Observation of a neutron spin resonance in the bilayered superconductor CsCa2Fe4As4F2.
Abstract:
We report inelastic neutron scattering (INS) investigations on the bilayer Fe-based superconductor CsCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub> above and below its superconducting transition temperature T <sub>c</sub> ≈ 28.9 K to investigate the presence of a neutron spin resonance. This compound crystallises in a body-centred tetragonal lattice containing asymmetric double layers of Fe<sub>2</sub>As<sub>2</sub> separated by insulating CaF<sub>2</sub> layers and is known to be highly anisotropic. Our INS study clearly reveals the presence of a neutron spin resonance that exhibits higher intensity at lower momentum transfer (Q) at 5 K compared to 54 K, at an energy of 15 meV. The energy E <sub>R</sub> of the observed spin resonance is broadly consistent with the relationship E <sub>R</sub> = 4.9k <sub>B</sub> T <sub>c</sub>, but is slightly enhanced compared to the values observed in other Fe-based superconductors. We discuss the nature of the electron pairing symmetry by comparing the value of E <sub>R</sub> with that deduced from the total superconducting gap value integrated over the Fermi surface.Dynamic spin fluctuations in the frustrated A-site spinel CuAl2O4
Abstract:
© 2020 American Physical Society. We performed nuclear magnetic resonance (NMR) and muon spin relaxation (μSR) experiments to identify the magnetic ground state of the frustrated quantum A-site spinel, CuAl2O4. Our results verify that the ground state does not exhibit a long-range magnetic ordering, but a glasslike transition manifests at T∗=2.3K. However, the Gaussian shape and the weak longitudinal field dependence of μSR spectra below T∗ show that the ground state has dynamic spin fluctuations, distinct from those of conventional spin glasses.Magnetism and Néel skyrmion dynamics in GaV4S8-ySey
Magnetic order and ballistic spin transport in a sine-Gordon spin chain
Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor CaKFe4As4
Abstract:
The upper critical field of multiband superconductors is an important quantity that can reveal details about the nature of the superconducting pairing. Here we experimentally map out the complete upper-critical-field phase diagram of a stoichiometric superconductor, CaKFe4As4, up to 90 T for different orientations of the magnetic field and at temperatures down to 4.2K. The upper critical fields are extremely large, reaching values close to ∼3 Tc at the lowest temperature, and the anisotropy decreases dramatically with temperature, leading to essentially isotropic superconductivity at 4.2K. We find that the temperature dependence of the upper critical field can be well described by a two-band model in the clean limit with band-coupling parameters favoring intraband over interband interactions. The large Pauli paramagnetic effects together with the presence of the shallow bands is consistent with the stabilization of an FFLO state at low temperatures in this clean superconductor.