Special Quantum Matter Seminar

Two-dimensional (2D) electron systems subjected to a strong magnetic field exhibit some of the most remarkable phenomena in physics. Among these are fractional quantum Hall states (FQHSs) at even-denominator Landau level filling factors (v), which are believed to host non-Abelian quasi-particles and be of potential use in topological quantum computing. These FQHSs, however, are scarce and have been observed predominantly in low-disorder 2D systems in the excited (N = 1) Landau level e.g., at v = 5/2. Here I will present our latest experimental results on magneto-transport measurements on new ultrahigh-quality 2D electron and hole systems confined to modulation-doped GaAs samples. These samples contain exceptionally low levels of disorder. They are among the purest solid-state materials, with the residual impurity concentration well below 1 part per 10 billion atoms, and exhibit low-temperature 2D carrier mobilities up to about 60x106 cm2/Vs. The samples reveal the emergence of new many-body phenomena, including numerous exotic even-denominator FQHSs in the lowest (N = 0) Landau level at v = ¾, 3/8, 3/10, ½, ¼, 1/6, and 1/8, thereby tremendously enriching the FQHS physics and expanding the potential reach of non-Abelian statistics. These states are evidently stabilized by Landau level mixing and a large charge layer thickness, which allow for a pairing between composite fermions and the emergence of FQHSs. In our wide GaAs quantum wells, we observe a FQHS at v = ½ with a transport energy gap of about 6 K, the highest gap reported for any even-denominator FQHS. These developments also highlight how progress in physics is intimately connected to our ability to grow high quality materials.

Based on work done in collaboration with Chengyu Wang, Adbhut Gupta, Pranav Thekke Madathil, Siddharth K. Singh, Casey Calhoun, Chia-Tse Tai, Yoon Jang (Edwin) Chung, Md. Shafayat Hossain, Meng K. Ma, Roland Winkler, Kirk Baldwin, and Loren Pfeiffer.