Quantum spin liquids (QSLs) are a novel class of materials in which geometric frustration suppresses magnetic order down to absolute zero temperature. Because of the topological character of the ground-state wave function with a special type of long-range quantum entanglement, QSLs exhibit exotic fractional excitations, which are believed to hold great potential for quantum communication and computation. These concepts were put on a firm footing in the seminal work by Alexei Kitaev who constructed an exactly solvable QSL model on the honeycomb lattice and demonstrated that the spins break-up (fractionalise) into a set of Majorana fermions. Although the emergent fermions don’t carry electric charge, they essentially behave like the electrons in graphene with a relativistic Dirac dispersion.
There exist materials that are well described by Kitaev’s toy model, but which exhibit additional interactions. These interactions stabilise magnetic order at very low temperatures. In addition, strain or magnetic anisotropy can drive topological phase transition between gapless and gapped QSLs.
The aim of this project is to understand the nature of such quantum phase transitions, in the Kitaev model and in related QSLs. You will learn to represent spin models in terms of interacting Majorana fermions and gauge fields. Using methods of quantum field theory, such as renormalisation-group calculations, you will analyse the behaviour near the magnetic ordering and topological phase transitions and compute critical exponents. You will investigate the changes of magnetic excitation spectra across the transitions and compare to experiments.
This project is part of the UCL EPSRC DTP (Doctoral Training Partnership). All studentships are fully funded for 4 years and provide:
- 4 years fees (Home rate) (International students will receive a UCL award to cover the home/international fee difference)
- Maintenance stipend at the UCL EPSRC DTP enhanced rate
- Research Training Support Grant (RTSG) of £4,800. This is to cover additional costs of training eg courses, project costs, conferences, travel
How to Apply:
- Informal inquiries regarding the project can be made by contacting Dr. Frank Kruger
- Formal applications should be made via UCL's Doctoral School here
- Please note that the 8 January deadline (1pm) includes the submission of references by that date.