Condensed Matter Seminars


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Thursday, March 26, 2020
11:00 AM
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"Investigation of the structural phase transitions in Weyl semimetal (Mo, W)Te2"

Yu Tao , University of Virginia - Department of Physics
[Host: Despina Louca]

Mo1-xWxTe2 belongs to the family of layered transition metal dichalcogenides (TMD) that are of intense interest recently because of their fascinating topological properties. The end members of this series, MoTe2 and WTe2 are Weyl semimetals upon cooling to the orthorhombic Td phase. Mo1-xWxTe2 undergoes a structural phase transition from a high-temperature monoclinic 1T' phase, to a non-centrosymmetric orthorhombic Td phase at low temperatures through a first-order structural phase transition. Both 1T' and Td phases are comprised of weakly-bound layers, and differ mainly by shifts of the layers along the c-axis. Despite much research, the structural properties of Mo1-xWxTe2 have not been thoroughly investigated. Neutron scattering experiments at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory were carried out on single crystals of Mo1-xWxTe2. Structural changes including changes in interlayer disorder were observed by focusing on the elastic scattering along (2, 0, L) on cooling and warming through the hysteresis loop at the transition. A Td* phase was discovered for the first time across the Td-1T’ phase boundary in Mo1-xWxTe2 with x up to ~0.2. In WTe2, a sharp transition from Td to 1T′ was observed at ambient pressure in the single crystal near ∼565 K, the transition proceeds without hysteresis. These results should clarify in microscopic detail the nature of these phase transitions.

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