Critical behaviour of thermopower and conductivity at the metal-insulator transition in high-mobility Si-MOSFETs

Fletcher, R.; Pudalov, V. M.; Radcliffe, A D B; Possanzini, C.

doi:10.1088/0268-1242/16/5/318

Cited by 31 publications

(29 citation statements)

References 53 publications

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“…Furthermore, the resistive coupling from the back gate to the channel and the small offset current from the nanovoltmeter will result in an offset voltage in OPefghi . This offset voltage, which is present even at zero heater current and is unrelated to the thermoelectric effect, as previously noted in other semiconducting channels such as Si MOSFETs, 33 could make Seebeck measurements further unreliable (for more details see Appendix C). When the device is in the ON state (the focus of this paper and where the Seebeck coefficient data presented below are measured), the channel resistance is small and as a result these spurious effects become rather small and insignificant.…”

Section: Measurementmentioning

confidence: 81%

“…33 As we get closer to the onset of the ON state, more parabolic behavior is observed in the open-circuit voltage (Figure 17c, blue curve) and finally it becomes completely parabolic once we are inside the ON regime of the FET (Figure 17c, red curve). Gate-dependent open-circuit voltage in the OFF state of the device for three different heater currents is shown in Figure 17d.…”

Section: C1 DC Measurementmentioning

confidence: 91%

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Gate-tunable and thickness-dependent electronic and thermoelectric transport in few-layer MoS2

Kayyalha

Maassen

Lundstrom

et al. 2016

Journal of Applied Physics

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Over the past few years, there has been a growing interest in layered transition metal dichalcogenides (TMD) such as molybdenum disulfide (MoS 2 ). Most studies so far have focused on the electronic and optoelectronic properties of single-layer MoS 2 , whose band structure features a direct bandgap, in sharp contrast to the indirect bandgap of thicker MoS 2 . In this paper, we present a systematic study of the thickness-dependent electrical and thermoelectric properties of few-layer MoS 2 . We observe that the electrical conductivity ( ) increases as we reduce the thickness of MoS 2 and peaks at about two layers, with six-time larger conductivity than our thickest sample (23-layer MoS 2 ). Using a back-gate voltage, we modulate the Fermi energy ( # ) of the sample where an increase in the Seebeck coefficient ( ) is observed with decreasing gate voltage ( # ) towards the subthreshold (OFF state) of the device, reaching as large as 500 µV/K in a four-layer MoS 2 .While previous reports have focused on a single-layer MoS 2 and measured Seebeck coefficient in the OFF state, which has vanishing electrical conductivity and thermoelectric power factor ( = / ), we show that MoS 2 -based devices in their ON state can have as large as > 50 12 345 6 in the two-layer sample. The increases with decreasing thickness then drops abruptly from double-layer to single-layer MoS 2 , a feature we suggest as due to a change in the energy dependence of the electron mean-free-path according to our theoretical calculation. Moreover, we show that care must be taken in thermoelectric measurements in the OFF state to avoid obtaining erroneously large Seebeck coefficients when the channel resistance is very high. Our study paves the way towards a more comprehensive examination of the thermoelectric performance of two-dimensional (2D)semiconductors.3

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Section: Measurementmentioning

confidence: 81%

Section: C1 DC Measurementmentioning

confidence: 91%

Gate-tunable and thickness-dependent electronic and thermoelectric transport in few-layer MoS2

Kayyalha

Maassen

Lundstrom

et al. 2016

Journal of Applied Physics

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“…On the insulating side the resistance resembles EfrosShklovskii hopping [4], which points towards the relevance of localized states and a soft gap in the density of states; also the thermopower has been interpreted in terms of an Anderson insulator [5]. From this point of view Anderson localization seems to be relevant for the transition.…”

Section: Introductionmentioning

confidence: 91%

Magnetoconductance of a two-dimensional metal in the presence of spin-orbit coupling

Schwab

Raimondi

2002

Eur. Phys. J. B

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We show that in the metallic phase of a two dimensional electron gas the spin-orbit coupling due to structure inversion asymmetry leads to a characteristic anisotropy in the magnetoconductance. Within the assumption that the metallic phase can be described by a Fermi liquid, we compute the conductivity in the presence of an in-plane magnetic field. Both the spin-orbit coupling and the Zeeman coupling with the magnetic field give rise to two spin subbands, in terms of which most of the transport properties can be discussed. The strongest conductivity anisotropy occurs for Zeeman energies of the order of the Fermi energy corresponding to the depopulation of the upper spin subband. The energy scale associated with the spin-orbit coupling controls the strength of the effect. More in particular, we find that the detailed behavior and the sign of the anisotropy depends on the underlying scattering mechanism. Assuming small angle scattering to be the dominant scattering mechanism our results agree with recent measurement on Si-MOSFET's in the vicinity of the metal-insulator transition.

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“…5 Several attempts to identify such a metal have been made with thermopower as a probe in the apparently metallic regime, notably in low-density 2D electron or hole systems 6,7 and highmobility Si MOSFETs. 8 While these studies indicate a definite change in the conduction mechanism and/or critical behavior in thermopower near the transition point between insulator and apparent metal, an unambiguous demonstration of a metallic state has never been achieved. Much of the uncertainty could be due to the very nature of the transition which has been suggested to be an inhomogeneity-driven, classical percolation transition 9,10 rather than an interaction-induced one.…”

Section: Introductionmentioning

confidence: 99%

Unconventional metallicity and giant thermopower in a strongly interacting two-dimensional electron system

et al. 2012

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We present thermal and electrical transport measurements of low-density (10 14 m −2 ), mesoscopic twodimensional electron systems (2DESs) in GaAs/AlGaAs heterostructures at sub-Kelvin temperatures. We find that even in the supposedly strongly localized regime, where the electrical resistivity of the system is two orders of magnitude greater than the quantum of resistance h/e 2 , the thermopower decreases linearly with temperature indicating metallicity. Remarkably, the magnitude of the thermopower exceeds the predicted value in noninteracting metallic 2DESs at similar carrier densities by over two orders of magnitude. Our results indicate a new quantum state and possibly a novel class of itinerant quasiparticles in dilute 2DESs at low temperatures where the Coulomb interaction plays a pivotal role.

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Critical behaviour of thermopower and conductivity at the metal-insulator transition in high-mobility Si-MOSFETs

Cited by 31 publications

References 53 publications

Gate-tunable and thickness-dependent electronic and thermoelectric transport in few-layer MoS2

Gate-tunable and thickness-dependent electronic and thermoelectric transport in few-layer MoS2

Magnetoconductance of a two-dimensional metal in the presence of spin-orbit coupling

Unconventional metallicity and giant thermopower in a strongly interacting two-dimensional electron system

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