Resonant Tunneling Research Articles

Circularly polarized plane terahertz waves radiated from a resonant tunneling diode integrated with a collimating metalens and quarter-wave plate

Terahertz flat optics based on metasurfaces can replace massive optical components with optically thin components. However, metasurfaces with unprecedented material properties frequently produce a specified function, and terahertz flat optics has yet to be commonly adopted in terahertz devices that require multiple functions. Here, we present a two-layer component composed of a collimating metalens and a quarter-wave plate that convert linearly polarized terahertz wide-angle radiation waves from a resonant tunneling diode to circularly polarized plane waves. Our findings would be applied to laminate structures with optical vortices, ultrahigh directivity and arbitrary wavefront control in 6 G wireless communications.

High-power in-phase and anti-phase mode emission from linear arrays of resonant-tunneling-diode oscillators in the 0.4-to-0.8-THz frequency range

Oscillators based on resonant tunneling diodes (RTDs) are able to reach the highest oscillation frequency among all electronic THz emitters. However, the emitted power from RTDs remains limited. Here, we propose linear RTD oscillator arrays capable of supporting coherent emission from both in-phase and anti-phase coupled modes. The oscillation modes can be selected by adjusting the mesa areas of the RTDs. Both the modes exhibit constructive interference at different angles in the far field, enabling high-power emission. Experimental demonstrations of coherent emission from linear arrays containing 11 RTDs are presented. The anti-phase mode oscillates at ∼450 GHz, emitting about 0.7 mW, while the in-phase mode oscillates at around 750 GHz, emitting about 1 mW. Moreover, certain RTD oscillator arrays exhibit dual-band operation: changing the bias voltage allows for controllable switching between the anti-phase and in-phase modes. Upon bias sweeping in both directions, a notable hysteresis feature is observed. Our linear RTD oscillator array represents a significant step forward in the realization of large arrays for applications requiring continuous-wave THz radiation with substantial power.

Oscillating direct electric current formed by a resonant tunneling diode inside a cavity with periodically oscillating mirrors.

A novel phenomenon is described that enables the control of the flux of free electrons through a resonance tunneling diode (RTD) via coupling the RTD to a quantized electromagnetic mode in a dark cavity. As the control parameter, one uses here the distance between the two cavity mirrors (which are set to oscillate in time). The effect is illustrated by carrying out standard scattering calculations of the electron flux. However, the only efficient way to rationalize the phenomenon and to be able to select the proper distance between the two cavity mirrors is to employ non-Hermitian quantum mechanics and the language of discrete resonance poles of the scattering matrix. The demonstrated ability to control the flux of free electrons by using a dark cavity might open a new field of research and development of controllable RTD devices.

Design and characterization of colloidal quantum dot photoconductors for multi-color mid-infrared detection

This report paves the way for low cost, multi-color, room-temperature, and easily-feasible mid-IR photodetector with distinct output currents. The proposed device is designed and simulated to be fabricated by the solution-process technology thanks to its simplicity and fabrication ease, room-temperature operation capability, low production cost, and excellent photoelectric properties. In this approach, the proposed structure is composed of an array of n × n pixels, where each pixel is designed to enable multi-wavelength detection. The absorber layer consists of different sized quantum dots that absorb distinct wavelengths simultaneously through interband transitions in the mid-infrared region. Selective energy contacts based on quantum well structures are designed to be deposited on interdigitated contacts as a means of extracting the stimulated carriers from the absorber layers to the metal contacts. Through resonant tunneling, the excited carriers are transferred, which generates the output photocurrent and significantly reduces the dark current. In order to model the designed multi-color photoconductor, coupled rate equations and three-dimensional Schrodinger-Poisson equations have been developed and solved self-consistently. As a way of demonstrating the validity of the introduced model, a experimentally fabricated photoconductor and a theoretically modeled photodetector using the nonequilibrium Green’s function (NEGF) model have been simulated; the comparison between the simulation results is quite satisfactory. In order to simplify the theoretical model, two different sizes of InSb/ZnSe core/shell quantum dots have been considered in the theoretical model to detect two MIR wavelengths (3 µm and 4 µm) of the incident light. Simulation results indicate that the peak responsivities are about 3.3(A/W) and 6(A/W), and the high specific detectivities D* are about 9 × 1010(cm.Hz1/2W−1) and 15 × 1010(cm.Hz1/2W−1) for the wavelengths of 4 µm and 3 µm, respectively.

