Evidence for topological behavior in superconducting CuxZrTe2−y

Abstract

We present structural, magnetic, electrical, thermal transport, Hall coefficient, and pressure-dependent resistivity measurements on $\mathrm{C}{\mathrm{u}}_{x}\mathrm{ZrT}{\mathrm{e}}_{2\ensuremath{-}y}$ compounds with $x=0.05$, 0.1, 0.15, 0.2, and 0.3, and $y$ varied between $0\ensuremath{\le}y\ensuremath{\le}0.8$. In order to calculate the ground state, ab initio calculations of the electronic structure of these materials were performed. Our results show that copper intercalation in $\mathrm{ZrT}{\mathrm{e}}_{2}$ induces superconductivity in the $\mathrm{ZrT}{\mathrm{e}}_{2}$ system. For the $\mathrm{C}{\mathrm{u}}_{0.3}\mathrm{ZrT}{\mathrm{e}}_{1.2}$ sample, Hall and Seebeck coefficient measurements show that the system is predominantly negatively charged with carrier density close to ${10}^{19}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$. The temperature dependence of the Hall coefficient, the Seebeck coefficient, and the lower critical field indicates that this material presents multiband character. Pressure-dependent resistivity vs temperature measurements reveal that while the normal-state resistivity decreases with increasing applied pressure, the superconducting transition temperature is completely insensitive to the applied pressure (for pressure in the range 0--1.3 GPa). This suggests that the Fermi gas is intrinsically degenerate under very high pressure, and therefore does not change much with varying external pressure. Finally the band structure calculation shows a dispersion curve containing a bulk three-dimensional Dirac conelike feature at the L point in the Brillouin zone, which is gapless in the absence of spin-orbit coupling, but develops a gap when this coupling is considered. Altogether, the results indicate that the superconducting compound $\mathrm{C}{\mathrm{u}}_{x}\mathrm{ZrT}{\mathrm{e}}_{2\ensuremath{-}y}$ presents a signature of multiband behavior and may possibly be a new example of a topological superconductor.