Superconducting fluctuations in small grains - the Universal Hamiltonian and the reduced BCS model
نویسنده
چکیده
Small superconducting grains are discussed in the frameworks of both the reduced BCS Hamiltonian and the Universal Hamiltonian. It is shown that fluctuations of electrons in levels far from the Fermi energy dominate superconducting properties in small and ultrasmall grains. Experimental consequences related to the spin susceptibility and persistent currents of grains and rings with weak electron-electron interactions are discussed.
منابع مشابه
Shape of nanosize superconducting grains: Does it influence pairing characteristics?
The Richardson exact solution for the reduced BCS Hamiltonian is applied to examine how sensitive are the pairing characteristics (condensation energy, spectroscopic gap, parity gap) to a specific configuration of single-electron energy levels in nanosize metallic grains. Using single-electron energy spectra in parallelepiped-shaped potential boxes with various volumes and aspect ratios as a mo...
متن کاملA small superconducting grain in the canonical ensemble
By means of the Lanczos method we analyze superconducting correlations in ultrasmall grains at fixed particle number. We compute the ground state properties and the excitation gap of the pairing Hamiltonian as a function of the level spacing δ. Both quantities turn out to be parity dependent and universal functions of the ratio δ/∆ (∆ is the BCS gap). We then characterize superconductivity in t...
متن کاملBardeen-Cooper-Schrieffer theory of finite-size superconducting metallic grains.
We study finite-size effects in superconducting metallic grains and determine the BCS order parameter and the low energy excitation spectrum in terms of the size and shape of the grain. Our approach combines the BCS self-consistency condition, a semiclassical expansion for the spectral density and interaction matrix elements, and corrections to the BCS mean field. In chaotic grains mesoscopic f...
متن کاملExact study of the effect of level statistics in ultrasmall superconducting grains
The reduced BCS model that is commonly used for ultrasmall superconducting grains has an exact solution worked out long ago by Richardson in the context of nuclear physics. We use it to check the quality of previous treatments of this model, and to investigate the effect of level statistics on pairing correlations. We find that the ground-state energies are on average somewhat lower for systems...
متن کاملCrossover from bulk to few-electron limit in ultrasmall metallic grains
We study the properties of ultrasmall metallic grains with sizes in the range 20–400 electrons. Using a particle-hole version of the density-matrix renormalization-group ~DMRG! method we compute condensation energies, spectroscopic gaps, pairing parameters, and particle-hole probabilities of the ground-state wave function. The results presented in this paper confirm that the bulk superconductin...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2008