  We show theoretically that spin and orbital degrees of freedom in the
pyrochlore oxide Y2Mo2O7, which is free of quenched disorder, can exhibit a
simultaneous glass transition, working as dynamical randomness to each other.
The interplay of spins and orbitals is mediated by the Jahn-Teller lattice
distortion that selects the choice of orbitals, which then generates variant
spin exchange interactions ranging from ferromagnetic to antiferromagnetic
ones. Our Monte Carlo simulations detect the power-law divergence of the
relaxation times and the negative divergence of both the magnetic and
dielectric non-linear susceptibilities, resolving the long-standing puzzle on
the origin of the disorder-free spin glass.
