By Josh Perry, Editor
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Scientists from the Skolkovo Institute of Science and Technology (Skoltech) and the Landau Institute for Theoretical Physics in Russia, the Institut Néel in France, the Weizmann Institute of Science in Israel, and the University of Utah in the U.S. have developed a theory that explains the low-temperature anomalies in disorganized superconductors.

Researchers have put forth a theory to explain low-temperature anomalies in disorganized superconductors. (Wikimedia Commons)

According to a report from Skoltech, the researchers believe that the anomaly is caused by thermal fluctuations of quantum Abrikosov vertices.

“The magnetic field that penetrates into the disordered superconductor has the form of vortices, i.e. tubes, each carrying magnetic flux equal to the fundamental value hc/2e, where h is the Plank constant, c is the speed of light, and e is the electron charge,” the report explained.

At absolute zero, these vortices are immobile and attached to the atomic structure but any nonzero temperature causes fluctuations of the vortex tubes, which grow as temperatures increase.

The report added, “Gaining an insight into the behavior of strongly disordered superconductors is essential for their successful use in superconducting quantum bits – key elements of quantum computers. It became obvious a few years ago that multiple applications in this field require very small elements with high inductance (electric inertia), and the strongly disordered superconductors are the best fit for such ‘super-inductance’ elements.”

The research was recently published in Nature Physics. The abstract read:

“Strongly disordered superconductors in a magnetic field exhibit many characteristic properties of type-II superconductivity—except at low temperatures, where an anomalous linear temperature dependence of the resistive critical field B_c2 is routinely observed. This behaviour violates the conventional theory of superconductivity, and its origin has posed a long-standing puzzle.

“Here we report systematic measurements of the critical magnetic field and current on amorphous indium oxide films with various levels of disorder. Surprisingly, our measurements show that the B_c2 anomaly is accompanied by mean-field-like scaling of the critical current. Based on a comprehensive theoretical study we argue that these observations are a consequence of the vortex-glass ground state and its thermal fluctuations.

“Our theory further predicts that the linear-temperature anomaly occurs more generally in both films and disordered bulk superconductors, with a slope that depends on the normal-state sheet resistance, which we confirm experimentally.”