2023
PhD/MSc Thesis Prize 2023
Many congratulations to Matthew Pearce, Ross Hunter, Sahl Rowther and Cait Cullen for their success in the 2023 Thesis Prize competition!
SEM Faculty Thesis Prize- Matthew Pearce
I did my undergraduate degree at Warwick, before continuing to do my PhD in the Superconductivity and Magnetism Group under the supervision of Paul Goddard. During my PhD I used a variety of experimental techniques including magnetometry (torque, SQUID, VSM and pulsed-field compensated coil), electrical transport (traditional 4-wire and PDO), heat capacity and x-ray scattering. I performed measurements at low temperatures and high magnetic fields, utilising both the in-house facilities in the laboratories at Warwick, as well as international high-field user facilities – where materials can be studied in some of the highest magnetic fields on earth.
My research focussed in part on Ho2Ir2O7, which belongs to a class of highly frustrated magnetic systems known as spin-ices, which are famous for hosting magnetic monopole quasiparticles. We found that not only do measurements of the electrical resistance in these systems act as an indicator for the density of magnetic monopoles, but also that, mediated by the monopoles on the Ho sublattice, an applied magnetic field is able to manipulate the antiferromagnetic Ir domains, with potential applications to areas such as spintronics. I also studied the compound CeOs4Sb12, which had previously been found to undergo a valence transition. This is a transition where f electrons undergo a transformation from quasi-localised to itinerant with perhaps the most dramatic example being that of elemental Ce, which is accompanied by a volume collapse often quoted to be as large as 15 %. We mapped out the phase boundary of this transition which exhibited an extremely unusual shape, owing to the influence of locally varying strain within the sample and quantum fluctuations.
Since completing my PhD I have been working at the University of Oxford with Radu Coldea studying quantum magnetism.
Springer Thesis Prize- Ross Hunter
My thesis contributed to the largest endeavour in modern particle physics: the search for a more complete theory of how the universe behaves on the most fundamental scales. Our current theory - the so-called "Standard Model" (SM) of particle physics - has for 50 years never been disproved at particle colliders, yet simultaneously has fundamental problems in its description of the universe - the most obvious example being the glaring omission of gravity. We search for a superseding theory by making measurements at increasing precision in the hope of seeing a discrepancy with the SM’s predictions. I worked towards two such high-precision tests. Both tests were carried out by analysing collision data from the LHCb experiment on the Large Hadron Collider (LHC), and both focused on the properties of the W boson: the fundamental "force-carrier" that mediates nuclear weak decay and part of the nuclear fusion process that keeps the stars shining. The first test was to measure the boson's mass, and true-to-form, our measured W-boson mass agreed remarkably well with the SM prediction. This difficult and stringent test was hitherto unenvisaged at LHCb, so establishes a new field of measurements of ever-higher precision. The second test is that of a fundamental assertion of the SM: that the W boson decays to electrons and their heavier cousins - particles called muons and taus - with exactly the same probability. This measurement is still ongoing, and I'm delighted to stay here in the EPP group at Warwick to finalise it as a Postdoctoral Research Fellow. My PhD's final contribution was to LHCb's "trigger" software, which decides which of the roughly 30 million LHC collisions per second we should save to be analysed later. Saving them all is practically impossible, and the vast majority of them are anyway uninteresting to the seasoned particle physicist, so only those that the trigger classifies as "interesting" are persisted. I wrote a software tool that helps LHCb physicists design the trigger’s classification algorithms in the most efficient way, and used the tool myself to write algorithms ensuring that collisions involving W bosons (and other related particles) will be saved for future precision tests of the SM
Winton Prize-Sahl Rowther
In their youth, protoplanetary discs are expected to be massive and gravitationally unstable (also referred to as a GI disc). A characteristic feature of such discs is non-axisymmetric spiral structures (left panel). However, such features remain rare despite an increasing amount of high resolution observations of protoplanetary discs revealing a wide variety of substructures. During my PhD, I used 3D smoothed particle hydrodynamics simulations to investigate plausible mechanisms that could resolve this discrepancy.
The first mechanism I considered was planet-disc interactions, as protoplanetary discs are expected to form planets. I showed that the spiral wakes from a massive planet can heat up the disc suppressing spiral structures (middle panel). Disc formation in its earliest phases (when they are likely to be gravitationally unstable) is influenced by its chaotic star forming environment where a disc is likely to become warped. Hence, the second mechanism I considered was how a warp impacts the evolution of a GI disc. As with a planet, the disc was heated up due to the warp, suppressing spiral structures (right panel).
While recent observations of protoplanetary discs suggest that GI discs may be intrinsically rare, the results in my thesis demonstrate that the observed rarity could be due to neglecting many of the complex processes (such as planets & warps) that can shape the evolution of a GI disc and suppress its spiral structures
MSc Thesis Prize- Cait Cullen