Resonant magnetic excitations are recognised as hallmarks of unconventional superconductivity in copper oxides, iron pnictides and heavy-fermion compounds. Model calculations have related these modes to the microscopic properties of the pair wave function, but the mechanisms of their formation are still debated. Here we report the discovery of a similar resonant mode in the non-superconducting antiferromagnetic heavy-fermion metal CeB₆. Unlike conventional magnons, the mode is non-dispersive and is sharply peaked around a wave vector separate from those characterising the antiferromagnetic order. It is likely associated with a co-existing order parameter of the unusual antiferro-quadrupolar phase of CeB₆, which has long remained hidden to neutron-scattering probes. The mode energy increases continuously below the onset temperature for antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap throughout the Brillouin zone. These attributes are similar to those of the resonant modes in unconventional superconductors. This unexpected commonality between the two disparate ground states indicates the dominance of itinerant spin dynamics in the ordered low-temperature phases of CeB₆ and throws new light on the interplay between antiferromagnetism, superconductivity and 'hidden' order parameters in correlated-electron materials.

Precision measurements of the specific heat and spectral intensity I(ω) of Raman scattering for Lu NB12 single crystal samples with various boron isotopes ( N= 10, 11, nat) have been performed at...

The results of wide-range measurements of the low-frequency, rf, and microwave conductivity in the typical mixed-valent narrow-gap semiconductor samarium hexaboride are presented. The established steplike anomaly of conductivity σ(ν) around 10 GHz is discussed in the framework of the exciton-polaron approach and coherent-state formation in ${\mathrm{SmB}}_6$ at helium temperatures. A combined analysis of the dc- and wide-range ac-transport characteristics and dielectric permittivity data at low temperatures is developed.

The dodecaboride ${\mathrm{LuB}}_{12}$ with cage-glass state and rattling modes has been studied to clarify the nature of the large amplitude vibrations of Lu ions. Discovered anisotropy of charge transport in conjunction with distortions of the conventional fcc symmetry of the crystal lattice may be attributed to coherent motion of Lu ions along a singular direction in the lattice. Arguments are presented in favor of cooperative dynamic Jahn-Teller effect in the boron sublattice to be the reason of the rattling mode, lattice distortion, and formation of the filamentary structure of the higher conducting channels—dynamic charge stripes.

Precision measurements of transport and magnetic parameters of high-quality CeB6single crystals are performed in the temperature range 1.8—300 K. It is shown that their resistivity in the...