Commensurability Oscillations in the Radio-Frequency Conductivity of Unidirectional Lateral Superlattices: Measurement of Anisotropic Conductivity by Coplanar Waveguide

Endo, Akira; Kajioka, Toshiyuki; Iye, Yasuhiro

doi:10.7566/jpsj.82.054710

Cited by 12 publications

(17 citation statements)

References 45 publications

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“…The microwaves propagating through a coplanar wave guide (CPW) 15 deposited on the surface of a 2DEG wafer are partially absorbed by, and raise the temperature of, the 2DEG underneath the slots of the CPW. 16,17 By placing a CPW along the outer periphery of a Corbino disk, we introduce a radial gradient in T e , and measure the resulting thermovoltages V rr . We observe the behavior of V rr expected for the diffusion contribution in the QH systems in the Corbino geometry.…”

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confidence: 99%

“…By detecting the transmission of the microwaves through the CPW with the network analyzer, one can also measure the longitudinal conductivity σ θθ = σ xx of the 2DEG underneath the slots. [15][16][17] From the amplitudes of the Shubnikov-de Haas (SdH) oscillations in the measured σ θθ , one can, in turn, estimate T e of the electrons heated by the microwaves, 16,17 which can be used to translate V TP into S rr (see the discussion below). Measurements are performed at T bath = 1.4 K in a 4 He cryostat using a probe equipped with semi-rigid coaxial cables.…”

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“…To this end, we estimate the T e,high of the electrons heated by the microwaves, using the SdH amplitudes of σ θθ deduced from the microwave transmission through the CPW. 16,17 We assume that T e,low at the IC equals the helium bath temperature T bath = T L = 1.4 K. With the temperature difference ∆T e = T e,high − T bath = R M R IC dr∇ r T e , the thermo- in the range ∆T e . We made the measurements for three different microwave powers: the output powers of the network analyzer P NA = −40, −30, and −20 dBm, corresponding to the powers at the entrance of the CPW (subtracting the power absorbed along the cables) 0.015, 0.15, and 1.5 µW, respectively.…”

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Diffusion Thermopower of Quantum Hall States Measured in Corbino Geometry

2013

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We have measured the diffusion thermopower of a quantum Hall system in a Corbino setup. A concentric electrontemperature gradient is introduced by irradiating microwaves, via a coplanar waveguide, near the outer rim of a circular mesa of a two-dimensional electron gas. The resulting radial thermovoltages exhibit sawtooth-like oscillations with the magnetic field, taking large positive (negative) values just below (above) integer fillings with sign reversal at the center of the quantum Hall plateaus. The behavior is in agreement with a recent theory [Y. Barlas and K. Yang: Phys. Rev. B 85 (2012) 195107], which treats disorder within the self-consistent Born approximation.KEYWORDS: diffusion thermopower, quantum Hall effect, Corbino disk, microwave heating, coplanar waveguide, conductivity, two-dimensional electron gasThe thermopower of quantum Hall (QH) systems has been attracting interest as a sensitive probe to examine the electronic properties of the systems, 1-8 which is further spurred by a recent proposal of the possibility to explore intriguing statistics of the quasiparticles in the ν = 5/2 fractional QH state. [9][10][11][12] The vast majority of the measurements have been performed in the Hall bar geometry thus far (see, e.g., ref.5 and references therein). As will be detailed below, the radial thermopower S rr measured in the Corbino geometry is qualitatively different from the longitudinal thermopower S xx measured in the Hall bar geometry.6, 10 The purpose of the present paper is to report our measurements of the diffusion thermopower in the Corbino geometry for integer QH states.The thermopower generally contains contributions from two distinct mechanisms: diffusion and phonon drag. 5 The high sensitivity to the electronic properties is expected for the former contribution. In a two-dimensional electron gas (2DEG) embedded in a GaAs/AlGaAs heterostructure, however, it is well known that the latter dominates the measured thermopower, 5, 6 unless measurements are done at very low temperatures 150 mK; 4, 11 in standard measurements using an external heater to introduce the temperature gradient ∇T , the resulting heat current is predominantly carried by the phonons in the host crystal, leading to the dominance of the phonon-drag contribution despite the weakness of the electron-phonon interaction. The measurement of Corbino thermopower in QH systems at 1.5 K was previously reported by Zalinge et al. 6 They used a laser spot as a heater to introduce ∇T , and therefore the measured thermovoltages were primarily attributed to the phonon-drag.The diffusion contribution can be selectively measured by introducing the gradient only to the electron temperature T e , leaving the lattice temperature T L intact. This can be achieved by directly passing a moderately large current to a section of 2DEG designated to serve as a heater.13, 14 It will be practically very difficult, however, to apply this Joule heating technique to a Corbino device, since it requires the heating current to pass only along the outer (or ...

