Krisztián Palotás

Wigner Research Centre for Physics · Institute for Solid State Physics and Optics

On the occasion of its 25th anniversary, we revise Chen's derivative rule for electron tunneling [C.J. Chen, Phys. Rev. B 42, 8841 (1990)] for the purpose of computationally efficient simulations of scanning tunneling microscopy (STM) based on first principles electronic structure data. The revised model allows the weighting of tunneling matrix ele...

We introduce a method for a combined calculation of charge and vector spin transport of elastically tunneling electrons in magnetic scanning tunneling microscopy (STM). The method is based on the three-dimensional Wentzel-Kramers-Brillouin (3D-WKB) approach combined with electronic structure calculations using first principles density functional th...

Tunneling spin transport characteristics of a magnetic skyrmion are described theoretically in magnetic scanning tunneling microscopy (STM). The spin-polarized charge current in STM (SP-STM) and tunneling spin transport vector quantities, the longitudinal spin current and the spin transfer torque are calculated in high spatial resolution within the...

Based on a combined charge and vector spin transport theory capable of imaging noncollinear magnetic textures on surfaces with spin-polarized scanning tunneling microscopy (SP-STM), the high-resolution tunneling electron charge and spin transport properties of a variety of N\'eel- and Bloch-type skyrmions are investigated. Axially symmetric skyrmio...

High-resolution tunneling electron spin transport properties (longitudinal spin current (LSC) and spin transfer torque (STT) maps) of topologically distinct real-space magnetic skyrmionic textures are reported by employing a 3D-WKB combined scalar charge and vector spin transport theory in the framework of spin-polarized scanning tunneling microsco...

We employ electronic-structure calculations to investigate the charge-density waves and periodic lattice distortions in bilayer 2 H − NbSe 2 . We demonstrate that the vertical stacking can give rise to a variety of patterns that may lower the symmetry of the charge-density waves exhibited separately by the two composing 1 H − NbSe 2 monolayers. The...

Scanning tunneling microscopy using a CO-functionalized tip is combined with simulations to explore the impact of the CO tilt angle on topographies of a single Cu atom and CO molecule adsorbed on Cu(111). Images of the Cu atom acquired with varying tip tilt angles and sample voltages are reproduced by the calculations. The agreement between measure...

Surface templating by electrostatic surface potentials is the least invasive way to design large-scale artificial nanostructures. However, generating sufficiently large potential gradients remains challenging. Here, we lay the groundwork for significantly enhancing local electrostatic fields by chemical modification of the surface. We consider the...

The honeycomb iridate Na2IrO3, as a candidate for the Kitaev model, has drawn increasing attention in recent years. It is a rare example of a strongly correlated, topologically nontrivial band structure that may have protected quantum spin Hall states. The nature of its intriguing insulating phase and magnetic order is still under debate. In the pr...

Scanning tunneling microscopy with a CO-functionalized tip is combined with simulations to explore the impact of the CO tilt angle on topographies of a single Cu atom and CO molecule adsorbed on Cu(111). Images of the Cu atom acquired with varying tip tilt angles and sample voltages are reproduced by the calculations. The agreement between measured...

The multifaceted physics of oxides is shaped by their composition and the presence of defects, which are often accompanied by the formation of polarons. The simultaneous presence of polarons and defects, and their complex interactions, pose challenges for first-principles simulations and experimental techniques. In this study, we leverage machine l...

We employ ab-initio electronic structure calculations to investigate the charge-density waves and periodic lattice distortions in bilayer 2H-NbSe2. We demonstrate that the vertical stacking can give rise to a variety of patterns that may lower the symmetry of the CDW exhibited separately by the two composing 1H-NbSe2 monolayers. The general tendenc...

In this paper we present an ab initio scheme based on linear response theory of exchange torque correlation, implemented into the real-space Korringa-Kohn-Rostoker (RS-KKR) framework to calculate diagonal elements of the atomic-site-dependent intrinsic Gilbert damping tensor. The method is first applied to bcc iron and fcc cobalt bulk systems. Besi...

The magnetic exchange interaction of Fen (n=1,2,3) clusters with the quasiparticles of superconducting Pb(111) is probed by scanning tunneling spectroscopy of Yu-Shiba-Rusinov states. The spectral weight of the Yu-Shiba-Rusinov resonances is shifted from the coherence peaks in the Fe monomer spectrum towards the Fermi energy in the Fe dimer spectru...

Incommensurate heterostructures of two-dimensional (2D) materials, despite their attractive electronic behaviour, are challenging to simulate because of the absence of translation symmetry. Experimental investigations of these structures often employ scanning tunneling microscopy (STM), however there is to date no comprehensive theory to simulate a...

