University of St Andrews

The ability to manipulate the surface and interface properties of correlated electron systems underpins the burgeoning field of “designer” quantum matter. Over the last few years there has been enormous interest in using surfaces and interfaces to tune the interacting electronic states in perovskite-based transition-metal oxides 1 but it is important to expand the search of materials systems which may be tuned to host new surface and interface phases. Here, we study the “ABO2” delafossite oxides,2 a particularly promising material class both because of its naturally layered structure, as well as the potential to drastically alter its physical properties by changing the A- and B- site cations.  MCoO2  [M=Pt,Pd] are non-magnetic metals with simple single-band Fermi surfaces. In bulk, they stand apart as the most conductive of all known normal-state oxides.3,4 The polar nature of their surfaces,5-6 however, opens the potential to stabilise local electronic environments and phases different to those of the bulk. Using angle-resolved photoemission spectroscopy we show how this drives an intrinsic Stoner-instability towards itinerant ferromagnetism at the Pd-terminated surface of both PdCoO2, and of its sister compound PdCrO2, a bulk antiferromagnet. Our measurements also reveal a large mass enhancement from electron-magnon coupling of the surface electrons. This work, altogether, could open potential routes for the creation, control and manipulation of collective phases in oxide surfaces and heterointerfaces.

References: 1Mannhart & Schlom, Science 327, 1607 (2010); 2 Mackenzie, Rep. Prog. Phys. 80, 32501 (2017); 3 Hicks et al., Phys. Rev. Lett. 109, 116401 (2012); 4 Kushwaha et al., Science Adv. 1, e1500692 (2015); 5 Sunko et al., Nature, 549, 492-496 (2017); 6 Kim et al., Phys. Rev. B., 80, 035116 (2009).

The Kuiper Belt, a population of icy bodies beyond Neptune, consists of material left over from the planet formation process.  Its architecture records its interaction with the giant planets, and it still supplies a variety of small bodies to the inner solar system, including comets.  The Kuiper Belt appears to be a universal phenomenon, its analog having been found in several extrasolar planetary systems.  This talk will give a brief summary of the Kuiper Belt’s most important features. 

The appearance of high-temperature superconductivity in the Fe-based superconductors is likely to be linked to the other ordered states found in their phase diagrams. Certain systems, including FeSe, exhibit an unusual `nematic' phase where fourfold symmetry of the lattice is spontaneously broken without long-range magnetic order. Angle-resolved photoelectron spectroscopy (ARPES) measurements of FeSe give a unique insight into the electronic structure in the nematic phase. Here I will argue that our high-resolution ARPES results obtained on twinned samples [1,2] which trace the evolution of the Fermi surface with temperature point towards a “unidirectional nematic bond ordering”. I will additionally present ARPES results on ``detwinned” FeSe crystals [3], revealing a remarkable anisotropy which is hidden in measurements of twinned samples: only the electron pocket oriented along the longer orthorhombic axis is observed by ARPES. I will also present detwinned ARPES results on NaFeAs [4] which suggest that this “one-ellipse” structure may be a universal feature of the nematic phase of Fe-based superconductors.1.      M. D. Watson et al. “Evidence for unidirectional nematic bond ordering in FeSe”, Phys. Rev. B 94, 201107(R) (2016)2.      M. D. Watson et al. “Shifts and Splittings of the Hole Bands in the Nematic Phase of FeSe”, J. Phys. Soc. Jpn. 86, 053703 (2017)3.      M. D. Watson et al. “Electronic anisotropies revealed by detwinned ARPES measurements of FeSe” New J. Phys. 19 103021 (2017)4.      M. D. Watson et al. “The three-dimensional electronic structure of the nematic and antiferromagnetic phases of NaFeAs from detwinned ARPES measurements” arXiv:1710.03717

The Tactile Universe is an innovative public engagement project by the Institute of Cosmology and Gravitation (University of Portsmouth), which is using 3D printed models of galaxies to engage the blind and vision impaired community with current, cutting-edge galaxies research.  A six month pilot project funded by the South East Physics Network culminated in January 2017 with an event for the vision impaired community in Portsmouth. At this event participants were able to explore the shapes of different galaxies using 3D printed images created from real data. We are now moving into Phase Two of the project where we will be expanding in a number of ways, including developing schools workshops using our existing 3D models, increasing the project’s geographical reach, and creating new props and demos using tactile and audio elements. In this talk we will provide an overview of the project (including the opportunity to interact with the props that were developed) and summarise the lessons learnt to date about how to engage with this traditionally hard-to-reach audience.