Anticorrelation between polar lattice instability and superconductivity in the Weyl semimetal candidate MoTe2

The relation between the polar structural instability and superconductivity in a Weyl semimetal candidate
MoTe
2
has been clarified by finely controlled physical and chemical pressure. The physical pressure as well as the chemical pressure, i.e., the Se substitution for Te, enhances the superconducting transition temperature
T
c
at around the critical pressure where the polar structure transition disappears. From the heat capacity and thermopower measurements, we ascribe the significant enhancement of
T
c
at the critical pressure to a subtle modification of the phonon dispersion or the semimetallic band structure upon the polar-to-nonpolar transition. On the other hand, the physical pressure, which strongly reduces the interlayer distance, is more effective on the suppression of the polar structural transition and the enhancement of
T
c
as compared with the chemical pressure, which emphasizes the importance of the interlayer coupling on the structural and superconducting instability in
MoTe
2
.