Hidden Crossover Phenomena in Strongly Pauli Limited Multiband Superconductors ---Application to CeCu${}_2$Si${}_2$

Abstract

Motivated by recent experiments on heavy fermion materials CeCu${}_2$Si${}_2$ and UBe${}_{13}$, we develop a framework to capture generic properties of multiband superconductors with strong Pauli paramagnetic effect (PPE). In contrast to the single band case, the upper critical field $H_{c2}$ can remain second order transition even for strong PPE cases. The expected first order transition is hidden inside $H_{c2}$ and becomes a crossover due to the interplay of multibandness. The present theory based on full self-consistent solutions of the microscopic Eilenberger theory explains several mysterious anomalies associated with the crossover and the "empty" vortex core state which is observed by recent STM experiment on CeCu${}_2$Si${}_2$.

5 pages, 4 figures + 3 pages, 1 figure (supplementary material), published version