We theoretically and numerically present the hybrid phonon modes for the double heterostructure GaAs/AlxGa1-xAs and their interactions with electrons. More specifically, we have calculated the electron capture within a symmetric quantum well via the emission of hybrid phonons. Our investigation shows that the capture rates via the hybrid phonons are matched to the rates predicted by the dielectric continuum (DC) model and the concentration of aluminium which is an important parameter for controlling the electron capture process in light emitting diodes (LED).
Characteristics of GaAs/In$_{x}$Ga$_{1-x}$As/GaAs heterostructures with a single quantum well, which were obtained at various growth parameters, are evaluated according to the results of measurements of low-temperature photoluminescence spectra and their corresponding theoretical analysis.
We report results of investigations of structural and transport properties of GaAs/Ga(1-x)In(x)As/GaAs quantum wells (QWs) having a 0.5-1.8 ML thick Mn layer, separated from the QW by a 3 nm thick spacer. The structure has hole mobility of about 2000 cm2/(V*s) being by several orders of magnitude higher than in known ferromagnetic two-dimensional structures. The analysis of the electro-physical properties of these systems is based on detailed study of their structure by means of high-resolution X-ray diffractometry and glancing-incidence reflection, which allow us to restore the depth profiles…
We used AlGaSb/AlGaAs material system for a theoretical study of photovoltaic performance of the proposed GaAs-based solar cell in which the type-II quantum dot (QDs) absorber is spatially separated from the depletion region. Due to inelastic scattering of photoelectrons on QDs and proper doping of both QDs and their spacers, concentrated sunlight is predicted to quench recombination through QDs. Our calculation shows that 500-sun concentration can increase the Shockley-Queisser limit from 35% to 40% for GaAs single-junction solar cells.
The influence of indium percentage on dynamical characteristics of InxGa1-xAs/GaAs(001) quantum dot lasers (QDLs) is investigated. Energy levels of self-organized truncated-cone-shape QDs are calculated by means of the eight-band k.p model, and their dependence to indium percentage is surveyed. Then, by presenting a three-level model and numerical solution of the resulting rate equations, laser properties are determined. Our results show that inclusion of more indium gives rise in the reduced energy gap and electron-hole recombination energy. Moreover, lasing process for both Ground State (GS)…
Tunneling of electrons through the barriers in heterostructures devices is investigated by using the unified Transfer Matrix Method. The effect of barrier width on electron transmission coefficients has also been examined for different pairs of semiconductor devices of significant research interest in current years. Such Pairs involve AlxGa1-xAs/GaAs, AlSb/InAs, and CdS/CdSe quantum barriers with varying dimensions reduced from 20 nm to 5nm to observe how tunneling properties are affected by scaling. The effective electron masses in the well and barrier regions typically vary with constituent …
The intermediate band (IB) cell is a concept of highly efficient solar cells proposed by Luque and Marti in 1997. The IB concept uses nonlinear effect of two photon absorption enforced with concentration of such photons for generation of additional photocurrent in single p-n-junction cells. In this theoretical work we demonstrate an important role of self-organized strained type-II AlyGa1-ySb quantum dots for operation in IB GaAs solar cells.
