George McArdle

George McArdle

Research Fellow in Theoretical Conedensed Matter Physics

Research

Topological Superconductivity

Topological superconductors are of interest for many reasons including the potential to be utilised in topological quantum computing. The reason for this is the prediction that they host Majorana zero modes - which can be utilised to store information in a way that is topologically protected. However, observing these Majorana modes experimentally has proved challenging, with their existence widely debated.

A common method to realise this topological state is in semiconductor-superconductor heterostructures where an external magnetic field is used to break time-reversal symmetry. However, this magnetic field can also destroy the superconducting state. Our research focuses on using altermagnet-superconductor heterostructures to realise topological superconductivty whilst maintaining zero net magnetisation. Our work analyses more advanced models in order to aid experiments in the search for topological superconductivity.

Electron-Phonon Decoupling

Many-body localisation (MBL) and its associated phenomena was originally predicted to occur in disordered systems of interacting electrons. However, its detection has remained elusive in these systems, often due to the presence of phonons which act as a thermal bath and therefore cause the system to thermalise, meaning the system can’t be in a localised state.

In our work we identify the conditions required for electron-phonon decoupling and then show how such decoupling can be identified experimentally. The key signatures are large hysteretic jumps in the current-voltage characteristics and a region of excluded electron temperatures.

See the following for more details

Transport in Quantum Dots

Quantum dots are effectively zero-dimensional systems and are characterised by the presence of the Coulomb interaction. For a dot containing a large number of electrons this leads to the classical Coulomb Blockade which is charaterised by two key transport characteristics of conductance peaks in linear response as a function of gate voltage and the Coulomb staircase in the non-equilibrium regime.

These well-established results assume that the electrons on the dot are fully thermalised, and therefore are described by a Fermi-Dirac distribution. However, in the absence of thermalisation this is no longer true. We have shown that a new regimes exist, and in particular, if the coupling to the leads is symmetric, the distribution function of the electrons changes to a double-step form heavily influenced by the interactions. This causes an additional peak in the non-equilibrium differential conductance compared to the Coulomb staircase.

See the following for more details