In this work we present an application of density-functional theory for superconductors (SCDFT) to superconductivity in hydrogenated carbon nanotubes and fullerane (hydrogenated fullerene). We show that these systems are chemically similar to graphane (hydrogenated graphene) and like graphane, upon hole doping, develop a strong electron phonon coupling. This could lead to superconducting states with critical temperatures approaching 100 K. However this possibility depends crucially on if and how metallization is achieved.
(Left) Real space anomalous potential ∆ (R, s) (left) and order parameter χ (R, s) (center and right) as a function of the Cooper pair center of mass R. On the top (a–c) an xy cut of the tube and on the bottom (d–f) a vertical cut of the tube. The doping level (rigid shift) is indicated on the top. The value of the functions is given according to the colorscale in the center (left scale refers to the left plot and the two right scales to the two right plots. A white dashed line in the a–c plots indicates the cut shown on the (d–f) plots.
This work is dedicated to Hardy Gross who, not only jointly invented SCDFT, but also devoted a large effort to develop the theoretical framework into a fully functioning method, investigating functionals, extensions and transforming it into a useful and predictive tool in material science.
Our latest results arising from a collaborative work with experimental groups in École Polytechnique Fédérale de Lausanne (EPFL), Neuchâtel, University of California Berkeley, National Institute of Advanced Industrial Science and Technology (AIST Japan) and the Institute for Nanotechnology, University of Twente, is published now in Journal of Physical Chemistry C (link).
In this work we studied transparent conductive oxides (TCOs), which are essential in technologies coupling light and electricity. For Sn-based TCOs, oxygen deficiencies and under-coordinated Sn atoms result in an extended density of states below the conduction band edge. While shallow states provide free carriers necessary for electrical conductivity, deeper states inside the bandgap are detrimental to transparency. In zinc tin oxide (ZTO), the overall optoelectronic properties can be improved by defect passivation via annealing at high temperatures. Yet, the high thermal budget associated with such treatment is incompatible with many applications. In our most recent work, we demonstrate an alternative, low-temperature passivation method, which relies on co-sputtering Sn-based TCOs with silicon dioxide (SiO2). Using amorphous ZTO and amorphous/polycrystalline tin dioxide (SnO2) as representative cases, we demonstrate through optoelectronic characterization and density functional theory simulations that the SiO2 contribution is two-fold. First, oxygen from SiO2 passivates the oxygen deficiencies that form deep defects in SnO2 and ZTO. Secondly, the ionization energy of the remaining deep defect centers is lowered by the presence of silicon atoms. Remarkably, we find that these ionized states do not contribute to subgap absorptance. This simple passivation scheme significantly improves the optical properties without affecting the electrical conductivity, hence overcoming the known transparency-conductivity trade-off in Sn-based TCOs.
Tittle of the article: “New Route for “Cold-Passivation” of Defects in Tin-Based Oxides“
We had the opportunity to attend the CECAM-Workshop “Crystal defects for qubits, single photon emitters and nanosensors” in Bremen (Germany), an interesting and forefront workshop in crystal defects for quibits.
Since we all know, the leading contender is the nitrogen-vacancy center in diamond which may be considered as a robust quantum tool. Several quantum algorithms and protocols for sensing have been already demonstrated by this center. However, researchers face many materials science problems in order to maintain the favorable intrinsic properties of this color center that can be perturbed by other defects either in bulk or at the surface of diamond that is difficult to resolve because of its chemical hardness and the concurrent stability of carbon allotropes.
Theory-driven search for alternative materials could identify other quantum bit candidates in technologically mature wide band gap semiconductors, particularly silicon carbide, that have been recently demonstrated in experiments. However, the knowledge about these color centers is scarce.
World-leaders, experts in the filed presented the state of the art in this research topic, invited among others:
David Awschalom (University of Chicago, Illinous) Adám Gali (Hungarian Academy of Science, Wigner Research Centre for Physics, Budapest) Audrius Alkauskas (Center for Physical Sciences and Technology, Vilnius)Sophia Economou (Virginia Polytechnic Institute and State University Blacksburg, Virginia) Ronald Hanson (Delft University of Technology) Marcus Doherty (Australian National University, Canberra) Arne Laucht (University of New South Wales, Sydney) Fedor Jelezko (Ulm University).
During this meeting we could exchange ideas of methods to use, and listen to discussions of new developments between scientists working on different aspects of diamond, silicon carbide and related materials. The interdisciplinary character of this workshop was a unique opportunity for me to learn and to have a better idea on which problems I should focus.
Stay tuned! this research topic is very promising and will lead to nice discoveries!
Our computing project has just been accepted to run in the SuperMUC Petascale System.
With more than 2.3 millions of computing cores at our disposition the grant in its first phase will serve to construct a database for materials under pressure. The project will runs until 2020 including a second phase with possible extension of the requested computing allocation.
The supercomputer is SuperMUC ranked top 4 as the fastest supercomputer in Germany. It is composed of more than 147,000 computing cores. SuperMUC (the suffix ‘MUC’ alludes to the IATA code of Munich’s airport) is operated by the Leibniz Supercomputing Centre, a European centre for supercomputing.
Stay tuned! coming months surely we will have very exciting news !