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We study the influence of the phase-change material VO2 on transverse magnetic (TM) surface plasmon (SP) modes in metallic arm-chair graphene nanoribbon (AGNR) qubits in the Lindhard approximation. We assess the effects of temperature as a dynamic knob for the transition from the insulating to the metallic phase on the TM SP modes in single-band (SB) and two-band (TB) transitions. We show that a VO2 substrate leads to TM SP modes in both SB and TB transitions. In addition, we observe that the SP modes have a lower frequency than those for a substrate of constant permittivity. In addition, we study the influence of the substrate-induced band gap Δ′ on SP modes in TB transitions for the insulating and metallic phases of VO2.

One-dimensional (1D) organic-inorganic hybrid lead halides with unique core-shell quantum wire structures and splendid photoluminescence properties have been considered one of the most promising high-efficiency broadband emitters. However, studies on the broadband emissions in 1D purely face-shared lead iodide hybrids are still rare so far. Herein, we report on a new 1D lead iodide hybrid, (2cepyH)PbI3 (2cepy = 1-(2-chloroethyl)pyrrolidine), characterized with face-sharing PbI6 octahedral chains. Upon UV photoexcitation, this material shows broadband yellow emissions originating from the self-trapped excitons associated with distorted Pb-I lattices on account of the strong exciton-phonon coupling, as proved by variable-temperature emission spectra. Moreover, experimental and calculated results reveal that (2cepyH)PbI3 is an indirect bandgap semiconductor, the band structures of which are governed by inorganic parts. Our work represents the first broadband emitter based on a 1D face-shared lead iodide hybrid and opens a new way to obtain the novel broadband emission materials.

The effect of shape of the confining potential along two different confined directions in Quantum Well Wire (QWW) on the heavy hole binding energy bound to an acceptor impurity has been computed using variational principle in the envelope function and effective mass approximation. In order to elucidate the importance of choosing the material parameters like effective masses to get the reliable theoretical results since the effective masses play a crucial role in determining the carrier mobility especially in Quantum Wire structures, two different effective masses like constant effective mass which is isotropic and the directional dependent effective mass which is anisotropic, have been employed in solving the Schrodinger equation and the results have been compared. The shift in the Polaronic energy which arises due to the exchange interaction between the spin of the Mn2+ ion and the spin of the carrier has been computed by using mean field theory with modified Brillouin function. The observed results show that Quantum Size Effects are evidenced near the Wire size of ~30 A and the binding energy is found to have enhanced values only for the case with isotropic effective mass than for the anisotropic effective mass. The magnetic tuning of the potential barrier leads to the probability for the quantum tunneling of the hole wavefunction into the barrier and thereby reduces the binding energy. The exchange interaction does not show its influence much on the Spin Polaronic Shift due to the competition between the square and parabolic confining potential in a QWW with such anisotropic confinement.

Impurity-induced absorption of light in quantum wires in the presence of external collinear electric and magnetic fields directed perpendicular to the nanowire axis is studied theoretically. The dopants in the quantum wire are modeled by a zero-radius potential. Expressions governing the light absorption coefficient are derived, and specificities of impurity light absorption are studied for all possible directions of polarization of the light wave. In particular, some of optical transitions that are forbidden in the absence of fields become allowed in the presence of external fields. Frequency dependences of light-absorption coefficient, along with the influence of electric and magnetic fields on the magnitude of absorption induced by impurities, are investigated. The possibility of controlling optical characteristics of nanowires by means of an electric field is demonstrated.

We study the effect of disorder and dephase in transmission of a CdS quantum wire using the Green’s function technique. Our results show that the transmission decreases with the increasing disorder strength. The resistance of a CdS quantum wire with phase-breaking scattering only increases with increasing dephasing. Obtained results show that the drain current of a CdS quantum wire with inelastic scattering by phonons with energy $$\hbar \omega = 30$$ meV decreases with the increasing disorder strength. Moreover, our theoretical results are independently supported by simulations of CdS disordered quantum wires based on a tight-binding model.

Electronic states of a single electron in doubly eccentric cylindrical quantum wire are theoretically investigated in this paper. The motion of electron in quantum wire is free along axial direction in a cylindrical quantum wire and restricted in annular regions by three different parallel finite cylindrical barriers as soft wall confinement. The effective mass Schrödinger equation with effective mass boundary conditions is used to find energy eigenvalues and corresponding wavefunctions. Addition theorem for cylindrical Bessel functions is used to shift the origin for applying boundary conditions at different circular boundaries. Fourier expansion is applied after addition theorem to get wavefunctions in analytical form. A determinant equation is obtained as a result of applications of effective mass boundary conditions which roots gives energy of various electronic states. The lowest root gives ground state energy. The variation in ground state energy with eccentricity is obtained numerically and presented graphically. Electronic states in massive wall confinement and hard wall confinement is further obtained as limiting behavior of the states obtained in soft wall confinement. The knowledge of electronic states in such cylindrical hetrostructures semiconductor material can lead to improve the efficiency of many quantum devices.

