Solitons in ultra-cold gases were first observed to be generated by phase-imprinting . More recently, their spontaneous formation in 1D gases was predicted as a result of bringing the cloud out of equilibrium via the Kibble-Zurek mechanism  or quantum quenches . We find that they actually occur generically in the thermal equilibrium state of a weakly-interacting elongated Bose gas, without the need for external forcing or perturbations . This can be understood via thermal occupation of the famous and somewhat elusive Type II excitations in the Lieb-Liniger model of a uniform 1D gas.
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