90 research outputs found
Unusual Nernst effect suggestive of time-reversal violation in the striped cuprate LaBaCuO
The striped cuprate LaBaCuO ( undergoes several
transitions below the charge-ordering temperature = 54 K. From Nernst
experiments, we find that, below , there exists a large, anomalous
Nernst signal that is symmetric in field , and remains
finite as . The time-reversal violating signal suggests that, below
, vortices of one sign are spontaneously created to relieve interlayer
phase frustration.Comment: 5 pages, 4 figure
Spin-triplet Supercurrent through Inhomogeneous Ferromagnetic Trilayers
Motivated by a recent experiment [J. W. A. Robinson, J. D. S. Witt and M. G.
Blamire, Science, \textbf{329}, 5987 (2010)], we here study the possibility of
establishing a long-range spin-triplet supercurrent through an inhomogeneous
ferromagnetic region consisting of a HoCoHo trilayer sandwiched
between two conventional s-wave superconductors. We utilize a full numerical
solution in the diffusive regime of transport and study the behavior of the
supercurrent for various experimentally relevant configurations of the
ferromagnetic trilayer. We obtain qualitatively very good agreement with
experimental data regarding the behavior of the supercurrent as a function of
the width of the Co-layer, . Moreover, we find a synthesis of
0- oscillations with superimposed rapid oscillations when varying the
width of the Ho-layer which pertain specifically to the spiral magnetization
texture in Ho. We are not able to reproduce the anomalous peaks in the
supercurrent observed experimentally in this regime, but note that the results
obtained are quite sensitive to the exact magnetization profile in the
Ho-layers, which could be the reason for the discrepancy between our model and
the experimental reported data for this particular aspect. We also investigate
the supercurrent in a system where the intrinsically inhomogeneous Ho
ferromagnets are replaced with domain-wall ferromagnets, and find similar
behavior as in the HoCoHo case. Furthermore, we propose a novel
type of magnetic Josephson junction including only a domain-wall ferromagnet
and a homogeneous ferromagnetic layer, which in addition to simplicity
regarding the magnetization profile also offers a tunable long-range
spin-triplet supercurrent. Finally, we discuss some experimental aspects of our
findings.Comment: 7 pages, 7 figures. Submitted to Physical Revie
Photoemission of BiSe with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?
Topological insulators are characterized by Dirac cone surface states with
electron spins aligned in the surface plane and perpendicular to their momenta.
Recent theoretical and experimental work implied that this specific spin
texture should enable control of photoelectron spins by circularly polarized
light. However, these reports questioned the so far accepted interpretation of
spin-resolved photoelectron spectroscopy. We solve this puzzle and show that
vacuum ultraviolet photons (50-70 eV) with linear or circular polarization
probe indeed the initial state spin texture of BiSe while circularly
polarized 6 eV low energy photons flip the electron spins out of plane and
reverse their spin polarization. Our photoemission calculations, considering
the interplay between the varying probing depth, dipole selection rules and
spin-dependent scattering effects involving initial and final states explain
these findings, and reveal proper conditions for light-induced spin
manipulation. This paves the way for future applications of topological
insulators in opto-spintronic devices.Comment: Submitted for publication (2013
Oscillatory surface dichroism of an insulating topological insulator Bi2Te2Se
Using circular dichroism-angle resolved photoemission spectroscopy
(CD-ARPES), we report a study of the effect of angular momentum transfer
between polarized photons and topological surface states on the surface of
highly bulk insulating topological insulator Bi2Te2Se. The photoelectron
dichroism is found to be strongly modulated by the frequency of the helical
photons including a dramatic sign-flip. Our results suggest that the observed
dichroism and its sign-flip are consequences of strong coupling between the
photon field and the spin-orbit nature of the Dirac modes on the surface. Our
studies reveal the intrinsic dichroic behavior of topological surface states
and point toward the potential utility of bulk insulating topological
insulators in device applications.Comment: 5 pages, 4 figure
Bulk crystal growth and electronic characterization of the 3D Dirac Semimetal Na3Bi
High quality hexagon plate-like Na3Bi crystals with large (001) plane
surfaces were grown from a molten Na flux. The freshly cleaved crystals were
analyzed by low temperature scanning tunneling microscopy (STM) and
angle-resolved photoemission spectroscopy (ARPES), allowing for the
characterization of the three-dimensional (3D) Dirac semimetal (TDS) behavior
and the observation of the topological surface states. Landau levels (LL) were
observed, and the energy-momentum relations exhibited a linear dispersion
relationship, characteristic of the 3D TDS nature of Na3Bi. In transport
measurements on Na3Bi crystals the linear magnetoresistance and Shubnikov-de
Haas (SdH) quantum oscillations are observed for the first time.Comment: To be published in a special issue of APL Material
Surface electronic structure of a topological Kondo insulator candidate SmB6: insights from high-resolution ARPES
The Kondo insulator SmB6 has long been known to exhibit low temperature (T <
10K) transport anomaly and has recently attracted attention as a new
topological insulator candidate. By combining low-temperature and high
energy-momentum resolution of the laser-based ARPES technique, for the first
time, we probe the surface electronic structure of the anomalous conductivity
regime. We observe that the bulk bands exhibit a Kondo gap of 14 meV and
identify in-gap low-lying states within a 4 meV window of the Fermi level on
the (001)-surface of this material. The low-lying states are found to form
electron-like Fermi surface pockets that enclose the X and the Gamma points of
the surface Brillouin zone. These states disappear as temperature is raised
above 15K in correspondence with the complete disappearance of the 2D
conductivity channels in SmB6. While the topological nature of the in-gap
metallic states cannot be ascertained without spin (spin-texture) measurements
our bulk and surface measurements carried out in the
transport-anomaly-temperature regime (T < 10K) are consistent with the
first-principle predicted Fermi surface behavior of a topological Kondo
insulator phase in this material.Comment: 4 Figures, 6 Page
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