arXiv subjects

Hibiki Takegami

Publications and source records attributed to Hibiki Takegami.

3 recordsLinked to original sources

arXiv2025

Angular Dependence of Specific Heat and Magnetization Effects in the Kitaev Model

We investigate the effect of a magnetic field on the Kitaev model using the equation of motion approach for the spin Green's function, considering both the case of suppressed magnetization ($m = 0$) and finite magnetization ($m \neq 0$). When magnetization is suppressed, the specific heat exhibits a clear $60^\circ$ periodicity in its angular dependence, with the locations of maxima and minima consistent with recent experimental observations in $α$-RuCl$_3$. A qualitative difference in their temperature dependence is observed: the minima show gap-like behavior that may signal Majorana gap formation due to time-reversal symmetry breaking, while the maxima do not exhibit the expected gapless Majorana fermion signature. In addition, a linear-in-field effect -- distinct from magnetization -- emerges, with the characteristic temperature below which angular dependence appears increasing linearly with the magnetic field. Importantly, this directional dependence becomes quantitatively significant only at very low temperatures. When finite magnetization is included, the angular dependence of the specific heat remains, and the qualitative behavior is similar to the $m = 0$ case: the minima continue to exhibit gap-like features, while the maxima do not show signatures of gapless Majorana fermions. These results suggest that suppressing magnetization alone is insufficient to realize quantum spin liquid behavior in the Kitaev model under a magnetic field.

cond-mat.str-el↗

arXiv2025

Static and Dynamical Spin Correlations in the Kitaev Model at Finite Temperatures via Green's Function Equation of Motion

The Kitaev model, renowned for its exact solvability and potential to host non-Abelian anyons, remains a focal point in the study of quantum spin liquids and topological phases. While much of the existing literature has employed Majorana fermion techniques to analyze the model, particularly at zero temperature, its finite-temperature behavior has been less thoroughly explored via alternative approaches. In this paper, we investigate the finite-temperature properties of the Kitaev model using the spin Green's function formalism. This approach enables the computation of key physical quantities such as spin correlations, magnetic susceptibility, and the dynamical spin structure factor, offering crucial insights into the system's thermal dynamics. In solving the equation of motion for the spin Green's function, we truncate the hierarchy of multi-spin Green's functions using a decoupling approximation, which proves to be particularly accurate at high temperatures. Our results show several similarities with Majorana-based numerical simulations, though notable differences emerge. Specifically, both static and dynamical spin-spin correlation functions capture not only $\mathbb{Z}_2$ flux excitations but also simple spin-flip excitations, with the latter overshadowing the former. Interestingly, without explicitly assuming fractionalization, our results for the spin susceptibility and spin relaxation rate still suggest the presence of fermionic degrees of freedom at low temperatures. This study provides a complementary approach to understanding the thermal properties of the Kitaev model, which could be relevant for future experiments and theoretical investigations.

cond-mat.str-el↗

arXiv2024

Spin-Spin Correlations in the Kitaev Model at Finite Temperatures: Approximate and Exact Results via Green's Function Equation of Motion

The Kitaev model, defined on a honeycomb lattice, features an exactly solvable ground state with fractionalized Majorana fermion excitations, which can potentially form non-Abelian anyons crucial for fault-tolerant topological quantum computing. Although Majorana fermions are essential for obtaining the exact ground state, their physical interpretation in terms of spin operators remains unclear. In this study, we employ a Green's function approach that maintains SU(2) symmetry to address this issue and explore the model's finite temperature properties. Our results demonstrate that the computed temperature dependence of the correlation functions closely approximates the exact values at zero temperature, confirming the accuracy of our method. We also present several exact results concerning the spin Green's function and spin-spin correlation functions that are specific to the Kitaev model.

cond-mat.str-el↗