33 research outputs found
Higher Chern Number States in Curved Periodic Nanowires
The coupling between the spin and momentum degrees of freedom due to
spin-orbit interactions (SOI) suggests that the strength of the latter can be
modified by controlling the motion of the charge carriers. In this paper, we
investigate how the effective SOI can be modulated by constraining the motion
of charge carriers to curved waveguides thereby introducing real-space
geometric curvature in their motion. The change in the SOI can in turn induce
topological phase transitions in the system. Specifically, we study how the
introduction of periodic sinusoidal curvature in nanowires with intrinsic SOC
can induce the onset of mid-gap topologically protected edge states, which can
be characterized by a topological invariant or Chern number. The Chern number
corresponds to the number of discrete charges that would be pumped across the
length of the nanowire when the phase of a sliding gate potential relative to
that of the sinusoidal curvature is varied adiabatically over a complete
period. In addition, coupling to an external magnetization can be utilized as
an experimental knob to modify the Chern number by changing the ordering of the
nanowire energy bands. The magnetization can be tuned to achieve large discrete
jumps in the number of pump charges per phase period
Quantum dots formed in three-dimensional Dirac semimetal CdAs nanowires
We demonstrate quantum dot (QD) formation in three-dimensional Dirac
semimetal CdAs nanowires using two electrostatically tuned pn
junctions with a gate and magnetic fields. The linear conductance measured as a
function of gate voltage under high magnetic fields is strongly suppressed at
the Dirac point close to zero conductance, showing strong conductance
oscillations. Remarkably, in this regime, the CdAs nanowire device
exhibits Coulomb diamond features, indicating that a clean single QD forms in
the Dirac semimetal nanowire. Our results show that a ptype QD can be formed
between two ntype leads underneath metal contacts in the nanowire by
applying gate voltages under strong magnetic fields. Analysis of the quantum
confinement in the gapless band structure confirms that pn junctions formed
between the ptype QD and two neighboring ntype leads under high magnetic
fields behave as resistive tunnel barriers due to cyclotron motion, resulting
in the suppression of Klein tunneling. The ptype QD with magnetic
field-induced confinement shows a single hole filling. Our results will open up
a route to quantum devices such as QDs or quantum point contacts based on Dirac
and Weyl semimetals
Impedance responses and size-dependent resonances in topolectrical circuits via the method of images
Resonances in an electric circuit occur when capacitive and inductive
components are present together. Such resonances appear in admittance
measurements depending on the circuit's parameters and the driving AC
frequency. In this study, we analyze the impedance characteristics of
nontrivial topolectrical circuits such as one- and two-dimensional
Su-Schrieffer-Heeger circuits and reveal that size-dependent anomalous
impedance resonances inevitably arise in finite circuits. Through the
\textit{method of images}, we study how resonance modes in a multi-dimensional
circuit array can be nontrivially modified by the reflection and interference
of current from the structure and boundaries of the lattice. We derive analytic
expressions for the impedance across two corner nodes of various lattice
networks with homogeneous and heterogeneous circuit elements. We also derive
the irregular dependency of the impedance resonance on the lattice size, and
provide integral and dimensionally-reduced expressions for the impedance in
three dimensions and above.Comment: 24 pages, 10 figure