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Condensed Matter > Superconductivity

Title: Non-s-wave superconductivity in noncentrosymmetric ThCoC2: Ab initio calculations and Eliashberg formalism

Abstract: Superconductors without inversion symmetry in their crystal structure are known to exhibit unconventional properties. Recently, based on the measured temperature dependence of the magnetic field penetration depth, superconductivity in noncentrosymmetric ThCoC2 was proposed to be a nodal $d$-wave and mediated by the spin fluctuations. Moreover, a non-BCS behavior of the temperature dependence of the electronic specific heat and the magnetic upper critical field were reported. In this work, the electronic structure, phonons and electron-phonon coupling are studied in ThCoC2 on the basis of ab initio computations. The effect of the spin-orbit coupling on the electronic structure and electron-phonon interaction is analyzed, and large average splitting of the electronic band structure $\Delta E_{SOC} = 150$ meV is found. The thermodynamic properties of the superconducting state were determined numerically by solving Eliashberg equations, assuming the conventional $s$-wave pairing symmetry. The evaluated electron-phonon coupling constant $\lambda = 0.59$ remains in a decent agreement with the experimental estimates, showing that the electron-phonon interaction is strong enough to explain the observed $T_c \simeq 2.5$ K, however it requires an enhanced value of the Coulomb pseudopotential $\mu^*$. Calculated temperature dependence of the electronic specific heat and magnetic penetration depth deviate from the BCS model. Moreover, neither the BCS model nor the presented Eliashberg solutions can explain their experimentally observed temperature dependence, supporting the non-$s$-wave picture of superconductivity in ThCoC2. To resolve the pairing mechanism, we propose to measure the carbon isotope effect, as our calculations based on the electron-phonon coupling predict the observation of the isotope effect with an exponent $\alpha \simeq 0.15$.
Comments: 15 pages, 14 figures
Subjects: Superconductivity (cond-mat.supr-con)
Cite as: arXiv:2105.03472 [cond-mat.supr-con]
  (or arXiv:2105.03472v1 [cond-mat.supr-con] for this version)

Submission history

From: Bartlomiej Wiendlocha [view email]
[v1] Fri, 7 May 2021 19:08:42 GMT (1770kb,D)

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