Recombination through quantum dots (QDs) is a major factor that limits efficiency of QD intermediate-band (IB) solar cells. Our proposal for a new IB solar cell based on type-II GaSb QDs located outside the depletion region of a GaAs p-n-junction aims to solve this problem. The important advantage of proposed heterostructure appears due to the outside location of IB. Such IB does not assist generation of additional leakage current flow through the depletion region. Carriers cannot escape from outside QDs through the buffer layer and the depletion region into GaAs substrate by tunneling because…
We propose a new intermediate band GaAs solar cell comprising an AlxGa1-xAs absorber with built-in GaSb type-II quantum dots (QDs) [a gradual AlxGa1-xAs absorber with built-in AlyGa1-ySb QDs (0<x=y<0.40) as a variant] separated from the depletion region. We study the modification of the band alignment at type-II interface by two-photon absorption of concentrated sunlight. Our calculation shows that photogenerated carriers produce localized exciton-like electron-hole pairs spatially separated at QDs. Local field of such pairs may essentially modify potential barrier surrounding QDs, increase re…
We measure the lifetime of the zone-center 340 GHz longitudinal phonon mode in a GaAs-AlAs superlattice excited and probed with femtosecond laser pulses. By comparing measurements conducted at room temperature and liquid nitrogen temperature we separate the intrinsic (phonon-phonon scattering) and extrinsic contributions to phonon relaxation. The estimated room temperature intrinsic lifetime of 0.95 ns is compared to available calculations and experimental data for bulk GaAs. We conclude that ~0.3 THz phonons are in the transition zone between Akhiezer and Landau-Rumer regimes of phonon-phonon…
We present electronic transport measurements of GaAs nanowires grown by catalyst-free metal-organic chemical vapor deposition. Despite the nanowires being doped with a relatively high concentration of substitutional impurities, we find them inordinately resistive. By measuring sufficiently high aspect-ratio nanowires individually in situ, we decouple the role of the contacts and show that this semi-insulating electrical behavior is the result of trap-mediated carrier transport. We observe Poole-Frenkel transport that crosses over to phonon-assisted tunneling at higher fields, with a tunneling …
Utilizing three-terminal tunnel emission of ballistic electrons and holes, we have developed a method to self-consistently measure the bandgap of semiconductors and band discontinuities at semiconductor heterojunctions without any prerequisite material parameter. Measurements are performed on lattice-matched GaAs/AlxGa1-xAs and GaAs/(AlxGa1-x)0.51In0.49P single-barrier heterostructures. The bandgaps of AlGaAs and AlGaInP are measured with a resolution of several meV at 4.2 K. For the GaAs/AlGaAs interface, the measured Gamma band offset ratio is 60.4:39.6 (+/-2%). For the GaAs/AlGaInP interfac…
Simultaneous study of acoustic and optic phonon scattering of electrons and holes in undoped $\mathrm{GaAs}$/$\mathrm{Al_{x} Ga_{1-x} As}$ heterostructures
本研究利用非掺杂 GaAs/AlGaAs 异质结构，通过电阻率温度依赖性测量，在 1.6-92.5K 范围内同步研究了二维电子和空穴的声学与光学声子散射，提取了耦合常数和 LO 激活能，验证了该方法的有效性。
The dynamics of an exciton-LO-phonon system after an ultrafast optical excitation in an InAs/GaAs quantum dot is studied theoretically. Influence of anharmonic phonon damping and its interplay with the phonon dispersion is analyzed. The signatures of the zone-edge decay process in the absorption spectrum and time evolution are highlighted, providing a possible way of experimental investigation on phonon anharmonicity effects.
Precise absolute far-infra-red magneto-transmission experiments have been performed in magnetic fields up to 33 T on a series of single GaAs quantum wells doped at different levels. The transmission spectra have been simulated with a multilayer dielectric model. The imaginary part of the optical response function which reveals new singular features related to the electron-phonon interactions has been extracted. In addition to the expected polaronic effects due to the longitudinal optical (LO) phonon of GaAs, a new kind of carrier concentration dependent interaction with interface phonons is ob…
Nanowires (NWs) with their quasi-one-dimensionality often present different structural and opto-electronic properties than their thin-film counterparts. The thinner they are the larger these differences are, in particular in the carrier-phonon scattering and thermal conductivity. In this work, we present femtosecond transient absorbance measurements on GaAs0.8P0.2 NWs of two different diameters, 36 and 51 nm. The results show that thinner NWs sustain the hot-carriers at a higher temperature for longer times than thicker NWs. We explain the observation suggesting that in thinner NWs, the build-…
We report first studies of long-lived oscillations in optical pump-probe measurements on GaSb-GaAs heterostructures. The oscillations arise from a photogenerated coherent longitudinal acoustic phonon wave, which travels from the top surface of GaSb across the interface into the GaAs substrate, providing information on the optical properties of the material as a function of time/depth. Wavelength-dependent studies of the oscillations near the bandgap of GaAs indicate strong correlations to the optical properties of GaAs.
We report the design of GaAs-based monolithic valley phononic crystals (VPnCs) with multiple complete phononic bandgaps, which support simultaneous valley-protected edge states with different symmetries in the gigahertz (GHz) range. Rotation of triangular holes in the unit cells breaks the mirror symmetry, and this orientation degree of freedom enables the structures to exhibit different valley vortex chiralities. We numerically demonstrate the transport of multi-band valley-protected edge states with suppressed backscattering at the sharp corners of the interfaces between different VPnCs. Suc…
We study phonon emission in a GaAs/AlGaAs double quantum dot by monitoring the tunneling of a single electron between the two dots. We prepare the system such that a known amount of energy is emitted in the transition process. The energy is converted into lattice vibrations and the resulting tunneling rate depends strongly on the phonon scattering and its effective phonon spectral density. We are able to fit the measured transition rates and see imprints of interference of phonons with themselves causing oscillations in the transition rates.
