Growth of Antiferromagetic Order in Superconducting State: Analysis Using Mode--Mode Coupling Theory

概要

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It has been considered since the first discovery of a high-T_{\text{c}} cuprate that an antiferromagnetic (AFM) order and a superconducting (SC) order compete with each other since they are separated in the phase diagram. However, the coexistence of the AFM and SC orders has recently been observed in Ba2Ca4Cu5O10(F,O)2. Moreover, this material shows a very intriguing AFM property, in which the drastic growth of the AFM order has been prompted by the onset of the SC order as temperature decreases in the AFM state. The mode--mode coupling theory can provide a clear elucidation of this novel phenomenon. A key point of this theory is that the AFM order consists of the random-phase-approximation (RPA) term and mode--mode coupling one. The RPA term works to make a positive contribution to the growth of the AFM order. In contrast, the mode--mode coupling term works to make a negative contribution to the growth of the AFM order. The growth of the SC gap in the dx^{2-wave SC state works to suppress this negative contribution of the mode--mode coupling term to the growth of the AFM order. For this reason, there is a possibility that the dx^{2-wave SC state will promote the growth of the AFM order. Therefore, the drastic growth of the AFM order in the coexistent phase of the AFM and SC orders observed in Ba2Ca4Cu5O10(F,O)2 can be explained qualitatively on the basis of this idea.
2012-09-15