Abnormal metal highlights ‘impossible’ state between superconductivity and insulation

Researchers at the Niels Bohr Institute at the University of Copenhagen have taken very thin conductors from superconductivity to insulation, creating a strange “impossible” state between the two mutually exclusive states.

Materials research is absolutely crucial when dealing with quantum states. Regardless of the material used as a basis for creating controllable quantum states, for example if you want to create applications using quantum states for computing, sensing or communication, the materials often define the extent to which you can eliminate the omnipresent noise that disrupts or even disrupts the desired “clean” quantum states or signals. It’s an ongoing battle.

The team led by Saulius Vaitiekenas, associate professor at the Niels Bohr Institute, managed to create what is believed to be an impossible intermediate state between superconductor = absolutely no resistance or loss of electrical connection – and total isolation = complete cutoff of the electrical signal.

The work is published in the journal Physical Examination Letters.

The crosstalk standard made this unexpected behavior possible

The group built an “array” made up of tiny superconducting islands equipped with a voltage knob – much like a transistor – that allowed them to control the crosstalk between these islands. According to an old prediction, the system was to move from the superconducting stage, when the islands are allowed to “talk” to each other, to the directly insulating stage, when they are disconnected.

Instead, the researchers discovered an intermediate state in which the islands continue to communicate with each other, but without superconductivity. Because of this unexpected behavior, the condition is called anomalous metallic regime.

“Our study sheds more light on this state, indicating that it is the quantum fluctuations, or, to be a little more precise, the uncertainty between the superconducting phase between the islands and the number of particles in the islands in our sample, that are causing this behavior,” says Vaitiekenas.

Quantum phase transitions – and their understanding – are one piece of a big puzzle

The experiment sheds light on the long-standing question about anomalous metal – an unexpected state of matter that was observed when devices transitioned from superconductor (perfect conductor) to insulator status.

As Vaitiekenas explains, “Understanding such quantum phase transitions is like solving a big puzzle. One piece at a time may not reveal the whole picture, but, in the long term, it could be a step forward toward electronics that waste less energy and more controllable and reliable quantum devices for future applications.”

Contributors to this work are Satyaki Sasmal, Maria Efthymiou-Tsironi, Gunjan Nagda, Emma Fugl, Lara Liva Olsen, Filip Krizek, Charles M. Marcus and S. Vaitiekėnas.