Quan Yujie, Liao Bolin
University of California, Department of Mechanical Engineering, Santa Barbara, California 93106, USA.
Phys Rev Lett. 2025 Jun 6;134(22):226301. doi: 10.1103/PhysRevLett.134.226301.
Electronic and thermal transport properties in two-dimensional (2D) semiconductors have been extensively investigated due to their potential to miniaturize transistors. Microscopically, electron-phonon interactions are considered the dominant momentum relaxation mechanism for electrons that limits carrier mobility beyond cryogenic temperatures. However, when electrons and phonons are considered as a single system, electron-phonon interactions conserve the total momentum and energy, leading to the possibility of low-dissipation transport. In this Letter, we systematically investigate the momentum circulation, in which momentum previously transferred from electrons to phonons (or vice versa) can be pumped back to the original carriers through interactions between nonequilibrium electrons and phonons, and its impact on carrier transport properties in 2D semiconductors with strong electron-phonon interactions. We find that, when strong momentum circulation is taken into account, the total momentum in the coupled electron-phonon system is weakly dissipated, leading to a coupled electron-phonon hydrodynamic transport regime, in which electrons and phonons exhibit a joint drift motion rather than separate diffusive behaviors. In this transport regime, charge transport properties are significantly enhanced. Contrary to previous belief, our results demonstrate that low-dissipation charge transport can occur despite strong electron-phonon interactions when there is effective momentum circulation between electrons and phonons. Our Letter advances fundamental understandings of carrier transport in 2D semiconductors.
由于二维（2D）半导体在使晶体管小型化方面的潜力，其电子和热输运特性已得到广泛研究。从微观角度来看，电子 - 声子相互作用被认为是电子主要的动量弛豫机制，这种机制在低温以上会限制载流子迁移率。然而，当将电子和声子视为一个单一系统时，电子 - 声子相互作用会守恒总动量和能量，从而导致低耗散输运的可能性。在本信函中，我们系统地研究了动量循环，即先前从电子转移到声子（或反之亦然）的动量可以通过非平衡电子和声子之间的相互作用被泵回到原始载流子，以及它对具有强电子 - 声子相互作用的二维半导体中载流子输运特性的影响。我们发现，当考虑到强动量循环时，耦合电子 - 声子系统中的总动量耗散较弱，从而导致一种耦合电子 - 声子流体动力学输运 regime，其中电子和声子呈现联合漂移运动而非单独的扩散行为。在这种输运 regime 中，电荷输运特性得到显著增强。与之前所认为的相反，我们的结果表明，当电子和声子之间存在有效的动量循环时，尽管存在强电子 - 声子相互作用，仍可发生低耗散电荷输运。我们的信函推进了对二维半导体中载流子输运的基本理解。
