topological insulators.ppt

刘洪梅 2012.12.14 拓扑绝缘体的电子输运性质 拓扑绝缘体 体态--绝缘体 表面态--导体 PRL 105, 266806 (2010) Science 325, 178 (2009); Bi2Te3 输运性质 平衡态的电子输运性质与费米能级和Dirac 点附近的电子态密切相关。 拓扑绝缘体在Dirac 点附近的电子态具有独特性质，表面态可以调节拓扑绝缘体的电子输运。 研究拓扑绝缘体的输运性质很有意义。 电导的实验测量 dI/dV(微分电导) spectrum taken on the Bi2Se3 (111) surface V-shaped spectrum Dirac point : -200 meV Bi2Se3, 50 QL STM, 4.2 K Scanning tunneling microscopy PRL 105, 076801 (2010) PHYSICAL REVIEW B 82, 081305R 2010 Bi2Se3(111) STM / STS tunneling spectrum taken on the Bi2Se3 (111) surface V-shaped spectrum Dirac point (Ed): -290 meV E Ed 时, 电导快速增加，体电子态 bulk bands Ed E 0, 电导线性增加，surface states E 0，电导快速增加，体电子态 bulk bands Ef Xue-Feng Wang, Yibin Hu and Hong Guo, PRB, 85, 241402(R) (2012) 电导的理论模拟 e Nanodcal 非平衡格林函数+DFT x, y 周期性重复 z 方向有真空层 左电极 右电极 Yonghong Zhao, Hong Guo, et al. Nano Lett. 2011, 11, 2088–2091 6 QL, 30 atomic layers, 60 atoms Vacuum 20 ? in z direction a = 4.017 ? c = 27.89 ? Nanodcal NEGF+DFT LSDA (local spin polarization approximation) With spin-orbit coupling TZDP triple-? polarization k points: 20?20?1 Energy cutoff 600 Ry G0 : conductance quantum G0=e2/h = 77.7 ?S G=G0 ? T e is the electron charge and h is Planck’s constant. STM E Ef 时, 电导快速增加 Ef E 250 meV, 电导线性缓慢增加 E 250 meV，电导快速增加 How robust of helical states in TI? Disorder configuration invested. Configuration means where the diagonal perturbing potential ?V is added. When the system suffers from a disorder configuration, does the properties change? Energy bands of helical sates (solid) and bulk states (dotted). The Fermi level -0.072 eV Transmission T(E,0) for electrons transporting along the ? to M direction for C1(thin solid), C3 (dashed), C4 (dotted), and C6(dashed-dotted). Inset: C1, C4, C6, C7, C5 (lines from up to down) T(E,0) for C5(dotted) and C7(dashed). Inset : T(Ef) of C8. Weak disorder Strong disorder Step transmission for perfect structure A gap of 0.27 eV for bulk state Between bulk gap, T(E,0)=2, doubly degenerate helical states If ?V~0.3 eV, helical s