10 research outputs found
Suppression of Conductance in a Topological Insulator Nanostep Junction
We investigate quantum transport via surface states in a nanostep junction on
the surface of a 3D topological insulator that involves two different side
surfaces. We calculate the conductance across the junction within the
scattering matrix formalism and find that as the bias voltage is increased, the
conductance of the nanostep junction is suppressed by a universal factor of 1/3
compared to the conductance of a similar planar junction based on a single
surface of a topological insulator. We also calculate and analyze the Fano
factor of the nanostep junction and predict that the Fano factor saturates at
1/5, five times smaller than for a Poisson process
Adiabatic quantum pumping through surface states in 3D topological insulators
We investigate adiabatic quantum pumping of Dirac fermions on the surface of
a strong 3D topological insulator. Two different geometries are studied in
detail, a normal metal -- ferromagnetic -- normal metal (NFN) junction and a
ferromagnetic -- normal metal -- ferromagnetic (FNF) junction. Using a
scattering matrix approach, we first calculate the tunneling conductance and
then the adiabatically pumped current using different pumping mechanisms for
both types of junctions. We explain the oscillatory behavior of the conductance
by studying the condition for resonant transmission in the junctions and find
that each time a new resonant mode appears in the transport window, the pumped
current diverges. We also predict an experimentally distinguishable difference
between the pumped current and the rectified current
Adiabatic quantum pumping in graphene NIS junctions
We investigate adiabatic quantum pumping through a normal
metal-insulator-superconductor (NIS) junction in a monolayer of graphene. The
pumped current is generated by periodic modulation of two gate voltages,
applied to the insulating and superconducting regions respectively. In the
bilinear response regime and in the limit of a thin high insulating barrier, we
find that the presence of the superconductor enhances the pumped current per
mode by a factor of 4 at resonance. Compared to the pumped current in an
analogous semiconductor NIS junction, the resonances have a phase
difference. We also predict experimentally distinguishable differences between
the pumped current and the tunneling conductance in graphene NIS junctions.Comment: 4 pages, 3 figure
Adiabatic quantum pumping of chiral Majorana fermions
We investigate adiabatic quantum pumping of chiral Majorana states in a system composed of two Mach-Zehnder type interferometers coupled via a quantum point contact. The pumped current is generated by periodic modulation of the phases accumulated by traveling around each interferometer. Using scattering matrix formalism we show that the pumped current reveals a definite signature of the chiral nature of the Majorana states involved in transport in this geometry. Furthermore, by tuning the coupling between the two interferometers the pump can operate in a regime where finite pumped current and zero conductance are expected.QN/Quantum NanoscienceApplied Science