New details in the superconducting phase diagram of $\lambda\text{-(BETS)}_2\text{GaCl}_4$: further evidence of a FFLO phase

New low-noise rf penetration depth measurements of the high-field superconducting state in the quasi-2d organic superconductor $\lambda\text{-(BETS)}_2\text{GaCl}_4$ are presented and compared to previous measurements of the same material\footnote{Coniglio, \emph{et al.}, Phys. Rev. B \textbf{83}, 224507 (2011)}$^,$\footnote{Mielke, \emph{et al.}, J. Phys.: Condens. Matter {\bf 13} (2001)}. The new data show very clear indication of a phase transition within the superconducting state, with the position of the $H_\text{P}$ phase line significantly lower than in less clean samples, while the $H_\text{c2}$ phase line is unchanged. Shubnikov-de Haas oscillations, previously never seen below 32 T in this material$^2$, are observed at fields as low as 13 T, indicating that there is less scattering in these new samples. $H_\text{c2}$ is usually sensitive to spin-orbit scattering, suggesting that the unchanged upper critical field is not traditional, but rather the destruction of a FFLO state. In contrast, $H_\text{P}$ should still be sensitive to changes of the spin-orbit scattering rate, consistent with the new data.