25 research outputs found
Interaction between counter-propagating quantum Hall edge channels in the 3D topological insulator BiSbTeSe
The quantum Hall effect is studied in the topological insulator BiSbTeSe.
By employing top- and back-gate electric fields at high magnetic field, the
Landau levels of the Dirac cones in the top and bottom topological surface
states can be tuned independently. When one surface is tuned to the
electron-doped side of the Dirac cone and the other surface to the hole-doped
side, the quantum Hall edge channels are counter-propagating. The opposite edge
mode direction, combined with the opposite helicities of top and bottom
surfaces, allows for scattering between these counter-propagating edge modes.
The total Hall conductance is integer valued only when the scattering is
strong. For weaker interaction, a non-integer quantum Hall effect is expected
and measured
Non-local signatures of the chiral magnetic effect in Dirac semimetal BiSb
The field of topological materials science has recently been focussing on
three-dimensional Dirac semimetals, which exhibit robust Dirac phases in the
bulk. However, the absence of characteristic surface states in accidental Dirac
semimetals (DSM) makes it difficult to experimentally verify claims about the
topological nature using commonly used surface-sensitive techniques. The chiral
magnetic effect (CME), which originates from the Weyl nodes, causes an
-dependent chiral charge polarization, which
manifests itself as negative magnetoresistance. We exploit the extended
lifetime of the chirally polarized charge and study the CME through both local
and non-local measurements in Hall bar structures fabricated from single
crystalline flakes of the DSM BiSb. From the non-local
measurement results we find a chiral charge relaxation time which is over one
order of magnitude larger than the Drude transport lifetime, underlining the
topological nature of BiSb.Comment: 6 pages, 6 figures + 7 pages of supplemental materia
periodic Andreev bound states in a Dirac semimetal
Electrons in a Dirac semimetals possess linear dispersion in all three
spatial dimensions, and form part of a developing platform of novel quantum
materials. BiSb supports a three-dimensional Dirac cone at the
Sb-induced band inversion point. Nanoscale phase-sensitive junction technology
is used to induce superconductivity in this Dirac semimetal. Radio frequency
irradiation experiments reveal a significant contribution of 4-periodic
Andreev bound states to the supercurrent in Nb-BiSb-Nb
Josephson junctions. The conditions for a substantial contribution to
the supercurrent are favourable because of the Dirac cone's topological
protection against backscattering, providing very broad transmission
resonances. The large g-factor of the Zeeman effect from a magnetic field
applied in the plane of the junction, allows tuning of the Josephson junctions
from 0 to regimes.Comment: Supplementary information is include
Zeeman effect induced 0- transitions in ballistic Dirac semimetal Josephson junctions
One of the consequences of Cooper pairs having a finite momentum in the
interlayer of a Josephson junction, is -junction behavior. The finite
momentum can either be due to an exchange field in ferromagnetic Josephson
junctions, or due to the Zeeman effect. Here, we report the observation of
Zeeman effect induced 0- transitions in BiSb, 3D Dirac
semimetal-based Josephson junctions. The large g-factor of the Zeeman effect
from a magnetic field applied in the plane of the junction allows tuning of the
Josephson junctions from 0- to - regimes. This is revealed by sign changes
in the modulation of the critical current by applied magnetic field of an
asymmetric superconducting quantum interference device (SQUID). Additionally,
we directly measure a non-sinusoidal current-phase relation in the asymmetric
SQUID, consistent with models for ballistic Josephson transport
Predicting 30-day mortality in intensive care unit patients with ischaemic stroke or intracerebral haemorrhage
