65 research outputs found
Molecular beam epitaxy of high structural quality Bi2Se3 on lattice matched InP(111) substrates
Epitaxial layers of the topological insulator Bi2Se3 have been grown by
molecular beam epitaxy on laterally lattice-matched InP(111)B substrates. High
resolution X-ray diffraction shows a significant improvement of Bi2Se3 crystal
quality compared to layers deposited on other substrates. The measured full
width at half maximum of the rocking curve is Delta omega=13 arcsec, and the
(omega-2theta) scans exhibit clear layer thickness fringes. Atomic force
microscope images show triangular twin domains with sizes increasing with layer
thickness. The structural quality of the domains is confirmed on the
microscopic level by transmission electron microscopy.Comment: 4 pages, 4 figure
Anisotropic and strong negative magneto-resistance in the three-dimensional topological insulator Bi2Se3
We report on high-field angle-dependent magneto-transport measurements on
epitaxial thin films of Bi2Se3, a three-dimensional topological insulator. At
low temperature, we observe quantum oscillations that demonstrate the
simultaneous presence of bulk and surface carriers. The magneto- resistance of
Bi2Se3 is found to be highly anisotropic. In the presence of a parallel
electric and magnetic field, we observe a strong negative longitudinal
magneto-resistance that has been consid- ered as a smoking-gun for the presence
of chiral fermions in a certain class of semi-metals due to the so-called axial
anomaly. Its observation in a three-dimensional topological insulator implies
that the axial anomaly may be in fact a far more generic phenomenon than
originally thought.Comment: 6 pages, 4 figure
Quantum transport and mobility spectrum of topological carriers in (001) SnTe/PbTe heterojunctions
Measurements of magnetotransport in SnTe/PbTe heterojunctions grown by the
MBE technique on (001) undoped CdTe substrates were performed. At low magnetic
fields, quantum corrections to conductivity were observed that may be
attributed to the presence of topological states at the junction interface. For
a sample with 5 nm thick SnTe layer, the data analysis suggests that midgap
states are actually gapped. However, the phase coherence effects in 10 nm and
20 nm SnTe/PbTe samples are fully explained assuming existence of gapless Dirac
cones. Magnetotransport at higher magnetic fields is described in the framework
of mobility spectrum analysis (MSA). We demonstrate that the electron- and
hole-like peaks observed simultaneously for all SnTe/PbTe heterojunctions may
originate from the concave and convex parts of the energy isosurface for
topological states -- and not from the existence of quasiparticles both
carrying negative and positive charges. This interpretation is supported by
numerical calculations of conductivity tensor components for gapless (100)
Dirac cones, performed within a classical model and based on the solutions of
Boltzmann transport equation. Our approach shows the feasibility of MSA in
application to magnetotransport measurements on topological matter
Magneto-optics of massive Dirac fermions in bulk Bi2Se3
We report on magneto-optical studies of Bi2Se3, a representative member of
the 3D topological insulator family. Its electronic states in bulk are shown to
be well described by a simple Dirac-type Hamiltonian for massive particles with
only two parameters: the fundamental bandgap and the band velocity. In a
magnetic field, this model implies a unique property - spin splitting equal to
twice the cyclotron energy: Es = 2Ec. This explains the extensive
magneto-transport studies concluding a fortuitous degeneracy of the spin and
orbital split Landau levels in this material. The Es = 2Ec match differentiates
the massive Dirac electrons in bulk Bi2Se3 from those in quantum
electrodynamics, for which Es = Ec always holds.Comment: 5 pages, 3 figures and Supplementary materials, to be published in
Physical Review Letter
Synthesis of the LTA-type AlPO4 in the presence of the diazapolyoxamacrocycle 'Kryptofix 222'
International audienc
Coincidence of superparamagnetism and perfect quantization in the quantum anomalous Hall state
Coexistence of Surface and Bulk Ferromagnetism Mimics Skyrmion Hall Effect in a Topological Insulator
Here, we report the investigation of the anomalous Hall effect in the magnetically doped topological insulator (V,Bi,Sb)_{2}Te_{3}. We find it contains two contributions of opposite sign. Both components are found to depend differently on carrier density, leading to a sign inversion of the total anomalous Hall effect as a function of applied gate voltage. The two contributions are found to have different magnetization reversal fields, which in combination with a temperature dependent study points towards the coexistence of two ferromagnetic orders in the system. Moreover, we find that the sign of total anomalous Hall response of the system depends on the thickness and magnetic doping density of the magnetic layer. The thickness dependence suggests that the two ferromagnetic components originate from the surface and bulk of the magnetic topological insulator film. We believe that our observations provide insight into the magnetic behavior, and thus will contribute to an eventual understanding of the origin of magnetism in this material class. In addition, our data bear a striking resemblance to anomalous Hall signals often associated with skyrmion contributions. Our analysis provides a straightforward explanation for both the magnetic field dependence of the Hall signal and the observed change in sign without needing to invoke skyrmions, and thus suggest that caution is needed when making claims of effects from skyrmion phases
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