Two-Dimensional Metal-Insulator Transition as a Percolation Transition in a High-Mobility Electron System

Sarma, S. Das; Lilly, Michael; Hwang, E. H.; Pfeiffer, L. N.; West, K. W.; Reno, John L.

doi:10.1103/physrevlett.94.136401

Cited by 115 publications

(145 citation statements)

References 33 publications

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“…The percolation transition also suggests an increasing transition density at the cross-over point with increasing impurity concentration [30][31][32] . In our MoS 2 samples, the transition density was in the range 10 12 -10 13 cm À 2 due to the presence of large amounts of impurities.…”

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

“…Below the threshold density n c , the 2D electron gas broke up into isolated puddles of carriers, with no conducting channels crossing the whole sample. The conductivity showed insulating behaviour and eventually vanished at T ¼ 0 K. In 2D systems, d is expected to be 4/3 and a cross-over point (Be 2 /h) above the percolation threshold density is suggested at finite temperatures 30,31 . Based on the percolation model, we fit our higher carrier densities, the conductivity would show a linear increase with gate voltages where the conductivity is mainly limited by the linearly screened charge impurity scattering 31 .…”

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

“…In the region where sufficient, large carrier densities are introduced, metal behaviour is observed 3 . Here we propose a percolation-type MIT in MoS 2 , driven by density inhomogeneity of electron states [28][29][30][31][32][33][34][35] that describes the systems in which charge carriers are transported through percolating conductive channels in the disorder landscapes due to the poor screening effect at low carrier densities. When carrier density is low enough, conductive paths are efficiently blocked and MIT occurs.…”

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

“…10 and Supplementary Note 7). To gain further insight into the transition behaviour, we applied the percolation model of conductivity 31,32,35 near the percolation threshold density n c , which is described by…”

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

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Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

et al. 2015

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The metal-insulator transition is one of the remarkable electrical properties of atomically thin molybdenum disulphide. Although the theory of electron-electron interactions has been used in modelling the metal-insulator transition in molybdenum disulphide, the underlying mechanism and detailed transition process still remain largely unexplored. Here we demonstrate that the vertical metal-insulator-semiconductor heterostructures built from atomically thin molybdenum disulphide are ideal capacitor structures for probing the electron states. The vertical configuration offers the added advantage of eliminating the influence of large impedance at the band tails and allows the observation of fully excited electron states near the surface of molybdenum disulphide over a wide excitation frequency and temperature range. By combining capacitance and transport measurements, we have observed a percolation-type metal-insulator transition, driven by density inhomogeneities of electron states, in monolayer and multilayer molybdenum disulphide. In addition, the valence band of thin molybdenum disulphide layers and their intrinsic properties are accessed.

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Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

Section: Mos 2 Vertical Heterostructural Capacitance Devicesmentioning

confidence: 99%

See 2 more Smart Citations

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

et al. 2015

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“…If the disorder is mainly long range, at low electron densities the system becomes increasingly inhomogeneous. Transport then behaves according to classical percolation law, masking possible interactions between electrons [13]. Hence, an experimental approach for investigating interaction effects in the presence of disorder should minimize the effects of longrange disorder and focus on short-range fluctuations.…”

mentioning

confidence: 99%

Low-Temperature Collapse of Electron Localization in Two Dimensions

et al. 2008

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We report direct experimental evidence that the insulating phase of a disordered, yet strongly interacting two-dimensional electron system becomes unstable at low temperatures. As the temperature decreases, a transition from insulating to metal-like transport behavior is observed, which persists even when the resistivity of the system greatly exceeds the quantum of resistivity h=e 2 . The results have been achieved by measuring transport on a mesoscopic length scale while systematically varying the strength of disorder. DOI: 10.1103/PhysRevLett.100.016805 PACS numbers: 73.21.ÿb, 73.20.Jc, 73.20.Qt Ever since the first two-dimensional electron systems (2DES) were realized, they have been used extensively to investigate various theories and concepts of charge localization [1]. The scaling theory of localization prohibits extended electronic states in two dimensions (2D) at absolute zero in the presence of disorder [2]. While there has been extensive theoretical work on the possibility of a delocalization caused by electron-electron interactions, e.g., [3][4][5][6][7][8][9], conclusive experimental evidence of such an effect has not been observed. On the contrary, the insulating phase in 2D at low temperatures has proven robust, in particular, in the case of strong localization, where the resistivity h=e 2 . For strong disorder, insulating variable-range hopping transport has been observed, with interaction effects leading only to a modification of the single-particle density of states [10]. In low but finite disorder an interaction driven localization mechanism has been suggested in the form of pinned charge-density waves [11,12]. However, no deviation from the insulating nature of transport has been reported in potential realizations of such phases, nor is it expected theoretically. The intermediate regime where disorder and interaction effects are equally important is very challenging to study theoretically and experimentally and is still not well understood. Our work represents an attempt to close this gap.A crucial property of disorder is the characteristic length scale of its potential fluctuations. If the disorder is mainly long range, at low electron densities the system becomes increasingly inhomogeneous. Transport then behaves according to classical percolation law, masking possible interactions between electrons [13]. Hence, an experimental approach for investigating interaction effects in the presence of disorder should minimize the effects of longrange disorder and focus on short-range fluctuations.In modulation doped GaAs=AlGaAs heterojunctions, the disorder mainly comes from the remote charged ions in the doping layer, and the strength of disorder depends strongly on the width of the undoped spacer layer between 2DES and the doping layer. The possibility of changing the strength of disorder by varying provides a powerful tool in the investigation of disorder effects. In theoretical treatment, an entirely random distribution of the dopants is generally assumed, giving a uniform spectral density of...

