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Symmetry properties of the order parameter are among the most fundamental characteristics of a superconductor. UTe₂, which was found to feature an exceedingly large upper critical field and striking reentrant behavior at low temperatures, is widely believed to possess a spin-triplet pairing symmetry. However, unambiguous evidence for such a pairing symmetry is still lacking, especially at zero and low magnetic fields. The presence of an inversion crystalline symmetry in UTe₂requires that, if it is indeed a spin-triplet superconductor, the order parameter must be of odd parity. We report here phase-sensitive measurements of the symmetry of the orbital part of the order parameter using the Josephson effect. The selection rule in the orientation dependence of the Josephson coupling between In, ans-wave superconductor, and UTe₂suggests strongly that UTe₂possesses the odd-parity pairing state of B₁usymmetry near zero magnetic field, making it a spin-triplet superconductor. We also report the apparent formation of Andreev surface bound states on the (1−10) surface of UTe₂. 

For some intermetallic compounds containing lanthanides, structural transitions can result in intermediate electronic states between trivalency and tetravalency; however, this is rarely observed for praseodymium compounds. The dominant trivalency of praseodymium limits potential discoveries of emergent quantum states in itinerant 4f¹systems accessible using Pr⁴⁺-based compounds. Here, we use in situ powder x-ray diffraction and in situ electron energy-loss spectroscopy (EELS) to identify an intermetallic example of a dominantly Pr⁴⁺state in the polymorphic system Pr₂Co₃Ge₅. The structure-valence transition from a nearly full Pr⁴⁺electronic state to a typical Pr³⁺state shows the potential of Pr-based intermetallic compounds to host valence-unstable states and provides an opportunity to discover previously unknown quantum phenomena. In addition, this work emphasizes the need for complementary techniques like EELS when evaluating the magnetic and electronic properties of Pr intermetallic systems to reveal details easily overlooked when relying on bulk magnetic measurements alone. 

Delocalized−localized electron interactions are central to strongly correlated electron phenomena. Here, we study the Kondo effect, a prototypical strongly correlated phenomena, in a tunable fashion using gold nanostructures (nanoparticle, NP, and nanoshell, NS) + molecule cross-linkers (butanedithiol, BDT). NP films exhibit hallmark signatures of the Kondo effect, including (1) a log temperature resistance upturn as temperature decreases in a metallic regime, and (2) zero-bias conductance peaks (ZBCPs) that are well fit by a Frota function near a percolation insulator transition, previously used to model Kondo peaks observed using tunnel junctions. Remarkably, NP + NS films exhibit ZBCPs that persist to >220 K, i.e., >10-fold higher than that in NP films. Magnetic measurements reveal that moments in NP powders align, and in NS powders, they antialign at low temperatures. Based on these observations, we propose a mechanism in which varying such material nanobuilding blocks can modify electron−electron interactions to such a large degree.