Prof. Arindam Ghosh : Broken symmetry states in high-performance atomically-patterned nanostructures in silicon and germanium

Recent advances in the material engineering have led to vertically confined doping of phosphorus (P) atoms inside bulk crystalline silicon and germanium, forming a new class of two-dimensional electron system. In this talk I shall present some of our recent experiments on quantum transport and noise in two-dimensionally P-doped Si and Ge over a wide range of dopant density, thereby tuning the on-site Coulomb interaction and hopping energy scales independently. We find that low-frequency flicker noise in these systems is exceptionally low when compared with different genre of low-dimensional materials, which is attributed to the physical embedding of the conduction electrons inside the crystalline semiconductor matrix. In addition, we observed a remarkable spontaneous time-reversal symmetry breaking when dopant density is reduced which is manifested in the suppression of both weak localization corrections and the universal conductance fluctuations. While the microscopic origin of this spontaneous time reversal symmetry breaking remains unknown, we believe this indicates a new many-body electronic phase in two-dimensionally doped silicon and germanium with a half-filled impurity band.