13972
2004
2004
eng
article
1
--
--
--
Photoemission from stepped W(110) : Initial or final state effect?
The electronic structure of the (110)-oriented terraces of stepped W(331) and W(551) is compared to the one of flat W(110) using angle-resolved photoemission. We identify a surface-localized state which develops perpendicular to the steps into a repeated band structure with the periodicity of the step superlattices. It is shown that a final-state diffraction process rather than an initial-state superlattice effect is the origin of the observed behavior and why it does not affect the entire band structure
0031-9007
allegro:1991-2014
10102595
Physical Review Letters. - ISSN 0031-9007. - 93 (2004), 14, S. 4
A. M. Shikin
Andrei Varykhalov
G. V. Prudnikova
V. K. Adamchuk
Wolfgang Gudat
Oliver Rader
Institut für Physik und Astronomie
Referiert
Institut für Physik
507
2005
eng
doctoralthesis
1
2005-09-08
--
2005-06-16
Quantum-size effects in the electronic structure of novel self-organized systems with reduced dimensionality
Quantisierungseffekte in der elektronischen Struktur von neuen selbstorganisierten Systemen mit reduzierter Dimensionalität
The Thesis is focused on the properties of self-organized nanostructures. Atomic and electronic properties of different systems have been investigated using methods of electron diffraction, scanning tunneling microscopy and photoelectron spectroscopy. Implementation of the STM technique (including design, construction, and tuning of the UHV experimental set-up) has been done in the framework of present work. This time-consuming work is reported to greater detail in the experimental part of this Thesis. The scientific part starts from the study of quantum-size effects in the electronic structure of a two-dimensional Ag film on the supporting substrate Ni(111). Distinct quantum well states in the sp-band of Ag were observed in photoelectron spectra. Analysis of thickness- and angle-dependent photoemission supplies novel information on the properties of the interface. For the first time the Ni(111) relative band gap was indirectly probed in the ground-state through the electronic structure of quantum well states in the adlayer. This is particularly important for Ni where valence electrons are strongly correlated. Comparison of the experiment with calculations performed in the formalism of the extended phase accumulation model gives the substrate gap which is fully consistent with the one obtained by ab-initio LDA calculations. It is, however, in controversy to the band structure of Ni measured directly by photoemission. These results lend credit to the simplest view of photoemission from Ni, assigning early observed contradictions between theory and experiments to electron correlation effects in the final state of photoemission. Further, nanosystems of lower dimensionality have been studied. Stepped surfaces W(331) and W(551) were used as one-dimensional model systems and as templates for self-organization of Au nanoclusters. Photon energy dependent photoemission revealed a surface resonance which was never observed before on W(110) which is the base plane of the terrace microsurfaces. The dispersion E(k) of this state measured on stepped W(331) and W(551) with angle-resolved photoelectron spectroscopy is modified by a strong umklapp effect. It appears as two parabolas shifted symmetrically relative to the microsurface normal by half of the Brillouin zone of the step superlattice. The reported results are very important for understanding of the electronic properties of low-dimensional nanostructures. It was also established that W(331) and W(551) can serve as templates for self-organization of metallic nanostructures. A combined study of electronic and atomic properties of sub-monolayer amounts of gold deposited on these templates have shown that if the substrate is slightly pre-oxidized and the temperature is elevated, then Au can alloy with the first monolayer of W. As a result, a nanostructure of uniform clusters of a surface alloy is produced all over the steps. Such clusters feature a novel sp-band in the vicinity of the Fermi level, which appears split into constant energy levels due to effects of lateral quantization. The last and main part of this work is devoted to large-scale reconstructions on surfaces and nanostructures self-assembled on top. The two-dimensional surface carbide W(110)/C-R(15x3) has been extensively investigated. Photoemission studies of quantum size effects in the electronic structure of this reconstruction, combined with an investigation of its surface geometry, lead to an advanced structural model of the carbide overlayer. It was discovered that W(110)/C-R(15x3) can control self-organization of adlayers into nanostructures with extremely different electronic and structural properties. Thus, it was established that at elevated temperature the R(15x3) superstructure controls the self-assembly of sub-monolayer amounts of Au into nm-wide nanostripes. Based on the results of core level photoemission, the R(15x3)-induced surface alloying which takes place between Au and W can be claimed as driving force of self-organization. The observed stripes exhibit a characteristic one-dimensional electronic structure with laterally quantized d-bands. Obviously, these are very important for applications, since dimensions of electronic devices have already stepped into the nm-range, where quantum-size phenomena must undoubtedly be considered. Moreover, formation of perfectly uniform molecular clusters of C60 was demonstrated and described in terms of the van der Waals formalism. It is the first experimental observation of two-dimensional fullerene nanoclusters with "magic numbers". Calculations of the cluster potentials using the static approach have revealed characteristic minima in the interaction energy. They are achieved for 4 and 7 molecules per cluster. The obtained "magic numbers" and the corresponding cluster structures are fully consistent with the results of the STM measurements.
