The use of ultra-low temperature cooling and of high hydrostatic pressure techniques has significantly expanded our understanding of the two-dimensional electron gas confined to GaAs/AlGaAs structures. This chapter reviews a selected set of experiments employing these specialized techniques in the study of the fractional quantum Hall states and of the charged ordered phases, such as the reentrant integer quantum Hall states and the quantum Hall nematic. Topics discussed include a successful cooling technique used, novel odd denominator fractional quantum Hall states, new transport results on even denominator fractional quantum Hall states and on reentrant integer quantum Hall states, and phase transitions observed in half-filled Landau levels.
Quantum-Hall to Insulator Transition in Ultra-low-carrier-density Topological Insulator Films and a Hidden Phase of the Zeroth Landau Level
在磁场作用下的拓扑表面态的一个关键特征是在零能量处存在第零朗道能级。尽管如此，探测第零朗道能级一直具有挑战性，因为大的电子空穴水坑涂抹了它的能量景观。在这里，通过开发超低载流子密度的拓扑绝缘体Sb $_2$ Te $_3$薄膜，我们能够达到一个极端的量子极限的拓扑表面状态，并揭示了一个隐藏的相位在零朗道水平。首先，我们发现了一个意想不到的量子霍尔到绝缘体的转变附近的零朗道水平。然后，通过详细的标度分析，我们发现这种量子霍尔到绝缘体的转变属于一个新的普适类，这意味着这里发现的绝缘相具有与非拓扑系统中的绝缘相根本不同的起源。
Exploring the apparent violation of the Mott relation in a noncentrosymmetric kagome ferromagnet
Virginia Tech（弗吉尼亚理工大学）；Virginia Tech National Security Institute（弗吉尼亚国家安全研究所）；Virginia Tech Center for Quantum Information Science and Engineering（弗吉尼亚量子信息科学与工程中心）；University of Virginia（弗吉尼亚大学）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；University of California, Davis（加州大学戴维斯分校）
