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TT: Fachverband Tiefe Temperaturen

TT 8: Correlated Electrons: Spin Systems and Itinerant Magnets 1

TT 8.6: Vortrag

Montag, 25. Februar 2008, 15:30–15:45, H 0104

Evolution of the ’Orbital Peierls State’ with doping — •C. Ulrich¹, G. Khaliullin¹, M. Reehuis^1,2, K. Schmalzl³, A. Ivanov³, K. Hradil⁴, J. Fujioka⁵, Y. Tokura⁵, and B. Keimer¹ — ¹MPI-FKF, Stuttgart — ²HMI, Berlin — ³ILL Grenoble, France — ⁴FRM II, Munich — ⁵University of Tokyo, Japan

Orbital degrees of freedom play an important role in the physics of strongly correlated electron systems. Our extensive investigation of insulating vanadates by neutron scattering has led to the discovery of an unusual magnetic ground state due to the interplay between spin and orbital degrees of freedom. YVO₃ exhibits two magnetic phases, a C-type phase between 116 K and 77 K and a G-type phase below 77 K. While the magnetic properties of the G-type phase are in accordance with standard theoretical descriptions, the C-type phase shows highly unusual static and dynamic spin correlations. Based on the idea of orbital fluctuations we were able to identify this phase as a theoretically predicted but hitherto unobserved ’orbital Peierls state’ [1].
Our latest neutron scattering experiments show that the C-type phase in Y_1−xCa_xVO₃, i.e., the ’orbital Peierls phase’, is stabilized upon doping, while the orbitally ordered G-type phase is quite unstable and disappears at x = 2 %. Furthermore, with doping this phase also exhibits a highly unusual spin wave dispersion. This leads us to the conclusion, that the ’orbital Peierls state’ becomes more robust with Ca-doping, whereas the formerly well defined G-type phase exhibits a more complex behavior, probably as a consequence of an increase in orbital fluctuations.

[1] C. Ulrich et al., PRL 91, 257202 (2003).