Fermi surface reconstruction in the magnetic-field-induced superconductorκ−(BETS)2FeBr4

Abstract

Shubnikov-de Haas (SdH) and angular dependent magnetoresistance oscillations (AMROs) are measured in the organic superconductor with magnetic anions, $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}\mathrm{Fe}{\mathrm{Br}}_{4}$. In the paramagnetic phase $({\ensuremath{\mu}}_{0}H>{\ensuremath{\mu}}_{0}{H}_{c}=5.5\phantom{\rule{0.3em}{0ex}}\mathrm{T})$, the AMROs and the SdH oscillations are clearly observed, which are basically consistent with the band structure calculation. In the canted antiferromagnetic phase $(H<{H}_{c})$, a low frequency SdH oscillation is observed. The observation of the oscillation is not interpreted by the simple FS reconstruction due to the long range order of the Fe $3d$ spins and implies that the strong correlation between the $\ensuremath{\pi}$ and $d$ electrons modifies the reconstruction. No sign of the enhancement of the critical quantum fluctuation at ${H}_{c}$ is observed in the SdH oscillations, the reason of which is also discussed.