Spontaneous magnetic field discovered in a new superconducting compound by UJ researcher and international collaborators

Doubly-surprising behaviour in an intermetallic compound cooled down to almost zero temperature was recently published by collaborating researchers from the University of Johannesburg, ISIS at the Rutherford Appleton Laboratory, Aoyama-Gakuin University in Japan and Max Planck Institute Dresden in Nature Scientific Reports, as part of their study of the frontiers in condensed matter physics.

Below the critical temperature in a superconductor, electrons dramatically start to conduct electrical current with apparent zero resistance. This is one of the most intensively studied phenomena in sci​ence and remains enigmatic more than 100 years after its discovery.

When a conventional superconductor is cooled to temperatures close to the absolute zero of temperature, it acquires the state of perfect diamagnetism: the material completely expels incoming magnetic flux by screening magnetic fields from the internal volume of the superconductor.

In the traditional understanding of superconductors, this perfect shielding of magnetic fields is the definitive test of superconductivity.

In addition, muon spin resonance is an extremely sensitive probe of magnetism and magnetic fields in matter.

The researchers, including Prof André M Strydom from the University of Johannesburg, chose muon spin resonance as one of the methods to study the new intermetallic superconductor Y5Rh6Sn18.

Prof Strydom is Research Professor in the Highly Correlated Matter Research Group at the UJ Department of Physics.

A double surprise awaited the experimenters when they found a magnetic field arising just inside the superconducting phase of this compound. It was completely unexpected because magnetic fields and superconductivity are mutually exclusive due to the screening effect.

Even more intriguing, none of the three elements in this tetragonal intermetallic compound are themselves chemical elements that produce magnetic fields. Because of this, finding a spontaneously arising magnetic field in the compound is even more unexpected.

The researchers found a superconducting ground state in the compound that supports magnetic fields, which presents a rare case of broken time-reversal symmetry states. Broken time-reversal symmetry states have also been proposed in the high-temperature class of superconductors.

Since mixed-symmetry states in superconducting compounds may produce spontaneous currents and magnetic moments, further research into the compound may reveal more surprising properties.

The research article, Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation, was published in Nature Scientific Reports (SREP) in August 2015. Nature SREP is an online journal from the Nature Publishing Group, which publishes primary research from all areas of the natural and clinical sciences.

Download the entire research article at: http://www.nature.com/articles/srep12926

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