19 research outputs found
One-dimensional electronic structure of phosphorene chains
Phosphorene, a 2D allotrope of phosphorus, is technologically very appealing
because of its semiconducting properties and narrow band gap. Further reduction
of the phosphorene dimensionality may spawn exotic properties of its electronic
structure, including lateral quantum confinement and topological edge states.
Phosphorene atomic chains self-assembled on Ag(111) have recently been
characterized structurally but were found by angle-resolved photoemission
(ARPES) to be electronically 2D. We show that these chains, although aligned
equiprobably to three directions of the Ag(111) surface, can be
characterized by ARPES because the three rotational variants are separated in
the angular domain. The dispersion of the phosphorus band measured along and
perpendicular to the chains reveals pronounced electronic confinement resulting
in a 1D band, flat and dispersionless perpendicular to the chain direction in
momentum space. Our density functional theory calculations reproduce the 1D
band for the experimentally determined structure of P/Ag(111). We predict a
semiconductor-to-metal phase transition upon increasing the density of the
chain array so that a 2D structure would be metallic
Recommended from our members
Self-organized formation of unidirectional and quasi-one-dimensional metallic Tb silicide nanowires on Si(110)
Terbium induced nanostructures on Si(110) and their growth are thoroughly characterized by low energy electron diffraction, scanning tunneling microscopy and spectroscopy, core-level and valence band photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy. For low Tb coverage, a wetting layer forms with its surface fraction continuously decreasing with increasing Tb coverage in favor of the formation of unidirectional Tb silicide nanowires. These nanowires show high aspect ratios for high annealing temperatures or on substrates already containing Tb in the bulk. Both wetting layer and nanowires are stable for temperatures up to 750°C. In contrast to the nanowires, the wetting layer is characterized by a band gap. Thus, the metallic nanowires, which show a quasi-one-dimensional electronic band structure, are embedded in a semiconducting surrounding of wetting layer and substrate, insulating the nanowires from each other
Recommended from our members
Suppression of nematicity by tensile strain in multilayer FeSe/SrTiO3 films
The nematicity in multilayer FeSe/SrTiO3 films has been previously suggested to be enhanced with decreasing film thickness. Motivated by this, there have been many discussions about the competing relation between nematicity and superconductivity. However, the criterion for determining the nematicity strength in FeSe remains highly debated. The understanding of nematicity as well as its relation to superconductivity in FeSe films is therefore still controversial. Here, we fabricate multilayer FeSe/SrTiO3 films using molecular beam epitaxy and study the nematic properties by combining angle-resolved photoemission spectroscopy, Se77 nuclear magnetic resonance, and scanning tunneling microscopy experiments. We unambiguously demonstrate that, near the interface, the nematic order is suppressed by the SrTiO3-induced tensile strain; in the bulk region further away from the interface, the strength of nematicity recovers to the bulk value. Our results not only solve the recent controversy about the nematicity in multilayer FeSe films, but also offer valuable insights into the relationship between nematicity and superconductivity
Suppression of nematicity by tensile strain in multilayer FeSe/SrTiO films
The nematicity in multilayer FeSe/SrTiO films has been previously
suggested to be enhanced with decreasing film thickness. Motivated by this,
there have been many discussions about the competing relation between
nematicity and superconductivity. However, the criterion for determining the
nematicity strength in FeSe remains highly debated. The understanding of
nematicity and its relation to superconductivity in FeSe films is therefore
still controversial. Here, we fabricate multilayer FeSe/SrTiO films using
molecular beam epitaxy and study the nematic properties by combining
angle-resolved photoemission spectroscopy, nuclear magnetic resonance, and
scanning tunneling microscopy experiments. We unambiguously demonstrate that,
near the interface, the nematicity is suppressed by the SrTiO-induced
tensile strain; in the bulk region further away from the interface, the
strength of nematicity recovers to the bulk value. Our results not only solve
the controversy about the nematicity in multilayer FeSe films, but also offer
valuable insights into the relationship between nematicity and
superconductivity.Comment: 23 pages, 4 figure
Surface floating 2D bands in layered nonsymmorphic semimetals : ZrSiS and related compounds
