Probing the insulating state of SmB ₆: When a metal is subjected to a strong magnetic field, its electrons start rearranging into new energy levels, causing its electronic properties to oscillate as a function of the field. Unexpectedly, Tan et al. observed this phenomenon, called quantum oscillations, in the Kondo insulator samarium hexaboride (SmB ₆ ), which does not conduct electricity. They measured the magnetic torque and detected quantum oscillations originating from the bulk of this heavy fermion compound. These oscillations had an unusual temperature dependence, which presents another puzzle to theorists seeking to understand the nature of the insulating state of SmB ₆ . Science , this issue p. 287

We have investigated the superconducting state of the noncentrosymmetric compound ${\mathrm{Re}}_{6}\mathrm{Zr}$ using magnetization, heat capacity, and muon-spin relaxation or rotation ($$\mu${}\mathrm{SR}$) measurements. ${\mathrm{Re}}_{6}\mathrm{Zr}$ has a superconducting transition temperature, ${T}_{c}=6.75\ifmmode\pm\else\textpm\fi{}0.05\text{ }\text{ }\mathrm{K}$. Transverse-field $$\mu${}\mathrm{SR}$ experiments, used to probe the superfluid density, suggest an $s$-wave character for the superconducting gap. However, zero and longitudinal-field $$\mu${}\mathrm{SR}$ data reveal the presence of spontaneous static magnetic fields below ${T}_{c}$ indicating that time-reversal symmetry is broken in the superconducting state and an unconventional pairing mechanism. An analysis of the pairing symmetries identifies the ground states compatible with time-reversal symmetry breaking.

Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures. While they are commonly portrayed as two dimensional objects, in reality magnetic skyrmions are thought to exist as elongated, tube-like objects extending through the thickness of the host material. The study of this skyrmion tube state (SkT) is vital for furthering the understanding of skyrmion formation and dynamics for future applications. However, direct experimental imaging of skyrmion tubes has yet to be reported. Here, we demonstrate the real-space observation of skyrmion tubes in a lamella of FeGe using resonant magnetic x-ray imaging and comparative micromagnetic simulations, confirming their extended structure. The formation of these structures at the edge of the sample highlights the importance of confinement and edge effects in the stabilisation of the SkT state, opening the door to further investigation into this unexplored dimension of the skyrmion spin texture.

By means of neutron scattering and magnetization measurements down to 90 mK, we determine the magnetic ground state of the spin-ice candidate ${\mathrm{Nd}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$. We show that, despite ferromagnetic interactions, ${\mathrm{Nd}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ undergoes a transition around 285 mK towards an all-in–all-out antiferromagnetic state, with a strongly reduced ordered magnetic moment. We establish the $(H,T)$ phase diagram in the three directions of the applied field and reveal a metamagnetic transition around 0.1 T, associated with an unexpected shape of the magnetization curves. We propose that this behavior results from the peculiar nature of the ${\mathrm{Nd}}^{3+}$ doublet, a dipolar-octupolar doublet, different from the standard Kramers doublet studied to date, thus revealing the importance of multipolar correlations in the properties of pyrochlore oxides.

The superconductivity of the noncentrosymmetric compound ${\mathrm{La}}_7{\mathrm{Ir}}_3$ is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature $T_{\mathit{c}}=2.25\mathrm{K}$—a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly $s$ wave with an enhanced binding strength. The results indicate that the superconductivity in ${\mathrm{La}}_7{\mathrm{Ir}}_3$ may be unconventional and paves the way for further studies of this family of materials.