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Register a new userInterband electron Raman scattering in a quantum wire in a transverse magnetic field
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Electron Raman scattering (ERS) is investigated in a parabolic semiconductor quantum wire in a transverse magnetic field neglecting by phonon-assisted transitions. The ERS cross-section is calculated as a function of a frequency shift and magnetic field. The process involves an interband electronic transition and an intraband transition between quantized subbands. We analyze the differential cross-section for different scattering configurations. We study selection rules for the processes. Some singularities in the Raman spectra are found and interpreted. The scattering spectrum shows density-of-states peaks and interband matrix elements maximums and a strong resonance when scattered frequency equals to the hybrid frequency or confinement frequency depending on the light polarization. Numerical results are presented for a GaAs/AlGaAs quantum wire.
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We compute the single-particle states of a two-dimensional electron gas confined to the surface of a cylinder immersed in a magnetic field. The envelope-function equation has been solved exactly for both an homogeneous and a periodically modulated magnetic field perpendicular to the cylinder axis. The nature and energy dispersion of the quantum states reflects the interplay between different lengthscales, namely, the cylinder diameter, the magnetic length, and, possibly, the wavelength of the field modulation. We show that a transverse homogeneous magnetic field drives carrier states from a quasi-2D (cylindrical) regime to a quasi-1D regime where carriers form channels along the cylinder surface. Furthermore, a magnetic field which is periodically modulated along the cylinder axis may confine the carriers to tunnel-coupled stripes, rings or dots on the cylinder surface, depending on the ratio between the the field periodicity and the cylinder radius. Results in different regimes are traced to either incipient Landau levels formation or Aharonov-Bohm behaviour.
The nanofabrication technology has taught us that an $m$-dimensional confining potential imposed upon an $n$-dimensional electron gas paves the way to a quasi-($n-m$)-dimensional electron gas, with $m le n$ and $1le n, m le 3$. This is the road to the (semiconducting) quasi-$n$ dimensional electron gas systems we have been happily traversing on now for almost three decades. Achieving quasi-one dimensional electron gas (Q-1DEG) [or quantum wire(s) for more practical purposes] led us to some mixed moments in this journey: while the reduced phase space for the scattering led us believe in the route to the faster electron devices, the proximity to the 1D systems left us in the dilemma of describing it as a Fermi liquid or as a Luttinger liquid. No one had ever suspected the potential of the former, but it took quite a while for some to convince the others on the latter. A realistic Q-1DEG system at the low temperatures is best describable as a Fermi liquid rather than as a Luttinger liquid. In the language of condensed matter physics, a critical scrutiny of Q-1DEG systems has provided us with a host of exotic (electronic, optical, and transport) phenomena revealing their unparallel behavior characteristics unseen in their higher or lower dimensional counterparts. Here, we embark on the systematic investigation of the inelastic electron scattering (IES) and of inelastic light scattering (ILS) from the elementary electronic excitations in quantum wires in the absence of an applied magnetic field. To that end, we begin with the Kubos correlation functions to derive the generalized nonlocal, dynamic dielectric function, the inverse dielectric function, and the Dyson equation for the dynamic screened potential in the framework of Bohm-Pines full and famous random-phase approximation...
We study the shot noise (nonequilibrium current fluctuation) associated with dynamic nuclear polarization in a nonequilibrium quantum wire (QW) fabricated in a two-dimensional electron gas. We observe that the spin-polarized conductance quantization of the QW in the integer quantum Hall regime collapses when the QW is voltage biased to be driven to nonequilibrium. By measuring the shot noise, we prove that the spin polarization of electrons in the QW is reduced to $sim 0.7$ instead of unity as a result of electron-nuclear spin-flip scattering. The result is supported by Knight shift measurements of the QW using resistively detected NMR.
The combined presence of a Rashba and a Zeeman effect in a ballistic one-dimensional conductor generates a spin pseudogap and the possibility to propagate a beam with well defined spin orientation. Without interactions transmission through a barrier gives a relatively well polarized beam. Using renormalization group arguments, we examine how electron-electron interactions may affect the transmission coefficient and the polarization of the outgoing beam.
We show that, in a magnetic field parallel to the 2D electron layer, strong electron correlations change the rate of tunneling from the layer exponentially. It results in a specific density dependence of the escape rate. The mechanism is a dynamical Mossbauer-type recoil, in which the Hall momentum of the tunneling electron is partly transferred to the whole electron system, depending on the interrelation between the rate of interelectron momentum exchange and the tunneling duration. We also show that, in a certain temperature range, magnetic field can enhance rather than suppress the tunneling rate. The effect is due to the magnetic field induced energy exchange between the in-plane and out-of-plane motion. Magnetic field can also induce switching between intra-well states from which the system tunnels, and a transition from tunneling to thermal activation. Explicit results are obtained for a Wigner crystal. They are in qualitative and quantitative agreement with the relevant experimental data, with no adjustable parameters.
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