Interplay between exchange-split Dirac and Rashba-type surface states at the MnBi2Te4/BiTeI interface

Based on ab initio calculations, we study the electronic structure of the BiTeI/MnBi2Te4 heterostructure interface composed of the antiferromagnetic topological insulator MnBi2Te4 and the polar semiconductor trilayer BiTeI. We found a significant difference in the electronic properties of the different contacts between the substrate and overlayer. While the case of a Te-Te interface forms a natural expansion of the substrate, when the Dirac cone state locates mostly in the polar overlayer region and undergoes a slight exchange splitting, the Te-I contact is the source of a four-band state contributed by the substrate Dirac cone and Rashba-type state of the polar trilayer. Owing to magnetic proximity, the pair of Kramers degeneracies for this state is lifted, which produces a Hall response in the transport regime. We believe our findings provide new opportunities to construct novel spintronic devices

Energy shift and wave function overlap of metal-organic interface states

The properties of Shockley-type interface states between π-conjugated organic molecular layers and metal surfaces are investigated by time-resolved two-photon photoemission experiments and density functional theory. For perylene- and naphthalene-tetracarboxylic acid dianhydride (PTCDA and NTCDA) adsorbed on Ag(111), a common mechanism of formation of the interface state from the partly occupied surface state of the bare Ag(111) is revealed. The energy position is found to be strongly dependent on the distance of the molecular carbon rings from the metal and their surface density. Bending of the carboxyl groups enhances the molecular overlap of the interface state.Peer Reviewe

Sample-dependent Dirac-point gap in MnBi2Te4 and its response to applied surface charge: A combined photoemission and ab initio study

Recently discovered intrinsic antiferromagnetic topological insulator MnBi2Te4 presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the MnBi2Te4 Dirac cone. Here, using micro(μ)-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different MnBi2Te4 samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the Néel temperature at about 10–16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available MnBi2Te4 samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Furthermore, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the MnBi2Te4 DP gap size.The authors acknowledge support by the Saint Petersburg State University Grant No. ID 73028629, Russian Science Foundation Grant No. 18-12-00062 in part of the photoemission measurements and total analysis of the results, Grant No. 18-12-00169-p in part of the electronic band structure calculations and Grant No. 20-42-08002 in part of analysis of magnetic properties and Science Development Foundation under the President of the Republic of Azerbaijan Grant No. EI F-BGM-4-RFTF1/2017-21/04/1-M-02. M.M.O. acknowledges the support by Spanish Ministerio de Ciencia e Innovación (Grant No. PID2019-103910GB-I00). K.K. and O.E.T. acknowledge the support from state assignment of IGM SB RAS and ISP SB RAS.Peer reviewe

Transformation of the Ag(111) surface state due to molecule-surface interaction with ordered organic molecular monolayers

We present a detailed study of 3,4,9,10-perylene- and 1,4,5,8-naphthalene- tetracarboxylic acid dianhydride monolayers adsorbed on Ag(111) film. The study is based on density functional theory with the use of a periodic slab model. The slab is chosen to contain an organic molecular monolayer on a silver thin film of different thicknesses (6, 9, and 12 layers) with the (111) orientation. We show that in both cases there is a similarity in formation of an unoccupied interface state from a surface state of the bare Ag(111) film due to the adsorbate-substrate interaction. The energy difference between the initial surface state and the resulting interface state varies with the film thickness, the adsorption distance, and the molecule size and geometry, whereas the effective mass of the state remains practically unchanged. Also, we demonstrate that the interface-state charge distribution preserves its localization in the interface region at different wave vectors k and in the vicinity of the molecular plane resembles lowest unoccupied orbitals of free molecules. © 2012 American Physical Society.We acknowledge partial support from the University of the Basque Country (Project GV-UPV/EHU, Grant No. IT-366-07) and the Spanish Ministerio de Ciencia y Tecnología (Grant No. FIS2010-19609-C02-00).Peer Reviewe

Spin-orbit split two-dimensional states of BiTeI/Au(1 1 1) interfaces

We present an ab initio study of interfaces formed by placing a single trilayer of BiTeI on the Au(1 1 1) surface. We consider two possible interfaces with the parallel and antiparallel orientation of the trilayer dipole moment with respect to the surface normal, i.e. Te-Bi-I/Au(1 1 1) and I-Bi-Te/Au(1 1 1). We show that the resulting interface state that originates from the modified spin-orbit split surface state of the clean Au(1 1 1) surface resides at high energy above the Fermi level and acquires a large spin-splitting and reversal helicity as compared with the original surface state. The former lowest conduction state of the trilayer, which is one of the hitherto known giant Rashba spin-split states of few-atomic-layer structures, becomes partly occupied. In the I-Bi-Te/Au(1 1 1) interface, this state represents a Rashba system with strong spin-orbit interaction, where the outer branch of the spin-split state is mostly populated.This work was partly supported by the Spanish Ministry of Science, Innovation and Universities (Project No. FIS2016-76617-P). We also thank the German Science Foundation (DFG) via SFB 1083 for funding. Computational resources were provided by HLR Stuttgar

Change in surface states of Ag(111) thin films upon adsorption of a monolayer of PTCDA organic molecules

7 páginas.The change in the electronic structure of silver thin films of different thicknesses with the Ag( 111) orientation due to the interaction with an adsorbed monolayer of ordered organic molecules of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) has been investigated in terms of density functional theory. It has been shown that one of the two surface states of the pure films transforms into an unocc upied interface state due to the interaction so that all the main features of the initial state are retained. The relation of the resulting state to the unoccupied state experimentally observed in the PTCDA/Ag( 111 ) system by scanning tunneling and two-photon photoemi ssion spectroscopy has been discussed.Peer reviewe

Adsorption geometry and electronic properties of flat-lying monolayers of tetracene on the Ag(111) surface

The geometrical and electronic properties of the monolayer (ML) of tetracene (Tc) molecules on Ag(111) are systematically investigated by means of DFT calculations with the use of a localized basis set. The bridge and hollow adsorption positions of the molecule in the commensurate γ-Tc/Ag(111) are revealed to be the most stable and equally favorable irrespective to the approximation chosen for the exchange-correlation functional. The binding energy is entirely determined by the long-range dispersive interaction. The former lowest unoccupied molecular orbital remains being unoccupied in the case of γ-Tc/Ag(111) as well as in the α phase with increased coverage. The unit cell of the α phase with point-on-line registry was adapted for calculations based on the available experimental data and computed structures of the γ phase. The calculated position of the Tc/Ag(111) interface state is found to be noticeably dependent on the lattice constant of the substrate, however its energy shift with respect to the Shockley surface state of the unperturbed clean side of the slab is sensitive only to the adsorption distance and in good agreement with the experimentally measured energy shift.This work is a project of the SFB 1083 “Structure and Dynamics of Internal Interfaces” funded by the Deutsche Forschungsgemeinschaft (DFG). We acknowledge partial support from the University of Basque Country UPV/EHU (IT-756-13), the Departamento de Educacion del Gobierno Vasco, The Tomsk State University Academic D.I. Mendeleev Fund Program (Grant No. 8.1.05.2015), the Spanish Ministry of Economy and Competitiveness MINECO (Grant No. FIS2013-48286-C2-1-P), and Saint Petersburg State University (Project No. 15.61.202.2015).Peer reviewe