Quantum Interference Transistor Research Articles

Destructive interference and Fano antiresonance in T-shaped double quantum dots coupled to Luttinger liquid leads

We investigate the interplay of quantum interference effects and the electronic correlation on the transport through T-shaped spinless double quantum dots coupled to Luttinger liquid leads by using the nonequilibrium Green's function method. We find that the weak intralead Coulomb interaction leads to a zero-bias antiresonance dip in the differential conductance for small interdot tunneling coupling, which is distinct destructive interference characteristic. In particular, an intriguing Fano antiresonance profile for asymmetrically coupling to the Luttinger liquid leads is exhibited, consistent with the experiment findings but different physics screening origin. The strong intralead Coulomb interaction or large interdot coupling tunneling quenches the quantum interference effects, resulting in the disappearance of Fano antiresonance. The scaling behavior of differential conductance on temperature is presented for different intralead interactions. The relationship between destructive interference and two-channel Kondo effect is given. Our results provide a way of adjusting in and out of antiresonance to achieve quantum interference transistors and of switching by tuning the gate voltage controlling the interdot tunneling. • The interplay of interference and intralead Coulomb interaction on transport of T-shaped quantum dots is studied. • Weak intralead interaction leads to zero-bias dip in differential conductance for small interdot tunneling. • New physical mechanism is presented to explain for the antiresonance dip and Fano effect. • Scaling behavior of differential conductance on temperature is presented for different intralead interactions.

Thermal superconducting quantum interference proximity transistor

Superconductors are known to be excellent thermal insulators at low temperature owing to the presence of the energy gap in their density of states (DOS). In this context, the superconducting \textit{proximity effect} allows to tune the local DOS of a metallic wire by controlling the phase bias ($\varphi$) imposed across it. As a result, the wire thermal conductance can be tuned over several orders of magnitude by phase manipulation. Despite strong implications in nanoscale heat management, experimental proofs of phase-driven control of thermal transport in superconducting proximitized nanostructures are still very limited. Here, we report the experimental demonstration of efficient heat current control by phase tuning the superconducting proximity effect. This is achieved by exploiting the magnetic flux-driven manipulation of the DOS of a quasi one-dimensional aluminum nanowire forming a weal-link embedded in a superconducting ring. Our thermal superconducting quantum interference transistor (T-SQUIPT) shows temperature modulations up to $\sim 16$ mK yielding a temperature-to-flux transfer function as large as $\sim 60$ mK/$\Phi_0$. Yet, phase-slip transitions occurring in the nanowire Josephson junction induce a hysteretic dependence of its local DOS on the direction of the applied magnetic field. Thus, we also prove the operation of the T-SQUIPT as a phase-tunable \textit{thermal memory}, where the information is encoded in the temperature of the metallic mesoscopic island. Besides their relevance in quantum physics, our results are pivotal for the design of innovative coherent caloritronics devices such as heat valves and temperature amplifiers suitable for thermal logic architectures.

Electronic Properties of Branched Molecular Structures Review

The design of new types of macromolecular architecture is one of the main directions in the development of modern polymer physics. As applied to electronics, electroconductive π-conjugated molecules occupy a special place. In this review, the distinctive features of the electronic properties of organic semiconductors when compared with their solid-state analogs are considered. Special attention is paid to the role of electron–electron and electron–phonon interactions in the formation of self-localized excited states, i.e., solitons and polaritons. The constructive and destructive interference effects in molecular structures containing branching nodes and ring groups are discussed. The size of a branched molecule should herewith be small to conserve quantum coherence. Self-localization effects in such molecules are insignificant and transport is determined by electrons and holes injected from contacts. Two approaches to the description of quantum interference in branched molecules are proposed, notably, based on molecular orbitals and in the scope of the pattern of localized atomic orbitals. These approaches make it possible to formulate design rules for molecular structures, in which interference is observed. The latest results on the design of quantum-interference molecular transistors with ultralow energy consumption are presented. Nonconjugated tree-branched polymers, so-called dendrimers, which can be efficient for designing systems of the collection and transformation of electromagnetic radiation are briefly considered.

