Low-temperature properties

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Low-temperature properties of the t2g1 Mott
insulators
Interatomic exchange-coupling constants by
2nd-order perturbation theory in t
t2g1 t2g1 t2g0 t2g2
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Empty crystal-field orbital, 3), in the
monoclinic phase
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The missing piece in the Sr2RhO4 puzzle
Sr2RhO4 is a K2NiF4-structured 4d (t2g)5
paramagnetic metal
Transition-metal oxides have interesting
properties because they have many lattice and
electronic (orbital, charge, and spin) degrees of
freedom, coupled by effective interactions
(electron-phonon, hopping t, Coulomb repulsion U,
and Hunds-rule coupling J). When some of the
interactions are of similar magnitude, competing
phases may exist in the region of controllable
compositions, fields, and temperatures.
The interactions tend to remove low-energy
degrees of freedom, e.g. to reduce the
metallicity
Guo-Qiang Liu, V.N. Antonov, O. Jepsen, and OKA,
PRL 101, 026408 (2008)
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Ru 4d (t2g)4
K2NiF4
(Ca1-xSrx)RuO4 The relatively small size and
strong covalency of Ca cause the RuO6 to rotate
and tilt. For x increasing from 0 to 1 these
distortions go away and the properties go from
insulating to metallic and from magnetic (AF/F
metamagn) to paramagnetic at low T. Sr2RuO4 is a
2D Fermi liquid whose Fermi surface agrees well
with LDA and has a mass enhancement of 3. It
becomes superconducting below 1K.
Ruddlesden-Popper (Ca,Sr)n1RunO3n1 where n1,
2, 3, ?
From Haverkort et al. PRL 026406 (2008)
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Alternating rotation of octahedra and cell
doubling in xy-plane gaps the broad, overlapping
xy and x2-y2 bands for a filling of 5 t2g
electrons.
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But still unusually bad agreement between
and
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The missing piece