Stability of the shell structure in 2D quantum dots

We study the effects of external impurities on the shell structure in semiconductor quantum dots by using a fast response-function method for solving the Kohn-Sham equations. We perform statistics of the addition energies up to 20 interacting electrons. The results show that the shell structure is generally preserved even if effects of high disorder are clear. The Coulomb interaction and the variation in ground-state spins have a strong effect on the addition-energy distributions, which in the noninteracting single-electron picture correspond to level statistics showing mixtures of Poisson and Wigner forms.Comment: 7 pages, 8 figures, submitted to Phys. Rev.

An efficient method for the Quantum Monte Carlo evaluation of the static density-response function of a many-electron system

In a recent Letter we introduced Hellmann-Feynman operator sampling in diffusion Monte Carlo calculations. Here we derive, by evaluating the second derivative of the total energy, an efficient method for the calculation of the static density-response function of a many-electron system. Our analysis of the effect of the nodes suggests that correlation is described correctly and we find that the effect of the nodes can be dealt with

Comment on "Diffusion Monte Carlo study of jellium surfaces: Electronic densities and pair correlation functions"

In a fixed-node diffusion Monte Carlo calculation of the total energy of jellium slabs, Acioli and Ceperley [Phys. Rev. B {\bf 54}, 17199 (1996)] reported jellium surface energies that at low electron densities were significantly higher than those predicted in the local-density approximation (LDA) of density-functional theory. Assuming that the fixed-node error in the slab and the bulk calculations cancel out, we show that their data yield surface energies that are considerably closer to the LDA and in reasonable agreement with those obtained in the random-phase approximation.Comment: 3 pages, 2 figures, to appear in Phys. Rev.

Isospin and density dependences of nuclear matter symmetry energy coefficients II

Symmetry energy coefficients of explicitly isospin asymmetric nuclear matter at variable densities (from .5$\rho_0$ up to 2 $\rho_0$) are studied as generalized screening functions. An extended stability condition for asymmetric nuclear matter is proposed. We find the possibility of obtaining stable asymmetric nuclear matter even in some cases for which the symmetric nuclear matter limit is unstable. Skyrme-type forces are extensively used in analytical expressions of the symmetry energy coefficients derived as generalized screening functions in the four channels of the particle hole interaction producing alternative behaviors at different $\rho$ and $b$ (respectively the density and the asymmetry coefficient). The spin and spin-isospin coefficients, with corrections to the usual Landau Migdal parameters, indicate the possibility of occurring instabilities with common features depending on the nuclear density and n-p asymmetry. Possible relevance for high energy heavy ions collisions and astrophysical objects is discussed.Comment: 16 pages (latex) plus twelve figures in four eps files, to be published in I.J.M.P.

Electron-Acoustic Phonon Energy Loss Rate in Multi-Component Electron Systems with Symmetric and Asymmetric Coupling Constants

We consider electron-phonon (\textit{e-ph}) energy loss rate in 3D and 2D multi-component electron systems in semiconductors. We allow general asymmetry in the \textit{e-ph} coupling constants (matrix elements), i.e., we allow that the coupling depends on the electron sub-system index. We derive a multi-component \textit{e-ph}power loss formula, which takes into account the asymmetric coupling and links the total \textit{e-ph} energy loss rate to the density response matrix of the total electron system. We write the density response matrix within mean field approximation, which leads to coexistence of\ symmetric energy loss rate $F_{S}(T)$ and asymmetric energy loss rate $F_{A}(T)$ with total energy loss rate $F(T)=F_{S}(T)+F_{A}(T)$ at temperature $T$. The symmetric component F_{S}(T) $is equivalent to the conventional single-sub-system energy loss rate in the literature, and in the Bloch-Gr\"{u}neisen limit we reproduce a set of well-known power laws$F_{S}(T)\propto T^{n_{S}}$, where the prefactor and power$n_{S}$depend on electron system dimensionality and electron mean free path. For$F_{A}(T)$we produce a new set of power laws F_{A}(T)\propto T^{n_{A}}$. Screening strongly reduces the symmetric coupling, but the asymmetric coupling is unscreened, provided that the inter-sub-system Coulomb interactions are strong. The lack of screening enhances $F_{A}(T)$ and the total energy loss rate $F(T)$. Especially, in the strong screening limit we find $F_{A}(T)\gg F_{S}(T)$. A canonical example of strongly asymmetric \textit{e-ph} matrix elements is the deformation potential coupling in many-valley semiconductors.Comment: v2: Typos corrected. Some notations changed. Section III.C is embedded in Section III.B. Paper accepted to PR

