Origin of the vortex displacement field in twisted bilayer graphene

A model description of patterns of atomic displacements in twisted bilayer systems has been proposed. The model is based on the consideration of several dislocation ensembles, employing a language that is widely used for grain boundaries and film/substrate systems. We demonstrate explicitly how the dislocation language relates to vortex lattice motives found in experiment and simulations. We show that three ensembles of parallel screw dislocations are sufficient both to describe the rotation of the layers as a whole, and for the vortexlike displacements resulting from elastic relaxation. The results give a clear explanation of the observed features of the structural state such as vortices, accompanied by alternating stacking. © 2020 American Physical Society.This work of M.I.K. was supported by the JTC-FLAGERA Project GRANSPORT and the work of Y.N.G. was financed by the Russian Ministry of Education and Science (topic “Structure” A18-118020190116-6)

Dislocation Structure and Mobility in the Layered Semiconductor InSe: a First-Principles Study

The structure and mobility of dislocations in the layered semiconductor InSe is studied within a multiscale approach based on generalized Peierls-Nabarro model with material-specific parametrization derived from first principles. The plasticity of InSe turns out to be attributed to peculiarities of the generalized stacking fault relief for the interlayer dislocation slips such as existence of the stacking fault with a very low energy and low energy barriers. Our results give a consistent microscopic explanation of recently observed (2020 Science 369, 542) exceptional plasticity of InSe. © 2021 The Author(s). Published by IOP Publishing Ltd

Molecular dynamic simulation of a homogeneous bcc -> hcp transition

We have performed molecular dynamic simulations of a Martensitic bcc->hcp transformation in a homogeneous system. The system evolves into three Martensitic variants, sharing a common nearest neighbor vector along a bcc direction, plus an fcc region. Nucleation occurs locally, followed by subsequent growth. We monitor the time-dependent scattering S(q,t) during the transformation, and find anomalous, Brillouin zone-dependent scattering similar to that observed experimentally in a number of systems above the transformation temperature. This scattering is shown to be related to the elastic strain associated with the transformation, and is not directly related to the phonon response.Comment: 11 pages plus 8 figures (GIF format); to appear in Phys. Rev.

Mechanical Behavior of Polycrystalline Rhenium under 3-Points Bending at a Low Homological Temperature

Mechanical behaviour of polycrystalline rhenium under 3-points bending at such low homological temperature as room is discussed. Two metallurgical technologies (electron beam melting and powder metallurgy) were used for the samples preparation. Fine-grained samples (PM metal) exhibit some plasticity prior the failure, while coarse-grained ones (EBM metal) behave like a brittle solid. The intergranular fracture is the fracture mode of rhenium in both cases. Basal slip and prismatic slip of dislocations are not active in rhenium at low homological temperature, but the grain boundary sliding occurs under these conditions. Therefore, polycrystalline rhenium cannot be machined at room temperature despite the growth of grain boundary cracks are braked in the samples due to grain boundary sliding. © Published under licence by IOP Publishing Ltd.Russian Science Foundation, RSF: 18-19-00217This work is supported by the Russian Science Foundation (#18-19-00217)

The frustration-based approach of supercooled liquids and the glass transition: a review and critical assessment

One of the most spectacular phenomena in physics in terms of dynamical range is the glass transition and the associated slowing down of flow and relaxation with decreasing temperature. That it occurs in many different liquids seems to call for a "universal" theory. In this article, we review one such theoretical approach which is based on the concept of "frustration". Frustration in this context describes an incompatibility between extension of the locally preferred order in a liquid and tiling of the whole space. We provide a critical assessment of what has been achieved within this approach and we discuss the relation with other theories of the glass transition.Comment: 48 pages, 13 figures, submitted to J. Phys : Cond. Matte