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Electrostatic Modulation of LaAlO₃/SrTiO₃ Interface Transport in an Electric Double‐Layer Transistor

Lin

Ding

et al. 2013

Adv Materials Inter

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The correlated charge, spin, orbital, and lattice degrees of freedom in transition metal oxides make them an attractive platform to explore rich physics and potential applications. [ 1,2 ] Oxide interfaces offer even more exciting opportunities due to the emerging effects such as broken inversion symmetry, interfacial exchange interaction, and spatial confi nement. [ 3,4 ] Heterostructures composed by non-magnetic band insulators LaAlO 3 (LAO) and SrTiO 3 (STO) have attracted much attention recently, and the unexpected conduction is often linked to the electronic reconstruction at the polar (LAO)-nonpolar (STO) heterointerface. [ 5,6 ] One defi ning feature of the interface conduction is the thickness dependence, i.e., it is insulating when the LAO thickness is below four unit cells (u.c.), whereas the conduction emerges above the critical thickness. [ 7 ] Furthermore, the carriers in the two-dimensional electron gas (2DEG) are confi ned within several nm near the interface as a result of broken symmetry, and the profi le of distribution has a sensitive dependence on the carrier density. [8][9][10][11][12][13] Based on the 2DEG at the LAO/ STO interface, nanoscale control of the insulator-to-metal transition using local probes has also been demonstrated. [ 14,15 ] The recent revelation of magnetism at the LAO/STO interface added another facet to the exciting physics. [16][17][18][19][20] Two notable sources were proposed for leading to the weak magnetism discovered in the LAO/STO heterostructures: One is the intrinsic electron reconstruction [ 16,21 ] and the other is the extrinsic oxygen vacancies. [ 22 ] In addition, the inhomogeneous distribution of magnetic dipoles as demonstrated in a recent scanning superconducting quantum interference device (SQUID) microscopy study clearly underscores the critical role of disorder in forging the magnetic landscape. [ 20 ] In spite of the efforts, [ 16,[18][19][20]23 ] the nature of magnetism discovered in samples prepared in a wide range of conditions remains as an issue of debate.To shed light on the physics of LAO/STO interface and to modulate its properties, electric fi eld effect was proven to be a powerful tool. [ 7,[24][25][26][27] In particular, an insulator-to-metal transition has been achieved by using electric fi eld gating at room temperature. [ 7 ] In these previous efforts, the STO substrates were used as the dielectric insulator in the back-gate confi guration, and high voltages of tens to hundreds of volts were required. Recently, ferroelectric Pb(Zr 0.2 Ti 0.8 )O 3 was used to bias the LAO/STO interface in a top-gate confi guration, and nonvolatile modulation of the 2DEG was demonstrated. [ 28 ] As a breakthrough in such electric fi eld effect studies, electric double-layer transistors (EDLTs) with the top-gate confi guration were employed to trigger the transformation of ground states in some key materials. [29][30][31] However, so far there has been no report on applying this powerful technique to exploring the transport properties of oxide interfaces.In...

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Two-Dimensional Metal-Insulator Transition as a Percolation Transition in a High-Mobility Electron System

Cited by 115 publications

References 33 publications

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

Low-Temperature Collapse of Electron Localization in Two Dimensions

Electrostatic Modulation of LaAlO₃/SrTiO₃ Interface Transport in an Electric Double‐Layer Transistor

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Two-Dimensional Metal-Insulator Transition as a Percolation Transition in a High-Mobility Electron System

Cited by 115 publications

References 33 publications

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures

Low-Temperature Collapse of Electron Localization in Two Dimensions

Electrostatic Modulation of LaAlO3/SrTiO3 Interface Transport in an Electric Double‐Layer Transistor

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Product

Resources

About

Electrostatic Modulation of LaAlO₃/SrTiO₃ Interface Transport in an Electric Double‐Layer Transistor