30 research outputs found
Magnetism and in-gap states of 3d transition metal atoms on superconducting Re
Magnetic atoms on heavy-element superconducting substrates are potential
building blocks for realizing topological superconductivity in one- and
two-dimensional atomic arrays. Their localized magnetic moments induce
so-called Yu-Shiba-Rusinov (YSR) states inside the energy gap of the substrate.
In the dilute limit, where the electronic states of the array atoms are only
weakly coupled, proximity of the YSR states to the Fermi energy is essential
for the formation of topological superconductivity in the band of YSR states.
Here, we reveal via scanning tunnel spectroscopy and ab initio calculations of
a series of 3d transition metal atoms (Mn, Fe, Co) adsorbed on the
heavy-element superconductor Re that the increase of the Kondo coupling and
sign change in magnetic anisotropy with d-state filling is accompanied by a
shift of the YSR states through the energy gap of the substrate and a crossing
of the Fermi level. The uncovered systematic trends enable the identification
of the most promising candidates for the realization of topological
superconductivity in arrays of similar systems
Spin excitations of individual Fe atoms on Pt(111): impact of the site-dependent giant substrate polarization
We demonstrate using inelastic scanning tunneling spectroscopy (ISTS) and
simulations based on density functional theory that the amplitude and sign of
the magnetic anisotropy energy for a single Fe atom adsorbed onto the Pt(111)
surface can be manipulated by modifying the adatom binding site. Since the
magnitude of the measured anisotropy is remarkably small, up to an order of
magnitude smaller than previously reported, electron-hole excitations are weak
and thus the spin-excitation exhibits long lived precessional lifetimes
compared to the values found for the same adatom on noble metal surfaces
Non-collinear spin states in bottom-up fabricated atomic chains
Non-collinear spin states with unique rotational sense, such as chiral
spin-spirals, are recently heavily investigated because of advantages for
future applications in spintronics and information technology and as potential
hosts for Majorana Fermions when coupled to a superconductor. Tuning the
properties of such spin states, e.g., the rotational period and sense, is a
highly desirable yet difficult task. Here, we experimentally demonstrate the
bottom-up assembly of a spin-spiral derived from a chain of Fe atoms on a Pt
substrate using the magnetic tip of a scanning tunneling microscope as a tool.
We show that the spin-spiral is induced by the interplay of the Heisenberg and
Dzyaloshinskii-Moriya components of the Ruderman-Kittel-Kasuya-Yosida
interaction between the Fe atoms. The relative strengths and signs of these two
components can be adjusted by the interatomic Fe distance, which enables
tailoring of the rotational period and sense of the spin-spiral.Comment: 16 pages, 5 figure
Long spin relaxation times in a transition metal atom in direct contact to a metal substrate
Long spin relaxation times are a prerequisite for the use of spins in data
storage or nanospintronics technologies. An atomic-scale solid-state
realization of such a system is the spin of a transition metal atom adsorbed on
a suitable substrate. For the case of a metallic substrate, which enables
directly addressing the spin by conduction electrons, the experimentally
measured lifetimes reported to date are on the order of only hundreds of
femtoseconds. Here, we show that the spin states of iron atoms adsorbed
directly on a conductive platinum substrate have an astonishingly long spin
relaxation time in the nanosecond regime, which is comparable to that of a
transition metal atom decoupled from the substrate electrons by a thin
decoupling layer. The combination of long spin relaxation times and strong
coupling to conduction electrons implies the possibility to use flexible
coupling schemes in order to process the spin-information
Stabilizing spin systems via symmetrically tailored RKKY interactions
The spin of a single atom adsorbed on a substrate is a promising building
block for future spintronics and quantum computation schemes. To process spin
information and also for increased magnetic stability, these building blocks
have to be coupled. For a single atom, a high symmetry of the environment is
known to lead to increased spin stability. However, little is known about the
role of the nature and symmetry of the magnetic couplings. Here, we study
arrays of atomic spins coupled via the ubiquitous Ruderman-Kittel-Kasuya-Yosida
(RKKY) interaction, focusing on its two anisotropic parts: the
Dzyaloshinskii-Moriya (DM) and the symmetric anisotropic exchange interactions.
First, we show that the high spin stability of an iron trimer can be remotely
detected by a nearby iron atom, and how the DM interaction can lead to its
destabilization. Second, we find that adding more nearby iron atoms almost
always leads to a destabilization of the trimer, due to a non-local effective
transverse anisotropy originating in the symmetric anisotropic exchange
interaction. This transverse anisotropy can be quenched only for highly
symmetric structures, for which the spin lifetime of the array is increased by
orders of magnitude
A scanning tunneling microscope capable of electron spin resonance and pump-probe spectroscopy at mK temperature and in vector magnetic field
In the last decade, detecting spin dynamics at the atomic scale has been
enabled by combining techniques like electron spin resonance (ESR) or
pump-probe spectroscopy with scanning tunneling microscopy (STM). Here, we
demonstrate an ultra-high vacuum (UHV) STM operational at milliKelvin (mK) and
in a vector magnetic field capable of both ESR and pump-probe spectroscopy. By
implementing GHz compatible cabling, we achieve appreciable RF amplitudes at
the junction while maintaining mK base temperature. We demonstrate the
successful operation of our setup by utilizing two experimental ESR modes
(frequency sweep and magnetic field sweep) on an individual TiH molecule on
MgO/Ag(100) and extract the effective g-factor. We trace the ESR transitions
down to MHz into an unprecedented low frequency band enabled by the mK base
temperature. We also implement an all-electrical pump-probe scheme based on
waveform sequencing suited for studying dynamics down to the nanoseconds range.
We benchmark our system by detecting the spin relaxation time T1 of individual
Fe atoms on MgO/Ag(100) and note a field strength and orientation dependent
relaxation time
Threefold enhancement of superconductivity and the role of field-induced odd-frequency pairing in epitaxial aluminum films near the 2D limit
BCS theory has been widely successful at describing elemental bulk
superconductors. Yet, as the length scales of such superconductors approach the
atomic limit, dimensionality as well as the environment of the superconductor
can lead to drastically different and unpredictable superconducting behavior.
Here, we report a threefold enhancement of the superconducting critical
temperature and gap size in ultrathin epitaxial Al films on Si(111), when
approaching the 2D limit, based on high-resolution scanning tunneling
microscopy/spectroscopy (STM/STS) measurements. In magnetic field, the Al films
show type II behavior and the Meservey-Tedrow-Fulde (MTF) effect for in-plane
magnetic fields. Using spatially resolved spectroscopy, we characterize the
vortex structure in the MTF regime and find strong deviations from the typical
Abrikosov vortex. We corroborate these findings with calculations that unveil
the role of odd-frequency pairing and a paramagnetic Meissner effect. These
results illustrate two striking influences of reduced dimensionality on a BCS
superconductor and present a new platform to study BCS superconductivity in
large magnetic fields
Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe's terrestrial ecosystems : a review
Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.Peer reviewe