![total annihilation band total annihilation band](https://i.ytimg.com/vi/M7MfWMpHlUc/hqdefault.jpg)
These band-edge excitons can therefore interact strongly with incident radiation 5, 6. In monolayer TMDCs, excitons can exhibit large optical transition strengths, giving rise to radiative lifetimes on the order of 150 fs 4-over 10,000 times shorter than those of atoms. In a semiconductor, at sufficiently low temperatures, an electron in the conduction band and a hole in the valence band can interact with each other to form a correlated state-an exciton. Further extension of such phenomena towards the visible spectral range is desirable, particularly in semiconductors that are promising for optoelectronic applications. Analogous multilevel systems in semiconductor quantum wells-intersubband transitions-have opened up applications in the infrared and terahertz frequency range 3. Coherent coupling can arise between transition pathways, giving rise to quantum-interference phenomena such as electromagnetically induced transparency (EIT) 1, 2.
![total annihilation band total annihilation band](https://static.wixstatic.com/media/17e171_ec3e5ed9fb724b56870fae262970b57b~mv2.png)
![total annihilation band total annihilation band](https://metalstorm.net/images/bands/11404.jpg)
Optical transitions in atoms occur between different discrete electronic states. These calculations suggest that the HX is comprised of electrons of negative mass. The coincidence of such high-lying excitonic species at around twice the energy of band-edge excitons rationalizes the excitonic quantum-interference phenomenon recently discovered in optical second-harmonic generation (SHG) and explains the efficient Auger-like annihilation of band-edge excitons.
#Total annihilation band full#
Ab initio GW-BSE calculations with full electron-hole correlations explain HX formation and unmask the admixture of upper conduction-band states to this complex many-body excitation. Strong electron-phonon coupling results in a cascaded phonon progression with equidistant peaks in the luminescence spectrum, resolvable to ninth order. The HX is populated through momentum-selective optical excitation in the K-valleys and is identified in upconverted photoluminescence (UPL) in the UV spectral region. Here, we report the existence of a new excitonic species, the high-lying exciton (HX), in single-layer WSe 2 with an energy of ~3.4 eV, almost twice the band-edge A-exciton energy, with a linewidth as narrow as 5.8 meV. Monolayer transition-metal dichalcogenides (TMDCs) show a wealth of exciton physics. Nature Communications volume 12, Article number: 5500 ( 2021) Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe 2