ABSTRACT
The honeycomb Kitaev-Heisenberg model is a source of a quantum spin liquid with Majorana fermions and gauge flux excitations as fractional quasiparticles. Here we unveil the highly unusual low-temperature heat conductivity κ of α-RuCl_{3}, a prime candidate for realizing such physics: beyond a magnetic field of B_{c}≈7.5 T, κ increases by about one order of magnitude, both for in-plane as well as out-of-plane transport. This clarifies the unusual magnetic field dependence unambiguously to be the result of severe scattering of phonons off putative Kitaev-Heisenberg excitations in combination with a drastic field-induced change of the magnetic excitation spectrum. In particular, an unexpected, large energy gap arises, which increases linearly with the magnetic field, reaching remarkable âω_{0}/k_{B}≈50 K at 18 T.
ABSTRACT
We investigate the heat conductivity κ of the Heisenberg spin-1/2 ladder at finite temperature covering the entire range of interchain coupling J(â¥), by using several numerical methods and perturbation theory within the framework of linear response. We unveil that a perturbative prediction κâJ(â¥)(-2), based on simple golden-rule arguments and valid in the strict limit J(â¥)â0, applies to a remarkably wide range of J(â¥), qualitatively and quantitatively. In the large J(â¥) limit, we show power-law scaling of opposite nature, namely, κâJ(â¥)(2). Moreover, we demonstrate the weak and strong coupling regimes to be connected by a broad minimum, slightly below the isotropic point at J(â¥)=J(â¥). Reducing temperature T, starting from T=∞, this minimum scales as κâT(-2) down to T on the order of the exchange coupling constant. These results provide for a comprehensive picture of κ(J(â¥),T) of spin ladders.
ABSTRACT
Thirty-five years ago, Sanders and Walton [Phys. Rev. B 15, 1489 (1977)] proposed a method to measure the phonon-magnon interaction in antiferromagnets through thermal transport which so far has not been verified experimentally. We show that a dynamical variant of this approach allows direct extraction of the phonon-magnon equilibration time, yielding 400 µs for the cuprate spin-ladder system Ca(9)La(5)Cu(24)O(41). The present work provides a general method to directly address the spin-phonon interaction by means of dynamical transport experiments.