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Low-temperature properties of the t 2g 1 Mott insulators

Explore the interatomic exchange coupling constants and orbital and magnetic orders in T2g1 Mott insulators using perturbation theory. Investigate the effects of superexchange and the Mott transition on orbital fluctuations in T2g2 perovskites.

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Low-temperature properties of the t 2g 1 Mott insulators

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  1. Low-temperature properties of the t2g1 Mott insulators Interatomic exchange-coupling constants by 2nd-order perturbation theory in t t2g1 + t2g1 = t2g0 + t2g2

  2. Orbital and Magnetic Orders Superexchange: JAF ~ 4t2/U tx=ty=99 meV tx=ty=48 meV tz=38 meV tz=105 meV F 3D AF

  3. Jse -4.7 3.0 5.0 -0.7

  4. High-temperature orthorhombic phase 92 meV 53 meV 0 meV 80 meV 0 meV 207 meV

  5. Mott transition and suppression of orbital fluctuations in t2g2 perovskites YVO3 LaVO3

  6. t2g2 770 K (orthorhombic PI phase) YVO3 LaVO3 2 1 3 Much stronger orbital fluctuations for the t2g2 La and Y vanadates than for the t2g1 titanates because of 1) Hunds rule and 2) less AB(O) covalency

  7. Empty crystal-field orbital, |3), in the monoclinic phase

  8. Vanadate t2g2 conclusions

  9. 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)

  10. Ru o Ca or Sr 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)n+1RunO3n+1 where n=1, 2, 3,  From Haverkort et al. PRL 026406 (2008)

  11. (t2g)5 (t2g)4 From Haverkort et al. PRL 026406 (08) 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.

  12. ARPES LDA But still unusually bad agreement between and

  13. ζeff + ζeff / εF 2-parameter fit + εF ζeff = 2.15 ζ why?

  14. Since Sr2RhO4 is paramagnetic at low temperature, HF mean field approximation We had: , leading to: where the polarization, p, should be determined selfconsistently. For each Bloch state, so the polarization function is:

  15. ζeff + ζeff / εF 2-parameter fit + εF ζeff = 2.2 ζ, why?

  16. The missing piece:

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