Direct Observation of a Long-Range Field Effect from Gate Tuning of Nonlocal Conductivity

Abstract

We report the direct observation of a long-range field-effect in WTe2 devices, leading to large gateinduced changes of transport through crystals much thicker than the electrostatic screening length. The phenomenon -which manifests itself very differently from the conventional field-effect-originates from the non-local nature of transport in the devices that are thinner than the carrier mean free path. We reproduce theoretically the gate dependence of the measured classical and quantum magnetotransport, and show that the phenomenon is caused by the gate-tuning of the bulk carrier mobility by changing the scattering at the surface. Our results demonstrate experimentally the possibility to gate tune the electronic properties deep in the interior of conducting materials, avoiding limitations imposed by electrostatic screening.Conventional field-effect transistors (FETs) exploit electrostatic gating to tune the electronic properties of materials by means of charge accumulation [1][2][3][4][5]. Gateinduced charge accumulation occurs close to the material surface, on a depth limited by the so-called screening length, which is typically very short, ∼1-2 nm. Electrostatic screening, therefore, seems to preclude the possibility to use FET devices to control the electronic properties in the interior of materials, i.e., their bulk response. Although this is indeed the case in conventional field-effect devices, here we report the observation of a much longer-range field-effect, affecting electronic transport through a material over a depth orders of magnitude longer than the electrostatic screening length. The phenomenon, which occurs because the electrical conductivity is governed by non-local processes, manifests itself in large gate-induced changes in the transport properties of conductors as long as their thickness is smaller than or comparable to the carrier mean free path.We observe such a long-range field-effect in crystals of WTe 2 , a material possessing remarkable electronic properties [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Transport experiments have shown that bulk WTe 2 is a nearly perfectly compensated semi-metal exhibiting record-high magnetoresistance (MR) because of the high electron and hole mobility [6,9,22]. They have also shown that whenever the crystal thickness is reduced below the mean-free path (few hundreds nanometers or even longer), the carrier mobility is suppressed by scattering at the surface [22]. As established long ago, this implies that transport at the microscopic scale is governed by non-local processes, i.e. the relation between current density and electric field is non-local [26][27][28][29][30][31] [32]. It is well-known that in this non-local regime different physical phenomena exhibit an unusual behavior, as illustrated by so-called anomalous skin effect [33][34][35], i.e. the possibility for electromagnetic waves to penetrate into a conductor over a distance much larger than that predicted by the conventional theory. Although in the past it had...

Thickness-dependent electronic structure in WTe2 thin films

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A room-temperature ferroelectric semimetal

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Direct measurement of ferroelectric polarization in a tunable semimetal

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