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We explore the evolution of the structural phase transition of ${(\mathrm{Sr},\mathrm{Ca})}_{3}{\mathrm{Ir}}_{4}{\mathrm{Sn}}_{13}$, a model system to study the interplay between structural quantum criticality and superconductivity, by means of high-energy x-ray diffraction measurements at high pressures and low temperatures. Our results confirm a rapid suppression of the superlattice transition temperature ${T}^{*}$ against pressure, which extrapolates to zero at a critical pressure of $\ensuremath{\approx}1.79(4)\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. The temperature evolution of the superlattice Bragg peak in ${\mathrm{Ca}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Sn}}_{13}$ reveals a drastic decrease of the intensity and an increase of the linewidth when $T\ensuremath{\rightarrow}0\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and $p\ensuremath{\rightarrow}{p}_{c}$. Such anomaly is likely associated with the emergence of quantum fluctuations that disrupt the formation of long-range superlattice modulation. The revisited temperature-pressure phase diagram of ${(\mathrm{Sr},\mathrm{Ca})}_{3}{\mathrm{Ir}}_{4}{\mathrm{Sn}}_{13}$ thus highlights the intertwined nature of the distinct order parameters present in this system and demonstrates some similarities between this family and the unconventional superconductors. more...

Quantum materials that feature magnetic long-range order often reveal complex phase diagrams when localized electrons become mobile. In many materials magnetism is rapidly suppressed as electronic charges dissolve into the conduction band. In materials where magnetism persists, it is unclear how the magnetic properties are affected. Here we study the evolution of the magnetic structure in Nd_{1-x}Ce_{x}CoIn_{5} from the localized to the highly itinerant limit. We observe two magnetic ground states inside a heavy-fermion phase that are detached from unconventional superconductivity. The presence of two different magnetic phases provides evidence that increasing charge delocalization affects the magnetic interactions via anisotropic band hybridization. more...

Raman spectroscopy experiments on single crystals of CuSb2O6 and CoSb2O6 quasi-one-dimensional antiferromagnets with trirutile crystal structure were performed, with a focus on the first material. The observed Raman-active phonon modes and previously reported infrared-active modes were identified with the aid of ab-initio lattice dynamics calculations. The structural transition between monoclinic beta-CuSb2O6 and tetragonal alpha-CuSb2O6 phases at Ts=400 K is manifested in our spectra by a "repulsion" of two accidentally quasi-degenerate symmetric modes below Ts, caused by a phonon mixing effect that is only operative in the monoclinic beta-CuSb2O6 phase due to symmetry restrictions. Also, two specific phonons, associated with CuO6 octahedra rotation and with a Jahn-Teller elongation mode, soften and broaden appreciably as T -> Ts. A crossover from a displacive to an order-disorder transition at Ts is inferred. more...

Strongly interacting phonons and orbital excitations are observed in the same energy range for CuSb$_2$O$_6$, unlocking a so-far unexplored type of electron-phonon interaction. An orbital wave at $\sim 550$ cm$^{-1}$ softens on warming and strongly interferes with a phonon at $\sim 500$ cm$^{-1}$, giving rise to a merged excitation of mixed character. An electronic continuum grows on warming to the orbital ordering temperature $T_{OO}$=400 K, generating an important phonon decay channel. This direct and simultaneous observation of orbital and vibrational excitations reveals details of their combined dynamics. In addition, phonon frequency anomalies due to magnetic correlations are observed below $\sim 150$ K, much above the three-dimensional magnetic ordering temperature $T_N^{3D}=8.5$ K, confirming one-dimensional magnetic correlations along Cu-O-O-Cu linear chains in the paramagnetic state., Comment: 5 pages, 4 figures more...