Materials Cloud is a platform designed to enable open and seamless sharing of resources for computational science, driven by applications in materials modelling. It hosts (1) archival and dissemination services for raw and curated data, together with their provenance graph, (2) modelling services and virtual machines, (3) tools for data analytics, and pre-/post-processing, and (4) educational materials. Data is citable and archived persistently, providing a comprehensive embodiment of entire simulation pipelines (calculations performed, codes used, data generated) in the form of graphs that allow retracing and reproducing any computed result. When an AiiDA database is shared on Materials Cloud, peers can browse the interconnected record of simulations, download individual files or the full database, and start their research from the results of the original authors. The infrastructure is agnostic to the specific simulation codes used and can support diverse applications in computational science that transcend its initial materials domain.

Experiments on bilayer graphene unveiled a fascinating realization of stacking disorder where triangular domains with well-defined Bernal stacking are delimited by a hexagonal network of strain solitons. Here we show by means of numerical simulations that this is a consequence of a structural transformation of the moiré pattern inherent of twisted bilayer graphene taking place at twist angles θ below a crossover angle θ = 1.2 • . The transformation is governed by the interplay between the interlayer van der Waals interaction and the in-plane strain field, and is revealed by a change in the functional form of the twist energy density. This transformation unveils an electronic regime characteristic of vanishing twist angles in which the charge density converges, though not uniformly, to that of ideal bilayer graphene with Bernal stacking. On the other hand, the stacking domain boundaries form a distinct charge density pattern that provides the STM signature of the hexagonal solitonic network. * oleg.yazyev@epfl.ch arXiv:1711.08647v2 [cond-mat.mes-hall] 11 Apr 2018 Bilayer graphene (BLG) shares many of the properties of monolayer graphene while also showing a number of pronounced differences. For instance, its equilibrium structural configuration reveals the massive nature of its charge carriers [1], the possibility of inducing a tunable band gap by applying a transverse electric field [2-4] and quantum Hall valley ferromagnetism [5]. These properties are a result of the coupling between the two layers.In order to describe the atomic structure of bilayer graphene the relative position of the two layers has to be defined. In many situations it is sufficient to specify a unique interlayer displacement vector that defines the stacking configuration. As a general property of graphitic structures, the low-energy configuration is represented by the Bernal stacking [6,7]. However, the stacking configuration is not immune to disorder which can manifest, for example, in boundaries that connect two domains with energetically degenerate yet topologically inequivalent stacking configurations, AB and BA [8][9][10][11]. Such stacking domain boundaries are realized by strain solitons, which are segments with a characteristic width where the strain that arises from interfacing two inequivalent stacking domains is confined.Recent studies have shown that strain solitons can be displaced by the action of a scanning tunneling microscope tip, but do not vanish due to their topological nature [8,12]. From the theoretical point of view, the two-dimensional extension of the Frenkel-Kontorova model predicts the emergence of strain solitons with a typical width of a few nanometers [13] while their density is defined by the twist angle.In other situations the stacking configuration cannot be uniquely defined on the whole surface of the sample since the two layers cannot be superimposed by a rigid in-plane shift. This is the case of twisted bilayer graphene where one layer is rotated relative to another, a system that has been widely reported ...

The ever-growing availability of computing power and the sustained development of advanced computational methods have contributed much to recent scientific progress. These developments present new challenges driven by the sheer amount of calculations and data to manage. Next-generation exascale supercomputers will harden these challenges, such that automated and scalable solutions become crucial. In recent years, we have been developing AiiDA (aiida.net), a robust open-source high-throughput infrastructure addressing the challenges arising from the needs of automated workflow management and data provenance recording. Here, we introduce developments and capabilities required to reach sustained performance, with AiiDA supporting throughputs of tens of thousands processes/hour, while automatically preserving and storing the full data provenance in a relational database making it queryable and traversable, thus enabling high-performance data analytics. AiiDA’s workflow language provides advanced automation, error handling features and a flexible plugin model to allow interfacing with external simulation software. The associated plugin registry enables seamless sharing of extensions, empowering a vibrant user community dedicated to making simulations more robust, user-friendly and reproducible.

Atomically thin rhenium disulphide (ReS2) is a member of the transition metal dichalcogenide family of materials. This two-dimensional semiconductor is characterized by weak interlayer coupling and a distorted 1T structure, which leads to anisotropy in electrical and optical properties. Here we report on the electrical transport study of mono- and multilayer ReS2 with polymer electrolyte gating. We find that the conductivity of monolayer ReS2 is completely suppressed at high carrier densities, an unusual feature unique to monolayers, making ReS2 the first example of such a material. Using dual-gated devices, we can distinguish the gate-induced doping from the electrostatic disorder induced by the polymer electrolyte itself. Theoretical calculations and a transport model indicate that the observed conductivity suppression can be explained by a combination of a narrow conduction band and Anderson localization due to electrolyte-induced disorder.

Atomically precise tailoring of graphene can enable unusual transport pathways and new nanometer-scale functional devices. Here we describe a recipe for the controlled production of highly regular "5-5-8" line defects in graphene by means of simultaneous electron irradiation and Joule heating by applied electric current. High-resolution transmission electron microscopy reveals individual steps of the growth process. Extending earlier theoretical work suggesting valley-discriminating capabilities of a graphene 5-5-8 line defect, we perform firstprinciples calculations of transport and find a strong energy dependence of valley polarization of the charge carriers across the defect. These findings inspire us to propose a compact electrostatically gated "valley valve" device, a critical component for valleytronics.2 Atomically-precise modification of low-dimensional materials such as graphene is exceedingly challenging since existing experimental techniques rarely achieve atomic precision. Nevertheless, if successful, atomic manipulations could have dramatic impact on graphene's electrical, magnetic, optical, mechanical, chemical, and thermal properties [1][2][3][4] , leading to novel functionalities that could be exploited in nanoscale devices.A recently emerging field is "valleytronics", a zero-magnetic-field analog to spintronics which exploits the quantum mechanical "valley" degree of freedom of charge carriers in graphene 2, 5-10 .At low energies the band structure of single-layer graphene is composed of two energetically degenerate valleys ("Dirac cones"), separated by ~30 nm -1 . 11 The intervalley coupling is quite weak in high quality graphene even at room temperature 12,13 , and hence this additional degree of freedom is a good quantum number. Valley polarization could be used for information processing much as the electron spin degree of freedom is used in spintronics, with the added benefit of temperature insensitivity.Generally, two approaches have been suggested for lifting the degeneracy and thus achieving graphene valley polarization: 1) application of external magnetic field, and 2) using local modifications of the crystalline lattice. The growth process of the 5-5-8 linear defect is intriguing, and we examine it in some detail here. The metastable 5-6 pair generated at the growth-leading end is the key to the growth mechanism. Figures 3a-3c illustrate critical formation steps as determined by TEM. Each experimental image is constructed from an average of 12 single shot TEM images taken in rapid succession to reduce the background noise and to include all possible configurations of the defect. As the line defect grows by one octagon, one carbon atom (marked by a blue dot in the illustrations) is ejected, and a new bond is formed between its nearest neighbors (marked by yellow dots). This process also creates a new 5-6 termination pair, which serves as a seed for continued growth. Since an 6 isolated pentagon cannot be sustained in otherwise ideal graphene 23 , an extended structural irre...