Heavy Hole Gas Research Articles

Long-wave Absorption of Few-Hole Gas in Prolate Ellipsoidal Ge/Si Quantum Dot: Implementation of Analytically Solvable Moshinsky Model.

In this paper, the behavior of a heavy hole gas in a strongly prolate ellipsoidal Ge/Si quantum dot has been investigated. Due to the specific geometry of the quantum dot, the interaction between holes is considered one-dimensional. Based on the adiabatic approximation, it is shown that in the z-direction, hole gas is localized in a one-dimensional parabolic well. By modeling the potential of pair interaction between holes in the framework of oscillatory law, the problem is reduced to a one-dimensional, analytically solvable Moshinsky model. The exact energy spectrum of the few-hole gas has been calculated. A detailed analysis of the energy spectrum is presented. The character of long-wave transitions between the center-of-mass levels of the system has been obtained when Kohn theorem is realized.

Measuring hole g -factor anisotropies using transverse magnetic focusing

Recent theoretical and experimental results from quasi-one dimensional heavy hole systems have suggested that heavy hole gases have a strongly anisotropic g factor. In this theoretical paper, we propose a method for measuring this anisotropy using transverse magnetic focusing (TMF). We demonstrate that for experimentally accessible fields, the g factor anisotropy leads to a relative variation in the characteristic of spin-splitting of the TMF spectrum which allows for the measurement of the anisotropy of the g factor. We show that this variation is insensitive to additional spin-orbit interactions, and is resolvable with current devices.

Terahertz quantum Hall effect for spin-split heavy-hole gases in strained Ge quantum wells

Spin-split heavy-hole gases in strained germanium quantum wells were characterized by polarisation-resolved terahertz time-domain spectroscopy. Effective masses, carrier densities, g-factors, transport lifetimes, mobilities and Rashba spin-splitting energies were evaluated, giving quantitative insights into the influence of strain. The Rashba coefficient was found to lower for samples with higher biaxial compressive strain, while heavy-hole mobilities were enhanced to over cm2 V−1 s−1 at 3 K. This high mobility enabled the observation of the optical quantum Hall effect at terahertz frequencies for spin-split two-dimensional heavy-holes, evidenced as plateaux in the transverse magnetoconductivity at even and odd filling factors.

Drude weight and optical conductivity of a two-dimensional heavy-hole gas with k-cubic spin-orbit interactions

We present a detailed theoretical study on zero-frequency Drude weight and optical conductivity of a two-dimensional heavy-hole gas (2DHG) with k-cubic Rashba and Dresselhaus spin-orbit interactions. The presence of k-cubic spin-orbit couplings strongly modifies the Drude weight in comparison to the electron gas with k-linear spin-orbit couplings. For large hole density and strong k-cubic spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. We establish a relation between optical conductivity and the Berry connection. Unlike two-dimensional electron gas with k-linear spin-orbit couplings, we explicitly show that the optical conductivity does not vanish even for equal strength of the two spin-orbit couplings. We attribute this fact to the non-zero Berry phase for equal strength of k-cubic spin-orbit couplings. The least photon energy needed to set in the optical transition in hole gas is one order of magnitude smaller than that of electron gas. Types of two van Hove singularities appear in the optical spectrum are also discussed.

Magnetotransport properties of 2D fermionic systems with k-cubic Rashba spin–orbit interaction

The spin–orbit interaction in heavy hole gas formed at p-doped semiconductor heterojunctions and electron gas at SrTiO3 surfaces is cubic in momentum. Here we report magnetotransport properties of k-cubic Rashba spin–orbit coupled 2D fermionic systems. We study longitudinal and Hall components of the resistivity tensor analytically as well as numerically. The longitudinal resistivity shows a beating pattern due to different Shubnikov-de Haas (SdH) oscillation frequencies f± for spin-up and spin-down fermions. We propose empirical forms of f± as exact expressions are not available, which are being used to find locations of the beating nodes. The beating nodes and the number of oscillations between any two successive nodes obtained from exact numerical results are in excellent agreement with those calculated from the proposed empirical formula. In the Hall resistivity, an additional Hall plateau appears between the two conventional ones as the spin–orbit coupling constant increases. The width of this additional plateau increases with spin–orbit coupling constant.

