136 research outputs found
Conductance oscillations and zero-bias anomaly in a single superconducting junction to a three-dimensional topological insulator
We experimentally investigate Andreev transport through a single junction
between an s-wave indium superconductor and a thick film of a three-dimensional
topological insulator. We study samples with different
bulk and surface characteristics, where the presence of a topological surface
state is confirmed by direct ARPES measurements. All the junctions demonstrate
Andreev transport within the superconducting gap. For junctions with
transparent interfaces we find a number of nearly periodic
conductance oscillations, which are accompanied by zero-bias conductance
anomaly. Both effects disappear above the superconducting transition or for
resistive junctions. We propose a consistent interpretation of both effects as
originating from proximity-induced superconducting correlations within the
topological surface state
Unoccupied topological surface state in BiTeSe
Bias voltage dependent scattering of the topological surface state is studied
by scanning tunneling microscopy/spectroscopy for a clean surface of the
topological insulator BiTeSe. A strong warping of constant energy
contours in the unoccupied part of the spectrum is found to lead to a
spin-selective scattering. The topological surface state persists to higher
energies in the unoccupied range far beyond the Dirac point, where it coexists
with the bulk conduction band. This finding sheds light on the spin and charge
dynamics over the wide energy range and opens a way to designing
opto-spintronic devices.Comment: 5 pages, 4 figure
Systematics of electronic and magnetic properties in the transition metal doped SbTe quantum anomalous Hall platform
The quantum anomalous Hall effect (QAHE) has recently been reported to emerge
in magnetically-doped topological insulators. Although its general
phenomenology is well established, the microscopic origin is far from being
properly understood and controlled. Here we report on a detailed and systematic
investigation of transition-metal (TM)-doped SbTe. By combining density
functional theory (DFT) calculations with complementary experimental
techniques, i.e., scanning tunneling microscopy (STM), resonant photoemission
(resPES), and x-ray magnetic circular dichroism (XMCD), we provide a complete
spectroscopic characterization of both electronic and magnetic properties. Our
results reveal that the TM dopants not only affect the magnetic state of the
host material, but also significantly alter the electronic structure by
generating impurity-derived energy bands. Our findings demonstrate the
existence of a delicate interplay between electronic and magnetic properties in
TM-doped TIs. In particular, we find that the fate of the topological surface
states critically depends on the specific character of the TM impurity: while
V- and Fe-doped SbTe display resonant impurity states in the vicinity
of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The
single-ion magnetic anisotropy energy and easy axis, which control the magnetic
gap opening and its stability, are also found to be strongly TM
impurity-dependent and can vary from in-plane to out-of-plane depending on the
impurity and its distance from the surface. Overall, our results provide
general guidelines for the realization of a robust QAHE in TM-doped
SbTe in the ferromagnetic state.Comment: 40 pages, 13 figure
The gigantic Rashba effect of surface states energetically buried in the topological insulator Bi2Te2Se
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.We have clarified that a topological insulator, Bi2Te 2Se, shows two surface states with gigantic Rashba-type spin-splitting located at a binding energy deeper than the topological surface state. The magnitude of the Rashba parameter, as well as the momentum splitting, is found to be large enough to realize a number of nanometer-sized spintronic devices. This novel finding paves the way to studies of gigantic Rashba systems that are suitable for future spintronic applications. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.A portion of this work has been done under the Japan–Russia Bilateral Joint Research Project (JSPS). This work was financially supported by KAKENHI (grant nos. 23340105, 23244066, 25800179), Grant-in-Aid for Scientific Research (A), (B) and for Young Scientists (B) of JSPS. KAK and OET acknowledge financial support by the RFBR (grant nos. 13-02-92105 and 12-02-00226), and by the Ministry of Education and Science of the Russian Federation.Peer Reviewe
Mapping the effect of defect-induced strain disorder on the Dirac states of topological insulators
We provide a detailed microscopic characterization of the influence of
defects-induced disorder onto the Dirac spectrum of three dimensional
topological insulators. By spatially resolved Landau-levels spectroscopy
measurements, we reveal the existence of nanoscale fluctuations of both the
Dirac point energy as well as of the Dirac-fermions velocity which is found to
spatially change in opposite direction for electrons and holes, respectively.
These results evidence a scenario which goes beyond the existing picture based
on chemical potential fluctuations. The findings are consistently explained by
considering the microscopic effects of local stain introduced by defects, which
our model calculations show to effectively couple to topological states,
reshaping their Dirac-like dispersion over a large energy range. In particular,
our results indicate that the presence of microscopic spatially varying stain,
inevitably present in crystals because of the random distribution of defects,
effectively couple to topological states and should be carefully considered for
correctly describing the effects of disorder
GROWTH AND CHARACTERIZATION OF BiTeX (X=I, Cl) 3D RASHBA MATERIALS
In this work, the surface structure and transport properties of BiTeCl and BiTeI 3D Rashba materials grown using the modified Bridgman method are studied in detail.The reported study was funded by RFBR, project number 19-29-12061
Buildup and dephasing of Floquet-Bloch bands on subcycle time scales
Strong light fields have created spectacular opportunities to tailor novel
functionalities of solids. Floquet-Bloch states can form under periodic driving
of electrons and enable exotic quantum phases. On subcycle time scales,
lightwaves can simultaneously drive intraband currents and interband
transitions, which enable high-harmonic generation (HHG) and pave the way
towards ultrafast electronics. Yet, the interplay of intra- and interband
excitations as well as their relation with Floquet physics have been key open
questions as dynamical aspects of Floquet states have remained elusive. Here we
provide this pivotal link by pioneering the ultrafast buildup of Floquet-Bloch
bands with time- and angle-resolved photoemission spectroscopy. We drive
surface states on a topological insulator with mid-infrared fields - strong
enough for HHG - and directly monitor the transient band structure with
subcycle time resolution. Starting with strong intraband currents, we observe
how Floquet sidebands emerge within a single optical cycle; intraband
acceleration simultaneously proceeds in multiple sidebands until high-energy
electrons scatter into bulk states and dissipation destroys the Floquet bands.
Quantum nonequilibrium calculations explain the simultaneous occurrence of
Floquet states with intra- and interband dynamics. Our joint experiment-theory
study opens up a direct time-domain view of Floquet physics and explores the
fundamental frontiers of ultrafast band-structure engineering.Comment: 45 pages, 4 figures, 10 extended data figure
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