Atomic matter of nonzero-momentum Bose-Einstein condensation and orbital current order

Abstract

The paradigm of Bose-Einstein condensation has been associated with zero momentum to which a macroscopic fraction of bosons condense. Here we propose a new quantum state where bosonic alkali-metal atoms condense at non-zero momenta, defying the paradigm. This becomes possible when the atoms are confined in the p-orbital Bloch band of an optical lattice rather than the usual s-orbital. The new condensate simultaneously forms an order of transversely staggered orbital currents, reminiscent of orbital antiferromagnetism or d-density wave in correlated electronic systems but different in fundamental ways. We discuss several approaches of preparing atoms to the p-orbital and propose an ``energy blocking'' mechanism by Feshbach resonance to protect them from decaying to the lowest s-orbital. Such a model system seems very unique and novel to atomic gases. It suggests a new concept of quantum collective phenomena of no prior example from solid state materials.