Quantum Wire Systems Research Articles

Effect of structural parameters, and spin-orbit interaction on the electronic properties of double quantum wire systems in the presence of external magnetic field

Effect of structural parameters, and spin-orbit interaction on the electronic properties of double quantum wire systems in the presence of external magnetic field

The Impact of a Strong Electromagnetic Wave on the Quantum Hall Effect in Cylindrical Quantum Wires

The impact of strong electromagnetic waves Hall effect is studied theoretically in a Cylindrical Quantum Wire (CQW) with infinitely high potential inside the wire and elsewhere subjected to a dc electric field , a magnetic field and a laser radiation . By using the quantum kinetic equation method for electrons interacting with Acoustic Phonon (AP) at low temperatures, we obtain analytical expressions for the conductivity tensor and the Hall Coefficient (HC), which are different from in comparison to those obtained for a rectangular quantum wire (RQW) or two-dimensional (2D) electron systems. Numerical calculations are also applied for GaAs/GaAsAl CQW to show the nonlinear dependence of the HC on the electromagnetic wave (EMW) frequency, and the radius, the length characteristic parameters of CQW. Wave function and energy spectrum in a CQW are dissiminar to those in Quantum Wires (QWs). Therefore, all numerical results are different from those in the case of QWs. The most important result is that the HC reaches saturation as the radius, the length of CQW or the EMW frequency increases.

Self-consistent quantum-kinetic theory for interacting drifting electrons and force-driven phonons in a 1D system

A self-consistent quantum-kinetic model is developed for studying strong-field nonlinear electron transport interacting with force-driven phonons within a nanowire system. For this model, phonons can be dragged into motion through strong electron–phonon scattering by fast-moving electrons along the opposite direction of the DC electric field. Meanwhile, the DC-field induced charge current of electrons can be either enhanced or reduced by the same electron–phonon scattering, depending on the relative direction of a DC field with respect to that of an applied temperature gradient for driving phonons. By making use of this quantum-kinetic model beyond the relaxation-time approximation, neither electron nor phonon temperature is required for describing ultrafast electron–phonon scattering and their correlated transports in this 1D electronic-lattice system.

Field-dependent THz transport nonlinearities in semiconductor nano structures.

Charge transport nonlinearities in semiconductor quantum dots and nanorods are studied. Using a density matrix formalism, we retrieve the field-dependent nonlinear mobility and show the possibility of intra-pulse gain. We further demonstrate that the dynamics of master equations can be captured in an analytical formula for the field-dependent charge carrier mobility, e.g. for two-level systems. This equation extends the linear response theory based Kubo-Greenwood result to nonlinear processes at elevated field strength, easily reached in THz transport spectroscopy. With these tools we analyze the field strength, chirp, temperature and dephasing dependence of the charge carrier mobility in the model system of CdSe quantum dots and wires. Stark broadening and Rabi splitting result in strong alterations of the mobility spectra, pronounced at low temperatures. The mobility spectra are strongly temperature and pulse shape dependent in the nonlinear regime. The findings are of immediate interest e.g. for nonlinear THz generation, conversion and amplification in 6G technology and nano electronics. Our results further enable experimentalists to fit and understand measured charge transport nonlinearities with analytical expressions and to design nanosystems with engineered material properties.

Induced Wigner crystallization in a coupled electron-hole quantum wire system at finite-temperature

We explore the possibility of induced Wigner crystallization in a coupled electron-hole (e-h) quantum wire system at finite-temperature T by calculating the intra- and inter-wire static structure factors in the dynamic mean-field approximation of Singwi et al (the qSTLS theory). We find that owing to the dynamics of severely correlated particles, the e-h system may favour an induced phase transition from quantum liquid to the Wigner crystal state at a non-zero T and sufficiently low particle (electron/hole) number density in the close proximity of two wires. On the other hand, the static STLS approximation does not predict such phase transition due to complete neglect of the dynamics of particle correlations.

