EMA 2021 Abstracts

Plenary Speaker 1

Despina Louca, Virginia Tech, usa

Title: Electronic band tuning under pressure in MoTe2 topological semimetal

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.

Plenary Speaker 2

Haiyan Wang, Purdue University, USA

Title: Field induced mass transport phenomena in flash sintered high temperature ceramics and their unique properties

Abstract: Flash sintering has attracted significant attention lately as its remarkable rapid densification process at relatively low sintering temperature leads to the retention of fine grains and enhanced dielectric properties. While the underlying mechanism of flash sintering in various ceramics remains as an interesting topic for further exploration, recent efforts in exploring high density nanostructured defects and novel ductile behaviors in various high temperature ceramics, as well as the formation of nanostructures all demonstrate the enormous potential of this non-equilibrium process in ceramic processing. Several case studies including highly defective and ductile 3 mol% yttria-stabilized zirconia (YSZ), TiO2, ZnO, and SrTiO3, all processed by flash sintering, are presented. Defect structures revealed by TEM and STEM are correlated with the findings under high temperature in-situ micropillar compression studies inside a scanning electron microscope (SEM). The results suggest that the presence of high-density defects generated during flash sintering plays a major role in the overall microstructure and mechanical behavior of ceramics.