Electric-field correlations in quantum charged fluids coupled to the radiation field

In a recent paper [S.El Boustani, P.R.Buenzli, and Ph.A.Martin, Phys.Rev. E 73, 036113 (2006) cond-mat/0511537], about quantum charges in equilibrium with radiation, among other things the asymptotic form of the electric-field correlation has been obtained by a microscopic calculation. It has been found that this correlation has a long-range algebraic decay (except in the classical limit). The macroscopic approach, in the Course of Theoretical Physics of Landau and Lifshitz, gives no such long-range algebraic decay. In this Brief Report, we revisit and complete the macroscopic approach of Landau and Lifshitz, we confirm their result, and suggest that, perhaps, the use of a classical electromagnetic field by El Boustani et al. was not justified.Comment: 10 pages. Title changed. Minor modifications, including a better justification of eq.(8

Dynamic spin response of a strongly interacting Fermi gas

We present an experimental investigation of the dynamic spin response of a strongly interacting Fermi gas using Bragg spectroscopy. By varying the detuning of the Bragg lasers, we show that it is possible to measure the response in the spin and density channels separately. At low Bragg energies, the spin response is suppressed due to pairing, whereas the density response is enhanced. These experiments provide the first independent measurements of the spin-parallel and spin-antiparallel dynamic and static structure factors and open the way to a complete study of the structure factors at any momentum. At high momentum the spin-antiparallel dynamic structure factor displays a universal high frequency tail, proportional to $\omega^{-5/2}$, where $\hbar \omega$ is the probe energy.Comment: Replaced with final versio

Mesoscopic Transport: The Electron-Gas Sum Rules in a Driven Quantum Point Contact

The nature of the electron gas is characterized, above all, by its multi-particle correlations. The conserving sum rules for the electron gas have been thoroughly studied for many years, and their centrality to the physics of metallic conduction is widely understood (at least in the many-body community). We review the role of the conserving sum rules in mesoscopic transport, as normative criteria for assessing the conserving status of mesoscopic models. In themselves, the sum rules are specific enough to rule out any such theory if it fails to respect the conservation laws. Of greater interest is the capacity of the compressibility sum rule, in particular, to reveal unexpected fluctuation effects in nonuniform mesoscopic structures.Comment: TeX, 11pp, no fi

Wavevector analysis of the jellium exchange-correlation surface energy in the random-phase approximation: detailed support for nonempirical density functionals

We report the first three-dimensional wavevector analysis of the jellium exchange-correlation (xc) surface energy in the random-phase approximation (RPA). The RPA accurately describes long-range xc effects which are challenging for semi-local approximations, since it includes the universal small-wavevector behavior derived by Langreth and Perdew. We use these rigorous RPA calculations for jellium slabs to test RPA versions of nonempirical semi-local density-functional approximations for the xc energy. The local spin density approximation (LSDA) displays cancelling errors in the small and intermediate wavevector regions. The PBE GGA improves the analysis for intermediate wavevectors, but remains too low for small wavevectors (implying too-low jellium xc surface energies). The nonempirical meta-generalized gradient approximation of Tao, Perdew, Staroverov, and Scuseria (TPSS meta-GGA) gives a realistic wavevector analysis, even for small wavevectors or long-range effects. We also study the effects of slab thickness and of short-range corrections to RPA.Comment: 7 pages, 7 figures, to appear in Phys. Rev.

Zero temperature optical conductivity of ultra-clean Fermi liquids and superconductors

We calculate the low-frequency optical conductivity sigma(w) of clean metals and superconductors at zero temperature neglecting the effects of impurities and phonons. In general, the frequency and temperature dependences of sigma have very little in common. For small Fermi surfaces in three dimensions (but not in 2D) we find for example that Re sigma(w>0)=const. for low w which corresponds to a scattering rate Gamma proportional to w^2 even in the absence of Umklapp scattering when there is no T^2 contribution to Gamma. In the main part of the paper we discuss in detail the optical conductivity of d-wave superconductors in 2D where Re sigma(w>0) \propto w^4 for the smallest frequencies and the Umklapp processes typically set in smoothly above a finite threshold w_0 smaller than twice the maximal gap Delta. In cases where the nodes are located at (pi/2, pi/2), such that direct Umklapp scattering among them is possible, one obtains Re sigma(w) \propto w^2.Comment: 7 pages, 3 figure