Interaction and exotic phases in low dimensions

Doped semiconductor systems have been in the arena for a long time, helping us understand novel phenomena like Quantum Hall effect, Metal insulator transition, Weak localization, etc. Delta doping of elemental semiconductors like silicon and germanium with phosphorous atoms have led to the development of new class of two dimensional systems where the phosphorous atoms are confined to a one or few atomic planes. In these systems, the electronic transport occurs in the impurity band which is intrinsically half-filled.

Our investigation reveals extremely low noise in Si:P δ-layers, one of the lowest values ever reported for doped semiconductors. Phosphorous doped Si systems being one of the standard materials for the semiconductor industry, the observation of ultra-low noise characteristics is extremely important and desirable. Additionally, these devices offer the possibility of investigating the novel and exotic phenomena that arises when the Fermi level lies at or close to the centre of the band. The devices exhibit weak localization and universal conductance fluctuations (UCF), but there exists an anomalous suppression of UCF for devices with low doping densities caused by a spontaneous breakdown of time reversal symmetry.

These systems give us an unprecedented control over the on-site coulomb interactions (by varying the doping concentrations of Phosphorous) thereby enabling the study of interaction driven Metal insulator transition, and also opening the scope of studying other exotic phases such as spin liquids in a 2D system. In 2D, possibility of various forms of charge density wave ground states, including Wigner crystalline, striped or bubble phases, has attracted significant theoretical and experimental attention, even though a convincing detection of such phases with conventional transport experiments remains inconclusive. Our research is directed in investigating these possibilities.

Selected Publications:

  • S. Shamim et al., Physical Review B 83, 233304 (2011).
  • S. Shamim et al., Physical Review Letters112, 236602 (2014).