A. Sawada

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

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

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.

Doubly Enhanced Skyrmions in ν = 2 Bilayer Quantum Hall States

We have studied bilayer quantum Hall (QH) effects in double-quantum-well structures at various Landau-level (LL) filling factors ν. The stability of various QH states are examined by varying the density balance between the two layers. We observe a remarkable ν-dependent behavior; the interlayer charge transfer is allowed for particular values of ν, which then repeat in a characteristic sequence with a period of 4. We employ a pseudospin picture, by which the interlayer charge transfer is expressed as a rotation of the total pseudospin. The ability or inability to accommodate the charge transfer represents the degree of pseudospin polarization in the bilayer QH state.

Anomalous stability of ν = 1 bilayer quantum Hall state

Skyrmion excitations were measured and compared for the first time in the bilayer quantum Hall (QH) state at the Landau-level filling factor ν=2 and in the monolayer QH state at ν=1. The observed number of flipped spins, N spin , is 14 in the bilayer sample with a large tunnelling gap, and N spin =7 in the bilayer sample with a small tunnelling gap, while it is N spin =7 in the monolayer sample. The difference is interpreted to be due to the interlayer exchange interaction.By tilting the samples in the magnetic field, we measured and compared the Skyrmion excitations in the bilayer quantum Hall (QH) state at the Landau-level filling factor

Crystal electric field and quadrupole ordering in semiconducting PrPtBi

\nu =2

de Haas-van Alphen Effect and Fermi Surface of USb

and in the monolayer QH state at

De Haas-van Alphen effect in CoS2

\nu =1

Interlayer quantum coherence and anomalous stability of ν=1 bilayer quantum Hall state

. The observed number of flipped spins is

Interlayer coherent phenomena in bilayer quantum Hall systems

N_s=14

Bilayer ν=2 quantum Hall state in parallel high magnetic field

in the bilayer system with a large tunneling gap, and