Tunneling Spectroscopy of Quantum Materials

Loop currents have been proposed as the origin of the pseudogap phase in the cuprate high-temperature superconductors, have been connected to the CDW phase of Kagome materials and proposed to occur at the surface layer of Sr₂RuO₄. These loop currents are extremely hard to detect, as they produce only tiny local magnetic fields. STM, being a local experimental technique, has been proposed as a way to detect them. In our recent preprint, we make realistic predictions for the signatures that loop currents would create in an STM experiment. Using our calcQPI code, we show that loop currents, in the presence of spin-orbit coupling, give rise to a spin polarization with a large enough signal to be detected by spin-polarized STM.

• V. Morisseau, L. C. Rhodes, P. Wahl, C. A. Marques, “How to measure loop currents in scanning tunneling microscopy”, arXiv:2607.20030 (2026).

Congratulations to Daniel Halliday for his PhD thesis on “Surface structure of the ruthenium oxides: correlating atomic displacements with electronic structure” and graduation earlier this month!

Condensed matter retreat at the Burn in Glenesk with lots of physics, some football and exciting discussions.

If you are interested in physics and art, come to see the exhibition Quantum Dialogues at the Byre Theatre – with exhibits on display 9th June until 31st July. Below ‘Superposition’ by Ru Christman with Siri Berge encapsulating the essence of real and momentum space, lattices, defects and the magic hiding behind atomic scale images obtained by quantum tunneling.

Ru (left) and Siri behind ‘Superposition’. If you are interested in this or other artworks by Ru Christman, see here.

It’s that time of year again – looking forward to our annual condensed matter retreat at the Burn in Glenesk and to an exciting programme and discussions. For more information see the dedicated webpage.

Submit an abstract by the (extended) submission deadline on 3 May for minicolloquia 02 and 06 at the CMD in Graz, with an exciting programme of invited speakers. Supported by ICAM-I2CAM, with limited funding available for travel bursaries for early career researchers.

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!