arXiv subjects

Lenart Dudy

Publications and source records attributed to Lenart Dudy.

7 recordsLinked to original sources

arXiv2023

Temperature dependent ARPES of the metallic-like bands in Si(553)-Au

We conducted a thorough investigation into the temperature dependence of the metallic-like bands of Si(553)-Au using angular-resolved photoemission spectroscopy (ARPES). Our study addresses the challenges posed by the short-term stability of the surface and photo-voltage effects, which we overcame to extract changes in the band-filling and Fermi-velocity. Our findings shed light on the low-temperature phase of the step edge in Si(553)-Au, which has been a topic of ongoing debate regarding its structural or electronic nature. Through comparison with theoretical predictions of a structural-related low-temperature to high-temperature phase transition, we discovered that the band-filling and Fermi-velocity do not change accordingly, thereby ruling out this scenario. Our study contributes to a better understanding of this material system and provides an important reference for future research.

cond-mat.mtrl-sci↗

arXiv2022

Hard x-ray angle-resolved photoemission from a buried high-mobility electron system

Novel two-dimensional electron systems at the interfaces and surfaces of transition-metal oxides recently have attracted much attention as they display tunable, intriguing properties that can be exploited in future electronic devices. Here we show that a high-mobility quasi-two-dimensional electron system with strong spin-orbit coupling can be induced at the surface of a KTaO$_3$ (001) crystal by pulsed laser deposition of a disordered LaAlO$_3$ film. The momentum-resolved electronic structure of the buried electron system is mapped out by hard x-ray angle-resolved photoelectron spectroscopy. From a comparison to calculations it is found that the band structure deviates from that of electron-doped bulk KTaO$_3$ due to the confinement to the interface. Nevertheless, the Fermi surface appears to be clearly three-dimensional. From the $k$ broadening of the Fermi surface and core-level depth profiling we estimate the extension of the electron system to be at least 1 nm but not much larger than 2 nm, respectively.

cond-mat.str-el↗

arXiv2022

ARPES in strongly disordered systems -- theory of electronic bands melting

It is well known that translational symmetry-breaking disorder will disrupt ARPES spectra up to the point where they become invisible. However, a theoretical framework to capture this phenomenon has been largely missing. Here, based on a rigorous theory of the ARPES process, we provide this much-needed framework. In particular, we show how the frequently used sudden electron approximation has to be modified in this situation. Our main result is an argument that links the photoemission line broadening with an operator content of a disorder operator and so with the criticality of the corresponding order-disorder phase transition. For concreteness, we focus here on the frustrated 2D trigonal (pseudo-)spin model, with Ising order-disorder operators behind the transition. Still, our formalism is general and can be applied in a much broader context.

cond-mat.str-el↗

arXiv2022

Toward Functionalized Ultrathin Oxide Films: the Impact of Surface Apical Oxygen

Thin films of transition metal oxides open up a gateway to nanoscale electronic devices beyond silicon characterized by novel electronic functionalities. While such films are commonly prepared in an oxygen atmosphere, they are typically considered to be ideally terminated with the stoichiometric composition. Using the prototypical correlated metal SrVO$_3$ as an example, it is demonstrated that this idealized description overlooks an essential ingredient: oxygen adsorbing at the surface apical sites. The oxygen adatoms, which persist even in an ultrahigh vacuum environment, are shown to severely affect the intrinsic electronic structure of a transition metal oxide film. Their presence leads to the formation of an electronically dead surface layer but also alters the band filling and the electron correlations in the thin films. These findings highlight that it is important to take into account surface apical oxygen or -- mutatis mutandis -- the specific oxygen configuration imposed by a capping layer to predict the behavior of ultrathin films of transition metal oxides near the single unit-cell limit.

cond-mat.mtrl-sci↗

arXiv2019

Tailoring the topological surface state in ultrathin $α$-Sn (111) films

We report on the electronic structure of $α$-Sn films in the very low thickness regime grown on InSb(111)A. High-resolution low photon energies angle-resolved photoemission (ARPES) allows for the direct observation of the linearly dispersing 2D topological surface states (TSSs) that exist between the second valence band and the conduction band. The Dirac point of this TSS was found to be 200meV below the Fermi level in 10-nm-thick $α$-Sn films, which enables the observation of the hybridization gap opening at the Dirac point of the TSS for thinner films. The crossover to a quasi-2D electronic structure is accompanied by a full gap opening at the Brillouin zone center, in agreement with our density functional theory calculations. We further identify the thickness regime of $α$-Sn films where the hybridization gap in TSS coexists with the topologically non-trivial electronic structure and one can expect the presence of a 1D helical edge states.

cond-mat.str-el↗

arXiv2018

Tailoring Materials for Mottronics: Excess Oxygen Doping of a Prototypical Mott Insulator

The Mott transistor is a paradigm for a new class of electronic devices---often referred to by the term Mottronics---, which are based on charge correlations between the electrons. Since correlation-induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal-insulator transition to be switched by electric gating. Here we demonstrate that thin films of the prototypical Mott insulator LaTiO$_3$ grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band-filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions, making LaTiO$_{3+x}$ a promising functional material for Mottronics devices.

cond-mat.mtrl-sci↗

arXiv2017

Double Band Inversion in $ α$-Sn: Appearance of Topological Surface States and the Role of Orbital Composition

The electronic structure of \graySn(001) thin films strained compressively in-plane was studied both experimentally and theoretically. A new topological surface state (TSS) located entirely within the gapless projected bulk bands is revealed by \textit{ab initio}-based tight-binding calculations as well as directly accessed by soft X-ray angle-resolved photoemission. The topological character of this state, which is a surface resonance, is confirmed by unravelling the band inversion and by calculating the topological invariants. In agreement with experiment, electronic structure calculations show the maximum density of states in the subsurface region, while the already established TSS near the Fermi level is strongly localized at the surface. Such varied behavior is explained by the differences in orbital composition between the specific TSS and its associated bulk states, respectively. This provides an orbital protection mechanism for topological states against mixing with the background of bulk bands.

cond-mat.str-el↗