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TT: Fachverband Tiefe Temperaturen

TT 38: CE: Quantum-Critical Phenomena 2

TT 38.6: Vortrag

Freitag, 26. März 2010, 12:00–12:15, H18

Multiscale Quantum Criticality: The Pomeranchuk Instability in Isotropic Metals — •Mario Zacharias¹, Peter Wölfle², and Markus Garst¹ — ¹Institut für Theoretische Physik, Universität zu Köln — ²Institut für Theorie der kondensierten Materie, Universität Karlsruhe

As a paradigmatic example of quantum criticality with multiple scales, we study the Pomeranchuk instability of an isotropic metal in d=2 dimensions. The effective Ginzburg-Landau theory has two modes with different dynamics. There is a Landau-damped mode with a dynamical exponent z_>=3 and a ballistic mode with z_<=2. The two modes are coupled to each other and become critical at the very same point.

Since the effective dimension, d+z_<, of the ballistic mode equals the upper critical dimension, d₊ =4, self-interactions lead to logarithmic singularities which we sum up by the renormalization group technique. We find that the ballistic mode governs the system at zero temperature, T=0, although the z_>=3 mode has the lower characteristic energy.

At finite T, the existence of two time scales results in a modified quantum-to-classical crossover, which extends over a parametrically large regime and leads to an intricate interplay of classical and quantum fluctuations. As a result, we find a universal T-dependence of the correlation length independent of the interaction amplitude.

The phase diagram and the critical thermodynamics also reflect the existence of multiple scales. In particular, there are two crossover lines between the low temperature and the quantum critical regime and the thermodynamic quantities differ in their sensitivity to them.