Nitrogen (N) doped graphene materials have been synthesized using the sole precursor adenine on the Ir(111) and Ru(0001) surfaces. X-ray photoelectron spectroscopy and scanning tunneling microscopy (STM) have been used to characterize the obtained N-doped graphene materials. Several graphitic and pyridinic N dopants have been identified on the atom...

One-dimensional systems comprising s-wave superconductivity with meticulously tuned magnetism realize topological superconductors hosting Majorana modes whose stability is determined by the gap size. However, for atomic spin chains on superconductors, the effect of the substrate’s spin-orbit coupling on the topological gap is largely unexplored. He...

In this paper the thermal properties of Au and Rh deposits are compared on hexagonal boron nitride (h-BN) “nanomesh” prepared on Rh(1 1 1), applying STM, XPS, low energy ion scattering (LEIS), LEED, and DFT. At room temperature, both metals essentially follow Volmer-Weber (3D) growth. Upon subsequent annealing, agglomeration (sintering), intercalat...

One-dimensional systems comprising s-wave superconductivity with meticulously tuned magnetism and spin-orbit coupling can realize topologically gapped superconductors hosting Majorana edge modes whose stability is determined by the gap's size. The ongoing quest for larger topological gaps evolved into a material science issue. However, for atomic s...

The exchange interaction of a brominated Co-porphyrin molecule with the Cooper pair condensate of Pb(111) is modified by reducing the Co-surface separation. The stepwise dehalogenation and dephenylation change the Co adsorption height by a few picometers. Only the residual Co-porphine core exhibits a Yu-Shiba-Rusinov bound state with low binding en...

Stabilization of the 2H phase of MoTe2 during molecular beam epitaxy (MBE) growth on graphene terminated 6H-SiC(0001) is highly desirable in order to take advantage of its promising properties in electronic applications. By properly adjusting the conditions, direct growth of the highly crystalline 2H phase of MoTe2 has been achieved. In such van de...

The longitudinal and transverse magnetoresistance curves MR( H ) and the magnetization isotherms M( H ) were measured at T = 3 K and 300 K up to high magnetic fields for a microcrystalline (µc) Ni foil with grain sizes above 1 µm (corresponding to bulk Ni) and for a nanocrystalline (nc) Ni foil with an average grain size of about 100 nm. At T = 3 K...

The magnetoresistance (MR) and the magnetization isotherms were studied up to high magnetic fields at T = 3 K and 300 K for a microcrystalline ($\mu$c) Ni foil corresponding to bulk Ni and for a nanocrystalline (nc) Ni foil. At T = 3 K, for the $\mu$c-Ni sample with a residual resistivity ratio (RRR) of 331, the field dependence of the resistivity...

We report on the structural, magnetic, and superconducting properties of single and double atomic layers of Mn on a clean and unreconstructed Nb(110) substrate. Low-temperature scanning tunneling spectroscopy measurements reveal a proximity-induced superconducting state and in-gap Yu-Shiba-Rusinov bands in the Mn thin films, which are found to grow...

The crystallographic and magnetic properties of an Fe monolayer (ML) grown on 2 ML Au/W(110) substrate are studied with spin-polarized low-energy electron microscopy, density functional theory, and relativistic screened Korringa–Kohn–Rostoker calculations. The single layer of iron atoms possesses hexagonal symmetry and reveals a ferromagnetic order...

The van der Waals (vdW) heterojunction often reveals unexpected characteristics distinct from conventional junctions. We investigate an emergent interface phenomenon between monolayer ReSe2 and graphene via combined studies of scanning tunneling microscopy (STM) and density functional theory (DFT). When probing monolayer ReSe2 on graphene at bias v...

Experimental scanning tunneling microscopy (STM) images of the hematite (0001) surface exhibit long-range superstructures formed by coexisting domains consisting of different terminations (α, β, γ) of the α-Fe2O3(0001) surface. In this work extensive simulations of STM images of different terminations of hematite (0001) surfaces are performed and c...

Accurate atomistic models for metal/oxide interfaces play a pivotal role in determining copper-based interfacial processes, ranging from electronic circuitry wirings to chemical catalysis. The “29” and “44” surfaces represent two of the most classical embryonic oxides on Cu(111). Although many attempts have been made to offer detailed atomistic mod...

Over the past decades, the rational synthesis of two-dimensional covalent organic framework (2D COFs) monolayer via on-surface chemistry has been widely explored. Herein, we propose the [2+2] photocycloaddition as a novel strategy for large-scale fabrication of COFs from theoretical perspective. Thanks to the symmetry forbidden of thermal [2+2] cyc...

