Details

Autor(en) / Beteiligte

• Pustogow, A.
• Luo, Yongkang
• Chronister, A.
• Su, Y.-S.
• Sokolov, D. A.
• Jerzembeck, F.
• Mackenzie, A. P.
• Hicks, C. W.
• Kikugawa, N.
• Raghu, S.
• Bauer, E. D.
• Brown, S. E.

Titel

Constraints on the superconducting order parameter in Sr2RuO4 from oxygen-17 nuclear magnetic resonance

Ist Teil von

• Nature (London), 2019-10, Vol.574 (7776), p.72-75

Ort / Verlag

London: Nature Publishing Group UK

Erscheinungsjahr

2019

Beschreibungen/Notizen

• Phases of matter are usually identified through spontaneous symmetry breaking, especially regarding unconventional superconductivity and the interactions from which it originates. In that context, the superconducting state of the quasi-two-dimensional and strongly correlated perovskite Sr 2 RuO 4 is considered to be the only solid-state analogue to the superfluid 3 He-A phase 1 , 2 , with an odd-parity order parameter that is unidirectional in spin space for all electron momenta and breaks time-reversal symmetry. This characterization was recently called into question by a search for an expected ‘split’ transition in a Sr 2 RuO 4 crystal under in-plane uniaxial pressure, which failed to find any such evidence; instead, a dramatic rise and a peak in a single-transition temperature were observed 3 , 4 . Here we use nuclear magnetic resonance (NMR) spectroscopy of oxygen-17, which is directly sensitive to the order parameter via hyperfine coupling to the electronic spin degrees of freedom, to probe the nature of superconductivity in Sr 2 RuO 4 and its evolution under strain. A reduction of the Knight shift is observed for all strain values and at temperatures below the critical temperature, consistent with a drop in spin polarization in the superconducting state. In unstrained samples, our results contradict a body of previous NMR work reporting no change in the Knight shift 5 and the most prevalent theoretical interpretation of the order parameter as a chiral p -wave state. Sr 2 RuO 4 is an extremely clean layered perovskite and its superconductivity emerges from a strongly correlated Fermi liquid, and our work imposes tight constraints on the order parameter symmetry of this archetypal system. 17 O nuclear magnetic resonance measurements on Sr 2 RuO 4 reveal a drop of the Knight shift in the superconducting state, contradicting previous work and imposing tight constraints on the order parameter symmetry of the system.