Hole spin helix: Anomalous spin diffusion in anisotropic strained hole quantum wells

We obtain the spin-orbit interaction and spin-charge coupled transport equations of a two-dimensional heavy hole gas under the influence of strain and anisotropy. We show that a simple two-band Hamiltonian can be used to describe the holes. In addition to the well-known cubic hole spin-orbit interaction, anisotropy causes a Dresselhaus-like term, and strain causes a Rashba term. We discover that strain can cause a shifting symmetry of the Fermi surfaces for spin up and down holes. We predict an enhanced spin lifetime associated with a spin helix standing wave similar to the Persistent Spin Helix which exists in the two-dimensional electron gas with equal Rashba and Dresselhaus spin-orbit interactions. These results may be useful both for spin-based experimental determination of the Luttinger parameters of the valence-band Hamiltonian and for creating long-lived spin excitations.

Spin Hall and longitudinal conductivity of a conserved spin current in two dimensional heavy-hole gases

The spin Hall and longitudinal conductivity of a 2D heavy-hole gas with {\it k}-cubic Rashba and Dresselhaus spin-orbit interaction is studied in the ac frequency domain. Using Kubo linear-response theory and a recently proposed definition for the (conserved) spin current operator suitable for spin-3/2 holes, it is shown that the spin conductivity tensor exhibit very distinguishable features from those obtained with the standard definition of the spin current. This is due to a significant contribution of the spin-torque term arisen from the alternative definition of spin current which strongly affects the magnitude and the sign of the dynamic spin current. In the dc (free of disorder) limit, the spin Hall conductivity for only (or dominant) {\it k}-cubic Rashba coupling is $\sigma^{s,z}_{xy}(0)=-9e/8\pi$, whereas $\sigma^{s,z}_{xy}(0)=-3e/8\pi$ for only (or dominant) {\it k}-cubic Dresselhaus coupling. Such anisotropic response is understood in terms of the absence of mapping the {\it k}-cubic Rashba $\leftrightarrow$ Dresselhaus Hamiltonians. This asymmetry is also responsible for the non-vanishing dc spin Hall conductivity ($\sigma^{s,z}_{xy}(0)=-6e/8\pi$) when the Rashba and Dresselhaus parameters have the same strength, in contrast with its corresponding case for electrons. These results are of relevance to validate the alternative definition of spin-current through measurements in the frequency domain of the spin accumulation and/or spin currents in 2D hole gases.

Spin susceptibility enhancement in a two-dimensional hole gas

The critical spin splitting needed to fully polarize a two-dimensional heavy-hole gas in a (Cd,Mn)Te quantum well thanks to the giant Zeeman effect is measured through photoluminescence and transmission spectroscopy. While the splitting between two circularly polarized peaks in photoluminescence remains equal to the bare spin splitting, the critical spin splitting which governs the polarization is enhanced, in good agreement with the prediction of a model of hole-hole interactions previously applied to conduction electrons. Consequences for carrier-induced ferromagnetism are discussed.

Electron‐phonon interactions in multi‐component plasma created by light‐ and heavy hole gas in polar semiconductors: from bulk to quantum dot structures

We study hole-phonon interactions as well as charge and spin scattering mechanisms from hole gas fluctuations including their overlapping with phonon features by using near infrared excitation of doped bulk p-GaAs and by self-assembled InAs/GaAs quantum dot structures. Theoretical arguments and experimental evidence of acoustic plasmon existence are presented. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Coherent dynamics of localized spins coupled with a two-dimensional hole gas in diluted-magnetic quantum wells

Spin dynamics in a quantum well made of diluted-magnetic semiconductor is studied theoretically. The exchange interaction of the ensemble of localized spins with two-dimensional heavy-hole gas is shown to affect time evolution of the spin system in an in-plane magnetic field. The Larmor frequency of localized spins is reduced under influence of an oscillating effective field of holes.

