Imaging emergent phases of matter

This project aims to establish an understanding of the subtle control of emergent phases in quantum materials near quantum criticality by providing a microscopic picture of how the electronic states evolve in the vicinity of a quantum phase transition. It builds on world-leading expertise and infrastructure in atomic-scale imaging and spectroscopy in the Ultra-low vibration laboratories at the University of St Andrews and in growth and characterization of the relevant advanced quantum materials at the Max Planck Institute for the Chemical Physics of Solids in Dresden.

These studies occur at the surface of materials, which poses a problem and opportunity at the same time: it raises important questions about how the presence of the surface affects the subtle quantum states in the material. The presence of the surface can result in significant changes to the physics, for example through the symmetry breaking of the surface [1] or, for a quantum critical system, mean that the system falls into a different universality class than the bulk of the material. In systems which approach a quantum critical point, often exciting new phases appear [2] whose properties still remain poorly understood – not least because of a lack of knowledge how the electronic structure changes in these phases. The successful applicant will take a holistic view on this problem, using our bespoke experimental tools for imaging the nascent quantum states near a quantum critical point at low temperatures and in vector magnetic fields, and at the same time developing the theoretical models (see, e.g., Ref. 4) to understand and describe the experimental data.

van Hove singularity and checkerboard charge order in the surface layer of Sr2RuO4 [3].

The results of this project will enable a microscopic understanding of how externally applied fields, such as uniaxial strain, magnetic field and electric fields, affect the electronic structure. This knowledge will enable unprecedented insight into the effect of emergent electronic phases on macroscopic properties of the material and their subtle interplay with tiny structural distortions, as well as potentially enabling their control. The successful applicant will take an active role in the measurements as well as the theoretical modelling of the data, providing them with unique opportunities to acquire skills across experimental, computational and theoretical physics to develop into a future leader.

The successful student will work with Prof Peter Wahl at the University of St Andrews and Prof Andy Mackenzie at the MPI Dresden to study high quality crystals, grown and characterized at MPI Dresden with the low temperature scanning tunnelling microscopes in the Ultra-low vibration laboratories in St Andrews.

References

[1] C.-M. Yim, D. Chakraborti, L.C. Rhodes, S. Khim, A.P. Mackenzie, P. Wahl
Quasi-particle interference and quantum confinement in a correlated Rashba spin-split 2D electron liquid
Sci. Adv. 7, eabd7361 (2021)
[2] R.A. Borzi, S.A. Grigera, J. Farrell, R.S. Perry, S.J.S. Lister, S.L. Lee, D.A. Tennant, Y. Maeno, A.P. Mackenzie
Formation of a Nematic Fluid at High Fields in Sr3Ru2O7
Science 315, 214 (2007)
[3] C.A. Marques, L.C. Rhodes, R. Fittipaldi, V. Granata, C.M. Yim, R. Buzio, A. Gerbi, A. Vecchione, A.W. Rost, P. Wahl
Magnetic-field tunable intertwined checkerboard charge order and nematicity in the surface layer of Sr2RuO4
Adv. Mat. 33, 2100593 (2021)
[4] A. Kreisel, C. A. Marques, L. C. Rhodes, X. Kong, T. Berlijn, R. Fittipaldi, V. Granata, A. Vecchione, P. Wahl, P.J. Hirschfeld
Quasiparticle Interference of the van-Hove singularity in Sr2RuO4
accepted in npj Quantum Materials, preprint available at arxiv/2103.06188

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