Dresden 2011 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 37: MLT: Quantum Liquids, Bose-Einstein Condensates, Ultra-cold Atoms, ...
TT 37.6: Talk
Wednesday, March 16, 2011, 15:30–15:45, HSZ 105
Functional renormalization group approach to interacting bosons at zero temperature — •Andreas Sinner1, Nils Hasselmann2, and Peter Kopietz3 — 1Universität Augsburg, Germany — 2Universidade Federal do Rio Grande do Norte, Brazil — 3Universität Frankfurt, Germany
We investigate the single-particle spectral density of interacting bosons within the non-perturbative functional renormalization group technique. The flow equations for a Bose gas are derived and solved within a truncation scheme which allows to extract the complete frequency and momentum structure of the normal and anomalous self-energies. Both the asymptotic small momentum regime, where perturbation regime fails, as well as the perturbative regime at larger momenta are well described within a single unified approach. The self-energies do not exhibit any infrared divergences, satisfy the U(1) symmetry constraints, and are in accordance with the exact relation which states that the anomalous self-energy vanishes at zero momentum and zero frequency. From the self-energies we extract the single-particle spectral density of the two-dimensional Bose gas. The dispersion is found to be of the Bogoliubov form and shows the crossover from linear Goldstone modes to the quadratic behavior of quasi-free bosons. The damping of the quasiparticles is found to be in accordance with the standard Beliaev damping.