1.School of Information Engineering, Hubei University for Nationlities, Enshi 445000, China 2.School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
Fund Project:Project supportedby the National Natural Science Foundation of China (Grant No. 11864011) and the Natural Science Foundation of Hubei Province, China (Grant No. 2018CFB390).
Received Date:05 November 2018
Accepted Date:09 December 2018
Available Online:01 March 2019
Published Online:05 March 2019
Abstract:The spin caloritronics device, because of the characteristics of spintronics and thermoelectronics, plays an important role in human sustainable development. A lot of spin caloritronic devices based carbon materials (such as graphene nanoribbons, carbon nanotubes) have been reported. However, there are few studies of the thermal spin transport properties in a hybrid structure of single-walled carbon nanotubes and zigzag-edge BN nanoribbons, and the thermal spin transport mechanism of this structure is still unclear. In this paper, using the nonequilibrium Green’s function (NEGF) combined with the first principle calculations, the electronic structures and the thermal spin transport properties of the zigzag edge BN nanoribbons functionalized single-walled carbon nanotubes are studied. It is shown that the ZBNRs-N-(6, 6)SWCNT is a half-metal, while the nZBNRs-N-(6, 6)SWCNT are magnetic metals (n = 2?8), and the nZBNRs-B-(6, 6)SWCNT are bipolar magnetic semiconductors (n = 1?8). The 4ZBNRs-N-(4, 4)SWCNT and 4ZBNRs-B-(4, 4)SWCNT are half-metals, while the 4ZBNRs-B-(m, m)SWCNT (m = 5?9)are magnetic metals, and the 4ZBNRs-N-(m, m)SWCNT (m = 5?9) are bipolar magnetic semiconductors. Then, some novel spin caloritronicdevices are designed based on nZBNRs-N-(6, 6)SWCNT and nZBNRs-B-(6, 6)SWCNT (n = 1, 8). For the ZBNRs-B-(6, 6)SWCNT, when the temperature of the left electrode is increased above a critical value, the thermal spin-up current then increases remarkably from zero. Meanwhile the thermal spin-down current remains approximately equal to zero in the entire temperature region, thus indicating the formation of a thermal spin filter. For the 8ZBNRs-N-(6, 6)SWCNT and nZBNRs-B-(6, 6)SWCNT (n = 1, 8), when a temperature gradient is produced between two electrodes, the spin-up and spin-down currents are driven in the opposite directions, which indicates that the spin-dependent Seebeck effect (SDSE) appears. In order to obtain the fundamental mechanism of thermal spin filter effect and SDSE, the Landauer-Büttiker formalism is adopted. It is found that the currents (Iup and Idn) mainly depend on two factors: 1)the transport coefficient; 2) the difference between the Fermi-Dirac distributions of the left and right electrode. Additionally, the electron current Ie and the hole current Ih will be generated when a temperature gradient is produced between the left and right lead. Furthermore, the Iup and Idn have the opposite directions for the spin up transmission peaksbelow the Fermi level while they have the opposite directions for the spin down transmission peaks above the Fermi level in the transmission spectrum, which demonstrates the presence of the SDSE in the 8ZBNRs-B-(6, 6)SWCNT and nZBNRs-N-(6, 6)SWCNT (n = 1, 8). Finally, the results indicate that nZBNR-N-(m, m)SWCNT and nZBNR-B-(m, m)SWCNT can have potential applications in thermospin electronic devices. Keywords:spin caloritronics/ spin dependent Seebeck effect/ thermal spin filter
全文HTML
--> --> -->
2.计算方法与模型nZBNRs-B-(6, 6)SWCNT的复合结构如图1(a)所示; nZBNRs-N-(6, 6)SWCNT的复合结构如图1(b)所示. 为研究BN纳米带功能化碳纳米管的热自旋输运性质, 设计了一个简单的热自旋电子学器件, 如图1(c)所示. 从左至右依次为源极、中心散射区、漏极, 且源极温度为TL, 漏极温度为TR, 两极之间的温差为$\Delta T$ = TL - TR. 图 1 (a) nZBNRs-B-(6, 6)SWCNT结构; (b) nZBNRs-N-(6, 6)SWCNT结构; (c)器件结构图; 图中灰色表示碳原子, 黑色表示氢原子, 蓝色表示氮原子, 棕色表示硼原子 Figure1. (a) Structure of nZBNRs-B-(6, 6)SWCNT; (b) the structure of nZBNRs-N-(6, 6)SWCNT; (c) the schematic illustration of the device. Gray, black, blue and brown balls indicate carbon, hydrogen, nitrogen and boron atoms, respectively.
计算过程中, 使用ATK软件包进行原胞优化和电子结构计算, 选取双数值极化基组, 截断能为200 Ry. 芯电子选用规范守恒赝势来描述, 交换-关联函数选取Perdew-Burke-Ernzerhof (PBE)形式的广义梯度近似(GGA). 器件的自旋相关电流可由下述方程得出: