Christoph Renner: Electronic Vortex Core Structure of a d-Wave High Temperature Superconductor

Abstract:
High temperature superconductivity (HTS) in copper oxides keeps challenging our understanding. Among the outstanding puzzles is the electronic structure of the Abrikosov vortex cores. The fundamental excitations bound to magnetic vortices in type-II superconductors carry information about essential properties of the superconducting state. Their proper identification is therefore of prime interest to elucidate the mechanism driving HTS. We will review recent vortex core studies and present new scanning tunneling microscopy data [1] at low magnetic field, which unveil the d wave electronic structure of the vortex core predicted by Wang and MacDonald in 1995 [2]. We show that previously reported unconventional electronic structures, including the checkerboard charge order in the vortex halo and the absence of a zero-bias conductance peak at the vortex center, are direct consequences of short inter-vortex distance and consequent vortex-vortex interactions prevailing in earlier experiments done at significantly higher field. The remarkable change of the spectroscopic footprint of the vortex cores we find between 0.16 Tesla and 3 Tesla is surprising for such a low energy scale and calls for further investigations.

[1] Gazdic, T., et al., arXiv:2103.05994, 2021.

[2] Y. Wang and A. H. MacDonald, Physical Review B 52, R3876 (1995).

Biography:

Christoph Renner is professor of physics at the department of quantum matter physics at the University of Geneva, Switzerland. He is leading a research group investigating electronic ground states and their interplay in low dimensional correlated electron systems using scanning probe microscopy and spectroscopy. Prior to joining Geneva in 2006, he was appointed senior and then principal research fellow at University College London (UCL), with affiliations in the London Centre for Nanotechnology (LCN), the Department of Physics & Astronomy, and the Department of Medicine. During his time in London, he was also a business fellow of the London Technology Network. Before moving to UCL, he held a visiting scientist position at the NEC Research Institute in Princeton.

With over 30 years of experience, Prof. Renner is an expert in developing and applying variable temperature scanning tunnelling microscopy to study correlated electron materials, in particular superconducting, charge ordered and low dimensional systems. His research is published in leading academic journals and has been selected as a physics highlight of 2017 by the editors of Physics. Currently, his team is focusing on high temperature superconductors and spectroscopy of tuneable electronic properties in transition metal dichalcogenides and devices by means of strain, space charge doping and thickness. Among recent scientific successes are the observation of the intrinsic vortex core signature expected for a superconductor whose gap has d-wave symmetry, the link between CDW contrast inversion in STM images and the CDW gap well below the Fermi level, and the exposure of a multiband CDW in a transition metal dichalcogenide.

Interested in public outreach, Prof. Renner was founding director of the Physiscope of the University of Geneva between 2007 and 2017. Since 2014, he is a founding member and president of the Scienscope, an initiative introducing junior and high school children as well as the public to science in a hands-on and entertaining manner. Prof. Renner is also actively promoting collaborations with industry, founding member and president of the Laboratory for Advanced Technology, a gateway supporting innovation by facilitating industry access to the competences and equipment at the University of Geneva. He was vice president of the physics section (2011-2014) and, since 2014, he is vice dean for innovation and infrastructures of the Faculty of Science of the University of Geneva.

Prof. Renner holds a PhD degree from the University of Geneva. He received the Jean Würth award for best PhD Thesis and the IBM award of the Swiss Physical Society. As hobbies, he enjoys piloting, travelling and cooking.