Superconducting spin smecticity evidencing the Fulde-Ferrell-Larkin-Ovchinnikov state in Sr2RuO4

Translational symmetry breaking in fluid is antagonistic but can be realized insuperconductivity, which is quantum-mechanical coherent fluid formed byelectron pairs. This novel superconducting state, known as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, can be induced by time-reversal-symmetrybreaking magnetic field applied to spin-singlet superconductors. This stateintrinsically causes the superconducting spin smecticity, spin-density-modulatedfluidity with spontaneous translational-symmetry breaking. Detection of suchspin smecticity provides indisputable evidence for the FFLO state but itsobservation has been quite challenging. Here, we report the characteristic“double-horn” nuclear-magnetic-resonance spectrum in the layeredsuperconductor Sr₂RuO₄ near its upper critical field, indicating the spatialsinusoidal modulation of spin density, namely the superconducting spinsmecticity. Our work reveals that Sr₂RuO₄ is an ideal compound for studyingthe FFLO physics.

These findings are published in 22nd Apr. 2022 in Science.

• Science
  “Superconducting spin smecticity evidencing the Fulde-Ferrell-Larkin-Ovchinnikov state in Sr₂RuO₄”
  https://doi.org/10.1126/science.abb0332
  
• Science Perspective
  “Superconductors gain momentum” by Eva Pavarini
  https://www.science.org/doi/10.1126/science.abn3794
  
• Kyoto University
  “Discovered superconducting state like liquid crystal predicted 60 years ago in oxide”
  https://www.kyoto-u.ac.jp/ja/research-news/2022-04-22