BACKGROUND Stroke patients admitted to an intensive care unit (ICU) follow a particular survival pattern with a high short-term mortality, but if they survive the first 30 days, a relatively favourable subsequent survival is observed. OBJECTIVES The development and validation of two prognostic models predicting 30-day mortality for ICU patients with ischaemic stroke and for ICU patients with intracerebral haemorrhage (ICH), analysed separately, based on parameters readily available within 24 h after ICU admission, and with comparison with the existing Acute Physiology and Chronic Health Evaluation IV (APACHE-IV) model. DESIGN Observational cohort study. SETTING All 85 ICUs participating in the Dutch National Intensive Care Evaluation database. PATIENTS All adult patients with ischaemic stroke or ICH admitted to these ICUs between 2010 and 2019. MAIN OUTCOME MEASURES Models were developed using logistic regressions and compared with the existing APACHE-IV model. Predictive performance was assessed using ROC curves, calibration plots and Brier scores. RESULTS We enrolled 14 303 patients with stroke admitted to ICU: 8422 with ischaemic stroke and 5881 with ICH. Thirty-day mortality was 27% in patients with ischaemic stroke and 41% in patients with ICH. Important factors predicting 30-day mortality in both ischaemic stroke and ICH were age, lowest Glasgow Coma Scale (GCS) score in the first 24 h, acute physiological disturbance (measured using the Acute Physiology Score) and the application of mechanical ventilation. Both prognostic models showed high discrimination with an AUC 0.85 [95% confidence interval (CI), 0.84 to 0.87] for patients with ischaemic stroke and 0.85 (0.83 to 0.86) in ICH. Calibration plots and Brier scores indicated an overall good fit and good predictive performance. The APACHE-IV model predicting 30-day mortality showed similar performance with an AUC of 0.86 (95% CI, 0.85 to 0.87) in ischaemic stroke and 0.87 (0.86 to 0.89) in ICH. CONCLUSION We developed and validated two prognostic models for patients with ischaemic stroke and ICH separately with a high discrimination and good calibration to predict 30-day mortality within 24 h after ICU admission.</p
Predicting 30-day mortality in intensive care unit patients with ischaemic stroke or intracerebral haemorrhage
BACKGROUND Stroke patients admitted to an intensive care unit (ICU) follow a particular survival pattern with a high short-term mortality, but if they survive the first 30 days, a relatively favourable subsequent survival is observed. OBJECTIVES The development and validation of two prognostic models predicting 30-day mortality for ICU patients with ischaemic stroke and for ICU patients with intracerebral haemorrhage (ICH), analysed separately, based on parameters readily available within 24 h after ICU admission, and with comparison with the existing Acute Physiology and Chronic Health Evaluation IV (APACHE-IV) model. DESIGN Observational cohort study. SETTING All 85 ICUs participating in the Dutch National Intensive Care Evaluation database. PATIENTS All adult patients with ischaemic stroke or ICH admitted to these ICUs between 2010 and 2019. MAIN OUTCOME MEASURES Models were developed using logistic regressions and compared with the existing APACHE-IV model. Predictive performance was assessed using ROC curves, calibration plots and Brier scores. RESULTS We enrolled 14 303 patients with stroke admitted to ICU: 8422 with ischaemic stroke and 5881 with ICH. Thirty-day mortality was 27% in patients with ischaemic stroke and 41% in patients with ICH. Important factors predicting 30-day mortality in both ischaemic stroke and ICH were age, lowest Glasgow Coma Scale (GCS) score in the first 24 h, acute physiological disturbance (measured using the Acute Physiology Score) and the application of mechanical ventilation. Both prognostic models showed high discrimination with an AUC 0.85 [95% confidence interval (CI), 0.84 to 0.87] for patients with ischaemic stroke and 0.85 (0.83 to 0.86) in ICH. Calibration plots and Brier scores indicated an overall good fit and good predictive performance. The APACHE-IV model predicting 30-day mortality showed similar performance with an AUC of 0.86 (95% CI, 0.85 to 0.87) in ischaemic stroke and 0.87 (0.86 to 0.89) in ICH. CONCLUSION We developed and validated two prognostic models for patients with ischaemic stroke and ICH separately with a high discrimination and good calibration to predict 30-day mortality within 24 h after ICU admission.</p