Alladi Ramakrishnan Hall

Correlated states in ultra-high-quality two-dimensional electron systems

Pranav Thekke Madathil

Princeton University

Two-dimensional electron systems (2DESs) under a strong, perpendicular magnetic field exhibit a
plethora of correlated phenomena like the fractional quantum Hall (FQH) effect and Wigner
crystallization. Advancements in the quality of these 2DESs have led to the realization of fragile, exotic
states that show unique, topological characteristics. Recent developments in molecular-beam-epitaxy
have enabled the growth of ultra-high-quality GaAs/AlGaAs quantum wells, producing 2DESs with
mobilities exceeding 50 million ; a substantial enhancement in quality from the previous generation
high-mobility 2DESs by a factor of 2. More importantly, improvements in low-density-2DESs have
allowed us to probe the physics at very small Landau-level filling factors within achievable laboratory
magnetic fields. In this talk, I will focus on the new physics we see at these very low fillings. In particular,
we see new, fragile FQH phases at fillings where the magnetically induced Wigner crystal dominates.
These emerge as competing FQH states amidst the strong insulating background of the Wigner crystal.
Transport measurements in the Wigner crystal phase show evidence of the quantum nature, and is
consistent with the theoretically predicted correlated composite-fermion crystal. Additional non-linear I-
V and spectral noise measurements indicate the presence of several transport regimes, revealing a rich
dynamic phase diagram of driven Wigner crystals.