arXiv subjects

Jize Zhao

Publications and source records attributed to Jize Zhao.

At least 19 recordsLinked to original sources

arXiv2026

Field-amplified readouts of weak altermagnetic exchange in MnF$_2$

MnF$_2$, the textbook two-sublattice antiferromagnet, has reemerged as a prototypical altermagnet, yet the sublattice-odd exchange that defines this identity remains under active debate: it enters the magnon splitting only in quadrature with the dipole--dipole interaction, its magnitude suppressed and its sign erased. An overdetermined first-principles total-energy mapping resolves this scale as a seventh-neighbor imbalance $\delta{J_7}\simeq+8~\mu$eV. The resulting Hamiltonian, with the dipole--dipole interaction included explicitly, reproduces the low-energy gap and the visible finite-momentum splitting. A longitudinal field $B\parallel c$ then acts as a linear amplifier of the hidden scale, opening two signed, field-linear readouts. The first is the compensation field $B^\ast(\mathbf Q)$, the position of minimum splitting, which is equal and opposite at the rotation-related partner momenta: a shift from zero field is itself evidence of a finite imbalance, its side gives the sign, and its magnitude, $|B^\ast|\simeq0.34$~T here, gives the scale. The second is the fixed-field contrast of the partner splittings, $\simeq0.14$~meV at $1$~T, six times the zero-field excess: a sign check from just two spectra. Both readouts survive a $0.12$~meV energy resolution, and the construction carries over to any easy-axis collinear altermagnet, bringing $\mu$eV altermagnetic exchange within present instrumental reach.

cond-mat.str-el↗

arXiv2026

Spin Splitter without Spin-Split Bands: A Reconfigurable Altermagnetic Texture

The altermagnetic spin-splitter effect converts an electric field into a transverse pure spin current, with no net magnetization and no charge-Hall counterpart. In established materials this function is tied to crystal-fixed spin-split bands that lock the polarization axis to the lattice. We show that the noncoplanar counter-spiral ground state of a frustrated honeycomb magnet instead carries the altermagnetic operation through a $\mathbf Q$-locked helicity mirror $g$. The mirror selects the spin-current polarization and forbids the perpendicular one, while an antitranslation $\Theta$ forbids even-parity spin splitting. Band splitting and spin-splitter response therefore rest on different symmetry elements. Either element alone enforces the charge-Hall zero---a redundancy absent from other spin--orbit-free noncollinear routes---and a charge Hall appears only when both elements are removed. Hole doping then realizes a \emph{spin splitter without spin-split bands}---the symmetry-allowed odd-parity residual below $2\times10^{-7}$ of the hopping $t$ at the Fermi level---with $\sigma_H^{(s_y)}=0.082\,e^2/h$ without spin--orbit coupling and with zero charge Hall response. Selecting among the three degenerate $\mathbf{Q}$ orientations rotates the polarization axis in exact $120^\circ$ steps at fixed magnitude and charge-Hall zero; the selection rules persist in a $32$-site cell accessible to programmable photonic and circuit lattices.

cond-mat.str-el↗

arXiv2026

Ground-state phase diagram and route to supersolidity in a two-component extended Bose-Hubbard model

We investigate the ground-state phase diagram of a two-component extended Bose-Hubbard model recently realized with dipolar excitons, using the projected entangled-pair states. For the experimentally relevant parameter regime, checkerboard, Mott-insulating, superfluid, and vacuum phases are identified. These phases exhibit orbital-selective character, wherein the two components occupy different quantum states, but we find no evidence for a supersolid phase. The absence of supersolidity is attributed to the strongly interaction-dominated microscopic energy scales, which severely restrict the superfluid regime. Guided by the supersolid mechanism, we further explore a nearby parameter regime with enhanced hopping of one component and identify an orbital-selective supersolid phase. Further finite bond-dimension and unit-cell analyses establish the robustness of this phase. Our results clarify the zero-temperature phase structure of the dipolar-exciton platform and provide a possible route toward realizing supersolidity in this setting.

cond-mat.quant-gas↗

arXiv2026

Generalized Holstein-Primakoff transformation with optimizable bosonic truncation

