Tunneling Spectroscopy of Quantum Materials

How does a Lifshitz transition look like in real space? Cool data hot off the press in Carolina and Luke’s new paper in Science Advances (here), imaging a magnetic-field induced Lifshitz transition in the surface layer of Sr₃Ru₂O₇ with our millikelvin STM. Lot’s of new puzzles. For example, why do stripes appear in magnetic field? Why is QPI so anisotropic? What does the behaviour of the surface tell us about the bulk? Stay tuned for more!

Can we link the shape of a domain wall in a van der Waals (vdW) ferromagnet to microscopic interaction parameters? Yes we can! Read our new paper to find out how we can link the details of the magnon dispersion from neutron scattering to the shape of a domain wall as measured by spin-polarized STM in the vdW ferromagnetic metal Fe_3-xGeTe₂.

C. Trainer et al., Physical Review B 106, L081405 (2022).

Meet us and hear about our research at the CMQM 2022 conference in Bath (20-22 June 2022). Here is a list of our contributions:

• Carolina de Almeida Marques on Monday, 15:25pm: Atomic-scale imaging of emergent order at a magnetic-field-induced Lifshitz transition.
• Olivia Armitage on Monday, 16:00pm (invited): Spin-polarised imaging and quasi-particle interference of the van-der-Waals ferromagnet Fe₃GeTe₂.
• Liam S. Farrar on Tuesday, 12:00pm: Electronic and magnetic structure of Fe₃Sn₂ characterised by scanning tunnelling microscopy.
• Luke C. Rhodes on Wednesday, 11:30am: Imaging the field-induced changes in the electronic structure of metamagnetic Sr₄Ru₃O₁₀.
• Izidor Benedičič on Wednesday, 11:45am: Compass-like manipulation of nematicity in Sr₃Ru₂O₇.
• Daniel Halliday with a poster on Revisiting the surface reconstruction of Sr₂RuO₄.

Congratulations to Carolina Marques who was awarded the IOP Superconductivity Group Thesis Prize for “the best thesis in the field of superconductivity submitted for a PhD in the UK or Ireland in a given year”!👏

In her thesis on “Imaging emergent correlated phases in the strontium ruthenates” Carolina has used ultra-low temperature STM to map out exotic electronic states found at the surfaces of ruthenates, revealing novel phases, a plethora of van-Hove singularities and a hitherto largely unexplored new playground to study correlated electron physics.

The 2022 recruitment round for PhD positions is open!

PhD positions are available, funded through a number of routes, including through EPSRC DTG places and an International Max Planck Research School. 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.

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

In a new paper in npj Quantum Materials we show how small rotations of the ruthenium oxide octahedra in the enigmatic superconductor Sr₂RuO₄ enable us to detect its van Hove singularity, which would otherwise be practically invisible for us due to its orbital character. Modelling of the quasiparticle interference shows excellent agreement with experiment once the rotation of the octahedra is accounted for, resulting in chiral scattering patterns around defects.

Analogous to Magellan’s circumnavigation of the earth enabling him to deduce information about the shape of the earth in 3D from its surface, read our new paper in Nature Communications to find out how we can use 2D quasi-particle interference at the surface of a rock to infer information about its 3D electronic structure.

Read our new paper in Physical Review Letters to find out how one can use helium to measure exchange interactions between a sample and the tip of a Scanning Tunneling Microscope. We show that helium becomes trapped in the tunneling junction, but can be ejected by the tunneling electrons enabling us to spatially map its binding energy. Alternative title could have been ‘how a helium leak enabled us to probe exchange interactions’.

Meet members of the group and hear about our most recent results in the following talks and posters at the virtual meeting of the condensed matter section of the DPG (27 September – 1 October 2021, see here for a list of our contributions, note that times are CEST (UTC+2)):

• Christopher Trainer on Monday, 27.9., 10:30, talk MA 1.2: The effect of trapped Helium atoms on spin polarized tunneling in an STM tunnel junction
• Olivia Armitage on Tuesday, 28.9., 10:30, talk MA 4.2: Spin-polarised imaging and quasi-particle interference of the van-der-Waals ferromagnet Fe₃GeTe₂
• Izidor Benedičič on Tuesday, 28.9., 13:30, poster TT 9.27: Anisotropic metamagnetism in trilayer ruthenate Sr₄Ru₃O₁₀
• Carolina Marques on Thursday, 30.9., 12:15, talk TT 19.5: Nematicity and checkerboard order in the surface layer of Sr₂RuO₄

In addition, Andreas Kreisel from University of Leipzig will talk about our joint work on Sr₂RuO₄ on Thursday, 30.9., 12:30, in talk TT 19.6 on Quasiparticle Interference of the van-Hove singularity in Sr₂RuO₄.

Our paper on magnetic-field tunable van-Hove singularities in Sr₂RuO₄ featured on the back cover of Advanced Materials. The image shows the structure of the van-Hove singularity and the two order parameters required to obtain it, nematicity and checkerboard charge order.

Read more in the original reference: Magnetic-Field Tunable Intertwined Checkerboard Charge Order and Nematicity in the Surface Layer of Sr₂RuO₄, 2021, 32, 2100593.

Cover image © Wiley-VCH GmbH. Reproduced with permission.