Electrons In Quantum Wires Research Articles

Evidences for non-Fermi liquid behavior of quantum wires

The present understanding of the physics of correlated electrons in quantum wires is explained by using two representative examples. Non-Fermi liquid collective excitations are obtained within the Luttinger liquid model. Charge and spin density modes are considered and compared with the data from resonant Raman scattering experiments. The results indicate that interactions dominate the low-frequency collective modes. The interplay in DC-transport between interaction, spin, backscattering by impurities and inhomogeneity is discussed and compared with recent experiments.

Generation of coherent confined acoustic phonons by drifting electrons in quantum wire

Generation of coherent confined acoustic phonons by drifting electrons in quantum wire

Photoluminescence from hot electrons in quasi-one- and two- dimensional systems

We report on the experimental studies of photoluminescence from hot electrons in quantum wires which were fabricated on AlGaAs/GaAs hetero-structures by using electron beam lithography and wet chemical etching. Spatially resolved photoluminescence of the quantum wires was observed by using microscopic photoluminescence (μ-PL) measurement at 70 K. We estimated the electron temperature from the μ-PL spectra in quantum well and wire. As a result, the spatial fluctuation of the electron temperature in the quantum wire was shown.

Interband collective electronic excitations in resonant Raman scattering of two-subband quantum wires

Using the bosonization technique, a theory for the collective excitations of the interacting electrons in quantum wires with two subbands occupied is developed. The dispersion relations for the inter-subband charge and spin density excitations are determined. The results are used to interpret the features observed in recent measurements of the Raman spectra of AlGaAs/GaAs quantum wires, particularly for photon energies near band gap resonance. It is shown that peaks previously identified as “single particle excitations” are signatures of higher order collective spin density excitations. Predictions about the observability of the interband modes are made.

Selective Control of Electrons in Quantum Wires Formed by Highly Uniform Multiatomic Step Arrays on GaAs(331) Substrates

Coherently aligned, multiatomic step arrays on GaAs(331) substrates generate a periodic array of conductive quantum wires in a two-dimensional (2D) electron gas. A small number of wires is selected by superimposing a constriction with independent side-gate control. By tuning the gate-voltage window, wires can be selected one by one. The resulting oscillatory current transmission provides a new functionality by switching between spatially separated electron channels. The wires are coupled by a small number of 2D electrons resulting in orders of magnitude reduced conductance perpendicular to the step edges.

Novel functionality by selective guidance of electrons in quantum wires on highly uniform multiatomic step arrays on GaAs (331) A substrates

We use coherently aligned, multiatomic step arrays on GaAs (331) A substrates to generate a periodic array of conductive quantum wires in a two-dimensional electron gas. A small number of quantum wires was selected for transport measurements by superimposing a submicrometer wide constriction parallel to the wires. With independent side-gate control the current could be switched between individual, spatially separated electron channels, thus demonstrating a new device functionality.

Delayed intersubband relaxation in quantum wires due to quantum kinetic Coulomb scattering

A theoretical analysis of the ultrafast intrasubband and intersubband dynamics of optically excited electrons in quantum wires is presented within the density matrix formalism. It is shown that the inclusion of non-Markovian electron-electron quantum kinetics, in addition to semiclassical optical phonon scattering, is necessary for an appropriate description. In particular, the dynamics of the two-particle density correlations must be explicitly taken into account. The electron-electron scattering processes, which are strongly restricted in quantum wires by energy and momentum conservation, are substantially enhanced on the quantum kinetic level, leading to fast intrasubband thermalization, and intersubband redistribution of the electrons which substantially delays the phonon-induced intersubband relaxation. Our simulations predict that the influence of electron-electron scattering becomes noticeable already at electron densities per unit length of the order of ${10}^{6} {\mathrm{}\mathrm{m}}^{\ensuremath{-}1}.$

Coupled charged Bose quantum wires

We investigate the effect of many-body correlations on the ground-state properties of two coupled charged Bose quantum wires. The intrawire and interwire correlations are treated on the same footing within the self-consistent mean-field theory of Singwi, Tosi, Land and Sjölander. Static properties, viz., pair-correlation functions, local-field correction factors, screened interactions and susceptibilities, are calculated for a range of wire spacings d, wire radii , and boson density parameters . We find that the qualitative dependence of intrawire correlations on and remains the same as found for an isolated wire, except that they become slightly weaker with the decreasing spacing d. The interwire correlations, on the other hand, depend strongly on d and are found to grow in magnitude with decreasing d. Further, we find no evidence for the existence of a charge-density-wave ground state in the density range investigated, , in the close proximity of wires. A comparison with the similar studies on the coupled electron quantum wires reveals that the charge-density-wave instability observed there may be an artifact of the neglect of interwire correlation effects.