Die aktuelle Doktorarbeit ist auf die Eigenschaften von selbst-organisierten Nanostrukturen fokussiert. Die strukturellen und elektronischen Eigenschaften von verschiedenen Systemen wurden mit den Methoden Elektronenbeugung, Rastertunnelmikroskopie und Photoelektronenspektroskopie untersucht. Insbesondere wurde die fuer die Rastertunnelmikroskopie in situ praeparierter Proben eingesetzte Apparatur im Rahmen dieser Arbeit konstruiert und aufgebaut. Einzelheiten hierzu sind im experimentellen Kapitel zu finden. Der wissenschftliche Teil beginnt mit Untersuchungen von Quantentrogeffekten in der elektronischen Struktur einer Ag-Schicht auf Ni(111)-Substrat. Charakteristische Quantentrogzustaende im Ag-sp-Band wurden in Photoelektronenspektren beobachtet. Die Analyse von schichtdicken- und winkelabhaengiger Photoemission hat neue und wesentliche Informationen ueber die Eigenschaften des Ag/Ni-Systems geliefert. Insbesondere konnte zum ersten Mal eine relative Bandluecke im Ni-Substrat durch das Verhalten der Quantentrogzustaende indirekt vermessen werden. Das ist fuer Ni besonders wichtig, weil es sich bei Ni um ein stark korreliertes Elektronensystem handelt. Die Ergebnisse wurden mit Rechnungen auf der Basis des erweiterten Phasenmodelles verglichen. Der Vergleich ergibt eine Bandluecke, die sehr gut mit ab-initio-Rechnungen auf Basis der lokalen Elektronendichte-Naehrung uebereinstimmen. Dennoch widersprechen die Daten der Ni-Bandstruktur, die direkt mit Photoemission gemessen wird. Diese Kontroverse zeigt deutlich, dass der Unterschied zwischen Theorie und Experiment Korrelationeffekten im Endzustand der Photoemission zugeordnet werden kann. Des weiteren wurden Nanosysteme von noch niedrigerer Dimensionalitaet untersucht. Gestufte Oberflaechen W(331) und W(551) wurden als eindimensionale Modellsysteme fuer die Selbstorganisation von Au-Nanoclustern benutzt. Photonenenergieabhaengige Photoemission hat eine neue Oberflaechen-resonanz aufgedeckt, die auf der Basisebene der Terrassen dieser Systeme auftritt. Die Dispersion E(k) von diesem Zustand, die mit winkelaufgeloester Photoemission vermessen wurde, zeigt deutlich die Einwirkung von Umklapp-Effekten. Diese zeigen sich als zwei Parabeln, die relativ zu der Terrassennormale symmetrisch um die Haelfte der Oberflaechen-Brillouinzone verschoben sind. Die erzielten Ergebnisse sind sehr wichtig fuer das Verstaendnis der elektronischen Eigenschaften von eindimensionalen Nanostrukturen. Ausserdem wurde gezeigt, dass W(331) und W(551) als Vorlage fuer selbstorganisierte metallische Nanostrukturen dienen koennen. Eine kombinierte Untersuchung von strukturellen und elektronischen Eigenschaften von unter-monolagen Mengen von Au auf diesen Substraten wurde durchgefuehrt. Es hat sich gezeigt, dass Au mit dem Substrat an der Oberflaeche legieren kann, wenn die Oberflaeche ein wenig oxidiert und die Temperatur erhoert ist. Als Folge formiert sich auf den Stufen eine Nanostruktur von gleichen (aber nicht regelmaessig verteilten) Nanoclustern aus dieser Au-W Legierung. Diese Oberflaechenlegierung bildet ein neuartiges sp-Band in der Naehe der Fermi-Kante. Zudem spaltet dieser neue elektronische Zustand in konstante Energieniveaus auf. Das beobachtete Phaenomen wird als laterale Quantisierung interpretiert. Das letzte Kapitel dieser Doktorarbeit bildet auch den Hauptteil. Es handelt von Selbstorganisierungsphaenomenen auf einer Oberflaechenrekonstruktion und den Eigenschaften von so hergestellten Nanostrukturen. Das zweidimensionale Oberflaechen-Karbid W(110)/C-R(15x3) wurde intensiv untersucht. Beobachtete Quantentrogeffekte in der