Tunneling Spectroscopy of Quantum Materials

How does a doped Mott insulator avoid becoming metallic? See our new paper in Nature Communications on the surface of the hidden Mott insulator PdCrO₂. The surface polarity results in clean doping, yet the system remains insulating. Hidden gem: the local order that prevents metallicity is highly degenerate with local disorder, see below the movie of its dynamics after a voltage pulse. Great collaboration with Phil King’s group and researchers at TDLI, CNR SPIN and the MPI for the Chemical Physics of Solids.

Full reference:
Chi Ming Yim, Gesa-R. Siemann, Srdjan Stavrić, Seunghyun Khim, Izidor Benedičič, Philip A. E. Murgatroyd, Tommaso Antonelli, Matthew D. Watson, Andrew P. Mackenzie, Silvia Picozzi, Phil D.C. King, and Peter Wahl, Avoided metallicity in a hole-doped Mott insulator on a triangular lattice, Nat. Commun. 15, 8098 (2024), arxiv/2311.17139.

Congratulations to Olivia and Dylan to their graduation!

Olivia graduated with her PhD thesis “Scanning Tunnelling Microscopy of Magnetic van der Waals Materials” and set up our STM4, which enables imaging of electronic states in thin films grown by molecular beam epitaxy and produces amazing data.

Dylan obtained his Master in Theoretical Physics with a  final year project in which he modelled electronic states in twisted bilayer graphene. For his work, he was awarded the prize for the best final year Theoretical Physics project and received the fifth year medal for theoretical physics.

Have you heard of the magic angle of Sr₂RuO₄? No? Read in our new preprint how small structural distortions affect superconductivity in Sr₂RuO₄. Our results not only explain why the surface is not superconducting, but also how to optimise T_c. Surprisingly, the phase diagram is quite different dependent on which method one uses to obtain the pairing instability. Using the superconducting order parameters predicted from RPA and FRG, we show how to detect the symmetry of the order parameter in quasi-particle interference.

The St Andrews part was led by Luke, with QPI calculations by Rebecca and Carolina. Great collaboration with Jonas Profe (FRG, Frankfurt) and Matteo Dürrnagel (RPA, Würzburg/Zürich).

Full reference:
Jonas B. Profe, Luke C. Rhodes, Matteo Dürrnagel, Rebecca Bisset, Carolina A. Marques, Shun Chi, Tilman Schwemmer, Ronny Thomale, Dante M. Kennes, Chris Hooley, and Peter Wahl, The magic angle of Sr₂RuO₄: optimizing correlation-driven superconductivity, arxiv/2405.14926.

Submit your abstract now for minicolloquium 42 “A quantum leap: unraveling the mysteries of correlated electronic states in quantum materials through atomic-scale imaging and spectroscopy” at the CMD conference in Braga, Portugal, and join us for lively discussions about new insights from atomic-scale imaging of correlated states.

See here for a list of confirmed invited speakers.

How can the magnetization direction in a ferromagnet drive a Lifshitz transition? In our new study of Sr₄Ru₃O₁₀ with QPI and ARPES we establish its low energy electronic structure and propose a tight-binding model that captures the key features, including the spin- and orbital character of the van Hove singularity closest to the Fermi energy. Using this model, we identify a mechanism for a Lifshitz transition that is based on the magnetization direction and spin-orbit coupling.

Reaching those conclusions was only possible by combing the millikelvin QPI results measured by Carolina and Weronika with DFT modelling from Luke and ARPES done in collaboration with Phil Murgatroyd and Phil King’s group.

Original publication:

• Carolina A. Marques, et al., Spin-orbit coupling induced Van Hove singularity in proximity to a Lifshitz transition in Sr₄Ru₃O₁₀, npj Quantum Materials 9, 35 (2024).

Meet members of the group at the APS March meeting in Minneapolis. Work of the group and its members features in the following contributions:

• Luke Rhodes in A16.00011: “Structural routes to stabilize superconducting La₃Ni₂O₇ at ambient pressure”, Mon 10am, room M100G.
• G10.00014: “Spin-orbit coupling induced Van Hove singularity in proximity to a Lifshitz transition in Sr₄Ru₃O₁₀“, Tue, 2.06pm, room M100A (talk by Phil Murgatroyd from Phil King’s group).
• Harry Lane in:
  • G21.00003: “Orbital-driven spin-singlet dimerization in La₂Ru₄O₁₀“, Tue, 12:18pm, room 101A.
  • N23.00006: “Sunny, a user-friendly Julia package for simulating generalized spin dynamics”, Wed, 12:54pm, room 101C.
  • Z62.00003: “Linear spin wave theory of large magnetic unit cells using the Kernel Polynomial Method”, Fri, 11:54am, room 208CD.

Congratulations to Olivia to her viva and a great PhD thesis on “Scanning Tunnelling Microscopy of Magnetic van der Waals Materials”, and many thanks to Philip Moriarty and Renald Schaub for examining the thesis!

How good are different surfaces at deactivating SARS-CoV-2 viruses. Copper beats them almost all – except cuprous oxide (Cu₂O)! Why is that? Read more in our new paper in Applied and Environmental Microbiology ahead of print. Great interdisciplinary collaboration across CDQM and with Cathy Adamson from the School of Biology and her team.

Congratulations to Izidor to his graduation and his PhD thesis “Imaging emergent surface magnetism in ruthenates”!

Looking forward to Izidors graduation this week. If you want to find out more about his work, come to his graduant talk Wednesday, 29 November at 2pm in Lecture Theatre C on Amazing atoms, exciting electrons and mysterious magnets (in person only). Hint: it might feature compasses …