Dr Tom Lancaster
(email at email@example.com)
I am now recruiting a PhD student to work in the muon group, starting in October 2013!
The PhD project involves using muons to study exotic magnetism and superconductivity in new materials. We use experimental facilities in the UK and Switzerland and enjoy collaborations with research groups from all over the world. A suitable candidate would have a strong interest across all of physics, but especially condensed matter, and a desire to push forward cutting-edge research on novel forms of matter.
More information about our work may be found below and in the CMP PhD project booklet. Please contact me directly for further details.
When atoms form a solid and electrons interact collective phenomena emerge. These phenomena include the phases of magnetic order, superfluidity and superconductivity, the emergence of new particles such as the magnon or the phonon and the occurence of topological objects such as kinks and vortices. Condensed matter physics is the investigation of this exotic world and provides the same fundamental insight into the Universe as the study of elementary particles or black holes.
I use muons to investigate condensed matter physics. Muons are subatomic particles that act as microscopic probes of magnetism. Subjects in which I'm interested include collective states of matter such as magnets, superconductors and glasses along with their excitations such as spin waves, vortices and diffusion. My work covers a wide range of scales from the quantum mechanical interaction of nuclei to the large scale dynamics of polymer chains.
Muons have a spin 1/2, which will Larmour precess in a magnetic field. They are also unstable and live for only 2.2 us (on average!). We detect their decay products and these tell us essentially which way each muon-spin was pointing at the moment of death. The technique we employ is known as muon-spin relaxation and involves stopping muons in materials where they precess until they decay. This tells us about the local magnetic fields in a material, making it useful for investigating magnets and the vortex phase in superconductors. Muons are produced using particle accelerators based at large facilities. I use the ISIS facility (http://www.isis.stfc.ac.uk/) in the UK, which is the world's most intense source of pulsed muons and neutrons and the Swiss Muon Source based at the Paul Scherrer Institut (http://www.psi.ch/).
II) Magnetism in reduced dimensions
Despite being one of the oldest discoveries in Physics, magnetism is relatively poorly understood. In some very beautiful systems, magnetic interactions may be constrained to act along a line of atoms (one-dimension) or in a plane of atoms (two-dimensions). These different dimensionalities are of fundamental importance and lead to exotic physical properties. An effective route to investigating these low-dimensional (i.e. 2D and 1D) phenomena is through the study of molecular magnets, which are self-assembled polymers formed through bridging paramagnetic cations (such as Cu2+) with organic molecular building blocks. The richness of carbon chemistry means that, in principle, molecular magnets can be nano-engineered to exhibit low dimensional properties.
III) Frustrated magnets
In some magnets interactions tend to oppose each other's influence and are therefore in competition. Such systems are said to be frustrated; it is not possible to satisfy all of the magnetic interactions to find the material's ground state. Materials showing these effects offer an insight into the factors that cause systems to adopt a particular ground state (such as permanently magnetic or disordered). One particularly exciting possibility for a frustrated system is the formation of a spin liquid state. This is a long sought after phase of matter which shows no long range magnetic order down to zero temperature, but which is nonetheless stable. In fact, we believe that we recently may have found such a state in an organic magnet!
IV) Unconventional superconductors
Understanding unconventional superconductors is perhaps the most urgent problem in condensed matter physics. Many of the clues suggest that the behaviour of these materials is caused by a subtle interplay of magnetism and superconductivity. Muons are ideal probes of such systems since not only are we able to probe magnetism, but we may also use muons to map the field distribution within the superconducting vortex state allowing an accurate determination of the superconducting penetration depth. My interests currently lie in the recently discovered iron arsenide superconductors, where magnetism, structural distortions and superconductivity coexist across a rich phase diagram.
Journal papers: academic
- (Published). Antiferromagnetic ordering through a hydrogen-bonded network in the molecular solid CuF2(H2O)(2)(3-chloropyridine). Chemical Communications 49(5): 499.
