0000000000082174
AUTHOR
Torsten Methfessel
Giant magnetic anisotropy energy and coercivity in Fe island and atomic wire on W(110)
We have directly investigated the giant magnetic anisotropy energy and coercivity of monolayer (ML) Fe islands and stripes on flat and stepped W(110) surfaces using x-ray magnetic circular dichroism. Both for islands and stripes, the magnetic anisotropy energy is $\ensuremath{\sim}$1.0 meV/atom, independent of the coverage below 0.5 ML. On the contrary, the coercive field of the islands rapidly drops from 4.3 T at 0.25 ML to 1.9 T at 0.50 ML, while that of the stripes moderately degrades from 3.5 T at 0.15 ML ($\ensuremath{\sim}$3 atom rows) to 3.0 T at 0.50 ML. We explain the contrastive behavior for the islands and stripes by different nucleation and remagnetization processes. Considering…
Evidence for eight node mixed-symmetry superconductivity in a correlated organic metal
We report a combined theoretical and experimental investigation of the superconducting state in the quasi-two-dimensional organic superconductor $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br. Applying spin-fluctuation theory to a low-energy material-specific Hamiltonian derived from ab initio density functional theory we calculate the quasiparticle density of states in the superconducting state. We find a distinct three-peak structure that results from a strongly anisotropic mixed-symmetry superconducting gap with eight nodes and twofold rotational symmetry. This theoretical prediction is supported by low-temperature scanning tunneling spectroscopy on in situ cleaved single crystals of $\kappa$-(ET)$_2$…
Disorder-induced gap in the normal density of states of the organic superconductorκ-(BEDT-TTF)2Cu[N(CN)2]Br
The local density of states (DOS) of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br, measured by scanning tunneling spectroscopy on in situ cleaved surfaces, reveals a logarithmic suppression near the Fermi edge persisting above the critical temperature T(c). The experimentally observed suppression of the DOS is in excellent agreement with a soft Hubbard gap as predicted by the Anderson-Hubbard model for systems with disorder. The electronic disorder also explains the diminished coherence peaks of the quasi-particle DOS below T(c).
Reconstructed bcc Co films on the surface
Abstract Ultrathin epitaxial Co films on Cr ( 1 1 0 ) are examined by scanning tunneling microscopy and spectroscopy (STM and STS). At room temperature Co grows as pseudomorphic bcc layers for the first two monolayers and forms close-packed Co layers with stacking faults for thicker coverages. A periodic lattice distortion appears in two equivalent (3 × 1) reconstruction domains in combination with a regular lattice of dislocation lines oriented along the in-plane close-packed row directions bcc [ 1 1 ¯ 1 ] and bcc [ 1 ¯ 1 1 ] . The reconstruction and the occurrence of dislocation lines are caused by the epitaxial strain. The local density-of-states function is mapped by scanning tunneling …
Morphology and electronic structure of bcc Co(110) and fcc/hcp Co(111) on Fe(110) investigated by STM and STS
Abstract We report on the growth of ultrathin epitaxial Co films on Fe(1 1 0) examined by scanning tunneling microscopy and spectroscopy (STM and STS). At room temperature Co forms pseudomorphic, ideally ordered body-centered cubic (bcc) layers for the first two monolayers as confirmed by atomically resolved STM images. This is in contrast to the related case of Co/Cr(1 1 0) where a superstructure occurs in the second layer. The third monolayer forms a close-packed structure and causes a transformation of the buried second monolayer into a close-packed structure. The Fe(1 1 0) substrate strongly influences the electronic structure of the first Co monolayer as concluded from the dI / dU spec…
Formation of an intermolecular charge-transfer compound in UHV codeposited tetramethoxypyrene and tetracyanoquinodimethane
Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane $({\text{TMP}}_{1}{\text{-TCNQ}}_{1})$ on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (${d}_{1}=0.894\text{ }\text{nm}$ and ${d}_{2}=0.677\text{ }\text{nm}$). A softening of the CN stretching vibration (redshift by $7\text{ }{\text{cm}}^{\ensuremath{-}1}$) of TCNQ is visible in the IR spectra, being indicative of a CT on the order of $0.3e$ f…
Structural, electronic, and magnetic properties of pseudomorphic CrFe nanostripes on W(110)
We have grown pseudomorphic binary ${\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}$ alloy monolayers and sequences of Cr and Fe nanostripes on W(110) by molecular-beam epitaxy in ultrahigh vacuum. By coadsorption of Cr and Fe a pseudomorphic random CrFe alloy grows on the W(110) substrate. At a substrate temperature of $700\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the CrFe alloy forms monolayer stripes in the step flow growth mode. We have measured magnetic properties of the monolayer alloy for $0.75\ensuremath{\leqslant}x\ensuremath{\leqslant}1$ using Kerr magnetometry. At a constant relative temperature $t=T∕{T}_{C}$ the saturation value of the Kerr rotation shows a maximum at $x=0.95$ an…
Tuning the hole injection barrier in the intermolecular charge-transfer compoundDTBDT-F4TCNQ at metal interfaces
Molecular monolayers of the charge-transfer salt dithienobenzodithiophene-tetrafluorotetracyanoquinodimethane (DTBDT-F${}_{4}$TCNQ) have been deposited on C(R$15\ifmmode\times\else\texttimes\fi{}3$)/W(110), Co/W(110), and hcp Co(0001) using molecular beam epitaxy in an ultrahigh vacuum. The integrity of the deposited molecules has been confirmed by scanning tunneling microscopy. Scanning tunneling spectroscopy has been used to determine the energetic positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital of acceptor and donor in the pure and in the mixed phase. The mixed charge transfer phase exhibits a new HOMO close to the Fermi edge depicting a charge tra…
Spin scattering and spin-polarized hybrid interface states at a metal-organic interface
Spin scattering at the interface formed between metallic Fe and Cu-phthalocyanine molecules is investigated by spin-polarized scanning tunneling spectroscopy and spin-resolved photoemission. The results are interpreted using first-principles electronic structure theory. The combination of experimental and theoretical techniques allows us to shed light on the role of hybrid interface states for the spin scattering. We show that Cu-phthalocyanine acts, via hybrid interface states, as a local spin filter up to room temperature both below and above the Fermi energy, ${E}_{\mathrm{F}}$. At the same time, the molecule behaves as a featureless scattering barrier in a region of about 1 eV around ${…