Z.F. Ezawa

PHASE TRANSITION IN THE NU = 2 BILAYER QUANTUM HALL STATE

The Hall-plateau width and the activation energy were measured in the bilayer quantum Hall state at filling factor \nu=2, 1 and 2/3, by changing the total electron density and the density ratio in the two quantum wells. Their behavior are remarkably different from one to another. The \nu=1 state is found stable over all measured range of the density difference, while the \nu=2/3

Chern-Simons gauge theory for double-layer electron system

state is stable only around the balanced point. The \nu=2 state, on the other hand, shows a phase transition between these two types of the states as the electron density is changed.

INTERLAYER COHERENCE IN UPSILON =1 AND UPSILON =2 BILAYER QUANTUM HALL STATES

We present a microscopic theory of the fractional quantum Hall effect at the filling factor ν with even denominator, which is recently observed in a double-layer electron system. In our approach electrons belonging to different layers are interpreted as different types of anyons with appropriate statistics. The wavefunction of the Hall state is calculated, which is found to coincide with that of Halperin. We also analyze vortex (quasihole) excitations. It is shown that a single vortex carries electric charges on both of the layers; for instance, a vortex at ν=½ has the electric charge on one layer and -⅛e on the other layer. The ground state at the vicinity of ν=½ is given by a Wigner crystal made of these vortices.

Quantum Hall ferromagnets

We have measured the Hall-plateau width and the activation energy of the bilayer quantum Hall (BLQH) states at the Landau-level filling factor

Spin-Pseudospin Coherence and C P-3 Skyrmions in Bilayer Quantum Hall Ferromagnets

\nu=1

Noncommutative geometry, extended W∞ algebra, and Grassmannian solitons in multicomponent quantum Hall systems

and 2 by tilting the sample and simultaneously changing the electron density in each quantum well. The phase transition between the commensurate and incommensurate states are confirmed at

Interlayer charge transfer in bilayer quantum Hall states at various filling factors

\nu =1

Chiral bosonization of superconformal ghosts on the Riemann surface and path-integral measure

and discovered at

Interlayer Exchange Interactions, SU(4) Soft Waves and Skyrmions in Bilayer Quantum Hall Ferromagnets

\nu =2

Simultaneous excitation of spins and pseudospins in the bilayer ν=1 quantum Hall state

. In particular, three different