We report on the structural and magnetic properties of single and double atomic layers of Mn on a clean and unreconstructed Nb(110) substrate. Low-temperature scanning tunneling spectroscopy measurements reveal a proximity-induced superconducting state in the Mn thin films, which are found to grow pseudomorphically on the Nb surface. Spin-polarized...

We present results for the electronic and magnetic structure of Mn and Fe clusters on Nb(110) surface, focusing on building blocks of atomic chains as possible realizations of topological superconductivity. The magnetic ground states of the atomic dimers and most of the monatomic chains are determined by the nearest-neighbor isotropic interaction....

We present results for the electronic and magnetic structure of Mn and Fe clusters on Nb(110) surface, focusing on building blocks of atomic chains as possible realizations of topological superconductivity. The magnetic ground states of the atomic dimers and most of the monatomic chains are determined by the nearest-neighbor isotropic interaction....

Magnetic atoms coupled to the Cooper pairs of a superconductor induce Yu-Shiba-Rusinov states (in short Shiba states). In the presence of sufficiently strong spin-orbit coupling, the bands formed by hybridization of the Shiba states in ensembles of such atoms can support low-dimensional topological superconductivity with Majorana bound states local...

Condensed-matter physics: Strain causes a change in charge patterns Researchers in South Korea, Hungary and Sweden have shown how strain influences the electronic patterns formed in two-dimensional materials. Some of the stranger properties of crystalline solids arise when electric charges organise themselves into ordered patterns. Charge density w...

Magnetic atoms coupled to the Cooper pairs of a superconductor induce Yu-Shiba-Rusinov states (in short Shiba states). In the presence of sufficiently strong spin-orbit coupling, the bands formed by hybridization of the Shiba states in ensembles of such atoms can support low-dimensional topological superconductivity with Majorana bound states local...

In electrochemical systems, upon applying an electrode potential, complicated surface reconstructions between halogen atoms (iodide anion) and the metal substrate (copper facet) have been observed from the ordered halide adlayers to ultrathin metal halide films. Although the global geometry of the ultrathin CuI film on Cu(111) was proposed, the loc...

Adsorption properties of azobenzene - the prototypical molecular switch – was investigated on hexagonal boron nitride (h-BN) monolayer (“nanomesh”) prepared on Rh(111). The h-BN layer was produced by decomposing borazine (B3N3H6) at 1000-1050 K. Temperature programmed desorption (TPD) studies revealed that azobenzene molecules adsorbed on the “wire...

High-resolution tunneling electron spin transport properties (longitudinal spin current and spin transfer torque (STT) maps) of topologically distinct real-space magnetic skyrmionic textures are reported by employing a 3D-WKB combined scalar charge and vector spin transport theory in the framework of spin-polarized scanning tunneling microscopy (SP...

The electrocatalytic reduction of nitrogen (N2) has recently emerged as an attractive technology for producing ammonia (NH3) at mild conditions. Nevertheless, achieving a high selectivity of N2 reduction with respect to the hydrogen evolution at relatively low overpotential, and thus increasing the energy efficiency of ammonia production, has remai...

Controlled shape and size distribution of metal nanoparticles for surface catalytic reactions are important. Through deposition onto the periodic surface of h-BN we can adjust these parameters of gold thereby we are able to influence the catalytic activity of the nanoparticles. In this study we investigated the decomposition of ethanol on gold nano...

Magnetic atoms on heavy-element superconducting substrates are potential building blocks for realizing topological superconductivity in one- and two-dimensional atomic arrays. Their localized magnetic moments induce so-called Yu-Shiba-Rusinov (YSR) states inside the energy gap of the substrate. In the dilute limit, where the electronic states of th...

Recent development of the magnetic material engineering led to achievement of the systems with a high interfacial Dzyaloshinskii-Moriya interaction (DMI). As a result, the formation of non-collinear magnetic soliton states or nonreciprocal spin wave dynamics is achievable. Typically used materials are based on bi-layers Heavy Metal/Ferromagnet, e.g...

We present results of first-principles calculations of the magnetic properties of Fe chains deposited on the Re(0001) surface. By increasing the length of the chain, a transition is found from an almost collinear antiferromagnetic state for a five-atom-long chain to a spin spiral state with the rotational plane slightly tilted from the surface of t...

Cu2O has been investigated for decades to understand the complex nature of oxidation and to utilize its high catalytic activity and intrinsic p-type character. However, the structures and intrinsic defects of Cu2O(111) surfaces have not been fully explored at the atomistic level, which is required to clarify some issues such as termination of Cu2O(...

Magnetic atoms on heavy-element superconducting substrates are potential building blocks for realizing topological superconductivity in one- and two-dimensional atomic arrays. Their localized magnetic moments induce so-called Yu-Shiba-Rusinov (YSR) states inside the energy gap of the substrate. In the dilute limit, where the electronic states of th...

