Nuclear magnetic resonance investigation of nematicity, superconductivity, and their interplay in FeSe

• Applicant: Dr. Seung-Ho Baek, Ph.D.
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2013 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 236584220

Firstly, in order to verify the close link between antiferromagnetic (AFM) spin fluctuations and the superconducting pairing mechanism, we will measure the pressure dependence of spin fluctuations in highquality FeSe single crystals using a standard BeCu clamp-type hybrid pressure cell (up to 3 GPa) with a hydrostatic pressure medium. If the AFM spin fluctuations were indeed connected to superconductivity, one has to assume that spin-lattice relaxation rate as a function of pressure is strongly anisotropic, corresponding to the anisotropic superconductivity. If confirmed, this will provide long-sought direct evidence for spin fluctuation mediated Cooper pairing. Secondly, we will carry out the NMR study on a detwinned single crystal, taking advantage of the strains applied by a piezo material. In the nematic state, the changes of nematic order parameter and the superconducting properties will be examined as a function of temperature and field orientations. These detwinning experiments will allow us to probe the interplay between nematic and superconducting orders. In addition, the effects of inhomogeneity on nematicity and superconductivity would be investigated.

• DFG Programme: Research Grants