17 research outputs found
Creation of equal-spin triplet superconductivity at the Al/EuS interface
In conventional superconductors, electrons of opposite spins are bound into
Cooper pairs. However, when the superconductor is in contact with a
non-uniformly ordered ferromagnet, an exotic type of superconductivity can
appear at the interface, with electrons bound into three possible spin-triplet
states. Triplet pairs with equal spin play a vital role in low-dissipation
spintronics. Despite the observation of supercurrents through ferromagnets,
spectroscopic evidence for the existence of equal-spin triplet pairs is still
missing. Here we show a theoretical model that reveals a characteristic gap
structure in the quasiparticle density of states which provides a unique
signature for the presence of equal-spin triplet pairs. By scanning tunnelling
spectroscopy we measure the local density of states to reveal the spin
configuration of triplet pairs. We demonstrate that the Al/EuS interface causes
strong and tunable spin-mixing by virtue of its spin-dependent transmission.Comment: 10 pages, 4 figures, 17 pages supplementary information, 14
supplementary figure
Modeling temperature-dependent population dynamics in the excited state of the nitrogen-vacancy center in diamond
The nitrogen-vacancy (NV) center in diamond is well known in quantum
metrology and quantum information for its favorable spin and optical
properties, which span a wide temperature range from near zero to over 600 K.
Despite its prominence, the NV center's photo-physics is incompletely
understood, especially at intermediate temperatures between 10-100 K where
phonons become activated. In this work, we present a rate model able to
describe the cross-over from the low-temperature to the high-temperature
regime. Key to the model is a phonon-driven hopping between the two orbital
branches in the excited state (ES), which accelerates spin relaxation via an
interplay with the ES spin precession. We extend our model to include magnetic
and electric fields as well as crystal strain, allowing us to simulate the
population dynamics over a wide range of experimental conditions. Our model
recovers existing descriptions for the low- and high-temperature limits, and
successfully explains various sets of literature data. Further, the model
allows us to predict experimental observables, in particular the
photoluminescence (PL) emission rate, spin contrast, and spin initialization
fidelity relevant for quantum applications. Lastly, our model allows probing
the electron-phonon interaction of the NV center and reveals a gap between the
current understanding and recent experimental findings
Temperature dependence of photoluminescence intensity and spin contrast in nitrogen-vacancy centers
We report on measurements of the photoluminescence (PL) properties of single
nitrogen-vacancy (NV) centers in diamond at temperatures between 4-300 K. We
observe a strong reduction of the PL intensity and spin contrast between ca.
10-100 K that recovers to high levels below and above. Further, we find a rich
dependence on magnetic bias field and crystal strain. We develop a
comprehensive model based on spin mixing and orbital hopping in the electronic
excited state that quantitatively explains the observations. Beyond a more
complete understanding of the excited-state dynamics, our work provides a novel
approach for probing electron-phonon interactions and a predictive tool for
optimizing experimental conditions for quantum applications.Comment: Companion paper: arXiv:2304.02521 | Model:
https://github.com/sernstETH/nvratemode
Experimental study on spectroscopic signatures of spin-triplet superconductivity
publishe
Single-electron transport through stabilised silicon nanocrystals
We have fabricated organically capped stable luminescent silicon nanocrystals with narrow size distribution by a novel, high yield and easy to implement technique. We demonstrate transport measurements of individual silicon nanocrystals by scanning tunnelling microscopy at a low temperature in a double-barrier tunnel junction arrangement in which we observed pronounced single electron tunnelling effects. The tunnelling spectroscopy of these nanocrystals with different diameters reveals quantum confinement induced bandgap modifications. Furthermore, from the features in the tunnelling spectra, we differentiate several energy contributions arising from electronic interactions inside the nanocrystal. By applying a magnetic field, we have detected a variation in the differential conductance profile that we attribute to arising from higher order tunnelling processes. We have also systematically simulated our experimental data with the Orthodox theory, and the results show good agreement with the experiment. The study establishes a correlation between the nanocrystal size and quantum confinement induced band-structure modifications which will pave the way to devise tailored nanocrystals.publishe
