Thermodynamic evidence for full-gap superconductivity in the dodecagonal quasicrystal Cu-doped Ta$_{1.6}$Te

TL;DR

This study provides thermodynamic evidence that Cu-doped Ta$_{1.6}$Te, a dodecagonal quasicrystal, exhibits a fully gapped superconducting state with unconventional pairing characteristics, distinct from traditional BCS superconductors.

Contribution

First thermodynamic demonstration of full-gap superconductivity in a quasicrystal, revealing unconventional pairing mechanisms in aperiodic systems.

Findings

Superconducting gap magnitude is smaller than BCS predictions.

Strong suppression of quasiparticle excitations observed.

Large upper critical field with pronounced anisotropy detected.

Abstract

We report the superconducting gap in the van der Waals layered quasicrystal Cu-doped Ta$_{1.6}$Te, using a fast relaxation technique that removes the large nuclear contribution of $^{181}$Ta. The initial-slope method enabled detection of the electronic specific heat down to 60~mK, revealing a fully gapped state with $\Delta(0)/k_{\rm B} = 1.43$~K. Both the gap magnitude and specific-heat jump are smaller than BCS predictions, while quasiparticle excitations are strongly suppressed, consistent with a theoretical expectation for aperiodic systems. AC-susceptibility measurements show a large upper critical field and pronounced anisotropy, reflecting the quasi-two-dimensional structure. These results provide the first thermodynamic evidence for a full-gap superconducting state in a quasicrystal and highlight unconventional pairing mechanisms beyond periodic lattices.