Eur. Phys. J. B (2014) 87: 173
https://doi.org/10.1140/epjb/e2014-50018-4

Regular Article

Thermal conductivity of anisotropic spin-1/2 two leg ladder: Green’s function approach

¹ Department of Physics, Razi University, Kermanshah 67149, Islamic Republic of Iran
² Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran, Islamic Republic of Iran
³ Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
⁴ Physikalisches Institut, University of Cologne, 50937 Köln, Germany
⁵ Department of Physics and Institute of Theoretical and Computational Physics, University of Crete, 71003, Heraklion, Crete, Greece

^a e-mail: rezania.hamed@gmail.com

Received: 9 January 2014
Received in final form: 28 May 2014
Published online: 1 August 2014

Abstract

We study the thermal transport of a spin-1/2 two leg antiferromagnetic ladder in the direction of legs. The possible effect of spin-orbit coupling and crystalline electric field are investigated in terms of anisotropies in the Heisenberg interactions on both leg and rung couplings. The original spin ladder is mapped to a bosonic model via a bond-operator transformation, where an infinite hard-core repulsion is imposed to constrain one boson occupation per site. The Green’s function approach is applied to obtain the energy spectrum of quasi-particle excitations responsible for thermal transport. The thermal conductivity is found to be monotonically decreasing with temperature due to increased scattering among triplet excitations at higher temperatures. A tiny dependence of thermal transport on the anisotropy in the leg direction at low temperatures is observed in contrast to the strong one on the anisotropy along the rung direction, due to the direct effect of the triplet densities. Our results reach asymptotically the ballistic regime of the spin-1/2 Heisenberg chain and present a complement regime for the exact diagonalization data.