Abstract
Topological superconductors (TSC) can host exotic quasiparticles such as Majorana fermions, poised as the fundamental qubits for 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, evidence for a new phase, we call Td* is observed and appears as the volume fraction of the Td phase decreases in the coexistence region. Td* is most likely centrosymmetric. 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.
Highlights
A Weylmetal is a new topological state of matter that hosts the condensed matter equivalent of relativistic Weyl fermions
A candidate topological Weyl semimetal is the quasi twodimensional transition metal dichalcogenide MoTe2.5–8 The transition to the non-trivial topologically protected crystal state occurs upon cooling from the high temperature 1T′ monoclinic phase to the low temperature orthorhombic Td phase
Analysis of the Berry curvature of the new nodes that appear in the Td phase from the band structure calculations performed at 0.15 GPa shown in Fig. 2 indicates that these new crossings are not trivial
Summary
A Weyl (semi)metal is a new topological state of matter that hosts the condensed matter equivalent of relativistic Weyl fermions. Weyl fermions exist as low-energy electronic excitations at Weyl nodes in three-dimensional momentum space, producing exotic physical properties such as unique surface Fermi arcs and negative magnetoresistance.[1,2,3,4] The topological Weyl state can be realized by breaking either time-reversal or lattice inversion symmetry. A candidate topological Weyl semimetal is the quasi twodimensional transition metal dichalcogenide MoTe2.5–8 The transition to the non-trivial topologically protected crystal state occurs upon cooling from the high temperature 1T′ monoclinic phase to the low temperature orthorhombic Td phase. Upon cooling to the non-centrosymmetric Td phase, Weyl quasiparticles are expected at characteristic electron and hole band crossings in momentum space The transition is driven by c-axis layer stacking order around 250 K.9–13 Upon cooling to the non-centrosymmetric Td phase, Weyl quasiparticles are expected at characteristic electron and hole band crossings in momentum space
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