20 research outputs found
Distinction of Nuclear Spin States with the Scanning Tunneling Microscope
We demonstrate rotational excitation spectroscopy with the scanning tunneling
microscope for physisorbed hydrogen and its isotopes hydrogen-deuterid and
deuterium. The observed excitation energies are very close to the gas phase
values and show the expected scaling with moment of inertia. Since these
energies are characteristic for the molecular nuclear spin states we are able
to identify the para and ortho species of hydrogen and deuterium, respectively.
We thereby demonstrate nuclear spin sensitivity with unprecedented spatial
resolution
Rotational Excitation Spectroscopy with the STM through Molecular Resonances
We investigate the rotational properties of molecular hydrogen and its
isotopes physisorbed on the surfaces of graphene and hexagonal boron nitride
(-BN), grown on Ni(111), Ru(0001), and Rh(111), using rotational excitation
spectroscopy (RES) with the scanning tunneling microscope. The rotational
thresholds are in good agreement with transitions of freely
spinning para-H and ortho-D molecules. The line shape variations in RES
for H among the different surfaces can be traced back and naturally
explained by a resonance mediated tunneling mechanism. RES data for
H/-BN/Rh(111) suggests a local intrinsic gating on this surface due to
lateral variations in the surface potential. An RES inspection of H, HD,
and D mixtures finally points to a multi molecule excitation, since either
of the three rotational transitions are simultaneously
present, irrespective of where the spectra were recorded in the mixed
monolayer
Sparse sampling for fast quasiparticle-interference mapping
Scanning tunneling microscopy (STM) is a notoriously slow technique; data-recording is serial, which renders complex measurement tasks, such as quasiparticle interference (QPI) mapping, impractical. However, QPI could provide insight into band-structure details of quantum materials that can be inaccessible to angle-resolved photoemission spectroscopy. Here we use compressed sensing (CS) to fundamentally speed-up QPI mapping. We reliably recover the QPI information from a fraction of the usual local density of state measurements. The requirement of CS is naturally fulfilled for QPI, since CS relies on sparsity in a vector domain, here given by few nonzero coefficients in Fourier space. We exemplify CS on a simulated Cu(111) surface using random sampling of uniform and varying probability density. The latter improves QPI recovery and mitigates Fourier artifacts. We further simplify the motion of the STM tip through an open traveling salesman's problem for greater efficiency and use the tip-path for drift correction. We expect that the implications of our CS approach will be transformative for the exploration of two-dimensional quantum materials
Thermal and magnetic field stability of holmium single atom magnets
We use spin-polarized scanning tunneling microscopy to demonstrate that Ho
atoms on magnesium oxide exhibit a coercive field of more than 8 T and magnetic
bistability for many minutes, both at 35 K. The first spontaneous magnetization
reversal events are recorded at 45 K for which the metastable state relaxes in
an external field of 8 T. The transverse magnetic anisotropy energy is
estimated from magnetic field and bias voltage dependent switching rates at 4.3
K. Our measurements constrain the possible ground state of Ho single atom
magnets to either Jz = 7 or 8, both compatible with magnetic bistability at
fields larger than 10 mT.Comment: 4 pages and supplemental informatio
Adaptive sparse sampling for quasiparticle interference imaging
Quasiparticle interference imaging (QPI) offers insight into the band structure of quantum materials from the Fourier transform of local density of states (LDOS) maps. Their acquisition with a scanning tunneling microscope is traditionally tedious due to the large number of required measurements that may take several days to complete. The recent demonstration of sparse sampling for QPI imaging showed how the effective measurement time could be fundamentally reduced by only sampling a small and random subset of the total LDOS. However, the amount of required sub-sampling to faithfully recover the QPI image remained a recurring question. Here we introduce an adaptive sparse sampling (ASS) approach in which we gradually accumulate sparsely sampled LDOS measurements until a desired quality level is achieved via compressive sensing recovery. The iteratively measured random subset of the LDOS can be interleaved with regular topographic images that are used for image registry and drift correction. These reference topographies also allow to resume interrupted measurements to further improve the QPI quality. Our ASS approach is a convenient extension to quasiparticle interference imaging that should remove further hesitation in the implementation of sparse sampling mapping schemes
Adaptive Sparse Sampling for Quasiparticle Interference Imaging
Quasiparticle interference imaging (QPI) offers insight into the band
structure of quantum materials from the Fourier transform of local density of
states (LDOS) maps. Their acquisition with a scanning tunneling microscope is
traditionally tedious due to the large number of required measurements that may
take several days to complete. The recent demonstration of sparse sampling for
QPI imaging showed how the effective measurement time could be fundamentally
reduced by only sampling a small and random subset of the total LDOS. However,
the amount of required sub-sampling to faithfully recover the QPI image
remained a recurring question. Here we introduce an adaptive sparse sampling
(ASS) approach in which we gradually accumulate sparsely sampled LDOS
measurements until a desired quality level is achieved via compressive sensing
recovery. The iteratively measured random subset of the LDOS can be interleaved
with regular topographic images that are used for image registry and drift
correction. These reference topographies also allow to resume interrupted
measurements to further improve the QPI quality. Our ASS approach is a
convenient extension to quasiparticle interference imaging that should remove
further hesitation in the implementation of sparse sampling mapping schemes.Comment: 10 pages, 5 figure
A quantum pathway to overcome the trilemma of magnetic data storage
The three essential pillars of magnetic data storage devices are readability,
writeability, and stability. However, these requirements compete as magnetic
domain sizes reach the fundamental limit of single atoms and molecules. The
proven magnetic bistability of individual holmium atoms on magnesium oxide
appeared to operate within this magnetic trilemma, sacrificing writeability for
unprecedented stability. Using the magnetic stray field created by the tip of a
spin-polarized scanning tunneling microscope (SP-STM), we controllably move the
Ho state into the quantum regime, allowing us to write its state via the
quantum tunneling of magnetization (QTM). We find that the hyperfine
interaction causes both the excellent magnetic bistability, even at zero
applied magnetic field, and the avoided level crossings which we use to control
the magnetic state via QTM. We explore how to use such a system to realize a
high-fidelity single atom NOT gate (inverter). Our approach reveals the
prospect of combining the best traits of the classical and quantum worlds for
next generation data storage