The study of the temporal evolution of systems undergoing symmetry breaking phase transitions—whether it is in condensed-matter physics, cosmology or finance^1,2,3,4,5,6—is difficult because they are hard to repeat, or they occur very rapidly. Here we report a high-time-resolution study of the evolution of both bosonic and fermionic excitations through an electronic charge-ordering symmetry breaking phase transition. Periodically quenching our system with femtosecond optical pulses, we subsequently detect hitherto-unrecorded coherent aperiodic undulations of the order parameter, critical slowing down of the collective mode and evolution of the particle–hole gap as the system evolves through the transition. Modelling on the basis of Ginzburg–Landau theory is used to reproduce the observations without free parameters. Of particular interest is the observation of spectrotemporal distortions arising from spontaneous annihilation of topological defects, analogous to those discussed by the Kibble–Zurek cosmological model^2,3.

The coupling of phonons with collective modes and single-particle gap excitations associated with one- (1d) and two-directional (2d) electronically driven charge-density wave (CDW) ordering in metallic $R{\mathrm{Te}}_3$ is investigated as a function of rare-earth ion chemical pressure ($R=\mathrm{Tb},\mathrm{Dy},\mathrm{Ho}$) using femtosecond pump-probe spectroscopy. From the $T$ dependence of the CDW gap ${\Delta }_{\mathrm{CDW}}$ and the amplitude mode, we find that while the transition to a 1d-CDW ordered state at $T_{c1}$ initially proceeds in an exemplary mean-field-like fashion, below $T_{c1}$, ${\Delta }_{\mathrm{CDW}}$ is depressed and departs from the mean-field behavior. The effect is apparently triggered by resonant mode mixing of the amplitude mode with a totally symmetric phonon at 1.75 THz. At low temperatures, when the state evolves into a 2d-CDW ordered state at $T_{c2}$ in the ${\mathrm{DyTe}}_3$ and ${\mathrm{HoTe}}_3$, additional much weaker mode mixing is evident but no soft mode is observed.

A series of 12 asphaltene samples extracted from heavy oils and the oxidized bitumen of different origin has been studied with high-frequency W-band (94 GHz) pulsed electron paramagnetic resonance (EPR) spectroscopy. Transverse (T_2e) and longitudinal (T_1e) relaxation times of the free radical (FR) and the vanadyl porphyrin (VO²⁺) were measured for each sample. A significant contribution of the spectral diffusion to T_2e has been revealed and ascribed to the dipole–dipole interaction between the FR and VO²⁺. This indicates that the distance between the FR and VO²⁺ does not exceed a few nanometers, which means, in turn, that VO²⁺ can participate in construction of the asphaltene aggregates via the intermolecular interactions.

${\mathrm{SrEr}}_2{\mathrm{O}}_4$ is a geometrically frustrated magnet which demonstrates rather unusual properties at low temperatures including a coexistence of long- and short-range magnetic order, characterized by two different propagation vectors. In the present work, the effects of crystal fields (CFs) in this compound containing four magnetically inequivalent erbium sublattices are investigated experimentally and theoretically. We combine the measurements of the CF levels of the ${\mathrm{Er}}^{3+}$ ions made on a powder sample of ${\mathrm{SrEr}}_2{\mathrm{O}}_4$ using neutron spectroscopy with site-selective optical and electron paramagnetic resonance measurements performed on single-crystal samples of the lightly Er-doped nonmagnetic analog, ${\mathrm{SrY}}_2{\mathrm{O}}_4$. Two sets of CF parameters corresponding to the ${\mathrm{Er}}^{3+}$ ions at the crystallographically inequivalent lattice sites are derived which fit all the available experimental data well, including the magnetization and dc susceptibility data for both lightly doped and concentrated samples.

Single-layer vanadium nitride (VN) and bilayer Pd_0.96Fe_0.04/VN and VN/Pd_0.92Fe_0.08 thin-film heterostructures for possible spintronics applications were synthesized on (001)-oriented single-crystalline magnesium oxide (MgO) substrates utilizing a four-chamber ultrahigh vacuum deposition and analysis system. The VN layers were reactively magnetron sputtered from a metallic vanadium target in Ar/N₂ plasma, while the Pd_1−xFe_x layers were deposited by co-evaporation of metallic Pd and Fe pellets from calibrated effusion cells in a molecular beam epitaxy chamber. The VN stoichiometry and Pd_1−xFe_x composition were controlled by X-ray photoelectron spectroscopy. In situ low-energy electron diffraction and ex situ X-ray diffraction show that the 30 nm thick single-layer VN as well as the double-layer VN(30 nm)/Pd_0.92Fe_0.08(12 nm) and Pd_0.96Fe_0.04(20 nm)/VN(30 nm) structures have grown cube-on-cube epitaxially. Electric resistance measurements demonstrate a metallic-type temperature dependence for the VN film with a small residual resistivity of 9 μΩ·cm at 10 K, indicating high purity and structural quality of the film. The transition to the superconducting state was observed at 7.7 K for the VN film, at 7.2 K for the Pd_0.96Fe_0.04/VN structure and at 6.1 K for the VN/Pd_0.92Fe_0.08 structure with the critical temperature decreasing due to the proximity effect. Contrary to expectations, all transitions were very sharp with the width ranging from 25 mK for the VN film to 50 mK for the VN/Pd_0.92Fe_0.08 structure. We propose epitaxial single-crystalline thin films of VN and heteroepitaxial Pd_1−xFe_x/VN and VN/Pd_1−xFe_x (x ≤ 0.08) structures grown on MgO(001) as the materials of a choice for the improvement of superconducting magnetic random access memory characteristics.