arXiv subjects

F. V. Kyrychenko

Publications and source records attributed to F. V. Kyrychenko.

11 recordsLinked to original sources

arXiv2011

Response properties of III-V dilute magnetic semiconductors: interplay of disorder, dynamical electron-electron interactions and band-structure effects

A theory of the electronic response in spin and charge disordered media is developed with the particular aim to describe III-V dilute magnetic semiconductors like GaMnAs. The theory combines a detailed k.p description of the valence band, in which the itinerant carriers are assumed to reside, with first-principles calculations of disorder contributions using an equation-of-motion approach for the current response function. A fully dynamic treatment of electron-electron interaction is achieved by means of time-dependent density functional theory. It is found that collective excitations within the valence band significantly increase the carrier relaxation rate by providing effective channels for momentum relaxation. This modification of the relaxation rate, however, only has a minor impact on the infrared optical conductivity in GaMnAs, which is mostly determined by the details of the valence band structure and found to be in agreement with experiment.

cond-mat.mtrl-sci↗

arXiv2009

Temperature-dependent resistivity of ferromagnetic GaMnAs: Interplay between impurity scattering and many-body effects

The static conductivity of the dilute magnetic semiconductor GaMnAs is calculated using the memory function formalism and time-dependent density-functional theory to account for impurity scattering and to treat Hartree and exchange interactions within the hole gas. We find that the Coulomb scattering off the charged impurities alone is not sufficient to explain the experimentally observed drop in resistivity below the ferromagnetic transition temperature: the often overlooked scattering off the fluctuations of localized spins is shown to play a significant role.

cond-mat.mtrl-sci↗

arXiv2007

Intersubband spin-orbit coupling and spin splitting in symmetric quantum wells

In semiconductors with inversion asymmetry, spin-orbit coupling gives rise to the well-known Dresselhaus and Rashba effects. If one considers quantum wells with two or more conduction subbands, an additional, intersubband-induced spin-orbit term appears whose strength is comparable to the Rashba coupling, and which remains finite for symmetric structures. We show that the conduction band spin splitting due to this intersubband spin-orbit coupling term is negligible for typical III-V quantum wells.

cond-mat.mtrl-sci↗

arXiv2007

Memory function formalism approach to electrical conductivity and optical response of dilute magnetic semiconductors

A combination of the memory function formalism and time-dependent density-functional theory is applied to transport in dilute magnetic semiconductors. The approach considers spin and charge disorder and electron-electron interaction on an equal footing. Within the weak disorder limit and using a simple parabolic approximation for the valence band we show that Coulomb and exchange scattering contributions to the resistivity in GaMnAs are of the same order of magnitude. The positional correlations of defects result in a significant increase of Coulomb scattering, while the suppression of localized spin fluctuations in the ferromagnetic phase contributes substantially to the experimentally observed drop of resistivity below T_c. A proper treatment of dynamical screening and collective excitations is essential for an accurate description of infrared absorption.

cond-mat.mtrl-sci↗

arXiv2006

Enhanced carrier scattering rates in dilute magnetic semiconductors with correlated impurities

In III-V dilute magnetic semiconductors (DMSs) such as Ga$_{1-x}$Mn$_x$As, the impurity positions tend to be correlated, which can drastically affect the electronic transport properties of these materials. Within the memory function formalism we have derived a general expression for the current relaxation kernel in spin and charge disordered media and have calculated spin and charge scattering rates in the weak-disorder limit. Using a simple model for magnetic impurity clustering, we find a significant enhancement of the charge scattering. The enhancement is sensitive to cluster parameters and may be controllable through post-growth annealing.

cond-mat.mtrl-sci↗

arXiv2005

Electronic states and cyclotron resonance in p-type InMnAs and InMnAs/(Al,Ga)Sb at ultrahigh magnetic fields

We present a theoretical and experimental study on electronic and magneto-optical properties of p-type paramagnetic InMnAs dilute magnetic semiconductor alloys and ferromagnetic p-type InMnAs/(Al,Ga)Sb thin films in ultrahigh (> 100 T) external magnetic fields \textbf{B}. We use an 8 band Pidgeon-Brown model generalized to include the wavevector dependence of the electronic states along B as well as s-d and p-d exchange interactions with localized Mn d-electrons. In paramagnetic p-InMnAs alloys, we compute the spin-dependent electronic structure as a function of Mn doping and examine how the valence band structure depends on parameters such as the sp-d exchange interaction strength and effective masses. The cyclotron resonance (CR) and magneto-optical properties of InMnAs are computed using Fermi's golden rule. In addition to finding strong CR for hole-active polarization in p-type InMnAs, we also find strong CR for electron-active polarization. The electron-active CR in the valence bands results from transitions between light and heavy hole Landau levels and is seen in experiments. In ferromagnetic p-InMnAs/(Al,Ga)Sb, two strong CR peaks are observed which shift with position and increase in strength as the Curie temperature is approached from above. This transition takes place well above the Curie temperature and can be attributed to the increase in magnetic ordering at low temperatures.

