High-field, high-frequency ESR in the one-dimensional quantum spin systems

We applied the high-field, high-frequency electron spin resonance (ESR) tec hnique to study the held-dependent behaviors of three representative exampl es of quantum spin chain. (1) In the half-integer (S = 1/2) antiferromagnet Cu-benzoate, Cu(C6H5COO)(2). 3H(2)O, we observed rather unusual temperatur e- and field-dependences of the shift and width of the resonance line. Thes e results are discussed in terms of the breather excitations predicted by O shikawa and Affleck for this compound. (2) For the integer (S = 1) antiferr omagnet NDMAZ, Ni(C5H14N2)(2)N-3 (ClO4), we observed various ESR modes both in the nonmagnetic Haldane phase (H < H-c) and in the magnetic high-field phase (H > H-c) where H-c is the critical field at which the Haldane gap cl oses. From the frequency-field diagram and the temperature dependence of th e signal intensity, we discuss the possible origin of these ESR modes. (3) For S = 1/2 trimerized chain, 3CuCl(2). 2dioxane, we observed unique featur es of a composite spin system, such as a dynamical process of the formation of S = 3/2 trimerized units from three S = 1/2 spins, as indicated by the signal splitting into 3 lines at most depending on the frequency and gradua l change of the resonance fields with decreasing temperature.