Ground-state correlations in a charged Bose quantum wire

We study the ground-state correlations in a charged Bose quantum wire within the self-consistent-field approximation of Singwi, Tosi, Land, and Sjölander. A simple cylindrical model for the quantum wire is used. Static properties (structure factor, pair correlation function, and screened interaction potential), elementary excitation spectra, and ground-state energies are calculated at different boson number densities and wire radii. Our study shows that, in addition to the density of bosons, the wire radius provides an extra control on the strength of the many-body correlations. The correlation effects are found to become increasingly important with decreasing wire radius at a fixed density, and vice versa. The results obtained using the lower-order random-phase approximation are also given. We have compared our results for the screened potential with those for the semiconductor electron quantum wire. It is found that the screened potential for charged bosons is more attractive than that for electrons for rs<8, while the two potentials become essentially the same for rs>8. Therefore, we conclude that the exchange effects associated with the electron statistics act to oppose the overscreening properties of the charged Bose system and are dominated by the Coulomb correlation effects at low carrier densities corresponding to rs>8.

Luttinger-liquid features in the resonant Raman spectra of quantum wires

Using the bosonization technique, we develop a theory for the Raman scattering of the interacting electrons in quantum wires. The energy spectra of the collective excitations in a two-subband model are given. The density correlation functions for the Raman cross section are calculated. The charge and spin density excitations observed in recent Raman experiments are identified. Hitherto unexplained “single particle excitations” which appear near resonance and are independent of the relative polarization of incoming and scattered light are shown to originate in higher order spin density excitations, which can be evaluated due to the bosonization. For the intraband excitations, the peak strengths in the Raman cross section as a function of the frequency of the incoming light is explicitely calculated. Power law behaviors depending on the strength of the interaction are predicted.

Luttinger‐liquid features in the resonant Raman spectra of quantum wires

AbstractUsing the bosonization technique, we develop a theory for the Raman scattering of the interacting electrons in quantum wires. The energy spectra of the collective excitations in a two‐subband model are given. The density correlation functions for the Raman cross section are calculated. The charge and spin density excitations observed in recent Raman experiments are identified. Hitherto unexplained “single particle excitations” which appear near resonance and are independent of the relative polarization of incoming and scattered light are shown to originate in higher order spin density excitations, which can be evaluated due to the bosonization. For the intraband excitations, the peak strengths in the Raman cross section as a function of the frequency of the incoming light is explicitely calculated. Power law behaviors depending on the strength of the interaction are predicted.

Theory of resonant Raman scattering from low-energy collective excitations of interacting electrons in quantum wires

The Raman spectra of quantum wires in the region of electronic intra-band excitations are investigated using one- and two-band models based on the Luttinger approximation with spin. Structures related to charge and spin density modes are identified, and analyzed with respect to their behavior with photon energy and temperature. It is found that the low-energy peaks in the polarized spectra, close to resonance that are commonly assigned to “single particle excitations”, can be interpreted as the signature of spin density excitations. A broad structure in the resonant depolarized spectrum is predicted above the frequency of the spin density excitations. This is due to simultaneous but independent propagation of spin and charge density modes. The results, when compared with experiment, show, that the electronic collective excitations of quantum wires at low energies are characteristic for a non-Fermi liquid.

Coulomb interaction during coherent transport of electrons in quantum wires

A model is found whereby the Coulomb interaction during electron transport in quantum wires of finite length with current-lead contacts can be taken into account exactly (within the framework of the bosonization method). It is established that the charge density distribution along a wire in the case of the real Coulomb interaction is strongly different from the Luttinger liquid model, where the interaction is assumed to be short-ranged. The charge density near the contacts is found to be much higher than in the model with a short-range interaction, but away from the contacts the two densities are closer to each other.

