Alexei Chepelianskii : Fun with Landau levels (or New and old puzzles in Landau flatland)

Abstract

While Landau levels, which are responsible for the integer and fractional quantum Hall effects in two-dimensional electron systems, have been extensively studied, new mysteries continue to emerge in ultra–high-quality materials and in older systems driven far from equilibrium. In this talk, we will review experimental efforts within the Meso group aimed at shedding light on longstanding and newly discovered puzzles.

In traditional GaAs/GaAlAs quantum wells, a new generation of molecular beam epitaxy developed by Loren Pfeiffer now makes it possible to observe stripe order, an exotic quantum Hall state competing with the fractional quantum Hall effect, at significantly lower magnetic fields. This enabled us, in collaboration with the University of Minnesota, to investigate the magnetic-field anisotropy of stripe phases and to uncover evidence for an intrinsic magnetic-field anisotropy. These results parallel an emergent ferromagnetic-like order arising from Landau quantization and electron–electron interactions.

Exfoliated two-dimensional electron systems are vibrant platform, offering the possibility to engineer new quantum states in moiré superlattices. We will show that the moiré potential created by an unusual member of the 2D materials family, lead iodide (PbI₂), can host ballistic channels that persist across transitions between integer quantum Hall plateaus. This enables dissipationless transport even at the transition between neighbour integer quantum Hall states, a phenomenon we refer to as a Chern junction.

Finally, photo-excited Landau levels give rise to exotic non-equilibrium states even in canonical systems such as electrons on helium. We will discuss the challenges of disentangling local and non-local effects in ultraclean electron systems where magnetoplasmons propagate everywhere accross the sample, and consider whether these exotic states are stabilized by bulk excitations, edge excitations, or a combination of both.