The synthesis of nitrogen-doped single-layer graphene has been achieved on the copper surface by using the nitrogen-containing sole precursor azafullerene. The synthesis process, doping properties, and doping-induced variation of local work function of graphene have been investigated on the atomic scale by combing scanning tunneling microscopy/spec...

Ultrathin oxidic layers of Mo (i.e. O/Mo) on the Au(111) substrate are investigated using first-principles density-functional theory calculations. Various polymorphic structural models of these O/Mo layers are proposed and compared with previous experimental results -- covering both spectroscopic and microscopic approaches of characterization. We f...

The coordination-restricted ortho-site C–H bond activation and dehydrogenative homocoupling of 4,4’-(1,3-phenylene)dipyridine (1,3-BPyB) and 4,4’-(1,4-phenylene)dipyridine (1,4-BPyB) on different metal surfaces were studied by a combination of scanning tunneling microscopy, non-contact atomic force microscopy and density functional theory calculati...

We present results of first-principles calculations of the magnetic properties of Fe chains deposited on the Re(0001) surface. By increasing the length of the chain, a transition is found from an almost collinear antiferromagnetic state for a 5-atom-long chain to a spin spiral state with the rotational plane slightly tilted from the surface of the...

We study the limits of SPM subatomic resolution in imaging orbital magnetic features on a model system of a Co atom on a p(2 × 1)Cu(110):O surface. We show that scanning tunneling spectroscopies allow the determination of the occupation of the Co d shells and the value of the Hubbard U in the DFT + U modeling, and that standard near-contact AFM can...

We report on the investigation of the atomic and electronic structures of a clean Si(331)-(12 × 1) surface using a first-principles approach with both plane wave and strictly localized basis sets. Starting from the surface structure proposed by Zhachuk and Teys [Phys. Rev. B 95, 041412(R) (2017)], we develop significant improvements to the atomic m...

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalc...

Based on ab initio calculations and spin dynamics simulations, we perform a detailed study on the magnetic properties of bulk MnN and the MnN/Fe interface. We determine the spin model parameters for the θ-phase of bulk MnN, and we find that the competition between the nearest and the next-nearest-neighbor interactions leads to antiferromagnetic ord...

Surface alloying is an important technique to change their chemical properties. In this study, by employing density functional theory (DFT) calculations, the atomic arrangements and energetics of an extensive set of Au–Rh structures in a confined (2×1) surface cell on a Rh(111) substrate are investigated. An ordered surface alloy layer composed of...

It is known that the hexagonal boron nitride (h-BN) monolayer has a periodically corrugated structure on Rh(111), termed “nanomesh”, while the h-BN layer is planar on close packed surfaces of coinage metals (Cu, Ag, Au) due the weak interaction. Our studies aimed at understanding the metal-h-BN interaction, when both Rh and Au are present. On the o...

Realizing Majorana bound states (MBS) in condensed matter systems is a key challenge on the way toward topological quantum computing. As a promising platform, one-dimensional magnetic chains on conventional superconductors were theoretically predicted to host MBS at the chain ends. We demonstrate a novel approach to design of model-type atomic-scal...

Based on a combined charge and vector spin transport theory capable of imaging noncollinear magnetic textures on surfaces with spin-polarized scanning tunneling microscopy (SP-STM), the high-resolution tunneling electron charge and spin transport properties of a variety of Néel-and Bloch-type skyrmions are investigated. Axially symmetric skyrmions...

Magnetic skyrmions are localized nanometer-sized spin configurations with particle_like properties, which are envisioned to be used as bits in next_generation information technology. An essential step towards future skyrmion-based applications is to engineer key magnetic parameters for developing and stabilizing individual magnetic skyrmions. Here...

Using first-principles calculations, we study the magnetic properties of a Co monolayer on a Pt(111) surface with a capping monolayer of selected $5d$ elements (Re, Os, Ir, Pt and Au). First we determine the tensorial exchange interactions and magnetic anisotropies characterizing the Co monolayer for all considered systems. We find a close relation...

The concept of screening in the Korringa–Kohn–Rostoker (KKR) multiple scattering electronic structure method for solids is briefly presented. The main advantages of the screened KKR (SKKR) method and recent applications are highlighted.

The correct identification of topological magnetic objects in experiments is an important issue. In the present paper we report on the characterization of metastable skyrmionic spin structures with various topological charges (Q=−3,−2,−1,0,+1,+2) in the (Pt1−xIrx)Fe/Pd(111) ultrathin magnetic film by performing spin-polarized scanning tunneling mic...