43 research outputs found
Hidden spin-orbital texture at the -located valence band maximum of a transition metal dichalcogenide semiconductor
Finding stimuli capable of driving an imbalance of spin-polarised electrons
within a solid is the central challenge in the development of spintronic
devices. However, without the aid of magnetism, routes towards this goal are
highly constrained with only a few suitable pairings of compounds and driving
mechanisms found to date. Here, through spin- and angle-resolved photoemission
along with density functional theory, we establish how the -derived bulk
valence bands of semiconducting 1T-HfSe possess a local, ground-state spin
texture spatially confined within each Se-sublayer due to strong
sublayer-localised electric dipoles orientated along the -axis. This hidden
spin-polarisation manifests in a `coupled spin-orbital texture' with
in-equivalent contributions from the constituent -orbitals. While the
overall spin-orbital texture for each Se sublayer is in strict adherence to
time-reversal symmetry (TRS), spin-orbital mixing terms with net polarisations
at time-reversal invariant momenta are locally maintained. These apparent
TRS-breaking contributions dominate, and can be selectively tuned between with
a choice of linear light polarisation, facilitating the observation of
pronounced spin-polarisations at the Brillouin zone centre for all . We
discuss the implications for the generation of spin-polarised populations from
1T-structured transition metal dichalcogenides using a fixed energy, linearly
polarised light source.Comment: 11 pages, 6 figure
Evidence for topological band inversion of the phase change material Ge2Sb2Te5
We present an angle-resolved photoemission study of a ternary phase change
material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable
cubic phase. The observed upper bulk valence band shows a minimum at Gamma-bar
being 0.3 eV below the Fermi level E_F and a circular Fermi contour around
Gamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is in
agreement with density functional theory calculations of the Petrov stacking
sequence in the cubic phase which exhibits a topological surface state. The
topologically trivial cubic KH stacking shows a valence band maximum at Gamma
in line with all previous calculations of the hexagonal stable phase exhibiting
the valence band maximum at Gamma for a trivial Z_2 topological invariant nu_0
and away from Gamma for non-trivial nu_0. Scanning tunneling spectroscopy
exhibits a band gap of 0.4 eV around E_F
2D layered transport properties from topological insulator BiSe single crystals and micro flakes
Low-field magnetotransport measurements of topological insulators such as
BiSe are important for revealing the nature of topological surface
states by quantum corrections to the conductivity, such as
weak-antilocalization. Recently, a rich variety of high-field magnetotransport
properties in the regime of high electron densities ( cm)
were reported, which can be related to additional two-dimensional layered
conductivity, hampering the identification of the topological surface states.
Here, we report that quantum corrections to the electronic conduction are
dominated by the surface states for a semiconducting case, which can be
analyzed by the Hikami-Larkin-Nagaoka model for two coupled surfaces in the
case of strong spin-orbit interaction. However, in the metallic-like case this
analysis fails and additional two-dimensional contributions need to be
accounted for. Shubnikov-de Haas oscillations and quantized Hall resistance
prove as strong indications for the two-dimensional layered metallic behavior.
Temperature-dependent magnetotransport properties of high-quality BiSe
single crystalline exfoliated macro and micro flakes are combined with high
resolution transmission electron microscopy and energy-dispersive x-ray
spectroscopy, confirming the structure and stoichiometry. Angle-resolved
photoemission spectroscopy proves a single-Dirac-cone surface state and a
well-defined bulk band gap in topological insulating state. Spatially resolved
core-level photoelectron microscopy demonstrates the surface stability.Comment: Sci. Rep. (2016
Electrical Transport Properties of Vanadium‐Doped Bi2Te2.4Se0.6
Vanadium‐doped Bi2–xTe2.4Se0.6 single crystals, with x = 0.015 and 0.03, are grown by the Bridgman method. Bandstructure characterization by angle‐resolved photoemission spectroscopy (ARPES) measurements shows gapless topological surface states for both vanadium concentrations. The Van‐der‐Pauw resistivity, the Hall charge carrier density, and the mobility in the temperature range from 0.3 to 300 K are strongly dependent on vanadium concentration, with carrier densities as low as 1.5 × 1016 cm−3 and mobilities as high as 570 cm2 V−1s−1. As expected for transport in gapless topological surface states, the resistivity, carrier density, and mobility are constant below 10 K. The magnetoresistance shows weak antilocalization for both vanadium concentrations in the same temperature range. The weak antilocalization is analyzed with the Hikami–Larkin–Nagaoka model, which yields phase‐coherence lengths of up to 250 nm for x = 0.015.Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659Helmholtz-Gemeinschaft
http://dx.doi.org/10.13039/501100001656Peer Reviewe
Observation of Quantum-Tunneling Modulated Spin Texture in Ultrathin Topological Insulator Bi2Se3 Films
Understanding the spin-texture behavior of boundary modes in ultrathin
topological insulator films is critically essential for the design and
fabrication of functional nano-devices. Here by using spin-resolved
photoemission spectroscopy with p-polarized light in topological insulator