Work at Argonne National Laboratory is supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357; additional support by National Science Foundation under Grant No. DMR-0703406. This work was partially supported by the DFG, proposal no. SCHO 1730/1-1.In this work, we present a model of the surface states of nonsymmorphic semimetals. These are derived from surface mass terms that lift the high degeneracy imposed on the band structure by the nonsymmorphic bulk symmetries. Reflecting the reduced symmetry at the surface, the bulk bands are strongly modified. This leads to the creation of two-dimensional floating or unpinned bands, which are distinct from Shockley states, quantum well states, or topologically protected surface states. We focus on the layered semimetal ZrSiS to clarify the origin of its surface states. We demonstrate an excellent agreement between density functional theory calculations and angle-resolved photoemission spectroscopy measurements and present an effective four-band model in which similar surface bands appear. Finally, we emphasize the role of the surface chemical potential by comparing the surface density of states in samples with and without potassium coating. Our findings can be extended to related compounds and generalized to other crystals with nonsymmorphic symmetries.Publisher PDFPeer reviewe
Colossal negative magnetoresistance in the complex charge density wave regime of an antiferromagnetic Dirac semimetal
Colossal magnetoresistance (MR) is a well-known phenomenon, notably observed
in hole-doped ferromagnetic manganites. It remains a major research topic due
to its potential in technological applications. Though topological semimetals
also show large MR, its origin and nature are completely different. Here, we
show that in the highly electron doped region, the Dirac semimetal CeSbTe
demonstrates similar properties as the manganites. CeSbTe
hosts multiple charge density wave (CDW) modulation-vectors and has a complex
magnetic phase diagram. We confirm that this compound is an antiferromagnetic
Dirac semimetal. Despite having a metallic Fermi surface, the electronic
transport properties are semiconductor-like and deviate from known theoretical
models. An external magnetic field induces a semiconductor-metal-like
transition, which results in a colossal negative MR. Moreover, signatures of
the coupling between the CDW and a spin modulation are observed in resistivity.
This spin modulation also produces a giant anomalous Hall response.Comment: 11 pages, 13 figure
Native and graphene-coated flat and stepped surfaces of TiC
Titanium carbide attracts growing interest as a substrate for graphene growth and as a component of the composite carbon materials for supercapacitors, an electrode material for metal-air batteries. For all these applications, the surface chemistry of titanium carbide is highly relevant and being, however, insufficiently explored especially at atomic level is a subject of our studies. Applying X-ray photoelectron spectroscopy (XPS) to clean (111) and (755) surfaces of TiC, we were able to obtain the detailed spectroscopic pattern containing information on the plasmon structure, shake up satellite, the peak asymmetry and, finally, surface core level shift (SCLS) in C 1s spectra. The latter is essential for further precise studies of chemical reactions. Later on, we studied interface between TiC (111) and (755) and graphene and found the SCLS variation due to strong chemical interaction between graphene and substrate. This interaction is also reflected in the peculiar band structure of graphene probed by angle-resolved photoelectron spectroscopy (ARPES). Based on LEED data the structure is close to (7√3 × 7√3)R30°, with graphene being slightly corrugated. We found that similarly to the graphene on metals, the chemical interaction between graphene and TiC can be weakened by means of intercalation of oxygen atoms underneath graphene.We thank Helmholtz-Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtimes at the Russian-German and UE112-PGM2 beamlines. The work was financially supported by the Russian Science Foundation (project 16-42-01093). DFT calculations were performed at “Lomonosov” MSU supercomputer.Peer reviewe
USPOREDNA RAČUNOVODSTVENA STRUKTURNA ANALIZA FINANCUSKIH IZVJEŠTAJA U DJELATNOSTI "HOTELI I RESTORANI" U CILJU EFIKASNIJEG UPRAVLJANJA
Djelatnost "Hoteli i restorani" sastoji se od nekoliko poddjelatnosti od kojih je najznačajnija "Hoteli". U radu se utvrđuju strukturni odnosi između pojedinih poddjelatnosti i financijsko stanje i profitabilnost poslovanja na razini djelatnosti i poddjelatnosti. Financijsko je stanje kod većina poddjelatnosti uneravnoteženo, što znači da nije uspostavljena ni dugoročna ni kratkoročna uravnoteženost. Profitabilnost pojedinih poddjelatnosti u razmatranom razdoblju je negativna. Sve to upućuje na zaključak da je stanje u djelatnosti "Hoteli i restorani" teško što podrazumijeva hitnu intervenciju na makro i na mikro području. Računovodstvena analiza je temelj na osnovu kojeg je moguće donijeti adekvatne odluke