Coulomb drag effect in coupled quantum wire systems: Finite-[formula omitted] and exchange–correlation effects

In this paper, we study the Coulomb drag in GaAs-based coupled electron–electron (e–e) and electron–hole (e–h) quantum wire systems by calculating the drag rate over a wide range of temperature T, particle (electron/hole) number density, and some selected values of inter-wire separation. The exchange–correlations among particles are treated within the self-consistent mean-field approximation of Singwi et al. (the STLS theory) and the inter-wire interaction potential is assumed to be statically screened. We find that the drag rate increases with decrease in particle number density and/or inter-wire separation due to the increased intra- and inter-wire coupling among particles. Further, the drag rate is found to be more for coupled e–h than the e–e quantum wire system due to the stronger e–h correlations on behalf of hole’s larger effective mass. As an important finding, we assert that the drag rate abruptly enhances at the critical system parameters for which the charge-density-wave (CDW) instability has been recently reported to occur in the e–h system. On the other side, the random-phase approximation (RPA) underestimates the drag rate in comparison to the STLS theory and the difference is seen to be more in the particle’s strong coupling domain i.e. at low inter-wire spacing and/or particle number density. In addition, we report for the first time the plasmon dispersion of both the coupled e–h and e–e systems at non-zero T and find that the plasma modes get dispersed into four branches among which two are recognized as optic (in-phase) and remaining two as the acoustic (out-of-phase) plasma modes. All the four plasma energy modes show a consistent blue shift with rise in T, however, the uppermost branches of the optical and acoustic plasma modes seem to repel each other as inter-wire spacing and/or particle number density is lowered. Interestingly, the inclusion of exchange–correlations in the RPA causes a red (blue)-shift in the upper (lower) branch of both the optic and acoustic plasma modes for each of the system leading to an overall enhancement in the Coulomb drag rate.

Spectral features and optical absorption of vertically stacked V-groove quantum wires

The spectral features and the linear, nonlinear, and total optical absorption coefficients of two realistic mathrm {GaAs/Ga}_{1-x}{mathrm{Al}}_x{mathrm{As}} vertically stacked V-groove quantum wires confining electronic states were theoretically studied. The compact density matrix formalism and the finite element method were used as solution frameworks. The influence of the barrier width, inter-sidewall angle, the crescent thickness of the stack, and the influence of a static electric field on the energy spectrum and the optical coefficients is addressed. Increasing the crescent thickness (inter-sidewall angle) leads to a reduction (non-monotonous increase) of the energy values, while the presence of a static electric field leads to controllable stark-like patterns. In all cases, anti-crossing points are reported. By increasing the crescent thickness, inter-sidewall angle, or barrier width, a non-monotonous blue-/red-shift of the resonant peaks of the optical absorption is observed. In addition, the results in asymmetric/symmetric vertically coupled V-groove quantum wire systems suggest that the quantum tunneling phenomenon can be linked to the enhancement of the total optical absorption due to the possibility of the generation of dipole moments by higher electron mobility. Thus, optical fields oriented along the growth direction enhance the optical absorption. Furthermore, the absorption coefficient maximum is drastically modified by varying the inter-sidewall angle, and even the evolution tendency can be inverted due to the anti-crossing points in the energy spectra. Since the obtained resonant peaks are located below 20 meV in the spectra, the analyzed system could be interesting for exploring and designing new Terahertz devices.

Quantum wires, Chern-Simons theory, and dualities in the quantum Hall system

Over the years, many theoretical frameworks have been developed to understand the remarkable physics of the quantum Hall system. In this work we discuss the interplay among quantum wires, Chern-Simons theory, bosonization, and particle-vortex duality, which enable a unified approach for the Laughlin states of the fractional quantum Hall system. Starting from the so-called quantum wires system, which is a semi-microscopic description in terms of 1+1 dimensional theories, we discuss the emergence of 2+1 dimensional low-energy effective field theories by using different maps connecting the microscopic degrees of freedom with the macroscopic ones. We show the origin of these maps by embedding the bosonized version of the original quantum wires model in a gauge invariant theory and using particle vortex-duality.

