13 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
Induced Topological Superconductivity in a BiSbTeSe2-Based Josephson Junction
A 4 π -periodic supercurrent through a Josephson junction can be a consequence of the presence of Majorana bound states. A systematic study of the radio frequency response for several temperatures and frequencies yields a concrete protocol for examining the 4 π -periodic contribution to the supercurrent. This work also reports the observation of a 4 π -periodic contribution to the supercurrent in BiSbTeSe 2 -based Josephson junctions. As a response to irradiation by radio frequency waves, the junctions showed an absence of the first Shapiro step. At high irradiation power, a qualitative correspondence to a model including a 4 π -periodic component to the supercurrent is found
The path of least resistance through topology
The primary focus of this dissertation is studying the interaction between topological materials and superconducting materials. Sandwiching a topological material between two superconductors, a structure known as a Josephson junction, is predicted to create a Majorana bound state. This state possesses the interesting property of non-Abelian exchange statistics. This allows the use of Majorana bound states for braiding, the process that is the foundation of topological quantum computation. Junctions were made of several types of topological materials: three-dimensional topological insulators, Dirac semimetals and nodal line semimetals. To back up the measurements of these junctions, normal state transport measurements were also performed, pinpointing the origin of the induced superconductivity in these materials. These measurements also show the formation of Landau levels in the topological insulator at high magnetic field and their interaction at high separation. The junctions based on the topological insulators and Dirac semimetals show signatures of Majorana bound states through a 4Ï€ periodicity of the current-phase relation. Through a careful study of the frequency and temperature dependence of the radio frequency response of the junctions, several other causes for the 4Ï€ periodicity could be excluded. The junctions based on the nodal line semimetal did not show any signs of the Majorana bound state, as their temperature dependence was different. The results yielded by these junctions between topological materials and superconductors grant us a compelling incentive to definitively prove the presence of Majorana bound states in these systems. The prospect of producing an interesting topological quantum computer would certainly make this endeavor worthwhile