Toward combined transport and optical studies of the 0.7‐anomaly in a quantum point contact

Abstract

A quantum point contact (QPC) causes a one‐dimensional constriction on the spatial potential landscape of a two‐dimensional electron system. By tuning the voltage applied on the QPC gates which form the constriction at low temperatures the resulting regular step‐like electron conductance quantization can show an additional kink near pinch‐off around 0.7false(2e2/hfalse), called 0.7‐anomaly. In a recent publication, we presented a combination of theoretical calculations and transport measurements that lead to a detailed understanding of the microscopic origin of the 0.7‐anomaly. Functional renormalization group‐based calculations were performed exhibiting the 0.7‐anomaly even when no symmetry‐breaking external magnetic fields are involved. According to the calculations the electron spin susceptibility is enhanced within a QPC that is tuned in the region of the 0.7‐anomaly. Moderate externally applied magnetic fields impose a corresponding enhancement in the spin magnetization. In principle, it should be possible to map out this spin distribution optically by means of the Faraday rotation technique. Here we report the initial steps of an experimental project aimed at realizing such measurements. Simulations were performed for a heterostructure designed to combine transport and optical studies. Based on the simulation results a sample was built and its basic transport and optical properties were investigated.

The 0.7-Anomaly in Quantum Point Contact; Many-Body or Single-Electron Effect?

“…It is commonly believed that the anomaly is a many-body effect, and accordingly numerous explanations have been proposed [2,5,6,10,11]. Currently, Kondo-like effects are mostly invoked for those explanation [5,12,13].…”