1,259 research outputs found
Structural and magnetic aspects of the metal insulator transition in CaSrRuO
The phase diagram of CaSrRuO has been studied by neutron
diffraction on powder and single-crystalline samples. The experiments reveal
antiferromagnetic order and structural distortions characterized by tilts and
rotations of the RuO-octahedra. There is strong evidence that the
structural details of the isovalent samples tune the magnetic as well as the
electronic behavior. In particular we observe for low Sr-concentration a metal
insulator transition associated with a structural change and magnetic ordering
Orbital Switching and the First-Order Insulator-Metal Transition in Paramagnetic V_2O_3
The first-order metal-insulator transition (MIT) in paramagnetic
is studied within the ab-initio scheme LDA+DMFT, which merges the local density
approximation (LDA) with dynamical mean field theory (DMFT). With a fixed value
of the Coulomb , we show how the abrupt pressure driven MIT is
understood in a new picture: pressure-induced decrease of the trigonal
distortion within the strong correlation scenario (which is not obtained within
LDA). We find good quantitative agreement with switch of the orbital
occupation of and the spin state S=1
across the MIT, thermodynamics and resistivity, and the
one-electron spectral function, within this new scenario.Comment: 4 pages, 4 figures, submitted to PR
Anomalous spin density distribution on oxygen and Ru in CaSrRuO: A polarised neutron diffraction study
By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6
K an anomalously large magnetization density is observed on the in-plane oxygen
in CaSrRuO. Field-induced moments of different ions are
determined by refinement on the flipping ratios, yielding =
0.346(11) , = 0.076(6) and = 0.009(6)
. The moment on the oxygen arises from the strong hybridization
between the Ru-4d and O-2p orbitals. %The maximum entropy method is used for
the %reconstruction of the magnetization density and reveals a strongly
anisotropic The maximum entropy magnetization density reconstruction reveals a
strongly anisotropic density at the Ru site, consistent with the distribution
of the {\it xy} ( band) {\it d}-orbitals.Comment: 4 pages 3 figure
Orbital and spin correlations in CaSrRuO: A mean field study
The alloy CaSrRuO exhibits a complex phase diagram with
peculiar magnetic metallic phases. In this paper some aspects of this alloy are
discussed based on a mean field theory for an effective Kugel-Khomskii model of
localized orbital and spin degrees of freedom. This model results from an
orbital selective Mott transition which in the three-band system localized two
orbitals while leaving the third one itinerant. Special attention is given to
the region around a structure quantum phase transition at
where the crystal lattice changes from tetragonal to orthorhombic symmetry
while leaving the system metallic. This transition yields, a change from
ferromagnetic to antiferromagnetic spin correlations. The complete mean field
phase diagram for this transition is given including orbital and spin order.
The anisotropy of spin susceptibility, a consequence of spin-orbit coupling and
orbital correlation, is a tell-tale sign of one of these phases. In the
predominantly antiferromagnetic phase we describe a metamagnetic transition in
a magnetic field and show that coupling of the itinerant band to the localized
degrees of freedom yields an anomalous longitudinal magnetoresistance
transition. Both phenomena are connected with the evolution of the
ferromagnetic and antiferromagnetic domains in the external magnetic field and
agree qualitatively with the experimental findings.Comment: 12 pages, accepted for publication in EPJ
Raman scattering studies of spin, charge, and lattice dynamics in Ca_{2-x}Sr_{x}RuO_{4} (0 =< x < 0.2)
We use Raman scattering to study spin, charge, and lattice dynamics in
various phases of Ca_{2-x}Sr_{x}RuO_{4}. With increasing substitution of Ca by
Sr in the range 0 =< x < 0.2, we observe (1) evidence for an increase of the
electron-phonon interaction strength, (2) an increased temperature-dependence
of the two-magnon energy and linewidth in the antiferromagnetic insulating
phase, and (3) evidence for charge gap development, and hysteresis associated
with the structural phase change, both of which are indicative of a first-order
metal-insulator transition (T_{MI}) and a coexistence of metallic and
insulating components for T < T_{MI}
Orbital Dependent Phase Control in Ca2-xSrxRuO4
We present first-principles studies on the orbital states of the layered
perovskites CaSrRuO. The crossover from antiferromagnetic (AF)
Mott insulator for to nearly ferromagnetic (FM) metal at is
characterized by the systematic change of the orbital occupation. For the
AF side (), we present firm evidence for the ferro-orbital
ordering. It is found that the degeneracy of (or ) states is
lifted robustly due to the two-dimensional (2D) crystal-structure, even without
the Jahn-Teller distortion of RuO. This effect dominates, and the
cooperative occupation of orbital is concluded. In contrast to recent
proposals, the resulting electronic structure explains well both the observed
X-ray absorption spectra and the double peak structure of optical conductivity.
For the FM side (), however, the orbital with half filling opens a
pseudo-gap in the FM state and contributes to the spin =1/2 moment (rather
than =1 for =0.0 case) dominantly, while states are itinerant
with very small spin polarization, explaining the recent neutron data
consistently.Comment: 17 pages, 5 figure
Pressure-Tuned Collapse of the Mott-Like State in Ca_{n+1}Ru_nO_{3n+1} (n=1,2): Raman Spectroscopic Studies
We report a Raman scattering study of the pressure-induced collapse of the
Mott-like phases of Ca_3Ru_2O_7 (T_N=56 K) and Ca_2RuO_4 (T_N=110 K). The
pressure-dependence of the phonon and two-magnon excitations in these materials
indicate: (i) a pressure-induced collapse of the antiferromagnetic (AF)
insulating phase above P* ~ 55 kbar in Ca_3Ru_2O_7 and P* ~ 5-10 kbar in
Ca_2RuO_4, reflecting the importance of Ru-O octahedral distortions in
stabilizing the AF insulating phase; and (ii) evidence for persistent AF
correlations above the critical pressure of Ca_2RuO_4, suggestive of phase
separation involving AF insulator and ferromagnetic metal phases.Comment: 3 figure
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