Cyclotron resonance harmonics in the organic superconductor $β^{\prime\prime}$-(BEDT-TTF)$_2$SF$_5$CH$_2$CF$_2$SO$_3$; observation of a new kind of effective mass renormalization

Abstract

Cyclotron resonance, along with its second and third harmonics, has been observed in the quasi-two-dimensional organic superconductor $β^{\prime\prime}$-(BEDT-TTF)$_2$SF$_5$CH$_2$CF$_2$SO$_3$. The harmonic content is richly angle-dependent, and is interpreted in terms of the interlayer warping of the Fermi surface giving rise to the cyclotron resonance. In a departure from Kohn's theorem, but in agreement with recent theoretical predictions, the effective mass deduced from the cyclotron resonance measurements is greater than that determined from magnetic quantum oscillations.