In this paper, we investigate renormalization of charge carrier effective masses and bandgap narrowing in n-GaAs and wurtzite-type n-GaN over a wide range of temperatures and dopant concentrations. The calculations are based on the Green's function formalism. Contrary to the previous works, we consider the regions below as well as above the Mott transition. Special attention is paid to formation of donor subband and condition for the Mott transition. We also take into account the effects caused by optical phonons. The latter strongly depend on the doping level because of dynamic screening. It …
Low-temperature electron magnetotransport in single GaAs quantum wells with two populated subbands is studied at large filling factors. Magneto-inter-subband (MIS) and acoustic-phonon induced oscillations of the dissipative resistance are found to be coexisting but interfering substantially with each other. The experiments show that amplitude of the MIS-oscillations enhances significantly by phonons, indicating "constructive interference" between the phonon scattering and the intersubband electron transitions. Temperature damping of the quantum oscillations is found to be related to broadening…
Considering scattering by unintentional background charged impurities and by charged dopants in the modulation doping layer as well as by GaAs acoustic phonons, we theoretically consider the practical intrinsic (phonons) and extrinsic (background and dopants) limits to carrier mobility in modulation doped AlGaAs-GaAs 2D semiconductor structures. We find that reducing background impurity density to $10^{12}$ cm$^{-3}$ along with a modulation doping separation of 1000 Åor above will achieve a mobility of $100 \times 10^6$ cm$^2$/Vs at a carrier density of $3\times 10^{11}$ cm$^{-2}$ for T=1K. At…
In this paper, thermal conductivity of crystalline GaAs is calculated using first-principles lattice dynamics. The harmonic and cubic force constants are obtained by fitting them to the force-displacement data from density functional theory calculations. Phonon dispersion is calculated from dynamical matrix constructed using the harmonic force constants and phonon relaxation times are calculated using Fermi Golden rule. The calculated GaAs thermal conductivity agrees well with experimental data. Thermal conductivity accumulations as a function of phonon mean free path and as a function of wave…
We study the mobility of Dirac fermions in monolayer graphene on a GaAs substrate, restricted by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (PA) and of the intrinsic deformation potential of acoustical eigen-phonons in graphene (DA). In the high temperature ($T$) regime the momentum relaxation rate exhibits the same linear dependence on $T$ but different dependences on the carrier density $n$, corresponding to the mobility $μ\propto 1/\sqrt{n}$ and $1/n$, respectively for the PA and DA scattering mechanisms. In the low $T$ Bloch-Grüneisen…
A contribution of the electron-phonon interaction into the energy of a unidirectional charge ordered state (stripe phase) of two-dimensional electrons in GaAs heterostructures is analyzed. The dependence of the energy on the direction of the electron density modulation is calculated. It is shown that in electrons layers situated close to the (001) surface the interference between the piezoelectric and the deformation potential interaction causes a preferential orientation of the stripes along the [110] axis.
Self-consistent calculations of acoustic and polar optical phonon scattering rates in GaAs quantum wire transistor structures were carried out with account of collisional broadening. The influence of the gate bias on the scattering rates was examined, too. It was shown that in order to treat the scattering rates rigorously it is important to search for electron energy levels by means of the self-consistent solution of Schrodinger and Poisson equations and to take into account the collisional broadening.
A fine structure of phonon replicas in the current-voltage characteristic of a resonant-tunneling diode has been investigated experimentally. A detailed study of the diode I-V curves in magnetic fields of different orientations has allowed to determine the origin of the features in the fine structure. The voltage positions of the features are shown to coincide with calculated that in the frame of two models: LO-phonon assisted tunneling and resonant tunneling of polarons.