Optical polarization is an indispensable component in photonic applications, the orthogonality of which extends the degree of freedom of information, and strongly polarized and highly efficient small-size emitters are essential for compact polarization-based devices. We propose a group III-nitride quantum wire for a highly-efficient, strongly-polarized emitter, the polarization anisotropy of which stems solely from its one-dimensionality. We fabricated a site-selective and size-controlled single quantum wire using the geometrical shape of a three-dimensional structure under a self-limited growth mechanism. We present a strong and robust optical polarization anisotropy at room temperature emerging from a group III-nitride single quantum wire. Based on polarization-resolved spectroscopy and strain-included 6-band k·p calculations, the strong anisotropy is mainly attributed to the anisotropic strain distribution caused by the one-dimensionality, and its robustness to temperature is associated with an asymmetric quantum confinement effect.

A triple lattice site quantum wire (QW) system is chosen to investigate nonequilibrium spin transport properties theoretically. We calculate the initial charge of the QW from the exactly derived ground state. Based on the Keldysh formalism, we describe theoretical methods and derive analytical formulas for nonequilibrium spin transport of the QW systems within Hartree-Fock approximation when Coulomb interactions are present. We report the numerical results of the nonequilibrium differential spin conductance, spin transport current, and electronic charge distribution of the triple site QW system. When only including Coulomb repulsions between the spin-up and spin-down electrons, the series of peaks and valleys in the conductance characteristics appears due to the spin resonant tunneling and spin blockade. With the increase of Coulomb interaction energy U, the conductance peaks start to split into two corresponding to the spin-up and spin-down conductance. Near the resonant points, the spin current polarization and the in-site spin charge polarizations take place. When additionally including spin-spin interactions, the differences between the spin-up and spin-down conductance characteristics are reduced, implying that the spin split is relaxed by spin-spin interactions. The spin splits, the spin current, and spin charge polarizations are relaxed at high temperatures due to the thermal fluctuations.

In this work I review of the theoretical and experimental issue related to the Rashba Spin-Orbit interaction in semiconductor nanostructures. The Rashba spin-orbit interaction has been a promising candidate for controlling the spin of electrons in the field of semiconductor spintronics. In this work, I focus study of the electrons spin and holes in isolated semiconductor quantum dots and rings in the presence of magnetic fields. Spin-dependent thermodynamic properties with strong spin-orbit coupling inside their band structure in systems are investigated in this work. Additionally, specific heat and magnetization in two dimensional, one-dimensional quantum ring and dot nanostructures with Spin Orbit Interaction are discussed.

We study the impact of surface defects on a condensate of electron pairs in a quantum wire. Based on previous results, we formulate a simple mathematical model accounting for such surface effects. For a system of noninteracting pairs, we prove the destruction of the condensate in the bulk. Finally, taking repulsive interactions between the pairs into account, we show that the condensate is recovered for pair densities greater than a critical density if the number of the surface defects is not too large.

Quantum dot cellular automata (QCA) constitute an emergent nanoscale-based digital nanoelectronics technology with comprehensive applications in nanocomputing based on the small nanometer size of such circuits and their ultralow power consumption, fast operation, and high clock frequency in comparison with transistor-based complementary metal–oxide–semiconductor (CMOS) technologies. A novel design for edge-triggered synchronous J-K flip-flop (FF) and D (data or delay) flip-flop memory elements based on QCA cells with quantum wires is presented herein. The proposed design has fewer QCA cells and lower latency and area and uses the coplanar crossover method to overcome the complexity of multilayer quantum wire crossing. The design is analyzed to determine the average output polarization (AOP) of the edge-triggered synchronous D-FF and JK-FF at different temperature levels and the optimized energy dissipation. The layout design and computational simulation of the circuit are carried out using QCADesigner V. 2.0.3 software, while the energy dissipation is analyzed using the QCADesigner-E V. 2.2 tool.

