US scientists have discovered that ruthenium compound layered perovskite (Ca_1.9Sr_0.1RuO₄) undergoes a metal-insulator transition (MIT) at significantly lower temperature than other materials with an odd number of ions.

The team, which included researchers from several US colleges, found that the transition to its metallic phase occurs at 130 kelvin compared with the bulk transition temperature of 154 kelvin, sciencemag.com reports.

The scientists have posited that this is due to surface stresses that allow the calcium Ca and strontium Sr ions to be pulled into the bulk, thus stabilising a surface phase that favours the Mott insulator ground state relative to the bulk structure.

This means that the MIT can occur before the phase transition.

Research into the properties of the compound was conducted by R.G. Moore of the Department of Physics and Astronomy, University of Tennessee and eminent scientists from a number of other US facilities.

Source:

A Surface-Tailored, Purely Electronic, Mott Metal-to-Insulator Transition
http://www.sciencemag.org/cgi/content/abstract/318/5850/615

A Stress on the Insulating Phase, 26/10/07
http://www.sciencemag.org/content/vol318/issue5850/twis.dtl#318/5850/529d

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