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Non-Hermitian Theory of Valley Excitons in Two-Dimensional Semiconductors.
Phys Rev Lett
December 2024
School of Physics and Electronics, Hunan University, Changsha 410082, China.
Electron-hole exchange interaction in two-dimensional transition metal dichalcogenides is extremely strong due to the dimension reduction, which promises valley-superposed excitonic states with linearly polarized optical emissions. However, strong circular polarization reflecting valley-polarized excitonic states is commonly observed in helicity-resolved optical experiments. Here, we present a non-Hermitian theory of valley excitons by incorporating optical pumping and intrinsic decay, which unveils an anomalous valley-polarized excitonic state with elliptically polarized optical emission.
View Article and Find Full Text PDFStrong electron-phonon coupling in magic-angle twisted bilayer graphene.
Nature
December 2024
Laboratory for Topological Physics and School of Physical Science and Technology, ShanghaiTech University, Shanghai, People's Republic of China.
The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked considerable research interest. However, despite the dedication of intensive experimental efforts and the proposal of several possible pairing mechanisms, the origin of its superconductivity remains elusive. Here, by utilizing angle-resolved photoemission spectroscopy with micrometre spatial resolution, we reveal flat-band replicas in superconducting MATBG, where MATBG is unaligned with its hexagonal boron nitride substrate.
View Article and Find Full Text PDFWe investigate the terahertz (THz) nonlinear absorption characteristics in a thin AlO crystal using nonlinear THz spectroscopy. A THz saturable absorption performance with a high modulation depth (27.5%) and a relatively low saturable intensity (6.
View Article and Find Full Text PDFSub-100 fs Formation of Dark Excitons in Monolayer WS.
Nano Lett
November 2024
Division of Chemical Physics, Lund University, P.O. Box 124, 221 00 Lund, Sweden.
Two-dimensional semiconducting transition metal dichalcogenides are promising materials for optoelectronic applications due to their strongly bound excitons. While bright excitons have been thoroughly scrutinized, dark excitons have been much less investigated, as they are not directly observable with far-field spectroscopy. However, with their nonzero momenta, dark excitons are significant for applications requiring long-range transport or coupling to external fields.
View Article and Find Full Text PDFStrain fingerprinting of exciton valley character in 2D semiconductors.
Nat Commun
August 2024
Department of Physics, Freie Universität Berlin, Arnimallee 14, Berlin, Germany.
Intervalley excitons with electron and hole wavefunctions residing in different valleys determine the long-range transport and dynamics observed in many semiconductors. However, these excitons with vanishing oscillator strength do not directly couple to light and, hence, remain largely unstudied. Here, we develop a simple nanomechanical technique to control the energy hierarchy of valleys via their contrasting response to mechanical strain.
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