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Superconductivity is a fascinating phenomenon that contains a rich spectrum of many-body physics. It is one of the most important topics in theoretical physics and a source of a host of practical applications such as permanent magnets for MRI. For a long time, it has been a fundamental belief that a hallmark feature of superconductivity is an inability to coexist with magnetism. However, in recent years this key feature of superconductivity has been disproved. Moreover, the growing body of experimental and theoretical evidence indicates that superconductivity itself can induce magnetism, leading to a superconducting state with broken time-reversal symmetry (BTRS). However, inconsistency between key experiments makes our understanding of this striking phenomenon very challenging. In this talk, I will show our recent results on unconventional superconductors with BTRS state. I will focus on two materials: Ba1-xKxFe2As2 and Sr2RuO4. The first one has the highest critical temperature among BTRS superconductors, and it is the first reported an s+is superconductor [1,2]. These unique properties make Ba1-xKxFe2As2 very promising for both fundamental studies and practical applications. Sr2RuO4 currently attracted a lot of attention. Despite being one of the most-studied materials in condensed matter physics, the origin of the superconductivity of Sr2RuO4 remains unknown. For many years it was thought to have a highly unusual spin-triplet, chiral order parameter [3-5]. Recent NMR data indicate more conventional singlet pairing [6], leading to a strong impact in the field. In turn, our recent experiments provide new evidence for BTRS superconductivity in Sr2RuO4 [7]. Moreover, these results suggest that chiral superconductivity is still a very strong possibility. Therefore, this system with possible a dxz+idyz chiral state present fundamental importance due to their nontrivial topology.
1. V. Grinenko et al., Phys. Rev. B 95, 214511 (2017).
2. V. Grinenko et al., Nat. Phys. 16, 789–794 (2020).
3. G. M. Luke, et al., Nature 394, 558 (1998).
4. F. Kidwingira et al., Science 314, 1267 (2006).
5. J. Xia et al., Phys. Rev. Lett. 97, 167002 (2006).
6. A. Pustogow et al., Nature 574, 72 (2019).
7. V. Grinenko et al., arXiv:2001.08152 (2020).
Dr. Vadim Grinenko graduated National Research Nuclear University (MEPhI), Moscow, Russia in 2004, with the specialization "Superconductivity and Nanotechnology". In 2008 he got a PhD degree in the Institute of Superconductivity and Solid State Physics, the part of National Research Center “Kurchatov Institute”, Russia. On results of the PhD work, he got a Russian Science Support Foundation prize in the nomination of "The best young doctors of the Russian Academy of Sciences”. At the end of 2008, he moved to Germany and joined IFW Dresden, Germany. He was working with applying the high temperatures superconductors in electrical motor and generators in collaboration with Toyota company. In 2012 he moved for one year to the Institute for Theoretical Solid State Physics, IFW-Dresden, Germany to work in the field of unconventional superconductivity. In 2013 Dr Grinenko moved to the Institute for Metallic Materials, IFW-Dresden, Germany. He was studying thin-film grows of iron-based superconductors. At the end of 2015 - present: he moved to the Institute of Solid State and Materials Physics, TU Dresden, Germany as principle investigator of DFG-project devoted to studying multiband superconductors that break time-reversal symmetry. This project is performed in strong collaboration with the Paul Scherrer Institut (PSI), Switzerland, where a big part of the research was performed. In 2016 Dr. Grinenko spent one month at Nagoya University (Graduate School of Engineering) as Associate Professor.