Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 1: Correlated Electrons: Low-dimensional Systems - Models 1
TT 1.10: Vortrag
Montag, 26. März 2012, 12:00–12:15, H 0104
Quantum paramagnetism in the Kagomé transverse field Ising model — •Michael Powalski1, Kris Cöster1, Roderich Moessner2, and Kai Phillip Schmidt1 — 1Lehrstuhl für Theoretische Physik I, TU Dortmund, Germany — 2Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany
We study the intriguing interplay of strong geometrical frustration and of quantum fluctuations. Using perturbative continuous unitary transformations to study the high-field phase, we have calculated the one-magnon excitation spectrum as a high-order series expansion for both Kagomé and for the triangular lattices. Most interestingly, the one-particle gap for the Kagomé transverse field Ising model shows no tendency to close for any finite magnetic field suggesting that the disordered quantum paramagnet is adiabatically connected to the low-field limit. In contrast, for the triangular lattice we find a quantum phase transition which is compatible with the 3dXY universality class. The different behaviour of both lattices can be traced back to the existence of an (almost) dispersionless lowest-energy band for the Kagomé lattice which is exactly flat up to order seven in perturbation theory. This behaviour is understood in terms of a local mode. Furthermore, we can understand the occurrence and the properties of such local modes for any lattice by the corresponding graph expansion.