Quantum mapping of nematic superconductors under extreme conditions

14 November 2019

Dr Amalia Coldea and her group at Oxford University’s Physics Department, with the support of international collaborators at high-magnetic field facilities in Tallahassee, USA and Toulouse, France, have been able to access quantum oscillations and reveal the quantum behaviour of electrons in a new family of nematic superconductors.

Superconductivity is a unique state of quantum materials in which electrical current flows without resistance and electrons pair up and condense in a coherent macroscopic quantum state. These unique properties make superconductors perfect candidates for a large range of applications from energy transmission and storage, medical applications as well as unique components of future quantum computers. One of the challenging aspects of superconductivity is to identify and predict quantum materials that would harbour these unique properties at room temperature; conventional superconductors used now in superconducting circuits only work at very low temperatures close to absolute zero.

Understanding superconductivity

Understanding superconductivity and predicting new materials with higher critical temperatures relies on the knowledge of the precise details of their Fermi surface as well as about the glue that causes the electrons to pair up and form the condensed state. The group was able to directly access the Fermi surface of a superconductor in different quantum regimes by observing quantum oscillations at very low temperatures and in ultra-high magnetic fields. They have identified for the first time how electrons respond in the proximity of a quantum nematic electronic state and their work was published recently in Nature Physics.

Pascal Reiss, who was the postdoctoral research assistant in Dr Coldea’s group, and is now developing new experiments under pressure emphasises that: ‘Hydrostatic pressure is a very powerful experimental tool which allows us to directly modify atomic structures. We can finely tune the underlying quantum mechanics right to the point that we want to study, and it comes as no surprise that the highest superconducting transition temperatures are observed under pressure.’

Specialist facilities and materials

The challenges of performing these quantum experiments was made possible by having access to specialist facilities and materials: the best single crystals, grown in Oxford by Dr Amir Haghighirard (now at the Karlsruhe Institute of Technology); the 16T magnet at the Oxford Centre for Applied Superconductivity at Oxford University’s Physics Department; the highest steady magnetic field in the world at the National High Magnetic Field Laboratory in Tallahassee and one of the highest pulsed field magnets in the world at the Laboratoire National des Champs Magnétiques Intenses, in Toulouse.

Dr Coldea concludes: ‘It is always a privilege to see quantum oscillations in a high-temperature superconductor and access their quantum behaviour for the first time. Nature gives us clues about how electrons are organised inside these materials; in our research, we work out quantum maps, a necessary step to establish the path towards room temperature superconductivity that will one day change our world.’

Find out more about Dr Coldea's work: https://www2.physics.ox.ac.uk/research/quantum-matter-in-high-magnetic-f...