Electronic Phases in Low-Dimensional Electron Systems under Ultra-High Magnetic Fields

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The purpose of this work is to find and to clarify new electronic phases which appear in low-dimensional electron systems under ultra-high magnetic fields beyond 100T. In the present work, we have tried to measure electric conduction under pulsed ultra-high magnetic fields with the width of several us, which have been generated by the electromagnetic flux compression method or the single-turn-coil direct discharge method. In order to overcome the experimental difficulties of huge induced voltage, huge discharge noise, and sample heating due to eddy current, we have developed techniques for RF transport measurement and microfabrication of samples.1. Electron Correlation under Ultra-High Magnetic FieldsHigh-field magnetotransport measurements for graphite and bismuth have revealed that the posions of the Shubnikov-de Haas oscillations near the high-magnetic-field quantum limit deviate from those expected from low-field oscillations. This fact strongly suggests that the self energy correc … More tion due to electron correlation is enhanced at high-field quantum limit where the electron orbit becomes smaller than the electron distance.2. Bloch Electron Systems under Ultra-High Magnetic FieldsIn quasi-one-dimensional conductor NbSe_3 which shows double Peierls transitions, one small thin electron pocket remains at the low-temperature phase. We have found that the magnetoresistance monotonously decreases in the high-field quantum limit where all electrons lie in the lowest Landau level. This anomalous behavior reflects the Harper broadening of the lowest Landau level due to the magnetic breakdown across the CDW gap.3. Two-Dimensional Electron System under Ultra-High Magnetic FieldsIn order to investigate the high-field phases in quantum Hall systems, we have developed the techniques for RF transport measurement in quantum Hall systems whose impedance oscillates between zero and high resistance. We have fabricated the Corbino samples with special shape, and have succeeded to measure σ_<xx>Ck up to 100T. A structure corresponding to the 1/3 fractional Hall state was observed about at 80T. Less