arXiv subjects

Jiefu Cen

Publications and source records attributed to Jiefu Cen.

6 recordsLinked to original sources

arXiv2026

Thermal and quantum fluctuations in extended Kitaev-Yao-Lee spin-orbital model

Building upon the spin-1/2 Kitaev model on a honeycomb lattice, the Yao-Lee spin-orbital model provides exactly solvable quantum spin liquids with potentially better stability against perturbations due to the additional degree of freedom. Recently, the microscopic mechanism underlying the Yao-Lee interaction in honeycomb materials has been uncovered, leading to an extended Kitaev-Yao-Lee spin-orbital model when the celebrated Kugel-Khomskii interaction is included. Numerical studies of this model have identified various disordered phases, including a broad region of the nematic phase that is reminiscent of a spin-orbital liquid. Here, we investigate the origin and stability of this nematic phase via thermal and quantum fluctuations using classical Monte Carlo simulations and a generalized spin wave theory appropriate for the spin-orbital model. We demonstrate that the additional spin-orbital degree of freedom gives rise to strong thermal and quantum fluctuations in spin-orbital models, providing insight into the emergence of disordered phases.

cond-mat.str-el↗

arXiv2026

Ferrichiral skyrmions with sublattice-resolved chirality in extended Kitaev model in triangular lattice

We study an extended Kitaev model on the triangular lattice in a limit where the symmetric off-diagonal bond-dependent and Heisenberg interactions together map onto an XXZ model, in addition to the Kitaev interaction. Within the previously identified $\mathbb{Z}_2$ vortex regime, we uncover a ferrichiral skyrmion phase characterized by a sublattice-resolved scalar chirality: two of the three sublattices carry unit skyrmion charge, while the third remains nonchiral. Using classical Monte Carlo simulations, we show that this ferrichiral skyrmion phase emerges at zero temperature and in the absence of both an external magnetic field and Dzyaloshinskii-Moriya interactions, in sharp contrast to conventional skyrmion-hosting systems. The phase is stable over a wide parameter window and persists to relatively high temperatures. Our results reveal an unconventional route to skyrmion physics driven purely by frustrated exchange interactions and highlight the emergence of rich topological structures. Since both XXZ anisotropy and Kitaev interactions originate from the same spin-orbit-coupling mechanism, materials traditionally classified as XXZ magnets are expected to host finite Kitaev interactions as well. The potential for ferrichirality in these systems therefore warrants further investigation.

cond-mat.str-el↗

arXiv2025

Intermediate phases in $\alpha$-RuCl$_3$ under in-plane magnetic field via interlayer spin interactions

$\alpha$-RuCl$_3$ has attracted significant attention as a prime candidate for the spin-1/2 Kitaev spin liquid in two-dimensional honeycomb lattices. Although its ground state is magnetically ordered, the order is suppressed under a moderate in-plane magnetic field. The intermediate regime of the field has exotic behaviors, some of which are claimed to originate from a Kitaev spin liquid. In resolving debates surrounding these behaviors, interlayer interactions in $\alpha$-RuCl$_3$ have been largely overlooked due to their perceived weakness in van der Waals materials. However, near the transition, they may become significant as the field energy approaches the interlayer coupling scale. Here we investigate the effects of interlayer couplings in $\alpha$-RuCl$_3$ with $R\bar{3}$ and $C2/m$ structures. We first examine their effects on the transition temperature ($T_N$) using classical Monte Carlo simulations. We found that the interlayer couplings have minimal effects on $T_N$, and the different $T_N$ between the two structures are mainly due to the anisotropy in intralayer interactions. Focusing on the $R{\bar 3}$ structure, we show that the nearest neighbor interlayer interaction is the XXZ type due to the symmetry, and the next nearest neighbor interaction of the Kitaev type is crucial for the transition between two zigzag orders under an in-plane field. Furthermore, an intermediate phase with a large unit cell emerges due to the interlayer interactions. Our findings provide insights into the exotic behaviors and sample dependence reported in $\alpha$-RuCl$_3$.

cond-mat.str-el↗

arXiv2024

Spin-orbit coupling controlled two-dimensional magnetism in chromium trihalides

CrX$_3$ (X = Cl, Br, I) have the same crystal structure and Hamiltonian but different ligand spin-orbit coupling (SOC) constant $\lambda_X$, providing excellent material platform exploring for exotic two-dimensional (2D) spin orders. Their microscopic mechanism underlying 2D spin physics remain unestablished, along with experimental corroboration of Kitaev exchange interaction, central to realizing topological quantum spin liquids. Finding direct evidence for Kitaev interaction and determining its value has been an essential but formidable challenge in Kitaev physics. Here we report the direct Kitaev interaction signature in magnetic anisotropy measured by ferromagnetic resonance (FMR) spectroscopy. We present measured values of Heisenberg $J$, Kitaev $K$, and off-diagonal symmetric $\Gamma$ exchange interactions in CrX$_3$ determined using FMR and exact diagonalization. $K$ and $\Gamma$ exhibit dominant dependencies on $\lambda_X$, indicating its central role in 2D magnetism. Our study provides a foundation for designing 2D magnetic materials exhibiting novel behaviors by tuning intrinsic material parameters such as SOC.

cond-mat.str-el↗

arXiv2022

Determining Kitaev interaction in spin-$S$ honeycomb Mott insulators

The Kitaev interaction in a honeycomb lattice with higher-spin $S$ has been one of the central attractions, as it may offer quantum spin liquids. A microscopic theory showed that when the Hund's coupling at the transition metal generates $S> \frac{1}{2}$, the spin-orbit coupling at the heavy ligands provides a route to the Kitaev interaction. However, there have been debates over its strength compared to other symmetry-allowed interactions. Investigating the symmetry of the Hamiltonian for general $S$, we show the magnon energies at two momentum points related by a broken mirror symmetry reflect the Kitaev interaction when a magnetic field is in the mirror plane. Applying the symmetry analysis to CrI$_3$ with $S=\frac{3}{2}$ together with the available angle-dependent ferromagnetic resonance data, we estimate the Kitaev interaction out of the full Hamiltonian and find that it is sub-dominant. Our theory can be tested by inelastic neutron scattering on candidate materials under the proposed magnetic field direction, which will advance the search for general $S$ Kitaev materials.

cond-mat.str-el↗

arXiv2022

Strategy to Extract Kitaev Interaction using Symmetry in Honeycomb Mott Insulators

The Kitaev spin liquid, a ground state of the bond-dependent Kitaev model in a honeycomb lattice has been a centre of attraction, since a microscopic theory to realize such an interaction in solid-state materials was discovered. A challenge in real materials though is the presence of the Heisenberg and another bond-dependent Gamma interactions detrimental to the Kitaev spin liquid, and there have been many debates on their relative strengths. Here we offer a strategy to extract the Kitaev interaction out of a full microscopic model by utilizing the symmetries of the Hamiltonian. Two tilted magnetic field directions related by a two-fold rotational symmetry generate distinct spin excitations originating from a specific combination of the Kitaev and Gamma interactions. Together with the in- and out-of-plane magnetic anisotropy, one can determine the Kitaev and Gamma interactions separately. Dynamic spin structure factors are presented to motivate future experiments. The proposed setups will advance the search for Kitaev materials.

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