Article

# Linear temperature dependence of the magnetic heat conductivity in CaCu2O3.

Leibniz-Institute for Solid State and Materials Research, IFW-Dresden, 01171 Dresden, Germany.

Physical Review Letters (Impact Factor: 7.73). 02/2007; 98(2):027201. DOI: 10.1103/PhysRevLett.98.027201 Source: PubMed

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**ABSTRACT:**We investigate the Heisenberg-Kitaev chain in order to uncover the interplay between two qualitatively different integrable points in the physics of heat transport in one-dimensional spin liquids. Based on linear response theory and analytical as well as numerical approaches, we explore several directions in parameter space including exchange-coupling ratios, anisotropies, and external magnetic fields. We show the emergence of purely ballistic energy transport at all integrable points, manifest in pronounced Drude weights and low-frequency suppression of regular-conductivity contributions. Moreover, off integrability, we find extended quantum chaotic regions with vanishing Drude weights and well-defined DC conductivities. In the vicinity of the Kitaev point, we observe clear signatures of the topological gap in the response function.Preprint. 12/2013; -
##### Article: Lower Bounds for Conductivities

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**ABSTRACT:**We show how one can obtain a lower bound for the electrical, spin or heat conductivity of correlated quantum systems described by Hamiltonians of the form H = H0 + g H1. Here H0 is an interacting Hamiltonian characterized by conservation laws which lead to an infinite conductivity for g=0. The small perturbation g H1, however, renders the conductivity finite at finite temperatures. For example, H0 could be a continuum field theory, where momentum is conserved, or an integrable one-dimensional model while H1 might describe the effects of weak disorder. In the limit g to 0, we derive lower bounds for the relevant conductivities and show how they can be improved systematically using the memory matrix formalism. Furthermore, we discuss various applications and investigate under what conditions our lower bound may become exact.04/2007; - [Show abstract] [Hide abstract]

**ABSTRACT:**We report a study on the heat transport of an S = 1 Haldane chain compound Ni(C3H10N2)2NO2ClO4 at low temperatures and in magnetic fields. The zero-field thermal conductivities show a remarkable anisotropy for the heat current along the spin-chain direction (κb) and the vertical direction (κc), implying a magnetic contribution to the heat transport along the spin-chain direction. The magnetic-field-induced change of the spin spectrum has obviously opposite impacts on κb and κc. In particular, κb(H) and κc(H) curves show peak-like increases and dip-like decreases, respectively, at ∼9 T, which is the critical field that minimizes the spin gap. These results indicate a large magnetic thermal transport in this material.Journal of Applied Physics 03/2013; 113(17). · 2.19 Impact Factor

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