# Dresden 2011 – wissenschaftliches Programm

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# A: Fachverband Atomphysik

## A 26: Poster III

### A 26.65: Poster

### Donnerstag, 17. März 2011, 16:00–18:30, P2

**Single particle and bound state condensation in interacting Bose gases** — •Michael Maennel^{1,2}, Klaus Morawetz^{1,3}, Pavel Lipavsky^{4,5}, and Michael Schreiber^{2} — ^{1}Department Physical Engineering, Münster University of Applied Science, 48565 Steinfurt, Germany — ^{2}Institute of Physics, Chemnitz University of Technology, 09107 Chemnitz, Germany — ^{3}International Institute of Physics, Universidade Federal do Rio grande do Norte, 59.072-970 Natal-RN, Brazil — ^{4}Institute of Physics, Academy of Sciences, 16253 Prague 6, Czech Republic — ^{5}Faculty of Mathematics and Physics, Charles University, 12116 Prague 2, Czech Republic

We investigate a Bose gas with finite-range interaction using a scheme to eliminate self interaction in the T-matrix approximation. In this way the corrected T-matrix becomes suitable to calculate properties below the critical temperature, without the use of anomalous functions. We calculate the phase diagram, excitation spectrum and equation of state. For attractive interaction, an Evans-Rashid transition occurs between a quasi-ideal Bose gas and a BCS-like phase. In the latter there is a condensation of bound states resulting in a gap in the excitation spectrum. The gap decreases with increasing density and vanishes at the critical density for Bose-Einstein condensation, where the single-particle dispersion becomes linear for small momenta. The investigation of the equation of state indicates however, that the mentioned phase transitions might be inaccessible due to a preceding liquefaction.