Double barrier structure of Mo/AlN/Mo/AlN/Mo multilayer and its resonant tunneling effect

We prepare a symmetrical double barrier structure of Mo/AlN/Mo/AlN/Mo by using the reactive magnetron sputtering on a sapphire substrate and examine its resonant tunneling effect. Characterizations of multilayers demonstrate that the AlN (0002) aligns well along the Mo (110). Direct current-voltage (DC I–V) test finds significant negative differential resistance at room temperature around 0.7 and 0.9 V carrier energy and with peak-to-valley current ratios of about 1.1 and 1.2. The simulation using conventional transfer matrix method suggests good consistence between the designed structure, the quantized energy level and the switching voltage. The large signal DC model also fits the experimental I–V properties. Our work provides a new type of resonant tunneling device in room temperature.

Klein tunneling and Fabry-Perot resonances in the α - T 3 bilayer with aligned stacking

This paper investigates the quantum tunneling effect on the α − T 3 bilayer with aligned stacking. An effective model is constructed to describe the properties around the triple band crossings for stacking with a vertical alignment of sites in the bilayer system. Focusing on these band crossings, it is found that while the energy spectrum remains gapless throughout, it is characterized by flat energy bands. Subsequently, the transmission coefficient, T, for Dirac quasi-electrons across a rectangular potential barrier is calculated, alongside the relationship between the transmission rate and the coupling parameter α. It is observed that super-tunnel phenomena occur at certain values of the quasiparticle energy, where the transmission is perfect regardless of the angle of incidence on the barrier, with α = 1. Furthermore, it is found that for a wide range of parameter values, the transmittance evolves monotonically and exponentially with increasing alpha. The paper also highlights the occurrence of the Klein paradox in the system, where quasiparticles approaching the barrier with zero-angle incidence exhibit ideal quantum transparency.

Resonant Plasmon-Assisted Tunneling in a Double Quantum Dot Coupled to a Quantum Hall Plasmon Resonator.

Edge magnetoplasmon is an emergent chiral bosonic mode promising for studying electronic quantum optics. While the plasmon transport has been investigated with various techniques for decades, its coupling to a mesoscopic device remained unexplored. Here, we demonstrate the coupling between a single plasmon mode in a quantum Hall plasmon resonator and a double quantum dot (DQD). Resonant plasmon-assisted tunneling is observed in the DQD through absorbing or emitting plasmons stored in the resonator. By using the DQD as a spectrometer, the plasmon energy and the coupling strength are evaluated, which can be controlled by changing the electrostatic environment of the quantum Hall edge. The observed plasmon-electron coupling encourages us for studying strong coupling regimes of plasmonic cavity quantum electrodynamics.

Phase-resolved measurement and control of ultrafast dynamics in terahertz electronic oscillators

As a key component for next-generation wireless communications (6 G and beyond), terahertz (THz) electronic oscillators are being actively developed. Precise and dynamic phase control of ultrafast THz waveforms is essential for high-speed beam steering and high-capacity data transmission. However, measurement and control of such ultrafast dynamic process is beyond the scope of electronics due to the limited bandwidth of the electronic equipment. Here we surpass this limit by applying photonic technology. Using a femtosecond laser, we generate offset-free THz pulses to phase-lock the electronic oscillators based on resonant tunneling diode. This enables us to perform phase-resolved measurement of the emitted THz electric field waveform in time-domain with sub-cycle time resolution. Ultrafast dynamic response such as anti-phase locking behaviour is observed, which is distinct from in-phase stimulated emission observed in laser oscillators. We also show that the dynamics follows the universal synchronization theory for limit cycle oscillators. This provides a basic guideline for dynamic phase control of THz electronic oscillators, enabling many key performance indicators to be achieved in the new era of 6 G and beyond.

Terahertz Spin-Conductance Spectroscopy: Probing Coherent and Incoherent Ultrafast Spin Tunneling.

Thin-film stacks | consisting of a ferromagnetic-metal layer and a heavy-metal layer are spintronic model systems. Here, we present a method to measure the ultrabroadband spin conductance across a layer between and at terahertz frequencies, which are the natural frequencies of spin-transport dynamics. We apply our approach to MgO tunneling barriers with thickness d = 0-6 Å. In the time domain, the spin conductance Gs has two components. An instantaneous feature arises from processes like coherent spin tunneling. Remarkably, a longer-lived component is a hallmark of incoherent resonant spin tunneling mediated by MgO defect states, because its relaxation time grows monotonically with d to as much as 270 fs at d = 6.0 Å. Our results are in full agreement with an analytical model. They indicate that terahertz spin-conductance spectroscopy will yield new and relevant insights into ultrafast spin transport in a wide range of spintronic nanostructures.

