Local quantum criticality out of equilibrium: Effective temperatures and scaling in the steady-state regime

Author： Ribeiro Pedro Si Qimiao Kirchner Stefan

E-ISSN： 1286-4854|102|5|50001-50001

ISSN： 0295-5075

Source： EPL (EUROPHYSICS LETTERS), Vol.102, Iss.5, 2013-06, pp. : 50001-50001

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Abstract

We study the out-of-equilibrium steady-state properties of the Bose-Fermi-Kondo model, describing a local magnetic moment coupled to two ferromagnetic leads that support bosonic (magnons) and fermionic (Stoner continuum electrons) low-energy excitations. This model describes the destruction of the Kondo effect as the coupling to the bosons is increased. Its phase diagram comprises three non-trivial fixed points. Using a dynamical large-N approach on the Keldysh contour, we study two different non-equilibrium setups: a) a finite bias voltage and b) a finite temperature gradient, imposed across the leads. The scaling behavior of the charge and energy currents is identified and characterized for all fixed points. We report the existence of a fixed-point–dependent effective temperature, defined though the fluctuation-dissipation relations of the local spin-susceptibility in the scaling regime, which permits to recover the equilibrium behavior of both dynamical and static spin-susceptibilities.