# Synopsis: Thin-Skinned Insulators

Researchers discover a subtle proximity effect at the interface between a normal metal and an antiferromagnetic insulator.

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 ($\text{Cu}$), grown on top of two insulators of distinct types, $\text{MgO}$ and $\text{CuO}$. 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 $\text{Cu}$) in the $\text{Cu}/\text{CuO}$ bilayers, which is not observed in the $\text{Cu}/\text{MgO}$ bilayers. Munakata et al. argue that the freezing of impurity spins is the consequence of an induced alternating spatial spin polarization inside $\text{Cu}$ by the antiferromagnetically ordered spins in $\text{CuO}$. 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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