Collision-dominated spin transport in graphene and Fermi liquids
Collision-dominated spin transport in graphene and Fermi liquids
复制标题
石墨烯和费米液体中碰撞主导的自旋输运
DOI：
10.1088/1367-2630/13/3/035009
复制
发表时间：
2010
影响因子：
3.3
通讯作者：
H. Nguyen
中科院分区：
文献类型：
--
作者：
Markus P. Mueller;H. Nguyen
在干净的费米液体中，由于自旋向上/自旋向下的对称性，即使在没有杂质的情况下，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σs在无无序极限下假设了一个明确的碰撞主导值，提供了电子-电子相互作用逆强度的直接度量。在中性石墨烯中，费米能量位于狄拉克点，库仑相互作用仍然异常强烈，使得非弹性散射率接近推测的上界τinel−1 > kBT/ h，类似于强耦合量子临界系统的情况。电子自旋的磁矩μs≈μB为电子自旋的磁矩，在Dirac点处，自旋电导率达到弱库仑耦合时的最小值。直到替换量子单位e2/ h→μs2/ h，这一结果等于之前得到的碰撞主导电导率。然而，这种偶然对称在相互作用强度上被打破为更高阶。对于门控石墨烯和一般的二维金属，我们发现输运时间参数小于碰撞时间。我们利用这一事实，对弱库仑耦合α，解析地计算了碰撞限制σs。
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 σs assumes a well-defined collision-dominated value in the disorder-free limit, providing a direct measure of 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 τinel−1≲kBT/ℏ, similar to the case of strongly coupled quantum critical systems. The strong scattering is reflected by a minimum of spin conductivity at the Dirac point, where it reaches at weak Coulomb coupling α, μs≈μB being the magnetic moment of the electronic spins. Up to the replacement of quantum units, e2/ℏ→μs2/ℏ, 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 two-dimensional metals in general, we show that the transport time is parametrically smaller than the collision time. We exploit this fact to compute the collision-limited σs analytically as , with for weak Coulomb coupling α.