Magnetic & Ferroic Materials

Prof Steven Bramwell

My research involves experiment (neutron scattering, magnetometry and specific heat) and theory (statistical mechanics) on spin model magnets. These are magnetic materials designed to mimic simple models of interacting spins or vectors. For many years I have been particularly interested in the scope of real materials to realise spin models that capture universal aspects of many body behaviour, and which therefore have applications well beyond magnetism. Much of my work has been concerned with two dimensional critical systems, analogues of turbulent flow, analogues of proton disorder in ice (spin ice, which I co-discovered) and analogues of Coulomb fluids.  I also have an interest in demagnetizing effects, in thermal electric field fluctuations and in the general properties of structure factors or scattering functions.

Dr Frank Kruger

Our group investigates the formation of novel states of quantum matter in strongly correlated electron systems. We use analytical tools such as quantum field theory and renormalisation group calculations to understand the collective behaviour of electrons and the nature of quantum phase transitions between different phases of matter. More recently, we have started to study quantum spin liquids. These are highly frustrated magnetic materials in which strong quantum fluctuations prevent the formation of magnetic order down to absolute zero temperature. Remarkably, the spin degrees of freedom can break up or fractionalise into particles that satisfy fermionic quantum statistics. Although the emergent fermions in insulating quantum spin liquids don’t carry electric charge, they behave in many respects like interacting electrons in metals. In addition, they are coupled to gauge fields, resulting in even richer behaviours.

Prof Marzena Szymanska

Our group researches out-of-equilibrium quantum phenomena in driven-dissipative light-matter systems. These systems bridge the gap between quantum optics and many-body quantum theory where many degrees-of-freedom give rise to emergent collective behaviour. The presence of drive and dissipation mean that the Hamiltonian is not the only source of dynamics, resulting in rich phenomena which is intrinsically different to its equilibrium counterpart. We apply a combination of analytical methods (Keldysh Field Theory, Renormalisation Group, Green’s Functions, Quantum Trajectories, Master Equations) in addition to numerical techniques (Stochastic Phase Space Simulations, Truncated Wigner,  Positive-P, Tensor Networks) to better understand novel behaviour in non-equilibrium, for example: superfluidity in condensates, phase transitions in low-dimensions and non-equilibrium universality classes such as Kardar-Parisi-Zhang (KPZ). Recently we have been extending our research to highly tuneable driven-dissipative lattices of bosons, spins and fermions. A large class of these can be faithfully represented by tensor networks and we are currently interested in extrapolating established ideas for closed systems to open systems to give insight into symmetry-protected phases and to address fundamental questions of entanglement growth.

Dr Roger Johnson

We work on the experimental determination of structure-property relationships in quantum materials, and develop phenomenological models of the underlying physical mechanisms via group-theoretical approaches and Landau theory. At present we are focused on magneto-orbital physics of novel quadruple perovskite manganites, and unusual effects of quantum magnetism found in hybrid organic/inorganic compounds and fully inorganic oxides. We perform in-house experiments to characterise the crystal structure and physical properties of new materials using, for example, single crystal and powder x-ray diffractometers, squid magnetometers, and bespoke dielectric and ferroelectric instrumentation. Our core research involves analysis of data collected during experiments at large-scale central facilities, mostly the ISIS Neutron and Muon Source and Diamond Light Source, both based in Oxfordshire, UK.

Dr Mark Buitelaar

The focus of our group is on the experimental study of solid-state quantum devices for quantum information processing applications. For device fabrication and development we benefit from the excellent fabrication facilities of the London Centre for Nanotechnology, including its class 6 cleanroom. Examples of the quantum devices we investigate are charge and spin qubits in carbon nanotube quantum dots, single-dopant spin qubits in silicon and topological qubits in semiconductor nanowires. Our lab is equiped with a number of dilution refrigerators that allow us to study these quantum devices at mK temperatures - using high-frequency measurement techniques for readout and control at the level of individual electron spins. We work closely with other groups within the UCL Quantum Science and Technology Institute as well as many other research groups and industry partners worldwide.