Due to their large bulk band gap, bismuthene, Sb and As on SiC offer intriguing new opportunities for room-temperature quantum spin Hall (QSH) applications. Although edge states have been observed in the local density of states (LDOS) of bismuthene/SiC , there has been no experimental evidence until now that they are spin-polarized and topologically protected. We predict experimentally testable fingerprints of these properties originating from magnetic fields, such as changes in the LDOS and in ballistic magnetotransport . We show that the edge termination, zigzag versus armchair, and large Rashba SOC result in fundamental differences of the helical edge states and their protection in bismuthene/SiC compared to those in the better studied HgTe quantum wells [3,4]. In particular, for armchair edges we find a distinctive behavior for out-of-plane fields (gap of a few meV between the QSH states) and fields along the edge direction (no gap). While we focus on bismuthene/SiC, our main findings are also applicable to other honeycomb-lattice-based QSH systems, revealing an unexpected robustness of the QSH states in these systems against magnetic fields due to the interplay between topology and geometry.
 F. Reis, G. Li, L. Dudy, M. Bauernfeind, S. Glass, W. Hanke, R. Thomale, J. Schäfer, R. Claessen, Science 357, 287 (2017)
 F. Dominguez, B. Scharf, G. Li, J. Schäfer, R. Claessen, W. Hanke, R. Thomale, E. M. Hankiewicz, preprint
 G. Tkachov, E. M. Hankiewicz, Phys. Rev. Lett. 104, 166803 (2010)
 B. Scharf, A. Matos-Abiague, J. Fabian, Phys. Rev. B 86, 075418 (2012); B. Scharf, A. Matos-Abiague, I. Zutic, J. Fabian, Phys. Rev. B 91, 235433 (2015)
Pristine materials seldom appear as we want them. Instead, their appeal typically comes from suitable modifications. Proximity effects are a versatile method to transform a given material by acquiring the properties of its neighbors and becoming, superconducting, magnetic, valley-polarized, or topologically nontrivial [1-3]. This approach is particularly suitable for 2D materials in which the length of the proximity effects exceeds their thickness [1,2]. Advances in (quantum) spin and anomalous Hall effect, as well as (anomalous) valley Hall effect suggest the electronic degrees of freedom (spin, charge and valley) can be used as different information carriers . The realization of multiple Hall effects in a single material provides a fascinating opportunity to manipulate the implementation of such information. Here we predict the realization and manipulation of multiple Hall effects in the proximitized 2D materials based on first-principles calculations and tight binding models. Harnessing such Hall effects associated with multiple degrees of freedom of electrons could enable novel applications in electronics, spintronics, and valleytronics.
. P. Lazić, K. D. Belashchenko, I. Žutić, Phys. Rev. B 2016, 93, 241401.
. B. Scharf, A. Matos-Abiague, J. E. Han, E. M. Hankiewicz, I. Žutić, Phys. Rev. Lett. 2016, 117, 166806.
. T. Zhou, J. Zhang, Y. Xue, B. Zhao, H. Zhang, H. Jiang, Z. Yang, Phys. Rev. B 2016, 94, 235449.
In condensed-matter systems Majorana bound states (MBSs) are emergent quasiparticles with non-Abelian statistics and particle-antiparticle symmetry. While realizing the non-Abelian braiding statistics under exchange would provide both an ultimate proof for MBS existence and the key element for fault-tolerant topological quantum computing, even theoretical schemes imply a significant complexity to implement such braiding. Frequently examined 1D superconductor/semiconductor wires provide a prototypical example of how to produce MBSs, however braiding statistics are ill-defined in 1D and complex wire networks must be used.
By placing an array of magnetic tunnel junctions (MTJs) above a 2D electron gas formed in a semiconductor quantum well grown on the surface of an s-wave superconductor, we have predicted the existence of highly tunable zero-energy MBSs and have proposed a novel scheme by which MBSs could be exchanged . This scheme may then be used to demonstrate the states’ non-Abelian statistics through braiding. The underlying magnetic textures produced by MTJ array provides a pseudo-helical texture which allows for highly-controllable topological phase transitions. By defining a local condition for topological nontriviality which takes into account the local rotation of magnetic texture, effective wire geometries support MBS formation and permit their controlled movement in 2D by altering the shape and orientation of such wires. This scheme then overcomes the requirement for a network of physical wires in order to exchange MBSs, allowing easier manipulation of such states.
 G. L. Fatin, A. Matos-Abiague, B. Scharf, and I. Zutic, arXiv:1510.08182, preprint.
Inversion symmetry breaking combined with strong spin-orbit coupling in transition metal dichalcogenides such as MoS2 offers important opportunities for spintronics. We investigate excitons in MoS2 monolayers in an applied in-plane electric field. Tight-binding and Bethe-Salpeter equation calculations predict a large quadratic Stark shift. The scaling of the Stark shifts with the exciton binding energy and the dielectric environment provides a path to engineering the MoS2 electro-optical response. Our results suggest that the excitonic Stark effect can be observed experimentally in a MoS2 monolayer and we explain its implications for spintronic devices.
We theoretically show how the interplay between spin-orbit coupling (SOC) and magnetism can result in a finite tunneling Hall conductance, transverse to the applied bias. For two-dimensional tunnel junctions with a ferromagnetic lead and magnetization perpendicular to the current flow, the detected anomalous Hall voltage can be used to extract information not only about the spin polarization but also about the strength of the interfacial SOC. In contrast, a tunneling current across a ferromagnetic barrier on the surface of a three-dimensional topological insulator (TI) can induce a planar Hall response even when the magnetization is oriented along the current flow. The tunneling nature of the states contributing to the planar Hall conductance can be switched from the ordinary to the Klein regimes by the electrostatic control of the barrier strength. This allows for an enhancement of the transverse response and a giant Hall angle, with the tunneling planar Hall conductance exceeding the longitudinal component. Despite the simplicity of a single ferromagnetic region, the TI/ferromagnet system exhibits a variety of functionalities. In addition to a spin-valve operation for magnetic sensing and storing information, positive, negative, and negative differential conductances can be tuned by properly adjusting the barrier potential and/or varying the magnetization direction. Such different resistive behaviors in the same system are attractive for potential applications in reconfigurable spintronic devices.
 B. Scharf, A. Matos-Abiague, J. E. Han, E. M. Hankiewicz, and I. Zutic, arXiv:1601.01009 (2016).