Magneto-Gyrotropic Photogalvanic Effects in Semiconductor Quantum Wells

We show that free-carrier (Drude) absorption of both polarized and unpolarized terahertz radiation in quantum well (QW) structures causes an electric photocurrent in the presence of an in-plane magnetic field. Experimental and theoretical analysis evidences that the observed photocurrents are spin-dependent and related to the gyrotropy of the QWs. Microscopic models for the photogalvanic effects in QWs based on asymmetry of photoexcitation and relaxation processes are proposed. In most of the investigated structures the observed magneto-induced photocurrents are caused by spin-dependent relaxation of non-equilibrium carriers

Spin noise in quantum dot ensembles

We study theoretically spin fluctuations of resident electrons or holes in singly charged quantum dots. The effects of external magnetic field and effective fields caused by the interaction of electron and nuclei spins are analyzed. The fluctuations of spin Faraday, Kerr and ellipticity signals revealing the spin noise of resident charge carriers are calculated for the continuous wave probing at the singlet trion resonance.Comment: 8 pages, 4 figure

Strong and weak coupling limits in optics of quantum well excitons

A transition between the strong (coherent) and weak (incoherent) coupling limits of resonant interaction between quantum well (QW) excitons and bulk photons is analyzed and quantified as a function of the incoherent damping rate caused by exciton-phonon and exciton-exciton scattering. For confined QW polaritons, a second, anomalous, damping-induced dispersion branch arises and develops with increasing damping. In this case, the strong-weak coupling transition is attributed to a critical damping rate, when the intersection of the normal and damping-induced dispersion branches occurs. For the radiative states of QW excitons, i.e., for radiative QW polaritons, the transition is described as a qualitative change of the photoluminescence spectrum at grazing angles along the QW structure. Furthermore, we show that the radiative corrections to the QW exciton states with in-plane wavevector approaching the photon cone are universally scaled by an energy parameter rather than diverge. The strong-weak coupling transition rates are also proportional to the same energy parameter. The numerical evaluations are given for a GaAs single quantum well with realistic parameters.Comment: Published in Physical Review B. 29 pages, 12 figure

Emerging Mechanisms of Magnetocaloric Effect in Phase-Separated Metals

We present a study of the magnetocaloric effect in metallic systems exhibiting first-order magnetic transitions and focus on consequences of magnetic phase separation. We account for ferrimagnetic, ferromagnetic, and Neel antiferromagnetic order. Based on the archetypal Hubbard model being treated within the mean-field approximation, we provide and explore its implications on the field-induced entropy change in metallic system with phase separation. Chosen framework allows us to properly analyze phase volumes' dependence on parameters of phase-separated (PS) system. Moreover, an account for phase separation boundaries as functions of magnetic field provides a natural splitting of the PS region, where each subregion corresponds to a different temperature dependence of entropy change: moving from one subregion to the other produces a kink, followed by a strong linear growth of entropy change. We encounter a second-order magnetic transition from paramagnetic to antiferromagnetic phase in PS region that occurs for particular parameter values. Despite the fact that both phases have zero total magnetization, the transition has a strong impact on entropy change. ©2021 American Physical Society.P.A.I. is grateful to A. A. Katanin and V. Yu. Irkhin for fruitful discussions. The research was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme “ Quantum” No. АААА-А18-118020190095-4), supported in part by RFBR (project No. 20-02-00252)

Theory of one-dimensional double-barrier quantum pump in two-frequency signal regime

A one-dimensional system with two $\delta$-like barriers or wells bi-chromaticaly oscillating at frequencies $\omega$ and $2\omega$ is considered. The alternating signal leads to the direct current across the structure (even in a symmetric system). The properties of this quantum pump are studied in a wide range of the system parameters.Comment: 4 pages, 5 figure

Chirality effects in carbon nanotubes

We consider chirality related effects in optical, photogalvanic and electron-transport properties of carbon nanotubes. We show that these properties of chiral nanotubes are determined by terms in the electron effective Hamiltonian describing the coupling between the electron wavevector along the tube principal axis and the orbital momentum around the tube circumference. We develop a theory of photogalvanic effects and a theory of d.c. electric current, which is linear in the magnetic field and quadratic in the bias voltage. Moreover, we present analytic estimations for the natural circular dichroism and magneto-spatial effect in the light absorption.Comment: 23 pages, 3 figure

Magnetic field effect on polarization and dispersion of exciton-polaritons in planar microcavities

The non-local dielectric response theory is extended to describe oblique reflection of light from quantum wells subjected to the magnetic field. This allows us to calculate the dispersion and polarization of the exciton-polariton modes in semiconductor microcavities in the presence of a magnetic field normal to the plane of the structure. We show that due to the interplay between the exciton Zeeman splitting and TE-TM splitting of the photon modes, four polariton dispersion branches are formed with a polarization gradually changing from circular in the exciton-like part to linear in the photon-like part of each branch. Faraday rotation in quantum microcavities is shown to be strongly enhanced as compared with the rotation in quantum wells.Comment: 19 pages, 5 figure

Linear polarization of the photoluminescence of quantum wells

The degree and orientation of the magnetic-field induced linear polarization of the photoluminescence from a wide range of heterostructures containing (Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a function of detection photon energy, applied magnetic field strength and orientation in the quantum well plane. A theoretical description of this effect in terms of an in-plane deformation acting on the valence band states is presented and is verified by comparison with the experimental data. We attempted to identify clues to the microscopic origin of the valence band spin anisotropy and to the mechanisms which actually determine the linear polarization of the PL in the quantum wells subject to the in-plane magnetic field. The conclusions of the present paper apply in full measure to non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain anisotropy.Comment: 21 pages, 10 figure

Spin noise spectroscopy of a single-quantum-well microcavity

We report on the first experimental observation of spin noise in a single semiconductor quantum well embedded into a microcavity. The great cavity-enhanced sensitivity to fluctuations of optical anisotropy has allowed us to measure the Kerr rotation and ellipticity noise spectra in the strong coupling regime. The spin noise spectra clearly show two resonant features: a conventional magneto-resonant component shifting towards higher frequencies with magnetic field and an unusual "nonmagnetic" component centered at zero frequency and getting suppressed with increasing magnetic field. We attribute the first of them to the Larmor precession of free electron spins, while the second one being presumably due to hyperfine electron-nuclei spin interactions.Comment: 5 pages, 6 figures + supplement (4 pages, 1 figure

Excitation spectroscopy of single quantum dots at tunable positive, neutral and negative charge states

We present a comprehensive study of the optical transitions and selection rules of variably charged single self-assembled InAs/GaAs quantum dots. We apply high resolution polarization sensitive photoluminescence excitation spectroscopy to the same quantum dot for three different charge states: neutral and negatively or positively charged by one additional electron or hole. From the detailed analysis of the excitation spectra, a full understanding of the single-carrier energy levels and the interactions between carriers in these levels is extracted for the first time.Comment: 8 pages, 5 figure