Photoemission in Kombination mit den Ergebnissen der Rastertunnelmikroskopuntersuchungen fuehren zu einem verbesserten Strukturmodell fuer das Oberflaechenkarbid. Es wurde auch gezeigt, dass W(110)/C-R(15x3) die Selbstorganisierung von Nanostrukturen mit sehr verschiedenen elektronischen und strukturellen Eigenschaften steuern kann. Es wurde gefunden, dass bei erhoehter Temperatur die R(15x3)-Ueberstruktur die Bildung von Nanostreifen aus unter-monolagiger Au Bedeckung, von denen jede 1 nm breit ist, kontrolliert. Die hergestellten Nanostreifen besitzen eine charakteristische eindimensionale elektronische Struktur mit lateral quantisierten d-Baendern. Basierend auf der Photoemission von Rumpfniveaus wird eine Kohlenstoff-induzierte Oberflaechenlegierung zwischen Au und W als Grund fuer die beobachtete Organisierung vorgeschlagen. Solche Phaenomene sind sehr wichtig fuer Anwendungen, seit die Mikroelektronik in den nm-Massstab eingetreten ist, in welchem mit Quantentrogeffekten zu rechnen ist. Zusaetzlich wurde die Bildung von perfekt uniformen molekularen Nanoclustern von C60 auf W(110)/C-R(15x3) demonstriert. Dieses Phaenomen kann im van-der-Waals Formalismus beschrieben werden. Die berichteten Ergebnisse sind eine erstmalige experimentelle Beobachtung von zweidimensionalen Fulleren-Nanoclustern mit "magischen Zahlen". Berechnungen der Clusterpotentiale in der statischen Naeherung im Girifalco-Modell zeigen Minima der Wechselwirkungsenergie fuer Cluster aus 4 und 7 C60-Molekuelen. Diese "magischen Zahlen" sowie die entsprechenden Clusterkonfigurationen sind vollkommen konsistent mit den Ergebnissen des STM-Experiments.
urn:nbn:de:kobv:517-opus-5784
578
UD 6100
varykhalov@bessy.de , (030) 6392 4888 , (0177) 966 09 40
Andrei Varykhalov
deu
swd
Nanostruktur
deu
swd
Selbstorganisation
deu
swd
Quantenwell
deu
swd
Quantendraht
deu
swd
Elektronische Eigenschaft
deu
swd
Oberflächenphysik
deu
swd
Eindimensionaler Festkörper
deu
uncontrolled
1D
deu
uncontrolled
2D
deu
uncontrolled
reduzierte Dimensionalität
deu
uncontrolled
elektronische Struktur
deu
uncontrolled
gestufte Oberfläche
deu
uncontrolled
Elektronen
eng
uncontrolled
1D
eng
uncontrolled
2D
eng
uncontrolled
reduced dimensionality
eng
uncontrolled
electronic structure
eng
uncontrolled
stepped surface
Physik
open_access
Institut für Physik und Astronomie
Universität Potsdam
Universität Potsdam
https://publishup.uni-potsdam.de/files/507/varykhalov.pdf
13852
2005
2005
eng
article
1
--
--
--
Structure and quantum-size effects in a surface carbide : W(110)/C-R(15 X 3)
Results of the combined investigation of atomic and electronic structure of the W(110)/C-R(15x3) surface carbide are reported. A variety of experimental techniques has been involved such as scanning tunneling microscopy (STM), low-energy electron diffraction, x-ray photoelectron spectroscopy, and angle-resolved photoemission (ARPES). Distance-dependent STM measurements show a nontrivial geometrical behavior in the topography data, demonstrating five different patterns representing the superstructure at different values of the tip-surface separation. Atomic resolution was achieved at lower tunneling gap resistance. An unexpected spatial asymmetry in the distribution of the local density of states across the surface unit cell has been observed as well. Photoelectron spectroscopy of C1s and W4f core levels clarifies the nature of the chemical bonding in the system. The band mapping with ARPES provides information on the wave- vector dependence of the electronic states. Notable quantum size and superlattice effects were discovered in the dispersion of the valence-band states. The experimental data suggests an apparent one-dimensional character of the electronic structure. Lateral quantization and umklapp scattering are proposed as explanation. Finally, based on photoemission and STM measurements, an improved crystallographic model of the tungsten surface carbide is introduced
