多空穴错位分布对石墨纳米带中热输运的影响

利用非平衡格林函数方法研究了石墨纳米带中三空穴错位分布对热输运性质的影响.研究结果发现:三空穴竖直并排结构对低频声子的散射较小,导致低温区域三空穴竖直并排时热导最大,而在高频区域,三空穴竖直并排结构对高频声子的散射较大,导致较高温度区域三空穴竖直并排时热导最小;三空穴的相对错位分布仅能较大幅度地调节面内声学模高频声子的透射概率,而三空穴的相对错位分布能较大幅度地调节垂直振动膜高频声子和低频声子的透射概率,导致三空穴的相对错位分布不仅能大幅调节面内声学模和垂直振动模的高温热导,也能大幅调节垂直振动模的低温热导.研究结果阐明了空穴位置不同的石墨纳米带的热导特性,为设计基于石墨纳米带的热输运量子器件提供了有效的理论依据.

Influence of multi-cavity dislocation distribution on thermal conductance in graphene nanoribbons

Using non-equilibrium Green's function method and keeping the zigzag carbon chains unchanged, we investigate the transmission rate of acoustic phonon and the reduced thermal conductance in the graphene nanoribbons with three cavities. The results show that the reduced thermal conductance approaches to 3π²k_B² T/(3h) in the limit T→0 K. Due to the fact that only long wavelength acoustic phonons with zero cutoff frequency are excited at such low temperatures, the scattering influence on the long wavelength acoustic phonons by the dislocation distribution of three cavities in the graphene nanoribbons can be ignored and these phonons can go through the scattering region perfectly. As the temperature goes up, the reduced thermal conductance decreases. This is because the high-frequency phonons are excited and these high-frequency phonons are scattered easily by the scattering structures. With the further rise of temperature, acoustic phonon modes with the cutoff frequency greater than zero are excited, which leads to a rapid increase of the reduced thermal conductance. This study shows that in higher frequency region, the transmission spectra display complex peak-dip structures, which results from the fact that in higher frequency region, more phonon modes are excited and scattered in the middle scattering region with three cavities, and the scattering phonons are coupled with the incident phonons. When the three cavities are aligned perpendicularly to the edge of the graphene nanoribbons, the scattering from low-frequency phonons by the scattering structures is smallest, which leads to the fact that the reduced thermal conductance is largest at low temperatures; however, at high temperatures, the reduced thermal conductance is smallest when the three cavities is aligned perpendicularly to the edge of the graphene nanoribbons. This is because the scattering from high-frequency phonons by the scattering structures is biggest. These results show that the acoustic phonon transport and the reduced thermal conductance are dependent on the relative position of the three cavities. In addition, the dislocation distribution of the three cavities can only modulate obviously the high-temperature thermal conductance of the in-plane modes (IPMs). This is because the change of the relative position of the quantum dots can only modulate greatly the high-frequency phonon transmission rate and less modulate the low-frequency phonon transmission rate of the IPMs. However, the dislocation distribution of the three cavities can adjust obviously not only the high-temperature thermal conductance of the flexural phonon modes (FPMs), but also the low-temperature thermal conductance of the FPMs. This is because the change of the relative position of the three cavities can modulate greatly phonon transmission rates of flexural phonon modes in the low-frequency and high-frequency regions. These results provide an effective theoretical basis for designing the thermal transport quantum devices based on graphene nanoribbons.