Experimental determination of the Andreev reflection probability using ballistic point contact spectroscopy

In this article, we present an experimental technique to determine the Andreev reflection probability—a quantity of central importance for superconductor/semiconductor-hybride structures. This is achieved with a point contact (PC) formed in a two-dimensional electron gas (2DEG) in front of a superconductor/semiconductor (SN) interface. The PC in the InGaAs/InP heterostructure emits electrons towards the SN interface and detects the reflected carriers. Due to the specific sample setup, the vast majority of the detected carriers are retroreflected holes and the signal is a direct measurement of the Andreev reflection probability. A(E) is found to be up to 20% by measuring the point contact conductance. The experimental results are compared with the predictions of two theoretical models. It is found that the Andreev reflection probability significantly differs from theoretical expectations. The main advantage of the presented technique is the direct way of measuring the Andreev reflection probability, independent of any model describing the SN interface.