1098-0121
allegro:1991-2014
10104400
Physical Review B. - ISSN 1098-0121. - 72 (2005), 11, S. 10
Andrei Varykhalov
Oliver Rader
Wolfgang Gudat
Institut für Physik und Astronomie
Referiert
Institut für Physik
13817
2005
2005
eng
article
1
--
--
--
Probing the ground state electronic structure of a correlated electron system by quantum well states: Ag/ Ni(111)
The ground state electronic properties of the strongly correlated transition metal Ni are usually not accessible from the excitation spectra measured in photoelectron spectroscopy. We show that the bottom of the Ni d band along [111] can be probed through the energy dependence of the phase of quantum-well states in Ag/Ni(111). Our model description of the quantum-well energies measured by angle-resolved photoemission determines the bottom of the Lambda(1) d band of Ni as 2.6 eV, in full agreement with standard local density theory and at variance with the values of 1.7-1.8 eV from direct angle-resolved photoemission experiments of Ni
0031-9007
allegro:1991-2014
10104401
Physical Review Letters. - ISSN 0031-9007. - 95 (2005), 24, S. 4
Andrei Varykhalov
A. M. Shikin
Wolfgang Gudat
P. Moras
C. Grazioli
C. Carbone
Oliver Rader
Institut für Physik und Astronomie
Referiert
Institut für Physik
11930
2006
2006
eng
article
1
--
--
--
Magic numbers in two-dimensional self-organization of C-60 molecules
Employing the chemically passive carbon reconstruction W(110)/C-R(15x3) as substrate for deposition of C-60 molecules, we have discovered by scanning tunneling microscopy two-dimensional self-assembly of fullerenes into uniform molecular nanoclusters with "magic" numbers. Our photoemission measurements determine van der Waals forces as the dominating interaction in this self-organizing two-dimensional molecular gas. Based on this, a theoretical determination of the cluster structures in the framework of the Girifalco model gives perfect agreement with the experiment
http://prb.aps.org/pdf/PRB/v73/i24/e241404
10.1103/Physrevb.73.241404
allegro:1991-2014
10101774
Physical review / b. - 73 (2006), 24, Art. No. 241404
Andrei Varykhalov
Wolfgang Gudat
V. K. Adamchuk
Oliver Rader
Institut für Physik und Astronomie
Referiert
Institut für Physik
42421
2018
2019
eng
7
612
postprint
1
2019-02-15
2019-02-15
--
Samarium hexaboride is a trivial surface conductor
SmB6 is predicted to be the first member of the intersection of topological insulators and Kondo insulators, strongly correlated materials in which the Fermi level lies in the gap of a many-body resonance that forms by hybridization between localized and itinerant states. While robust, surface-only conductivity at low temperature and the observation of surface states at the expected high symmetry points appear to confirm this prediction, we find both surface states at the (100) surface to be topologically trivial. We find the (Gamma) over bar state to appear Rashba split and explain the prominent (X) over bar state by a surface shift of the many-body resonance. We propose that the latter mechanism, which applies to several crystal terminations, can explain the unusual surface conductivity. While additional, as yet unobserved topological surface states cannot be excluded, our results show that a firm connection between the two material classes is still outstanding.
Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
10.25932/publishup-42421
urn:nbn:de:kobv:517-opus4-424213
1866-8372
online registration
Nature Communications 9 (2018), Art. 517 DOI 10.1038/s41467-018-02908-7
517
<a href="http://publishup.uni-potsdam.de/53582">Bibliographieeintrag der Originalveröffentlichung/Quelle</a>
CC-BY - Namensnennung 4.0 International
Peter Hlawenka
Konrad Siemensmeyer
Eugen Weschke
Andrei Varykhalov
Jaime Sánchez-Barriga
Natalya Y. Shitsevalova
A.V. Dukhnenko
V. B. Filipov
Slavomir Gabáni
Karol Flachbart
Oliver Rader
Emile D. L. Rienks
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
612
eng
uncontrolled
topological Kondo-insulator
eng
uncontrolled
SmB 6
eng
uncontrolled
photoemission
eng
uncontrolled
states
eng
uncontrolled
gap
Naturwissenschaften und Mathematik
open_access
Mathematisch-Naturwissenschaftliche Fakultät
Referiert
Open Access
Universität Potsdam
https://publishup.uni-potsdam.de/files/42421/pmnr612.pdf
50967
2019
2019
eng
423
428
19
7787
576
article
Nature Publ. Group
London
1
--
2019-12-18
--
Large magnetic gap at the Dirac point in Bi2Te3/MnBi2Te4 heterostructures
Magnetically doped topological insulators enable the quantum anomalous Hall effect (QAHE), which provides quantized edge states for lossless charge-transport applications(1-8). The edge states are hosted by a magnetic energy gap at the Dirac point(2), but hitherto all attempts to observe this gap directly have been unsuccessful. Observing the gap is considered to be essential to overcoming the limitations of the QAHE, which so far occurs only at temperatures that are one to two orders of magnitude below the ferromagnetic Curie temperature, T-C (ref. (8)). Here we use low-temperature photoelectron spectroscopy to unambiguously reveal the magnetic gap of Mn-doped Bi2Te3, which displays ferromagnetic out-of-plane spin texture and opens up only below T-C. Surprisingly, our analysis reveals large gap sizes at 1 kelvin of up to 90 millielectronvolts, which is five times larger than theoretically predicted(9). Using multiscale analysis we show that this enhancement is due to a remarkable structure modification induced by Mn doping: instead of a disordered impurity system, a self-organized alternating sequence of MnBi2Te4 septuple and Bi2Te3 quintuple layers is formed. This enhances the wavefunction overlap and size of the magnetic gap(10). Mn-doped Bi2Se3 (ref. (11)) and Mn-doped Sb2Te3 form similar heterostructures, but for Bi2Se3 only a nonmagnetic gap is formed and the magnetization is in the surface plane. This is explained by the smaller spin-orbit interaction by comparison with Mn-doped Bi2Te3. Our findings provide insights that will be crucial in pushing lossless transport in topological insulators towards room-temperature applications.
Nature : the international weekly journal of science
10.1038/s41586-019-1826-7
31853081
0028-0836
1476-4687
wos:2019
WOS:000504660500092
Rader, O (reprint author), Helmholtz Zentrum Berlin Mat & Energie, Elektronenspeicherring BESSY 2, Berlin, Germany.; Springholz, G (reprint author), Johannes Kepler Univ Linz, Inst Halbleiter & Festkorperphys, Linz, Austria., rader@helmholtz-berlin.de; gunther.springholz@jku.at
Austrian Science Fund (FWF)Austrian Science Fund (FWF) [P30969-N27, P28185-N27]; Austrian Federal Ministry for Digital and Economic Affairs; National Foundation for Research, Technology and Development of the Christian Doppler Laboratory for Nanoscale Phase Transformations; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [SPP 1666, SFB 1143, SFB 1277]; Central European Institute of Technology (CEITEC) Nano research infrastructure [LM2015041]; Computational and Experimental Design of Advanced Materials with New Functionalities (CEDAMNF) of the Czech Ministerstvo Skolstvi Mladeze a Telovychovy (MSMT) [CZ.02.1.01/0.0/0.0/15_00 3/0000358]; Impuls-und Vernetzungsfonds der Helmholtz-Gemeinschaft (Virtual Institute New States of Matter and their Excitations); Impuls-und Vernetzungsfonds der Helmholtz-Gemeinschaft (Helmholtz-Russia Joint Research Group) [HRSF-0067]; European Union Horizon 2020 programme [823717-ESTEEM3]
