Synopsis: Thin-Skinned Insulators

Researchers discover a subtle proximity effect at the interface between a normal metal and an antiferromagnetic insulator.
Synopsis figure
K. Munakata et al., Phys. Rev. B (2011)

The so-called proximity effect manifests itself as a mutual induction of physical properties from one material into an adjacent one, across their interface. In the most famous example, superconducting electron pairs are induced in a neighboring normal metal, and conversely, normal electrons in the metal permeate the superconductor. However, at the interface between a metal and an insulator, one would not expect such a behavior. Now, in a Rapid Communication published in Physical Review B, Ko Munakata and collaborators from Stanford University, California, present evidence for a subtle proximity effect that arises between a normal metal and an antiferromagnetic insulator.

The researchers compare bilayers of an ordinary metal, copper (Cu), grown on top of two insulators of distinct types, MgO and CuO. The former is a conventional band insulator, while the latter is an antiferromagnetic Mott insulator, a material where strong Coulomb interactions prohibit electronic conduction. Low-temperature transport measurements show that the well-understood effects of weak localization due to material disorder are different in the two cases. Their analysis shows that the difference arises from a quenching of spin-flip scattering from trace magnetic impurities (commonly found in pure Cu) in the Cu/CuO bilayers, which is not observed in the Cu/MgO bilayers. Munakata et al. argue that the freezing of impurity spins is the consequence of an induced alternating spatial spin polarization inside Cu by the antiferromagnetically ordered spins in CuO. These results not only demonstrate a new phenomenon but may also provide a new mechanism to control spins at solid-state interfaces and possible applications in spintronic devices. – Alex Klironomos


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