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TT: Fachverband Tiefe Temperaturen

TT 6: Postersession Correlated Electrons: (General) Theory, Low-Dimensional Systems, Kondo Physics, Heavy Fermions, Quantum-Critical Phenomena

TT 6.63: Poster

Montag, 23. März 2009, 13:00–16:45, P1A

Quantum Criticality of the Pomeranchuk Instability: Interplay of Multiple Dynamical Exponents — •Mario Zacharias¹, Markus Garst¹, Achim Rosch¹, and Peter Wölfle² — ¹Institut für Theoretische Physik, Universität zu Köln — ²Institut für Theorie der Kondensierten Materie, Universität Karlsruhe

We consider the Pomeranchuk instability of an isotropic Fermi liquid in two dimensions, d=2. The effective Ginzburg-Landau theory contains two critical modes with different dynamics. There is a ballistic mode with dynamical exponent z=2 and a Landau-damped mode with z=3. While the z=3 mode dominates thermodynamics at T>0 the T=0 quantum dynamics is governed by the z=2 mode. As the T=0 theory is at its upper critical dimension we use the renormalization group (RG) to analyse the leading logarithmic singularities. The resulting universality class is found to be distinct from the Ising- as well as from the XY-model.

At finite temperatures, there is an intricate interplay between the two modes. At criticality, the length scales ξ_T ∼ T^−1/z separates the quantum from the classical regime. The different dynamical exponents yield an overlap regime where the ballistic mode still has its quantum character while the damped mode is already classical. We find that this regime dominates the properties at finite T. In particular, we argue that the usual separation of quantum and classical dynamics at T>0 is not valid, implying a breakdown of "dimensional reduction". Further, this interplay leads to a universal T dependence of the correlation length at criticality.