2021-06-15T08:31:56+00:00
sword
importub
filename=package.tar
e9a2c8397a0d823660689ebf85f79567
false
true
Emile D. L. Rienks
S. Wimmer
Jaime Sanchez-Barriga
O. Caha
Partha Sarathi Mandal
J. Ruzicka
A. Ney
H. Steiner
V. V. Volobuev
H. Groiss
M. Albu
G. Kothleitner
J. Michalicka
S. A. Khan
J. Minar
H. Ebert
G. Bauer
F. Freyse
Andrei Varykhalov
Oliver Rader
G. Springholz
Physik
Institut für Physik und Astronomie
Referiert
Import
Green Open-Access
53582
2018
2018
eng
7
9
article
Nature Publ. Group
London
1
2018-02-06
2018-02-06
--
Samarium hexaboride is a trivial surface conductor
SmB6 is predicted to be the first member of the intersection of topological insulators and Kondo insulators, strongly correlated materials in which the Fermi level lies in the gap of a many-body resonance that forms by hybridization between localized and itinerant states. While robust, surface-only conductivity at low temperature and the observation of surface states at the expected high symmetry points appear to confirm this prediction, we find both surface states at the (100) surface to be topologically trivial. We find the (Gamma) over bar state to appear Rashba split and explain the prominent (X) over bar state by a surface shift of the many-body resonance. We propose that the latter mechanism, which applies to several crystal terminations, can explain the unusual surface conductivity. While additional, as yet unobserved topological surface states cannot be excluded, our results show that a firm connection between the two material classes is still outstanding.
Nature Communications
10.1038/s41467-018-02908-7
29410418
2041-1723
wos:2018
517
WOS:000424291600013
Rienks, EDL (reprint author), Helmholtz Zentrum Berlin Mat & Energie, Elektronenspeicherring BESSY 2, Albert Einstein Str 15, D-12489 Berlin, Germany.; Rienks, EDL (reprint author), Tech Univ Dresden, Inst Festkorperphys, D-01062 Dresden, Germany.; Rienks, EDL (reprint author), Leibniz Inst Festkorper & Werkstoffforsch Dresden, Helmholtzstr 20, D-01069 Dresden, Germany., emile.rienks@helmholtz-berlin.de
Deutsche Forschungsgemeinschaft through SPP 1666; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [SFB 1143]; "Impuls- und Vernetzungsfonds der Helmholtz-Gemeinschaft" through Helmholtz-Russia Joint Research Group [408]; Helmholtz Virtual Institute " New states of matter and their excitations"; Slovak grant agencyVedecka grantova agentura MSVVaS SR a SAV (VEGA) [VEGA 2/0032/16, APVV-14-0605]; CFNT MVEP of the Slovak Academy of Sciences
2022-01-24T13:38:23+00:00
sword
importub
filename=package.tar
9dc51d53960bfa39dc7d831b8675f4fb
<a href="https://doi.org/10.25932/publishup-42421">Zweitveröffentlichung in der Schriftenreihe Postprints der Universität Potsdam : Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe ; 612 </a>
Rienks, Emilie D. L
false
true
CC-BY - Namensnennung 4.0 International
Peter Hlawenka
Konrad Siemensmeyer
Eugen Weschke
Andrei Varykhalov
Jaime Sanchez-Barriga
Natalya Y. Shitsevalova
A. V. Dukhnenko
V. B. Filipov
Slavomir Gabani
Karol Flachbart
Oliver Rader
Emile D. L. Rienks
Mathematik
Institut für Mathematik
Referiert
Import
Gold Open-Access
DOAJ gelistet
54741
2017
2017
eng
11
3
4
article
IOP Publ. Ltd.
