Angle-resolved photoemission in doped charge-transfer Mott insulators

A theory of angle-resolved photoemission (ARPES) in doped cuprates and other charge-transfer Mott insulators is developed taking into account the realistic (LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon interaction, and a random field potential. In most of these materials the first band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated in the non-crossing (ladder) approximation and with the exact spectral function of a one-dimensional hole in a random potential. Some unusual features of ARPES including the polarisation dependence and spectral shape in YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or small. The theory is compatible with the doping dependence of kinetic and thermodynamic properties of cuprates as well as with the d-wave symmetry of the superconducting order parameter.Comment: 8 pages (RevTeX), 10 figures, submitted to Phys. Rev.

Temperature shift of intraband absorption peak in tunnel-coupled QW structure

An experimental study of the intersubband light absorption by the 100-period GaAs/Al0.25Ga0.75As double quantum well heterostructure doped with silicon is reported and interpreted. Small temperature redshift of the 1–3 intersubband absorption peak is detected. Numerical calculations of the absorption coefficient including self-consistent Hartree calculations of the bottom of the conduction band show good agreement with the observed phenomena. The temperature dependence of energy gap of the material and the depolarization shift should be accounted for to explain the shift. © 2017 Elsevier B.V

Terahertz luminescence in strained GaAsN:Be layers under strong electric fields

The authors report on the experimental studies of terahertz emission from strained GaAsN/GaAs microstructures doped with beryllium at the conditions of electric breakdown of the shallow impurity. The terahertz emission spectrum demonstrates several distinctive signatures that are related to spontaneous optical transitions between resonant and localized states of the acceptor. The energy spectrum calculated for the Be acceptor in the GaAsN/GaAs heterostructure fits reasonably well with the experimentally observed peaks

Two-dimensional plasmons in a GaN/AlGaN heterojunction

We report the studies on optical properties of a GaN/AlGaN heterostructure with a surface metal grating. The fabricated structures were optimized for the observation of 2D plasmon resonances in the spectral range of 2–5 THz. The spectra of the equilibrium optical transmission were experimentally investigated and the 2D plasmon resonance was found. The current-voltage characteristics of the grating sample and a reference sample without grating were measured and the dependence of the hot 2D electron temperature on electric field was established. Terahertz electroluminescence was studied in both samples in the sensitivity band of the Ge:Ga detector in electric fields of up to 400 V/cm. It has been shown that, due to the contribution of nonequilibrium 2D plasmons, the integral photoresponse signal for the sample with a surface metal grating increases 2–4 times as compared with the sample without grating, where the terahertz emission is due only to hot 2D electrons.Peer reviewe