Seminar By Hironori Saki, Japan Atomic Energy Agency

Title: Unconventional Superconductivity in UTe2 and Emerging Magnetism in α-UTe3

Series: Condensed Matter Sciences Seminar

Abstract: Uranium-based compounds provide a fascinating platform for exploring unconventional superconductivity and magnetism arising from strongly correlated 5f electrons. In this talk, I will present our recent studies of two uranium tellurides, UTe2 and α-UTe3, which exhibitremarkably different ground states.

UTe2 has attracted considerable attention as a candidate spin-triplet superconductor with multiple superconducting phases under magnetic fields. Recent advances in single-crystal growth have enabled us to obtain high-quality crystals with a superconducting transition temperature exceeding 2 K and exceptionally large residual resistivity ratios. Using these crystals, we have investigated the rich magnetic-field–temperature phase diagram, revealing distinct superconducting phases and their close relationship with magnetic-field-induced phenomena. I will discuss how improved crystal quality provides new insights into the unconventional superconducting states of UTe2.

In the second part, I will introduce our recent work on α-UTe3, a semiconducting van der Waals antiferromagnet. Combining NMR and neutron diffraction, we have identified an incommensurate amplitude-modulated antiferromagnetic structure, consistent with singletinduced magnetism near a quantum critical point. Furthermore, Cu intercalation significantly modifies the electrical conductivity and magnetic ordering, eventually suppressing long-range magnetic order at higher Cu concentrations. Recent NMR results on Cu-intercalated crystals will also be discussed.