arXiv subjects

Chun-Jiong Huang

Publications and source records attributed to Chun-Jiong Huang.

13 recordsLinked to original sources

arXiv2026

Signatures of field-induced multi-color kagome spin liquids in the dipole-octupole pyrochlore $\mathrm{Ce_2Hf_2O_7}$

We report low-temperature magnetization and magnetostriction measurements on the dipole-octupole pyrochlore $\mathrm{Ce_2Hf_2O_7}$, revealing an unconventional field response for $\mathbf B\parallel[111]$. The magnetization shows no kagome-ice plateau; instead it evolves continuously and exhibits two rapid changes in slope near 0.35~T and 1.2~T, accompanied by magnetostriction features at the same field scales. Classical Monte Carlo simulations, exact diagonalization, and ground-state analysis of the Hamiltonian show that a representative QSI-compatible parameter set captures the data. For this parameter set, the lower-field anomaly marks a closely spaced transition sequence from a two-color kagome spin liquid (KSL) through a narrow three-color KSL into a mixed two-/three-color KSL, while the upper-field anomaly marks the transition from the mixed KSL into a nearly polarized state. These results identify $\mathrm{Ce_2Hf_2O_7}$, and dipole-octupole pyrochlore magnets more broadly, as promising platforms for exotic KSLs beyond conventional spin ice.

cond-mat.str-el↗

arXiv2025

Nematic correlations and nematic Berezinskii-Kosterlitz-Thouless transition in spin-1 kagome lattice antiferromagnets

Nematicity plays an important role in strongly correlated electron systems. We explore the spin nematicity of a spin-1 kagome lattice antiferromagnet with the bilinear-biquadratic model and single-ion anisotropy using a generalized semiclassical approximation and Monte Carlo simulations. We reveal a rich ground state phase diagram, characterized by two main regions: a pure spin nematic phase and a region featuring the coexistence of a classical spin liquid and ferroicities for both dipolar and quadrupolar moments. The thermal fluctuation melts the spin nematic order into a critical phase with a quasi-long-range nematic order. Due to the fluctuating vortices of the spin nematic order, this critical phase further undergoes a nematic Berezinskii-Kosterlitz-Thouless transition to a paramagnetic phase, marked by an anomalous stiffness jump. Additionally, the single-ion anisotropy leads to weak ferromagnetism, resulting in spontaneous time-reversal symmetry breaking at very low temperatures. Remarkably, both two types of ferroic ordering are accompanied by classical spin liquid behaviors. Our results provide an intriguing glimpse into the interplay between geometric frustration and intertwining spin orders with different ranks and are expected to stimulate further studies on spin-1 systems and relevant materials.

cond-mat.str-el↗

arXiv2024

Subsystem symmetries, critical Bose surface, and immobile excitations in an extended compass model

We propose an extended compass model that hosts subsystem symmetries and has potential experimental relevance with 3d transition metal compounds. The subsystem symmetries strongly constrain the mobility of spin excitations and lead to profound consequences. At the quantum critical point we find the presence of "critical Bose surface" along the entire $k_x$ and $k_y$ axis. Across which we find a nodal-line spin liquid that undergoes nematic instability at low temperatures. In the ferro-quadrupole phase, we find that one excitation is immobile individually analogous to "fractons".

cond-mat.str-el↗

arXiv2023

Searching for Unconventional Superfluid in Excitons of Monolayer Semiconductors

It is well known that two-dimensional (2D) bosons in homogeneous space cannot undergo real Bose-Einstein condensation, and the superfluid to normal phase transition is Berezinskii-Kosterlitz-Thouless (BKT) type, associated with vortex-antivortex pair unbinding. Here we point out a 2D bosonic system whose low energy physics goes beyond conventional paradigm of 2D {\it homogeneous} bosons, i.e., intralayer excitons in monolayer transition metal dichalcogenides. With intrinsic valley-orbit coupling and valley Zeeman energy, exciton dispersion becomes linear at small momentum, giving rise to a series of novel features. The critical temperature of Bose-Einstein condensation of these excitons is nonzero, suggesting true long-range order in 2D homogeneous system. The dispersion of Goldstone mode at long wavelength has the form $\varepsilon(\boldsymbol{q})\sim\sqrt{q}$, in contrast to conventional linear phonon spectrum. The vortex energy deviates from the usual logarithmic form with respect to system size, but instead has an additional linear term. Superfluid to normal phase transition is no longer BKT type for system size beyond a characteristic scale, without discontinuous jump in superfluid density. With the recent experimental progress on exciton fluid at thermal equilibrium in monolayer semiconductors, our work points out an experimentally accessible system to search for unconventional 2D superfluids beyond BKT paradigm.

cond-mat.quant-gas↗

arXiv2022

Spiral-spin-liquid behaviors and persistent reciprocal kagomé structure in frustrated van der Waals magnets and beyond

