Evidence for an Orbital Peierls state in YVO3

Full text: Neutron spectroscopy has revealed a highly unusual magnetic structure and dynamics in YVO3, an insulating pseudocubic perovskite that undergoes a series of temperature induced phase transitions between states with different spin and orbital ordering patterns. A good description of the neutron data is obtained by a theoretical analysis of the spin and orbital correlations of a quasi-one-dimensional model with spins S=1. At small Hund's coupling jh we discover dimerization in a pure electronic system solely due to a dynamical spin-orbital coupling. Above a critical value jh, a uniform ferromagnetic state is stabilized at zero temperature. More surprisingly, we observe a temperature driven dimerization of the ferrochain, which occurs due to a large entropy released by dimer states. This leads to the tentative identification of one of the phases of YVO3 with the 'orbital Peierls state', a theoretically proposed many-body state comprised of orbital singlet bonds