D. Lamago

Direct observation of dynamic charge stripes in La2–xSrxNiO4

The insulator-to-metal transition continues to be a challenging subject, especially when electronic correlations are strong. In layered compounds, such as La2-xSrxNiO4 and La2-xBaxCuO4, the doped charge carriers can segregate into periodically spaced charge stripes separating narrow domains of antiferromagnetic order. Although there have been theoretical proposals of dynamically fluctuating stripes, direct spectroscopic evidence of charge-stripe fluctuations has been lacking. Here we report the detection of critical lattice fluctuations, driven by charge-stripe correlations, in La2-xSrxNiO4 using inelastic neutron scattering. This scattering is detected at large momentum transfers where the magnetic form factor suppresses the spin fluctuation signal. The lattice fluctuations associated with the dynamic charge stripes are narrow in q and broad in energy. They are strongest near the charge-stripe melting temperature. Our results open the way towards the quantitative theory of dynamic stripes and for directly detecting dynamical charge stripes in other strongly correlated systems, including high-temperature superconductors such as La2-xSrxCuO4.

Chiral criticality in the doped helimagnets Mn1−yFeySi

S. V. Grigoriev, E. V. Moskvin, V. A. Dyadkin, D. Lamago, 3 Th. Wolf, H. Eckerlebe, and S. V. Maleyev Petersburg Nuclear Physics Institute, Gatchina, 188300 Saint-Petersburg, Russia Laboratoire Léon Brillouin, CEA Saclay, F-91191 Gif-sur-Yvette Cedex, France Karlsruher Institut für Technologie, Institut für Festkörperphysik, P.O. box 3640, D-76021 Karlsruhe, Germany Helmholtz Zentrum Geesthacht, 21502 Geesthacht, Germany (ΩDated: January 19, 2013)

Magnetic blue phase in the chiral itinerant magnet MnSi.

Chiral nematic liquid crystals sometimes form blue phases characterized by spirals twisting in different directions. By combining model calculations with neutron-scattering experiments, we show that the magnetic analogue of blue phases does form in the chiral itinerant magnet MnSi in a large part of the phase diagram. The properties of this blue phase explain a number of previously reported puzzling features of MnSi such as partial magnetic order and a two-component specific-heat and thermal-expansion anomaly at the magnetic transition.

Competition between commensurate and incommensurate magnetic ordering in Fe1+yTe

The Fe1+y Te1-x Sex compounds belong to the family of iron-based high temperature superconductors, in which superconductivity often appears upon doping antiferromagnetic parent compounds. Unlike other Fe-based superconductors (in which the antiferromagnetic order is at the Fermi surface nesting wavevector [1/2,1/2,1]), the Fe1+y Te1-x Sex parent compound Fe1+y Te orders at a different wavevector, [1/2, 0, 1/2]. Furthermore, the ordering wavevector depends on y, the occupation of interstitial sites with excess iron; the origin of this behavior is controversial. Using inelastic neutron scattering on Fe1.08 Te, we find incommensurate magnetic fluctuations above the Neel temperature, even though the ordered state is bicollinear and commensurate with gapped spin waves. This behavior can be understood in terms of a competition between commensurate and incommensurate order, which we explain as a lock-in transition caused by the magnetic anisotropy.

Polaronic metal phases in L a 0.7 S r 0.3 Mn O 3 uncovered by inelastic neutron and x-ray scattering

Among colossal magnetoresistive manganites the prototypical ferromagnetic manganite

Fluctuating defects in the incipient relaxor K1-xLixTaO3 (x=0.02)

\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}

Effects of charge inhomogeneities on elementary excitations in La2-xSrxCuO₄

has a relatively small magnetoresistance, and has been long assumed to have only weak electron-lattice coupling. Here we report that

Spurious peaks arising from multiple scattering events involving the sample environment in inelastic neutron scattering

\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}

Helical spin structure of Mn 1 − y Fe y Si under a magnetic field: Small angle neutron diffraction study

has strong electron-phonon coupling: Our neutron and x-ray scattering experiments show strong softening and broadening of transverse acoustic phonons on heating through the Curie temperature

Highly Anisotropic Anomaly in the Dispersion of the Copper-Oxygen Bond-Bending Phonon in Superconducting YBa2Cu3O7 from Inelastic Neutron Scattering

{T}_{C}=350\phantom{\rule{0.16em}{0ex}}\mathrm{K}