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Diffusion Thermopower of Quantum Hall States Measured in Corbino Geometry

2013

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“…(Strictly speaking, these formulae are for B=0.0 T and do not take the Landau quantization into consideration. We assume that they are still applicable in the relatively weak magnetic field regime studied in the present paper [32].) We used the following material parameters for GaAs [32,[37][38][39][40]: the deformation potential D=−9.3 eV, the piezoelectric constant h 14 =1.…”

Section: Discussionmentioning

confidence: 99%

“…To see which part of the device has made the dominant contribution to the thermoelectric voltages, we examine how the integral in equation (32) varies during the course of the integration. In figure 14, we plot y D   ( ) y yx given by equation (35) as a function of  y at B=0.0 T and 0.5 T. Without the magnetic field, the contribution of the voltage arms is negligibly small and y D  i j , almost exclusively derives from the main bar.…”

Section: Simulating Thermoelectric Voltages From the Calculated Spatimentioning

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Spatial distribution of thermoelectric voltages in a Hall-bar shaped two-dimensional electron system under a magnetic field

et al. 2019

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We have investigated the spatial distribution of the electron temperature generated in a twodimensional electron system (2DES) subjected to a perpendicular magnetic field. We measure thermoelectric voltages between Ohmic contacts located at the end of the voltage-probe arms of a Hall bar fabricated from a GaAs/AlGaAs 2DES wafer, immersed in the mixing chamber of a dilution refrigerator held at 20 mK. Magneto-oscillations due to the Landau quantization are examined for the thermoelectric voltages between the contact pairs straddling the main bar (arrangement to measure the transverse component V yx ), and between the pairs located along the same side of the main bar (arrangement for the longitudinal component V xx ). For the former arrangement, the oscillation amplitude diminishes with the distance from the heater. For the latter arrangement, the pair on one side exhibits much larger amplitude than the pair on the opposite side, and the relation becomes reversed by inverting the magnetic field. The behaviours of the oscillation amplitude are qualitatively explained by the spatial distribution of the electron temperature numerically calculated taking into consideration the thermal diffusion into the voltage contacts and the electron-phonon interaction. For both arrangements, the oscillations are shown to derive predominantly from the transverse (Nernst) component, S yx , of the thermopower tensor. The calculation also reveals that the voltage probes, introducing only minor disturbance at zero magnetic field, substantially reduce the temperature once a magnetic field is applied, and the thermoelectric voltages generated at the voltage arms account for a significant part of the measured voltages.

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Contactless measurement of alternating current conductance in quantum Hall structures

Drichko

Diakonov

Malysh

et al. 2014

Journal of Applied Physics

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We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods -acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized p-SiGe/Ge/SiGe heterostructure.

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Commensurability Oscillations in the Radio-Frequency Conductivity of Unidirectional Lateral Superlattices: Measurement of Anisotropic Conductivity by Coplanar Waveguide

Cited by 12 publications

References 45 publications

Diffusion Thermopower of Quantum Hall States Measured in Corbino Geometry

Diffusion Thermopower of Quantum Hall States Measured in Corbino Geometry

Spatial distribution of thermoelectric voltages in a Hall-bar shaped two-dimensional electron system under a magnetic field

Contactless measurement of alternating current conductance in quantum Hall structures

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