CPM Seminar

Topological superconductivity and Majorana Fermions at semiconductor/superconductor interfaces

Jay Sau

JQI & Condensed Matter Theory Center
University of Maryland

Majorana Fermions are hitherto unobserved exotic Fermionic excitations, which are their own anti-particles. Recently there has been a lot of excitement over the possibility of realizing Majorana Fermions for the first time as quasi-particle excitations in solid state systems. In the solid state these excitations also provide a way to realize degeneracies of the ground state of macroscopic quantum system which may be used as a topologically protected qubit. For over a decade the only candidate systems for observing such excitations were the non-abelian v=5/2 Fractional Quantum Hall state and chiral p-wave superconductors. More recently, motivated by developments in the area of Topological insulators, it was realized that a more general class of topological superconductors, some of which may be as simple as the interface InAs and Al in the appropriate parameter regime might have exotic topological properties and Majorana Fermions. In this talk, we will review the properties of Majorana Fermions in superconductors starting from BCS theory. Following this I will discuss our recent work on showing the existence of Majorana Fermions both at the cores of vortices of semiconductor/superconductor interfaces such as InAs/Al and also at the ends of semiconductor nanowires placed on superconductors. Through an explicit tunneling current calculating using non-equilibrium Green functions, we will show that the Majorana Fermions at the end of a nanowire appear as a zero-bias peak in the STM spetrum in the topological phase. Such a peak will disappear once the magnetic field is reduced to push the system into the non-topological phase strengthening the evidence that the peak is associated with a phase transition. I will also discuss a recent proposal to observe a fractional Josephson effect which may be a smoking gun signature of a Majorana Fermion.