COMPOSITION AND PRESSURE DEPENDENT STUDY ON WEYL SEMIMETAL Mo1-xWxTe2

In this work, the doping and pressure effects on the Weyl semimetal Mo1−xWxTe2 have been investigated. A series of single crystals of Mo1−xWxTe2 for x = 0, 0.10, 0.30, 0.40, 0.50, 0.70, 0.75, 0.90, and 1 were synthesized using the self-flux method (for parent compounds MoTe2 and WTe2) and the chemical vapor transport method (for doped compounds). The single crystals were then characterized by energy- dispersive X-ray spectroscopy and X-ray diffraction (XRD). Temperature-dependent resistivity measurements at ambient pressure show metallic behavior for all dop- ing levels. Transverse magnetoresistance (MR) measurements show that the parent compounds exhibit large non-saturating MR, which might result from electron-hole compensation, whereas the doped compounds have low MR values, indicating doping- induced electron-hole asymmetry. Doping-dependent resistivity measurements up to 650 K at ambient pressure reveal that the structural transition temperature (Ts) increases linearly with increasing W content in Mo1−xWxTe2. The observed Ts of MoTe2 at ambient pressure is 249 K and that of WTe2 is 613 K. Temperature- dependent synchrotron XRD measurements further confirm the structural transition in WTe2 at ambient pressure. Pressure was found to continuously suppress the Ts in Mo0.90W0.10Te2, Mo0.60W0.40Te2, and Mo0.25W0.75Te2, and superconductivity emerges in Mo0.90W0.10Te2 and Mo0.60W0.40Te2 above 1.25 K when Ts is suppressed to a lower temperature. Magnetotransport measurements of Mo0.50W0.50Te2 under pressure re- veal that, at a critical pressure of 0.9 GPa, the transverse MR is suppressed, the Hall coefficient changes sign, and superconductivity emerges, suggesting a significant reconstruction of the Fermi surface. The superconducting transition temperature (Tc) continuously increases with increasing pressure above 0.9 GPa up to 14.3 GPa. With further increasing pressure above 14.3 GPa, the Tc remains constant and then begins to decrease monotonically at 17.5 GPa.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Physics

Grantor

University of Houston

Year dc:date.issued

2020

Author dc:creator

• Dahal, Rabin

Advisor dc:contributor.advisor

• Chu, Paul C. W.

Committee members dc:contributor.committeemember

• Ren, Zhifeng
• Chen, Shuo
• Hosur, Pavan
• Bao, Jiming

• Wel Semimetal, Superconductivity, Structural Transition, High Pressure

Statement dc:rights

• The author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/10657/8024

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/8024