Abstract

Any superconducting (SC) state breaks spontaneously U(1) gauge symmetry at the SC transition temperature (T_c). In some cases, an SC state breaks in addition time reversal symmetry (Z₂). Usually, Z₂ is broken at T_c^Z2 ≤ T_c. However, it was predicted that fluctuations could push T_c below T_c^Z2 [1]. Here, we study the multiband Ba_1-xK_xFe₂As₂ system experimentally. At high K doping levels, Lifshitz transition triggers superconductivity that breaks time reversal symmetry (BTRS) [2,3]. The BTRS SC state exists at a narrow doping range of 0.7 ≤ x ≤ 0.85. The most intriguing is that at x ~ 0.8, we found the BTRS state at  T_c^Z2 > T_c [4]. Based on the theoretical analysis, we proposed that T_c^Z2 is associated with a quartic order - a correlated state between pairs of Cooper pairs.

[1] T. A. Bojesen, E. Babaev, and A. Sudbø, Phys. Rev. B 89, 104509 (2014).
[2] V. Grinenko, P. Materne, R. Sarkar et al., Phys. Rev. B 95, 214511 (2017).
[2] V. Grinenko, R. Sarkar, K. Kihou et al., Nat. Phys. 16, 789–794 (2020).
[3] V. Grinenko, D. Weston, F. Caglieris et al., Nat. Phys. 17, 1254–1259 (2021).

Short CV

Prof. Vadim Grinenko

Tsung Dao Lee Institute, 520 Shengrong Road, Pudong New Area, Shanghai 201210, China

Professional Experience

2022-present T. D. Lee Fellow, Tsung-Dao Lee Institute
Tenure Track Associate Professor, School of Physics and Astronomy, Shanghai Jiao Tong University
2015-2022 scientist, principal investigator of a DFG project Institute of Solid State and Materials Physics, TU Dresden, Germany
2008-2015 scientist, Institute for Metallic Materials, IFW Dresden, Germany

Education Background

2004- 2008 Doctor of Philosophy (Ph. D.) Institute of Superconductivity and Solid State Physics, National Research Center "Kurchatov Institute", Russia
1997- 2004 Master of Science (M. Sc.), Superconductivity and Nanotechnology, National Research Nuclear University, EPhI, Russia