氮化硼纳米带功能化碳纳米管的热自旋输运性质

热自旋电子学器件结合了自旋电子学和热电子学各自的优点,对人类可持续发展具有重要作用.本文研究了锯齿形BN纳米带(ZBNRs)共价功能化碳纳米管(SWCNT)的电子结构,发现ZBNRs-B-(6,6)SWCNT为磁性半金属,nZBNRs-B-(6,6)SWCNT(n=2—8)为磁性金属;nZBNRs-N-(6,6)SWCNT(n=1—8)为双极化铁磁半导体;4ZBNRs-B-(4,4)SWCNT和4ZBNRs-N-(4,4)SWCNT为磁性半金属,4ZBNRs-B-(m,m)SWCNT(m=5—9)为磁性金属;4ZBNRs-N-(m,m)SWCNT(m=5—9)为双极化铁磁半导体.然后,基于锯齿形BN纳米带共价功能化碳纳米管设计了新型热自旋电子学器件,发现基于ZBNRs-N-(6,6)SWCNT的器件具有热自旋过滤效应;而8ZBNRs-N-(6,6)SWCNT和nZBNRs-B-(6,6)SWCNT(n=1,8)都存在自旋相关塞贝克效应.这些发现表明BN纳米带功能化碳纳米管在热自旋电子学器件方面具有潜在的应用.     

Ferrimagnetism induced by asymmetrical ferromagnetic next-nearest-neighbour exchange interactions in an antiferromagnetic spin-1/2 zigzag chain

The magnetic properties of an antiferromagnetic bond alternating spin-1/2 zigzag chain with asymmetrical ferromagnetic next-nearest-neighbour exchange interactions at finite temperature are investigated by using the many-body Green's function theory. It is found that the ferrimagnetic ordering does not appear in the symmetrical next-nearest-neighbour coupling case, and takes place only for the asymmetrical next-nearest-neighbour case at finite temperature rather than the ground state. Furthermore, as the asymmetry degree of the next-nearest-neighbour exchange interactions increases, the ferrimagnetism becomes more and more dominant. It is shown that the elementary excitation spectra are responsible for the observed magnetic behaviour.     

Percolation Model of the Temperature Dependence of Exotic Magnetic Field in Doped Manganese Perovskites

We investigate the magnetic transitions in a （La1-x）2/3Ca1/3MnO3 system, which consists of paramagnetic and ferromagnetic domains, based on a magnetic theoretical percolation model In the mean-field approximation, the resistance as a function of temperature and magnetic field has been derived analytically and simulated numerically. It is found that the dependence of the critical temperature on magnetic field is linear when applied magnetic field is not too strong. Our theoretical predications are in good agreement with recent experimental observations.     

Generation of Fabry–Pérot oscillations and Dirac state in two-dimensional topological insulators by gate voltage

We investigate electron transport through Hg Te ribbons embedded by strip-shape gate voltage through using a nonequilibrium Green function technique. The numerical calculations show that as the gate voltage is increased, an edgerelated state in the valence band structure of the system shifts upwards, then hangs inside the band gap and merges into the conduction band finally. It is interesting that as the gate voltage is increased continuously, another edge-related state in the valence band also shifts upwards in the small-k region and contacts the previous one to form a Dirac cone in the band structure. Meanwhile in this process, the conductance spectrum displays as multiple resonance peaks characterized by some strong antiresonance valleys in the band gap, then behaves as Fabry–P′erot oscillations and finally develops into a nearly perfect quantum plateau with a value of 2e~2/h. These results give a physical picture to understand the formation process of the Dirac state driven by the gate voltage and provide a route to achieving particular quantum oscillations of the electronic transport in nanodevices.     

基于有机分子准一维亚铁磁体自旋系统的热容量性质

基于交替自旋链Ising-Hamiltonian模型，采取量子转移矩阵方法，对基于有机分子准一维亚铁磁体热容量在全温区范围内进行了研究．在不同结构序参量比的条件下，热容量曲线呈现双峰结构，显示有机亚铁磁系统在铁磁和反铁磁作用相互竞争下的复杂热力学行为；在逐渐增加外场的情况下，低温区的比热峰向高温区移动，而高温区的比热峰则刚好相反，这意味着其中一峰来源于铁磁相互作用，而另一峰来源于反铁磁相互作用．这与量子Monte Carlo方法和精确对角化方法的结果相比，更符合客观实际，为设计分子磁性材料提供了理论依据．