52 research outputs found
Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine
The electronic structure of ZnPc, from sub-monolayers to thick films, on bare
and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy
(XPS), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy
(STM). Our results suggest that at low coverage ZnPc lies almost parallel to
the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt
attraction, leading to an inhomogeneous charge distribution within the molecule
and charge transfer to the molecule. ZnPc does not form a complete monolayer on
the Pt surface, due to a surface-mediated intermolecular repulsion. At higher
coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate
interaction. Our photoemission results illustrate that ZnPc is practically
decoupled from Pt, already from the second layer. Pre-deposition of iodine on
Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in
contact with Pt(111)-I or Pt(111)-I
, and a more homogeneous charge
distribution and charge transfer at the interface. On increased ZnPc thickness
iodine is dissolved in the organic film where it acts as an electron acceptor
dopant.Comment: 12 pages, 9 figure
Direct observation of decoupled Dirac states at the interface between topological and normal insulators
Several proposed applications and exotic effects in topological insulators
rely on the presence of helical Dirac states at the interface between a
topological and a normal insulator. In the present work, we have used
low-energy angle-resolved photoelectron spectroscopy to uncover and
characterize the interface states of BiSe thin films and
BiTe/BiSe heterostuctures grown on Si(111). The results
establish that Dirac fermions are indeed present at the
topological-normal-insulator boundary and absent at the
topological-topological-insulator interface. Moreover, it is demonstrated that
band bending present within the topological-insulator films leads to a
substantial separation of the interface and surface states in energy. These
results pave the way for further studies and the realization of
interface-related phenomena in topological-insulator thin-film
heterostructures.Comment: 9 pages, 5 figure
The J_{eff}=1/2 insulator Sr3Ir2O7 studied by means of angle-resolved photoemission spectroscopy
The low-energy electronic structure of the J_{eff}=1/2 spin-orbit insulator
Sr3Ir2O7 has been studied by means of angle-resolved photoemission
spectroscopy. A comparison of the results for bilayer Sr3Ir2O7 with available
literature data for the related single-layer compound Sr2IrO4 reveals
qualitative similarities and similar J_{eff}=1/2 bandwidths for the two
materials, but also pronounced differences in the distribution of the spectral
weight. In particuar, photoemission from the J_{eff}=1/2 states appears to be
suppressed. Yet, it is found that the Sr3Ir2O7 data are in overall better
agreement with band-structure calculations than the data for Sr2IrO4.Comment: 5 pages, 3 figure
Study of the mixed state of La_{1.83}Sr_{0.17}CuO_{4} by means of muon-spin rotation and magnetization experiments in a low magnetic field
Muon-spin rotation (muSR) experiments are often used to study the magnetic
field distribution in type-II superconductors in the vortex state. Based on the
determination of the magnetic penetration depth it is frequently
speculated---also controversially---about the order-parameter symmetry of the
studied superconductors. This article reports on a combined muSR and
magnetization study of the mixed state in the cuprate high-temperature
superconductor La_{1.83}Sr_{0.17}CuO_{4} in a low magnetic field of 20 mT
applied along the c axis of a single crystal. The macroscopic magnetization
measurements reveal substantial differences for various cooling procedures.
Yet, indicated changes in the vortex dynamics between different temperature
regions as well as the results of the microscopic muSR experiments are
virtually independent of the employed cooling cycles. Additionally, it is found
that the mean magnetic flux density, locally probed by the muons, strongly
increases at low temperatures. This can possibly be explained by a non-random
sampling of the spatial field distribution of the vortex lattice in this
cuprate superconductor caused by intensified vortex pinning.Comment: 10 pages, 8 figures, accepted for publication in Physical Review
Magnetism in the 2D Limit and Interface Superconductivity in Metal-Insulator La(2-x)Sr(x)CuO(4) Superlattices
We show, by means of low-energy muon spin rotation measurements, that
few-unit-cells thick La(2)CuO(4) layers synthesized digitally by molecular beam
epitaxy synthesis are antiferromagnetically ordered. Below a thickness of about
5 CuO(2) layers the long-range ordered state breaks down, and a magnetic state
appears with enhanced quantum fluctuations and a reduced spin stiffness. This
magnetic state can exist in close proximity (few Angstrom) to high-temperature
superconducting layers, without transmitting supercurrents.Comment: 4 pages, 3 figure
Magnetism, superconductivity and coupling in cuprate heterostructures probed by low-energy muon-spin rotation
We present a low-energy muon-spin-rotation study of the magnetic and
superconducting properties of YBa2Cu3O7/PrBa2Cu3O7 trilayer and bilayer
heterostructures. By determining the magnetic-field profiles throughout these
structures we show that a finite superfluid density can be induced in otherwise
semiconducting PrBa2Cu3O7 layers when juxtaposed to YBa2Cu3O7 "electrodes"
while the intrinsic antiferromagnetic order is unaffected.Comment: 10 pages, 9 figures; figure 9 corrected in version
Topological crystalline insulator states in Pb(1-x)Sn(x)Se
Topological insulators are a novel class of quantum materials in which
time-reversal symmetry, relativistic (spin-orbit) effects and an inverted band
structure result in electronic metallic states on the surfaces of bulk
crystals. These helical states exhibit a Dirac-like energy dispersion across
the bulk bandgap, and they are topologically protected. Recent theoretical
proposals have suggested the existence of topological crystalline insulators, a
novel class of topological insulators in which crystalline symmetry replaces
the role of time-reversal symmetry in topological protection [1,2]. In this
study, we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a
topological crystalline insulator for x=0.23. Temperature-dependent
magnetotransport measurements and angle-resolved photoelectron spectroscopy
demonstrate that the material undergoes a temperature-driven topological phase
transition from a trivial insulator to a topological crystalline insulator.
These experimental findings add a new class to the family of topological
insulators. We expect these results to be the beginning of both a considerable
body of additional research on topological crystalline insulators as well as
detailed studies of topological phase transitions.Comment: v2: published revised manuscript (6 pages, 3 figures) and
supplementary information (5 pages, 8 figures
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