Negative Differential Resistance in Single‐Molecule Junctions Based on Heteroepitaxial Spherical Au/Pt Nanogap Electrodes

AbstractSingle‐molecule junctions exploit the internal structure of molecular orbitals to construct a new class of functional quantum devices. The demonstration of negative differential resistance (NDR) in single‐molecule junctions is direct evidence of quantum mechanical tunneling through a molecular orbital. Here, a pronounced NDR effect is reported with a peak‐to‐valley ratio of 30.1 on a single‐molecule junction of π‐conjugated quinoidal‐fused oligosilole derivatives, Si2 × 2, embedded between the unique electroless gold‐plated heteroepitaxial spherical Au/Pt nanogap electrodes. This NDR feature persists in a consecutive endurance test of 180 current traces. the thermally stable NDR effects in the Si2 × 2 single‐molecule junctions between 9 and 300 K are demonstrated. The density functional theory calculations under electric fields indicate that the NDR effect can be ascribed to the bias‐dependent resonant tunneling transport via the polarized HOMO, which has asymmetrically changed electrode coupling with increased bias voltages. The results confirm a promising electrical platform for constructing functional quantum devices at the single‐molecule level.

In Situ Leaf Water Status Sensor Using Resonant Tunneling Diodes as Terahertz Source and Sensor

In Situ Leaf Water Status Sensor Using Resonant Tunneling Diodes as Terahertz Source and Sensor

Analysis of One-dimensional Double-potential Barrier Structures Resonant Tunnelling Based on Transmission Matrices

The comprehension of the tunnel effect, the passage of matter waves and particles across a high potential barrier, was the most astounding of all discoveries in quantum mechanics. Research on tunnelling in semiconductors and superconductors, as well as the development of scanning tunnelling microscopy, garnered five Nobel prizes in physics. In this study, the resonant tunnelling effect of electron tunnelling through a one-dimensional double-potential barrier was found and verified by solving the time-independent Schrödinger equation and calculating the transmittance rate of the electron tunnelling through the two potential barriers by using the transmission matrix technique performed by MATLAB. According to the analysis, the transmittance rate was one under certain specific conditions (under some specific incident energy values or some specific distance between two potential barriers), which was called as resonant tunnelling. However, in this study, square potential wells were analyzed, which can be considered merely as ideal models in real life, and therefore all results are idealized. For further investigations, researchers can use more realistic parameters to set up potential wells and analyze real-life problems.

Analysis of Electron Double Barrier Tunneling Based on Python

Tunneling is a common phenomenon in microphysics, and resonant tunneling is a tunneling phenomenon under special conditions. Double barrier tunneling is an important quantum mechanical phenomenon, which has important application and research value in condensed matter physics, semiconductor devices, quantum mechanics, and nanotechnology. This study takes the double barrier as an example to observe electron tunneling and find out the influence of different parameters on the tunneling effect. In this study, the wave function is calculated by using the method of Schrodinger equation and transpose matrix, and the image is drawn by Python and numerical operation. In this study, it is found that the barrier width is inversely proportional to the transmittance, and the transmittance and reflectance will change periodically with the distance between the two barriers, and the electrons will reach full transmission at a certain incident energy value. Studying the characteristics and mechanisms of double barrier tunneling helps develop new quantum technologies and devices and promotes technological innovation in related fields.

Electronic and transport properties of U-cut edge patterned AGNR superlattice for RTD application

In this paper, we first characterize a superlattice structure created by repeating a heterostructure formed from two armchair graphene nanoribbon (AGNR) segments with different widths. We investigate the electronic and transport properties of this structure by varying its widths and lengths to demonstrate the tunability of its overall band gap. The plot of the local density of states shows the formation of localized states at the low band gap segments of the superlattice. The superlattice is then used as a barrier to create a double barrier quantum well (DBQW) to design a proposed resonant tunneling diode (RTD) structure. We observe this device's negative differential resistance (NDR) operation for a range of bias voltages between the contacts. We study the effect of dimensional parameters on the RTD performance. The non-equilibrium Green's function method, based on a tight-binding model, is employed for numerical computation.

