Computational Condensed Matter Physics Group

Abstract:

Using ultrafast optical-pump terahertz-probe spectroscopy (OPTP) and ultrafast terahertz emission spectroscopy, we showcase the electron and hole dynamics in Cd3As2 nanowires (NWs), a well-known 3D Dirac semimetal a subgroup of the newly discovered . A temperature-dependent photoconductivity measurement was carried out yielding an incredibly high electron mobility ~ 16,000 cm2/Vs at 5K. Strong THz emission due to helicity-dependent surface photocurrents was also observed for both nanowires and single crystal (SC) which is highly desirable for devices such as THz sources.

Abstract:

Accurate prediction of fundamental band gaps of crystalline solid-state systems entirely within density functional theory is a long-standing challenge. Here, we present a simple and inexpensive method that achieves this by means of nonempirical optimal tuning of the parameters of a screened range-separated hybrid functional. The tuning involves the enforcement of an ansatz that generalizes the ionization potential theorem to the removal of an electron from an occupied state described by a localized Wannier function in a modestly sized supercell calculation. The method is benchmarked against experiment for a set of systems ranging from narrow band-gap semiconductors to large band-gap insulators, spanning a range of fundamental band gaps from 0.2 to 14.2 electronvolts (eV), and is found to yield quantitative accuracy across the board, with a mean absolute error of ∼0.1 eV and a maximal error of ∼0.2 eV.