Dynamical spin–orbital correlation in thefrustrated magnet Ba3CuSb2O9

摘要

At low temperatures, atomic magnetic moments usually exhibit some order, for exampleferromagnetic order. An exception is frustrated magnets, in which the symmetry impedes theminimization of energy by pairwise magnetic interactions. In such frustrated magnets, newquantum phases, such as spin liquids, are expected. Theoretically, a quantum liquid based onthe orbital degree of freedom has also been considered possible when spin and orbitaldegrees of freedom are entangled. However, to date, experimental observation of such adynamic spin–orbital state has been a challenge. Here we report an X-ray scattering study of adynamic spin–orbital state in the frustrated magnet Ba3CuSb2O9. Orbital dynamical motionand increasing short-range orbital correlation with cooling are observed. The most significantfeature is that the temperature variation of the orbital correlation is clearly affected by themagnetic interaction. This finding strongly supports a new quantum state in which spins andorbitals are entangled.