Slow imbalance relaxation and thermoelectric transport in graphene
Slow imbalance relaxation and thermoelectric transport in graphene
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DOI：
10.1103/physrevb.79.085415
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发表时间：
2009-02-01
影响因子：
3.7
通讯作者：
Aleiner, Igor L.
中科院分区：
文献类型：
--
作者：
Foster, Matthew S.;Aleiner, Igor L.
我们计算了流体动力学范围内单层石墨烯的热导率和热电势（α）的电子分量（kappa），并考虑了载流子布居不平衡弛豫的缓慢速率。由于相对论能谱的非衰变性质，带间电子空穴生成和复合过程效率低下。因此，在应用热梯度时，通常会引起导带和价带的布居不平衡[即 mu(e)+mu(h) 不等于 0 的非平衡状态，其中 mu(e) (mu(h)) 表示电子（空穴）化学势]。我们表明，石墨烯单层的热电响应取决于样品长度与由不平衡弛豫率设定的固有长度尺度 l(Q) 的比率。同时，我们考虑了热电测量（在开路边界条件下）所需的金属接触的关键影响，因为与接触的载流子交换也缓解了不平衡。这些效应对于干净的石墨烯尤其明显，其中热电传输仅受到载流子间碰撞的限制。对于短于 l(Q) 的样本，总体不平衡会延伸到整个样本； kappa 和 alpha 渐近于零不平衡松弛极限。在长于 l(Q) 的石墨烯板的相反极限中，在非零掺杂下，kappa 和 alpha 接近无限不平衡松弛极限的固有值特征。掺杂（未掺杂）情况下的中间（长）长度样品预计会表现出不均匀的温度分布，而 kappa 和 alpha 随系统尺寸线性增长。在除最短器件之外的所有情况下，我们绘制了在导热引线之间流动的体电子和空穴数电流的图像，其中稳态复合和生成过程缓解了累积的不平衡。此外，我们的分析还考虑了（弱）猝灭无序的影响。
We compute the electronic component (kappa) of the thermal conductivity and the thermoelectric power (alpha) of monolayer graphene within the hydrodynamic regime, taking into account the slow rate of carrier population imbalance relaxation. Interband electron-hole generation and recombination processes are inefficient due to the nondecaying nature of the relativistic energy spectrum. As a result, a population imbalance of the conduction and valence bands [i.e., a nonequilibrium state with mu(e)+mu(h)not equal 0, where mu(e) (mu(h)) denotes the electron (hole) chemical potential] is generically induced upon the application of a thermal gradient. We show that the thermoelectric response of a graphene monolayer depends upon the ratio of the sample length to an intrinsic length scale l(Q) set by the imbalance relaxation rate. At the same time, we incorporate the crucial influence of the metallic contacts required for the thermopower measurement (under open circuit boundary conditions) since carrier exchange with the contacts also relaxes the imbalance. These effects are especially pronounced for clean graphene, where the thermoelectric transport is limited exclusively by intercarrier collisions. For specimens shorter than l(Q), the population imbalance extends throughout the sample; kappa and alpha asymptote toward their zero imbalance relaxation limits. In the opposite limit of a graphene slab longer than l(Q), at nonzero doping kappa and alpha approach intrinsic values characteristic of the infinite imbalance relaxation limit. Samples of intermediate (long) length in the doped (undoped) case are predicted to exhibit an inhomogeneous temperature profile, while kappa and alpha grow linearly with the system size. In all cases except for the shortest devices, we develop a picture of bulk electron and hole number currents that flow between thermally conductive leads, where steady-state recombination and generation processes relax the accumulating imbalance. Our analysis incorporates, in addition, the effects of (weak) quenched disorder.