Electron Optics in Phosphorene pn Junctions: Negative Reflection and Anti-Super-Klein Tunneling

Graphene-Based Photonic-like Highly Integrated Programmable Electronic Devices

Photonic-crystal-like devices and photonic-crystal-like microcavities in graphene are investigated theoretically. The results show that the size of the photonic-crystal-like device and the photonic-crystal-like microcavity is able to be scaled down to more than 2 orders of magnitude smaller than that of the realistic conventional photonic crystal with the same energy, due to the shorter optical-like transport wavelength in graphene. So, the graphene-based photonic-like devices offer a higher degree of integration than their conventional counterparts. By changing the applied voltage, the mutual conversion of photonic-like devices with different functions can be realized, while the performance of such photonic-like devices can be manipulated. Therefore, this kind of photonic-like device has high programmability and adjustability. And the photonic-like devices can be integrated with traditional microelectronic circuits. It will have important application prospects in photonic-like integrated circuits and photonic-like computing.

Angular-Dependent Klein Tunneling in Photonic Graphene

The Klein paradox consists in the perfect tunneling of relativistic particles through high potential barriers. It is responsible for the exceptional conductive properties of graphene. It was recently studied in atomic condensates and topological photonics and phononics. While in theory the perfect tunneling holds only for normal incidence, so far the angular dependence of the Klein tunneling and its strong variation with the barrier height were not measured experimentally. In this Letter, we capitalize on the versatility of atomic vapor cells with paraxial beam propagation and index patterning by electromagnetically induced transparency. We report the first experimental observation of perfect Klein transmission in a 2D photonic system (photonic graphene) at normal incidence and measure the angular dependence. Counterintuitively, but in agreement with the Dirac equation, we observe that the decay of the Klein transmission versus angle is suppressed by increasing the barrier height, a key result for the conductivity of graphene and its analogs.

Pseudospin-one particles in the time-periodic dice lattice: a new approach to transport control

The controlling of the transmission in the pseudospin-one Dirac-Weyl systems offers a rich tool to study new concepts of massive Dirac electron tunneling by means of a time-dependent potential. The time-periodic potential is one of the experimental techniques to have more control over the tunneling effect. In this paper, we study the transmission coefficient for different sidebands to obtain total transmission. We show how the super Klein tunneling under special conditions is independent of the incidence angle, oscillation amplitude, frequency, and barrier width. We consider a band gap opening with different locations of the flat band and modulate the resonances by tuning free parameters in our system.

Electronic cloaking of confined states in phosphorene junctions

We study the electronic transport of armchair (AC) and zigzag (ZZ) gated phosphorene junctions. We find confined states for both direction-dependent phosphorene junctions. In the case of AC junctions confined states are reflected in the transmission properties as Fabry-Pérot resonances at normal and oblique incidence. In the case of ZZ junctions confined states are invisible at normal incidence, resulting in a null transmission. At oblique incidence Fabry-Pérot resonances are presented in the transmission as in the case of AC junctions. This invisibility or electronic cloaking is related to the highly direction-dependent pseudospin texture of the charge carriers in phosphorene. Electronic cloaking is also manifested as a series of singular peaks in the conductance and as inverted peaks in the Seebeck coefficient. The characteristics of electronic cloaking are also susceptible to the modulation of the phosphorene bandgap and an external magnetic field. So, electronic cloaking in phosphorene junctions in principle could be tested through transport, thermoelectric or magnetotransport measurements.

Quenching effect of oscillating potential on anisotropic resonant transmission through a phosphorene electrostatic barrier

The anisotropy in resonant tunneling transport through an electrostatic barrier in monolayer black phosphorus either in presence or in absence of an oscillating potential is studied. Non-perturbative Floquet theory is applied to solve the time dependent problem and the results obtained are discussed thoroughly. The resonance spectra in field free transmission are Lorentzian in nature although the width of the resonance for the barrier along the zigzag (Г–Y) direction is too thinner than that for the armchair (Г–X) one. Resonant transmission is suppressed for both the cases by the application of oscillating potential that produces small oscillations in the transmission around the resonant energy particularly at low frequency range. Sharp asymmetric Fano resonances are noted in the transmission spectrum along the armchair direction while a distinct line shape resonance is noted for the zigzag direction at higher frequency of the oscillating potential. Even after the angular average, the conductance along the Г–X direction retains the characteristic Fano features that could be observed experimentally. The present results are supposed to suggest that the phosphorene electrostatic barrier could be used successfully as switching devices and nano detectors.

Unveiling Electron Optics in Two-Dimensional Materials by Nonlocal Resistance Mapping

We propose a technique based on nonlocal resistance measurements for mapping transport in electron optics experiments. Utilizing tight-binding transport methods, we show how to use a four-terminal measurement to isolate the ballistic transport from a single lead of interest and reconstruct its contribution to the local density of states. This enables us to propose an experimentally tractable four-terminal device with via contacts for measuring Veselago lensing in a graphene p-n junction. Furthermore, we demonstrate how to extend this method as a scanning probe technique, implementing mapping of complex electron optics experiments including angled junctions, collimation optics, and beam steering. Our results highlight the fundamental importance of electron dephasing in ballistic transport and provide guidelines for isolating electron optics signals of interest. These findings unveil a fresh approach to performing electron optics experiments, with a plethora of two-dimensional material platforms to explore.