We study classical $J_1$-$J_2$ models with distinct spin degrees of freedom on a honeycomb lattice. For the XY and Heisenberg spins, the system develops a spiral spin liquid (SSL) that is a thermal cooperative paramagnetic regime with spins fluctuating around the spiral contours in the momentum space, and at low temperatures supports a vector spin-chirality order despite the absence of long-range magnetic order. In a strong contrast, for the Ising moments, the low-temperature spin correlation forms a reciprocal "kagomé" structure in the momentum space that resembles the SSL behaviors and persists for a range of exchange couplings. The unexpected emergence and persistence of the reciprocal "kagomé" are attributed to the stiffness of the Ising moments and the frustration. At higher temperatures when the thermal fluctuations is strong and the spin correlation is not fully melted, the reciprocal structures evolve from the "kagomé" towards the ones demanded by the soft spin limit. This contrasts strongly with the behaviors of the spiral contours in the SSL regime for the continuous spins. We suggest various experimentally relevant systems including van der Waals magnets such as the transition metal phosphorus trichalcogenides TMPX$_3$, Cr$_2$Ge$_2$Te$_6$, the rare-earth chalcohalides (like HoOF, ErOF and DyOF) and other isostructural systems to realize the SSL-like behaviors and/or the reciprocal kagomé structure.

cond-mat.str-el↗

arXiv2021

Generic Spiral Spin Liquids

Spiral spin liquids are unique classical spin liquids that occur in many frustrated spin systems, but do not comprise a new phase of matter. Owing to extensive classical ground-state degeneracy, the spins in a spiral spin liquid thermally fluctuate cooperatively from a collection of spiral configurations at low temperatures. These spiral propagation wavevectors form a continuous manifold in reciprocal space, \textit{i.e.}, a spiral contour or a spiral surface, that strongly governs the low-temperature thermal fluctuations and magnetic physics. In this paper, the relevant spin models conveying the spiral spin liquid physics are systematically explored and the geometric origin of the spiral manifold is clarified in the model construction. The spiral spin liquids based on the dimension and the codimension of the spiral manifold are further clarified. For each class, the physical properties are studied both generally and for specific examples. The results are relevant to a wide range of frustrated magnets. A survey of materials is given and future experiments are suggested.

cond-mat.str-el↗

arXiv2020

Emergent Halperin-Saslow mode and Gauge Glass in quantum Ising magnet TmMgGaO$_4$

We propose quenched disorders could bring novel quantum excitations and models to certain quantum magnets. Motivated by the recent experiments on the quantum Ising magnet TmMgGaO$_4$, we explore the effects of the quenched disorder and the interlayer coupling in this triangular lattice Ising antiferromagnet. It is pointed out that the weak quenched (non-magnetic) disorder would convert the emergent 2D Berezinskii-Kosterlitz-Thouless (BKT) phase and the critical region into a gauge glass. There will be an emergent Halperin-Saslow mode associated with this gauge glass. Using the Imry-Ma argument, we further explain the fate of the finite-field $C_3$ symmetry breaking transition at the low temperatures. The ferromagnetic interlayer coupling would suppress the BKT phase and generate a tiny ferromagnetism. With the quenched disorders, this interlayer coupling changes the 2D gauge glass into a 3D gauge glass, and the Halperin-Saslow mode persists. This work merely focuses on addressing a phase regime in terms of emergent U(1) gauge glass behaviors and hope to inspire future works and thoughts in weakly disordered frustrated magnets in general.

cond-mat.str-el↗

arXiv2020

Percolation of the two-dimensional XY model in the flow representation

We simulate the two-dimensional XY model in the flow representation by a worm-type algorithm, up to linear system size $L=4096$, and study the geometric properties of the flow configurations. As the coupling strength $K$ increases, we observe that the system undergoes a percolation transition $K_{\rm perc}$ from a disordered phase consisting of small clusters into an ordered phase containing a giant percolating cluster. Namely, in the low-temperature phase, there exhibits a long-ranged order regarding the flow connectivity, in contrast to the qusi-long-range order associated with spin properties. Near $K_{\rm perc}$, the scaling behavior of geometric observables is well described by the standard finite-size scaling ansatz for a second-order phase transition. The estimated percolation threshold $K_{\rm perc}=1.105 \, 3(4)$ is close to but obviously smaller than the Berezinskii-Kosterlitz-Thouless (BKT) transition point $K_{\rm BKT} = 1.119 \, 3(10)$, which is determined from the magnetic susceptibility and the superfluid density. Various interesting questions arise from these unconventional observations, and their solutions would shed lights on a variety of classical and quantum systems of BKT phase transitions.

