Nodeless superconductivity in type-II Dirac semimetal PdTe2: low-temperature London penetration depth and symmetry analysis

TL;DR

This study investigates the superconducting gap structure of PdTe2, a type-II Dirac semimetal, revealing evidence for nodeless, fully gapped superconductivity with potential topological characteristics, through London penetration depth measurements and symmetry analysis.

Contribution

The paper provides the first detailed experimental and theoretical analysis indicating PdTe2 hosts nodeless superconductivity with possible topological states, narrowing down pairing symmetries to three candidates.

Findings

Superconducting gap in PdTe2 is fully gapped and consistent with s-wave symmetry.

Electrical resistivity shows low anisotropy and typical phonon scattering behavior.

Symmetry analysis limits possible pairing states to three nodeless candidates, including topologically non-trivial triplet states.

Abstract

Superconducting gap structure was probed in type-II Dirac semimetal PdTe$_2$ by measuring the London penetration depth using tunnel diode resonator technique. At low temperatures, the data for two samples are well described by weak coupling exponential fit yielding $\lambda(T=0)=230$~nm as the only fit parameter at a fixed $\Delta(0)/T_c\approx 1.76$, and the calculated superfluid density is consistent with a fully gapped superconducting state characterized by a single gap scale. Electrical resistivity measurements for in-plane and inter-plane current directions find very low and nearly temperature-independent normal- state anisotropy. The temperature dependence of resistivity is typical for conventional phonon scattering in metals. We compare these experimental results with expectations from a detailed theoretical symmetry analysis and reduce the number of possible superconducting pairing states in PdTe$_2$ to only three nodeless candidates: a regular, topologically trivial, $s$-wave pairing, and two distinct odd-parity triplet states that both can be topologically non-trivial depending on the microscopic interactions driving the superconducting instability.