Correlating the crystal structure and electronic ground state of type-II Weyl semimetal MoTe$_2$: structural measurements*

The reported pressure dependent superconductivity of the type-II Weyl semimetal MoTe$_2$ has led to speculation about the possibility of a topologically non-trivial superconducting state in this material. A key question about the topology of this superconducting state is the evolution of the crystal structure of MoTe$_2$ at pressures and temperatures relevant for superconductivity, as the non-centrosymmetric T$_d$ orthorhombic phase is needed for the Weyl state. Semimetallic MoTe$_2$ has two metastable polymorphs, with a first order structural transition between the centrosymmetric monoclinic 1T’ and the orthorhombic T$_d$ structure near 270 K. This structural transition has a demonstrated pressure dependence, with a suppression of the T$_d$ phase at increased pressures. We have grown single crystals of MoTe$_2$, and using a combination of elastic neutron scattering, magnetotransport, and spectroscopic techniques we have investigated the nature of this transition. We report pressure and temperature dependent neutron scattering measurements which elucidate the nature of this phase transition at temperature and pressures relevant for the previously reported superconductivity.