Nanohelices as superlattices: Bloch oscillations and electric dipole transitions

Abstract

Subjecting a nanohelix to a transverse electric field gives rise to superlattice behavior with tunable electronic properties. We theoretically investigate such a system and find Bloch oscillations and negative differential conductance when a longitudinal electric field (along the nanohelix axis) is also applied. Furthermore, we study dipole transitions across the transverse-electric-field-induced energy gap, which can be tuned to the eulogized terahertz frequency range by experimentally attainable external fields. We also reveal a photogalvanic effect by shining circularly polarized light onto our helical quantum wire.

Rényi and Tsallis Entropies of the Aharonov–Bohm Ring in Uniform Magnetic Fields

“…Since Ψ m (ϕ r ) and [2m * E m (θ)] 1/2 describe the eigenstates of the angular momentum of this AB rotator, the corresponding Rényi uncertainty relation is saturated by them and does not depend on α and β [29]. Let us also note that this model can apparently be used as a foundation of the quantum-informational analysis of the relevant more complicated structures, such as, for example, nanohelices [68][69][70][71]. Armed with the expression for the Rényi entropies, one can build up shape Rényi complexities [72]:…”

Double-Gated Nanohelix as a Novel Tunable Binary Superlattice

“…3a, the dispersions could be approximated as a quasi-relativistic linear dispersion yielding Dirac-like physics, which could permit superfluiditiy [81] for example. The advantage in using nanohelices lies in introducing such phenomena to portable nanostructure based devices, while also exhibiting unusual responses of the charge carriers to circularly polarized radiation [44, 45, 82–85] (or indeed magnetic fields [86, 87]) due to the helical spatial confinement.…”

“…In order to understand how our double-gated nanohelix system interacts with electromagnetic radiation, we study the inter-subband momentum operator matrix element , which is proportional to the corresponding transition dipole moment, and dictates the transition rate between subbands ψ f and ψ g . Here, is the projection of the radiation polarization vector onto the coordinate axes ( j = x,y , z ) and the respective self-adjoint momentum operators are [44, 45, 82–84] …”

“…An intuitive mechanical analogue would be the rotary motion of Archimedes’ screw being converted into the linear motion of water along the direction of the screw axis dictated by the handedness of the thread. As such, our system of a double-gated nanohelix irradiated by circularly polarized light exhibits a photogalvanic effect, whereby one can choose the net direction of current by irradiating with either right- or left-handed circularly polarized light [44, 45, 89]. This differs from conventional one-dimensional superlattices, wherein the circular photogalvanic effect stems from the spin-orbit term appearing in the effective electron Hamiltonian and is consequently a weaker and hard-to-control phenomenon [90, 91].…”

“…In particular, subjecting a nanohelix to a transverse electric field (normal to the helix axis) gives rise to superlattice behaviour such as Bragg scattering of electrons on a super-periodic potential, leading to an energy splitting at the edge of the superlattice Brillouin zone between the lowest states linearly tunable by the electric field [42, 43]. This behaviour may result in Bloch oscillations and negative differential conductance [44, 45], and can emphasize spin-polarized transport through helices [31, 46], as well as yield a circular dichroism enhancement useful in nanophotonic chiroptical applications [47]. This system constitutes a unary superlattice and further opens the possibility to use nanohelices as either tunnel diodes or Gunn diodes for frequency multiplying, amplification, and generation or absorption of radiation in the eulogized terahertz range [48–51].…”