We implement the lasing eigenvalue problem (LEP) approach to study the electromagnetic field in the presence of a circular quantum wire (QW) made of a gain material and wrapped in graphene cover and a dimer of two identical graphene-covered QWs, at the threshold of stationary emission. LEP delivers the mode-specific eigenvalue pairs, namely the frequencies and the threshold values of the QW gain index for the plasmon and the wire modes of such nanolasers. In our analysis, we use quantum Kubo formalism for the graphene conductivity and classical Maxwell boundary-value problem for the field functions. The technique involves the resistive boundary conditions, the separation of variables in the local coordinates, and, for the dimer, the addition theorem for the cylindrical functions. For single-wire plasmonic laser, we derive approximate engineering expressions for the lasing frequencies and threshold values of the gain index that complement the full-wave computations. For the dimer, we derive separate determinantal equations for four different classes of symmetry of the lasing supermodes and solve them numerically. Our investigation of the mode frequencies and thresholds versus the graphene and QW parameters shows that plasmon modes or, for the dimer, plasmon supermodes have lower frequencies and thresholds than the wire modes provided that the QW radius is smaller than 10 μm, however in thicker wires they are comparable. Only the plasmon-mode characteristics are well-tunable using the graphene chemical potential. In the dimer, all lasing supermodes form closely located quartets, however, they quickly approach the single-wire case if the inter-wire separation becomes comparable to the radius. These results open a way for building essentially single-mode plasmonic nanolasers and their arrays and suggest certain engineering rules for their design.

We use the Lasing Eigenvalue Problem (LEP) approach to study the source-free problem of the electromagnetic field in the presence of a circular quantum wire (QW) wrapped in graphene cover. Our instrument is the method of separation of variables and the Kubo formalism for the graphene conductivity. We analyze the lasing conditions for the plasmon modes of such a laser with microsize and nanosize QW diameters. We find eigenvalue pairs, i.e. the frequencies and the threshold values of the QW gain index for several plasmon modes and investigate their dependences on the QW and graphene parameters.

We consider the Lasing Eigenvalue Problem (LEP) for a circular quantum wire, made of a gain material, with a partial cover, made of a graphene strip. This boundary value problem is reduced to a dual series equation for the Fourier series coefficients of the magnetic field function. Using the Riemann-Hilbert Problem solution, we transform this equation to a Fredholm second-kind set of linear algebraic equations. To find the LEP eigenvalues, we apply the method of the residual inverse iteration. Some preliminary results of the lasing mode frequencies, threshold gains and field patterns are presented.

Semiconductor nanowires are attractive building blocks of optoelectronics due to high efficiency and optical controllability. In particular, the mutual controllability of wavelength and polarization of light is essential for versatile applications such as displays, precise metrology, and bioimaging. We present quantum wire network emitters embedded in a single microrod capable of exhibiting orthogonally polarized dual-wavelength visible light at room temperature. The InGaN/GaN shell layers were grown on a single hexagonal GaN core microrod, spontaneously forming site-selective In-rich InGaN quantum wires on each edge between the nonpolar facets as well as each boundary between the nonpolar and semipolar facets. The orthogonally self-arranged, two sets of six quantum wires formed on the edges and the boundaries showed efficient violet and blue-green color emissions with strong linear polarization parallel and perpendicular to the c-axis at room temperature, respectively. This intriguing emission from a single microrod allows us to mutually manipulate the color and the polarization of light, which would be beneficial for photonic applications with unprecedented controllability and functionality.

Summary In this paper, we formulate and quantitatively examine the effect of dissipation on topological systems. We use a specific model of Kitaev quantum wire with an onsite Ohmic dissipation and perform a numerically exact method to investigate the effect of dissipation on the topological features of the system (e.g., the Majorana edge mode) at zero temperature. We find that even though the topological phase is robust against weak dissipation as it is supposed to be, it will eventually be destroyed by sufficiently strong dissipation via either a continuous quantum phase transition or a crossover depending on the symmetry of the system. The dissipation-driven quantum criticality has also been discussed., Graphical Abstract, Highlights • Dissipation can destroy topological phase either by phase transitions or by crossovers • The phase transitions or crossovers are determined by the symmetry of system, State of Matter; Quantum Phenomena; Quantum Mechanics

The energy spectrum and optical absorption in a quantum wire of monolayer transition metal dichalcogenides in the shape of a straight strip are investigated theoretically. It is established that edge-like states with energies within the band gap of an infinite sample are absent in strips whose width is smaller than the critical one. Depending on the mutual parity of the quantum-confinement subbands in the valence and conduction bands, optical transitions are characterized by significantly differing threshold behaviors of the absorption strength. The strongest absorption corresponds to transitions between subbands with the same indices.

Electron scattering rate and electron mobility limited by LO-phonons are calculated for a cylindrical polar semiconductor quantum wire with core-shell structure. Longitudinal optical phonons modes are developed within a dielectric continuum model. The influence of the thickness of the shell on the electron scattering rate by phonons is studied. Numerical calculations performed for a GaAs/AlGaAs quantum wire show that the electron–LO-phonon scattering rate changes with the thickness of the shell layer and is reduced considerably in the quantum wires having thicker shell, leading to higher electron mobility. The mobility can be improved up to several orders of magnitude.

