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arXiv 0709.3064cond-mat.supr-concond-mat.mes-hall
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二维非均匀d波超导体中的涡旋钉扎模型

Model for Vortex Pinning in a Two-Dimensional Inhomogeneous d-wave Superconductor

Daniel Valdez-Balderas, David Stroud

摘要:

我们研究了二维非均匀II型超导体混合态中涡旋钉扎的模型。该模型基于Ginzburg-Landau(GL)自由能泛函,其系数由平均场转变温度T_{c0}和零温穿透深度λ(0)决定。我们发现,如果(i)T_{c0}和λ(0)是位置的函数,(ii)λ^2(0)与T_{c0} ^y成比例,且y大于0,则在T_{c0}以及超导序参量Δ的大小较大的地方,涡旋趋于被钉扎。这种行为与II型超导体中通常的钉扎现象相反,在II型超导体中钉扎发生在小间隙区域。我们还计算了一个具有d波对称性的BCS模型的局域态密度,其中对场由GL自由能的蒙特卡罗模拟得到。我们的模型很好地再现了在YBa_2Cu_3 O_{6+x}和Bi_2Sr_2CaCu_2 O_{8+x}的扫描隧道谱测量中观察到的几个特征:远离核,局域态密度谱具有小的能隙和尖锐的相干峰,而靠近核,局域态密度谱具有较大的能隙和低而宽的峰。此外,也与实验一致,在核心附近的光谱没有表现出零能量峰,然而,在其他理论研究中观察到。

英文摘要:

We study a model for the pinning of vortices in a two-dimensional, inhomogeneous, Type-II superconductor in its mixed state. The model is based on a Ginzburg-Landau (GL) free energy functional whose coefficients are determined by the mean-field transition temperature T_{c0} and the zero-temperature penetration depth λ(0). We find that if (i) T_{c0} and λ(0) are functions of position, and (ii) λ^2(0) is proportional to T_{c0}^y, with y greater than 0, then the vortices tend to be pinned where T_{c0}, and hence the magnitude of the superconducting order parameter Δ, are large. This behavior is in contrast to the usual picture of pinning in Type-II superconductors, where pinning occurs in the small-gap regions. We also compute the local density of states of a model BCS Hamiltonian with d-wave symmetry, in which the pairing field is obtained from Monte Carlo simulations of a GL free energy. Several features observed in scanning tunneling spectroscopy measurements on YBa_2Cu_3O_{6+x} and Bi_2Sr_2CaCu_2O_{8+x} are well reproduced by our model: far from the cores, the local density of states spectrum has a small gap and sharp coherence peaks, while near the cores it has a larger gap with low, broad peaks. Additionally, also in agreement with experiment, the spectrum near the core does not exhibit a zero-energy peak which is, however, observed in other theoretical studies.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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