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

这项工作的目的是发现和澄清在超过100T的超高磁场下出现在低维电子系统中的新电子相。在本工作中，我们尝试测量了几μ m宽的脉冲超高磁场下的电导率，这两种磁场分别是用磁通量压缩法和单匝圈直接放电法产生的。为了克服巨大的感应电压、巨大的放电噪声和涡流引起的样品加热等实验困难，我们开发了射频输运测量和样品微加工技术。超高磁场下的电子相关石墨和铋的高磁场磁输运测量表明，在高磁场量子极限附近的舒布尼科夫-德哈斯振荡的位置偏离了低场振荡的预期位置。这一事实有力地表明，在高场量子极限下，当电子轨道小于电子距离时，由电子相关引起的自能正性增强。超高磁场下的布洛赫电子系统在呈现双佩尔斯跃迁的准一维导体NbSe_3中，低温相保留了一个小的薄电子袋。我们发现，在所有电子都处于最低朗道能级的高场量子极限下，磁电阻单调减小。这种异常行为反映了由于穿过CDW间隙的磁击穿而导致的最低朗道能级的哈珀加宽。为了研究量子霍尔系统中的高场相，我们开发了阻抗在零和高阻之间振荡的量子霍尔系统的射频输运测量技术。我们制作了具有特殊形状的Corbino样品，并成功地测量了σ_<xx>Ck至100T。在80T左右观察到1/3分数霍尔态对应的结构。少

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