1. Evolution of the orbital Peierls state with doping
Neutron scattering in Y1-xCaxVO3
C. Ulrich1, J. Fujioka2, G. Khaliullin1, M. Reehuis3, K. Schmalzl4, A. Ivanov4,
K. Hradil5, S. Miyasaka2, Y.Tokura2, and B. Keimer1
1Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
2University of Tokyo, Tokyo, Japan
3Hahn-Meitner-Institut, Berlin, Germany
4Institut Laue-Langevin, Grenoble, France
5FRM II, Munich, Germany
physics of the 3d simple cubic perovskites
spin, charge, orbital degrees of freedom
YVO3 : 3d2 two magnetic phases (C- and G-type)
Krakow, 20. June 2008

2. Crystal Structure 3D - perovskite structure Pm3mg - O
rbital t 2g – x 2 y 3z r 3 z yz xz xy
Jahn
Teller
Aufspaltung
splitting
cubic splitting
tetragonal
VO6
octahedra Y
Pm3m
ideal cubic perovskite
Pbnm
GdFeO3 - type distortion
Tilt and rotation of the VO6 octahedra
Distortion of the VO6 octahedra

3. YVO3: Elastic Neutron Scattering
m0 = 1.72 mB / V3+-ion
m0 = 1.05 mB / V3+-ion

4. YVO3: Low Temperature Phase
conventional
orbital order

5. YVO3: High Temperature Phase
C-type
reduced magnetic moment
total: m0 = 1.05 mB/V3+
total ordered moment:
2.00 mB (free ion moment)
1.72 mB (ordered moment of
the G-type phase)
canting angle = 160 out of plane
C-type:
mx = 0.49 mB
my = 0.89 mB
G-type:
mz = 0.30 mB
C. Ulrich et al., PRL 91, (2003).

6. YVO3: High Temperature Phase
overall collapse of the magnon band width (20 meV C-type vs. 35 meV G-type)
band width larger in the ferromagnetic c-direction than in the
antiferromagnetic ab-plane (assuming Goodenough-Kanamori
rules one would expect the opposite)
Excelent fit obtained by using three exchange parameters:
Jab = 2.6 meV, Jc1 = -2.2 meV, Jc2 = -4 meV
=> dimerization of exchange bonds along the c-axis
C. Ulrich et al.,
PRL 91, (2003).

7. Resonating Orbitals in the YVO3xz
xz / yz yz xy xy
undistorted xy
Pbnm phase
G-type
C-type c
77 K
116 K
210 K
G-type phase: T < 77 K
strong JT effect orbitally ordered phase
C-type phase: 77 K < T < 116 K
static xy orbital stabilizes the
AF magnetic order in plane
orbital fluctuations along the c-axis
between xz and yz orbital
orbital
pseudospin t = ½, ) )( 1 ( 2 4 + = å i SE S J H t
Khaliullin et al., PRL 86, 3879 (2001).

8. Orbital Peierls State Orbital Peierls State c
Consequence of the orbital fluctuations
C-type phase: 77 K < T < 118 K c
orbital singlet
spin triplet
strong ferro.
weak ferro.
strong ferro.
G. Khaliullin et al., PRL 86, 3879 (2001).
C. Ulrich et al., PRL 91, (2003).
P. Horsch et al., PRL 91, (2003).
A.M. Oleś et al., PRB 75, (2007).
structural evidence for the dimerized phase Pb11: A.A. Tsvetkov et al., PRB 69, (2004).

9. LaVO3: Inelastic Neutron Scattering
Tstruc. = 145 K Pbnm monoclinic P21/a
Tmag. = 143 K C-type, spins within the ab-plane
magnon
phonon
no splitting into an optical and acoustic magnon branch
exchange parameters: Jab = 6.5 meV Jc = meV

10. LaVO3: Inelastic Neutron Scattering
L.D. Tung, D.M.K. Paul, University of Warwick, UK
LaVO3 Tmag. = 136 K C-type
ILL – experimental report

11. Effect of doping: 2 t2g Þ 1 t2g
Doping dependence of the Orbital Peierls State
Y1-xCaxVO3
Effect of doping: 2 t2g Þ 1 t2g
S. Miyasaka, PRL 85, 5388 (2000).
J. Fujioka, PRB 72, (2005).
Y. Tokura, University of Tokyo
G-type phase disappears at 1.5 % Ca doping
C-type mag. phase (Orbital Peierls phase) is robust
50% Ca-doping: Metal Insulator Transition

12. Doping dependence of the Orbital Peierls State
Y1-xCaxVO3:
Magnetic phase transition temperatures decrease with doping
C-type phase: magnetic structure at T = 85 K almost unchanged
G-type phase: magnetic moment decreases with doping

13. Y1-xCaxVO3: C-type phase
Doping dependence of the Orbital Peierls State
YCaVO % K
Y1-xCaxVO3: C-type phase
Y1-xCaxVO % K
YCaVO % K

14. Doping dependence of the Orbital Peierls State
Y1-xCaxVO3
IN22 ILL-Grenoble 2 %
PUMA FRMII-Munich 5 %
Magnon
Magnon
Phonon
raw data taken at the IN22/ILL-Grenoble and Puma/FRMII-Munich
data were taken above and below the magnetic phase transition

15. new Si-monochromator IN20/ILL
Doping dependence of the Orbital Peierls State
new Si-monochromator IN20/ILL

16. Doping dependence of the Orbital Peierls State
(0.5,0.5,1.25)
(0.5,0.5,1)
spin gap
slight increase in the spin wave energies
Orbital Peierls State is confirmed and even more robust

17. Y1-xCaxVO3: 1 % G-type phase perfect orbitally ordered state
YVO3 : G-type phase
Y1-xCaxVO3: 1 % G-type phase
Magnetic structure and
spin wave dispersion as in YVO3
perfect orbitally ordered state

18. Y1-xCaxVO3: 1 % CG-mixed phase
YVO3 : G-type phase
Y1-xCaxVO3: 1 % CG-mixed phase
(1/2, 1/2, 0)
C-type magnetic
Bragg peak
Depending in the cooling history
- pure G-type phase at T = 2 K
- C-type / G-type mixed phase
Hysteresis between the
C-type and G-type phase

19. Y1-xCaxVO3: 1 % CG-mixed phase
YVO3 : CG-mixed phase
Y1-xCaxVO3: 1 % CG-mixed phase
spin gap
C-type
G-type
Magnon branches of the C-type phase and G-type phase coexist
Spin gap demonstrates: microscopic interaction between both phases

20. Conclusions Orbital fluctuations Y1-xCaxVO3 x = 0% 1% 2% 5%
magnetic structure and dynamics measured by neutron scattering
Orbital fluctuations
C-type phase is stabilized by
realization of spin-orbital chains in 3D insulator
entropy driven orbital Peierls state identified
Effects of Ca-doping:
G-type – orbitally ordered phase disappears rapidly
C-type phase: orbital Peierls state is stabilized
C/G-mixed phase with a microscopic interaction

21. LaVO3: Inelastic Neutron Scattering
Tstruc. = 145 K Pbnm monoclinic P21/a
Tmag. = 143 K C-type, spins within the ab-plane