A theoretical investigation of optical properties of a cylindrical quantum wire (CQW) is presented. The properties studied were optical absorption coefficient (AC) and change in refractive index (CRI) of the quantum wire. In particular, effect of an inverse parabolic potential on the optical properties of CQWs was investigated. This was done by solving the Schrödinger equation within the effective mass approximation to obtain the wave functions. The inverse parabolic potential reduces transition energies and therefore redshifts peaks of the AC, as well as the anomalous dispersion region of the dependence of change in refractive index on the photon energy. The inverse parabolic potential also has effect on the magnitudes of these optical quantities, reducing the AC and enhancing the CRI. These properties of the inverse parabolic confining electric potential can have a wide range of applications in nanodevice technology, some details of which are discussed.

The electron effective mass in GaAs quantum wires has been estimated by using a full dynamical random-phase approximation to examine its properties versus spin polarization, temperature, and carrier density. A decrease of mass with spin polarization is seen. The minority mass increases with the polarization while the majority mass decreases and this behaviour is seen for all densities. A maximal enhancement of mass at moderate temperature around 25 K is also presented. These calculations show a qualitative consistence with results in two-dimensional systems and help to control the electronic transport in quantum wires.

The results of theoretical modeling from the first principles of atomic structure and properties of promising low-dimensional structures from semiconductors, performed for the past five years at the Center of Nanoelectronics and Novel Materials of Belarusian state university of informatics and radioelectronics, are summarized. The discovered principal new properties of two-dimensional structures from dichalcogenides of refractory metals and semiconductor silicides, one-dimensional structures of silicon, А3В5 semiconductors and semiconductor metal oxides, and zero-dimensional structures of carbon - nanodiamonds - are presented.

Electron mobility limited by surface roughness scattering in free-standing GaAs thin ribbon with an internal parabolic quantum well caused by surface state is investigated in detail. Based on analyzing the parabolic quantum well including the energy subband level, wave function and the confined potential profile in the thin ribbon by solving Schrödinger and Poisson equations self-consistently, the electron mobility could be investigated. Conclusion indicates that remote surface roughness (RSR) of the thin ribbon will change the two dimensional electron gas (2DEG) mobility through the medium of barrier height fluctuation of the parabolic well in atomic scale. Calculation results reveal that the 2DEG mobility decreases with increasing roughness amplitude, which is characterized in terms of the surface roughness height and the roughness lateral size.

We propose to explore analytically one of the most promising effects (soliton) for future applications in optical communication processing and memory devices, due to the nonlinearity inside low dimensional semiconductor systems. We focus on soliton propagation in microcavity wires. We derive analytical exact solutions that describe the stationary states of the soliton’s profile in the cavity. We present a scheme that gives such profiles for a given external confining potential. The obtained profiles compare favorably with existing experimental and numerical results. Keywords: Solitons, Quantum wire

The wavefunction of the transverse motion of electrons in a quantum wire located near a two-dimensional layer of dipole excitons is perturbed by fluctuations of the exciton density through the electron-exciton interaction. This polaron effect is responsible for the shift of levels of the wire and can be observed through a change in the intersubband transition frequency. In this work, the polaron shift of the main intersubband transition frequency under the conditions of the Bose-Einstein condensation of excitons, as well as for the normal state of the degenerate Bose gas, is calculated.

The theory of energy loss rate of non-equilibrium electrons due to inelastic interaction with intravalley piezoelectric phonons in a nano-dimensional semiconductor wire has been developed under the condition of low lattice temperatures, without recourse to the standard approximations which are usually made when developing theories at relatively higher temperatures. Such approximations are hardly valid when the lattice temperature is low. As expected, compared to the well-known earlier results, the theory here, reveals a complex and altogether different dependence of the energy loss rate upon the carrier energy and the lattice temperature. The numerical results have been obtained for narrow channel wires of GaAs and GaN. On comparison with other available results, it is revealed that the finite energy of piezoelectric phonons and the full form of the phonon distribution bring about quite significant changes in the energy loss characteristics at low temperatures.

We study the effect of the phase-change material VO2 on plasmons in metallic arm-chair graphene nanoribbons (AGNRs) within the random-phase approximation (RPA) for intra- and inter-band transitions. We assess the influence of temperature as a knob for the transition from the insulating to the metallic phase of VO2 on localized and propagating plasmon modes. We show that AGNRs support localized and propagating plasmon modes and contrast them in the presence and absence of VO2 for intra-band (SB) transitions while neglecting the influence of a substrate-induced band gap. The presence of this gap results in propagating plasmon modes in two-band (TB) transitions. In addition, there is a critical band gap below and above which propagating modes have a linear negative or positive velocity. Increasing the band gap shifts the propagating and localized modes to higher frequencies. In addition, we show how the normalized Fermi velocity increases plasmon modes frequency.

