An unconventional superconducting state was recently discovered in UTe2, where spin-triplet superconductivity emerges from the paramagnetic normal state of a heavy fermion material. The coexistence of magnetic fluctuations and superconductivity, together with the crystal structure of this material, suggest that a unique set of symmetries, magnetic properties, and topology underlie the superconducting state. Here, we report observations of a non-zero polar Kerr effect and of two transitions in the specific heat upon entering the superconducting state, which together suggest that the superconductivity in UTe2 is characterized by a two-component order parameter that breaks time reversal symmetry. These data place constraints on the symmetries of the order parameter and inform the discussion on the presence of topological superconductivity in UTe2.

Muon relaxation experiments reveal a slowly fluctuating magnetic field in the pseudogap phase of a cuprate superconductor.

Background: Much less is known about neutron structure than that of the proton due to the absence of free neutron targets. Neutron information is usually extracted from data on nuclear targets such as deuterium, requiring corrections for nuclear binding and nucleon off-shell effects. These corrections are model dependent and have significant uncertainties, especially for large values of the Bjorken scaling variable x. As a consequence, the same data can lead to different conclusions, for example, about the behavior of the d quark distribution in the proton at large x.Purpose: The Barely Off-shell Nucleon Structure (BONuS) experiment at Jefferson Lab measured the inelastic electron-deuteron scattering cross section, tagging spectator protons in coincidence with the scattered electrons. This method reduces nuclear binding uncertainties significantly and has allowed for the first time a (nearly) model-independent extraction of the neutron structure function F2(x, Q 2 ) in the resonance and deep-inelastic regions.Method: A novel compact radial time projection chamber was built to detect protons with momentum between 70 and 150 MeV/c and over a nearly 4π angular range. For the extraction of the free-neutron structure function F n 2 , spectator protons at backward angles (> 100• relative to the momentum transfer) and with momenta below 100 MeV/c were selected, ensuring that the scattering took place on a nearly free neutron. The scattered electrons were detected with Jefferson Lab's CLAS spectrometer, with data taken at beam energies near 2, 4 and 5 GeV. Results:The extracted neutron structure function F n 2 and its ratio to the inclusive deuteron structure function F d 2 are presented in both the resonance and deep-inelastic regions for momentum transfer squared Q 2 between 0.7 and 5 GeV 2 /c 2 , invariant mass W between 1 and 2.7 GeV/c 2 , and Bjorken x between 0.25 and 0.6 (in the DIS region). The dependence of the semi-inclusive cross section on the spectator proton momentum and angle is investigated, and tests of the spectator mechanism for different kinematics are performed.Conclusions: Our data set on the structure function ratio F n 2 /F d 2 can be used to study neutron resonance excitations, test quark-hadron duality in the neutron, develop more precise parametrizations of structure functions, as well as investigate binding effects (including possible mechanisms for the nuclear EMC effect) and provide a first glimpse of the asymptotic behavior of d/u at x → 1.