CONDENSED MATTER AND STATISTICAL PHYSICS SECTION SEMINAR

[Condensed_Matter_Group]

CONDENSED MATTER AND
STATISTICAL PHYSICS SECTION

SEMINAR

Friday, 6 August 2010    -    16:00 p.m.

L. Stasi Seminar Room
ICTP Leonardo Building - 1st floor

C.I. VENTURA
(Centro Atomico Bariloche and Univ. Nac. de Rio Negro, Bariloche, Argentina)

"Spin Excitations in Strongly Correlated
Electron Systems"

Abstract
One way to probe magnetic order is to measure spin excitations, such as
magnons, by inelastic neutron scattering experiments, and compare them
with those characteristic of each proposed magnetic phase. Here we will
describe our recent studies of magnetic excitations in two families of
strongly correlated electron systems.

First, for half-doped colossal magnetoresistance manganites, I will report
on our study of the spin excitations of the CE phase originally proposed
by J. Goodenough. Using a localized spin model we calculated magnons for
3D-perovskite compounds such as La1-xMxMnO3, where M=Ca,Sr,Ba, and for
their 2D-laminar counterparts, as e.g. La0.5Sr1.5MnO4 .

I will then briefly describe our study for the magnons observed in heavy
fermions with antiferromagnetic long-range order (Tneel~TKondo),
concretely in CeIn3 and CePd2Si2 single crystals. We used a microscopic
model including a lattice of correlated f-electron orbitals (as in Ce,U)
hybridized with the conduction band, with competing RKKY (Heisenberg-like
J H) and Kondo (JK) couplings.Through a series of unitary transformations,
we perturbatively derived a second order effective Hamiltonian which,
projected on the antiferromagnetic fermion ground state, describes the
spin wave excitations, renormalized by their interaction with the
conduction electrons. Our calculated magnon dispersion relations agree
well with the experimental data in cubic CeIn 3 [M.Acquarone, C.I.Ventura,
Journal of Mag. & Magnetic Mats. 321, 2648 (2009)].