Valley Polarized Single Photon Source Based on Transition Metal Dichalcogenides Quantum Dots

Photonic quantum computer, quantum communication, quantum metrology, and optical quantum information processing require a development of efficient solid‐state single photon sources. However, it still remains a challenge. We report theoretical framework and experimental development on a novel kind of valley‐polarized single‐photon emitter (SPE) based on two‐dimensional transition metal dichalcogenides (TMDCs) quantum dots. In order to reveal the principle of the SPE, we make a brief review on the electronic structure of the TMDCs and excitonic behavior in photoluminescence (PL) and in magneto‐PL of these materials. We also discuss coupled spin and valley physics, valley‐polarized optical absorption, and magneto‐optical absorption in TMDC quantum dots. We demonstrate that the valley‐polarization is robust against dot size and magnetic field, but optical transition energies show sizable size‐effect. Three versatile models, including density functional theory, tight‐binding and effective k⋅p method, have been adopted in our calculations and the corresponding results have been presented

Stability and Superconductivity of K–P Compounds under Pressure

We explore the phase diagram, structures, electron properties, and potential superconductivity of the K–P system at pressures of up to 200 GPa through unbiased structure searching techniques and first-principles calculations. Five stable chemical stoichiometries (K₄P, K₃P, K₂P, KP, and KP₂) have been theoretically predicted. In particular, P₂ units or P-chains are uncovered in K₂P, KP, and KP₂ compounds with the existence of covalent bonds by analyzing the electron localization functions. And the Bader analysis demonstrates that charges transfer from K atoms to P atoms. Electron–phonon calculations show that the <i>T</i>_c of metallic <i>I</i>4/<i>mmm</i>-KP₂ is 22.01 K at 5 GPa. The investigating of the K–P system is in favor of understanding the crystal structures and corresponding properties of potassium phosphides, which also give a strong motivation to search and design new superconductor materials in other phosphides