435 research outputs found
Magnetic properties of substitutional Mn in (110) GaAs surface and subsurface layers
Motivated by recent STM experiments, we present a theoretical study of the
electronic and magnetic properties of the Mn-induced acceptor level obtained by
substituting a single Ga atom in the (110) surface layer of GaAs or in one of
the atoms layers below the surface. We employ a kinetic-exchange tight-binding
model in which the relaxation of the (110) surface is taken into account. The
acceptor wave function is strongly anisotropic in space and its detailed
features depend on the depth of the sublayer in which the Mn atom is located.
The local-density-of-states (LDOS) on the (110) surface associated with the
acceptor level is more sensitive to the direction of the Mn magnetic moment
when the Mn atom is located further below the surface. We show that the total
magnetic anisotropy energy of the system is due almost entirely to the
dependence of the acceptor level energy on Mn spin orientation, and that this
quantity is strongly dependent on the depth of the Mn atom.Comment: 14 pages, 13 figure
Elastic Scattering Susceptibility of the High Temperature Superconductor Bi2Sr2CaCu2O8+x: A Comparison between Real and Momentum Space Photoemission Spectroscopies
The joint density of states (JDOS) of Bi2Sr2CaCu2O8+x is calculated by
evaluating the autocorrelation of the single particle spectral function
A(k,omega) measured from angle resolved photoemission spectroscopy (ARPES).
These results are compared with Fourier transformed (FT) conductance
modulations measured by scanning tunneling microscopy (STM). Good agreement
between the two experimental probes is found for two different doping values
examined. In addition, by comparing the FT-STM results to the autocorrelated
ARPES spectra with different photon polarization, new insight on the form of
the STM matrix elements is obtained. This shines new light on unsolved
mysteries in the tunneling data.Comment: Revised now available at: Phys. Rev. Lett. 96, 067005 (2006
Spin-polarization of platinum (111) induced by the proximity to cobalt nanostripes
We measured a spin polarization above a Pt (111) surface in the vicinity of a
Co nanostripe by spin-polarized scanning tunneling spectroscopy. The spin
polarization is exponentially decaying away from the Pt/Co interface and is
detectable at distances larger than 1 nm. By performing self-consistent
ab-initio calculations of the electronic-structure for a related model system
we reveal the interplay between the induced magnetic moments within the Pt
surface and the spin-resolved electronic density of states above the surface.Comment: 19 pages, 6 figure
Correction of systematic errors in scanning tunnelling spectra on semiconductor surfaces: the energy gap of Si(111)-7x7 at 0.3 K
The investigation of the electronic properties of semiconductor surfaces
using scanning tunnelling spectroscopy (STS) is often hindered by
non-equilibrium transport of the injected charge carriers. We propose a
correction method for the resulting systematic errors in STS data, which is
demonstrated for the well known Si(111)-(7x7) surface. The surface has an odd
number of electrons per surface unit cell and is metallic above 20 K. We
observe an energy gap in the ground state of this surface by STS at 0.3 K.
After correction, the measured width of the gap is (70 +- 15) meV which is
compatible with previous less precise estimates. No sharp peak of the density
of states at the Fermi level is observed, in contrast to proposed models for
the Si(111)-(7x7) surface.Comment: 10 pages, 4 figure
Jahn-Teller stabilization of a "polar" metal oxide surface: Fe3O4(001)
Using ab initio thermodynamics we compile a phase diagram for the surface of
Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto
ignored polar termination with octahedral iron and oxygen forming a wave-like
structure along the [110]-direction is identified as the lowest energy
configuration over a broad range of oxygen gas-phase conditions. This novel
geometry is confirmed in a x-ray diffraction analysis. The stabilization of the
Fe3O4(001)-surface goes together with dramatic changes in the electronic and
magnetic properties, e.g., a halfmetal-to-metal transition.Comment: 4 pages, 4 figure
Magnetic light
In this paper we report on the observation of novel and highly unusual
magnetic state of light. It appears that in small holes light quanta behave as
small magnets so that light propagation through such holes may be affected by
magnetic field. When arrays of such holes are made, magnetic light of the
individual holes forms novel and highly unusual two-dimensional magnetic light
material. Magnetic light may soon become a great new tool for quantum
communication and computing.Comment: Submitted to Phys.Rev.Lett., 3 figure
High-energy photoemission on Fe3O4: Small polaron physics and the Verwey transition
We have studied the electronic structure and charge ordering (Verwey)
transition of magnetite (Fe3O4) by soft x-ray photoemission. Due to the
enhanced probing depth and the use of different surface preparations we are
able to distinguish surface and volume effects in the spectra. The pseudogap
behavior of the intrinsic spectra and its temperature dependence give evidence
for the existence of strongly bound small polarons consistent with both dc and
optical conductivity. Together with other recent structural and theoretical
results our findings support a picture in which the Verwey transition contains
elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb
interaction
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