Zero-field Ambipolar Wigner Solids in the 2D Topological Insulator Cd₃As₂

Wigner crystals are predicted to form in a dilute and clean two-dimensional electron system (2DES) when Coulombic repulsion dominates the kinetic energy, causing the electrons to freeze into a lattice. In this talk, we present transport signatures of electron- and hole-like Wigner solids in thin films of the 2D topological insulator Cd₃As₂. Switching current-voltage (I-V) behavior is observed as the pinned solid is freed from the disorder potential by a finite bias. Hysteresis and voltage fluctuations in the I-V appear due to domain motion, which disappear simultaneously when the solid is depinned. Furthermore, the transport signatures disappear above a critical temperature as thermal fluctuations overcome the pinning potential. These Wigner solids are present at zero magnetic field and, surprisingly, are destroyed by a small field, in contrast to previous reports in other systems. We discuss their unconventional origin involving spatial inversion asymmetry and spin-orbit coupling.