Strong electron-phonon coupling in the rare-earth carbide superconductorLa2C3

Abstract

We present the results of a crystal structure determination using neutron powder diffraction as well as the superconducting properties of the rare-earth sesquicarbide La2C3 (Tc ≈ 13.4 K) by means of specific heat and upper critical field measurements. From the detailed analysis of the specific heat and a comparison with ab-initio electronic structure calculations, a quantitative estimate of the electron-phonon coupling strength and the logarithmic average phonon frequency is made. The electron-phonon coupling constant is determined to λ ph ∼ 1.35. The electron-phonon coupling to low energy phonon modes is found to be the leading mechanism for the superconductivity. Our results suggest that La2C3 is in the strong coupling regime, and the relevant phonon modes are Larelated rather than C-C stretching modes. The upper critical field shows a clear enhancement with respect to the Werthamer-Helfand-Hohenberg prediction, consistent with strong electron-phonon coupling. Possible effects on the superconducting properties due to the non-centrosymmetry of the crystal structure are discussed.

Evidence for persistent spin fluctuations in uranium sesquicarbide

“…For UC, we obtain γ ∼ 21 mJ mol −1 U K −2 and D ∼ 262 K. U 2 C 3 has therefore a Sommerfeld coefficient twice as large as UC and four times larger than La 2 C 3 . 40 Such a relatively high γ value suggests a high density of electronic states at the Fermi energy, in agreement with x-ray photoemission spectra 41 and first-principles calculations. 22 As shown in the inset of Fig.…”

Superconducting Gap Structure of the Cage Compound Sc5Rh6Sn18

“…At low temperatures, H c2 (T ) can be fitted by the Ginzburg-Landau (GL) equation [9,10]: H c2 (T ) = H c2 (0)(1 − t 2 )/(1 + t 2 ). Fitting our data to this expression yields µ 0 H c2 (0) = 7.24 T. We consider that the enhancement of H c2 (T ) over the WHH model is due to the strong electron-phonon coupling [14].…”

Superconducting State of the Binary Boride Ru7B3 with the Noncentrosymmetric Crystal Structure

“…The low-field susceptibility displays a strong diamagnetic signal due to a superconducting transition temperature with T onset c ¼ 2:8 K. We confirmed that the polycrystalline sample shows T onset c ¼ 3:3 K, being slightly higher than that of the single-crystal sample. What causes the difference in T c might depend on the lack of Boron from the stoichiometry such as Ln 2 C 3À (Ln = Y, La) [14][15][16][17] or NbB 2À . [18][19][20][21][22] The fractional contraction of the lattice constants for the single crystals also supports the scenario.…”