Low temperature heat capacities of superconducting molybdenum carbides

Density functional theory study of phase stability, vibrational, and electronic properties of Mo3Al2C

“…1 optical modes with imaginary frequencies around Γ arise. The dynamical instability seems surprising considering the well-established crystal structure of Mo 3 Al 2 C. [1][2][3][4][5][6][7][8][9][10] One should, however, be aware that the actual carbon content is experimentally difficult to discern by X-ray diffraction because of carbons comparatively small Xray cross section 23 and therefore there exists some uncertainty with respect to carbon vacancies. In general, many carbides are prone to have vacancies on the C sublattice.…”

“…Mo 3 Al 2 C has been already synthesized in the 1960s 1 and subsequently classified as a superconductor. [2][3][4][5] Recently it has attracted renewed attention, [6][7][8][9][10] because its cubic β-Mn type crystal structure does not contain a center of inversion. In such noncentrosymmetric superconductors, as first discussed for CePt 3 Si, 11 the electron pairing process is described to be be a mixture of spinsinglet and spin-triplet states.…”

Distortion-induced scattering due to vacancies in NbC0.72

“…For instance, its superconducting transition temperature varies with composition. Although the precise reason for this relationship is not yet clear (Gigri, Szklarz, Storms, Bowman & Mattias, 1962;Toth, Wang & Yen, 1966;Toth & Zbasnik, 1968;Toth, Ichikawa & Chang, 1968), Bowman (1972) has suggested that vacancy ordering may play a role. The Fermi level shifts with C content, and the density of states changes shape (Klein, Papakonstantopoulos & Boyer, 1980).…”

Unconventional superconductivity in weakly correlated, non-centrosymmetric $\rm{Mo_3Al_2C}$

“…Carbides based on Mo comprise a large body of refractory compounds, where carbon atoms (in trigonal prismatic or octahedral Mo 6 C subunits) occupy a fraction of the interstitial sites either in an ordered or in a random manner. Among Mo-based carbides for which superconductivity (SC) was reported (αMoC at T c = 9.95 K, ηMoC at 7.57 K, Mo 2 BC at 6.33 K and Mo 3 Al 2 C at 9.05 K) the crystal structure of Mo 3 Al 2 C is outstanding, since the respective β-Mn type does not possess a center of inversion [1]. The missing inversion symmetry might initiate a mixture of spin-singlet and spin-triplet pairs in the SC condensate [2] as was recently proposed to explain SC in CePt 3 Si [3], UIr [4], CeRhSi 3 [5], and CeIrSi 3 [6].…”