arXiv subjects

R J Cava

Publications and source records attributed to R J Cava.

5 recordsLinked to original sources

arXiv2016

First principles calculation and experimental investigation of lattice dynamics in the rare earth pyrochlores R2Ti2O7 (R=Tb, Dy, Ho)

We present a model of the lattice dynamics of the rare earth titanate pyrochlores R2Ti2O7 (R=Tb, Dy, Ho), which are important materials in the study of frustrated magnetism. The phonon modes are obtained by density functional calculations, and these predictions are verified by comparison with scattering experiments. Single crystal inelastic neutron scattering is used to measure acoustic phonons along high symmetry directions for R=Tb, Ho; single crystal inelastic x-ray scattering is used to measure numerous optical modes throughout the Brillouin zone for R=Ho; and powder inelastic neutron scattering is used to estimate the phonon density of states for R=Tb, Dy, Ho. Good agreement between the calculations and all measurements is obtained, allowing confident assignment of the energies and symmetries of the phonons in these materials under ambient conditions. The knowledge of the phonon spectrum is important for understanding spin-lattice interactions, and can be expected to be transferred readily to other members of the series to guide the search for unconventional magnetic excitations.

cond-mat.mtrl-sci↗

arXiv2014

Superconducting properties and electronic structure of NaBi

Resistivity, dc magnetization, and heat capacity measurements are reported for superconducting NaBi. Tc, the electronic contribution to the specific heat γ, the ΔCp/γTc ratio, and the Debye temperature are found to be 2.15 K, 3.4 mJmol-1K-2, 0.78, and 140 K respectively. The calculated electron-phonon coupling constant (λep = 0.62) implies that NaBi is a moderately coupled superconductor. The upper critical field and coherence length are found to be 250 Oe and 115 nm, respectively. Electronic structure calculations show NaBi to be a good metal, in agreement with the experiments; the px and py orbitals of Bi dominate the electronic states at the Fermi Energy.

cond-mat.str-el↗

arXiv2011

Helical magnetism and structural anomalies in triangular lattice α-SrCr2O4

α-SrCr2O4 has a triangular planar lattice of d3 Cr3+ made from edge sharing CrO6 octahedra; the plane shows a very small orthorhombic distortion from hexagonal symmetry. With a Weiss temperature of -596 K and a three-dimensional magnetic ordering temperature of 43 K, the magnetic system is quasi two-dimensional and frustrated. Neutron powder diffraction shows that the ordered state is an incommensurate helical magnet, with an in-plane propagation vector of k = (0,0.3217(8),0). Temperature dependent synchrotron powder diffraction characterization of the structure shows an increase in the inter-plane spacing on cooling below 100 K and an inflection in the cell parameters at the magnetic ordering temperature. These anomalies indicate the presence of a moderate degree of magneto-structural coupling.

cond-mat.str-el↗

arXiv2009

Low temperature magnetic structure of the quasi 1-dimensional magnet Ni2SiO4

Ni2SiO4, Liebenbergite, is an example of a quasi-one-dimensional magnet made up of frustrated corner sharing triangles of Ni2+ (S = 1) ions that propagate parallel to the b axis. Ni2SiO4 is isostructural with olivine, a common mineral of varying composition Fe2-xMgxSiO4, and is described in the orthorhombic space group Pnma. A synthetic polycrystalline sample of Ni2SiO4 was studied using constant wavelength powder neutron diffraction. Diffraction spectra were collected above and below the antiferromagnetic ordering transition (TN ~ 34 K) and were used to refine the atomic and magnetic structures of Ni2SiO4. Corepresentational theory was used to determine the symmetry-allowed magnetic structures after the Neel transition and the refned magnetic structure evidences both ferromagnetic and antiferromagnetic inter-chain interactions, and ferromagnetic intra-chain coupling. The competition between the magnetic interactions can be seen in the canting of the moments away from a collinear arrangement.

cond-mat.str-el↗

arXiv2009

Metal - Insulator transition in Fe1.01-xCuxSe

Iron Selenide, Fe1.01Se, the layered parent compound of the recently discovered superconducting arsenide family, has previously been shown to be non magnetic and superconducting with a critical temperature of 8 K. Here we show that copper can be substituted at the iron site in Fe1.01Se up to a solubility limit of 20-30 %, after which a first order transition to the three-dimensional CuFeSe2 structure type is observed. As little as 1.5 % percent copper is sufficient to suppress the superconductivity, and 4 % drives the system through a metal-insulator transition. A local magnetic moment is introduced, which maximizes near 12% doping, where a spin-glass transition near 15 K is observed.

cond-mat.supr-con↗