A team of physicists at Université Grenoble Alpes, CNRS, in France, working with a colleague from Karlsruhe Institute of Technology, in Germany, has observed an odd quantum phase transition in indium oxide films. In their study published in the journal Nature Physics, the group used microwave spectroscopy to study the internal properties and behavior of indium oxide films as they transitioned between superconducting and insulating states.
Prior research has shown that when a superconductor undergoes a phase transition between superconductivity and insulation, its superfluid stiffness generally occurs in a smooth, continuous fashion. Superfluid stiffness is a measurement that has been developed to gauge how resistant a material is to changing from one phase to another. In this new study, the research team found an exception to that rule in indium oxide films.
In their work, the researchers were investigating the properties of indium oxide, a material that, when chilled to a certain temperature, changes to a superconductor—it is also known to have multiple disorders at multiple levels. Such disorders give the material unusual properties.
To learn more about them, the research team first created indium oxide films in order to use microwave spectroscopy, a tool that lets them monitor the superfluid stiffness of a sample. They found that rather than seeing the expected gradual shift as a phase change occurred due to a rise in temperature, there was a sharp drop.
They also noted that during the phase change, the critical temperature was not determined by how strongly the Cooper pairs (pairs of electrons that form during transitions that move in a coordinated fashion) moved together—instead, it was determined by the superfluid stiffness. The researchers were not able to find an explanation for that.
In concluding their research, the group stated that the behavior exhibited by indium oxide films was not only rare, but could open up new avenues of research involving the use of quantum materials, perhaps leading to a way to make them more stable.
More information:
Thibault Charpentier et al, First-order quantum breakdown of superconductivity in an amorphous superconductor, Nature Physics (2025). DOI: 10.1038/s41567-024-02713-8
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Quantum phase transition in indium oxide films defies superconductor norms (2025, January 6)
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