlation-induced $(\pi,0)$ SDW instability. Within this phase, an introduced uniaxial staggered electric potential alters the underlying symmetry: it breaks the original combined time-reversal and spatial translation symmetry ($T_{d}\mathcal{T}$) and retains a combined time-reversal and mirror invariance ($M\mathcal{T}$), thereby unlocking the pronounced nonrelativistic spin splitting. Crucially, the exact finite-size scaling from our determinant quantum Monte Carlo simulations confirms that this correlation-driven SOAM phase stably survives at accessible finite temperatures. Our study pushes the frontier of altermagnetism beyond the conventional antiferromagnetic paradigm into the realm of SDW instability, advancing the fundamental understanding of altermagnetism in strongly correlated electron systems.

cond-mat.str-el↗

arXiv2026

Magnetic fluctuations near the Van Hove singularity in the kagome-lattice Hubbard model at finite doping

The kagome-lattice Hubbard model attracts widespread interest due to its flat-band and Van Hove singularity features, which can give rise to unconventional magnetism. We employ determinant quantum Monte Carlo simulations to systematically investigate the uniform magnetic susceptibility across a range of on-site interactions and electron fillings on a two-dimensional kagome lattice. Beyond the Van Hove singularity, dominant ferromagnetic fluctuations emerge. Magnetic susceptibility grows markedly with increasing interaction strength and decreasing temperature, indicating that the Van Hove singularity acts as a critical point for the crossover of dominant magnetic fluctuations. Finite-size analysis further suggests the potential stabilization of a finite-temperature ferromagnetic phase. We also examine the sign problem to identify numerically reliable parameter regimes. These results provide valuable insights into controlling magnetic fluctuations in kagome systems and establish a computational framework for exploring flat-band physics in regimes characterized by novel quantum phases and competing orders.

cond-mat.str-el↗

arXiv2025

Charge stripe and superconductivity tuned by interlayer interaction in a sign-problem-free bilayer extended Hubbard model

Competing orders represent a central challenge in understanding strongly correlated systems. In this work, we employ projector quantum Monte Carlo simulations to study a sign-problem-free bilayer extended Hubbard model. In this model, a charge stripe phase, characterized by a peak at momentum $k_x=2\pi\delta$ is induced by highly anisotropic interlayer spin-exchange coupling $J_z$, and strongly suppressed upon introducing the spin-flip term $J_\bot$; in contrast, $J_\perp$ favors the emergence of interlayer pairing superconductivity. We further demonstrate that the anisotropy of the interlayer spin-exchange directly governs the competition between these two phases, while the on-site interaction $U$ plays a complex role in tuning both the charge stripe and superconductivity. Our work identifies the key factors driving charge stripe formation, highlights the sensitivity of both the charge stripe and superconducting phases to interaction parameters, and thereby provides valuable insights into competing orders in strongly correlated systems.

cond-mat.supr-con↗

arXiv2025

Time-reversal symmetry breaking superconductivity in the presence of loop-current fluctuations

Loop currents have been proposed in various superconductors and recently confirmed in kagome materials, raising a fundamental question regarding their intrinsic connection to superconductivity. Here, we study a sign-problem-free bilayer $t-J_{\perp}-V$ model hosting a spontaneous interlayer loop-current parent state, and explore the interplay between loop-current fluctuations and superconductivity using unbiased projector quantum Monte Carlo simulations. Near half-filling, unbiased interlayer interactions induce spontaneous loop currents that break time-reversal symmetry. Upon hole doping, the loop-current order is suppressed, and interlayer $s$-wave superconductivity emerges where loop-current fluctuations become dominant. We establish a phase diagram revealing a transition from the loop-current parent to a superconducting state, reminiscent of the evolution from an antiferromagnetic parent to superconductivity in cuprates. Strikingly, a coexisting regime emerges near the phase boundary, yielding time-reversal-symmetry-breaking superconductivity. Our study reveals an intrinsic connection between loop currents and superconductivity, and identifies a promising mechanism for time-reversal symmetry breaking in superconductors. Furthermore, our results offer insights into unconventional superconductivity in loop-current systems and establish a minimal theoretical framework for understanding time-reversal symmetry breaking in bilayer correlated electron systems.

cond-mat.supr-con↗

arXiv2025

Interplay of magnetic and thermodynamic responses in the kagome-triangular system

Inspired by the recent experimental progress in pyrochlore derivative RE$_3$Sb$_3$A$_2$O$_{14}$ (A = Mg, Zn), we investigate the Hubbard model on the kagome lattice with an additional hopping $t'/t$, which enables continuous interpolation between the kagome and triangular lattices by using determinant quantum Monte Carlo simulations. We find that increasing $t'/t$ suppresses the nearest-neighbor antiferromagnetic correlations. Concurrently, the next-nearest-neighbor antiferromagnetic correlations are enhanced and closely associated with the emergence of a pronounced low-temperature peak in the specific heat. Increasing on-site interaction $U$ enhances magnetic correlations and shifts the associated $t'/t$ crossover points to larger values. We also discuss the sign problem to clarify which parameter region of our numerical simulations is accessible and reliable. Our results uncover the competition between frustration and correlations and the interplay of magnetic and thermodynamic responses in the kagome lattice, providing insights into correlated states in frustrated materials.

cond-mat.str-el↗

arXiv2025

Breathing-Driven Metal-Insulator Transition in Correlated Kagome Systems

Inspired by the recent discovery of breathing kagome materials $\rm Nb_3Cl_8$ and $\rm Nb_3TeCl_7$, we have explored the influence of the breathing effect on the Hubbard model of the kagome lattice. Utilizing the determinant quantum Monte Carlo method, we first investigated the average sign problem in the breathing kagome lattice, which is significantly affected by both the breathing strength and the interaction strength. Secondly, we calculated the electronic kinetic energy, the direct current conductivity, and the electronic density of states at the Fermi level to determine the critical interaction strength for the metal-insulator transition. Our results indicate that the breathing effect, in conjunction with the interaction strength, drives the kagome system from a metal to an insulator. Finally, we evaluated the magnetic properties and constructed a phase diagram incorporating both transport and magnetic properties. The phase diagram reveals that as the interaction strength increases, the system transitions from a paramagnetic metal to a Mott insulator. Our research provides a theoretical guidance for utilizing the breathing effect to control the band gaps, conductivity, and magnetic properties of kagome materials with electronic interactions.

cond-mat.str-el↗

arXiv2023

Evolution of magnetic correlation in an inhomogeneous square lattice

We explore the magnetic properties of a two-dimensional Hubbard model on an inhomogeneous square lattice, which provides a platform for tuning the bandwidth of the flat band. In its limit, this inhomogeneous square lattice turns into a Lieb lattice, and it exhibits abundant properties due to the flat band structure at the Fermi level. By using the determinant quantum Monte Carlo simulation, we calculate the spin susceptibility, double occupancy, magnetization, spin structure factor, and effective pairing interaction of the system. It is found that the antiferromagnetic correlation is suppressed by the inhomogeneous strength and that the ferromagnetic correlation is enhanced. Both the antiferromagnetic correlation and ferromagnetic correlation are enhanced as the interaction increases. It is also found that the effective $d$-wave pairing interaction is suppressed by the increasing inhomogeneity. In addition, we also study the thermodynamic properties of the inhomogeneous square lattice, and the calculation of specific heat provide good support for our point. Our intensive numerical results provide a rich magnetic phase diagram over both the inhomogeneity and interaction.

cond-mat.str-el↗