cond-mat.stat-mech↗

arXiv2004

Dark-bright magneto-exciton mixing induced by Coulomb interaction in strained quantum wells

Coupled magneto-exciton states between allowed (`bright') and forbidden (`dark') transitions are found in absorption spectra of strained In$_{0.2}$Ga$_{0.8}$As/GaAs quantum wells with increasing magnetic field up to 30 T. We found large (~ 10 meV) energy splittings in the mixed states. The observed anticrossing behavior is independent of polarization, and sensitive only to the parity of the quantum confined states. Detailed experimental and theoretical investigations indicate that the excitonic Coulomb interaction rather than valence band complexity is responsible for the splittings. In addition, we determine the spin composition of the mixed states.

cond-mat.other↗

arXiv2004

Ultrahigh-Field Hole Cyclotron Resonance Absorption in InMnAs Films

We have carried out an ultrahigh-field cyclotron resonance study of p-type In1-xMnxAs films, with Mn composition x ranging from 0% to 2.5%, grown on GaAs by low-temperature molecular-beam epitaxy. Pulsed magnetic fields up to 500 T were used to make cyclotron resonance observable in these low-mobility samples. The clear observation of hole cyclotron resonance is direct evidence of the existence of a large number of itinerant, effective-mass-type holes rather than localized d-like holes. It further suggests that the p-d exchange mechanism is more favorable than the double exchange mechanism in this narrow gap InAs-based dilute magnetic semiconductor. In addition to the fundamental heavy-hole and light-hole cyclotron resonance absorption appearing near the high-magnetic-field quantum limit, we observed many inter-Landau-level absorption bands whose transition probabilities are stronglydependent on the sense of circular polarization of the incident light.

cond-mat.mtrl-sci↗

arXiv2003

Electronic States and Cyclotron Resonance in n-type InMnAs

We present a theory for electronic and magneto-optical properties of n-type In(1-x)Mn(x)As magnetic alloy semiconductors in a high magnetic field, B. We use an 8-band Pidgeon-Brown model generalized to include the wavevector (Kz) dependence of the electronic states as well as s-d and p-d exchange interactions with localized Mn d-electrons. Calculated conduction-band Landau levels exhibit effective masses and g factors that are strongly dependent on temperature, magnetic field, Mn concentration (x), and Kz. Cyclotron resonance (CR) spectra are computed using Fermi's golden rule and compared with ultrahigh-magnetic-field (> 50 T) CR experiments, which show that the electron CR peak position is sensitive to x. Detailed comparison between theory and experiment allowed us to extract s-d and p-d exchange parameters, alpha and beta. we find that not only alpha but also beta affects the electron mass because of the strong interband coupling in this narrow gap semiconductor. In addition, we derive analytical expressions for the effective masses and g facors within the 8-band model. Results indicate that (alpha - beta) is the crucial parameter that determines the exchange interaction correction to the cyclotron masses. These findings sould be useful for designing novel devices based on ferromagnetic semiconductors.

cond-mat.mes-hall↗

arXiv2003

Cyclotron Resonance in Ferromagnetic InMnAs/(Al,Ga)Sb Heterostructures

We report the observation of hole cyclotron resonance (CR) in InMnAs/(Al,Ga)Sb heterostructures in a wide temperature range covering both the paramagnetic and ferromagnetic phases. We observed two pronounced resonances that exhibit drastic changes in position, linewidth, and intensity at a temperature higher than the Curie temperature, indicating possible local magnetic ordering or clustering. We attribute the two resonances to the fundamental CR transitions expected for delocalized valence-band holes in the quantum limt. Using an 8-band {\bf k$\cdot$p} model, which incorporates ferromagnetism within a mean-field approximation, we show that the temperature-dependent CR peak shift is a direct measure of the carrier-Mn exchange interaction. Significant line narrowing was observed at low temperatures, which we interpret as the suppression of localized spin fluctuations.

cond-mat.mes-hall↗

arXiv2001

Diluted magnetic semiconductor quantum dots: an extreme sensitivity of the hole Zeeman splitting on the aspect ratio of the confining potential

The valence band states confined in infinitely deep quantum dots made of diluted magnetic semiconductors (DMS) are considered theoretically. A complex anisotropic structure of the valence bands in DMSs with cubic symmetry described by the full Luttinger Hamiltonian is taken into account. It is found that the Zeeman splitting is very sensitive to the shape of the confining potential and, in particular, to its orientation relative to the direction of an external magnetic field. This sensitivity has its origin in a mixing of different spin components of a hole wave function which takes place for finite hole wave vectors ${\bf k}$. Several consequences of the effect are discussed, including a possibility to control the inter-dot tunneling by an external magnetic field. It is shown also that the polarizations of optical transitions in a single DMS quantum dot depend on details of geometry of its confining potential as well as on the strength of the magnetic field.

cond-mat↗