Low Temperature Properties of the Double Layer Quantum Heisenberg Antiferromagnet -Modified Spin Wave Method-

The low temperature properties of the double layer quantum Heisenberg antiferromgnet are studied by the modified spin wave method proposed by Takahashi. As expected from the lowest order spin wave analysis, the spin fluctuation decreases with the increase of the interlayer coupling J K for small J K , while it turns to increase for large J K for the antiferromagnetic J K . The long range order is destroyed for large enough J K . The disordered phase is the singlet gas phase. The low temperature behaviors of the spin-spin correlation length are also calculated and characters of the low temperature phase are discussed.