Abstract
Low temperature ($\sim$ 20~K) electron irradiation with 2.5 MeV relativistic electrons was used to study the effect of controlled non-magnetic disorder on the normal and superconducting properties of the type-II Dirac semimetal PdTe$_2$. We report measurements of longitudinal and Hall resistivity, thermal conductivity and London penetration depth using tunnel-diode resonator technique for various irradiation doses. The normal state electrical resistivity follows Matthiessen rule with an increase of the residual resistivity at a rate of $\sim$0.77$ \mu \Omega$cm/$(\textrm{C}/\textrm{cm}^2)$. London penetration depth and thermal conductivity results show that the superconducting state remains fully gapped. The superconducting transition temperature is suppressed at a non-zero rate that is about sixteen times slower than described by the Abrikosov-Gor'kov dependence, applicable to magnetic impurity scattering in isotropic, single-band $s$-wave superconductors. To gain information about the gap structure and symmetry of the pairing state, we perform a detailed analysis of these experimental results based on insight from a generalized Anderson theorem for multi-band superconductors. This imposes quantitative constraints on the gap anisotropies for each of the possible pairing candidate states. We conclude that the most likely pairing candidate is an unconventional $A_{1g}^{+-}$ state. While we cannot exclude the conventional $A_{1g}^{++}$ and the triplet $A_{1u}$, we demonstrate that these states require additional assumptions about the orbital structure of the disorder potential to be consistent with our experimental results, e.g., a ratio of inter- to intra-band scattering for the singlet state significantly larger than one. Due to the generality of our theoretical framework, we think that it will also be useful for irradiation studies in other spin-orbit-coupled multi-orbital systems.
Highlights
The layered transition-metal dichalcogenide (TMD) superconductor PdTe2 [1,2] has received renewed interest recently after the discovery of type-II Dirac points in its bulk band structure [3]
We use the linear dependence of residual resistivity on dose with the slope of 0.77 μ cm/(C/cm2) for determination of resistivity in samples used in penetration depth studies; see Fig. 1(c)
We report on the impact of electron irradiation on the properties of the normal and superconducting state in PdTe2
Summary
The layered transition-metal dichalcogenide (TMD) superconductor PdTe2 [1,2] has received renewed interest recently after the discovery of type-II Dirac points in its bulk band structure [3]. Superconductivity was reported to be of type-I based on magnetization [7] and muon spin rotation [11] studies. This is consistent with an exp√erimentally observed Ginzburg ratio of κ = ξ /λ 0.52 < 1/ 2, when ξ and λ are directly extracted from critical field Hc(0) [7] and penetration depth [8] measurements, respectively
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