arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1012.2960cond-mat.str-elcond-mat.mes-hall
收藏

石墨烯和费米液体中碰撞主导的自旋输运

Collision-dominated spin transport in graphene and Fermi liquids

Markus Mueller, Hai Chau Nguyen

摘要:

在干净的费米液体中,由于自旋上/自旋下对称性,即使在没有杂质的情况下,由磁场梯度驱动的直流自旋电流也是有限的。因此,自旋电导率sigma_s假设在无无序极限中具有明确的碰撞主导值,从而提供了对电子-电子相互作用的逆强度的直接测量。在中性石墨烯中,当费米能处于狄拉克点时,库仑相互作用仍然非常强,使得非弹性散射率接近于一个严格的上限1/τ_{inel} <= k_B T/ \hbar,类似于强耦合量子临界系统。强散射由狄拉克点处的自旋电导率的最小值反映,在狄拉克点处,在弱库仑耦合α处,自旋电导率达到sigma_s =(0.121/alpha^2)*(mu_B^2/ \hbar)。直到替换量子单位,e^2/ \hbar -> mu_s^2/ \hbar,这个结果等于前面得到的碰撞主导的电导率。然而,这种偶然的对称性在相互作用强度中被破坏到更高的阶次。对于门控石墨烯,和二维金属一般,我们表明,传输时间是参数小于碰撞时间。我们利用这一点来计算碰撞限制的sigma_s,解析式为sigma_s=(1/C)*(mu/T)^2 *(mu_B^2/ \hbar),其中C=4 pi^2 α ^2 [2/3 ln(1/(2α))-1],用于弱库仑耦合α。

英文摘要:

In a clean Fermi liquid, due to spin up/spin down symmetry, the dc spin current driven by a magnetic field gradient is finite even in the absence of impurities. Hence, the spin conductivity sigma_s assumes a well-defined collision-dominated value in the disorder-free limit, providing a direct measure for the inverse strength of electron-electron interactions. In neutral graphene, with Fermi energy at the Dirac point, the Coulomb interactions remain unusually strong, such that the inelastic scattering rate comes close to a conjectured upper bound 1/τ_{inel} <= k_B T/\hbar, similarly as in strongly coupled quantum critical systems. The strong scattering is reflected by a minimum of the spin conductivity at the Dirac point, where it reaches sigma_s = (0.121/alpha^2) * (mu_B^2/\hbar) at weak Coulomb coupling alpha. Up to the replacement of quantum units, e^2/\hbar -> mu_s^2/\hbar, this result equals the collision-dominated electrical conductivity obtained previously. This accidental symmetry is, however, broken to higher orders in the interaction strength. For gated graphene, and 2d metals in general, we show that the transport time is parametrically smaller than the collision time. We exploit this to compute the collision-limited sigma_s analytically as sigma_s= (1/C) * (mu/T)^2 * (mu_B^2/\hbar) with C=4 pi^2 alpha^2 [2/3 ln(1/(2α))-1] for weak Coulomb coupling alpha.

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。

↑