Nonequilibrium Fluctuations of Light and Heavy Hole Gas and Observation of Acoustic Plasma Oscillations Associated with Inter-Valence-Band Photoeffect in p-GaAs

Nonequilibrium Fluctuations of Light and Heavy Hole Gas and Observation of Acoustic Plasma Oscillations Associated with Inter-Valence-Band Photoeffect in p-GaAs

Studies on the development of magnetism in the Kondo semimetal CeNiSn caused by doping with La, Cu and Pt

Muon spin-rotation - relaxation experiments were performed at low temperature in transverse, zero and longitudinal field on , , and as an extension of our previous studies of the CeTSn (T = Ni, Pt, Pd) series. In CeNiSn we have proven the formation of weakly dynamic paramagnetic spin correlations, below 1 K which, however, do not lead to long-range magnetic order even at T = 10 mK. For the predicted heavy-hole gas antiferromagnetism is not seen, but rather a reduction of magnetic correlations. Both Pt-doped compounds exhibit no significant enhancement of spin correlations although CePtSn is an antiferromagnet with . The magnetic correlations increase strongly for up to the point of forming a spin - glass-like state at T < 0.9 K. Doping with either 20% Pt or 10% Cu increases the unit cell volume by roughly 1%. Volume expansion in CeTSn is a known cause for a reduction of the hybridization between f electron states and conduction electrons, thereby strengthening magnetic interactions. Yet, the marked differences in magnetic behaviour between replacing Ni in part by either isoelectronic Pt or by Cu, which has two more d electrons, indicates that the dominating effect must be the increase of the d electron density instead.

Magnetism in doped Kondo insulators

Abstract We consider the effect of substitution of small amounts of non-magnetic La for Ce in Kondo insulators of the CeNiSn type. In stoichiometric Kondo insulators, it appears that a gap on the scale of the Kondo temperature TK, is opened in the excitation spectrum. Doping with small amounts of La introduces a dilute heavy-hole gas in which we argue that the hole-hole exchange coupling can lead to an antiferromagnetic ground state at relatively low doping levels. For higher doping levels the system becomes a dirty metal and, depending on the value of the effective conduction-electron-f-electron magnetic coupling JK, may revert to a nonmagnetic state. Thus we anticipate the possibility of a ‘tongue’ of antiferromagnetic phase protruding into the non-magnetic region of the phase diagram at low to intermediate doping levels.

Present status of molecular beam epitaxial growth and properties of HgTe–CdTe superlattices

We report here on recent characterizations of HgTe–CdTe superlattices and on the growth of related novel superlattice systems. X-ray diffraction investigations carried out during the annealing of HgTe–CdTe superlattices have shown that an appreciable interdiffusion occurs at the HgTe–CdTe interface for a temperature of 185 °C, which is the growth temperature. Hg1−xCdxTe–CdTe superlattices have been grown for the first time. Their Hall characterization, along with magnetotransport experiments seem to indicate that high hole mobilities observed in p-type HgTe–CdTe superlattices are due to some type of relationship between the 2D heavy hole gas and the interface state existing in type III superlattices. We report also on the successful growth of a novel strained superlattice system, i.e., HgTe–ZnTe, which appears to be an interesting infrared material.

Molecular beam epitaxial growth and characterization of a novel superlattice system: Hg1−xCdxTe-CdTe

Hg1−xCdxTe-CdTe superlattices of both type I and type III have been grown for the first time using the molecular beam epitaxy technique. The superlattices were grown at 190 °C. They have been characterized by electron and x-ray diffraction, infrared transmission, and Hall measurements. The presence of satellite peaks in the x-ray spectra shows the superlattices to be of high quality. Infrared transmission spectra show that HgCdTe-CdTe superlattices have narrower band gaps than equivalent HgCdTe alloys. These superlattices are p type. Their Hall characterizations, along with magnetotransport experiments, seem to indicate that high hole mobilities observed in p-type HgTe-CdTe superlattices are due to some type of relationship between the two-dimensional heavy hole gas and the interface state existing in type III superlattices.