Abstract
The Berezinskii-Kosterlitz-Thouless (BKT) theorem predicts that two-dimensional bosonic condensates exhibit quasi-long-range order which is characterized by a slow decay of the spatial coherence. However previous measurements on exciton-polariton condensates revealed that their spatial coherence can decay faster than allowed under the BKT theory, and different theoretical explanations have already been proposed. Through theoretical and experimental study of exciton-polariton condensates, we show that the fast decay of the coherence can be explained through the simultaneous presence of multiple modes in the condensate.
Highlights
Two-dimensional bosonic systems at low temperatures have been observed to exhibit spatial coherence over long distances [1,2,3,4,5]
The Berezinskii-Kosterlitz-Thouless (BKT) theorem predicts that two-dimensional bosonic condensates exhibit quasi-long-range order which is characterized by a slow decay of the spatial coherence
Previous measurements on exciton-polariton condensates revealed that their spatial coherence can decay faster than allowed under the BKT theory, and different theoretical explanations have already been proposed
Summary
Two-dimensional bosonic systems at low temperatures have been observed to exhibit spatial coherence over long distances [1,2,3,4,5]. Bose-Einstein condensation with true long-range order is not possible in such systems [6,7], they can still exhibit quasi-long-range order by condensing into a state which is described by the Berezinskii-KosterlitzThouless (BKT) theory [8,9] In this case, the first-order spatial correlation function is predicted to decay with a power law (algebraically), whose exponent must always be 1/4 [5,10]. The Nozieres principle [11] in general predicts that condensation will only occur into a single mode since condensate fragmentation is energetically costly due to the Fock exchange term; multimode condensation is possible in the studied exciton-polariton system where the energy uncertainty caused by the short boson lifetime is greater than the Fock exchange energy
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