Non-Hermitian Hamiltonians and Quantum Transport in Multi-Terminal Conductors.

We study the transport properties of multi-terminal Hermitian structures within the non-equilibrium Green’s function formalism in a tight-binding approximation. We show that non-Hermitian Hamiltonians naturally appear in the description of coherent tunneling and are indispensable for the derivation of a general compact expression for the lead-to-lead transmission coefficients of an arbitrary multi-terminal system. This expression can be easily analyzed, and a robust set of conditions for finding zero and unity transmissions (even in the presence of extra electrodes) can be formulated. Using the proposed formalism, a detailed comparison between three- and two-terminal systems is performed, and it is shown, in particular, that transmission at bound states in the continuum does not change with the third electrode insertion. The main conclusions are illustratively exemplified by some three-terminal toy models. For instance, the influence of the tunneling coupling to the gate electrode is discussed for a model of quantum interference transistor. The results of this paper will be of high interest, in particular, within the field of quantum design of molecular electronic devices.

Electronic Structure of Molecular Switches on Splitters Based on trans-Polyacetylene

The electronic characteristics are studied for a Y-splitter based on trans-polyacetylene molecules using analytical calculations in the scope of a tight-binding approximation, as well as an ab initio simulation using the density functional theory (DFT). It is shown that based on such a splitter both a quantum interference transistor and a molecular diode could be developed. A semiphenomenological model of an interference transistor based on the Fano resonance is proposed. The effect of conformational transitions connected with the rotation of branches exerted on the distribution of the density of π-electron is studied.

Coherent molecular transistor: Control through variation of the gate wave function

In quantum interference transistors (QUITs), the current through the device is controlled by variation of the gate component of the wave function that interferes with the wave function component joining the source and the sink. Initially, mesoscopic QUITs have been studied and more recently, QUITs at the molecular scale have been proposed and implemented. Typically, in these devices the gate lead is subjected to externally adjustable physical parameters that permit interference control through modifications of the gate wave function. Here, we present an alternative model of a molecular QUIT in which the gate wave function is directly considered as a variable and the transistor operation is discussed in terms of this variable. This implies that we specify the gate current as well as the phase of the gate wave function component and calculate the resulting current through the source-sink channel. Thus, we extend on prior works that focus on the phase of the gate wave function component as a control parameter while having zero or certain discrete values of the current. We address a large class of systems, including finite graphene flakes, and obtain analytic solutions for how the gate wave function controls the transistor.

Singlet-triplet superconducting quantum magnetometer

Motivated by the recent experimental realization of a quantum interference transistor based on the superconducting proximity effect, we here demonstrate that the inclusion of a textured ferromagnet both strongly enhances the flux sensitivity of such a device and additionally allows for singlet-triplet switching by tuning a bias voltage. This functionality makes explicit use of the induced spin-triplet correlations due to the magnetic texture. Whereas the existence of such triplet correlations is well-known, our finding demonstrates how spin-triplet superconductivity may be utilized for concrete technology, namely to improve the functionality of ultra-sensitive magnetometers.

Toward graphene-based quantum interference devices

A new type of quantum interference device based on a graphene nanoring in which alledges are of the same type is studied theoretically. The superposition of the electronwavefunction propagating from the source to the drain along the two arms of the nanoringgives rise to interesting interference effects. We show that a side-gate voltage applied acrossthe ring allows for control of the interference pattern at the drain. The electron currentbetween the two leads can therefore be modulated by the side gate. The lattermanifests itself as conductance oscillations as a function of the gate voltage. We studyquantum nanorings with two edge types (zigzag or armchair) and argue that thearmchair type is more advantageous for applications. We demonstrate finallythat our proposed device operates as a quantum interference transistor with highon/off ratio.

