Investigating Majorana fermions with shot-noise STM

Jan Cuperus, j.p.cuperus@uu.nl
Sponsor: ERC, since September 2020
Supervisors: dr. Ingmar Swart, prof. dr. Daniël Vanmaekelbergh

Majorana zero modes, Shot-noise measurements, Scanning Tunneling Microscopy

In the field of condensed matter, there is a broad interest in topological materials. In such materials, certain electronic states are protected from local defects. This makes these states robust and possible candidates for next-gen electronic applications. Majorana bound states are an example of topological states. These states can be seen as a type of quasiparticle: Majorana fermions. Majorana fermions possess the exotic properties to (1) be their own antiparticle and (2) obey non-Abelian statistics. This last property may open the path towards topological quantum computing.

There are several publications reporting the observation of Majorana fermions in atomic chains that are in the proximity of a superconductor. However, none of these reports are conclusive; the observations could be explained by alternative reasonings. In my research, we hope to shed some light on the existence of Majorana particles by using two techniques: atom manipulation and shotnoise measurements.

Both these techniques will be combined within framework of scanning tunneling microscopy (STM). Using a STM, the surfaces of semi-, normal and superconductors can be investigated both physically and electronically. Moreover, the extreme resolution of the STM (sub-pm) can be used to alter the structure of a surface atom-by-atom. We would like to use that ability to create atomic structures (e.g. chains) in proximity to a superconductor. Subsequently, we would like to perform shot-noise spectroscopy measurements on these chains. Such measurements are predicted to be able to distinguish Majorana fermions from other, similar (quasi)particles. To be able to perform shot-noise measurements with atomic precision, requires the use of a specially designed MHz preamplifier[1], which will be installed in our new 300 mK STM.

Figure 1: a) 35 Xe atoms arranged one by one to form the letters IBM.[2] b) Atomic line defect in the surface of Fe(Te, Se) hosting the states shown in c). c) dI/dV mapping of the line defect showing the presence of what might be a pair of Majorana particles. [3]