Towards the identification of a quantum critical line in the (p, B) phase diagram of CeCoIn5

The low-temperature thermal expansion of CeCoIn5 single crystals measured parallel and perpendicular to magnetic fields B oriented along the c axis yields the volume thermal-expansion coefficient $\beta$. Considerable deviations of $\beta (T)$ from Fermi-liquid behavior occur already within the superconducting region of the (B, T) phase diagram and become maximal at the upper critical field $B_{c2}^0$. However, $\beta (T)$ and the Gr"uneisen parameter $\mathrm{\Gamma }$ are incompatible with a quantum critical point (QCP) at $B_{c2}^0$, but allow for a QCP shielded by superconductivity and extending to negative pressures for $B<B_{c2}^0$. Together with literature data we construct a tentative (p, B, T) phase diagram of CeCoIn5 suggesting a quantum critical line in the (p, B) plane.