  Dynamics of vortices reflects the electronic states of quasiparticles in the
core. To understand this, we investigated the following three issues. (1) We
investigated the complex surface impedance, Zs, of YBa2Cu3Oy as a function of
magnetic field, H. The total features were well expressed by the Coffey-Clem
model. From the data, we estimated the viscosity and pinning frequency, which
were found to be independent of frequency. In particular, the obtained
viscosity definitely shows that the core of vortex of YBa2Cu3Oy is moderately
clean. This result suggests that new physics will show up, for the physics of
quantum moderately clean vortex core is unknown at all. (2) An anomaly found in
the surface reactance at the first order transition (FOT) of vortex lattice was
investigated in Bi2Sr2CaCu2Oy with various doping levels. As a result, the
anomaly was found only in the samples exhibiting the FOT. On the other hand, we
did not observe the anomaly in YBa2Cu3Oy. These suggest that the anomaly is due
to the change in the electronic states of the vortices characteristic of
materials with very strong anisotropy. (3) We measured H dependence of both the
thermal conductivity \kappa(H) and Zs(H) in exactly the same pieces of crystal.
We could not find any anomaly in Zs(H) even at the onset of the plateau. This
result suggests that the origin of the plateau in \kappa(H) is not a drastic
phase transition but is rather gradual crossover.
