Photoemission and Strain Tuning of Correlated Electron Systems

Strong interactions lie at the heart of correlated electron materials and yield striking collective states such as superconductivity or magnetism. Often, these interactions mediate giant responses to small external perturbations. This offers unique opportunities to tune these subtle quantum many-body systems, to shed new light on their underlying physics and ultimately to engineer desired functional properties. 

Our approach for such controlled tuning is to apply uniaxial pressure in order to directly drive anisotropic changes in the nearest-neighbor overlap integrals between atomic sites, which typically results in much larger changes to the electronic structure of materials than equal hydrostatic pressures. Uniaxial pressure can also reversibly and precisely lift lattice symmetries; symmetry is a basic paradigm for analysis of problems in solid state physics, and controllably breaking symmetries is a powerful probe of novel forms of order in correlated electron systems, for example superconductivity and density wave orders. In a recent breakthrough we have developed a passive device based on differential thermal contraction, and used it to show spectroscopically that we can tune the unconventional superconductor Sr2RuO4 through a topological Fermi surface transition [1].

In this project, you will perform low-temperature measurements as a function of uni-axial strain using custom apparatus within the world-leading facilities of the Max Planck Institute for the Chemical Physics of Solids in Dresden, Germany. You will also study the effect of strain on correlated systems by angle-resolved photoemission (ARPES), a vital tool for studying the electronic structure of materials, and lead measurements both using the state-of-the-art ARPES system in St Andrews, and at synchrotron light sources in the UK, Europe, and the USA. Thus, a willingness to travel is an essential prerequisite. Further essential qualifications for this project are a curiosity about basic science and an interest in practical engineering problems.


[1] V. Sunko, E. Abarca Morales, I. Marković, M.E. Barber, D. Milosavljević, F. Mazzola, D.A. Sokolov, N. Kikugawa, C. Cacho, P. Dudin, H. Rosner, C.W. Hicks, P.D.C. King, and A.P. Mackenzie
Direct observation of a uniaxial stress-driven Lifshitz transition in Sr2RuO4
npj Quantum Materials 4, 46 (2019)

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