Bi2Se3 thin films, we report tunneling-dependent evolution of spin
configuration in topological insulator thin films across the metal-to-insulator
transition. We observe strongly binding energy- and wavevector-dependent spin
polarization for the topological surface electrons in the ultra-thin
gapped-Dirac-cone limit. The polarization decreases significantly with enhanced
tunneling realized systematically in thin insulating films, whereas magnitude
of the polarization saturates to the bulk limit faster at larger wavevectors in
thicker metallic films. We present a theoretical model which captures this
delicate relationship between quantum tunneling and Fermi surface spin
polarization. Our high-resolution spin-based spectroscopic results suggest that
the polarization current can be tuned to zero in thin insulating films forming
the basis for a future spin-switch nano-device.Comment: To appear in Nature Communications (2014); Expanded version of
http://arxiv.org/abs/1307.548
Hedgehog Spin-texture and Berry's Phase tuning in a Magnetic Topological Insulator
Understanding and control of spin degrees of freedom on the surfaces of
topological materials are key to future applications as well as for realizing
novel physics such as the axion electrodynamics associated with time-reversal
(TR) symmetry breaking on the surface. We experimentally demonstrate
magnetically induced spin reorientation phenomena simultaneous with a
Dirac-metal to gapped-insulator transition on the surfaces of manganese-doped
Bi2Se3 thin films. The resulting electronic groundstate exhibits unique
hedgehog-like spin textures at low energies, which directly demonstrate the
mechanics of TR symmetry breaking on the surface. We further show that an
insulating gap induced by quantum tunnelling between surfaces exhibits spin
texture modulation at low energies but respects TR invariance. These spin
phenomena and the control of their Fermi surface geometrical phase first
demonstrated in our experiments pave the way for the future realization of many
predicted exotic magnetic phenomena of topological origin.Comment: 38 pages, 18 Figures, Includes new text, additional datasets and
interpretation beyond arXiv:1206.2090, for the final published version see
Nature Physics (2012
Ferromagnetic MnSb2Te4: A p-type topological insulator with magnetic gap closing at high Curie temperatures of 45-50K
Resumen del trabajo presentado al APS March Meeting, celebrado de forma virtual del 13 al 19 de marzo de 2021Mn enables the formation of intrinsic magnetic topological insulatorsfor the quantum anomalous Hall effect with A1B2C4 stoichiometry, e. g., antiferromagnetic MnBi2Te4 with 25 K Néel temperature. Here, we showthat p-type MnSb2Te4, previously considered topologically trivial, is a ferromagnetic topological insulator with high Curie temperature of 45 to 50 K.It displays out-of-plane magnetic anisotropy, the nontrivial topology is robust in band structure calculations towards magnetic disorder, provides aDirac point of the topological surface state close to the Fermi level with out-of-plane spin polarization in spin-ARPES, and exhibits a magneticallyinduced band gap of 17 meV that closes at the Curie temperature as demonstrated by scanning tunneling spectroscopy. Moreover, it displays acritical exponent of magnetization β≈1, indicating the vicinity of a quantum critical point. We identify the influences of structural and magneticdisorder that render MnSb2Te4 the ideal system for tuning electric and magnetic properties of quantum anomalous Hall systems.Peer reviewe
Impact of measurable residual disease by decentralized flow cytometry: a PETHEMA real-world study in 1076 patients with acute myeloid leukemia
The role of decentralized assessment of measurable residual disease (MRD) for risk stratification in acute myeloid leukemia (AML) remains largely unknown, and so it does which methodological aspects are critical to empower the evaluation of MRD with prognostic significance, particularly if using multiparameter flow cytometry (MFC). We analyzed 1076 AML patients in first remission after induction chemotherapy, in whom MRD was evaluated by MFC in local laboratories of 60 Hospitals participating in the PETHEMA registry. We also conducted a survey on technical aspects of MRD testing to determine the impact of methodological heterogeneity in the prognostic value of MFC. Our results confirmed the recommended cutoff of 0.1% to discriminate patients with significantly different cumulative-incidence of relapse (-CIR- HR:0.71, P < 0.001) and overall survival (HR: 0.73, P = 0.001), but uncovered the limited prognostic value of MFC based MRD in multivariate and recursive partitioning models including other clinical, genetic and treatment related factors. Virtually all aspects related with methodological, interpretation, and reporting of MFC based MRD testing impacted in its ability to discriminate patients with different CIR. Thus, this study demonstrated that “real-world” assessment of MRD using MFC is prognostic in patients at first remission, and urges greater standardization for improved risk-stratification toward clinical decisions in AML.This study was supported by the Centro de Investigación Biomédica en Red – Área de Oncología - del Instituto de Salud Carlos III (CIBERONC; CB16/12/00369, CB16/12/00233, CB16/12/00284 and CB16/12/00400), Instituto de Salud Carlos III/Subdirección General de Investigación Sanitaria (FIS No. PI16/01661, PI16/00517 and PI18/01946), Gerencia Regional de Salud de CyL (GRS 1346/A/16) and the Plan de Investigación de la Universidad de Navarra (PIUNA 2014-18). This study was supported internationally by the Cancer Research UK, FCAECC and AIRC under the Accelerator Award Program EDITOR