Exchange-correlation effects in coupled quantum wire systems at finite temperature

We investigate the exchange-correlation effects in coupled quantum wire systems at finite-temperature within the self-consistent mean-field approximation of Singwi et al by assuming the charge carriers to be electrons in one wire and electrons or heavier holes in the other. Numerical results are presented for the intra- and inter-wire static structure factors, pair-correlation functions and the static charge density susceptibility over a wide range of system parameters (viz. temperature T, particle number density and inter-wire spacing) at equal and fixed transverse width of both the wires. We find for the first time that the coupled electron-hole (e-h) quantum wire system may favor a charge-density-wave (CDW) instability at sufficiently low T and carrier density in the close proximity of the wires, where as no such phase transition is observed in the electron-electron (e-e) quantum wire system at any non-zero T. The intra-wire contact pair-correlation functions of both the systems show a non-monotonous behavior with increasing (decreasing) T (carrier number density), and increase consistently with decrease in inter-wire spacing. On the other hand, the corresponding inter-wire contact pair-correlation functions show a non-monotonous T-dependence and consistent increase with decrease in carrier number density and/or inter-wire separation. Results of free exchange-correlation energy for both the e-h and e-e coupled systems are also reported which are found to have a noticeable dependence upon T. To highlight the effect of exchange-correlations, our results have been compared with the predictions of the random-phase approximation (RPA).

Theoretical study of electronic and optical properties in doped quantum structures with Razavy confining potential: effects of external fields

We investigate the energy states of confined electrons in doped quantum structures with Razavy-like confining potentials. The theoretical investigation is performed within the effective mass and parabolic band approximations, including the influence of externally applied electric and magnetic fields. First, we analyze the case of a Razavy quantum well and determine its conduction subband spectrum, focusing on the lowest energy levels and their probability densities. These properties have been numerically determined by self-consistently solving the coupled system of Schrödinger, Poisson, and charge neutrality equations. Doping is introduced via an on-center $$\delta$$ -like layer. In order to evaluate the associated total (linear plus nonlinear) optical absorption coefficient (TOAC), we have calculated the corresponding diagonal and off-diagonal electric dipole matrix elements, the main energy separation, and the occupancy ratio which are the main factors governing the variation in this optical response. A detailed discussion is given about the influence of doping concentration as well as electric and magnetic fields, which can produce shifts in the light absorption signal, toward either lower or higher frequencies. As an extension of the self-consistent method to a two-dimensional problem, the energy states of quantum wire system of circular cross section, with internal doping and Razavy potential, have been calculated. The response of eigenvalues, self-consistent potentials and electron densities is studied with the variation in $$\delta$$ -doping layer width and of the donor density. Finally, the origin of Friedel-like oscillations, that arise in the density profile, generated by the occupation of internal and surface electronic states has been explained.

Coulomb drag rate in a coupled electron-electron quantum wire system

In this paper, we calculate the Coulomb drag rate in a coupled electron-electron (e-e) quantum wire system over a wide range of temperature T, and some selected values of electron number densityandinter-wire spacing. The intra- and inter-wire exchange-correlations are treated within the self-consistent mean-field approximation of Singwi et al (the so called STLS theory) suitably generalized to the coupled system at finite-T. At a fixed T, the drag rate is found to increase with decrease in inter-wire separation and/or electron number density due to increased intra- and inter-wire coupling among electrons. Further, we note that the magnitude of drag rate is more in the STLS theory as compared to the random-phase approximation (RPA), and the difference consistently increases with decrease in inter-wire spacing.

