Tuning magnetotransport in a compensated semimetal at the atomic scale

Abstract

Either in bulk form, or in atomically thin crystals, layered transition metal dichalcogenides continuously reveal new phenomena. The latest example is 1T'-WTe2, a semimetal found to exhibit the largest known magnetoresistance in the bulk, and predicted to become a topological insulator in strained monolayers. Here we show that reducing the thickness through exfoliation enables the electronic properties of WTe2 to be tuned, which allows us to identify the mechanisms responsible for the observed magnetotransport down to the atomic scale. The longitudinal resistance and the unconventional magnetic field dependence of the Hall resistance are reproduced quantitatively by a classical two-band model for crystals as thin as six monolayers, whereas a crossover to an Anderson insulator occurs for thinner crystals. Besides establishing the origin of the magnetoresistance of WTe2, our results represent a complete validation of the classical theory for two-band electron-hole transport, and indicate that atomically thin WTe2 layers remain gapless semimetals.

Observation of Optical and Electrical In-Plane Anisotropy in High-Mobility Few-Layer ZrTe5

“…Since then great efforts have been made towards expanding the spectrum of topological materials and bringing many conceptual materials into reality. Transition metal pentatellurides such as ZrTe5 and HfTe5 have been widely studied in bulk form since early 1980's due to their anomalous resistivity peak and X-ray diffraction intensity peak at low temperature 3,4 , large thermoelectric power 5 , pressure-induced superconductivity 6,7 , absence of a structural phase transition corresponding to resistivity anomaly 8 , and chiral magnetic effect 9 . In recent years, ZrTe5 research has been revived because of its non-trivial topological properties.…”

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

“…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].…”

“…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 been realized that gate-tuning of surface scattering could result in gate dependence of transport properties in systems -such as metals-in which no field-effect should be expected [36,37], no direct experimental demonstration of this phenomenon and of its long-range nature has been provided [38].Our devices consist of WTe 2 crystals with thickness ranging from 10 to 50 nm exfoliated onto a highly doped Silicon substrate covered with a 285 nm SiO 2 insulating layer [22]. The doped Silicon substrate can be used as a gate electrode, even though for most devices -and certainly in the 50 nm thick crystals-no significant gate-induced modulation of transport is a priori expected.…”

“…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].…”

“…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.…”