Point-contact spectroscopic study of Weyl semimetals MoTe₂ and WTe₂

The Andreev-reflection (AR) double-minimum structure was observed in dV/dI curves of “hard” MoTe₂/Ag point contacts (PCs) with enhanced. T_c up to 5 K. The extracted superconducting (SC) gap Δ has a BCS-like dependence with 2Δ/k_BT_c =3.7+/-0.4 averaged over 9 PCs. Remarkably, the observation of a single zero-bias minimum in dV/dI of “soft” PCs (i.e. using silver paint instead of Ag wire) may indicate a topological “gapless-like” SC state of the MoTe₂ surface, since “soft” contacts probe mainly the interface and avoid pressure effect. The Yanson point-contact (PC) electron-phonon interaction (EPI) spectra of MoTe₂ demonstrate only a broad maximum around 18 meV. Contrary, dV/dI curves of WTe₂ PCs show tiny SC features if at all, but display an EPI structure with maxima at 8 and 16 meV. Thus, Yanson PC spectra demonstrate the presence of solely phononic excitations for both MoTe₂ and WTe₂, while AR spectra show a “gapless-like” SC state only in MoTe₂ (at least above 2.5K). Interestingly. For both compounds a broad maximum in dV/dI at large voltages (>100mV) was observed indicating some phase transition. The latter might be induced by the high current density in the PC and/or local heating, thus enabling the manipulation of the quantum electronic states at the interface in the PC core.