Microwave Absorption in Low-Carrier Density and Strongly Correlated Electron Systems at Low Temperature under High Magnetic Field

We have studied the microwave response on the following systems.(1)organic conductors forming the quasi two-dimensional systems such as BEDT-TTF and BEDT-TSF salts。(2)Semiconductor superlattice。(3)Strongly correlated electron systems with low-carrier density.The microwave experiments with frequency 10-200 GHz have been performed at the temperature 0.5-300K under the magnetic field up to 10T.The research results are briefly summarized below.(A)We have measured the surface impedance in rare-earth intermetallic superconductor CeRu-D22锡D2。The complex conductivity has been determined as a function of temperature.There appears a remarkable coherence peak just below T y D2c锡D2.The penetration depth follows the BCS theory for strong coupling.Our microwave experiments confirm that CeRu I D22 I D 2 is a conventional BCS superconductor with s-wave symmetry.(B)Cyclotron resonance and electron spin resonance have been measured in low-carrier density system Yb I D 24 ii D 2 As I D 2.The cyclotron mass can be obtained as 0.7m I D20 I D2，which is consistent with the band structure calculations.(C)Cyclotron resonance ofα-(BEDT-TTF)I D22 ii D2 NX I D24 ii D2Hg(SCN)I D24 ii D2(X=H，D)indicates that the cyclotron mass ofπelectron is never changed by the deuteration.Reflecting the Kohn‘s theorem，the cyclotron mass is lighter than the mass obtained by SdH and dHvA effects.(D)In connection with the microwave，we have carried out the measurements of electrical resistivity，magnetic susceptibility，NMR and acoustic dHvA effect，etc。

We have studied the microwave response on the following systems. (1) organic conductors forming the quasi two-dimensional systems such as BEDT-TTF and BEDT-TSF salts. (2) Semiconductor superlattice. (3) Strongly correlated electron systems with low-carrier density. The microwave experiments with frequency 10〜200 GHz have been performed at the temperature 0.5〜300 K under the magnetic field up to 10 T. The research results are briefly summarized below.(A) We have measured the surface impedance in rare-earth intermetallic superconductor CeRuィイD22ィエD2. The complex conductivity has been determined as a function of temperature. There appears a remarkable coherence peak just below TィイD2cィエD2. The penetration depth follows the BCS theory for strong coupling. Our microwave experiments confirm that CeRuィイD22ィエD2 is a conventional BCS superconductor with s-wave symmetry.(B) Cyclotron resonance and electron spin resonance have been measured in low-carrier density system YbィイD24ィエD2AsィイD23ィエD2. The cyclotron mass can be obtained as 0.7mィイD20ィエD2, which is consistent with the band structure calculations.(C) Cyclotron resonance of α-(BEDT-TTF)ィイD22ィエD2NXィイD24ィエD2Hg(SCN)ィイD24ィエD2 (X=H,D) indicates that the cyclotron mass of πelectron is never changed by the deuteration. Reflecting the Kohn's theorem, the cyclotron mass is lighter than the mass obtained by SdH and dHvA effects.(D) In connection with the microwave, we have carried out the measurements of electrical resistivity, magnetic susceptibility, NMR and acoustic dHvA effect, etc.