Demet Usanmaz

Robust topological surface state in Kondo insulator SmB6 thin films

Abstract : Topological insulators are a class of materials with insulating bulk but protected conducting surfaces due to the combination of spin-orbit interactions and time-reversal symmetry. The surface states are topologically non-trivial and robust against non-magnetic backscattering, leading to interesting physics and potential quantum computing applications. Recently there has been a fast growing interest in samarium hexboride (SmB6), a Kondo insulator predicted to be the first example of a correlated topological insulator. Here we fabricated smooth thin films of nanocrystalline SmB6 films. Their transport behavior indeed shows that SmB6 is a bulk insulator with topological surface states. Upon decreasing the temperature, the resistivity rho of Sm0.14B0.86 (SmB6) films display significant increase below 50 K due to hybridization gap formation, and it shows a saturation behavior below 10 K. The saturated resistance of our textured films is similar to that of the single crystals, suggesting that this conduction is from the surface and robust against grain boundary scatterings. Point contact spectroscopy (PCS) of the film using a superconducting tip displays both a Kondo Fano resonance and Andreev reflection, suggesting the existence of both an insulating Kondo lattice and metallic surface states.Fabrication of smooth thin films of topological insulators with true insulating bulk are extremely important for utilizing their novel properties in quantum and spintronic devices. Here, we report the growth of crystalline thin films of SmB6, a topological Kondo insulator with true insulating bulk, by co-sputtering both SmB6 and B targets. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy indicate films that are polycrystalline with a (001) preferred orientation. When cooling down, resistivity ρ shows an increase around 50 K and saturation below 10 K, consistent with the opening of the hybridization gap and surface dominated transport, respectively. The ratio ρ2K/ρ300K is only about two, much smaller than that of bulk, which indicates a much larger surface-to-bulk ratio. Point contact spectroscopy using a superconductor tip on SmB6 films shows both a Kondo Fano resonance and Andeev reflection, indicating an insulating Kondo lattice with metallic surface states.

An efficient and accurate framework for calculating lattice thermal conductivity of solids: AFLOW—AAPL Automatic Anharmonic Phonon Library

One of the most accurate approaches for calculating lattice thermal conductivity,

High-throughput prediction of finite-temperature properties using the quasi-harmonic approximation

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Spinodal Superlattices of Topological Insulators

DMPSID=1, is solving the Boltzmann transport equation starting from third-order anharmonic force constants. In addition to the underlying approximations of ab-initio parameterization, two main challenges are associated with this path: high computational costs and lack of automation in the frameworks using this methodology, which affect the discovery rate of novel materials with ad-hoc properties. Here, the Automatic Anharmonic Phonon Library (AAPL) is presented. It efficiently computes interatomic force constants by making effective use of crystal symmetry analysis, it solves the Boltzmann transport equation to obtain

Systematic Band Gap Tuning of BaSnO3 via Chemical Substitutions: The Role of Clustering in Mixed-Valence Perovskites

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Automated combinatorial method for fast and robust prediction of lattice thermal conductivity

DMPSID=2, and allows a fully integrated operation with minimum user intervention, a rational addition to the current high-throughput accelerated materials development framework AFLOW. An “experiment vs. theory” study of the approach is shown, comparing accuracy and speed with respect to other available packages, and for materials characterized by strong electron localization and correlation. Combining AAPL with the pseudo-hybrid functional ACBN0 is possible to improve accuracy without increasing computational requirements.Thermal conductivity: Framework for calculating heat flow in solidsA new theoretical framework could provide a more efficient method for calculating a material’s thermal conductivity. Understanding how materials conduct heat is crucial for a range of applications, from heat sinks to thermal insulation. Despite its fundamental importance, predicting a material’s lattice thermal conductivity is challenging, and often requires experimental data or knowledge of specific properties to be entered during the process. An international team of researchers led by Stefano Curtarolo from Duke University now present a framework that can predict the lattice thermal conductivity of single-crystal and polycrystalline materials using just a single input file, with no further intervention. Called the Automatic Anharmonic Phonon Library, the methods computes certain parameters using symmetry analysis, before solving the Boltzmann transport equation, providing information on both the electronic structure and phonon-dependent properties.