Quantum Oscillations, Thermoelectric Coefficients, and the Fermi Surface of SemimetallicWTe2

Abstract

We present a study of angle-resolved quantum oscillations of electric and thermoelectric transport coefficients in semi-metallic WTe2, which has the particularity of displaying a large B 2 magnetoresistance. The Fermi surface consists of two pairs of electron-like and hole-like pockets of equal volumes in a "Russian doll" structure. Carrier density, Fermi energy, mobility and the mean-freepath of the system are quantified. An additional frequency is observed above a threshold field and attributed to magnetic breakdown across two orbits. In contrast to all other dilute metals, the Nernst signal remains linear in magnetic field even in the high-field (ωcτ ≫ 1) regime. Surprisingly, none of the pockets extend across the c-axis of the first Brillouin zone, making the system a three-dimensional metal with moderate anisotropy in Fermi velocity yet a large anisotropy in mean-free-path. 2 ) was reported with no sign of saturation up to 60 T[6]. This is the expected behavior of a perfectly-compensated semi-metal [7], but has not been seen in bismuth [8] or graphite [9], two compensated semi-metals whose Fermi surface is accurately known. A first step towards uncovering the ultimate reason behind the quadratic magnetoresistance of WTe 2 is a quantitative determination of the structure of the Fermi surface and the components of the mobility tensor.In this letter, we report on a study of quantum oscillations of resistivity, Seebeck and Nernst coefficients in high-quality single crystals of WTe 2 and find that the Fermi surface consists of two pairs of electron-like and hole-like pockets. Each pair is concentric with identical structure like a set of Russian dolls. The anisotropy is much smaller than one would naively expect in a layered system. The longer axis of the pockets is much shorter than the height of the Brillouin zone, in contrast to the theoretical expectations. Moreover, we find another distinctive feature of this semi-metal in addition to quadratic magnetoresistance, which is a Nernst response linear in magnetic field deep inside the high-field limit. Our results quantify carrier concentration of the system and set plausible quantitative windows for mobilities and Fermi energies leading to the huge quadratic magnetoresistance and large field-linear Nernst signal.

Anomalous magnetotransport properties of high-quality single crystals of Weyl semimetal WTe2: Sign change of Hall resistivity

“…One such example is WTe2, which shows extremely large non-saturating magnetoresistance suggesting the compensation of electrons and holes [6]. Fourier transform spectra of Shubnikov-de Haas oscillations show that WTe2 has four Fermi pockets, i.e., two sets of concentric electron-and hole-Fermi pockets [7][8][9][10], being consistent with band structure calculations [7]. Unsaturated magnetoresistance even in 60 T suggests that electron and hole carrier densities are highly compensated [6].…”

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

“…[11,26]) as well as laser excited ARPES [16] is the lack of any evident spectral intensity at the zone center Γ. Nevertheless, the observation of small frequency quantum oscillations suggests the presence of tiny electron pockets at both side of, and almost touching at, the Γ point [5,16]. Our measured Fermi surface reports no clear evidence of these type of structures up to a binding energy larger than ∼ 100 meV from the Fermi level (see Fig.…”

“…It is equally mandatory that the carrier mobility does not depend on the applied magnetic field, a feature met by WTe 2 [1] but not for example by pure bismuth [15]. The bulk electronic structure of WTe 2 has been so far only investigated by means of transport measurements [5,6]. The behavior of the resistivity under an external magnetic field is hard to reconcile with the picture of a layered solid: when the magnetic field is applied parallel to the layers, unexpected quantum oscillations were observed, suggesting that electrons may travel in a coherent way also across the weakly bonded layers [6].…”

“…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 .…”

“…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 .…”