Nature and origin of unconventional superconductivity in ultra-clean UTe2

Quantum materials host collective phenomena that defy a semi-classical description, for example because they arise from strong correlations or involve topological order. The diversity of these collective phenomena, their reach into practicable temperature regions and their tunability enable new technologies. Foremost among them is superconductivity, a macroscopic quantum phenomenon with multiple applications ranging from powerful magnets used in MRI scanners, fusion research reactors and particle accelerators to lightweight motors and generators, low-noise rf filters, low-power electronics, and quantum devices used in sensing or computing. In most superconductors, the required electronic interactions are produced by dynamic lattice distortions. Alternatively, these interactions can be caused by more complex quantum processes similar to those which give rise to magnetism. Such unconventional 'superconductivity without phonons' is associated with a rich range of properties, some of which are highly desirable, such as resilience to high magnetic fields, current densities or temperatures.

The challenge the project addresses and how it will be applied to this
Unconventional superconductors are sparsely distributed in material space but clustered in families, which include copper-oxide, iron, or cerium compounds. There are also surprisingly many uranium-based unconventional superconductors, some of which display highly unusual phenomena such as multiple or even multi-component pairing states. Although these materials may not themselves be ideal for applications, their properties could be. They need to be studied and understood, to replicate their properties in more accessible materials.

Here, we focus on the new superconductor UTe2, which displays several distinct, switchable superconducting states and in which superconductivity can survive in ?elds exceeding 60 T, indicating triplet (odd-parity) pairing. In addition, UTe2 has two important advantages: (i) ultra-clean single crystals with purity levels an order of magnitude better than previous best efforts are now available, facilitating probing studies of lasting relevance; (ii) its electronic structure near the Fermi energy is unusually simple, vastly simplifying any theoretical and computational description.

These advantages turn UTe2 into a clean reference material in which to decode the connection between microscopic material properties and its diverse superconducting pairing states, its magnetic or charge order, and its correlated normal state properties.

We will tackle this challenge by investigating the nature of the superconducting pairing states and the pair-forming interaction, the nature of the underlying strongly correlated normal state, and their interplay with nearby magnetic or charge order.