Tunneling Spectroscopy of Quantum Materials

Meet members of the group at the DPG spring meeting in Dresden. Work of the group and its members features in the following contributions:

• Siri A. Berge in TT5.10: “Atomic scale imaging of the effect of chemical pressure in Sr_2−xBa_xRuO₄“, Mon 12pm, room CHE/0089.
• Rebecca Bisset in TT29.2: “Determining the superconducting order parameter of UPt₃ using scanning tunneling microscopy”, Tue 9.45am, room CHE/0091.
• Carolina A. Marques in O80.3 (Gerhard Ertl Young Investigator Award Competition): “Exchange-driven magnetoelastic coupling in a correlated itinerant ferromagnet”, Thu 11:30am, room TRE/PHYS.
• Uladzislau Mikhailau in O93.5: “Imaging stripe dynamics in superconducting nickelate “, Fri 10:30am, room HSZ/0201.
• Peter Wahl in O93.7: “calcQPI – a tool to simulate quasiparticle interference”, Fri 11:00am, room HSZ/0201.

Look for a PhD position? Apply for a PhD project in the stimulating environment of the Centre for Designer Quantum Materials, working on experimental physics, instrument development or numerical modelling.

You can find example projects here, a few projects for which we specifically are looking for candidates this year are listed here:

• joint Bonn-St Andrews St Leonhard scholarship: Combining Correlation and Non-Equilibrium Effects with Band Structure in Strongly Correlated Quantum Materials, Probed by Quasiparticle Interference (co-supervised with Prof Hans Kroha, University of Bonn). Application deadline: 27 February 2026.

Submit applications here.

Need some Christmas reading?🎄 How about our new preprint where we show how Andreev bound state spectroscopy can be used to determine the symmetry of the order parameter in the case of UPt₃. Turns out, it’s important that there is spin-orbit coupling.

Spoiler alert: looks like singlet pairing with E_1g symmetry is most consistent with our data.

Read the full preprint at:

• Rebecca Bisset, Luke C. Rhodes, Hugo Decitre, Matthew J. Neat, Ana Maldonado, Andrew Huxley, Carolina A. Marques, and Peter Wahl, Determining the superconducting order parameter of UPt₃ using scanning tunneling microscopy, arxiv/2512.15845.

Congratulations to Luke to an EPSRC Open Fellowship and starting his own group, the Rhodeslab, at the School of Physics and Astronomy at the University of St Andrews, focussing on modelling of properties of and electronic states in quantum materials!

Does the surface layer of an itinerant ferromagnet change its magnetization direction at the same field as the bulk? Not always – at least not in Sr₄Ru₃O₁₀. Domain wall pinning allows us to precisely control the magnetic configuration of surface and bulk. Using scanning tunneling microscopy at ultra-low temperatures, Carolina Marques found how the electronic states change between ferromagnetic and antiferromagnetic alignment of the surface layer and bulk magnetizations. Intriguingly, through control of the magnetic configuration, we were able to detect the tiny structural change that accompanies the change in magnetic configuration. While tiny in the grand scheme of things, our measurements reveal a giant magnetoelastic coupling that is driven by exchange interactions, qualitatively as expected from the Bethe-Slater curve sketched almost a century ago. Our results highlight the coupling between electronic, magnetic and structural degrees of freedom, and how these effects are enhanced through electronic correlations.

Read more in our publication at:

• Carolina A. Marques, Luke C. Rhodes, Weronika Osmolska, Harry Lane, Izidor Benedičič, Masahiro Naritsuka, Siri A. Berge, Rosalba Fittipaldi, Mariateresa Lettieri, Antonio Vecchione, and Peter Wahl, Emergent exchange-driven giant magnetoelastic coupling in a correlated itinerant ferromagnet, Nat. Phys. 21, 1243 (2025).

Read in our new preprint about how QPI, combined with photoemission and Density functional theory, can be used to determine the low energy electronic structure of a 2D magnetic materials. Nice QPI data from Olivia measured on our STM4 which she has built and films grown by Akhil. Great collaboration with the King group.

• Olivia Armitage, Naina Kushwaha, Akhil Rajan, Luke C. Rhodes, Sebastian Buchberger, Bruno Kenichi Saika, Shu Mo, Matthew D. Watson, Phil D. C. King, and Peter Wahl, Electronic structure of monolayer-CrTe₂: an antiferromagnetic 2D van der Waals material, arxiv/2505.07942, submitted.

Meet members of the group and hear about our research at the following contributions at the APS March meeting in Anaheim:

• Peter Wahl on Wd, March 19, 11:54am, Room 255C on Why the surface of Sr₂RuO₄ is not superconducting
• Carolina de Almeida Marques on Fri, March 21, 12:06pm (invited), Room 159 on Exchange-driven Magnetoelastic Coupling in a Strongly Correlated Electron Material

Applications for the 2025 entry are open!

Interested in an exciting PhD project working with cutting-edge instrumentation in a stimulating environment and combining advanced experiments, development of bespoke instrumentation, complex data analysis and numerical modelling of quantum materials? We are currently searching for outstanding candidates who are seeking to pursue a PhD on a funded scholarship. You can find a list of example projects on the web page of the School of Physics and Astronomy.

Our group develops and operates cutting edge instrumentation for atomic scale studies of electronic structure, complex magnetic orders and unconventional superconductivity in quantum materials. The experiments are undertaken in dedicated ultra-low vibration labs. Projects are embedded in the Centre for Designer Quantum Materials, offering a vibrant and stimulating environment. Our work is highly collaborative, and usually we combine characterisation by multiple techniques with advanced numerical modelling using calcQPI.

If you have any questions, do not hesitate to get in touch. Submit applications through the University portal.

Last year we posted a preprint (arxiv, now published in Phys. Rev. Mat.) in which Luke suggested that it should be possible to stabilise the high-pressure superconductivity seen in La₃Ni₂O₇ in thin films at ambient pressure by exploiting epitaxial strain (see figure on the right), informed by Density Functional Theory calculations. Harold Hwang and collaborators have now reported evidence for ambient pressure superconductivity in strained thin films of La₃Ni₂O₇ (with independent confirmation from the group of Qi-kun Xue and Zhuoyu Chen)! Besides being exciting in its own right, the work opens up the possibility to study the gap structure by STM, QPI and ARPES to resolve the symmetry of the order parameter and pairing mechanism.

When Diracula gets rotten teeth 🎃 Van Hove singularities appear – read in our new paper, how to engineer sharper teeth through higher order Van Hove singularities. Congratulations to Kong, Vlad, Evgenia, Becca, and Siri for winning the Halloween pumpkin competition of the School!

Admittedly, the analogy has its flaws as it is blunter teeth in k-space that result in sharper Van Hove singularities …

Full reference:
A. Chandrasekaran, L.C. Rhodes, E.A. Morales, C.A. Marques, P.D.C. King, P. Wahl, and J.J. Betouras, On the engineering of higher-order Van Hove singularities in two dimensions, Nat. Commun. 15, 9521 (2024).