Core-shell nanostructures are highly attractive; their electrical and optical properties can be tuned by engineering their shapes and types of core-shell materials to achieve optimal nanomaterials for a variety of applications. Unfortunately, in the synthesis process of core-shell structures, geometric defects may unintentionally happen and possibly lead to undesired properties. In this Letter, the defect due to eccentricity in a core-shell square quantum wire is numerically investigated using the finite difference approach. The effects of the core shifting diagonally and vertically on optical transitions are reported. The results show that even a small core shift causes fully polarization-dependent transitions. The shift also affects the splitting of absorption coefficients due to x - and y -polarized light, leading to polarization-selective absorption in some photon energy ranges. As a result, the considered quantum wire is an alternative structure for polarizing light or detecting polarized light.

We construct a global Lindblad master equation for a Kitaev quantum wire of finite length, weakly coupled to an arbitrary number of thermal baths, within the Born-Markov and secular approximations. We find that the coupling of an external bath to more than one lattice site generates quantum interference effects, arising from the possibility of fermions to tunnel through multiple paths. In the presence of two baths at different temperatures and/or chemical potentials, the steady-state particle current can be expressed through the Landauer-B\"uttiker formula, as in a ballistic transport setup, with the addition of an anomaly factor associated with the presence of the $p$-wave pairing in the Kitaev Hamiltonian. Such a factor is affected by the ground-state properties of the chain, being related to the finite-size equivalent of its Pfaffian topological invariant., Comment: 14 pages, 9 figures. Final version

Electron transition rates due to interaction with circularly polarized light incident along the axis of a free-standing solid cylindrical nanowire are evaluated in the dipole approximation. The electric confinement potential of the nanowire is modeled as a superposition of two parts, in general, of different strengths; viz; parabolic and inverse parabolic in the radial distance. Additional confinement of the charge carriers is through the vector potential of the axial applied magnetic field. In systems with cylindrical symmetry, the electronic states are in part characterized by azimuthal quantum numbers: m=0, ±1, ±2,..., which in the absence of the axial applied magnetic field are doubly degenerate. In the dipole approximation and for circularly polarized light the selection rules are such that optical transitions are allowed between electronic states whose azimuthal quantum numbers differ by unity. Transition rates are characterized by peaks whenever the energy of the incident electromagnetic radiation matches transition energies for states between which transitions occur. The parabolic potential blue shifts peak of transition rates while the inverse parabolic potential redshifts the peaks. Results also indicate that transition rates are higher in nanowires of smaller radii. The homogeneous magnetic field lifts the double-degeneracies of electrons with opposite angular momenta, which leads to the emergence of two branches of the transition rates.

Quantum battery is one of the most prominent micro-devices in the rapid-developing quantum thermodynamics. We propose a quantum charging protocol in which both battery and charger are consisted of a many-spin system. The battery and charger are connected via the Kittle mode of the magnon system, that serves as a charging wire and then enables a long-range charging protocol. Counter-intuitively, we find that the spin-spin couplings insider both battery and charger can be used to promote the charging performance in comparison to the noninteracting condition. And a remarkable promotion is realized at a "sweet" spot in terms of the average coupling strength. Moreover, we apply the quantum-state-diffusion equation to test the robustness of our magnon-mediated charging protocol to the systematic errors about the magnon frequency.

Quantum wires (QWs) and quantum point contacts (QPCs) have been realized in GaAs/AlGaAs heterostructures in which a two-dimensional electron gas resides at the interface between GaAs and AlGaAs layered semiconductors. The electron transport in these structures has previously been studied experimentally and theoretically, and a 0.7 conductance anomaly has been discovered. The present paper is motivated by experiments with a QW in shallow symmetric and asymmetric confinements that have shown additional conductance anomalies at zero magnetic field. The proposed device consists of a QPC that is formed by split gates and a top gate between two large electron reservoirs. This paper is focussed on the theoretical study of electron transport through a wide top-gated QPC in a low-density regime and is based on density functional theory. The electron–electron interaction and shallow confinement make the splitting of the conduction channel into two channels possible. Each of them becomes spin-polarized at certain split and top gates voltages and may contribute to conductance giving rise to additional conductance anomalies. For symmetrically loaded split gates two conduction channels contribute equally to conductance. For the case of asymmetrically applied voltage between split gates conductance anomalies may occur between values of 0.25(2e 2/h) and 0.7(2e 2/h) depending on the increased asymmetry in split gates voltages. This corresponds to different degrees of spin-polarization in the two conduction channels that contribute differently to conductance. In the case of a strong asymmetry in split gates voltages one channel of conduction is pinched off and just the one remaining channel contributes to conductance. We have found that on the perimeter of the anti-dot there are spin-polarized states. These states may also contribute to conductance if the radius of the anti-dot is small enough and tunneling between these states may occur. The spin-polarized states in the QPC with shallow confinement tuned by electric means may be used for the purposes of quantum technology.

