Papers by Frank Marsiglio
Physical Review B, 2002
Inelastic neutron scattering profiles of spin waves in the dilute quasi-onedimensional Ising-like... more Inelastic neutron scattering profiles of spin waves in the dilute quasi-onedimensional Ising-like antiferromagnet CsCo 0.83 Mg 0.17 Br 3 have been investigated. Calculations of S xx (Q, ω), based on an effective spin Hamiltonian, *
Australian Journal of Physics, 1997
Australian Journal of Physics, 1997
We compute the single-particle inverse lifetime, along with the conductivityderived scattering ra... more We compute the single-particle inverse lifetime, along with the conductivityderived scattering rate, for a metallic system in an s-wave superconducting state. When both electron-phonon and electron-impurity scattering are included, we find that while these scattering rates are in qualitative agreement, in general quantitative agreement is lacking. We also derive results for the quasiparticle lifetime within the BCS framework with impurity scattering, which makes it clear that impurity scattering is suppressed for electrons near the Fermi surface in the superconducting state.
We test the canonical BCS wave functions for fixed number of electrons for the attractive Hubbard... more We test the canonical BCS wave functions for fixed number of electrons for the attractive Hubbard model. We present results in one dimension for various chain lengths, electron densities, and coupling strengths. The ground-state energy and energy gap to the first excited state are compared with the exact solutions obtained by the Bethe ansatz as well as with the results from the conventional grand-canonical BCS approximations. While the canonical and grand-canonical BCS results are both in very good agreement with the exact results for the ground state energies, improvements due to conserving the electron number in finite systems are manifest in the energy gap. As the system size is increased, the canonical results converge to the grand-canonical ones. The "parity" effect that arises from the number parity (even or odd) of electrons are studied with our canonical scheme.
Electron-Phonon Superconductivity
Superconductivity, 2008
Refractometric sensitivity and thermal stabilization of fluorescent core microcapillary sensors: theory and experiment
Applied Optics, 2015
ABSTRACT Fluorescent-core microcapillaries (FCMs) present a robust basis for the application of o... more ABSTRACT Fluorescent-core microcapillaries (FCMs) present a robust basis for the application of optical whispering gallery modes toward refractometric sensing. An important question concerns whether these devices can be rendered insensitive to local temperature fluctuations, which may otherwise limit their refractometric detection limits, mainly as a result of thermorefractive effects. Here, we first use a standard cylindrical cavity formalism to develop the refractometric and thermally limited detection limits for the FCM structure. We then measure the thermal response of a real device with different analytes in the channel and compare the result to the theory. Good stability against temperature fluctuations was obtained for an ethanol solvent, with a near-zero observed thermal shift for the transverse magnetic modes. Similarly good results could in principle be obtained for any other solvent (e.g., water), if the thickness of the fluorescent layer can be sufficiently well controlled.
Gap function and density of states in the strong-coupling limit for an electron-boson system
Physical review. B, Condensed matter, 1991
ABSTRACT
Asymptotic limits for the penetration depth of strong-coupling superconductors
Physical review. B, Condensed matter, 1990
ABSTRACT
Dependence of some electromagnetic properties of superconductors on coupling strength
Physical review. B, Condensed matter, 1990
ABSTRACT
Asymptotic limit for Hc2 in Eliashberg theory
Physical review. B, Condensed matter, 1990
ABSTRACT
Dependence of the second upper critical field on coupling strength
Physical review. B, Condensed matter, 1990
We have calculated the second upper critical magnetic field Hc2(T) in the clean and dirty limit f... more We have calculated the second upper critical magnetic field Hc2(T) in the clean and dirty limit for a number of known strong-coupling superconductors based on tunneling-derived kernels. The microscopic theory is used to derive a simple semiphenomenological analytic form for the strong-coupling corrections that involve the single parameter Tc/omegaln, namely the ratio of critical temperature (Tc) to characteristic phonon energy
Eliashberg treatment of the microwave conductivity of niobium
Physical review. B, Condensed matter, 1994
ABSTRACT
Signatures of the electron-phonon interaction in the far-infrared
Physical review. B, Condensed matter, 1995
Motivated by a recent optical experiment on Ba1-xKxBiO3, we calculate the far-infrared conductivi... more Motivated by a recent optical experiment on Ba1-xKxBiO3, we calculate the far-infrared conductivity in the normal and superconducting states of an electron-phonon driven superconductor, and note the signatures of the electron-phonon interaction. We find that two methods in particular are effective ways to determine the electron-phonon coupling strength, both of which are applicable in the normal state. One relies on a sum rule, and requires independent knowledge of the plasma frequency, the other relies on the Drude-like width, and was used by Puchkov et al. in their infrared measurements. We note quantitative corrections to this latter method. However, we support their conclusion that the electron-phonon interaction in Ba1-xKxBiO3 is too weak to account for superconductivity. A third method relies on observing shifts of structure in the superconducting state. However, we find that for systems with intermediate-coupling strength, such structure can be very difficult to detect, especially if the system is moderately dirty.
