  Neutron spectroscopy has revealed a highly unusual magnetic structure and
dynamics in YVO$_3$, 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
realistic one-dimensional model. This leads to the tentative identification of
one of the phases of YVO$_3$ with the ``orbital Peierls state'', a
theoretically proposed many-body state comprised of orbital singlet bonds.

Strongly Correlated Electrons