Cyclotron-resonance (CR) spectra of a gas of interacting polarons confined in a GaAs/AlAs quantum well are theoretically investigated taking into account the magneto-plasmon-phonon mixing and band nonparabolicity. Contributions of different magneto-plasmon-phonon modes to the total magneto-polaron coupling strength are investigated as a function of the electron density. It is confirmed theoretically, that the resonant magneto-polaron coupling in a high-density GaAs/AlAs quantum well occurs near the GaAs TO-phonon frequency rather than near the GaAs LO-phonon frequency. Calculated CR spectra ar…
Recently, longitudinal acoustic phonons have been identified as the main source of the intensity damping observed in Rabi rotation measurements of the ground-state exciton of a single InAs/GaAs quantum dot. Here we report experiments of intensity damped Rabi rotations in the case of detuned laser pulses, the results have implications for the coherent optical control of both excitons and spins using detuned laser pulses.
The phonon-induced spin relaxation in a two-dimensional quantum dot embedded inside a semiconductor slab is investigated theoretically. An enhanced relaxation rate is found due to the phonon van Hove singularities. Oppositely, a vanishing deformation potential may also result in a suppression of the spin relaxation rate. For larger quantum dots, the interplay between the spin orbit interaction and Zeeman levels causes the suppression of the relaxation at several points. Furthermore, a crossover from confined to bulk-like systems is obtained by varying the width of the slab.
We have measured the lifetimes of two zone-center longitudinal acoustic phonon modes, at 320 GHz and 640 GHz respectively, in a 14 nm GaAs / 2 nm AlAs superlattice structure. By comparing measurements at 296 K and 79 K we separate the intrinsic contribution to phonon lifetime determined by phonon-phonon scattering from the extrinsic contribution due to defects and interface roughness. At 296 K, the 320-GHz phonon lifetime has approximately equal contributions from intrinsic and extrinsic scattering, whilst at 640 GHz it is dominated by extrinsic effects. These measurements are compared with fi…
We report experimental evidence identifying acoustic phonons as the principal source of the excitation-induced-dephasing (EID) responsible for the intensity damping of quantum dot excitonic Rabi rotations. The rate of EID is extracted from temperature dependent Rabi rotation measurements of the ground-state excitonic transition, and is found to be in close quantitative agreement with an acoustic-phonon model.
We study the anisotropic orbital effect in the electric field tunability of the phonon induced spin-flip rate in quantum dots (QDs). Our study shows that anisotropic gate potential enhances the spin-flip rate and reduces the level crossing point to a lower quantum dot radius due to the suppression of the Land$\acute{e}$ g-factor towards bulk crystal. In the range of $10^4-10^6$ V/cm, the electric field tunability of the phonon induced spin-flip rate can be manipulated through strong Dresselhaus spin-orbit coupling. These results might assist the development of a spin based solid state quantum …
Phonon-assisted transport and hole-phonon coupling in GaAs double quantum dots
University of Science and Technology of China（中国科学技术大学）；CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China（中国科学技术大学量子信息与量子物理前沿协同创新中心）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）
The results of recent measurements of the cyclotron resonance (CR) spectra for a GaAs quantum well are interpreted in terms of the resonant magnetopolaron effect. Owing to this effect, the CR peaks split near the TO-phonon frequency and also change their positions with respect to those obtained without electron-phonon interaction. The theoretical peak positions of the CR spectra calculated within the many-polaron approach compare well with experimental data, as distinct from the CR energies calculated without electron-phonon interaction, which show no particular features in the region of the o…
Strong increase in the intensity of the peaks of excited magneto-exciton (ME) states in the photoluminescence excitation (PLE) spectra recorded for the ground heavy-hole magneto-excitons (of the 1sHH type) has been found in a GaAs/AlGaAs superlattice in strong magnetic field B applied normal to the sample layers. While varying B the intensities of the PLE peaks have been measured as functions of energy separation $ΔE$ between excited ME peaks and the ground state of the system. The resonance profiles have been found to have maxima at $ΔE_{\rm max}$ close to the energy of the GaAs LO-phonon. Ho…
Electron-hole recollisions are induced by resonantly injecting excitons with a near-IR laser at frequency $f_{\text{NIR}}$ into quantum wells driven by a ~10 kV/cm field oscillating at $f_{\text{THz}} = 0.57$ THz. At $T=12$ K, up to 18 sidebands are observed at frequencies $f_{\text{sideband}}=f_{\text{NIR}}+2n f_{\text{THz}}$, with $-8 \le 2n \le 28$. Electrons and holes recollide with total kinetic energies up to 57 meV, well above the $E_{\text{LO}} = 36$ meV threshold for longitudinal optical (LO) phonon emission. Sidebands with order up to $2n=22$ persist up to room temperature. A simple …
We report on a new class of magnetoresistance oscillations observed in a high-mobility two-dimensional electron gas (2DEG) in GaAs-Al$_x$Ga$_{1-x}$As heterostructures. Appearing in a weak magnetic field ($B<$ 0.3 T) and only in a narrow temperature range (2 K $<T<$ 9 K), these oscillations are periodic in 1/B with a frequency proportional to the electron Fermi wave vector, $k_F$. We interpret the effect as a magnetophonon resonance of the 2DEG with leaky interface-acoustic phonon modes carrying a wave vector $q=2k_F$. Calculations show a few branches of such modes on the GaAs-Al$_x$Ga$_{1-x}$A…
We report a photon number resolving detector using two-dimensional electron gas (2DEG) based transistors. When the photon pulses impinge on the absorption region, the generated phonons dissipate ballistically in the 2DEG toward the trench isolated nanowire transistors near the surface. The phonon-electron interaction induces a positive conductance in the transistors, resulting in a current increase. With this principle, we obtain an internal quantum efficiency for this type of detector of up to 85%.
