Blog entry

Majorana states in graphene

By José Luis Lado, INL

The constituents of conventional matter, electrons and protons, have their antiparticle, an entity with analogous physical properties but opposite electrical charge. Both electrons, protons and neutrons fall in a class called fermions, in comparison with those responsible of mediate interactions, like the photon, that fall into the bosonic class.
On top of matter and anti-matter,  it was predicted back in time a third possibility for fermions: the so called  Majorana particles, that  would be simultaneously particle and anti-particle. However,  no basic constituent of matter has proven yet to realize such an intriguing possibility. 

The world that surrounds us is entirely made of matter, anti-matter usually only being produced in particle accelerators. Nevertheless, anti-matter already
has crucial applications in medicine, using the so called positron emission tomography, that requires large scale facilities. But, how could this ever apply to a nanoscale systems? Is there something in the exotic matter anti-matter play, that could have a role in your future smartphone?

Emergence is the appearing of new properties as the complexity of a system grows. Chemistry, life, consciousness, language, social movements all of them appear when smaller entities come together, the group does not behave like just one member:  more is different, as  famously noted by the Physics Nobel laureate PW Anderson.
In solid state systems, emergence takes place making systems behave like they if had new particles. Electrons and protons are no longer the only players,
collective behavior creates new entities: phonons, magnons, polaritons,  and many others. Could any of this newcomers be a elusive Majorana particle?
The answer is yes.

Usually, the mechanism that involve the emergence of the Majorana state involve heavy elements, with the associated problems
of sparsity of the materials, expensiveness or even toxicity that can come along. Luckily, it has been shown  there exist a route to create the Majorana particle in 
graphene, a single layer of carbon.  The proposal is based on a nano-device made of graphene and a superconductor. Due to the interplay of interaction and topological
effects, it was shown that Majorana states can appear at the interface of graphene and a superconductor under strong magnetic field.
Whether if the ultimate ingredient for the future electronics will be Majorana states of graphene is yet an uncertainty: only the upcoming research efforts put in graphene superconducting spintronics will shed light on it.

The importance of the appearance of this exotic entity is simple yet remarkable: Majorana particles could be used as  building blocks to create a quantum
computer. Quantum computers would be able to perform tasks far beyond the limit of classical computers. Computational design of pharmaceutical drugs, design of smart materials, complex system simulation as cell metastasis and even breaking of some of the most powerful cryptographic algorithms, compromising secret communications. Tasks never achievable by the biggest classical computer, whose realization only need a reliable quantum computer building block. Majorana fermions will probably not have a role on your next mobile phone, but they can have it in quantum computers that might help us to answer  questions that can change our lives, in the same way nowadays anti-matter in hospitals helps us already to locate tumors.