Seminar 3 Transport through quantum point contacts

Abstract

The presence of bound spins in quantum point contacts (QPCs) near pinch-off has potentially profound effects on transport through quantum dots, with QPCs as leads. A QPC is a narrow constriction in a two-dimensional electron gas, where electrons are forced to flow through a quasi-1d section of the sample. Conductance through quantum point contacts, smoothly coupled to two dimensional leads, increases in the units of 2 e 2 / h . In addition, experiments on such point contacts have highlighted an anomalous conductance plateau at 0.7(2 e 2 / h ). The physics behind this phenomenon is explained in terms of the Kondo effect, resulting from the binding of an electron in the vicinity of the point contact. In particular, the leads may act as magnetic impurities and cause the apparent saturation of the dephasing time in transport through open semiconductor quantum dots at low temperatures.; hence, may complicate attempts to measure the spin of dot electrons. Experimental attempts to directly probe the binding of this state are currently underway.