Specific heat, magnetic susceptibility, resistivity and thermal expansion of the superconductor ZrB12

摘要: In an attempt to clarify conflicting published data, we report new measurements of specific heat, resistivity, magnetic susceptibility, and thermal expansivity up room temperature for the 6 K superconductor ZrB12, using well-characterized single crystals with a residual resistivity ratio 9. The heat gives bulk result 20/ kBTc=3.7 superconducting gap ratio, excludes multiple gaps d-wave symmetry Cooper pairs. Sommerfeld constant n=0.34 mJ 2 gat 1 susceptibility =2.1 10 5 indicate low density states at Fermi level. Debye D is in range 1000‐1200 near zero temperature, but decreases by factor 2a t35 K. curves are inverted yield approximations phonon F spectral electron-phonon scattering function tr F, respectively. Both unveil 15 meV mode, attributed Zr vibrations oversized B cages, which rise coupling. further shows that this mode anharmonic, while vanishingly small discontinuity Tc establishes cell volume nearly optimal respect Tc.