In lateral quantum dots, the combined effect of both Dresselhaus and Bychkov-Rashba spin-orbit coupling is equivalent to an effective magnetic field +/- B(SO) which has the opposite sign for s(z)= +/- 1/2 spin electrons. When the external magnetic field is perpendicular to the planar structure, the field B(SO) generates an additional splitting for electron states as compared to the spin splitting in the in-plane field orientation. The anisotropy of spin splitting has been measured and then analyzed in terms of spin-orbit coupling in several AlGaAs/GaAs quantum dots by means of resonant tunneling spectroscopy. From the measured values and sign of the anisotropy we are able to determine the dominating spin-orbit coupling mechanism.
We have studied the single-electron transport spectrum of a quantum dot in GaAs/AlGaAs resonant tunneling device. The measured spectrum has irregularities indicating a broken circular symmetry. We model the system with an external potential consisting of a parabolic confinement and a negatively charged Coulombic impurity placed in the vicinity of the quantum dot. The model leads to a good agreement between the calculated single-electron eigenenergies and the experimental spectrum. Furthermore, we use the spin-density-functional theory to study the energies and angular momenta when the system contains many interacting electrons. In the high magnetic field regime the increasing electron number is shown to reduce the distortion induced by the impurity.
Single-electron tunneling through a zero-dimensional state in an asymmetric double-barrier resonant-tunneling structure is studied. The broadening of steps in the I-V characteristics is found to strongly depend on the polarity of the applied bias voltage. Based on a qualitative picture for the finite-life-time broadening of the quantum dot states and a quantitative comparison of the experimental data with a non-equilibrium transport theory, we identify this polarity dependence as a clear signature of Coulomb interaction.Single-electron tunneling through zero-dimensional states has been observed in a wide variety of systems, including metallic islands, lateral quantum dots in gated semiconductor devices, vertical dots in double-barrier resonant tunneling structures, and molecular systems such as carbon nanotubes [1]. The I-V characteristics has the shape of a staircase, in which each step is associated with the opening of a new transport channel through the system. Many features observed in the transport measurements [2,3,4,5,6] can be explained either within a single-particle picture for non-interacting electrons or by the orthodox theory of sequential tunneling [7,8,9] valid for weak dot-lead tunnel coupling. This is no longer the case for interaction effects on transport beyond the weak-tunneling limit. A famous example is the zero-bias anomaly of Kondo-assisted tunneling [10,11].In this work, we report on a new clear signature of Coulomb interaction beyond weak tunneling, that is achieved under much less stringent experimental conditions than required for the Kondo effect to occur. This signature is contained in the width of the first step of the I-V characteristics. We observe that the width strongly depends on the polarity of the applied bias voltage. This behavior can neither be explained within a single-particle picture nor by sequential-tunneling theory [7,8,12]. Due to Coulomb interaction, the finite-life-time broadening of the dot levels becomes energy dependent. As a consequence, the values for the broadening at the two considered steps of opposite polarity can differ by up to a factor of two for strongly asymmetric coupling strengths of the two tunnel barriers. We use the results of a diagrammatic real-time transport theory [13] that includes the above described physics to find reasonable quantitative agreement with the experimental data.The experiment was performed with a highly asymmetric double-barrier resonant-tunneling device grown by molecular beam epitaxy on an n + -type GaAs substrate. An undoped 10 nm wide GaAs quantum well is sandwiched between 5 and 8 nm thick Al 0.3 Ga 0.7 As tunneling barriers separated from highly-doped GaAs contacts (Sidoped with n Si = 4 × 10 17 cm −3 ) by 7 nm thick undoped FIG. 1: (a) Schematic energy diagram of the asymmetric double-barrier device under finite bias. (b) First current step in negative bias direction. (c) Comparison of the full width half maximum (FWHM)-value of the differentialconductance peaks for both bias polarities at base temperature (T=20 mK).G...
Measurements of resonant tunneling through a localized impurity state are used to probe fluctuations in the local density of states of heavily doped GaAs. The measured differential conductance is analyzed in terms of correlation functions with respect to voltage. A qualitative picture based on the scaling theory of Thouless is developed to relate the observed fluctuations to the statistics of single-particle wave functions. In a quantitative theory correlation functions are calculated. By comparing the experimental and theoretical correlation functions, the effective dimensionality of the emitter is analyzed and the dependence of the inelastic lifetime on energy is extracted.
We have studied the photoresponse ͑transmission and photoconductivity of Corbino-shaped devices͒ of structures with InSb quantum wells ͑AlInSb barriers͒. To characterize the devices, the Shubnikov-de Haas ͑SdH͒ effect up to magnetic fields B of 7 T and current-voltage ͑I-V͒ characteristics at various magnetic fields were measured. Some of the samples showed clearly resolvable SdH oscillations. The I-V curves showed pronounced nonlinearities. The phototransmission and the photoconductivity at various terahertz ͑THz͒ frequencies were measured around 2.5 THz generated by a p-Ge laser. From the cyclotron resonance ͑transmis-sion measurements͒ we deduced a cyclotron mass of 0.022m 0 . We also performed photoconductivity measurements on Corbino-shaped devices in the THz frequency range. Oscillations of the photoconductivity with maxima near the minima of the conductivity in the dark were observed. Thus, these devices are potentially suitable for the detection of THz radiation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.