Negative thermal expansion of MgB$_{2}$ in the superconducting state and anomalous behavior of the bulk Grüneisen function
arXiv:cond-mat/0510515 · doi:10.1103/PhysRevB.72.220505
Abstract
The thermal expansion coefficient $α$ of MgB$_2$ is revealed to change from positive to negative on cooling through the superconducting transition temperature $T_c$. The Grüneisen function also becomes negative at $T_c$ followed by a dramatic increase to large positive values at low temperature. The results suggest anomalous coupling between superconducting electrons and low-energy phonons.
5 figures. submitted to Phys. Rev. Lett