Szczęśniak Dominik, Ennaoui Ahmed, Ahzi Saïd
Qatar Energy and Environment Research Institute, Hamad bin Khalifa University, Qatar Foundation, PO Box 5825, Doha, Qatar.
J Phys Condens Matter. 2016 Sep 7;28(35):355301. doi: 10.1088/0953-8984/28/35/355301. Epub 2016 Jul 1.
Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M = Mo, W; X = S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.
最近，过渡金属二硫属化物因其低维形式在纳米电子学和光电子学中的潜在应用而再次受到关注。在这类应用中，单层过渡金属二硫属化物的电子和输运性质起着关键作用。本文通过研究常见过渡金属二硫属化物单层（MX₂，其中M = Mo、W；X = S、Se、Te）的复杂能带结构，同时考虑自旋轨道耦合效应，对这些基本性质提供了新的见解。基于对称性的紧束缚计算表明，从实能带结构到复动量空间的解析延拓会导致非线性广义特征值问题。本文提出了一种求解此类非线性问题的有效方法，并得到了一套完整的物理相关特征值。用该方法得到的解被表征并分为传播态和倏逝态，其中后者不仅表现出单调衰减特性，还表现出振荡衰减特性。观察到一些振荡倏逝态在MX₂单层的直接带隙处形成特征性的复环，电子可以在带隙边缘之间直接隧穿。为了描述这些隧穿电流，阐明了禁能区电子态的衰减行为，并简要讨论了它们在弹道输运 regime 中的重要性。
