KTH/Nordita/SU seminar in Theoretical Physics

Towards an understanding of transport through junctions in quantum-Hall systems

by Siddharta Lal (ASICTP Trieste)



Motivated by recent experimental findings (e.g., Roddaro et al., PRL 95, 156804 (2005)), we study transport in a simple phenomenological model of a quantum Hall edge system with a gate-voltage controlled constriction lowering the local filling factor. The current backscattered from the constriction is seen to arise from the matching of the properties of the edge-current excitations in the constriction ($\nu_{2}$) and bulk ($\nu_{1}$) regions. We develop a hydrodynamic theory for bosonic edge modes inspired by this model, finding that a competition between two tunneling process, related by a quasiparticle-quasihole symmetry, determines the fate of the low-bias transmission conductance. A novel generalisation of the Kane-Fisher quantum impurity model is found, describing transitions from a weak-coupling theory at partial transmission to strong-coupling theories for perfect transmission and reflection as well as a new symmetry dictated fixed point. These results provide satisfactory explanations for many recent puzzling experimental results at filling-factors of 1/3 and 1.