Multiband Superconductivity and Charge Density Wave in HfxZr1-xTe3 single crystals
We report on the bulk multiband superconductivity and charge density wave (CDW) in HfxZr1-xTe3 single crystals. The parent compound ZrTe3 is a layered van der Waals material that undergoes a CDW transition near 63 K and exhibits only filamentary superconductivity below 2.0 K. Upon the introduction of a small amount of Hf (x = 0.02), the CDW transition temperature is reduced to TCDW ~ 53 K, while a robust bulk superconducting state emerges at Tc ~ 3.3 K, underscoring a subtle competition between CDW order and superconductivity in this quasi-one-dimensional system. Electrical resistivity, magnetic susceptibility, Hall effect, Seebeck coefficient, and specific heat measurements consistently confirm the bulk nature of the superconducting phase. The temperature dependence of the upper critical field Hc2(T) deviates markedly from single-band behavior, and it is well described by a two-band model, consistent with multiband superconductivity. Analysis of the Hall effect, and thermoelectric behavior reveal pronounced electronic anisotropy, with enhanced effective carrier masses, indicating that the subtle structural modification introduced by Hf substitutions affects the Fermi surface topology, as well as electronic correlations. Measurements of electrical resistivity in hydrostatic pressures up to ~ 2 GPa reveal that pressure drives TCDW to higher temperatures while suppressing Tc. These findings show that Hf doping can be used to fine-tune the balance between the CDW instability and superconductivity, possibly by means of chemical pressure effects, stabilizing a multiband superconducting state in Hf-doped ZrTe3.