Topological materials and Majorana Fermions

The exotic edge states in topological materials have an even broader appeal in the superconducting case owing to their Majorana fermion character. Zero-energy Majorana bound states (MBS) are particularly interesting due to their non-Abelian braiding properties, which are potentially relevant for topological quantum computation. It has been known for years that MBS excitations may appear in many condensed matter systems (such as e. g. exotic quantum Hall states and superconductors), but the real breakthrough came with proposals to engineer topological superconductors based on conventional s-wave superconductors coupled to a topological insulator, or a semiconductor with strong spin-orbit coupling. The possibility of obtaining topological superconductivity using these realistic materials spurred a race towards detecting Majorana fermions in solid state devices.

In fact, recent experiments have reported measurements in InSb nanowires coupled to superconductors that show signatures, an emergent zero bias anomaly (ZBA) in the electrical conductance as a magnetic field is increased, consistent with MBS. Similar ZBA features have been also reported in subsequent experiments. However, alternative physical explanations, ranging from Kondo physics to non-trivial magnetic dependence of Andreev levels, cannot be ruled out in most of these experiments. Thus the field is in need of ”smoking gun” experiments beyond this first ZBA generation.

Selected publications

Mapping the topological phase diagram of multiband semiconductors with supercurrents
Pablo San-Jose, Elsa Prada, Ramón Aguado (PRL, in press)
Physical Review Letters 112, 137001 (2014), arXiv:1309.2239

Transport spectroscopy of NS nanowire junctions with Majorana fermions
Elsa Prada, Pablo San-Jose, and Ramón Aguado
Phys. Rev. B 86, 180503(R)
Zero-Bias Anomaly in a Nanowire Quantum Dot Coupled to Superconductors
Eduardo J. H. Lee, Xiaocheng Jiang, Ramón Aguado, Georgios Katsaros, Charles M. Lieber, and Silvano De Franceschi
Phys. Rev. Lett. 109, 186802

Magnetic-field instability of Majorana modes in multiband semiconductor wires
Jong Soo Lim, Llorenç Serra, Rosa López, and Ramón Aguado
Phys. Rev. B 86, 121103(R)

ac Josephson Effect in Finite-Length Nanowire Junctions with Majorana Modes
Pablo San-Jose, Elsa Prada, and Ramón Aguado
Phys. Rev. Lett. 108, 257001