Transport properties of GaAs/δ<Mn>/GaAs/In\timesGa1-\timesAs/GaAs structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content, are studied. In these structures DL is separated from QW by GaAs spacer with the thickness ds = 2-5 nm. All structures possess a dielectric character of conductivity and demonstrate a maximum in the resistance temperature dependence Rxx(T) at the temperature {\approx} 46K which is usually associated with the Curie temperature Tc of ferromagnetic (FM) transition in DL. Howeve…
We study optically driven Rabi rotations of a quantum dot exciton transition between 5 and 50 K, and for pulse-areas of up to $14π$. In a high driving field regime, the decay of the Rabi rotations is nonmonotonic, and the period decreases with pulse-area and increases with temperature. By comparing the experiments to a weak-coupling model of the exciton-phonon interaction, we demonstrate that the observed renormalization of the Rabi frequency is induced by fluctuations in the bath of longitudinal acoustic phonons, an effect that is a phonon analogy of the Lamb-shift.
Using a recently-developed time-of-flight measurement technique with 1 ps time resolution and electron-energy spectroscopy, we developed a method to measure the longitudinal-optical-phonon emission rate of hot electrons travelling along a depleted edge of a quantum Hall bar. A comparison of the experimental results to a single-particle model implies that the main scattering mechanism involves a two-step process via intra-Landau-level transition. We show this scattering can be suppressed by controlling the edge potential profile, and a scattering length > 1 mm can be achieved, allowing the use …
A dispersion equation for the interface waves has been derived for the interface of two cubic crystals in the plane perpendicular to [001]. A reasonable hypothesis has been made about the total number of the acoustic modes. Due to this hypothesis the number is 64, but not all of the modes have physical meaning of the interface waves. The rules have been worked out to select physical branches among all 64 roots of dispersion equation. The physical meaning of leaky interface waves is discussed. The calculations have been made for the interface Al$_{0.3}$Ga$_{0.7}$As/GaAs. In this case all physic…
Similar to electron waves, the phonon states in semiconductors can undergo changes induced by external boundaries. Modification of acoustic phonon spectrum in structures with periodically modulated elastic constant or mass density - referred to as phononic crystals - has been proven experimentally and utilized in practical applications. A possibility of modifying acoustic phonon spectrum in individual nanostructures via spatial confinement would bring tremendous benefits for controlling phonon-electron interaction and thermal conduction at nanoscale. However, despite strong scientific and prac…
Understanding and control of the spin relaxation time $T_1$ is among the key challenges for spin based qubits. A larger $T_1$ is generally favored, setting the fundamental upper limit to the qubit coherence and spin readout fidelity. In GaAs quantum dots at low temperatures and high in-plane magnetic fields $B$, the spin relaxation relies on phonon emission and spin-orbit coupling. The characteristic dependence $T_1 \propto B^{-5}$ and pronounced $B$-field anisotropy were already confirmed experimentally. However, it has also been predicted 15 years ago that at low enough fields, the spin-orbi…
The Frohlich interaction is one of the main electron-phonon intrinsic interactions in polar materials originating from the coupling of one itinerant electron with the macroscopic electric field generated by any longitudinal optical (LO) phonon. Infra-red magneto-absorption measurements of doped GaAs quantum wells structures have been carried out in order to test the concept of Frohlich interaction and polaron mass in such systems. These new experimental results lead to question the validity of this concept in a real system.
