We are studying the charge dynamics of electrons in a solid via measuring the electrical conductivity in a wide frequency range. From these measurements of electrons' response to time- and spacial-dependent electric fields, we can analyze the dynamical conductivity (dynamical dielectricity) dependent on temperature and/or magnetic field and then can clarify fundamental properties of electrons such as dynamical relaxational phenomena and low-lying excitations near a Fermi level.
Our techniques covering the frequency range from dc up to Tera Hertz are;
1. Low-frequency range (0.01 Hz - 200 kHz) --- phase-sensitive detection using a capacitance bridge, with four (or three) terminals
2. Radio-wave range (300 kHz - 2 GHz) --- reflection measurements of electromagnetic fields with a network analyzer, with two terminals
3. Microwave range (10 GHz - 50 GHz) --- cavity-perturbation technique for measuring the center frequency and the width of standing waves in a cavity, without any terminals
4. Terawave (sub-millimeter waves) range (0.1 THz - 4 THz) --- TDTS (Time-Domain Terahertz Spectroscopy) for simultaneously measuring both the amplitude and phase of transmitted waves.
5. Infrared range (200-8000 cm-1) --- FT-IR spectrometer equipped with Cassegrain microscope.
These different techniques having characteristic features are used for each research subject. To note, any samples can be cooled down to helium temperature independent of the techniques 1-5, and particularly, in 1 and 3, down to 0.4 K under magnetic fields up to 14 T.
So far we have been involved mainly in studying low-dimensional molecular conductors. With TDTS recently installed, we are extensively measuring the optical conductivity for superconducting films. (There we take a very high-speed, semi-continuous snapshots of the photon-induced breakdown of Copper pairs and the low-lying quasiparticles. Those pictures include the interaction spectral density, a most fundamental information of superconductivity. )
Measurement of low frequency physical property
Microwave and millimeter-wave measurement
Ratlling phonon in type-I clathrate compounds
Dynamics of confined water and proton conductions in water nanotube
Physical properties of confined water in manganese oxide and octosilicate
Hydration and dynamics of metallic ion doped DNA
Sendai 980-8578, Japan