- (Published). Spin Waves and Revised Crystal Structure of Honeycomb Iridate Na2lr03 S K Choi et al.,Phys.Rev.Lett. 108, 127204.
- Pratt, F.L., Lancaster, T. , Blundell, S.J. & Baines, C. (2013). Low-Field Superconducting Phase of (TMTSF)2ClO4. Physical Review Letters 110(10): 107005.
- (2012). Dimensionality Selection in a Molecule-Based Magnet P A Goddard et al., Phys. Rev. Lett. 108, 077208.
- Burrard-Lucas, Maththew, Free, David G., Sedlmaier, Stefan J. Wright, Jack D., Cassidy, Simon J, Hara, Yoshiaki Corkett, Alex J. Lancaster, Tom, Baker, Peter J. Blundell, Stephen J. & Clarke, Simon J. (2012). Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer. Nature Materials 1476-1122 (print), 1476-4660 (electronic).
- (2012). Spin Waves and Revised Crystal Structure of Honeycomb Iridate Na2IrO3. Physical Review Letters 108(12).
- Pratt, F.L., Baker, P.J., Blundell, S.J., Lancaster, T., Ohira-Kawamura, S., Baines, C., Shimizu, Y., Kanoda, K., Watanabe, I. & Saito, G. (2011). Magnetic and non-magnetic phases of a quantum spin liquid. Nature 471(7340): 612–616.
- J. D. Wright, T. Lancaster, I. Franke, A. J. Steele, J. S. M¨oller, M. J. Pitcher, A. J. Corkett, D. R. Parker, & D. G. Free, F. L. Pratt, P. J. Baker, S. J. Clarke, and S. J. Blundell (2011). The gradual destruction of magnetism in the superconducting family NaFe1xCoxAs.
- Parker, Dinah R., Smith, Matthew J.P., Lancaster, Tom, Steele, Andrew J., Franke, Isabel, Baker, Peter J., Pratt, Francis L., Pitcher, Michael J., Blundell, Stephen J. & Clarke, Simon J. (2010). Control of the Competition between a Magnetic Phase and a Superconducting Phase in Cobalt-Doped and Nickel-Doped NaFeAs Using Electron Count. Physical Review Letters 104(5): 057007.
- Drew, A.J., Niedermayer, Ch., Baker, P.J., Pratt, F.L., Blundell, S.J., Lancaster, T., Liu, R.H., Wu, G., Chen, X.H., Watanabe, I., Malik, V.K., Dubroka, A., Roessle, M., Kim, K.W., Baines, C. & Bernhard, C. (2009). Coexistence of static magnetism and superconductivity in SmFeAsO(1-x)F(x) as revealed by muon spin rotation. Nature Materials 8(4): 310-314.
- Parker, Dinah R., Pitcher, Michael J., Baker, Peter J., Franke, Isabel, Lancaster, Tom, Blundell, Stephen J. & Clarke, Simon J. (2009). Structure, antiferromagnetism and superconductivity of the layered iron arsenide NaFeAs. Chemical Communications 16: 2189-2191
- Lancaster, T., Blundell, S.J., Baker, P.J., Brooks, M.L., Hayes, W., Pratt, F.L., Coldea, R., Soergel, T. & Jansen, M. (2008). Anomalous temperature evolution of the internal magnetic field distribution in the charge-ordered triangular antiferromagnet AgNiO(2). Physical Review Letters 100(1): 017206.
- Drew, A.J., Pratt, F.L., Lancaster, T., Blundell, S.J., Baker, P.J., Liu, R.H., Wu, G., Chen, X.H., Watanabe, I., Malik, V.K., Dubroka, A., Kim, K.W., Roessle, M. & Bernhard, C. (2008). Coexistence of magnetic fluctuations and superconductivity in the pnictide high temperature superconductor SmFeAsO(1-x)F(x) measured by muon spin rotation. Physical Review Letters 101(9): 097010.