Superconductivity in systems with local inversion symmetry breaking

Published : 1 January 2023

Global inversion symmetry or time reversal symmetry have been long regarded as fundamental ingredients to form a superconducting state. However nowadays, several systems have been found which are superconducting even though they break locally inversion symmetry, sometimes together with broken time reversal symmetry. Prominent examples are the uranium based ferromagnetic superconductors URhGe and UCoGe (breaking both symmetries), or the new systems UTe2, and CeRh2As2, breaking local inversion symmetry. All these systems remain superconducting in very high magnetic fields, often showing even a reinforcement of superconductivity under field. Transitions between spin-triplet and spin-singlet superconducting are suspected in UTe2 and CeRh2As2, which are up to now unique in nature.

In this these, we want to develop a new high precession ac susceptometer, working at low temperatures in a dilution refrigerator, in order to explore the magnetic properties of superconducting phases of these superconductors. In addition, with the same set-up it will be possible to determine properties of the Fermi surface by the measurements of quantum oscillations of the magnetization. First focus will be on UTe2, which has a complex superconducting phase diagram as a function magnetic field and pressure, as shown in the figure. Remarkably, multiple superconducting phases occur in UTe2 and superconductivity survives under magnetic fields up to 35 T for some specific directions. In a further step we will extend the technique to measurements under high pressure and to look for superconductivity in systems with the same crystal structure as CeRh2As2.

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