Spin-wave theory provides a quasiparticle description of excitation spectra in quantum spin systems. In this theory, the spin operators are usually bosonized by the Holstein-Primakoff transformation or the Dyson-Maleev transformation. In practical calculations, the bosonized Hamiltonian has to be truncated, and thus the resulting excitation spectra depend on the choice of bosonic representation. Here, we introduce a generalized Holstein-Primakoff transformation that continuously interpolates between the conventional Holstein-Primakoff and Dyson-Maleev transformations through a single parameter. The formulation naturally extends to the SU(N) algebra and provides a flexible framework for optimizing bosonic truncations beyond harmonic order. As an application, we investigate the spin-1 bilinear-biquadratic model on the square lattice. By combining the generalized Holstein-Primakoff transformation with continuous similarity transformations, we obtain excitation spectra in excellent agreement with tensor-network calculations. Our results demonstrate that optimizing the bosonic representation substantially reduces truncation errors and provides quantitatively reliable descriptions of both quasiparticle dispersions and multi-boson continua.

cond-mat.str-el↗

arXiv2026

Crossover and Changeover in Spin-1 Kitaev-$\Gamma$ Chain with Uniaxial Single-ion Anisotropy

Recent advances in bond-directional spin chains have revealed extensive emergent phenomena and unconventional criticality. Here we investigate the spin-1 Kitaev-$\Gamma$ chain with uniaxial single-ion anisotropy (SIA) using large-scale density-matrix renormalization group calculations and bosonization analysis. Tuning the SIA strength reveals a crossover from the Kitaev phase to the large-$D$ phase, evidenced by the excitation gap changing from quadratic to linear, the coexistence and smooth evolution of spin-nematic and string order parameters, and the suppression of the double-peak specific heat. For negative SIA, we uncover a changeover from a first-order transition to a continuous one between the dimerized and Haldane phases. The continuous transition belongs to the \textrm{SU(2)$_2$} Wess-Zumino-Witten universality class with central charge $c=3/2$, a rare instance in a system without continuous symmetry. Our results establish the Kitaev-$\Gamma$ chain as a minimal platform for controlling crossover and changeover phenomena.

cond-mat.str-el↗

arXiv2026

Beyond-adiabatic flat Chern bands from a double-helix skyrmion crystal

A central challenge in flat-band engineering is suppressing kinetic energy without sacrificing Berry curvature. We show that a double-helix skyrmion crystal (DHSKX)--two sublattice-resolved skyrmion textures locked at opposite helicities, obtained here as the classical ground state of a frustrated honeycomb spin model--provides such a route under double exchange. The key mechanism is a single real-space organization, phase clustering: the $\pi$-locked helicities expel the wave function's phase winding from the skyrmion cores, and the magnetic $C_3$ symmetry pins it into three phase-locked clusters whose distributed destructive interference cancels net transport while preserving the Berry curvature. Ordinary skyrmion crystals, even with the same symmetry, do not develop this organization. Phase clustering yields isolated flat $|C| = 1$ Chern bands over broad coupling windows, one of which surpasses the adiabatic reference in quantum geometry at intermediate coupling. In this beyond-adiabatic window, band-projected exact diagonalization gives finite-size evidence consistent with $\nu = 1/3$ Laughlin-type fractional-Chern-insulator physics; the same texture also hosts a higher-Chern ($C = -2$) flat band. Built from site-resolved complex hoppings alone, the DHSKX architecture is directly programmable in topolectric, acoustic, and photonic platforms.

cond-mat.str-el↗

arXiv2025

Strong enhancement of d-wave superconductivity in an extended checkerboard Hubbard ladder

By employing the density-matrix renormalization group method, we study an extended checkerboard Hubbard model on the two-leg ladder, which includes an intraplaquette nearest-neighbour attraction V. The simulated results show that V plays a significant role in enhancing the d-wave superconductivity when the electron density is close to half-filling. In the homogeneous case t'=t (t and t' are the intraplaquette and interplaquette hopping integrals), large critical |Vc| is required to induce the superconducting ground state. With decreasing t', |Vc| is substantially diminished and the pair state has a nearly C4 symmetry. In the extremely inhomogeneous case t'<0.2t, the system transits to the d-wave superconducting phase at V\sim-0.3t and V\sim-0.4t for U=8t and U=12t, respectively, accompanying with a shift of spin and single-particle excitations from gapless to gapped type.

cond-mat.supr-con↗

arXiv2025

Emergent supercounterfluid and quantum phase diagram of two-component interacting bosons in one-dimensional optical lattice

