Costa Natanael C, de Lima José P, Paiva Thereza, El Massalami Mohammed, Dos Santos Raimundo R
Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
J Phys Condens Matter. 2018 Jan 31;30(4):045602. doi: 10.1088/1361-648X/aaa1ab.
With the purpose of investigating coexistence between magnetic order and superconductivity, we consider a model in which conduction electrons interact with each other, via an attractive Hubbard on-site coupling U, and with local moments on every site, via a Kondo-like coupling, J. The model is solved on a simple cubic lattice through a Hartree-Fock approximation, within a 'semi-classical' framework which allows spiral magnetic modes to be stabilized. For a fixed electronic density, n , the small J region of the ground state (T = 0) phase diagram displays spiral antiferromagnetic (SAFM) states for small U. Upon increasing U, a state with coexistence between superconductivity (SC) and SAFM sets in; further increase in U turns the spiral mode into a Néel antiferromagnet. The large J region is a (singlet) Kondo phase. At finite temperatures, and in the region of coexistence, thermal fluctuations suppress the different ordered phases in succession: the SAFM phase at lower temperatures and SC at higher temperatures; also, reentrant behaviour is found to be induced by temperature. Our results provide a qualitative description of the competition between local moment magnetism and superconductivity in the borocarbides family.
为了研究磁有序与超导性之间的共存关系，我们考虑一个模型，其中传导电子通过吸引性的哈伯德在位耦合U相互作用，并通过类似近藤耦合J与每个格点上的局域磁矩相互作用。该模型在简单立方晶格上通过哈特里-福克近似求解，在一个“半经典”框架内，该框架允许螺旋磁模式稳定。对于固定的电子密度n，基态（T = 0）相图的小J区域在小U时显示螺旋反铁磁（SAFM）态。随着U的增加，出现超导（SC）与SAFM共存的状态；U的进一步增加将螺旋模式转变为尼尔反铁磁体。大J区域是一个（单重态）近藤相。在有限温度下，在共存区域，热涨落依次抑制不同的有序相：较低温度下的SAFM相和较高温度下的SC；此外，发现温度会诱导再入行为。我们的结果对硼碳化物家族中局域磁矩磁性与超导性之间的竞争提供了定性描述。
