arXiv subjects

R. A. Ng

Publications and source records attributed to R. A. Ng.

3 recordsLinked to original sources

arXiv2023

Stark effect tunable terahertz transitions in finite carbon chains

We employ a tight-binding model to calculate the optical selection rules of gold-terminated carbyne chains in the presence of an applied electric field. We show that both the magnitude of the edge-state gap and the strength of optical transitions across it can be tuned via the Stark effect. In the case of sufficiently long carbyne chains, the dipole transitions between edge states occur within the THz frequency range.

cond-mat.mes-hall↗

arXiv2022

Tuning terahertz transitions in cyclo[n]carbon rings

We develop an analytic model for an ideal polyyne ring which describes the induced THz gap in the molecular spectrum due to the Stark effect. This simple model can also be used to describe an odd-dimered cyclocarbon which has undergone a spontaneous symmetry-breaking event (due to the Jahn-Teller effect) as an effective dipole across an ideal ring. We show that both the size of the gap, and the strength of optical transitions across it, can be modulated by varying the external electric field strength. A THz emission scheme based on optical excitation is proposed, thus paving the way for a new class of THz emitters based on cyclo[n]carbon.

cond-mat.mes-hall↗

arXiv2021

Mapping borophene onto graphene: Quasi-exact solutions for guiding potentials in tilted Dirac cones

We show that if the solutions to the (2+1)-dimensional massless Dirac equation for a given 1D potential are known, then they can be used to obtain the eigenvalues and eigenfunctions for the same potential, orientated at an arbitrary angle, in a tilted anisotropic 2D Dirac material. This simple set of transformations enables all the exact and quasi-exact solutions associated with 1D quantum wells in graphene to be applied to the confinement problem in tilted Dirac materials such as borophene. We also show that smooth electron waveguides in tilted Dirac materials can be used to manipulate the degree of valley polarization of quasiparticles travelling along a particular direction of the channel. We examine the particular case of the hyperbolic secant potential to model realistic top-gated structures for valleytronic applications.

cond-mat.mes-hall↗