DRAFT

Materials Science Research Lecture

Wednesday, November 16, 2022
4:00pm to 5:00pm
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Noyes 147 (J. Holmes Sturdivant Lecture Hall)
Exotic Magnetoresistive Materials
Despina Louca, Maxine S. and Jesse W. Beams Professor of Physics, University of Virginia,

NOTE! Every student or postdoc (any option!) will receive a $5 SmartCash "coffee credit" for each Materials Research lecture attended, in person or online. The credits will be tallied and issued after the last speaker of the term. *If you attend in person be sure to put your name on the sign-in sheet so you are counted.

Link to join Webinar: https://caltech.zoom.us/j/85010413991

Webinar ID 850 1041 3991

Abstract:

Topological superconductors (TSC) can host exotic quasiparticles such as Majorana fermions, poised as the fundamental qubits of quantum computers. TSC's are predicted to form a superconducting gap in the bulk, and gapless surface/edges states which can lead to the emergence of Majorana zero energy modes. A candidate TSC is the layered dichalcogenide MoTe2, a type-II Weyl (semi)metal in the non-centrosymmetric orthorhombic (Td) phase. It becomes superconducting upon cooling below 0.25 K, while under pressure, superconductivity extends well beyond the structural boundary between the orthorhombic and monoclinic (1T¢) phases. Here, we show that under pressure, coupled with the electronic band transition across the Td to 1T¢ phase boundary, a new phase we call Td* appears as the volume fraction of the Td phase decreases in the co-existence region. Td* is centrosymmetric with a four-layer unit cell and AABB layer stacking (and its twin, ABBA). In the region of space where Td* appears, Weyl nodes are destroyed. Td* disappears upon entering the monoclinic phase as a function of temperature or on approaching the suppression of the orthorhombic phase under pressure above 1 GPa. Our calculations in the orthorhombic phase under pressure show significant band tilting around the Weyl nodes that most likely changes the spin-orbital texture of the electron and hole pockets near the Fermi surface under pressure that may be linked to the observed suppression of magnetoresistance with pressure.

More about the Speaker:

Despina Louca is the Maxine and Jesse Beams Professor of Physics and chair of the department of Physics at the University of Virginia. Louca probes the atomic and magnetic structures and dynamics using scattering techniques performed at national and international neutron and X-ray facilities. She is a Fellow of the American Physical Society and the Neutron Scattering Society of America (NSSA). She was president of the NSSA from 2017-2021. Louca holds a Ph.D. from the University of Pennsylvania in Materials Physics, an A.M. in Physics and an A.B. in Physics and Biology from Bryn Mawr College. She was a postdoctoral fellow at Los Alamos National Laboratory in 1997, prior to joining the University of Virginia faculty in 1999.

For more information, please contact Jennifer Blankenship by email at jennifer@caltech.edu.