Electron-phonon (e-ph) interactions are usually treated in the lowest order of perturbation theory. Here we derive next-to-leading order e-ph interactions, and compute from first principles the associated two-phonon e-ph scattering rates. The derivation involves Matsubara sums of the relevant two-loop Feynman diagrams, and the numerical calculations are challenging since they involve Brillouin zone integrals over two crystal momenta and depend critically on the intermediate state lifetimes. Using random grids and Monte Carlo integration, together with a self-consistent update of the intermedia…
We present thermopower measurements on a high electron mobility two-dimensional electron gas (2DEG) in a thin suspended membrane.We show that the small dimension of the membrane substantially reduces the thermal conductivity compared to bulk material so that it is possible to establish a strong thermal gradient along the 2DEG even at a distance of few micrometers. We find that the zero-field thermopower is significantly affected by the micro patterning. In contrast to 2DEGs incorporated in a bulk material, the diffusion contribution to the thermopower stays dominant up to a temperature of 7 K …
Recent studies reveal that a double-quantum-dot system hosting more than two electrons may be superior in certain aspects as compared to the traditional case in which only two electrons are confined (a singlet-triplet qubit). We study the electron-phonon dephasing occurring in a GaAs multi-electron double-quantum-dot system, in a biased case in which the singlet state is hybridized, as well as in an unbiased case in which the hybridization is absent. We have found that while the electron-phonon dephasing rate increases with the number of electrons confined in the unbiased case, this does not h…
The compound semiconductor gallium arsenide (GaAs) provides an ultra-clean platform for storing and manipulating quantum information, encoded in the charge or spin states of electrons confined in nanostructures. The absence of inversion symmetry in the zinc-blende crystal structure of GaAs however, results in strong piezoelectric coupling between lattice acoustic phonons and electrons, a potential hindrance for quantum computing architectures that can be charge-sensitive during certain operations. Here we examine phonon generation in a GaAs double dot, configured as a single- or two-electron c…
Phonon interference effects in GaAs-GaP superlattice nanowires
Universität Basel（巴塞尔大学）；Istituto Nanoscienze-CNR and Scuola Normale Superiore（国家纳米科学技术研究所和比萨高等师范学院）；Institut de Ciencia de Materials de Barcelona, ICMAB−CSIC（巴塞罗那材料科学研究所）
The effect of an in-plane magnetic field on resonant tunneling in a symmetric GaAs/AlYGa1-YAs triple-barrier resonant tunneling TBRT structure is presented. The splitting of the resonant lines (and hence the coupling energy vs. magnetic induction) for the ground and the first excited resonant doublet shifts up in energy by increasing the magnetic induction. Each of branches in the resonant dispersion relations shows a parabolic behavior with the location of the cyclotron orbit center. It is expected that, at very high fields, the interaction with confined phonons be enhanced, due to phonon cou…
We report on linewidth analysis of optical transitions in InAs/GaAs coupled quantum dots as a function of bias voltage, temperature, and tunnel coupling strength. A significant line broadening up to 100 $μ$eV is observed at hole tunneling resonances where the coherent tunnel coupling between spatially direct and indirect exciton states is maximized, corresponding to a phonon-assisted transition rate of 150 ns${}^{-1}$ at 20 K. With increasing temperature, the linewidth shows broadening characteristic of single-phonon transitions. The linewidth as a function of tunnel coupling strength tracks t…
We report on the first measurements of the drag effect between coupled 2D-hole gases. We investigate the coupling by changing the carrier densities in the quantum wells, the widths of the barriers between the gases and the perpendicular magnetic field. From the data we are able to attribute the frictional drag to phonon coupling, because the non-parabolicity allows to tune the Fermi wavevector and the Fermi velocity separately and, thereby, to distinguish between phonon- and plasmon-dominated coupling.
We study the dephasing of two-electron states in a single quantum dot in both GaAs and Si. We investigate dephasing induced by electron-phonon coupling and by charge noise analytically for pure orbital excitations in GaAs and Si, as well as for pure valley excitations in Si. In GaAs, polar optical phonons give rise to the most important contribution, leading to a typical dephasing rate of ~5.9 GHz. For Si, intervalley optical phonons lead to a typical dephasing rate of ~140 kHz for orbital excitations and ~1.1 MHz for valley excitations. For harmonic, disorder-free quantum dots, charge noise i…