We show that for a quantum wire with a local asymmetric scattering potential the principal channels for charge and heat rectification decouple and renormalise differently under electron interactions, with heat rectification generally being more relevant. The polarisation of the rectification results from quantum interference and is tuneable through external gating. Furthermore, for spin polarised or helical electrons and sufficiently strong interactions a regime can be obtained in which heat transport is strongly rectified but charge rectification is very weak., Comment: 8 pages, 3 figures

Typical physical scales characterizing quantum electron decoherence are embodied in the femtosecond evolution of optically generated carriers interacting with phonons. A variety of quantum effects can be observed on these scales, such as non- Markovian evolution, giving rise to the Retardation effect, Collision Broadening which is a result of the lack of energy conservation in the early times of the evolution, as well as the Intra-Collisional Field Effect which is the effect of the field on the process of interaction Such effects are accounted by models which are beyond the Boltzmann equation, such as the Levinson and the Barker-Ferry equations, originally devised for homogeneous transport conditions.

The carrier transport in nowadays electronic structures is characterized by the nanometer scale and evolution times in the order of a few picoseconds. Under such conditions decoherence effects due to the lattice coexist with quantum coherent dynamics. The hierarchy of models presented in this chapter accounts on different levels of approximation for the effects of the lattice vibrations on the electron dynamics. On the top of the hierarchy is the for the whole electron-phonon system generalized Wigner equation. In the weak scattering limit it reduces to an equation, where the electron-potential interaction is fully considered as in the standard Wigner theory, while the electron-phonon coupling is described on the quantum level. The hierarchy includes the quantum electron-phonon Levinson and Barker-Ferry equations, generalized to describe the evolution of an initial packet in a quantum wire. The Wigner-Boltzmann equation describes the electron-potential interaction on a rigorous quantum level, while the electron-phonon interaction is considered as classical scattering. For slowly varying potentials the equation reduces to the classical Boltzmann equation, which is at the bottom of the hierarchy.

Solid-state spin qubits are based on the electron spin in solid materials. We want to manufacture a spin system by confining/trapping a single electron in a quantum two-level system containing spin up or spin down, and then use electron spin resonance to control the spin. This chapter will discuss methods of trapping single electrons and implementing quantum computing in solid materials.

We discuss the temperature-dependent thermoelectric transport properties of semiconductor nanostructures comprising a quantum dot coupled to quantum wires: the thermal dependence of the electrical conductance, thermal conductance, and thermopower. We explore the universality of the thermoelectric properties in the temperature range associated with the Kondo crossover. In this thermal range, general arguments indicate that any equilibrium property's temperature dependence should be a universal function of the ratio ${T}^{*}=T/{T}_{K}$, where ${T}_{K}$ is the Kondo temperature. Considering the particle-hole symmetric, spin-degenerate Anderson model, the zero-bias electrical conductance has already been shown to map linearly onto a universal conductance through a quantum dot embedded or side-coupled to a quantum wire. Employing rigorous renormalization-group arguments, we calculate universal thermoelectric transport coefficients that allow us to extend this result to the thermopower and the thermal conductance. We present numerical renormalization-group results to illustrate the physics in our findings. Applying the universal thermoelectric coefficients to recent experimental results of the electrical conductance and thermovoltages versus ${V}_{\mathrm{gate}}$, at different temperatures in the Kondo regime, we calculate all the thermoelectric properties and obtain simple analytical fitting functions that can be used to predict the experimental results of these properties. However, we cannot check all of them, due to the lack of available experimental results over a broad temperature range.

