arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 0807.3931cond-mat.supr-concond-mat.str-el
收藏

无序二维超导体:温度和相互作用强度的作用

Disordered two-dimensional superconductors: roles of temperature and interaction strength

Felipe Mondaini, Thereza Paiva, Raimundo R. dos Santos, R. T. Scalettar

摘要:

我们考虑了正方形格子上的半满无序吸引Hubbard模型,其中在一小部分$f$上的在位吸引被关闭,而在其余的位置上保持有限的$f$.通过量子蒙特卡罗(QMC)模拟的$f$和$U$的几个值,并为系统的大小范围从$8\times 8$到$16\times 16$,我们已经计算出的等时对结构因子$P_s$的配置平均值,并为一组更严格的变量,螺旋模量,$ρ_s$,作为温度的函数。对$P_s$采用了两种有限尺寸标度{ \it ansatze},一种用于零温度,另一种用于有限温度。我们已经发现,该系统维持超导性在基态的临界杂质浓度,$f_c$,这增加与$U$,至少高达U=4(在跳跃能量的单位)。此外,作为$f$的函数的归一化零温度间隙在$f\sim 0.07$附近显示出最大值,对于$2\lesssim U\lesssim 6$。螺旋模量和对结构因子的分析导致确定作为$f$的函数的临界温度,对于$U=3,$ 4和6:它们也在$f\sim 0.07$附近显示最大值,最高$T_c$随着$U$在此范围内增加。我们认为,总体而言,所观察到的行为的结果从CDW超导简并性的击穿和自由网站倾向于“推”电子吸引力的网站,后者的效果是更激烈的弱耦合的事实。

英文摘要:

We have considered the half-filled disordered attractive Hubbard model on a square lattice, in which the on-site attraction is switched off on a fraction $f$ of sites, while keeping a finite $U$ on the remaining ones. Through Quantum Monte Carlo (QMC) simulations for several values of $f$ and $U$, and for system sizes ranging from $8\times 8$ to $16\times 16$, we have calculated the configurational averages of the equal-time pair structure factor $P_s$, and, for a more restricted set of variables, the helicity modulus, $ρ_s$, as functions of temperature. Two finite-size scaling {\it ansatze} for $P_s$ have been used, one for zero-temperature and the other for finite temperatures. We have found that the system sustains superconductivity in the ground state up to a critical impurity concentration, $f_c$, which increases with $U$, at least up to U=4 (in units of the hopping energy). Also, the normalized zero-temperature gap as a function of $f$ shows a maximum near $f\sim 0.07$, for $2\lesssim U\lesssim 6$. Analyses of the helicity modulus and of the pair structure factor led to the determination of the critical temperature as a function of $f$, for $U=3,$ 4 and 6: they also show maxima near $f\sim 0.07$, with the highest $T_c$ increasing with $U$ in this range. We argue that, overall, the observed behavior results from both the breakdown of CDW-superconductivity degeneracy and the fact that free sites tend to "push" electrons towards attractive sites, the latter effect being more drastic at weak couplings.

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。

↑