arXiv subjects

Gang V. Chen

Publications and source records attributed to Gang V. Chen.

5 recordsLinked to original sources

arXiv2025

Fermionized dual vortex theory for magnetized kagomé spin liquid

Inspired by the recent quantum oscillation measurement on the kagomé lattice antiferromagnet in finite magnetic fields, we raise the question about the physical contents of the emergent fermions and the gauge fields if the U(1) spin liquid is relevant for the finite-field kagomé lattice antiferromagnet. Clearly, the magnetic field is non-perturbative in this regime, and the finite-field state has no direct relation with the U(1) Dirac spin liquid proposal at zero field. We here consider the fermionized dual vortex liquid state as one possible candidate theory to understand the magnetized kagomé spin liquid. Within the dual vortex theory, the $S^z$ magnetization is the emergent U(1) gauge flux, and the fermionized dual vortex is the emergent fermion. The magnetic field polarizes the spin component that modulates the U(1) gauge flux for the fermionized vortices and generates the quantum oscillation. Within the mean-field theory, we discuss the gauge field correlation, the vortex-antivortex continuum and the vortex thermal Hall effect.

cond-mat.str-el↗

arXiv2024

Inelastic neutron scattering on Ce pyrochlores: Signatures of electric monopoles

We revisit the pyrochlore spin liquid materials Ce$_2$Sn$_2$O$_7$ and Ce$_2$Zr$_2$O$_7$ by examining the existing experiments. We continue to rely on the special properties of the dipole-octupole nature of the Ce$^{3+}$ moment. The inelastic neutron scattering (INS) measurement in the octupolar U(1) spin liquid selects the (gapped) spinon continuum, and thus has suppressed spectral weights below the energy threshold of two spinon gaps. This measurement, however, includes all other emergent excitations at lower energies in the dipolar U(1) spin liquid, in particular, the gapless photon and the continuum of the electric monopoles. Although the electric monopole continuum is weakly gapped (compared to the larger spinon gap), the energy scale is actually close to the gauge photons, and the spectrum largely overlaps with the photons. Due to the background dual $π$ flux for the electric monopoles, the density of states is enhanced at lower energies, creating peak structures. This can be contrasted with the linearly suppressed spectral weight of the gauge photons at low energies. We propose that the electric monopole continuum should be mostly responsible for the low-energy spectrum in the INS measurement in the dipolar U(1) spin liquid. With these understanding and calculation, we discuss the available experimental results and predict further experiments for Ce$_2$Sn$_2$O$_7$ and Ce$_2$Zr$_2$O$_7$.

cond-mat.str-el↗

arXiv2024

Emergent Berezinskii-Kosterlitz-Thouless and Kugel-Khomskii physics in the triangular lattice bilayer colbaltate

Motivated by the experiments on the triangular lattice bilayer colbaltate K$_2$Co$_2$(SeO$_3$)$_3$, we formulate a theory to explore the underlying physics from a couple observation. The model is composed of interacting Co$^{2+}$ dimers on the triangular lattice, where the Co$^{2+}$ ion provides an effective spin-1/2 local moment via the spin-orbit coupling and the crystal field effect. The intra-dimer interaction is dominant and would simply favor the local spin singlet, and the inter-dimer interactions compete with the inter-dimer interaction, leading to rich behaviors. With the easy-axis anisotropy, it is shown that, in the ground state manifold of the intra-dimer Ising interaction, the system realizes an effective transverse field Ising model, where the ground state is either a three-sublattice order or Ising disordered. The finite temperature regime naturally realizes the Berezinskii-Kosterlitz-Thouless physics. To explore the full excitations, we incorporate the excited state manifold of the intra-dimer Ising interaction and establish the emergent Kugel-Khomskii physics. Thus, the triangular lattice bilayer colbaltate is an excellent platform to explore the interplay between geometrical frustration and anisotropic interactions as well as the emergent effective models and the resulting physics.

cond-mat.str-el↗

arXiv2024

Chiral phonons induced from spin dynamics via magnetoelastic anisotropy

We propose a mechanism to obtain chiral phonon-like excitations from the bond-dependent magnetoelastic couplings in the absence of out-of-plane magnetization and magnetic fields. By mapping the hybrid excitation to its phononic analog, we reveal the impact of the lattice symmetry on the origin of the chirality. In the example of a triangular lattice ferromagnet, we recognize that the system is equivalent to the class D of topological phonons, and show the tunable chirality and topology by an in-plane magnetic field. As a possible experimental probe, we evaluate the phonon magnetization and planar thermal Hall conductivity. Our study gives a new perspective on tunable topological and chiral excitations beyond the Raman spin-lattice coupling, suggesting possible applications of spintronics and phononics in various anisotropic magnets and/or Kitaev materials.

cond-mat.mes-hall↗

arXiv2023

Multiflavor Mott insulators in quantum materials and ultracold atoms

Mott insulators with large and active (or multiflavor) local Hilbert spaces widely occur in quantum materials and ultracold atomic systems, and are dubbed "multiflavor Mott insulators". For these multiflavored Mott insulating materials, the spin-only description with the quadratic spin interactions is often insufficient to capture the major physical processes. In the situation with active orbitals, the Kugel-Khomskii superexchange model was then proposed. We briefly review this historical model and discuss the modern developments beyond the original spin-orbital context. These include and are not restricted to the $4d$/$5d$ transition metal compounds with the spin-orbit-entangled $J=3/2$ quadruplets, the rare-earth magnets with two weakly-separated crystal field doublets, breathing magnets and/or the cluster and molecular magnets, et al. We explain the microscopic origin of the emergent Kugel-Khomskii physics in each realization with some emphasis on the $J=3/2$ quadruplets, and refer the candidate multiflavor Mott insulators as "$J=3/2$ Mott insulators". For the ultracold atoms, we review the multiflavor Mott insulator realization with the ultracold alkaline and alkaline-earth atoms on the optical lattices. Despite a large local Hilbert space from the atomic hyperfine spin states, the system could naturally realize a large symmetry group such as the Sp($N$) and SU($N$) symmetries. These ultracold atomic systems lie in the large-$N$ regime of these symmetry groups and are characterized by strong quantum fluctuations. The Kugel-Khomskii physics and the exotic quantum ground states with the "baryon-like" physics can appear in various limits. We conclude with our vision and outlook on this subject.

cond-mat.str-el↗