Bose polarons at finite temperature and strong coupling
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A mobile impurity coupled to a weakly interacting Bose gas, a Bose polaron, displays several interesting effects. While a single attractive quasiparticle is known to exist at zero temperature, we show here that the spectrum splits into two quasiparticles at finite temperatures for sufficiently strong impurity-boson interaction. The ground state quasiparticle has minimum energy at Tc, the critical temperature for Bose-Einstein condensation, and it becomes overdamped when T»Tc. The quasiparticle with higher energy instead exists only below Tc, since it is a strong mixture of the impurity with thermally excited collective Bogoliubov modes. This phenomenology is not restricted to ultracold gases, but should occur whenever a mobile impurity is coupled to a medium featuring a gapless bosonic mode with a large population for finite temperature.
CitationGuenther, N., Massignan, P., Lewenstein, M., Bruun, G. Bose polarons at finite temperature and strong coupling. "Physical review letters", 1 Febrer 2018, vol. 120, núm. 5, p. 1-6.