FellowKrisztian Palotas
Project NameDevelopment of Scanning Tunneling Microscopy Simulation Tools for Spin Transport
Host organisationInstitute of Physics
Duration of the project01.01.2016 - 31.03.2018

Abstract
The scanning tunneling microscope (STM) is undoubtedly a successfully used tool to study physical and chemical phenomena on surfaces of materials. The progress of experimental techniques since the invention of the STM was remarkable, particularly for magnetic tunnel junctions, thus more sophisticated theoretical models and simulation tools are needed that are able to explain all relevant details of electron tunneling transport measurements. Therefore, the project aims at the development of advanced high resolution scanning tunneling microscopy simulation tools, particularly for spin transport, and the implementation of the models into computer codes. The key objectives of this proposal are: 1. To implement arbitrary orientations of the STM tip into standard electron tunneling models, and study tip orientation and geometry effects on the electron tunneling; 2. To implement an interface between an electron transport code (BSKAN) and the non-collinear magnetic version of an electronic structure code (VASP), and analyze electron tunneling above non-collinear magnetic surfaces with standard STM models; 3. To implement the theory of vector spin transport within standard electron tunneling models, and investigate the tunneling spin transport characteristics in high resolution above magnetic surfaces, particularly having complex magnetic structure. The successful completion of this project is expected to beat present state of the art, and shows a potential to develop relevant technologies based on the tunneling spin transport phenomenon, thus reinforcing the excellence of the European Research Area, with possible consequences for boosting the economic growth in the long-term.

Project Summary with Interim Results
The project is running according to the Work Plan, in places in advance to the planned activities. Implementation of arbitrary tip orientations in the BSKAN code has been done and computer simulations of tip geometry effects on scanning tunneling microscopy (STM) images have been performed for a wide variety of surface structures in form of international collaborations (Ireland, China, Poland, Republic of Korea). A variety of ultrathin magnetic films exhibiting complex magnetic order (domain walls, skyrmionic structures) has been investigated in collaboration with a Hungarian group for the purpose of the study of subsequent vector spin transport characterization of such surfaces. The theory of combined charge and vector spin transport has been implemented in the 3D-WKB-STM code, and first results have been published above a collinear magnetic surface.
During the first 9 months of the project 6 journal articles have been published with total journal impact factors of 32.1; 2 journal articles are submitted, 1 book chapter has been prepared to appear in Springer Proceedings in Physics, 5 invited talks, 2 contributed talks and 2 other conference contributions have been delivered.
[1] K. Palotás, G. Mándi, and L. Szunyogh: "Enhancement of the spin transfer torque efficiency in magnetic STM junctions", Physical Review B 94, 064434 (2016)
[2] B. Walls, O. Lübben, K. Palotás, K. Fleischer, K. Walshe, and I. V. Shvets: "Oxygen vacancy induced surface stabilization: (110) terminated magnetite", Physical Review B 94, 165424 (2016)
[3] Y. Liu, K. Palotás, X. Yuan, T. Hou, H. Lin, Y. Li, and S.-T. Lee: "The atomistic origins of surface defects in CH3NH3PbBr3 perovskite and their electronic structures", ACS Nano, DOI: 10.1021/acsnano.6b08260 (2017)
[4] Gy. J. Vida, E. Simon, L. Rózsa, K. Palotás, and L. Szunyogh: "Domain-wall profiles in Co/Irn/Pt(111) ultrathin films: Influence of the Dzyaloshinskii-Moriya interaction", Physical
Review B 94, 214422 (2016)
[5] S. Ayissi, K. Palotás, H. Qin, L. Yang, and P. A. Charpentier: "Nanostructural adsorption of vanadium oxide on functionalized graphene: A DFT study", Physical Chemistry Chemical Physics 18, 29208 (2016)
[6] K. Palotás, I. Bakó, and L. Bugyi: "Structural, electronic and adsorption properties of Rh(111)/Mo(110) bimetallic catalyst: A DFT study", Applied Surface Science 389, 1094 (2016)
[7] L. Rózsa, K. Palotás, A. Deák, E. Simon, R. Yanes, L. Udvardi, L. Szunyogh, and U. Nowak: "Metastable skyrmionic spin structures with various topologies in an ultrathin film. I.
Formation and stability"
, submitted. arXiv:1609.07012
[8] K. Palotás, L. Rózsa, E. Simon, L. Udvardi, and L. Szunyogh: "Metastable skyrmionic spin structures with various topologies in an ultrathin film. II. Characterization with scanning
tunneling microscopy calculations"
, submitted. arXiv:1609.07016
[9] K. Palotás and L. Szunyogh: "Screened KKR", to appear in Springer Proceedings in Physics series: Multiple Scattering Theory for Spectroscopies, Editors: D. Sébilleau, K.
Hatada, H. Ebert, Springer, New York (2017)