arXiv subjects

Nelson Studart

Publications and source records attributed to Nelson Studart.

31 records · Page 2Linked to original sources

arXiv2001

Electron correlation effects in a wide channel from the $ν=1$ quantum Hall edge states

The spatial behavior of Landau levels (LLs) for the $nu=1$ quantum Hall regime at the edge of a wide channel is studied in a self-consistent way by using a generalized local density approximation proposed here. Both exchange interaction and strong electron correlations, due to edge states, are taken into account. They essentially modify the spatial behavior of the occupied lowest spin-up LL in comparison with that of the lowest spin-down LL, which is totally empty. The contrast in the spatial behavior can be attributed to a different effective one-electron lateral confining potentials for the spin-split LLs. Many-body effects on the spatially inhomogeneous spin-splitting are calculated within the screened Hartree-Fock approximation. It is shown that, far from the edges, the maximum activation energy is dominated by the gap between the Fermi level and the bottom of the spin-down LL, because the gap between the Fermi level and the spin-up LL is much larger. In other words, the maximum activation energy in the bulk of the channel corresponds to a highly asymmetric position of the Fermi level within the gap between spin-down and spin-up LLs in the bulk. We have also studied the renormalization of the edge-state group velocity due to electron correlations. The results of the present theory are in line with those suggested and reported by experiments on high quality samples.

cond-mat.mes-hall↗

arXiv2000

Inhomogeneous broadening of tunneling conductance in double quantum wells

The lineshape of the tunneling conductance in double quantum wells with a large-scale roughness of heterointerfaces is investigated. Large-scale variations of coupled energy levels and scattering due to the short-range potential are taken into account. The interplay between the inhomogeneous broadening, induced by the non-screened part of large-scale potential, and the homogeneous broadening due to the scattering by short-range potentials is considered. It is shown that the large inhomogeneous broadening can be strongly modified by nonlocal effects involved in the proposed mechanism of inhomogeneity. Related change of lineshape of the resonant tunneling conductance between Gaussian and Lorentzian peaks is described. The theoretical results agree quite well with experimental data.

cond-mat.mes-hall↗

arXiv2000

Plasma dispersion of multisubband electron systems over liquid helium

Density-density response functions are evaluated for nondegenerate multisubband electron systems in the random-phase approximation for arbitrary wave number and subband index. We consider both quasi-two-dimensional and quasi-one- dimensional systems for electrons confined to the surface of liquid helium. The dispersion relations of longitudinal intrasubband and transverse intersubband modes are calculated at low temperatures and for long wavelengths. We discuss the effects of screening and two-subband occupancy on the plasmon spectrum. The characteristic absorption edge of the intersubband modes is shifted relatively to the single-particle intersubband separation and the depolarization shift correction can be significant at high electron densities.

cond-mat.str-el↗

arXiv2000

Two-subband electron transport in nonideal quantum wells

Electron transport in nonideal quantum wells (QW) with large-scale variations of energy levels is studied when two subbands are occupied. Although the mean fluctuations of these two levels are screened by the in-plane redistribution of electrons, the energies of both levels remain nonuniform over the plane. The effect of random inhomogeneities on the classical transport is studied within the framework of a local response approach for weak disorder. Both short-range and small-angle scattering mechanisms are considered. Magnetotransport characteristics and the modulation of the effective conductivity by transverse voltage are evaluated for different kinds of confinement potentials (hard wall QW, parabolic QW, and stepped QW).

cond-mat.mes-hall↗

arXiv2000

High field transport in strained Si/GeSi double heterostructure: a Fokker-Planck approach

We report calculations of high electric field transport for the case of a strained Si/GeSi double heterostructure (DHS) considering transport along the Si channel and by applying the analytical Fokker-Planck approach (FPA), where the process is modeled as drift-diffusion in energy space. We limit ourselves to electronic transport in the conduction band of the strained Si, where an energy shift between the otherwise degenerate six energy valleys characterizes the band alingment in the DHS. Intervalley phonon scatterings are considered while intravalley acoustic phonon scattering is ignored, leading to results valid for high enough temperatures. Our results are compared to previous theoretical works where Monte Carlo simulations were applied. A reasonable agreement between the two approaches is obtained in the high electric field regime.

cond-mat.mtrl-sci↗

arXiv1999

Polaron states of electrons over the anisotropic surface of liquid helium

The energetics and transport properties of the polaron in the anisotropic surface over liquid helium are investigated. The localization radii and the energy of the ground and excited states are calculated using the variational method within the hydrodynamic model of the polaron. In particular, we have considered maximal anisotropy which corresponds to the system of electrons in quasi-one-dimensional channels over liquid helium. The polaron binding energy is found and the temperature for the polaron formation is estimated below 0.1 K. Solving the hydrodynamic equations for fluid velocities, the polaron mobilities along and across the channel are determined. The possibility of experimental observation of polarons by measuring the frequency of spectroscopic transitions as well the mobility as functions of the holding electric field is addressed.

