Topological Superconductivity and Majorana Fermions

Topological superconductivity denotes a class of superconducting states distinguished by non-trivial topology of their bulk wavefunctions and the emergence of protected boundary modes. In such systems, electron pairing acquires an effective p-wave character, giving rise to zero-energy quasiparticles that are their own antiparticles—so-called Majorana fermions. These exotic excitations obey non-Abelian exchange statistics, making them prime candidates for fault-tolerant quantum computation. Realisations span one-dimensional models such as the Kitaev chain, semiconductor–superconductor nanowires, magnetic atom chains on superconducting substrates, planar Josephson junctions and vortices in unconventional superconductors. Central challenges include unambiguous detection of zero-energy modes, materials optimisation to suppress disorder and quasiparticle poisoning, and the demonstration of coherent braiding operations. Advances in materials growth, device fabrication and spectroscopic techniques have together propelled the field from theoretical proposals to concrete experimental platforms, laying the groundwork for topologically protected quantum devices.

Research from Nature Portfolio

Recent studies have engineered a minimal Kitaev chain by coupling two spin-polarised quantum dots in an InSb nanowire through finely tuned elastic co-tunnelling and crossed Andreev reflection. At the optimal tuning point, transport measurements reveal pairwise correlations, zero net charge transfer and robustness against local perturbations, consistent with emergent Majorana end states. Foundational work on Josephson junctions formed with topological insulator surface states has demonstrated a 4π-periodic contribution to the supercurrent under radio-frequency irradiation, signalling the presence of gapless Andreev bound-state doublets protected by topology. Complementary experiments in epitaxial semiconductor–superconductor heterostructures have achieved atomically pristine interfaces, a hard proximity-induced superconducting gap and quantized conductance doubling through a gate-defined quantum point contact, offering a scalable platform for topological superconducting channels.

Topological Superconductivity and Majorana Fermions publication trend

The graph below shows the total number of articles in topological superconductivity and majorana fermions across all publications each year (not limited to Nature Index journals).

Technical terms

Topological superconductor: A superconducting phase characterised by non-trivial topology of bulk states, supporting protected boundary excitations.

Majorana fermion: A zero-energy quasiparticle equal to its own antiparticle, emerging at defects or ends of topological superconductors.

Kitaev chain: A theoretical one-dimensional model of spinless p-wave superconductivity that hosts unpaired Majorana modes at its termini.

Andreev reflection: A process at a normal–superconductor interface whereby an incident electron is retroreflected as a hole, enabling Cooper-pair formation.

Zero-bias conductance peak: A pronounced feature at zero voltage in tunnelling spectroscopy, indicative of a zero-energy state.

Non-Abelian anyon: A quasiparticle whose exchange operations do not commute, allowing for topological quantum gate implementations.

Shiba band: A subgap band formed by overlapping impurity-induced bound states (Shiba states) in a magnetic atom chain on a superconductor.

References

1. Realization of a minimal Kitaev chain in coupled quantum dots. Nature (2023).
2. 4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions. Nature Communications (2016).
3. Quantized conductance doubling and hard gap in a two-dimensional semiconductor–superconductor heterostructure. Nature Communications (2016).
4. Probing atomic structure and Majorana wavefunctions in mono-atomic Fe chains on superconducting Pb surface. npj Quantum Information (2016).
5. Robust and Clean Majorana Zero Mode in the Vortex Core of High-Temperature Superconductor (Li0.84Fe0.16)OHFeSe. Physical Review X (2018).
6. Topological Superconductivity in a Planar Josephson Junction. Physical Review X (2017).