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TT: Fachverband Tiefe Temperaturen

TT 48: Correlated Electrons: Quantum-Critical Phenomena - Theory

TT 48.1: Topical Talk

Mittwoch, 13. März 2013, 16:45–17:15, H19

Transport as a sensitive indicator for quantum criticality — •Gernot Schaller, Malte Vogl, and Tobias Brandes — Institut für Theoretische Physik, TU Berlin, Berlin, Germany

Quantum-critical systems exhibit a non-analytic behavior of the ground state with respect to an external control parameter, separating macroscopically different phases. At zero temperature, this is transfered to order parameters such as e.g. the energy or other observables. However, when dealing with fragile quantum systems one has to take the inevitable interaction with a reservoir into account. The fate of the quantum criticality in this regime is less understood.

We argue that due to the closure of the energy gap above the ground state, at finite reservoir temperatures the non-analytic ground state properties will be suppressed in most observables. This can also be expected in non-equilibrium setups, where the system is placed in contact with multiple thermal reservoirs at different temperatures. In contrast, we propose the stationary current through the quantum-critical system itself (e.g. the heat current transferred between the reservoirs through the system) to be much more sensitive to quantum criticality: We expect signatures in the stationary current even in the far from equilibrium regime. These findings are made explicit at a toy model for adiabatic computation corresponding to a first order quantum phase transition and at the quantum Ising model in a transverse field with a second order quantum phase transition.
[1] M. Vogl, G. Schaller, and T. Brandes, Phys. Rev. Lett. (in press), arXiv:1208.5989 (2012).