Physicists offer explanation for strange magnetic behavior at semiconductor interfaces

Aug 25, 2013 by Pam Frost Gorder
Electronic orbitals and charge localization. a, Schematic of Tit2g energy levels. At the interface dxy is lower than the dyz and dxz orbitals. Vconf(z) is the confining potential. b, Phase diagram of the single-band extended Hubbard model at quarter-filling. A COI is obtained for moderate values of on-site Hubbard U and next-neighbour Coulomb V, above the (solid red) phase boundary. Coupling to the breathing-mode phonon further stabilizes the COI. Credit: Nature, DOI: 10.1038/nphys2702

The new discovery could one day lead to electronic materials that provide both computation and data storage.

They're not exactly the peanut butter and jelly of semiconductors, but when you put them together, something magical happens.

Alone, neither aluminate nor strontium exhibit any particularly notable properties. But when they are layered together, they become not only conductive, but also magnetic.

In the current online edition of Nature Physics, researchers at The Ohio State University report the first-ever theoretical explanation to be offered for this phenomenon since it was discovered in 2004.

Understanding how these two semiconductors interact at their interface could someday lead to a different kind of material—one that provides a single platform for computation and , said Mohit Randeria, co-author of the paper and professor of physics at Ohio State.

"The whole question is, how can you take two materials which do not conduct electricity and do not have , make a sandwich out of them and—lo and behold—at the interface tween them, charge begins to flow and interesting happen?" he said.

"It's like taking two pieces of bread and putting them together and having the sandwich filling magically appear."

By making calculations and modeling the basic physical properties of both materials, Randeria's team has hit upon an explanation for the behavior that seems ironic: the interface between two non- exhibits magnetism.

The team showed how the elemental units of magnetism, called "local moments," are formed at the interface of the two materials. They then showed how these moments interact with the conducting electrons to give rise to a magnetic state in which the moments are arranged in an unusual spiral pattern.

If the physicists' explanation is correct, then perhaps someday, electronic devices could be constructed that exploit the interface between two oxides. Theoretically, such devices would combine the computational abilities of a silicon chip with the magnetic data storage abilities of permanent magnets like iron.

"If you had conduction and magnetism available in the same platform, it could be possible to integrate computer memory with data processing. Maybe different kinds of computation would be possible," Randeria said.

But those applications are a long way off. Right now, the physicists hope that their for the strange magnetic behavior will enable other researchers to perform experiments and confirm it.

Randeria's coauthors included Ohio State postdoctoral researcher Sumilan Banerjee and former doctoral student Onur Erten, who graduated this summer and is about to begin a postdoctoral fellowship at Rutgers, The State University of New Jersey.

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More information: Ferromagnetic exchange, spin–orbit coupling and spiral magnetism at the LaAlO3=SrTiO3 interface, DOI: 10.1038/nphys2702

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