Electronic transport in low-dimensional structures

We present a semiclassical description of the level density of a two-dimensional circular quantum dot in a homogeneous magnetic field. We model the total potential (including electron-electron interaction) of the dot containing many electrons by a circular billiard, i.e., a hard-wall potential. Using the extended approach of the Gutzwiller theory developed by Creagh and Littlejohn, we derive an analytic semiclassical trace formula. For its numerical evaluation we use a generalization of the common Gaussian smoothing technique. In strong fields orbit bifurcations, boundary effects (grazing orbits) and diffractive effects (creeping orbits) come into play, and the comparison with the exact quantum-mechanical result shows major deviations. We show that the dominant corrections stem from grazing orbits, the other effects being much less important. We implement the boundary effects, replacing the Maslov index by a quantum-mechanical reflection phase, and obtain a good agreement between the semiclassical and the quantum result for all field strengths. With this description, we are able to explain the main features of the gross-shell structure in terms of just one or two classical periodic orbits.

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“…16. The thick lines in the frames (1a) and (1b) correspond to a function 15 sin(kG (1,2) ) + sin(kG (1,3) …”

Section: Semiclassical Interpretation Of the Shell Structurementioning

confidence: 99%

Periodic orbit theory of a circular billiard in homogeneous magnetic fields

Blaschke

Brack

1997

Phys. Rev. A

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“…36) we have T = 1.65 K, / = 5 μΑ, W ch = 4 μηι, p = 20 Ω. We thus find τ ε ~ 10 ~1 0 s, which is not an unreasonable value for the 2DEG in GaAs-AlGaAs heterostructures at helium temperatures [14].…”

Section: ίmentioning

confidence: 67%

“…(12)- (14). The inadequacy of the Sommerfeld expansion is a consequence of the strong energy dependence of t(E) near E F .…”

Section: =mentioning

confidence: 99%

Thermal and Thermo-Electric Transport Properties of Quantum Point Contacts

Molenkamp

Houten

Beenakker

et al. 1993

Semiconductor Superlattices and Interfaces

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A quantum point contact (QPC) is a short constriction of variable width, comparable to the Fermi wavelength, usually defined using a split-gate technique in a high-mobüity two-dimensional electron gas (2DEG). QPC's are best known for their quantized conductance at integer multiples of 2e 2 //i [l-3]. In addition, they have proven to be versatile probes for the study of electrical conduction in the ballistic and quantum Hall effect regime[3j. Recently, we have used QPC's in studies of thermal conduction and of thermo-electric cross-phenomena. Our results are reviewed in this lecture. Electrical conduction in linear response can be understood using the Landauer-Büttiker formalism [4, δ], which relates the conduction to transmission probabilities. This scattering formalism has been generalized to thermal and thermo-electric transport properties by SIVAN and lMRY[6] and by Bur-CHER [7]. STREDA [8] has considered specifically the problem of the thermopower of a QPC. He found that the thermopower vanishes whenever the conductance of the point contact is quantized, and that it exhibits peaks between plateaux of quantized conductance. Within this theoretical framework one can show that the thermal conductance κ and the Peltier coefficient Π should exhibit quantum size effects similar to those in the conductance G and the thermopower S, respectively. We review the theory in sect. 2.

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“…One low temperature characteristic of Si-doped GaAs/AlGaAs-HEMTs is the deep donor complexes known as DX-centers with approximately 140 meV activation energy which gives rise to the persistent photo conductivity (PPC) by illumination at temperatures below 150 K. [5][6][7] Up to now there were three well investigated methods to change the carrier concentration of such a HEMT at low temperatures. 8 These are illumination, gate voltage, and hydrostatic pressure. We report a fourth method: By applying high source-drain-voltages $10 V at the ohmic contacts of the sample for a time of maximum a few seconds, the carrier concentration is decreased even hours after the voltage has been turned off.…”

Section: Transient and Persistent Current Induced Conductivity Changementioning

confidence: 99%

“…To show this more clearly the sample was cooled down to 1.6 K in a pumped superfluid Hebath. The voltage pulses were applied in the middle of the sample (contacts 7,8,19,20). By waiting about an hour, we ensured that the transient is decayed almost completely and n 2D does not change significantly within a measurement.…”

Section: Transient and Persistent Current Induced Conductivity Changementioning

confidence: 99%

Transient and persistent current induced conductivity changes in GaAs/AlGaAs high-electron-mobility transistors

Schulte-Braucks

Valentin

Ludwig

et al. 2014

Applied Physics Letters

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We report the observation of a current induced change of the low temperature conductivity of two-dimensional electron gases in GaAs/AlGaAs-high-electron-mobility transistors. By applying voltage pulses on the ohmic contacts of a Hall bar-mesa-structure, both sheet-carrier-density n2D and electron mobility μ are decreased. At temperatures below 50 K, a persistent change combined with a partial transient recovery of n2D has been observed. The transient behaviour and the lateral spreading of the effect are studied. Moreover, a temperature dependent investigation has been done in order to get insight into the addressed defect energy levels. A model based on the phenomenology of the effect is proposed. The observed effect is not a permanent degradation as the original carrier concentration can be restored by warming up the sample to room temperature and recooling it.

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Electronic transport in low-dimensional structures

Cited by 90 publications

References 243 publications

Periodic orbit theory of a circular billiard in homogeneous magnetic fields

Periodic orbit theory of a circular billiard in homogeneous magnetic fields

Thermal and Thermo-Electric Transport Properties of Quantum Point Contacts

Transient and persistent current induced conductivity changes in GaAs/AlGaAs high-electron-mobility transistors

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