arXiv subjects

G. D. Sanders

Publications and source records attributed to G. D. Sanders.

24 records · Page 2Linked to original sources

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↗

arXiv2002

Ultrahigh field electron cyclotron resonance absorption in In$_{1-x}$Mn$_x$As films

We have carried out an ultrahigh field cyclotron resonance study of $n$-type In$_{1-x}$Mn$_x$As films, with Mn composition $x$ ranging from 0 to 12%, grown on GaAs by low temperature molecular beam epitaxy. We observe that the electron cyclotron resonance peak shifts to lower field with increasing $x$. A detailed comparison of experimental results with calculations based on a modified Pidgeon-Brown model allows us to estimate the {\em s-d} and {\em p-d} exchange coupling constants, $α$ and $β$, for this important III-V dilute magnetic semiconductor system.

cond-mat.mtrl-sci↗

arXiv2002

Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells

A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric fields into account. In addition, the many-body Coulomb ineraction is treated in the screened time-dependent Hartree-Fock approximation. We find that under typical experimental conditions, our microscopic theory can be simplified and mapped onto a loaded string problem which can be easily solved.

cond-mat.mes-hall↗

arXiv2000

A scalable solid-state quantum computer based on quantum dot pillar structures

We investigate an optically driven quantum computer based on electric dipole transitions within coupled single-electron quantum dots. Our quantum register consists of a freestanding n-type pillar containing a series of pair wise coupled asymmetric quantum dots, each with a slightly different energy structure, and with grounding leads at the top and bottom of the pillar. Asymmetric quantum wells confine electrons along the pillar axis and a negatively biased gate wrapped around the center of the pillar allows for electrostatic confinement in the radial direction. We self-consistently solve coupled Schrodinger and Poisson equations and develop a design for a three-qubit quantum register. Our results indicate that a single gate electrode can be used to localize a single electron in each of the quantum dots. Adjacent dots are strongly coupled by electric dipole-dipole interactions arising from the dot asymmetry, thus enabling rapid computation rates. The dots are tailored to minimize dephasing due to spontaneous emission and phonon scattering and to maximize the number of computation cycles. The design is scalable to a large number of qubits.

cond-mat↗

arXiv1999

An optically driven quantum dot quantum computer

We propose a quantum computer structure based on coupled asymmetric single-electron quantum dots. Adjacent dots are strongly coupled by means of electric dipole-dipole interactions enabling rapid computation rates. Further, the asymmetric structures can be tailored for a long coherence time. The result maximizes the number of computation cycles prior to loss of coherence.

quant-ph↗