arXiv subjects

Philip Richard

Publications and source records attributed to Philip Richard.

3 recordsLinked to original sources

arXiv2026

Evolution from Kitaev to XXZ spin chains via distortion: Application to BaCo$_2$V$_2$O$_8$

BaCo$_2$V$_2$O$_8$ is a prototypical spin-orbit-coupled Ising-chain antiferromagnet that provides a unique platform for studying field-induced quantum magnetism. Under a transverse magnetic field, it exhibits unusual magnetic properties, including an anomalous staggered magnetization and a pronounced anisotropy of the critical field with respect to the in-plane field direction. While these phenomena have been attributed phenomenologically to a site-dependent anisotropic $g$-tensor, a recent microscopic theory has shown that spin-orbit coupling naturally generates bond-dependent Heisenberg, Kitaev, and $\Gamma$ exchange interactions. Here, we unify these two pictures by extending the microscopic theory to incorporate distortions of the CoO$_6$ octahedra. We show that the distortions not only generate the site-dependent anisotropic $g$-tensor but also renormalize the staggered exchange interactions through a distortion-induced contribution that partially compensates the Kitaev-derived staggered term. Using point-charge calculations to estimate the $g$-tensor of BaCo$_2$V$_2$O$_8$, we demonstrate that the strong anisotropy of the critical field originates from the combined effects of the modified exchange interactions and the anisotropic $g$-tensor. Our work provides a unified microscopic framework for understanding the magnetic anisotropy of spin-orbit-coupled Ising-chain materials.

cond-mat.str-el↗

arXiv2025

Microscopic Theory Revealing Ising Criticality with Distinct Sublattice Orders in Pseudospin-1/2 Chain

The one-dimensional transverse Ising model is a paradigmatic example of quantum criticality. In spin-orbit coupled systems, however, effective Ising interactions arise alongside bond-dependent couplings such as Kitaev ($K$) and $\Gamma$ terms in addition to the Heisenberg ($J$) interaction, leading to complex magnetic orders beyond the pure Ising limit. We first explore how the generic $J-K-\Gamma$ model with four-fold screw symmetry in a spin-orbit-entangled pseudospin-1/2 chain manifests via sublattice order, and then test whether field-driven transitions retain Ising universality. We find sublattice-dependent magnetic order below the critical field and a distinct sublattice pattern persisting above it. Despite these complex magnetic order structures, the transition remains in the Ising universality class with central charge $c=1/2$. Our work provides a route to the microscopic Hamiltonian and emergent Ising criticality while allowing microscopic physics of the sublattice orders to manifest at low and high fields. Application to antiferromagnetic Ising materials such as BaCo$_2$V$_2$O$_8$ is also discussed.

cond-mat.str-el↗

arXiv2023

Disorder induced topological phase transition in a driven Majorana chain

We study a periodically driven one dimensional Kitaev model in the presence of disorder. In the clean limit our model exhibits four topological phases corresponding to the existence or non-existence of edge modes at zero and pi quasienergy. When disorder is added, the system parameters get renormalized and the system may exhibit a topological phase transition. When starting from the Majorana $\pi$ Mode (MPM) phase, which hosts only edge Majoranas with quasienergy pi, disorder induces a transition into a neighboring phase with both pi and zero modes on the edges. We characterize the disordered system using (i) exact diagonalization (ii) Arnoldi mapping onto an effective tight binding chain and (iii) topological entanglement entropy.

cond-mat.supr-con↗