Topological quantum structures in bismuth ferrite superlattices

Topologically non-trivial structures with particle-like properties in condensed matter systems, known as skyrmions, have recently been proposed for quantum computing.

One of the key challenges for quantum computing with skyrmions is identifying optimal materials, and crucially, to be considered a quantum object the size of the skyrmion must be on the order of nanometres.

Skyrmions have been observed in both ferromagnetic and ferroelectric materials, and in one instance topological structures as small as 3 nm have been revealed.

In this project we propose to deposit multiferroic bismuth ferrite (BFO) superlattices in which there are alternating layers of BFO and another oxide such as strontium titanate (STO) or strontium ruthenate (SRO).

As a multiferroic, BFO offers exciting prospects over and above purely ferromagnetic or ferroelectric materials, as the coexistence of both polar and spin topologies would enable e.g. electric field control of the magnetism.

At the interfaces of the BFO layers in a superlattice, strain and depolarisation effects can combine to curl the polarisation and generate topological quantum structures.

The superlattices will be grown in the Royce deposition facility and characterised by electron microscopy, X-ray diffraction and scanning probe microscopy using the Bragg Centre facilities. We will establish the growth conditions for observation of topological structures.

Further, by applying an electric field, we aim to tune the topology of the structures as a pre-requisite for manipulating quantum information. Finally, we will investigate the potential for macroscopic quantum tunnelling between the structures.