Motivated by a recent experiment that realizes nearest-neighbor dipolar couplings in an optical lattice [C. Lagoin, $\textit{et al.}$, Nature $\textbf{609}$, 485 (2022)], we study a one-dimensional version of the two-component extended Bose-Hubbard model via the density-matrix renormalization group method. By using the nearest-neighbor and on-site interaction parameters from the experiment, we start by mapping the quantum phase diagram in the hopping parameters $t_{A}\mbox{-}t_{B}$ plane with boson densities $\rho_{A}=\rho_{B}=1/2$. In addition to the density wave phase reported in the experiment, we find several regimes of superfluidity when one or two hopping parameters are large enough, and interestingly there is a supercounterfluid phase at moderate and comparable hopping parameters. The universality classes of these phase transitions are analyzed from the correlation functions, excitation gaps, and entanglement entropy. In particular, a Berezinskii-Kosterlitz-Thouless type is recognized several gapped-to-gapless transitions. In addition, we also study the quantum phase transitions when varying $\rho_{B}$ from 0 to 1 while keeping $\rho_A = 1/2$. We identify a supersolid phase in a wide range of $1/2<\rho_B<1$. Our work paves the way for realizing exotic many-body phases in cold atom experiments upon proper tuning of experimental parameters.

cond-mat.quant-gas↗

arXiv2025

Energy Dispersion, Superconductivity and Magnetic Fluctuations in Stacked Altermagnetism Materials

Recently, altermagnetism (AM) has emerged as a new category of magnetism, alongside conventional antiferromagnetism (AFM) and ferromagnetism (FM). In an AM, superconductivity (SC) is faced with a dilemma that the spin-polarized bands, induced by the broken time reversal (T ) symmetry, dominantly supports spin-triplet pairing. In contrast, AM spin fluctuations routinely facilitate spin-singlet pairing as in AFM. Consequently, unconventional SC is either absent or weak in AM materials. Here, we propose that stacking 2D AM materials could resolve this dilemma. Stacked 2D materials have yielded a variety of new electronic properties by altering the symmetries inherent in the monolayer. In a 2D anisotropic Hubbard model, we investigate the general energy dispersions of both single-layer and stacked AM materials. We demonstrate that AM sheet stacking can alter the original symmetries, consequently affecting the energy dispersion. The interlayer magnetic coupling enhances the low q magnetic fluctuations. T symmetry is restored in the AA stacking with an antiferromagnetic interlayer coupling, and then both the energy dispersion and pairing interaction are in favor of spin-singlet SC. The ferromagnetic interlayer coupling in the AB stacking not only recovers T symmetry but also supports spin-triplet pairing. It is further anticipated that twisted bilayer AM sheets could exhibit additional novel electronic properties, including topology, flat bands, and collective excitations. Our work illustrates that stacking sheets of AM materials could open up a unique research domain in exploring novel quantum phenomena and offer a fertile ground for potential electronic applications.

cond-mat.supr-con↗

arXiv2025

Altermagnetism and beyond in the $t$-$t^\prime$-$\delta$ Fermi-Hubbard model

In this work, we revisit the phase diagram of the $t$-$t^\prime$-$\delta$ Fermi-Hubbard model on the square lattice to gain a more comprehensive understanding of this correlated model at half filling. This model has recently become a prominent topic of research because it hosts altermagnetic phases. Using mean-field analysis, we identify four metallic phases and two insulating phases with nontrivial magnetic orders at an intermediate value of $\delta = 0.5$, presenting a rich ground-state phase diagram in the $U$-$t^\prime$ plane. We also highlight the distinct features of the Fermi surface topology for each metallic phase. To go beyond the mean-field theory, we employ the density-matrix renormalization group method to simulate the ground state numerically. The phase boundaries are determined from the discontinuities and peaks in the entanglement entropy and magnetizations. In addition to the phases identified in the mean-field theory, we find a valence-bond solid state in a narrow intermediate-$t'$ region. Our work offers a firm step forward in understanding the complex behaviors of correlated electrons in the $t$-$t^\prime$-$\delta$ Hubbard model over a large parameter space.

cond-mat.str-el↗

arXiv2024

Interplay of Kitaev Interaction and Off-diagonal Exchanges: Exotic Phases and Quantum Phase Diagrams

Aligning with the everlasting search for quantum spin liquids (QSLs), identifying the QSL in Kitaev magnets has garnered great research interest during the past decade and remains nevertheless an enormous challenge. One of the major difficulties lies in that Kitaev QSL is typically fragile against competing interactions like off-diagonal exchanges, which are ubiquitous in real materials due to spin-orbit coupling and crystal-field effect. This, in turn, gives rise to many intriguing field-induced novel phases and thermal Hall effect. In this review, we will focus on the interplay of Kitaev interaction and off-diagonal $\Gamma$ and $\Gamma'$ exchanges from a numerical perspective. This review discusses some representative exotic phases such as $\Gamma$ spin liquid, nematic ferromagnet, spin-flop phase, and distinct chiral-spin states with spontaneously time-reversal symmetry breaking. It also presents quantum phase diagrams of anisotropic Kitaev-$\Gamma$ chains that exhibit kaleidoscopes of both ordered and disordered phases.

