Valley-Contrasting Linear Dichroism and Excitonic Condensation in LaOBiS<sub>2</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 39899290.
- Also identified by DOI 10.1021/acs.nanolett.4c05983.
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Abstract
In conjunction with the first-principles calculations, we confirm the fascinating valley-selective linear dichroism and the possibility of excitonic condensation in multiatomic-layer LaOBiS<sub>2</sub> of a tetragonal lattice by the effective tight-binding model and many-body perturbation theory. In LaOBiS<sub>2</sub>, which indicates a spontaneous valley polarization due to crystalline symmetry reduction rather than conventional time-reversal symmetry breaking, we unravel that the excitons in X and X' valleys exclusively coupled to <i>x</i>- and <i>y</i>-linearly polarized lights, respectively. In sharp contrast to coupled quantum wells and van der Waals architectures, a new type of spatially indirect exciton is identified in single-crystal LaOBiS<sub>2</sub>, manifesting itself as an engaging platform for investigating the excitonic Bose-Einstein condensation (BEC) and superfluidity. In light of large binding energy, large radius, and small effective mass of the exciton, the transition temperature for BEC and superfluidity achieves record-high values of 325.1 and 81.3 K, respectively.