Diffusion Thermopower of Quantum Hall States Measured in Corbino Geometry

Abstract

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 ...

Thermoelectricity in Quantum Hall Corbino Structures

“…Between the conductance minima, the thermovoltage V tp now changes to a sawtoothlike behavior, still changing sign at both the maxima and the minima of the conductance. Such sign changes have not been observed in the earlier Hall-bar experiments but have already been seen in the previous rf-based Corbino experiments [15] and have been expected theoretically [8].…”

“…Early thermopower experiments in Corbino geometry have failed to observe the expected sign-changing behavior [14]. It has been reported, however, in other experimental works using the Corbino geometry [15]. The latter have used rf heating of the 2DES to produce the temperature gradient directly in the 2DES, claiming that no phonons are involved in the measured thermopower.…”

Magnetocapacitance oscillations and thermoelectric effect in a two-dimensional electron gas irradiated by microwaves

“…In contrast to the case of voltage modulation, the effect of microwaves on the charging current is strong and apparently not related to weak oscillations of the capacitance discussed above. The theory suggests that the result of our observation can be understood as the influence of microwaves on the magnetothermoelectric effect in Corbino geometry, when the thermopower or, more generally, the thermoinduced voltage, is inversely proportional to dissipative conductivity [28][29][30]. According to Eqs.…”

Conductance resonances and crossing of the edge channels in the quantum Hall ferromagnetic state of Cd(Mn)Te microstructures

“…farthest from the edge) channel 29,30 . Moreover, quantized resistance plateaus are not observed for Corbino samples, instead, the conductance drops to zero for integer filling factors 31 . Clearly, it is also observed for our device.…”