К вопросу о бозе-эйнштейновском конденсате экситонов в кристаллах с дефектами

The paper considers the possibility of forming a Bose-Einstein condensate (BEC) of excitons in a model non-ideal lattice of a molecular crystal. The spectrum of the corresponding exciton excitations is analyzed. Within the framework of the virtual crystal approximation, a numerical simulation of the potential dependence on the concentration of structural defects was performed, and on this basis, the features of the appearance of exciton condensate in a non-ideal system were studied. It is shown under what conditions the appearance of light and dark excitons BEC is possible.

Millimetre-long transport of photogenerated carriers in topological insulators

Excitons are spin integer particles that are predicted to condense into a coherent quantum state at sufficiently low temperature. Here by using photocurrent imaging we report experimental evidence of formation and efficient transport of non-equilibrium excitons in Bi2-xSbxSe3 nanoribbons. The photocurrent distributions are independent of electric field, indicating that photoexcited electrons and holes form excitons. Remarkably, these excitons can transport over hundreds of micrometers along the topological insulator (TI) nanoribbons before recombination at up to 40 K. The macroscopic transport distance, combined with short carrier lifetime obtained from transient photocurrent measurements, indicates an exciton diffusion coefficient at least 36 m2 s−1, which corresponds to a mobility of 6 × 104 m2 V−1 s−1 at 7 K and is four order of magnitude higher than the value reported for free carriers in TIs. The observation of highly dissipationless exciton transport implies the formation of superfluid-like exciton condensate at the surface of TIs.