cond-mat.stat-mech↗

arXiv2020

Worm-algorithm-type Simulation of Quantum Transverse-Field Ising Model

We apply a worm algorithm to simulate the quantum transverse-field Ising model in a path-integral representation of which the expansion basis is taken as the spin component along the external-field direction. In such a representation, a configuration can be regarded as a set of non-intersecting loops constructed by "kinks" for pairwise interactions and spin-down (or -up) imaginary-time segments. The wrapping probability for spin-down loops, a dimensionless quantity characterizing the loop topology on a torus, is observed to exhibit small finite-size corrections and yields a high-precision critical point in two dimensions (2D) as $h_c \! =\! 3.044\, 330(6)$, significantly improving over the existing results and nearly excluding the best one $h_c \! =\! 3.044\, 38 (2)$. At criticality, the fractal dimensions of the loops are estimated as $d_{\ell \downarrow} (1{\rm D}) \! = \! 1.37(1) \! \approx \! 11/8 $ and $d_{\ell \downarrow} (2{\rm D}) \! = \! 1.75 (3)$, consistent with those for the classical 2D and 3D O(1) loop model, respectively. An interesting feature is that in one dimension (1D), both the spin-down and -up loops display the critical behavior in the whole disordered phase ($ 0 \! \leq \! h \! < \! h_c$), having a fractal dimension $d_{\ell} \! = \! 1.750 (7)$ that is consistent with the hull dimension $d_{\rm H} \! = \! 7/4$ for critical 2D percolation clusters. The current worm algorithm can be applied to simulate other quantum systems like hard-core boson models with pairing interactions.

cond-mat.stat-mech↗

arXiv2020

Cooling and entangling ultracold atoms in optical lattices

Scalable, coherent many-body systems can enable the realization of previously unexplored quantum phases and have the potential to exponentially speed up information processing. Thermal fluctuations are negligible and quantum effects govern the behavior of such systems with extremely low temperature. We report the cooling of a quantum simulator with 10,000 atoms and mass production of high-fidelity entangled pairs. In a two-dimensional plane, we cool Mott insulator samples by immersing them into removable superfluid reservoirs, achieving an entropy per particle of $1.9^{+1.7}_{-0.4} \times 10^{-3} k_{\text{B}}$. The atoms are then rearranged into a two-dimensional lattice free of defects. We further demonstrate a two-qubit gate with a fidelity of 0.993 $\pm$ 0.001 for entangling 1250 atom pairs. Our results offer a setting for exploring low-energy many-body phases and may enable the creation of large-scale entanglement

cond-mat.quant-gas↗

arXiv2020

Intrinsic quantum Ising model on a triangular lattice magnet TmMgGaO$_{4}$ and beyond

The rare-earth magnet TmMgGaO$_{4}$ is proposed to be an intrinsic quantum Ising magnet described by the antiferromagnetic transverse field Ising model (TFIM) on a triangular lattice, where the relevant degrees of freedom are the non-degenerate dipole-multipole doublets of the Tm$^{3+}$ ions and the transverse field has an intrinsic origin from the weak splitting of the doublet. We compare this special doublet of Tm$^{3+}$ with the dipole-octupole Kramers doublet. We study the proposed effective model for the Tm-based triangular lattice and consider the effects of external magnetic fields and finite temperatures. From the "orthogonal operator approach", we show that the TFIM with the three-sublattice intertwined ordered state agrees with the experiments and further clarify the discrepancy in the nubmers of the magnetic sublattices and the measured magnon branches. We make specific predictions for the evolution of the magnetic properties with the external magnetic field. Furthermore, we demonstrate that an emergent U(1) symmetry emerges in thermal melting of the underlying orders and at the criticality, and summarize the previously known signatures related to the finite-temperature Berezinskii-Kosterlitz-Thouless (BKT) physics. We discuss the broad relevance of intrinsic quantum Ising magnets to many other systems, especially the Tm-based materials.

cond-mat.str-el↗

arXiv2018

Extended Coulomb liquid of paired hardcore boson model on a pyrochlore lattice

There is a growing interest in the $U(1)$ Coulomb liquid in both quantum materials in pyrochlore ice and cluster Mott insulators and cold atom systems. We explore a paired hardcore boson model on a pyrochlore lattice. This model is equivalent to the XYZ spin model that was proposed for rare-earth pyrochlores with "dipole-octupole" doublets. Since this model has no sign problem for quantum Monte Carlo (QMC) simulations in a large parameter regime, we carry out both analytical and QMC calculations. We find that the $U(1)$ Coulomb liquid is quite stable and spans a rather large portion of the phase diagram with boson pairing. Moreover, we numerically find thermodynamic evidence that the boson pairing could induce a possible $\mathbb{Z}_2$ liquid in the vicinity of the phase boundary between Coulomb liquid and $\mathbb{Z}_2$ symmetry-broken phase. Besides the materials' relevance with quantum spin ice, we point to quantum simulation with cold atoms on optical lattices.

cond-mat.str-el↗

arXiv2018

Dynamics of Topological Excitations in a Model Quantum Spin Ice

We study the quantum spin dynamics of a frustrated XXZ model on a pyrochlore lattice by using large-scale quantum Monte Carlo simulation and stochastic analytic continuation. In the low-temperature quantum spin ice regime, we observe signatures of coherent photon and spinon excitations in the dynamic spin structure factor. As the temperature rises to the classical spin ice regime, the photon disappears from the dynamic spin structure factor, whereas the dynamics of the spinon remain coherent in a broad temperature window. Our results provide experimentally relevant, quantitative information for the ongoing pursuit of quantum spin ice materials.

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