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Cobaltates
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Cobaltates

A thirsty superconductor

In 2003, in the scientific journal Nature, a Japanese team announced they had discovered superconductivity in an oxide containing cobalt triangular layers, but only when water was added !

In 2003, in the scientific journal Nature, a Japanese team announced they had discovered superconductivity in an oxide containing cobalt triangular layers, but only when water was added ! A few years before, surprising thermoelectric powers had already been observed in this oxide: this material converts heat in electricity better than any other. A new research subject was born… These materials are not superconducting. However, when water molecules are added between the sodium layers and the cobalt layers, they become superconducting under 4 K, -269°C. Of course, this temperature is really low and not very promising as far as applications are concerned. However, this phenomenon is very strange for superconductivity specialists: why would water molecules, totally inert from an electric point of view, enable superconductivity? In that particular case, what mechanism enables the electrons to attract each other and form Cooper pairs? Is it a classical superconductivity as in aluminium or niobium, or on the contrary is it an exotic mechanism as in high-temperature superconductors?

Cobaltates properties against dopingPhysicists and chemists like to show what happens to these cobalt oxides depending on their doping (the number of sodium atoms) on a “phase diagram” (FIGURE). At a low temperature, the same compound appears to be both insulating and magnetically ordered for some very specific compositions, and superconducting for other compositions.

 

 

 

CNRSSociété Française de PhysiqueTriangle de la physique
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CNRSSociété Française de PhysiqueTriangle de la physique