Magnetic field dependence of the atomic and electronic structure of monovalent metallic nanocontacts unveiled in transport experiments

We measure Au and Ag atomic-size contacts in magnetic fields, from zero field to 20 T. We find a magnetic field induced torque which leads to atomic binding at shorter distances than at zero field. Furthermore, the conductance drops below G₀ at high magnetic fields by about 15% in Au. We calculate the conduction through nanosized Au contacts containing residual O₂ molecules attached to the contact region and find a spin polarized current when O₂ is located at the atomic contact. We discuss the role of spin-orbit coupling in the magnetic properties of O₂ attached to Au.