Coupled electron and hole quantum wires

We have investigated the effect of many-body correlations on properties of coupled electron-hole quantum wires using a Singwi-Tosi-Land-Sj\olander approach. At ${r}_{s}=4$ the acoustic collective mode traverses the single-electron excitation region as a narrow resonance peak and reemerges in the undamped region on the high-$q$ side of the excitation region. The acoustic collective mode, but not the optic mode, is sensitive to the separation between the wires. For ${r}_{s}g2.5$ the effective interaction acting between the electrons which is mediated by the heavier holes becomes attractive when the separation between the wires drops to a critical value. For $0.8l~{r}_{s}l~2.5$ we detect a charge-density-wave ground state for small wire separations.

Resonant light scattering induced by Coulomb interaction in semiconductor microstructures

We consider inelastic light scattering by electron excitations in a two-dimensional electron system, which is induced by the Coulomb coupling between the Fermi sea and the interband excitons. The distinguishing feature of this mechanism of inelastic light scattering is a strong enhancement of the intensity in resonance with high two-dimensional subbands. Such resonant behaviour of the light scattering was observed in recent experiments for a two-dimensional electron plasma, quantum wires, and dots. In this paper we focus on the effect of the normal electric field on the intensity of the light scattering. We show that the interference between various virtual processes leads to the specific electric field dependence of the intensity. The intensity of the light scattering by charge-density excitations as a function of the normal electric field has a maximum at non-zero field. This maximum arises from the Coulomb direct interaction between the polarized exciton and the electron gas. Light scattering by spin-density excitations is assisted by the exchange interaction, and its intensity decreases with increasing electric field.

Bound states in waveguides and bent quantum wires. II. Electrons in quantum wires

Charged particles which move through bent quantum wires should possess one or more bound states. One way to observe these bound states is by measuring electron conductance in quantum wires. In the previous paper, we calculated the location and properties of bound states in quantum wires with two rectangular bends, and we found these confined states by measuring microwave transmission in bent rectangular waveguides. In this paper we calculate the conductance for electrons in quantum wires of the same geometry. Experimental measurements of such electrons observe conductance below the threshold for free propagation. It was conjectured that this effect resulted from quantum tunneling through an impurity state in the substrate. We compare the observed subthreshold conductance with theoretical calculations of electron tunneling through bound states in the bent quantum wire. We also compare our results with previous theoretical calculations of electron conductance in a system with this geometry.

Nonlinear boundary oscillations in strongly correlated electron quantum wires

We study the influence of a boundary point contact voltage on Coulomb blockadelike oscillations of the conductance in mesoscopic quantum wires of strongly correlated electrons. Bethe ansatz techniques allow one to understand lattice boundary effects together with nonconformal many-body behavior for such systems. We predict a nonlinear dependence of the initial (coherent) shift on oscillations with boundary potentials. The results are obtained for both spinless and spin cases.

Semi-classical treatment of electrons in quantum wires

For linear quantum wires, we show that the two-dimensional Thomas-Fermi approximation provides excellent agreement with more elaborate Poisson-Schrödinger calculations. Further we show that the Shikin density profile gives a very accurate though approximate analytic solution to the Thomas-Fermi equations.

Dynamical response of a one-dimensional quantum-wire electron system.

We provide a self-contained theoretical analysis of the dynamical response of a one-dimensional electron system, as confined in a semiconductor quantum wire, within the random-phase approximation. We carry out a detailed comparison with the corresponding two- and three-dimensional situations, and discuss the peculiarities arising in the one-dimensional linear response from the nonexistence of low energy single-particle excitations and from the linear nature of the long wavelength plasmon mode. We provide a critical discussion of the analytic properties of the complex dielectric function in the complex frequency plane. We investigate the zeros of the complex dielectric function, and calculate the plasmon dispersion, damping, and plasmon spectral weight in one dimension. We consider finite temperature and impurity scattering effects on one-dimensional plasmon dispersion and damping. \textcopyright{} 1996 The American Physical Society.

Comment on "Negative transport lifetime of electrons in quantum wires"

Comment on "Negative transport lifetime of electrons in quantum wires"