Bristol
1
2017-07-21
2017-07-21
--
Nanostructural origin of giant Rashba effect in intercalated graphene
To enhance the spin-orbit interaction in graphene by a proximity effect without compromising the quasi-free-standing dispersion of the Dirac cones means balancing the opposing demands for strong and weak graphene-substrate interaction. So far, only the intercalation of Au under graphene/Ni(111) has proven successful, which was unexpected since graphene prefers a large separation (similar to 3.3 angstrom) from a Au monolayer in equilibrium. Here, we investigate this system and find the solution in a nanoscale effect. We reveal that the Au largely intercalates as nanoclusters. Our density functional theory calculations show that the graphene is periodically stapled to the Ni substrate, and this attraction presses graphene and Au nanoclusters together. This, in turn, causes a Rashba effect of the giant magnitude observed in experiment. Our findings show that nanopatterning of the substrate can be efficiently used for engineering of spin-orbit effects in graphene.
2D Materials
10.1088/2053-1583/aa7ad8
2053-1583
wos:2017
035010
WOS:000406018600001
Varykhalov, A (reprint author), Helmholtz Zentrum Berlin Mat & Energie, Elektronenspeicherring BESSY 2, Albert Einstein Str 15, D-12489 Berlin, Germany., andrei.varykhalov@helmholtz-berlin.de
Deutsche Forschungsgemeinschaft [SPP 1459]; Impuls- und Vernetzungsfonds der Helmholtz-Gemeinschaft [HRJRG-408]
2022-04-11T11:28:08+00:00
sword
importub
filename=package.tar
cc88ab95c1cc47a0ecff5cb248876714
false
true
Maxim Krivenkov
Evangelos Golias
Dmitry Marchenko
Jaime Sanchez-Barriga
Gustav Bihlmayer
Oliver Rader
Andrei Varykhalov
eng
uncontrolled
quasi-free-standing graphene
eng
uncontrolled
Ni(111)
eng
uncontrolled
gold intercalation
eng
uncontrolled
spin-orbit interaction
eng
uncontrolled
nanoclusters
eng
uncontrolled
STM
eng
uncontrolled
DFT
Astronomie und zugeordnete Wissenschaften
Institut für Physik und Astronomie
Referiert
Import
Green Open-Access
59831
2020
2020
eng
6
8
102
article
American Institute of Physics; American Physical Society (APS)
Woodbury, NY
1
2020-08-21
2020-08-21
--
Absence of a giant Rashba effect in the valence band of lead halide perovskites
For hybrid organic-inorganic as well as all-inorganic lead halide perovskites a Rashba effect has been invoked to explain the high efficiency in energy conversion by prohibiting direct recombination. Both a bulk and surface Rashba effect have been predicted. In the valence band of methylammonium (MA) lead bromide a Rashba effect has been reported by angle-resolved photoemission and circular dichroism with giant values of 7-11 eV angstrom. We present band dispersion measurements of MAPbBr(3) and spin-resolved photoemission of CsPbBr3 to show that a large Rashba effect detectable by photoemission or circular dichroism does not exist and cannot be the origin of the high effciency.
Physical review : B, Condensed matter and materials physics
10.1103/PhysRevB.102.081116
2469-9950
2469-9969
outputup:dataSource:WoS:2020
081116
WOS:000561717200001
Sajedi, Maryam (corresponding author), Helmholtz Zentrum Berlin Mat & Energie, Albert Einstein Str 15, D-12489 Berlin, Germany.; Sajedi, Maryam (corresponding author), Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany.
Helmholtz Association (Impuls-und Vernetzungsfonds der; Helmholtz-Gemeinschaft) [HRSF-0067]
2023-06-30T05:23:43+00:00
sword
importub
filename=package.tar
b7c09ebbaba101674c99c4e11c9188d7
209770-9
2844160-6
2079455-1
Sajedi, Maryam
false
true
Maryam Sajedi
Maxim Krivenkov
Dmitry Marchenko
Andrei Varykhalov
Jaime Sanchez-Barriga
Emile D. L. Rienks
Oliver Rader
Physik
Institut für Physik und Astronomie
Referiert
Import
61373
2021
2021
eng
15
3
8
article
IOP Publ. Ltd.
