Showing papers by "Eugene J. Mele published in 2015"
TL;DR: It is shown that the CPGE can arise from interband transitions at the metal contacts to silicon nanowires, where inversion symmetry is locally broken by an electric field, and will enable new functionalities in silicon that can be integrated with conventional electronics.
Abstract: Electronic bands in crystals can support nontrivial topological textures arising from spin-orbit interactions, but purely orbital mechanisms can realize closely related dynamics without breaking spin degeneracies, opening up applications in materials containing only light elements. One such application is the circular photogalvanic effect (CPGE), which is the generation of photocurrents whose magnitude and polarity depend on the chirality of optical excitation. We show that the CPGE can arise from interband transitions at the metal contacts to silicon nanowires, where inversion symmetry is locally broken by an electric field. Bias voltage that modulates this field further controls the sign and magnitude of the CPGE. The generation of chirality-dependent photocurrents in silicon with a purely orbital-based mechanism will enable new functionalities in silicon that can be integrated with conventional electronics.
81 citations
TL;DR: This work studies a three-dimensional crystal constructed by stacking two-dimensional TCI layers to shed light on the role of the MCNs on inequivalent mirror-symmetric planes in reciprocal space and open new possibilities for finding new topological materials.
Abstract: Topological crystalline insulators (TCIs) are insulating materials whose topological property relies on generic crystalline symmetries. Based on first-principles calculations, we study a three-dimensional (3D) crystal constructed by stacking two-dimensional TCI layers. Depending on the interlayer interaction, the layered crystal can realize diverse 3D topological phases characterized by two mirror Chern numbers (MCNs) (μ1,μ2) defined on inequivalent mirror-invariant planes in the Brillouin zone. As an example, we demonstrate that new TCI phases can be realized in layered materials such as a PbSe (001) monolayer/h-BN heterostructure and can be tuned by mechanical strain. Our results shed light on the role of the MCNs on inequivalent mirror-symmetric planes in reciprocal space and open new possibilities for finding new topological materials.
28 citations
TL;DR: In this article, the authors identify a hidden chiral symmetry which supports symmetry protected zero modes in projected bulk gaps and study the topological transitions in the occupied manifolds of the bulk systems that are joined at an interface.
Abstract: Electronic states confined to zero angle grain boundaries in single layer graphene are analyzed using topological band theoretic arguments. We identify a hidden chiral symmetry which supports symmetry protected zero modes in projected bulk gaps. These branches occupy a finite fraction of the interface-projected Brillouin zone and terminate at bulk gap closures, manifesting topological transitions in the occupied manifolds of the bulk systems that are joined at an interface. These features are studied by numerical calculations on a tight binding lattice and by analysis of the geometric phases of the bulk ground states.
10 citations
TL;DR: In this article, a brief discussion of the discovery of topological insulators from a consideration of the low energy properties of single layer graphene is given, and experimental realizations are briefly discussed.
Abstract: This note gives a brief discussion of the discovery of topological insulators from a consideration of the low energy properties of single layer graphene. Topological band theoretic classification of insulating states in two and three-dimensions and experimental realizations are briefly discussed.
7 citations
TL;DR: Charles Kane, Eugene Mele, and Shoucheng Zhang showed that there is a third class of materials which are insulators in their bulk, but which must inevitably have gapless surface states, and thus a finite surface conductivity, regardless of surface treatment.
Abstract: Modern solid state physics began in 1928 when Felix Bloch established the band theory of solids, which classified, importantly, solid behavior into insulators and conductors, a distinction that underlies all subsequent work in this field. In the work described here, an exotic third possibility has been established. Charles Kane, Eugene Mele, and Shoucheng Zhang showed that there is a third class of materials which are insulators in their bulk, but which must inevitably have gapless surface states, and thus a finite surface conductivity, regardless of surface treatment. An award for this work is a fitting recognition of an exciting discovery which also shows the constructive interaction between theoretical prediction and experimental work in the physics of materials.