Material Physics

From Nanocurrents to Superconductors

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© CEA-GONIN

The neutron guides of the Orphée reactor, in Saclay, direct the neutron flux, generated in the heart of the reactor, to the sample.

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Using Orphée, the highest neutron flux medium-size reactor in Europe, scientists from CNRS and CEA, led by Dr. Philippe Bourges,¹ have made a major advance in the process of understanding superconductivity in high-temperature superconductors like copper oxides.²

Superconductivity is a state that occurs in certain metallic materials when cooled to extremely low temperatures. It is characterized by, among other things, the loss of all electrical resistance, meaning that once generated, the electrical current will flow on forever. Understanding superconductivity, which takes place when the normal metallic state becomes unstable, requires understanding the nature of the normal state itself. Bourges's team actually worked on copper-oxides, which are a particular type of superconductors with a transition temperature much higher than that of conventional metallic superconductors (-135°C instead of -250°C). They are therefore called high-temperature superconductors. Interestingly, well above their transition temperature, copper oxides behave as strange metals, with unusual electronic properties.

Using neutron scattering³ on high-temperature superconductors, Bourges's team observed a novel magnetic structure of the material when cooling it down from room temperature toward superconductivity. This magnetic state could correspond to a spontaneous circulation of microscopic currents, as theoretically proposed by C.M. Varma (University of Riverside, California),⁴ who argues that superconductivity would emerge from such a novel state.

But more experiments are needed to further explain the origin of this novel magnetic state, and to understand its role in superconductivity. A challenging goal, since developing room-temperature superconductors could potentially trigger a new industrial revolution.

Marion Girault-Rime