We measured 101Ru Knight shift (101K) in Sr 2RuO4 superconductor under low magnetic fields parallel to the RuO2 plane (ab direction) in order to determine the direction of superconducting d vector in zero magnetic field. Kab was measured in a small field down to 550 Oe and in a temperature range down to 97 mK, by using nuclear-quadrupole-resonance (NQR) spectra. We found that Kab is invariant with respect to temperature on passing through Tc. Our results indicate that the spins of the superconducting pair are in the RuO 2 plane (with the superconducting d vector pointing in the c direction) when fields greater than 550 Oe are applied to the RuO2 plane. Taking into account the previous results that 101K is unchanged in the superconducting state when fields greater than 200 Oe are applied along the c axis. We suggest that the effect to fix the spins of the superconducting pairs in a certain crystal direction is weak in Sr 2RuO4 even if there exists a significant spin-orbit interaction originating from the Ru-4d orbitals and additional interactions between the chiral Cooper-pair electrons.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)