20 research outputs found
Quantum Spin Holography with Surface State Electrons
In a recent paper Moon and coworkers [C.R. Moon et al., Nature Nanotechnology
4, 167 (2009)] have shown that the single-atom limit for information storage
density can be overcome by using the coherence of electrons in a
two-dimensional electron gas to produce quantum holograms comprised of
individually manipulated molecules projecting an electronic pattern onto a
portion of a surface. We propose to further extend the concept by introducing
quantum spin holography - a version of quantum holographic encoding allowing to
store the information in two spin channels independently.Comment: 5 pages, 3 figure
Confined bulk states as a long-range sensor for impurities and a transfer channel for quantum information
We show that confinement of bulk electrons can be observed at low-dimensional
surface structures and can serve as a long-range sensor for the magnetism and
electronic properties of single impurities or as a quantum information transfer
channel with large coherence lengths. Our ab initio calculations reveal
oscillations of electron density in magnetic chains on metallic surfaces and
help to unambiguously identify the electrons involved as bulk electrons. We
furthermore discuss the possibility of utilizing bulk state confinement to
transfer quantum information, encoded in an atom's species or spin, across
distances of several nanometers with high efficiency.Comment: 5 pages, 2 figure
Relativistic peculiarities at stepped surfaces: surprising energetics and unexpected diffusion patterns
We revive intriguing, yet still unexplained, experimental results of Ehrlich
and co-workers [ Phys. Rev. Lett. 77 1334 (1996); Phys. Rev. Lett. 67 2509
(1991)] who have observed, that 5d adatoms distributed on (111) surface islands
of 5d metals favor the adsorption at the cluster's edge rather than at the
cluster's interior, which lies in contrast with the behavior of 4d and 3d
elements. Our state of the art ab initio calculations demonstrate that such
behavior is a direct consequence of the relativity of 5d metals.Comment: 5 pages, 5 figure
Potential Energy Driven Spin Manipulation via a Controllable Hydrogen Ligand
Spin-bearing molecules can be stabilized on surfaces and in junctions with
desirable properties such as a net spin that can be adjusted by external
stimuli. Using scanning probes, initial and final spin states can be deduced
from topographic or spectroscopic data, but how the system transitioned between
these states is largely unknown. Here we address this question by manipulating
the total spin of magnetic cobalt hydride complexes on a corrugated boron
nitride surface with a hydrogen- functionalized scanning probe tip by
simultaneously tracking force and conductance. When the additional hydrogen
ligand is brought close to the cobalt monohydride, switching between a corre-
lated S = 1 /2 Kondo state, where host electrons screen the magnetic moment,
and a S = 1 state with magnetocrystalline anisotropy is observed. We show that
the total spin changes when the system is transferred onto a new potential
energy surface defined by the position of the hydrogen in the junction. These
results show how and why chemically functionalized tips are an effective tool
to manipulate adatoms and molecules, and a promising new method to selectively
tune spin systems
Quantum Engineering of Spin and Anisotropy in Magnetic Molecular Junctions
Single molecule magnets and single spin centers can be individually addressed
when coupled to contacts forming an electrical junction. In order to control
and engineer the magnetism of quantum devices, it is necessary to quantify how
the structural and chemical environment of the junction affects the spin
center. Metrics such as coordination number or symmetry provide a simple method
to quantify the local environment, but neglect the many-body interactions of an
impurity spin when coupled to contacts. Here, we utilize a highly corrugated
hexagonal boron nitride (h-BN) monolayer to mediate the coupling between a
cobalt spin in CoHx (x=1,2) complexes and the metal contact. While the hydrogen
atoms control the total effective spin, the corrugation is found to smoothly
tune the Kondo exchange interaction between the spin and the underlying metal.
Using scanning tunneling microscopy and spectroscopy together with numerical
simulations, we quantitatively demonstrate how the Kondo exchange interaction
mimics chemical tailoring and changes the magnetic anisotropy
MCP-Based Detectors: Calibration and First Photon Radiation Measurements
Detectors based on microchannel plates (MCPs) are used to detect radiation from free-electron lasers. Three MCP detectors have been developed by JINR for the European XFEL (SASE1, SASE2 and SASE3 lines). These detectors are designed to operate in a wide dynamic range from the level of spontaneous emission to the SASE saturation level (between a few nJ up to 25 mJ), in a wide wavelength range from 0.05 nm to 0.4 nm for SASE1 and SASE2, and from 0.4 nm to 4.43 nm for SASE3. The detectors measure photon pulse energies with an anode and a photodiode. The photon beam image is observed with an MCP imager with a phosphor screen. At present, the SASE1 and SASE3 MCP detectors are commissioned with XFEL beams. Calibration and first measurements of photon radiation in multibunch mode are performed with the SASE1 and SASE3 MCPs. The MCP detector for SASE2 and its electronics are installed in the XFEL tunnel, technically commissioned, and are now ready for acceptance tests with the X-ray beam
MCP Based Detectors Installation in European XFEL
An important task of the photon beam diagnostics at the European XFEL is providing reliable tools for measurements aiming at the search for and fine tuning of the FEL creating SASE process. Radiation detectors based on micro channel plates (MCP) will be use at the European XFEL. Detectors operate in a wide dynamic range from the level of spontaneous emission to the saturation level (between a few nJ and 25 mJ), and in a wide wavelength range from 0.05 nm to 0.4 nm for SASE1 and SASE2, and from 0.4 nm to 4.43 nm for SASE3. Photon pulse energies are measured by MCP with anode and with photodiode. The photon beam image is measured by MCP imager with phosphor screen anode. Three MCP devices will be installed, one after each SASE undulator of the European XFEL (SASE1, SASE2, and SASE3). At present time MCP SASE1 and MCP SASE3 were installed in XFEL tunnel. Calibration and acceptance test experiments with MCP detectors and their electronic is under discussion
Measurements of Ultrasmall Charges with MCP Detector in FLASH Accelerator
Structure of the dark current passed through the undulator is a matter of great concern. Two effects can contribute to the dark current: emission of electrons from "hot" spots in the gun, and generation of "ghost" bunches due to possible leakage of the photoinjector laser. MCP based photon detector has been used for measurements of radiation energy from electron bunch. For small radiation densities the light is detected by direct illumination of the MCP plate, and for large densities a small angle scattering scheme is realized when metallic mesh scatters tiny fraction of light on the MCP plate. In the present experiment we used geometry of direct illumination of MCP plate aiming detection of "ghost" bunches which may generate parasitically from the laser driven electron gun. Reduction of background conditions allowed us to detect light produced by electron bunches with extremely small charges, on a sub-femtocoulomb values. We measured for the first time structure of the dark current passing through the FLASH undulator. We have also been able to measure a high contrast of radiation produced by the photoinjector laser pulses switched on and off by a 1 MHz repetition rate Pockels cells