Investigation of the Macro Coherence in Bilayer Quantum Hall State by Micro Wave

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We investigated interlayer coherence of the bilayer quantum Hall states. The microwave cryostat was constructed for measurement of Josephson plasmon and then the experiments were done at 2 K. The quantum Hall effects were clearly observed, but Josephson plasmon was not observed. The cause we cannot observe Josephson plasmon is due to the low quality of the sample and the higher temperature. We will soon improve the experimental way to detect Josephson plasmon. The other hand, we get important experimental results for interlayer coherence from transport.(1) : We study a pseudospin (layer degree of freedom) domain structure in bilayer v=1 quantum Hall states by detailed transport measurements in tilted magnetic fields. We find that the magnetoresistance R_<xx> shows a broad peak at the commensurate-incommensurate transition. An extrapolated value of R_<xx> at the peak down to 0 K is finite, showing the existence of a dissipative ground state. From the comparison of B_<//> dependence of R_<xx> and activation energy with theories, we suggest that the origin of the dissipation is pseudospin domain walls in the soliton lattice. This is the first observation in the quantum Hall state that a resistance peak is induced not by the crossing of two Landau levels, but possibly by a number of pseudospin domains, i.e., interlayer phase twists.(2) : We examine an anisotropic transport in a bilayer system around the quantum Hall state at the total Landau level filling factor v=1. We find that the anisotropy becomes remarkable at the phase transition point between the commensurate and incommensurate states. This results that a unidirectional state appears around the transition.