In this work, the dynamical analysis of carrier transportation in a typical piezoelectric device working in the ballistic regime is conducted. Based on the quantum scatting theory, the Poisson and Schrodinger equations are combined for calculating the dynamical transmission coefficient of the metal–piezoelectric ZnO–metal structure subject to sinusoidal and rectangular external stresses. The roles played by the spanning width of induced piezopotential and incident electron energy in affecting transmission probability are further discussed and clarified, respectively. The cutoff frequency of the piezoelectric device is also studied. Moreover, MEMS/NEMS hybrids specified by double/single-clamped ZnO quantum wire micro/nano-electromechanical resonator hybrids are proposed. Through a comprehensive numerical simulation, it is revealed that the rich nonlinear dynamics of the resonator can be subtly transferred to the piezoelectric device, and the chaotic transmission in the piezoelectric device can arise in two-dimensional parameter space with respect to time and incident electron energy. Therefore, the hybrids are endowed with the ability to detect amplitude changes by measuring ultra-sensitive quantum tunneling current. The study sheds light on developing quantum piezotronics and its related MEMS/NEMS integrations.

A theoretical investigation has been made of the magnetoplasmon excitations in a quasi-one-dimensional electron system comprised of vertically stacked, self-assembled InAs/GaAs quantum dots. The smaller length scales involved in the experiments impel us to consider a perfectly periodic system of two-dimensionally confined InAs quantum dot layers separated by GaAs spacers. Subsequent system is subjected to a two-dimensional confining (harmonic) potential in the x-y plane and an applied magnetic field (B) in the symmetric gauge. This scheme defines virtually a system of quantum wire comprised of vertically stacked quantum dots (VSQD). We derive and discuss the Dyson equation, the generalized (nonlocal and dynamic) dielectric function, and the inverse dielectric function for investigating the single-particle and collective (magnetoplasmon) excitations within the framework of (full) random-phase approximation (RPA). As an application, we study the influence of the confinement potential and the magnetic field on the component eigenfunctions, the density of states (DOS), the Fermi energy, the collective excitations, and the inverse dielectric functions. These findings demonstrate, for the very first time, the significance of investigating the system of VSQD subjected to a quantizing magnetic field. Given the edge over the planar quantum dots and the foreseen applications in the single-electron devices and quantum computation, investigating the system of VSQD is deemed vital. The results suggest exploiting magnetoplasmon qubits to be a potential option for implementing the solemn idea of quantum state transfer in devising quantum gates for the quantum computation and quantum communication networks., Comment: 36 pages, 15 figures

In this paper, we theoretically investigate the effect of temperature T and electron number density on the plasmon dispersion in a coupled electron-electron quantum wire system using the random phase approximation (RPA). We find that at non-zero T, there are four branches of plasmon dispersion and all of them seem to damp at some critical value of wave vector. Further, increase in T and/or decrease in electron number density causes the plasmon modes to shift upward in energy.

Microscopic response theory is used to study the linear electromagnetics of a Möbius jellium quantum wire. In the energy range of interest ( ℏ ω ∼ 1 − 200 m e V ), the wire can be considered as a Möbius band with complete transverse electron confinement ( ∼ one-level quantum well with width w ∼ k F − 1 ≪ λ = c / ω ). The electronic energy eigenvalues and eigenstates are calculated numerically via a diagonalization of a scalar determinant in which the relevant matrix elements of the geometrical potential (given in terms of string curvature and torsion) occur. The exact lowest lying states for a 50 nm long heavily doped GaAs wire are compared to those obtained in lowest-order perturbation theory. The sequence (from the bottom) EOEEOEOO… of the even (E) and odd (O) parity states is not the even–odd sequence EOEOEOEO… of a harmonic potential. The interchanges originate in the peak structure of the geometrical potential. Significant energy splitting of the lowest lying eigenvalues of the Möbius wire is observed when compared to the degenerate energy eigenvalues of a corresponding circular wire. The frequency dependence of the conductivity tensor components are calculated, and the peak structure is identified from the E → E , and O → O and E ↔ O transitions. It is shown that elastic light scattering might be a versatile probe for determining the Möbius wire’s electronic-state structure.

We derive a closed equation of motion for the one particle density matrix of a quantum system coupled to multiple baths using the Redfield master equation combined with a mean-field approximation. The steady-state solution may be found analytically with perturbation theory. Application of the method to a one-dimensional non-interacting quantum wire yields an expression for the current that reproduces the celebrated Landauer's formula. Nonlinear rectification is found for the case of a mesoscopic three-dimensional semiconductor p-n junction. The results are in good agreement with numerical simulations obtained using non-equilibrium Green's functions, supporting the validity of the Redfield equations for the description of transport., Comment: 14 pages and 5 figures

We consider a single electron confined within a quantum wire in a system of two electrostatically-induced QDs defined by nearby gates. The time-varying electric field, of single GHz frequency, perpendicular to the quantum wire, is used to induce the Rashba coupling and enable spin-dependent resonant tunneling of the electron between two adjacent potential wells with fidelity over 99.5%. This effect can be used for the high fidelity all-electrical electron-spin initialization or readout in the spin-based quantum computer. In contrast to other spin initialization methods, our technique can be performed adiabatically without increase in the energy of the electron. Our simulations are supported by a realistic self-consistent time-dependent Poisson-Schroedinger calculations., 7 pages, 3 figures

