Electronic properties of WTe2 and MoTe2 single crystals

Physical Review B

Physical review letters, 2014

The electronic structure basis of the extremely large magnetoresistance in layered nonmagnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at low temperatures, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. A change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior of the magnetoresistance in WTe2 was identified.

properties that make it attractive for a variety of electronic applications. Although WTe 2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We experimentally and theoretically investigate the structure, dynamics and electronic properties of WTe 2 , and verify that WTe 2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like transport. Our findings unambiguously confirm the metallic nature of WTe 2 , introduce new information about the Raman modes of Td-WTe 2 , and demonstrate that Td-WTe 2 is readily oxidized via environmental exposure. Finally, these findings confirm that, in its thermodynamically favored Td form, the utilization of WTe 2 in electronic device architectures such as field effect transistors may need to be reevaluated.

AIP Advances, 2018

We measure the electrical resistivity ρ of type-II Weyl semimetal WTe 2 using highquality single crystals for the current I along the a and b crystallographic directions in rotating magnetic fields in the plane perpendicular to the current direction. In zero field, ρ exhibits huge anisotropy and the ratio ρ b /ρ a develops with decreasing temperature approaching ∼30 at T = 0. A low-T power-law behavior of ρ∝T n with n = 2.7-2.9 may reflect the characteristic carrier scattering mechanism, probably associated with the strongly T-dependent mobilities, which lead to the sign change in the Hall resistivity. In the Kohler plot, the magnitude of the transverse magnetoresistance (MR) differs by more than two orders of magnitude depending on the Iand B-directions. It also shows clear deviation of MR from the B 2 dependence for all the configurations. No singular directions (magic angles) appear in the rotating B measurements.

2021

We combined the bond-order-length-strength (BOLS) and bond charge (BC) models and the topological concept to obtain the nonbonding, bonding, and antibonding states of the T-type WTe2/MoS2 heterostructure. We found that the electronic probability and electronic dispersion in the valence band of the WTe2/MoS2 heterostructure can be determined precisely based on electronic information entropy. The energy-band projection method and electronic information entropy are remarkable approaches for analyzing the electronic properties of various structures based on DFT calculations. This study provides a new way to describe the electronic properties of Ttype heterostructures and calculate the electron and bonding state probabilities.

Materials

Single crystals of Pb1−3x▯xNd2x(MoO4)1−3x(WO4)3x (PNMWO) with scheelite-type structure, where ▯ denotes cationic vacancies, have been successfully grown by the Czochralski method in air and under 1 MPa. This paper presents the results of structural, optical, magnetic and electrical, as well as the broadband dielectric spectroscopy measurements of PNMWO single crystals. Research has shown that replacing diamagnetic Pb2+ ions with paramagnetic Nd3+ ones, with a content not exceeding 0.01 and possessing a screened 4f-shell, revealed a significant effect of orbital diamagnetism and Van Vleck’s paramagnetism, n-type electrical conductivity with an activation energy of 0.7 eV in the intrinsic area, a strong increase of the power factor above room temperature for a crystal with x = 0.005, constant dielectric value (~30) and loss tangent (~0.01) up to room temperature. The Fermi energy (~0.04 eV) and the Fermi temperature (~500 K) determined from the diffusion component of thermopower showe...

APPLIED PHYSICS OF CONDENSED MATTER (APCOM 2019), 2019

Molybdenum dichalcogenides are probably the most studied single layer TMDCs by virtue of being appealing for sundry possible applications suchlike transistors, diodes, solar cells or more fundamental studies of spin or valley pseudospin and their interactions. Tungsten-based counterparts are on the other hand evincing much stronger spin-orbit coupling due to which all the spin-related effects are more stable at room temperature and thus more feasible for application. WTe 2 , a type-II Weyl semimetal is in particular interesting due to having two pairs of spin-differentiated Weyl points above Fermi energy. We have conducted several experiments following the evolution of the band dispersion in the vicinity of X and Y points of the Brillouin zone of WTe 2 which is substantial for understanding the fundamental properties of the structure-property relation of the system. Ab-initio set of photoemission calculations was performed using SPR-KKR package and compared to experimental results.

Solid State Ionics, 2005

Layer type tungsten mixed molybdenum sulphoselenide, Mo 0.5 W 0.5 S x Se 2Àx (0VxV2) starting from ternary Mo 0.5 W 0.5 Se 2 compound and by substituting selenium with sulphur ended with Mo 0.5 W 0.5 S 2 which is also a ternary compound, have been prepared and characterized. Xray diffraction studies showed that all the compounds possess 2H-MoS 2 structure with a small change in a-and c-parameters. X-ray line profile analysis has been used to calculate the microstructural defect parameters of all these compounds. It showed that sulphur and selenium rich compounds possess relatively small crystallite size (P), high r.m.s. strain (he 2 i) 1/2 and dislocation density (q dis). However, Mo 0.5 W 0.5 SSe has large P, low (he 2 i) 1/2 and (q). Fractional change in interlayer spacing and proportion of the planes affected by defects increased with increasing sulphur contents in Mo 0.5 W 0.5 Se 2 and it was maximum in case of Mo 0.5 W 0.5 S 2. Radial distribution function (RDF) analysis showed that interatomic distances, 2.80, 3.40 and 3.86 2 corresponds to metal-chalcogen, for intra and interlayer chalcogenbonding, respectively. The coupling constants corresponding to these and other higher pair of atoms have also been calculated. Room temperature thermoelectric power experiments temperature variation of conductivity confirmed their p-type semiconducting behaviour. Attempts have also been made to correlate the conductivity of these compounds with their size of the crystallites. The band gaps of these compounds are in the range of 1.20 eV for Mo 0.5 W 0.5 S 2 to 1.07 eV for Mo 0.5 W 0.5 Se 2 , respectively.

Physica Status Solidi (a), 1983

The electrical resistivity of the single crystal solid solutions Mo,W-,Se, (0 5 z l), grown by a direct vapour transport technique is studied in the temperature range from 300 to about 600 K. The room temperature values of resistivity are 1.43 Q cm for p-type 2H-WSe, and 2.36 0 cm for p-type 2H-MoSe2. The study reveals that the crystals are intrinsic semiconductors in the temperature range of investigation. I m Temperaturbereich von 300 bis ctwa 600 K wird der elektrische Widerstand von Einkristallen des Mischsystems Mo,W1-,Se2 (0 5 x 5 l), die mit einer direkten Dampftransporttechnik hergestellt werden, untersucht. Die Zimmertemperaturwerte des Widerstands betragen 1,43 0 cm fur p-leitendes 2H-WSe, und 2,36 0 cm fur p-leitendes 2H-MoSe,. Die Untersuchung zeigt, da13 die Kristalle Eigenhalbleiter im untersuchten Temperaturbereich sind.

Crystals

Owing to their low dielectric loss and high permittivity values, dielectric ceramics have garnered a lot of interest from the scientific and industrial sectors. These properties allow for their downsizing and use in a variety of electronic circuits. This present work focuses on the impact of the substitution of W6+ with Mo6+ on the structural and dielectric features of the crystalline phases in a similar TTB structure within the Ba0.54Na0.46Nb1.29W(0.37−x)MoxO5 system, with 0 ≤ x ≤ 0.33 mol%. These crystalline phases were elaborated using the conventional solid-state reaction method and analyzed with XRD, Raman, and dielectric techniques. The Rietveld refinement method showed that all these phases are characterized by tetragonal structure and the P4bm space group. The Raman spectra corresponded well to a TTB-like structure, and all the bands were assigned. The dielectric measurements of the prepared ceramic samples facilitated the determination of their phase transition temperature ...