Low-temperature specific heat of κ-(BEDT-TTF)2Cu[N(CN)2]Br in the superconducting state

The low-temperature specific heat of single crystals of κ-(BEDT-TTF${)}_2$ Cu[N(CN${)}_2$ ]Br was studied in the temperature range between 0.11 and 4.5 K. The electronic specific heat, ${\mathrm{C}}_{\mathrm{el}}$, in the superconducting state shows a quadratic temperature dependence that is most reasonably attributed to the quasiparticle excitations found in unconventional superconductors with line nodes in the gap structure. The magnetic-field dependence of the temperature-linear term in ${\mathrm{C}}_{\mathrm{el}}$ is also consistent with this picture of superconductivity.