Layer-dependent quantum cooperation of electron and hole states in the anomalous semimetal WTe2

Das, Pranab K.; Sante, Domenico Di; Vobornik, I.; Fujii, Jun; Okuda, Takashi; Bruyer, E.; Gyenis, András; Feldman, Benjamin E.; Tao, Jing; Ciancio, Regina; Rossi, G.; Ali, Mazhar N.; Picozzi, Silvia; Yadzani, A.; Panaccione, G.; Cava, R. J.

doi:10.1038/ncomms10847

Cited by 113 publications

(129 citation statements)

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“…Bulk WTe 2 exhibits a nonsaturated and extremely large magnetoresistance (MR) which could be used to design devices such as magnetic sensors [1]. It is believed that the peculiar magnetoresistance occurs due to the nearly equal electron and hole concentrations with high carrier mobility [1][2][3][4][5][6][7][8], and forbidden backscattering due to strong spin-orbit coupling also plays an important role [9]. Surprisingly, although WTe 2 is a layered material, the anisotropy of the effective mass is small [10], and quantum oscillations can be observed along three different crystal axes [3,11], which makes it essentially a three-dimensional (3D) instead of two-dimensional (2D) electronic system [12].…”

Section: Introductionmentioning

confidence: 99%

Thickness-dependent electronic structure in WTe2 thin films

Xiang

Srinivasan

et al. 2018

Phys. Rev. B

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X. (2018). Thickness-dependent electronic structure in WTe2 thin films. Physical Review B: Covering condensed matter and materials physics, 98 (3), 035115-1-035115-10. Thickness-dependent electronic structure in WTe2 thin films AbstractWe study the electronic structure of WTe2 thin films with different thicknesses. High-quality thin-film samples are obtained with carrier mobility up to 5000 cm2 V−1 s−1, which enables us to resolve the four main Fermi pockets from Shubnikov-de Haas (SdH) oscillations. Angle-resolved SdH oscillations show that the WTe2 thin films cross from three-dimensional to two-dimensional electronic systems at a thickness of ∼ 20 nm. Using the field effect, the nature of the Fermi pockets in thin-film WTe2 is identified, and the evolution of SdH oscillation frequencies is traced over different sample thicknesses. It is found that the frequencies dramatically decrease at a thickness of approximately 12 nm, which indicates the onset of finite-size effects on the band structure. Our work pins down two critical length scales of the thickness-dependent electronic structure in WTe2 thin films. Disciplines Engineering | Physical Sciences and Mathematics Publication DetailsXiang, F., Srinivasan, A., Du, Z. Z., Klochan, O., Dou, S., Hamilton, A. We study the electronic structure of WTe 2 thin films with different thicknesses. High-quality thin-film samples are obtained with carrier mobility up to 5000 cm 2 V −1 s −1 , which enables us to resolve the four main Fermi pockets from Shubnikov-de Haas (SdH) oscillations. Angle-resolved SdH oscillations show that the WTe 2 thin films cross from three-dimensional to two-dimensional electronic systems at a thickness of ∼ 20 nm. Using the field effect, the nature of the Fermi pockets in thin-film WTe 2 is identified, and the evolution of SdH oscillation frequencies is traced over different sample thicknesses. It is found that the frequencies dramatically decrease at a thickness of approximately 12 nm, which indicates the onset of finite-size effects on the band structure. Our work pins down two critical length scales of the thickness-dependent electronic structure in WTe 2 thin films.

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Section: Introductionmentioning

confidence: 99%

Thickness-dependent electronic structure in WTe2 thin films

Xiang

Srinivasan

et al. 2018

Phys. Rev. B

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“…k perpendicular (k z ) dispersion and cross-layer compensation of electrons and holes [11]. However, a direct inspection of the electronic properties by means of bulk sensitive soft-X-ray ARPES technique, and more accurate calculations are urgently needed in order to prove the three-dimensional (3D) character of the bulk electronic structure.…”

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Three-Dimensional Electronic Structure of the Type-II Weyl Semimetal WTe2

et al. 2017

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By combining bulk sensitive soft-X-ray angular-resolved photoemission spectroscopy and accurate first-principles calculations we explored the bulk electronic properties of WTe2, a candidate type-II Weyl semimetal featuring a large non-saturating magnetoresistance. Despite the layered geometry suggesting a two-dimensional electronic structure, we find a three-dimensional electronic dispersion. We report an evident band dispersion in the reciprocal direction perpendicular to the layers, implying that electrons can also travel coherently when crossing from one layer to the other. The measured Fermi surface is characterized by two well-separated electron and hole pockets at either side of the Γ point, differently from previous more surface sensitive ARPES experiments that additionally found a significant quasiparticle weight at the zone center. Moreover, we observe a significant sensitivity of the bulk electronic structure of WTe2 around the Fermi level to electronic correlations and renormalizations due to self-energy effects, previously neglected in first-principles descriptions.Introduction -The observation of unconventional transport properties in WTe 2 [1], such as the large non-saturating magnetoresistance with values among the highest ever reported, prompted experiments and theory to address the electronic structure of this semimetallic transition metal dichalcogenides (TMD) [2][3][4][5][6]. WTe 2 consists of layers of transition metal (TM) atoms sandwiched between two layers of chalcogen atoms, similarly to other TMDs such as MoS 2 and MoSe 2 . Because of the layered structure, TMDs have commonly been considered as quasi-two-dimensional solids. The easiness of exfoliation down to a single layer makes them appealing for nanoscale electronic applications. WTe 2 has also been theoretically described, in a recent paper, as the prototypical system to host a new topological state of matter called type-II Weyl semimetal [7]. At odds with standard type-I Weyl semimetals showing a point-like Fermi surface, type-II Weyl excitations arise at the contact between hole and electron pockets. Theoretical predictions were immediately followed by several surface sensitive angle-resolved photoemission (ARPES) studies claiming evidence of topological Fermi arcs [8][9][10].

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“…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].…”

mentioning

confidence: 99%

“…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].…”

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confidence: 99%

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

et al. 2016

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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...

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Layer-dependent quantum cooperation of electron and hole states in the anomalous semimetal WTe2

Cited by 113 publications

References 32 publications

Thickness-dependent electronic structure in WTe2 thin films

Thickness-dependent electronic structure in WTe2 thin films

Three-Dimensional Electronic Structure of the Type-II Weyl Semimetal WTe2

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

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