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Register a new userA polarized neutron-scattering study of the Cooper-pair moment in Sr2RuO4
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We report a study of the magnetization density in the mixed state of the unconventional superconductor S2RuO4. On entering the superconducting state we find no change in the magnitude or distribution of the induced moment for a magnetic field of 1 Tesla applied within the RuO2 planes. Our results are consistent with a spin-triplet Cooper pairing with spins lying in the basal plane. This is in contrast with similar experiments performed on conventional and high-Tc superconductors.
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Recent observations [A.~Pustogow et al. Nature 574, 72 (2019)] of a drop of the $^{17}$O nuclear magnetic resonance (NMR) Knight shift in the superconducting state of Sr$_2$RuO$_4$ challenged the popular picture of a chiral odd-parity paired state in this compound. Here we use polarized neutron scattering to show that there is a $34 pm 6$ % drop in the magnetic susceptibility at the ruthenium site below the superconducting transition temperature. Measurements are made at lower fields $H sim tfrac{1}{3} H_{c2}$ than a previous study allowing the suppression to be observed. Our results are consistent with the recent NMR observations and rule out the chiral odd-parity $mathbf{d}=hat{mathbf{z}}(k_xpm ik_y)$ state. The observed susceptibility is consistent with several recent proposals including even-parity $B_{1g}$ and odd-parity helical states.
We have investigated the ac susceptibility of the spin triplet superconductor Sr$_2$RuO$_4$ as a function of magnetic field in various directions at temperatures down to 60 mK. We have focused on the in-plane field configuration (polar angle $theta simeq 90^{circ}$), which is a prerequisite for inducing multiple superconducting phases in Sr$_2$RuO$_4$. We have found that the previous attribution of a pronounced feature in the ac susceptibility to the second superconducting transition itself is not in accord with recent measurements of the thermal conductivity or of the specific heat. We propose that the pronounced feature is a consequence of additional involvement of vortex pinning originating from the second superconducting transition.
We use radio-frequency reflectometry to measure quasiparticle tunneling rates in the single-Cooper-pair-transistor. Devices with and without quasiparticle traps in proximity to the island are studied. A $10^2$ to $10^3$-fold reduction in the quasiparticle tunneling rate onto the island is observed in the case of quasiparticle traps. In the quasiparticle trap samples we also measure a commensurate decrease in quasiparticle tunneling rate off the island.
The eutectic system Sr2RuO4-Ru is referred to as the 3-K phase of the spin-triplet supeconductor Sr2RuO4 because of its enhanced superconducting transition temperature Tc of ~3 K. We have investigated the field-temperature (H-T) phase diagram of the 3-K phase for fields parallel and perpendicular to the ab-plane of Sr2RuO4, using out-of-plane resistivity measurements. We have found an upturn curvature in the Hc2(T) curve for H // c, and a rather gradual temperature dependence of Hc2 close to Tc for both H // ab and H // c. We have also investigated the dependence of Hc2 on the angle between the field and the ab-plane at several temperatures. Fitting the Ginzburg-Landau effective-mass model apparently fails to reproduce the angle dependence, particularly near H // c and at low temperatures. We propose that all of these charecteric features can be explained, at least in a qualitative fashion, on the basis of a theory by Sigrist and Monien that assumes surface superconductivity with a two-component order parameter occurring at the interface between Sr2RuO4 and Ru inclusions. This provides evidence of the chiral state postulated for the 1.5-K phase by several experiments.
We observed in superconducting (Tl,Rb)2Fe4Se5 spin-wave branches that span an energy range from 6.5 to 209 meV. Spin dynamics are successfully described by a Heisenberg localized spin model whose dominant in-plane interactions include only the nearest (J1 and J1) and next nearest neighbor (J2 and J2) exchange terms within and between the tetramer spin blocks, respectively. These experimentally determined exchange constants would crucially constrain the theoretical viewpoints on magnetism and superconductivity in the Fe-based materials.
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