title: Spontaneous solitons in the thermal equilibrium of a quasi-1D Bose gas.
abstract: We show that solitons occur generically in the thermal equilibrium state of a weakly interacting elongated Bose gas, without the need for external forcing or perturbations. This reveals a major new quality to the experimentally widespread quasicondensate state, usually thought of as primarily phase-fluctuating. Thermal solitons are seen in uniform 1D, trapped 1D, and elongated 3D gases, appearing as shallow solitons at low quasicondensate temperatures, becoming widespread and deep as temperature rises. This behavior can be understood via thermal occupation of the type II excitations in the Lieb-Liniger model of a uniform 1D gas. Furthermore, we find that the quasicondensate phase includes very appreciable density fluctuations while leaving phase fluctuations largely unaltered from the standard picture derived from a density-fluctuation-free treatment.
authors.affiliation: Wydział Fizyki, Uniwersytet w Białymstoku, Lipowa 41, 15-424 Białystok, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Karpiuk
authors.forename: Piotr
authors.initials: P
authors.lastname: Deuar
authors.forename: Przemysław
authors.initials: P
authors.lastname: Bienias
authors.forename: Emilia
authors.initials: E
authors.lastname: Witkowska
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Pawłowski
authors.forename: Mariusz
authors.initials: M
authors.lastname: Gajda
authors.forename: Kazimierz
authors.initials: K
authors.lastname: Rzążewski
authors.forename: Mirosław
authors.initials: M
authors.lastname: Brewczyk