Simulation of one-dimensional ring quantum interference transistors using the time-dependent finite-difference beam propagation method

A time-dependent finite-difference beam propagation method is presented to analyze quantum interference transistor (QUIT) structures, employing the Aharonov–Bohm effect, in both steady state and transient conditions. Current–voltage characteristics of two ring structures having 0.2 and 0.05 μm channel lengths, respectively, are presented. Additionally, the wave functions are calculated, and reflections are observed in both the ON and OFF states of the device. Cutoff frequency fT values of 3 and 8.5 THz, respectively, are calculated from the switching response to a gate pulse of 200 fs, for the 0.2 μm device, and to a pulse of 50 fs, for the 0.05 μm device. Results indicate that reflections at the drain may degrade frequency performance of these devices, which is not evident from earlier analytical studies. These structures are further explored to investigate the effects of imperfections introduced in fabricating the quantum wire channels. We compare two QUITs, one realized by a 1 nm resolution lithography process (representing an advanced fabrication technique) and the other realized by a 10 nm resolution (representing current state-of-the-art lithography). We also present an asymmetric 10 nm resolution structure, to represent the case when errors in fabrication significantly alter the QUIT topology. This simulation shows strong dependence of the electron transmission probability on the channel topology and roughness determined by the lithographic resolution.

Conductance of quantum interference transistors in parallel and in series

We theoretically study the electronic conductance G and the current–voltage characteristics of two quantum interference transistors in parallel and in series. We use two different definitions of conductance,G∼T and G∼T/R. Neither can reproduce the classical additivity law in the case of coherent transport due to quantum interference for the elements in series and quasibound states when elements are in parallel. In the case of two transistors in series, we find that the quantityT/R only qualitatively better represents the additivity law, which is probably expected because this model avoids counting the contact resistance twice. However, for the parallel configuration of transistors, the conductance is almost additive for the majority of energies when G∼T, except for the single-mode regime. Possible use of these configurations in digital electronics for basic logic functions is discussed.

Electrostatic Aharonov–Bohm effect in solids revised

We consider the Aharonov–Bohm [Phys. Rev. 115, 485 (1959)] interferometer (or a hypothetical quantum interference transistor) that consists of a single-channel quantum wire split into a mesoscopic loop, whose conductance is controlled by a voltage applied between a gate electrode coupled capacitively to one branch of the loop and the wire. It is deduced from fundamental properties of one-dimensional conductors that putting a single elementary charge on the gate–wire capacitor dramatically alters the interference conditions in the device by introducing the phase shift π/2. This surprising result means that the electrostatic Aharonov–Bohm effect belongs in fact to the category of single-electron phenomena in solids and that inherent charge fluctuations can make its clear observation impossible.

Quantum Dynamics Analysis of Electron Wave Packet Behaviors in Quantum Interference Transistor Controlled by Electric and/or Magnetic Fields.

Numerical simulations using the time dependent quantum dynamics are carried out on the electron wave packet behaviors through a GaAs quantum interference transistor (QUIT). In order to trace the respective electron wave packets passing through the two hyper fine channels of QUIT, an attempt to introduce their relative phase difference results well in solving the equation system of time dependent quantum dynamics in terms of one dimensional finite difference scheme. The performance as QUIT strongly depends on the interference characteristics of two wave packets, and the interference is well controlled with the aid of externally impressed external electric and/or magnetic fields. The simulation results show the possibility that GaAs QUITs are potential devices which operate as 0-1 controller with ultra high speed and accuracy due to the optimum electric and/or magnetic fields. The present QD simulation may contribute to practical designing and fabricating of QUIT devices.

10 Tera Hertz operation in one-dimensional quantum interference transistor (1-D QUIT) devices

A high performance quantum interference transistor (QUIT) realized using high mobility 1-D MODFET channels is presented. The operation of this 1-D QUIT is based on electrostatic Aharonov-Bohm quantum interference effect. The channel length of the device is smaller than the inelastic coherence length of the electrons in the quantum well wire channel, otherwise scattering will randomize electron's phase and destroy the quantum interference effect. Transport characteristics of the 0.2 μm channel 1-D QUIT are calculated at 4.2 °K and compared with a two-dimensional QUIT device reported in literature. Our calculations show a significant improvement of the transconductance in one-dimensional transistors compared with its two-dimensional counterpart. The maximum frequency of operation of the 1-D QUIT is in the Tera Hertz regime, which makes it very attractive device for high frequency applications.

