The discovery challenges existing theories: physicists observed unusual quantum behavior in superconductors.

A new study reveals that highly disordered superconductors exhibit a first-order quantum phase transition. This transition occurs abruptly from a superconducting state to an insulating state. This discovery is truly astonishing, as such sudden changes are not typically observed in superconductors. Normally, they undergo second-order quantum phase transitions, which are slow and gradual. Physicists believe that the sharp phase transitions identified could aid in the development of new quantum materials. The research is published in the journal Nature Physics, as reported by Interesting Engineering.

Phase transitions refer to changes in a material's state, such as transitioning from solid to liquid or from superconducting to insulating. These changes occur when certain parameters, like temperature or pressure, cross a critical threshold.

Another property that influences phase transition is known as superfluid stiffness. This measures how resistant the superconducting state of a material is to phase changes, playing a crucial role in understanding how superconductivity is disrupted during phase transitions.

Typically, when superconductors undergo a phase transition, superfluid stiffness decreases continuously and smoothly. However, physicists observed something unusual while studying amorphous indium oxide films. Indium oxide possesses several structural, chemical, and atomic defects. To understand how these defects can be precisely tuned, physicists examined how the material behaves as it becomes more disordered.

To achieve this, researchers employed microwave spectroscopy, a method that allowed for accurate measurement of the superfluid stiffness of indium oxide. The study revealed that instead of a gradual change, there was an unexpectedly sharp drop in the superfluid stiffness of the indium oxide films.

The material behaves as a superconductor when pairs of electrons, known as Cooper pairs, move together in a coordinated manner. During the study, physicists found that introducing disorder into the material caused the Cooper pairs to behave in an unusual way.

Typically, Cooper pairs assist the material in conducting electricity without resistance, but with sufficient disorder, these pairs begin to compete with one another. This leads to a conflict between the superconducting state and the insulating state.

Physicists discovered that the temperature at which the studied material lost its superconducting ability was no longer determined by how strongly the electrons paired, but rather by the superfluid stiffness itself.

This indicates that the material entered a special state where electron pairs are formed but do not behave in a coordinated manner to maintain superconductivity. Such a quantum state represents a critical phase in certain quantum materials, especially high-temperature superconductors, as it helps to explain their behavior and reveals potential for applications in quantum technologies, physicists say.