Penetration of a magnetic field in a very strong coupling superconductor
Physical review. B, Condensed matter, 1988
We have calculated the absolute value and temperature dependence of the London penetration depth ... more We have calculated the absolute value and temperature dependence of the London penetration depth for several values of the strong-coupling index Tc/wln and find large characteristic differences between the weak coupling Tc/wln~0, conventional strong coupling Tc/wln<~0.25, and very strong coupling Tc/wln~1 regimes. Our results do not depend sensitively on the value of Coulomb pseudopotential, nor on the shape of the
Tunneling inversion with an excitonic contribution
Physical review. B, Condensed matter, 1989
ABSTRACT
Slope of specific-heat jump at Tc in a very strong-coupling superconductor
Physical review. B, Condensed matter, 1989
We have calculated the normalized slope of the specific heat at the critical temperature Tc as a ... more We have calculated the normalized slope of the specific heat at the critical temperature Tc as a function of coupling strength. As the coupling is increased the slope first increases rapidly from its Bardeen-Cooper-Schrieffer value of 2.63, reaches a maximum and then decreases as we reach the very strong coupling regime. Using a delta-function spectral density, a local maximum is established which must be satisfied by any Eliashberg superconductor. Comparison with a recent experiment indicates a serious violation of this bound which, if confirmed, implies that some important modification of the theory is required.
Asymptotic limit for the thermodynamics of a boson-exchange superconductor
Physical review. B, Condensed matter, 1989
We establish formulas for the free-energy difference (DeltaF) between the superconducting and nor... more We establish formulas for the free-energy difference (DeltaF) between the superconducting and normal states of an Eliashberg superconductor valid in the asymptotic limit lambda-->∞ where lambda is the mass-renormalization parameter. It is shown that (DeltaF) varies as lambdaomega2E times a universal function of the reduced temperature t=T/Tc. Here omegaE is the characteristic energy of the exchanged boson. The universal function is calculated numerically for finite t>0.
Upper bound on strong-coupling corrections to the second upper critical field
Physical review. B, Condensed matter, 1988
ABSTRACT
Thermodynamic and other properties of a high-Tc excitonic superconductor
Physical review. B, Condensed matter, 1987
We have calculated the isotope effect, the thermodynamics and the gap (Delta0) to critical temper... more We have calculated the isotope effect, the thermodynamics and the gap (Delta0) to critical temperature (Tc) ratio for an excitonic superconductor. We consider the possibility that some contribution to the pairing interaction is due to the electron-phonon interaction. As the amount of electron-phonon contribution is increased from zero, the thermodynamic ratios start deviating from Bardeen-Cooper-Schrieffer behavior, but in the opposite direction from conventional strong-coupling superconductors. The isotope effect increases very slowly from zero and 2Delta0/kBTc remains close to 3.54 for a significant range of phonon coupling strength.
Physical review. B, Condensed matter, 1987
Uploads
Papers by Frank Marsiglio