Noise thermometry in narrow two-dimensional electron gas heat baths connected to a quasi-one-dimensional interferometer

Physica Status Solidi (a)

et al. 2016

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Low‐dimensional transport in semiconductor meso‐ and nanostructures is a topical field of fundamental research with potential applications in future quantum devices. However, thermal non‐equilibrium may destroy phase‐coherence and remains to be explored experimentally. Here, we present effects of thermal non‐equilibrium in various implementations of low‐dimensional (non‐interacting) electron systems, fabricated by etching AlGaAs/GaAs heterostructures. These include narrow quasi‐two‐dimensional (2D) channels, quasi‐one‐dimensional (1D) waveguide networks, quantum rings (QRs), and single 1D constrictions, such as quantum point contacts (QPCs). Thermal non‐equilibrium is realized by current heating. The charge carrier temperature is determined by noise thermometry. The electrical conductance and the voltage–noise are measured with respect to bath temperatures, heating currents, thermal gradients, and electric fields. We determine and discuss heat transport processes, electron‐energy loss rates, and electron–phonon interaction, and our results are consistent with the Wiedemann–Franz relation. Additionally, we show how non‐thermal current fluctuations can be used to identify electric conductance anomalies due to charge states.

“…The exponent

n = 2.2

indicates that the electron‐energy relaxation is not dominated by a single mechanism. Our finding of

P_{e} \propto false(T_{e}^{2.2} - T_{bath}^{2.2} false)

() for the narrow 2D channel is lower than that observed for 2DEGs with a width of typically several 10

μ

Section: Resultscontrasting

confidence: 60%

“…We studied structure (I), a narrow 2DEG channel of 2

μ

m width with a measurement setup as depicted in Fig. a (). The length of 410

μ

Section: Resultsmentioning

confidence: 99%

“…Fabrication details for structures (I) and (II) are given in Ref. (), for structure (III) in Ref. (), and for structure (IV) in Ref.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Heat flow, transport and fluctuations in etched semiconductor quantum wire structures

Riha

Chiatti

Physica Status Solidi (a)

et al. 2016

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Electron waveguide interferometers for spin‐dependent transport experiments

Chiatti

Physica Status Solidi (b)

Kunze

et al. 2014

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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.Semiconductor nanostructures are of interest in the field of spintronics, because they allow us to employ special features of low-dimensional transport for spin polarization, manipulation, and detection. Proposals for spintronic devices are based on coherent transport and interference effects in extended electron waveguide (EWG) structures. We present the state-ofthe-art of low-dimensional EWGs and Aharonov-Bohm (AB) interferometers, fabricated in GaAs/AlGaAs heterostructures. Low-temperature measurements in etched quantum point contacts (QPCs) show large subband spacing and, in the presence of a source-drain DC bias, the differential conductance is resonantly enhanced due to a many-body modification of the barrier potential because of spin fluctuations. Multiterminal asymmetric quantum wire rings (QRs) have been fabricated and AB conductance oscillations are used to detect electrostatically induced continuous phase shifts and π-phase jumps, due to resonances and reflections at cross-junctions. The effects of measurement configuration and non-equilibrium in QR structures are also studied. By embedding a QPC into the leads of a QR, coherent mode-filtered injection of electrons into a few-mode AB interferometer is demonstrated. Single-and few-mode spin transport in EWG interferometers is discussed and the opportunities offered by embedding quantum dots for studying interaction and spin effects are presented. The results encourage the investigation of spin-dependent quantum transport in extended EWG interferometers.

Mode-selected heat flow through a one-dimensional waveguide network

Riha

Miechowski

Applied Physics Letters

et al. 2015

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Cross-correlated measurements of thermal noise are performed to determine the electron temperature in nanopatterned channels of a GaAs/AlGaAs heterostructure at 4.2 K. Two-dimensional (2D) electron reservoirs are connected via an extended one-dimensional (1D) electron waveguide network. Hot electrons are produced using a current I h in a source 2D reservoir, are transmitted through the ballistic 1D waveguide and relax in a drain 2D reservoir. We find that the electron temperature increase ∆T e in the drain is proportional to the square of the heating current I h , as expected from Joule's law. No temperature increase is observed in the drain when the 1D waveguide does not transmit electrons. Therefore, we conclude that electron-phonon interaction is negligible for heat transport between 2D reservoirs at temperatures below 4.2 K. Furthermore, mode control of the 1D electron waveguide by application of a top-gate voltage reveals that ∆T e is not proportional to the number of populated subbands N , as previously observed in single 1D conductors. This can be explained with the splitting of the heat flow in the 1D waveguide network.The transport properties of a one-dimensional (1D) waveguide are dominated by the wave-like character of electrons. The nanoscale confinement potential is typically created by applying advanced lithographic methods to high mobility two-dimensional electron gases (2DEGs). In ballistic 1D waveguides electric conductance quantization is observed 1,2 and is shown to scale linearly with the thermal conductance at low temperatures.3-5 This indicates the validity of the WiedemannFranz relation in the ballistic 1D regime, when electronphonon and electron-electron interactions can be neglected. 6,7 In previous works by van Houten et al. 3 and Chiatti et al.4 comparable heating measurements between two AlGaAs/GaAs 2DEGs were performed. The two 2DEGs were connected via a single quantum point contact (QPC) and the increase in electron temperature ∆T e of the indirectly heated 2D reservoir was measured by a second QPC. ∆T e was found to be proportional to the number of populated subbands N of the QPC. The question that arises is how the mode-dependent heat transfer evolves in networks of extended 1D waveguides, where phase-coherent effects have been investigated inand out-of-equilibrium. 8,9Here, we perform cross-correlated electronic noise measurements to determine the charge carrier temperature in an extended 1D waveguide network made from an AlGaAs/GaAs heterostructure. We investigate the heat transport through an asymmetric quantum ring, 9 which is a network of 1D electron waveguides with 2D contacts as depicted in Fig. 1. A global top-gate enables the control of the conductivity of the 2D reservoirs and the 1D electron waveguides. One electron reservoir is heated above the lattice temperature via the current heating a) E-mail: riha@physik.hu-berlin.de technique.10 The increase in electron temperature ∆T e of the other electron reservoir is extracted by the means of Johnson-Nyquist noise thermometr...