Degenerated superconductivity and fluctuation induced phases in multiband systems: Sr2RuO4 and Ba1-xKxFe2As2

Date

Mar 16, 2023

Time

1:00 PM - 2:00 PM

Speaker

Prof. Hans-Henning Klauss

Affiliation

TU Dresden

Language

en

Main Topic

Materialien

Host

Dr. Silvia Seiro

Description

From the very beginning of quantum mechanics the concept of degeneracy of states has been an important topic throughout the quantum world. For example, the Landau-Zener dynamics of avoided level crossing describes quantum tunneling in single-molecule magnets as well as the deficiency in the flux of solar electron neutrinos at the earth. In solid state physics degeneracy can lead to multi-component order-parameters in symmetry broken phases such as superconductors and magnets. The topologically non-trivial skyrmion phase in the itinerant ferromagnet MnSi can be described as a triple-q antiferromagnet. In particular in multi-band superconductors the degeneracy of superconducting order parameters with the same or different symmetry can lead to a coherent superposition. Unlike in magnets these states are experimentally difficult to detect. One indication is the appearance of time-reversal symmetry breaking (TRSB) superconductivity. In my talk I will discuss two important systems in this context. In Sr2RuO4 we used uniaxial and hydrostatic pressure muon spin relaxation (µSR) experiments [1,2] to prove the two-component nature of the superconducting state using the concept of explicit symmetry breaking under uniaxial pressure. I will present uniaxial pressure studies along (100) and (110) directions in this system and discuss the implications on the superconducting state. In Ba1-xKxFe2As2 we found TRSB superconductivity in µSR experiments at high doping x~0.8 due to the competition of single-component order parameters with different symmetry [3]. This competition appears close to a Lifshitz transition of the multi-band fermi surface. Supported by detailed thermodynamic and transport experiments we found a new TRSB phase also above TC. This state can be understood as a fluctuation-induced Z2 symmetry breaking with four fermion correlations [4]. [1] V. Grinenko, S. Ghosh, et al., Nat. Phys. 17, 748 (2021),[2] V. Grinenko, et al., Nat. Comm. 12, 3920 (2021),[3] V. Grinenko, et al., Nat. Phys.1, 789 (2020), [4] V. Grinenko, et al., Nat. Phys. 17, 1245 (2021).

Links

• Seminars at the IFW

Last modified: Mar 16, 2023, 7:40:07 AM