Antiferromagnetism in doped anisotropic two-dimensional spin-Peierls systems

Abstract

We study the formation of antiferromagnetic correlations induced by impurity doping in anisotropic twodimensional spin-Peierls systems. Using a mean-field approximation to deal with the interchain magnetic coupling, the intrachain correlations are treated exactly by numerical techniques. The magnetic coupling between impurities is computed for both adiabatic and dynamical lattices and is shown to have an alternating sign as a function of the impurity-impurity distance, hence suppressing magnetic frustration. An effective model based on our numerical results supports the coexistence of antiferromagnetism and dimerization in this system.

Spin-Peierls transition in an anisotropic two-dimensionalXYmodel

“…the XY model is believed to contain the essential elements for the spin-Peierls transition [5]. We point out that the similar problem based on the Heisenberg model was studied previously by some authors [7,8]. However, they all treated the interchain coupling within the so called chain mean-field theory and actually still studied a 1D system.…”

“…But we believe that the above qualitative results for the XY model, especially the rapid increasing property for η c away from zero, is not changed by the extra Ising terms except that the U phase in Fig. 1 is replaced by more precisely called Néel phase (i.e., uniform state with antiferromagnetic LRO) [7,8]. More work is necessary for justification.…”

“…Beyond adiabatic approximation it was found that the spinphonon coupling must be larger than some nonzero critical value for the SP instability to occur [5,6]. The interchain exchange coupling is also a possible mechanism [7][8][9]. This mechanism is often not negligible for real SP materials, especially for the material CuGeO 3 where a relatively large interchain coupling, about J ⊥ /J = 0.1 (J represents the intrachain exchange) was found experimentally [10].…”

“…Furthermore it is of great interest to extend this work to study the phase diagram for doped quasi-1D SP system. In addition, we also notice that the nonadiabatic effect as refered before is important for really modelling CuGeO 3 [5,6,8,27], so inclusion of dynamic phonons beyond this work is another interesting topic for future investigation.…”

Dynamics of weakly coupled random antiferromagnetic quantum spin chains

“…Amazingly, when doping reaches certain levels the spins become Néel ordered at low temperature, which has been observed experimentally in Zn-and Si-doped CuGeO 3 . [11][12][13][14][15][16][17][18][19][20] Since these experimental discoveries a number of theoretical papers have addressed the static Néel ordering in these systems [24][25][26][27][28][29][30][31][32][33][34][35][36] using meanfield theory. On the other hand the collective excitations and dynamical response functions which have been studied experimentally using inelastic neutron scattering, 20 have not been studied theoretically thus far.…”