Modeling temperature-dependent population dynamics in the excited state of the nitrogen-vacancy center in diamond
The nitrogen-vacancy (NV) center in diamond is well known in quantum metrology and quantum information for its favorable spin and optical properties, which span a wide temperature range from near zero to over 600 K. Despite its prominence, the NV center's photophysics is incompletely understood, especially at intermediate temperatures between 10–100 K where phonons become activated. In this paper, we present a rate model able to describe the crossover from the low-temperature to the high-temperature regime. Key to the model is a phonon-driven hopping between the two orbital branches in the excited state (ES), which accelerates spin relaxation via an interplay with the ES spin precession. We extend our model to include magnetic and electric fields as well as crystal strain, allowing us to simulate the population dynamics over a wide range of experimental conditions. Our model recovers existing descriptions for the low- and high-temperature limits and successfully explains various sets of literature data. Further, the model allows us to predict experimental observables, in particular the photoluminescence (PL) emission rate, spin contrast, and spin initialization fidelity relevant for quantum applications. Lastly, our model allows probing the electron-phonon interaction of the NV center and reveals a gap between the current understanding and recent experimental findings.ISSN:1098-0121ISSN:0163-1829ISSN:1550-235XISSN:0556-2805ISSN:2469-9969ISSN:1095-3795ISSN:2469-995
Scanning nitrogen-vacancy magnetometry down to 350mK
We report on the implementation of a scanning nitrogen-vacancy (NV) magnetometer in a dry dilution refrigerator. Using pulsed optically detected magnetic resonance combined with efficient microwave delivery through a co-planar waveguide, we reach a base temperature of 350 mK, limited by experimental heat load and thermalization of the probe. We demonstrate scanning NV magnetometry by imaging superconducting vortices in a 50-nm-thin aluminum microstructure. The sensitivity of our measurements is approximately 3 μT per square root Hz. Our work demonstrates the feasibility for performing non-invasive magnetic field imaging with scanning NV centers at sub-Kelvin temperatures.ISSN:0003-6951ISSN:1077-311
Temperature Dependence of Photoluminescence Intensity and Spin Contrast in Nitrogen-Vacancy Centers
We report on measurements of the photoluminescence properties of single nitrogen-vacancy centers in diamond at temperatures between 4 K and 300 K. We observe a strong reduction of the PL intensity and spin contrast between ca. 10 K and 100 K that recovers to high levels below and above. Further, we find a rich dependence on magnetic bias field and crystal strain. We develop a comprehensive model based on spin mixing and orbital hopping in the electronic excited state that quantitatively explains the observations. Beyond a more complete understanding of the excited-state dynamics, our work provides a novel approach for probing electron-phonon interactions and a predictive tool for optimizing experimental conditions for quantum applications.ISSN:0031-9007ISSN:1079-711
Imaging of submicroampere currents in bilayer graphene using a scanning diamond magnetometer
We report on nanometer magnetic imaging of two-dimensional current flow in bilayer graphene devices at room temperature. By combining dynamical modulation of the source-drain current with ac quantum sensing of a nitrogen-vacancy center in the diamond probe tip, we acquire magnetic field and current density maps with excellent sensitivities of 4.6 nT and 20 nA/µm, respectively. The spatial resolution is 50-100 nm. We introduce a set of methods for increasing the technique’s dynamic range and for mitigating undesired back-action of magnetometry operation (scanning tip, laser and microwave pulses) on the electronic transport. Finally, we show that our imaging technique is able to resolve small variations in the current flow pattern in response to changes in the background potential. Our experiments demonstrate the feasibility for detecting and imaging subtle spatial features of nanoscale transport in two-dimensional materials and conductors.ISSN:2331-701