Transfer efficiency of hot electrons in a metal(CoSi 2)/insulator(CaF 2) quantum interference transistor

We report on the transfer efficiency of hot electrons with monochromatic energy across a nanometer-thick metal epilayer in a metal(CoSi 2)/insulator(CaF 2) quantum interference transistor. The transfer efficiency from emitter to collector is estimated to be more than 0.96 from the negative differential resistance characteristics of the transistor.

The nonlinear transport regime of a T-shaped quantum interference transistor

We present the current–voltage characteristics of a T-shaped semiconductor electron waveguide structure in the nonlinear regime. This system is interesting as a potential quantum interference transistor. Calculated zero-temperature I–V characteristics are with multiple peaks and exhibit regions of negative-differential resistance. The peak-to-valley ratio has maximum value of 3:1. The calculated values of the transconductance and the differential drain conductance are small, which suggests limited abilities for conventional applications of the transistor.

Terahertz quantum interference transistors (QUIT) using one-dimensional modfet-type electron waveguides

A one-dimensional quantum interference transistor (1-D QUIT) structure consisting of two MODFET-type electron waveguides is presented. Our calculations show that the unity current-gain cut-off frequency (fτ) of the 1-D QUIT with a charnel length of 0.25 μm is greater than 1 THz. The transconductance per unit gate width of the device is about two times better than the 2-D QUIT reported in the literature.

Quantum transport through one-dimensional double-quantum-well systems.

We investigate the lateral tunneling properties of electrons through a one-dimensional double-quantum-well system using the recursive Green's-function technique. The conductance exhibits a number of interesting quantum-interference effects, including a strong resonance at the onset of conductance, a ``beating'' effect due to competing characteristic times for the system, and a finite conductance at large Fermi energies, where the densities of states for the individual wells is small. It is shown that the last property may be exploited to use this system as a quantum-interference transistor.

Semiconductor quantum devices

The operation of devices with small enough dimensions for electrons to exhibit wavelike behavior is explained. Two types of device are examined: vertical quantum devices, which include the resonant tunneling structure and the single-electron transistor, and lateral, which include the quantum interference transistor and the spin precession device. The advantages and drawbacks of the two types are identified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A proposal of a vacuum micro quantum interference transistor

A quantum interference transistor that can be fabricated by available technology and can operate at room temperature is proposed. This device uses the phase interference effect of a vacuum electron that is not influenced by thermal fluctuations, in contrast to an electron in solid-state materials. The device consists of a field emitter, a collector, and segmented capacitors between the emitter and the collector. The capacitors control electron trajectories and the phase interference of the electron in vacuum by their electrical potential. This quantum interference effect is found not to be the same as the Aharonov–Bohm effect contrary to our expectations. We are convinced that the new transistor is capable of room-temperature operation because the large kinetic energy of the electron in vacuum suppresses energy fluctuations caused by the field emission itself and by thermal fluctuations in the emitter material to about 50 meV. The switching time of the transistor is limited in order to average the number of electrons at the collector to allow the emitter-collector current to be a deterministic variable against the quantum stochastic property. The threshold of the switching time is estimated to be of the order of magnitude of 10−11 s for the field emitter reported by C. A. Spindt, I. Brodie, L. Hummphrey, and E. R. Westerberg [J. Appl. Phys. 47, 5248 (1976)].

Device performance of mesoscopic T-structure quantum interference transistors

We present an analysis of the device performance of quantum interference transistors that utilize electron interference in ultrasmall semiconductor T-structures. The major drawback of these devices is found to be the extreme sensitivity of the device characteristics to structural variations that seriously impede their implementation in integrated circuits. However, the most significant advantage is the low threshold voltage for switching that makes it possible to switch these devices optically. We propose using these devices as ultrafast optoelectronic switches in which the switching action is realized optically, rather than electronically, so that the switching speed is not linited by the RC time constant of the switching circuit or that of the interconnects.