cond-mat.str-el↗

arXiv1999

Edge magnetoplasmons in periodically modulated structures

We present a microscopic treatment of edge magnetoplasmons (EMP's) within the random-phase approximation for strong magnetic fields, low temperatures, and filling factor $ν=1(2)$, when a weak short-period superlattice potential is imposed along the Hall bar. The modulation potential modifies both the spatial structure and the dispersion relation of the fundamental EMP and leads to the appearance of a novel gapless mode of the fundamental EMP. For sufficiently weak modulation strengths the phase velocity of this novel mode is almost the same as the group velocity of the edge states but it should be quite smaller for stronger modulation. We discuss in detail the spatial structure of the charge density of the renormalized and the novel fundamental EMP's.

cond-mat.str-el↗

arXiv1999

High-field transport properties of bulk Si: A test for the Fokker-Planck approach

High electric-field transport parameters are calculated using an analytical Fokker-Planck approach (FPA), where transport is modeled as a drift-diffusion process in energy space. We have applied the theory to the case of Si, taking into account the six intervalley phonons, aiming to test the FPA. The obtained results show a quite reasonable agreement with experimental data and Monte Carlo simulations confirming in this case that the FPA works very well for high enough electric fields.

cond-mat↗

arXiv1999

Temperature Effects on Edge Magnetoplasmons in the Quantum Hall Regime

A microscopic treatment of edge magnetoplasmons (EMPs) is presented for the case of not-too-low temperatures in which the inequality $k_{B}T\gg \hbar v_{g}/\ell_{0}$, where $v_{g}$ is the group velocity of the edge states and $\ell_{0}$ is the magnetic length, is fulfilled, and for filling factors $ν=1(2)$. We have obtained independent EMP modes spatially symmetric and antisymmetric with respect to the edge. We describe in detail the spatial structure and dispersion relations of the new edge waves (edge helicons, dipole, quadrupole and octupole EMPs), which have the characteristic length $\ell_{T}=\ell_{0}^{2}k_{B}T/\hbar v_{g}$. We have found that, in contrast to well-known results for a spatially homogeneous dissipation within the channel, the damping of the fundamental EMP at not-too-low temperatures is not quantized and has a $T^{-1}$ dependence.

cond-mat.mes-hall↗

arXiv1999

Coupled phonon-ripplon modes in a single wire of electrons on the liquid-helium surface

The coupled phonon-ripplon modes of the quasi-one-dimensional electron chain on the liquid helium sutface are studied. It is shown that the electron-ripplon coupling leads to the splitting of the collective modes of the wire with the appearance of low-frequency modes and high-frequency optical modes starting from threshold frequencies. The effective masses of an electron plus the associated dimple for low frequency modes are estimated and the values of the threshold frequencies are calculated. The results obtained can be used in experimental attempts to observe the phase transition of the electron wire into a quasi-ordered phase.

cond-mat.mes-hall↗

arXiv1999

Hidden spin-current conservation in 2d Fermi liquids

We report the existence of regimes of the two dimensional Fermi liquid that show unusual conservation of the spin current and may be tuned by varying some parameter like the density of fermions. We show that for reasonable models of the effective interaction the spin current may be conserved in general in 2d, not only for a particular regime. Low temperature spin waves propagate distinctively in these regimes and entirely new ``spin-acoustic'' modes are predicted for scattering-dominated temperature ranges. These new high-temperature propagating spin waves provide a clear signature for the experimental search of such regimes.

cond-mat↗

arXiv1999

Ripplonic Polaron in the Quasi-One-Dimensional Electron System over Liquid Helium

We study the energetics and transport properties of polarons in the quasi-one dimensional electron system over the liquid helium surface. The localization lengths and the energy of the ground and excited states are calculated within the hydrodynamic model of the polaron. The polaron bound energy is found and the temperature for the polaron formation is estimated below 0.1 K. We examine the possibility of observation of the polarons by measuring both the spectroscopic transitions and the mobility.

cond-mat↗

arXiv1998

Edge helicons and repulsion of fundamental edge magnetoplasmons in the quantum Hall regime

A quasi-microscopic treatment of edge magnetoplasmons (EMP) is presented for very low temperatures and confining potentials smooth on the scale of the magnetic length $\ell_{0}$ but sufficiently steep at the edges such that Landau level (LL) flattening can be discarded. The profile of the unperturbed electron density is sharp and the dissipation taken into account comes only from electron intra-edge and intra-LL transitions due to scattering by acoustic phonons. For wide channels and filling factors $ν=1$ and 2, there exist independent EMP modes spatially symmetric and antisymmetric with respect to the edge. Some of these modes, named edge helicons, can propagate nearly undamped even when the dissipation is strong. Their density profile changes qualitatively during propagation and is given by a rotation of a complex vector function. For $ν>2,$ the Coulomb coupling between the LLs leads to a repulsion of the uncoupled fundamental LL modes: the new modes have very different group velocities and are nearly undamped. The theory accounts well for the experimentally observed plateau structure of the delay times as well as for the EMP's period and decay rates.

cond-mat.str-el↗