Study of Multiple Quantum Wire Hg0.8Cd0.2Te/CdTe Laser

The optoelectronic properties of Hg0.8Cd0.2Te/CdTe quantum wire laser are investigated, with emphasis on the effect of wire width (W) and barrier width (B) on the optical confinement factor (Г), the optical threshold gain (gth ) and the effect number of well (Nw ) on the confinement factor have been calculated. The laser operation system has been studied in the two cases; the number of well (2 and 3). It found that in our theoretical study, the values affect the work of a multiple laser system operating a number of well 2 was (W= 65nm, B = 40 nm), the value of optical confinement factor equals (Г= 0.055) and the amount of optical threshold gain was (gth = 38 cm −1). Further, the suitable values for multi quantum wire system is running a number of well 3 was (W= 42 nm, B = 60 nm), optical confinement factor equal to (Г= 0.048) and the threshold gain (gth = 42 cm −1). Theoretically, the principle of operation of a laser device depends on the resonator, the effective medium, and the stimulated emission of light radiation which is represented the important process in the work of device. It is found that the effect of optical confinement factor causes an increase in the reflectivity of laser beam in the cavity therefore decrease in the amount of optical threshold gain, noted that the amount of reflection was installed to study the change of other electronic characteristics of the multiple quantum wire.

Theoretical Investigation of Nonequilibrium Spin Transport Through a Triple Site Quantum Wire System

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.

Self-consistent quantum-kinetic theory for interplay between pulsed-laser excitation and nonlinear carrier transport in a quantum-wire array.

We propose a self-consistent many-body theory for coupling the ultrafast dipole-transition and carrier-plasma dynamics in a linear array of quantum wires with the scattering and absorption of ultrashort laser pulses. The quantum-wire non-thermal carrier occupations are further driven by an applied DC electric field along the wires in the presence of resistive forces from intrinsic phonon and Coulomb scattering of photo-excited carriers. The same strong DC field greatly modifies the non-equilibrium properties of the induced electron-hole plasma coupled to the propagating light pulse, while the induced longitudinal polarization fields of each wire significantly alters the nonlocal optical response from neighboring wires. Here, we clarify several fundamental physics issues in this laser-coupled quantum wire system, including laser pulse influence on local transient photo-currents, photoluminescence spectra, and the effect of nonlinear transport in a micro-scale system on laser pulse propagation. Meanwhile, we also anticipate some applications from this work, such as specifying the best combination of pulse sequence through a quantum-wire array to generate a desired THz spectrum and applying ultra-fast optical modulations to nonlinear carrier transport in nanowires.

From quantum wires to the Chern-Simons description of the fractional quantum Hall effect

We show the explicit connection between two distinct and complementary approaches to the fractional quantum Hall system (FQHS): the quantum wires formalism and the topological low-energy effective description given in terms of an Abelian Chern-Simons theory. The quantum wires approach provides a description of the FQHS directly in terms of fermions arranged in an array of one-dimensional coupled wires. In this sense it is usually referred to as a microscopic description. On the other hand, the effective theory has no connection with the microscopic modes, involving only the emergent topological degrees of freedom embodied in an Abelian Chern-Simons gauge field, which somehow encodes the collective motion of the strongly correlated electrons. The basic strategy pursued in this work is to bosonize the quantum wires system and then consider the continuum limit. By examining the algebra of the bosonic operators of the Hamiltonian, we are able to identify the bosonized microscopic fields with the components of the field strength (electric and magnetic fields) of the emergent gauge field. Thus our study provides a bridge between the microscopic physical degrees of freedom and the emergent topological ones, without relying on the bulk-edge correspondence.

Reconfigurable quantum logic gates using Rashba controlled spin polarized currents

A reconfigurable logic gate is proposed in a two-dimensional double quantum wire system with a coupling window enabled by a Rashba field. Manipulating the spin states of incoming electrons several quantum logic gates (OR, AND, XOR, CNOT) can be implemented. The logic gate functionality can be switched by tuning the Rashba parameter only. In this context, we investigate suitable configurations of the device region by embedding a quantum point contact located in the coupling region to obtain all four logic gates. The ballistic spin polarized transmission functions are calculated using an effective mass scattering formalism in the framework of a multi-channel, multi-terminal system. Owing its versatility, the proposed logic gate can be integrated in programmable architectures, able to implement both classical and quantum algorithms.