Antenna-enhanced high-resistance photovoltaic infrared detectors based on quantum ratchet architecture

We demonstrate a quantum ratchet detector, which is a high-resistance photovoltaic mid-infrared detector based on an engineered spatial arrangement of subbands. In photovoltaic quantum-well photodetectors, in which unidirectional photocurrent is generated by asymmetric quantum-well structures, maximization of device resistance by suppressing undesired electron transports is crucial for minimizing noise. A semi-quantitative guideline suggests the significance of spatial separation between wavefunctions for reducing the conductance from the ground state. Here, we employ a step quantum well made of a shallow floor and a deep well. Photoexcited electrons are quickly transferred to a separated location from the ground state through fast resonant tunneling and phonon scattering, and then they are allowed to flow in only one direction. This architecture is made possible by the use of a GaAs/AlGaAs material system, and it achieves a resistance as high as 6.0 × 104 Ωcm2 with a single-period structure. Combined with optical patch antennas for responsivity enhancement, we demonstrate a maximum background-limited specific detectivity of 6.8 × 1010 cmHz1/2/W at 6.4 μm, 77 K for normal incidence, and a background-limited-infrared-photodetector temperature of 98 K.

Non-reciprocal optical bistability of sandwiched structure containing magnetic Weyl semimetals

We investigate non-reciprocal optical bistability (OB) of sandwiched structure comprising of two magnetic Weyl semimetal (WSM) layers and a nonlinear layer. The resonant tunneling mode in the sandwiched structure with a nonlinear layer creates favorable conditions for the emergence of OB. Besides, the inherent non-reciprocal nature of WSM enables non-reciprocal transmission of OB in the absence of an external magnetic field. By employing the transfer matrix method, we simulate the OB curves for forward and backward propagations, as well as analyze the non-reciprocity of OB. Furthermore, the impacts of various parameters on non-reciprocal OB are comprehensively discussed. The results demonstrate that the non-reciprocal OB curve and the width of the isolation of the non-reciprocal OB can be tuned by adjusting the thickness and the axial vector of the WSM, the temperature as well as the incident angle. This work would provide crucial insights for the design of high-performance non-reciprocal devices.

Exact prime density reproduced through resonant tunneling across a double barrier system

A solid-state experiment based on quantum tunneling is proposed to reproduce the natural numbers and prime numbers as resonant tunneling energies in a double barrier system (DBS). For getting the prime numbers as eigenvalues the well potential is considered as the superposition of a smooth potential which is estimated using a semi-classical approach and a weak local fluctuating potential. We use the transfer matrix approach and finite element method by taking only the smooth part of the potential to obtain resonant energies which reproduces the local average prime density and the local average prime gap exactly. The methodology when applied to a quadratic potential of the well, produces whole numbers as eigenvalues except for a constant zero-point energy —the energy levels of a simple harmonic oscillator.

Resonant Tunneling of Photons in Layered Optical Nanostructures (Metamaterials)

Resonant Tunneling of Photons in Layered Optical Nanostructures (Metamaterials)

Theory of Resonant Tunneling of Charge Carriers within the Framework of the Green’s Function Method and the Biorthogonal Formalism

Theory of Resonant Tunneling of Charge Carriers within the Framework of the Green’s Function Method and the Biorthogonal Formalism

Double ferromagnetic barriers resonant tunneling diodes (RTD) based on the surface of a topological insulator

Resonant tunneling diodes (RTDs), which are based on double barrier quantum well structures, are typically achieved by combining different materials with varying band gap sizes. However, this approach often poses challenges such as material mismatching and dislocations. In this study, we present a novel resonant tunneling diode scheme utilizing the unique properties of topological insulator materials. Specifically, we exploit the gap opening in the band structure of the topological insulator by employing perpendicular magnetization. In this proposed RTD platform, the barrier regions are formed from a ferromagnetic topological insulator through the proximity effect. By adjusting the thickness and spacing of the ferromagnetic barriers, a well region with confined states emerges between the barrier regions. Theoretical analysis reveals that by tuning the back gate voltage, the I-V characteristics exhibit two significant behaviors: negative differential resistance (NDR) and step-like behavior for Fermi energy values of EF = −3 and EF = 3, respectively. Furthermore, we observe an increase in the peak-to-valley ratio (PVR) with higher magnetization values. Notably, the PVR reaches a value of 7.13 for a magnetization value of m = 9. Additionally, we investigate the influence of the well width and barrier thickness on the transport properties of the device.