cond-mat.str-el↗

arXiv2024

Quantum dynamics in a spin-1/2 square lattice $J_{1}$-$J_{2}$-$\delta$ altermagnet

A key feature of the newly discovered altermagnet is that its spin degeneracy is lifted, although it has an antiferromagnetic order and zero net magnetization. In this work, we investigate a frustrated spin-1/2 $J_1$-$J_2$-$\delta$ Heisenberg model on the square lattice by the tensor network methodin combination with the linear spin-wave theory, with our focus on both the magnon excitations and longitudinal excitations.For a small $J_2$ and a finite range of $\delta$ we demonstrate that such a model hosts an altermagnetic ground state. Its magnon spectrum is split into two branches and the largest splitting occurs at $\left(\pm\pi/2, \pm\pi/2\right)$ in the Brillouin zone. The magnitudes of splitting in the two magnon modes are equal with respect to the case of $\delta=0$. Dynamical spin structure factors show that the low-energy peak in the longitudinal spectral weight around $(\pi/2, \pi/2)$ is also split, and thus the relative positions of the magnon modes and longitudinal modes in energy may change in the presence of a finite $\delta$. These findings demonstrate that the altermagnets harbor more complex quantum dynamics than the conventional collinear antiferromagnets.

cond-mat.str-el↗

arXiv2024

Successive topological phase transitions in two distinct spin-flop phases on the honeycomb lattice

The Kitaev magnets with bond-dependent interactions have garnered considerable attention in recent years for their ability to harbor exotic phases and nontrivial excitations. The topological magnons, which are indicated by nonzero Chern number that can enhance the thermal Hall conductivity, are proposed to partially explain thermal Hall measurements in real materials. Hitherto, topological magnons have been extensively explored when the magnetic field is normal to the honeycomb plane, but their topological characteristics are less studied in the presence of in-plane magnetic field. Here, we study two distinct in-plane field induced spin-flop phases in the $\Gamma$-$\Gamma'$ model, both of which are off-diagonal couplings that have intimate relation to the Kitaev interaction. The two spin-flop phases are distinguished by their out-of-plane spin components which can be either antiparallel or parallel, thus dubbing antiferromagnetic (AFM) or ferromagnetic (FM) spin-flop phases, respectively. We map out topological phase diagrams for both phases, revealing a rich pattern of the Chern number over exchange parameters and magnetic field. We analytically calculate the boundaries of topological phase transitions when the magnetic field is along the $a$ and $b$ directions. We find that the thermal Hall conductivity and its derivative display contrasting behaviors when crossing different topological phase transitions. The striking difference of the two phases lies in that when the magnetic field is along the $b$ direction, topological magnons are totally absent in the AFM spin-flop phase, while they can survive in the FM analogue in certain parameter regions.

cond-mat.str-el↗

arXiv2024

Chiral spin state and nematic ferromagnet in the spin-1 Kitaev-$\Gamma$ model

The higher-spin Kitaev magnets, in which the Kitaev interaction and off-diagonal exchange couplings are overwhelmingly large, have emerged as a fertile avenue to explore exotic phases and unusual excitations. In this work, we study the quantum phase diagram of the spin-1 Kitaev-$\Gamma$ model on the honeycomb lattice using density-matrix renormalization group. It harbours six distinct phases and the intriguing findings are three magnetically ordered phases in which both time-reversal symmetry and lattice symmetry albeit of different sort are broken spontaneously. The chiral spin state originates from the order-by-disorder effect and exhibits an almost saturated scalar spin chirality at the quantum level. Depending on the relative strength of the two interactions, it also features columnar-like or plaquette-like dimer pattern as a consequence of the translational symmetry breaking. In parallel, the nematic ferromagnets are situated at ferromagnetic Kitaev side and possess small but finite ferromagnetic ordering. The lattice-rotational symmetry breaking enforces nonequivalent bond energy along one of the three bonds. Although the intrinsic difference between the two nematic ferromagnets remains elusive, the discontinuities in the von Neumann entropy, hexagonal plaquette operator, and Wilson loop operator convincingly suggest that they are separated via a first-order phase transition.

cond-mat.str-el↗

arXiv2023

Topological phase transitions and thermal Hall effect in a noncollinear spin texture

