科研之友
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摘要
Spontaneous symmetry breaking is deeply related to the dimensionality of a system. The Neel order going with spontaneous breaking of U(1) symmetry is safely allowed at any temperature for three-dimensional systems but allowed only at zero temperature for purely two-dimensional systems. We closely investigate how smoothly the ordering process of the three-dimensional system is modulated into that of the two-dimensional one with reduction of dimensionality, considering spatially anisotropic quantum antiferromagnets. We first show that the Neel temperature is kept finite even in the two-dimensional limit although the Neel order is greatly suppressed for low dimensionality. This feature of the Neel temperature is highly nontrivial, which dictates how the order parameter is squashed under the reduction of dimensionality. Next, we investigate this dimensional modulation of the order parameter. We develop our argument taking as an example a coupled spin-ladder system relevant for experimental studies. The ordering process is investigated multidirectionally using theoretical techniques of a mean-field method combined with analytical (exact solutions of quantum field theories) or numerical (density-matrix renormalization-group) methods, a variational method, a renormalization-group study, linear spin-wave theory, and quantum Monte Carlo simulations. We show that these methods independent of each other lead to the same conclusion about the dimensional modulation.
- 出版日期2016-10-3
- 单位RIKEN
