Tunneling Spectroscopy of Quantum Materials

Does the surface of a strongly correlated electron material have the same properties of the bulk? Dan’s new paper (https://lnkd.in/e_nD57-Q) shows from an incredibly detailed structural characterization of the surface of Ca₃Ru₂O₇ how distortions stabilize a surface Mott insulator – seems a common theme in ruthenates that they respond highly sensitively to tiny structural distortions. Great collaborative work within the Centre for Designer Quantum Materials (https://www.cdqm.uk) with the group of Phil King combining structural characterization by low energy electron diffraction with ARPES, STM and DFT calculations, and with samples from MPI Dresden.

Full reference:
Daniel Halliday, Izidor Benedičič, Andela Zivanovic, Masahiro Naritsuka, Brendan Edwards, Tommaso Antonelli, Naoki Kikugawa, Dmitry A. Sokolov, Craig Polley, Andrew P. Mackenzie, Georg Held, Phil D. C. King, and Peter Wahl, Correlated insulator at the surface of the polar metal Ca₃Ru₂O₇, Phys. Rev. Lett. 137, 096503 (2026).

How does the quasiparticle interference (QPI) of moiré-induced flat bands look like? Read Bruno’s preprint (https://arxiv.org/abs/2511.05648) about a new route to stabilise flat bands in emergent moiré periodicities, and how the flat bands look like in ARPES and QPI. Not only do we show QPI of the flat bands, but the manuscript introduces a new way to stabilise functional moiré heterostructures by exploiting CDW periodicities. Great collaboration with the group of Phil King and the Centre for Designer Quantum Materials (https://www.cdqm.uk/).

How can one use real space imaging to obtain k-space information of the electronic states in a material? Our preprint on quasiparticle interference imaging of strongly correlated and 2D materials summarises the state of the art in theory and experiment and is an attempt at a comprehensive review. Great collaboration across continents, with contributions from Luke Rhodes, Yuhki Kohsaka, Tetsuo Hanaguri, and Carolina Marques.

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.