The noncollinear spin textures provide promising avenues to stabilize exotic magnetic phases and excitations. They have attracted vast attention owning to their nontrivial band topology in the past decades. Distinct from the conventional route of involving the Dzyaloshinskii-Moriya interaction in a honeycomb magnet, the interplay of bond-dependent Kitaev and $\Gamma$ interactions, originating from the spin-orbit coupling and octahedra crystal field in real materials, has demonstrated to be another source to generate noncollinear spin textures with multiple spins in a magnetic unit cell. Notably, earlier works have revealed a triple-meron crystal (TmX) consisting of eighteen spins in the frustrated Kitaev-$\Gamma$ model. Aligning with previous efforts, here we attempt to identify that the TmX hosts several peculiar features with the help of the linear spin-wave theory. To begin with, the symmetric anisotropic exchanges are beneficial for the existence of nonreciprocal magnons, which are stabilized by an external magnetic field. Further, within the regime of TmX, successive topological phase transitions occur, accompanied by the changes of Chern number in value and thermal Hall conductivity in sign. In addition, topological nature of magnons is also verified by the onset of chiral edge modes in a nanoribbon geometry. Our findings pave the way to study topological phenomena of noncollinear spin textures in potential Kitaev materials.

cond-mat.str-el↗

arXiv2023

Bose-Einstein condensation of a two-magnon bound state in a spin-one triangular lattice

In ordered magnets, the elementary excitations are spin waves (magnons), which obey Bose-Einstein statistics. Similarly to Cooper pairs in superconductors, magnons can be paired into bound states under attractive interactions. The Zeeman coupling to a magnetic field is able to tune the particle density through a quantum critical point (QCP), beyond which a "hidden order" is predicted to exist. Here we report direct observation of the Bose-Einstein condensation (BEC) of the two-magnon bound state in Na$_2$BaNi(PO$_4$)$_2$. Comprehensive thermodynamic measurements confirmed the two-dimensional BEC-QCP at the saturation field. Inelastic neutron scattering experiments were performed to establish the microscopic model. An exact solution revealed stable 2-magnon bound states that were further confirmed by electron spin resonance and nuclear magnetic resonance experiments, demonstrating that the QCP is due to the pair condensation and the phase below saturation field is likely the long-sought-after spin nematic phase.

cond-mat.str-el↗

arXiv2023

Spontaneous dimerization, spin-nematic order, and deconfined quantum critical point in a spin-1 Kitaev chain with tunable single-ion anisotropy

The Kitaev-type spin chains have been demonstrated to be fertile playgrounds in which exotic phases and unconventional phase transitions are ready to appear. In this work, we use the density-matrix renormalization group method to study the quantum phase diagram of a spin-1 Kitaev chain with a tunable negative single-ion anisotropy (SIA). When the strength of the SIA is small, the ground state is revealed to be a spin-nematic phase which escapes conventional magnetic order but is characterized by a finite spin-nematic correlation because of the breaking spin-rotational symmetry. As the SIA increases, the spin-nematic phase is taken over by either a dimerized phase or an antiferromagnetic phase through an Ising-type phase transition, depending on the direction of the easy axis. For large enough SIA, the dimerized phase and the antiferromagnetic phase undergo a ``Landau-forbidden" continuous phase transition, suggesting new platform of deconfined quantum critical point in spin-1 Kitaev chain.

cond-mat.str-el↗

arXiv2023

Robust superconducting correlation against inter-site interactions in the extended two-leg Hubbard ladder

The Hubbard and related models serve as a fundamental starting point in understanding the novel experimental phenomena in correlated electron materials, such as superconductivity, Mott insulator, magnetism and stripe phases. Recent numerical simulations indicate that the emergence of superconductivity is connected with the next nearest-neighbor hopping $t^\prime$ in the Hubbard model. However, the impacts of complex inter-site electron interaction in the $t^\prime$-Hubbard model are less explored. Utilizing the state-of-art density-matrix renormalization group method, we investigate the $t^\prime$-Hubbard model on a two-leg ladder with inter-site interactions extended to the fourth neighbor sites. The accurate numerical results show that the quasi-long-range superconducting correlation remains stable under the repulsive nearest-neighbor and the next nearest-neighbor interactions though these interactions are against the superconductivity. The ground state properties are also undisturbed by the longer-range repulsive interactions. In addition, inspired by recent experiments on one-dimensional cuprates chain $\mathrm{Ba}_{2-x}\mathrm{Sr}_x\mathrm{CuO}_{3+\delta}$, which implies an effective attraction between the nearest neighbors may exist in the cuprates superconductors, we also show that the attractive interaction between the nearest neighbors significantly enhances the superconducting correlation when it is comparable to the strength of the nearest-neighbor hopping $t^\prime$. Stronger attraction drives the system into a Luther-Emery liquid phase. Nevertheless, with the attraction further increasing, the system enters an electron-hole phase separation and the superconducting correlation is destroyed. Finally, we investigate the effects of on-site Coulomb interaction on superconductivity.

cond-mat.str-el↗