Magnetic response of microwave complex conductivities in antiferromagnetic insulating states of -(BEDT-TSF) ₂FeCl ₄

Abstract
Microwave conductivities and dielectric constants along the c axis at 44.5 GHz in a - d correlated metal -(BEDT-TSF) ₂FeCl ₄ have been measured by a cavity perturbation technique as a function of temperature and magnetic field. In the anomalous metallic states at 8.3 K(= T_MI) < T < 70 K(= T_FM), the microwave conductivity is much lower than the dc conductivity, while the dielectric constant is enhanced to the order of 10 ³, taking a broad maximum around 30 K. From the results of ¹H-NMR and recent X-ray diffraction measurements, it is expected that dielectric domains or stripes might emerge heterogeneously in the metallic background. Drastic changes have been observed in the microwave response below T_MI which shifts to lower temperatures by external magnetic fields. The anomalous metallic state is found to recover in the reentrant metallic states under magnetic fields higher than the critical field for the reentrant transition. Key words. Microwave - dielectric constant - complex conductivity - -(BEDT-TSF) ₂FeCl ₄.