Symmetry-resolved elastic anomalies in spin-crossover cobaltite LaCoO3_3

Ultrasound velocity measurements of the pseudo-cubic spin-crossover cobaltite LaCoO$_3$ and the lightly Ni-substituted La(Co$_{0.99}$Ni$_{0.01}$)O$_3$ reveal two types of symmetry-resolved elastic anomaly in the insulating paramagnetic state that are commonly observed in these compounds. The temperature dependence of the bulk modulus exhibits Curie-type softening upon cooling below 300 K down to $\sim$70 K, indicating the presence of isostructural lattice instability arising from orbital fluctuations. The temperature dependence of the tetragonal and trigonal shear moduli exhibits unusual hardening upon cooling below 300 K, indicating the occurrence of elasticity crossover arising from the spin crossover. The present study also reveals that the isostructural lattice instability in LaCoO$_3$ is sensitively suppressed with the Ni substitution, indicating the suppression of orbital fluctuations with the light Ni substitution. This Ni substitution effect in LaCoO$_3$ can be explained on the basis that the isostructural lattice instability arises from the coupling of the lattice to the Co spin state fluctuating between the high-spin state and intermediate-spin state.Comment: 7 pages, 5 figure

Modified Cross-Correlation for Efficient White-Beam Inelastic Neutron Scattering Spectroscopy

We describe a method of white-beam inelastic neutron scattering for improved measurement efficiency. The method consists of matrix inversion and selective extraction. The former is to resolve each incident energy component from the white-beam data, and the latter eliminates contamination by elastic components, which produce strong backgrounds that otherwise obfuscate the inelastic scattering components. In this method, the optimal experimental condition to obtain high efficiency will strongly depend on the specific aim of the individual experiments.Comment: 6 pages, 3 figure

Neutron scattering study of role of partial disorder-type spin fluctuations in conductivity of frustrated conductor Mn3_3Pt

The spin-frustrated conductor Mn$_3$Pt exhibits a characteristic magnetic structure called partial disorder in which some spin sites can form magnetic order through the generation of non-ordered sites that locally relieve the frustration. Here we report the results of a single-crystal inelastic neutron scattering study of this compound. The measured momentum $\vec{Q}$ correlations of diffusive magnetic scattering reveal that the paramagnetic phase exhibits short-range spin fluctuations with the same type of partial disorder. Its relation to conductivity is also discussed.Comment: 5 pages, 4 figure

Coulomb correlations intertwined with spin and orbital excitations in LaCoO3_3

We carried out temperature-dependent (20 - 550 K) measurements of resonant inelastic X-ray scattering on LaCoO$_3$ to investigate the evolution of its electronic structure across the spin-state crossover. In combination with charge-transfer multiplet calculations, we accurately quantized the renormalized crystal-field excitation energies and spin-state populations. We show that the screening of the on-site Coulomb interaction of 3d electrons is orbital selective and coupled to the spin-state crossover in LaCoO$_3$. The results establish that the gradual spin-state crossover is associated with a relative change of Coulomb energy versus bandwidth, leading to a Mott-type insulator-to-metal transition.Comment: 6 pages, 4 figures. Submitted to Phys. Rev. Let