Electron Transport Properties of Graphene-Based Quantum Wires**Supported by the Foundation of Scientific Innovative Research Team of Education Department of Guizhou Province under Grant No. 201329, the Science and Technology Foundation of Guizhou Province Grant No. J20122311 and University Scientific and Technological Innovation Talents Program of Guizhou Province Grant No. 2013154

We study the electronic transport in quantum wire structures made of graphene. By using the nonequilibrium Green function method, the transmission is studied for varies sizes samples. Our results show that the transmission sensitive depends on the size of the system and exhibits fluctuations due to the mismating of propagating modes between the central region and the leads. The number of resonant transmission peaks increases with the increase of length of the wire, while the width of the leads mainly affect the transmission in the region of low energy. A central energy gap in the transmission spectrum is more likely to appear in the quantum wire system than in the uniform armchair graphene nanoribbons. Moreover, the energy gap can be widened for a certain size of the quantum wire system by changing the width of the leads. These results may have potential applications in designing graphene-based devices.

Tuning directional dependent metal–insulator transitions in quasi-1D quantum wires with spin–orbit density wave instability

We study directional dependent band gap evolutions and metal–insulator transitions (MITs) in model quantum wire systems within the spin–orbit density wave (SODW) model. The evolution of MIT is studied as a function of varying anisotropy between the intra-wire hopping () and inter-wire hopping () with Rashba spin–orbit coupling. We find that as long as the anisotropy ratio () remains below 0.5, and the Fermi surface nesting is tuned to , an exotic SODW induced MIT easily develops, with its critical interaction strength increasing with increasing anisotropy. As (2D system), the nesting vector switches to , making this state again suitable for an isotropic MIT. Finally, we discuss various physical consequences and possible applications of the directional dependent MIT.

Influence of substrate misorientation on the photoluminescence and structural properties of InGaAs/GaAsP multiple quantum wells.

InGaAs/GaAsP multiple quantum wells (MQWs) were grown by metal-organic chemical vapor deposition on vicinal GaAs (001) substrates with different miscut angles of 0°, 2° and 15° towards [110]. The crystal structures of InGaAs/GaAsP were characterized by high-resolution X-ray diffraction and Raman spectroscopy. The surface morphologies of InGaAs/GaAsP MQWs were observed by atomic force microscopy. The mechanisms for step flow, step bunching and pyramid growth on 0°, 2° and 15° misoriented substrates were discussed. The results provide a comprehensive phenomenological understanding of the self-ordering mechanism of vicinal GaAs substrates, which could be harnessed for designing the quantum optical properties of low-dimensional systems. From low-temperature photoluminescence, it was observed that the luminescence from the MQWs grown on a vicinal surface exhibits a red-shift with respect to the 0° case. An extra emission was observed from the 2° and 15° off samples, indicating the characteristics of quantum wire and pyramidal self-controlled quantum-dot systems, respectively. Its absence from the PL spectrum on 0° surfaces indicates that indium segregation is modified on the surfaces. The relationship between InGaAs/GaAsP MQWs grown on vicinal substrates and their optical and structural properties was explained, which provides a technological basis for obtaining different self-controlled nanostructures.

The geometry effect on energy transfer rate in a coupled-quantum-wires structure

The geometry effect on energy transfer rate in a coupled cylindrical quantum wires system is investigated. The corrected random phase approximation by the zero-temperature static Hubbard correction is employed to calculate dielectric function of the system. The geometry effect on energy transfer rate is studied for statically and dynamically screened electron–electron interaction. Both the linear and nonlinear regimes correspond respectively to weak and strong external field are considered. The calculations show that increasing wire radius increases energy transfer rate in both the static and dynamic screening approximations for electron–electron interactions. Moreover, the same trend is predicted by the calculations for both the linear and nonlinear regimes.