•G. Goll¹, F. Laube¹, H. v. Löhneysen^1,2 und F. Lichtenberg^3
1Physikalisches Institut, Universität Karlsruhe, 76128 Karlsruhe
²Forschungszentrum Karlsruhe, Institut für Festkörperphysik, 76021 Karlsruhe
³Experimentalphysik VI, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universität Augsburg, 86135 Augsburg

A low-temperature magnetic-field induced insulating state in the normal state of the unconventional superconductor Sr₂RuO₄ has been detected by point-contact spectroscopy: For Pt-Sr₂RuO₄ heterocontacts in a large applied magnetic field a conductance minimum occurs in dI/dV vs V around V = 0 which becomes more pronounced with increasing field and persists up to several K. We observe this minimum in field only when structures attributed to superconductivity (T_c = 1.5 K) are found in the superconducting phase as well [1], suggesting that this minimum is a property of Sr₂RuO₄ and does not originate from a strongly disordered layer at the surface. The minimum occurs independent of the relative field-to-surface orientation. Its depth increases with increasing field, reaching a few percent relative to the background, while the width remains nearly constant within the accuracy of the measurement. The origin of this minimum is not yet understood. Several scenarios, including magnetic or Kondo-type origin, a lattice distortion at the surface or a structural instability of Sr₂RuO₄, will be discussed.