Cyclotron resonance in the layered perovskite superconductor Sr2RuO4

We report a detailed study of the magnetic-field-orientation dependence of the millimetre-wave magnetoconductivity of the superconductor Sr2RuO4. We find two harmonic series of cyclotron resonances. We assign the first, corresponding to a quasiparticle mass of 4.29±0.05 me, where me is the free-electron mass, to the β Fermi-surface section. We assign the second series, which contains only odd harmonics, to cyclotron resonance of the γ Fermi-surface section, yielding a quasiparticle mass of 12.35±0.20 me. A third, single cyclotron resonance, corresponding to a quasiparticle mass of 5.60±0.03 me, is attributed to the α Fermi-surface section. In addition, we find a very strong absorption mode in the presence of a magnetic field component parallel to the quasi-two-dimensional planes of the sample. Its dependence on the orientation of the magnetic field cannot be described in the context of conventional cyclotron resonance, and the origin of this mode is not yet clear. Finally, magnetic quantum oscillations due the α and β Fermi-surface sections are observed in the millimetre-wave magnetoconductivity of Sr2RuO4, and a detailed study of their magnetic-field-orientation dependence is presented. (author)