Bristol
1
2021-03-23
2021-03-23
--
Origin of the band gap in Bi-intercalated graphene on Ir(111)
Proximity to heavy sp-elements is considered promising for reaching a band gap in graphene that could host quantum spin Hall states. The recent report of an induced spin-orbit gap of 0.2 eV in Pb-intercalated graphene detectable by spin-resolved photoemission has spurred renewed interest in such systems (Klimovskikh et al 2017 ACS Nano 11, 368). In the case of Bi intercalation an even larger band gap of 0.4 eV has been observed but was assigned to the influence of a dislocation network (Warmuth et al 2016 Phys. Rev. B 93, 165 437). Here, we study Bi intercalation under graphene on Ir(111) and report a nearly ideal graphene dispersion without band replicas and no indication of hybridization with the substrate. The band gap is small (0.19 eV) and can be tuned by +/- 25 meV through the Bi coverage. The Bi atomic density is higher than in the recent report. By spin-resolved photoemission we exclude induced spin-orbit interaction as origin of the gap. Quantitative agreement of a photoemission intensity analysis with the measured band gap suggests sublattice symmetry breaking as one of the possible band gap opening mechanisms. We test several Bi structures by density functional theory. Our results indicate the possibility that Bi intercalates in the phase of bismuthene forming a graphene-bismuthene van der Waals heterostructure.
2D Materials
10.1088/2053-1583/abd1e4
2053-1583
outputup:dataSource:WoS:2021
035007
WOS:000632374900001
Varykhalov, Andrei (corresponding author), Helmholtz Zentrum Berlin Mat & Energie, Elektronenspeicherring BESSY 2, Albert Einstein Str 15, D-12489 Berlin, Germany., andrei.varykhalov@helmholtz-berlin.de
Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [SPP 1459]; [HRJRG-408]; [HRSF-0067]
Varykhalov, Andrei
2023-11-15T08:38:15+00:00
sword
importub
filename=package.tar
a7880e6af549bd98c7535d15206ca578
2779376-X
false
true
Maxim Krivenkov
Dimitry Marchenko
Jaime Sánchez-Barriga
Evangelos Golias
Oliver Rader
Andrei Varykhalov
eng
uncontrolled
graphene
eng
uncontrolled
bismuth
eng
uncontrolled
Ir(111)
eng
uncontrolled
spin-orbit interaction
eng
uncontrolled
ARPES
eng
uncontrolled
STM
eng
uncontrolled
bismuthene
Physik
Institut für Physik und Astronomie
Referiert
Import
Hybrid Open-Access
54989
2020
2020
eng
11
1
postprint
1
2020-03-19
2020-03-19
--
Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well
We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics.
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
urn:nbn:de:kobv:517-opus4-549892
1866-8372
10.25932/publishup-54989
online registration
publish
<a href="http://publishup.uni-potsdam.de/60814">Bibliographieeintrag der Originalveröffentlichung/Quelle</a>
Phys. Rev. Research 2, 013343 (2020). https://doi.org/10.1103/PhysRevResearch.2.013343
Version of Record
false
true
CC-BY - Namensnennung 4.0 International
Andrei Varykhalov
Friedrich Freyse
Irene Aguilera
Marco Battiato
Maxim Krivenkov
Dmitry Marchenko
Gustav Bihlmayer
Stefan Blugel
Oliver Rader
Jaime Sanchez-Barriga
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
1354
eng
uncontrolled
AG
eng
uncontrolled
films
Physik
open_access
Institut für Physik und Astronomie
Referiert
Green Open-Access
Universität Potsdam
https://publishup.uni-potsdam.de/files/54989/zmnr1354.pdf
60814
2020
2020
eng
1
9
9
1
2
article
American Physical Society
Ridge, NY
1
2020-03-19
2020-03-19
--
Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well
We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics.
Physical Review Research
10.1103/PhysRevResearch.2.013343
0031-9007
013343
Sanchez-Barriga, Jaime
208853-8
<a href="https://doi.org/10.25932/publishup-54989">Zweitveröffentlichung in der Schriftenreihe Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe ; 1354</a>
false
false
CC-BY - Namensnennung 4.0 International
Andrei Varykhalov
Friedrich Freyse
Irene Aguilera
Marco Battiato
Maxim Krivenkov
Dmitry Marchenko
Gustav Bihlmayer
Stefan Blugel
Oliver Rader
Jaime Sanchez-Barriga
eng
uncontrolled
AG
eng
uncontrolled
Flims
Physik
Institut für Physik und Astronomie
Referiert
Gold Open-Access