Length dependence of the fractional conductance anomaly in constricted conducting channels

Abstract

In addition to the integer conductance quantization in units of Go (=2e(2) 1h), a quantum point contact (QPC) often reveals a fractional conductance plateau, especially at 0.7G(0), which is called the 0.7 anomaly. The one-dimensionality of the constriction (or QPC) has been debated as to whether or not it is a key element in the appearance of the anomaly. In this study, we specifically focused on the length dependence of the conductance anomaly in QPC's for a nominally identical width of nano-constrictions. The anomaly was shown to be more likely caused by the Kondo effect in a carrier-confining region formed inside a short QPC with its length comparable to its width while spontaneous spin polarization along with the opening of a spin gap better explains the anomalous conductance behavior in a longer QPC.