Static and dynamical properties of frustrated two-dimensional square quantum Heisenberg antiferromagnets - art. no. 024412

Two-dimensional square quantum Heisenberg antiferromagnets with competing i nteractions up to third neighbors (J(1)-J(2)-J(3) model) are investigated b y using the high-temperature series expansion method. From the analyses of the wave-vector-dependent susceptibility X(k), we find four kinds of the st able paramagnetic phases depending on the coupling constants, i.e., Neel, c ollinear, and two helical paramagnetic phases, H-1 and H-2. They are charac terized by thr critical wave vector k(A)(c) (A = N, C, H-1, or H-2), at whi ch the functions X(k) show the maximum value. Except around the H-1-H-2 pha se boundary, they are destabilized and show the intermediate phases in the neighborhood of the phase boundaries, where the relevant critical wave vect or k(A)(c) is not specified uniquely. The analogy between the paramagnetic phase diagram obtained here and the ordered ones derived by the simple spin wave theory suggests the possibility of the spin liquid state in the inter mediate phase at T=0. The first-order transition occurs between H-1 and H-2 phases, so the intermediate phase is not seen there. The dynamical spectru m function F(k,omega) is calculated in the form of Mori's continued fractio n with the frequency moments. The dynamical aspects for the stable paramagn etic phases are also characterized by the critical wave vector k(A)(c). Whi le the side peak or shoulder shape appears in F(k(c)(A),omega) at T=infinit y, the line shape becomes considerably narrow when decreasing the temperatu re at k(A)(c). These behaviors are attributed to the spin flip-flop motion for the former case, and the quasicollective motion for the latter one. In the intermediate phase, at T=infinity the line shape undergoes slow change versus the wave vector k except for the drastic narrowing around k similar or equal to0, due to the absence of the unique critical wave vector. It is found that the high-temperature dynamical aspect keeps there, even though t he temperature is decreased, due to the frustration effect.