We propose a new route of getting controlled electron transmission through a molecular wire having a single loop geometry, by irradiating the loop with an arbitrarily polarized light. Along with conventional junction current, a new current called bias driven circular current can be established in the loop under certain conditions depending on the junction configuration. This current, on the other hand, induces a strong magnetic field that can even reach to few tesla. All the physical phenomena can be regulated selectively by adjusting the irradiation parameters. In addition, we put forward another new route of regulating transport behavior by introducing a new path due to the proximity of the contact electrodes for a typical junction configuration. Employing a tight-binding framework, we include the effect of light irradiation within a minimal coupling scheme following the well known Floquet ansatz. Using the wave-guide theory we compute two-terminal transmission probability, and the currents are determined through the Landauer–Büttiker formalism. The present analysis may be utilized to investigate transport phenomena in any other molecular wires as well as tailor-made geometries having simple and/or complex loop sub-structures.

In tunnel field-effect transistors (tFETs), the preferred mechanism for switching occurs by alignment ( on ) or misalignment ( off ) of two energy levels or band edges. Unfortunately, energy levels are never perfectly sharp. When a quantum dot interacts with a wire, its energy is broadened. Its actual spectral shape controls the current/voltage response of such transistor switches, from on (aligned) to off (misaligned). The most common model of spectral line shape is the Lorentzian, which falls off as reciprocal energy offset squared. Unfortunately, this is too slow a turnoff, algebraically, to be useful as a transistor switch. Electronic switches generally demand an on / off ratio of at least a million. Steep exponentially falling spectral tails would be needed for rapid off-state switching. This requires a new electronic feature, not previously recognized: narrowband, heavy-effective mass, quantum wire electrical contacts, to the tunneling quantum states. These are a necessity for spectrally sharp switching.

Recently demonstrated 3D networks of Ge quantum wires in an alumina matrix, produced by a simple magnetron sputtering deposition enables the realization of nanodevices with tailored conductivity and opto-electrical properties. Their growth and ordering mechanisms as well as possibilities in the design of their structure have not been explored yet. Here, we investigate a broad range of deposition conditions leading to the formation of such quantum wire networks. The resulting structures show an extraordinary tenability of the networks&rsquo, geometrical properties. These properties are easily controllable by deposition temperature and Ge concentration. The network&rsquo, s geometry is shown to retain the same basic structure, adjusting its parameters according to Ge concentration in the material. In addition, the networks&rsquo, growth and ordering mechanisms are explained. Furthermore, optical measurements demonstrate that the presented networks show strong confinement effects controllable by their geometrical parameters. Interestingly, energy shift is the largest for the longest quantum wires, and quantum wire length is the main parameter for control of confinement. Presented results demonstrate a method to produce unique materials with designable properties by a simple self-assembled growth method and reveal a self-assembling growth mechanism of novel 3D ordered Ge nanostructures with highly designable optical properties.

Despite being known of for decades, the actual realization of memory devices based on the memristive effect is progressing slowly, due to processing requirements and the need for exotic materials which are not compatible with today’s complementary-metal-oxide-semiconductor (CMOS) technology. Here, we report an experimental study on a Ge quantum wire device featuring distinct signatures of memristive behavior favorable for integration in CMOS platform technology. Embedding the quasi-1D Ge quantum wire into an electrostatically modulated back-gated field-effect transistor, we demonstrate that individual current transport channels can be addressed directly by controlling the surface trap assisted electrostatic gating. The resulting quantization of the current represents the ultimate limit of memristors with practically zero off-state current and low footprint. In addition, the proposed device has the advantage of non-destructive successive reading cycles capability. Importantly, our findings provide a framework towards fully CMOS compatible ultra-scaled Ge based memristors.

In this work, we first use the finite-differential time-domain (FDTD) to calculate the eigenenergies and eigenfunctions of a three dimensional (3D) cylindrical quantum wire. We assume that the inside of the wire is at zero potential. But, the outside of the wire has been chosen at different potentials as infinite and finite values. This is a true 3D procedure based on a direct implementation of the time-dependent Schrodinger equation. Then, we apply the Shannon and Tsallis entropy to obtain entropy and specific of the system. The results show that (i) the specific heat obtained by Tsallis has a peak structure. (ii) The entropy behavior for the finite and infinite confining potential has the same behavior at low temperatures. (iii) The peak value of specific heat increases with enhancing the quantum wire radius.