The relation between the polar structural instability and superconductivityin a Weyl semimetal candidate MoTe2 has been clarified by finely controlledphysical and chemical pressure. The physical pressure as well as the chemicalpressure, i.e., the Se substitution for Te, enhances the superconductingtransition temperature Tc at around the critical pressure where the polarstructure transition disappears. From the heat capacity and thermopowermeasurements, we ascribe the significant enhancement of Tc at the criticalpressure to a subtle modification of the phonon dispersion or the semimetallicband structure upon the polar-to-nonpolar transition. On the other hand, thephysical pressure, which strongly reduces the interlayer distance, is moreeffective on the suppression of the polar structural transition and theenhancement of Tc as compared with the chemical pressure, which emphasizes theimportance of the interlayer coupling on the structural and superconductinginstability in MoTe2.
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