Detecting bound spins using coupled quantum point contacts

Abstract

For many years now, there has been ongoing interest in the manifestations of many bodyphenomena in the conductance of strongly confined, one-dimensional (1D) electronsystems. One important aspect of this research has centered on the study of the so-called‘0.7 feature’ in the low-temperature conductance of 1D conductors known as quantumpoints (QPCs). There have been numerous reports in the literature suggesting that the0.7 feature should be related to some kind of spontaneous spin polarization inthe QPCs, which persists even at zero magnetic field. In this report, we reviewthe results of our recent work on this problem, in which we make use of coupledQPCs to probe the properties of transport very close to pinch off. We observe aresonant interaction between two QPCs whenever one of them pinches off, whichwe believe is associated with the binding of a single spin to the QPC that ispinching off. A phenomenological theoretical model is developed that relates theobserved resonance to a tunnel-induced correlation that arises from the interactionbetween a presumed bound spin on one QPC and conducting states in the other.Building on these ideas, we use this measurement technique to probe the microscopicproperties of the bound spin, finding it to be robustly confined and to show aZeeman splitting in a magnetic field. The spin binding occurs for stronger gateconfinement than the 0.7 feature, and we therefore suggest an alternative scenario forunderstanding the formation of this feature. In this, one considers the evolution of theself-consistent bound state as the gate potential is weakened from pinch off to allow forelectron transmission through the QPC. The suggestion of this work is that a QPCmay serve as a naturally formed single-spin system with electrical readout, afinding that may be useful for the development of future generations of single-spinelectronics.