19 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
Factors affecting atmospheric vertical motions as analyzed with a generalized omega equation and the OpenIFS model
A statistical analysis of the physical causes of atmospheric vertical motions is conducted using a generalized omega equation and a one-year simulation with the OpenIFS atmospheric model. Using hourly output from the model, the vertical motions associated with vorticity advection, thermal advection, friction, diabatic heating, and an imbalance term are diagnosed. The results show the general dominance of vorticity advection and thermal advection in extratropical latitudes in winter, the increasing importance of diabatic heating towards the tropics, and the significant role of friction in the lowest troposphere. As this study uses notably higher temporal resolution data than previous studies which applied the generalized omega equation, our results reveal that the imbalance term is larger than the earlier results suggested. Moreover, for the first time, we also explicitly demonstrate the seasonal and geographical contrasts in the statistics of vertical motions as calculated with the generalized omega equation. Furthermore, as our analysis covers a full year, significantly longer than any other previous studies, statistically reliable quantitative estimates of the relative importance of the different forcing terms in different locations and seasons can be made. One such important finding is a clear increase in the relative importance of diabatic heating for midtropospheric vertical motions in the Northern Hemisphere midlatitudes from the winter to the summer, particularly over the continents. We also find that, in general, the same processes are important in areas of both rising and sinking motion, although there are some quantitative differences.Peer reviewe
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
OZO v.1.0 : software for solving a generalised omega equation and the Zwack-Okossi height tendency equation using WRF model output
A software package (OZO, Omega-Zwack-Okossi) was developed to diagnose the processes that affect vertical motions and geopotential height tendencies in weather systems simulated by the Weather Research and Forecasting (WRF) model. First, this software solves a generalised omega equation to calculate the vertical motions associated with different physical forcings: vorticity advection, thermal advection, friction, diabatic heating, and an imbalance term between vorticity and temperature tendencies. After this, the corresponding height tendencies are calculated with the Zwack-Okossi tendency equation. The resulting height tendency components thus contain both the direct effect from the forcing itself and the indirect effects (related to the vertical motion induced by the same forcing) of each physical mechanism. This approach has an advantage compared with previous studies with the Zwack-Okossi equation, in which vertical motions were used as an independent forcing but were typically found to compensate the effects of other forcings. The software is currently tailored to use input from WRF simulations with Cartesian geometry. As an illustration, results for an idealised 10-day baroclinic wave simulation are presented. An excellent agreement is found between OZO and the direct WRF output for both the vertical motion and the height tendency fields. The individual vertical motion and height tendency components demonstrate the importance of both adiabatic and diabatic processes for the simulated cyclone. OZO is an open-source tool for both research and education, and the distribution of the software will be supported by the authors.Peer reviewe
Multi-Instrument Observations and Tracking of a Coronal Mass Ejection Front From Low to Middle Corona
The shape and dynamics of coronal mass ejections (CMEs) varies significantly based on the instrument and wavelength used. This has led to significant debate about the proper definitions of CME/shock fronts, pile-up/compression regions, and cores observed in projection in optically thin vs. optically thin emission. Here we present an observational analysis of the evolving shape and kinematics of a large-scale CME that occurred on May 7, 2021 on the eastern limb of the Sun as seen from 1 au. The eruption was observed continuously, consecutively by the Atmospheric Imaging Assembly (AIA) telescope suite on the Solar Dynamics Observatory (SDO), the ground-based COronal Solar Magnetism Observatory (COSMO) K-coronagraph (K-Cor) on Mauna Loa, and the C2 and C3 telescopes of the Large Angle Solar Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SoHO). We apply the recently developed Wavetrack Python suite for automated detection and tracking of coronal eruptive features to evaluate and compare the evolving shape of the CME front as it propagated from the solar surface out to 20 solar radii. Our tool allows tracking features beyond just the leading edge and is an important step towards semi-automatic manufacturing of training sets for training data-driven image segmentation models for solar imaging. Our findings confirm the expected strong connection between EUV waves and CMEs. Our novel, detailed analysis sheds observational light on the details of EUV wave-shock-CME relations that is lacking for the gap region between the low and middle corona