Vertex corrections in nearly ferroelectric superconductors

We calculate the electron-ion potential for a thin metallic layer ͑in the a-b plane͒ sandwiched between two semi-infinite dielectrics. The dielectric constant of the dielectrics varies strongly in the a-b plane. We show that there is an overscreening effect, and the electron-ion interaction is strongly enhanced, for certain values of the parameters. This suggests the possibility of a greatly enhanced electron-phonon coupling in a nearly ferroelectric metal, such as the high-T c perovskites.

Section: Discussionmentioning

confidence: 99%

Electron-ion interaction in a nearly ferroelectric metal

Gersten

Weger

2002

“…From Eqns. (1),(2),(4), (6) and (7) we obtain the equation for the electric field The field equations describe the coupled electromagnetic field, the soft mode NFE oscillator, and the London supercurrent. We now look for a transverse (T) plane-wave solution for E, and recalling that ∇ × ∇ × E = −∇ 2 E for such solutions, we obtain our new result, the dispersion equation for T waves…”

Section: Model and Dispersionmentioning

confidence: 99%

“…The host SrTiO 3 is known to be a "nearly-ferroelectric" material, where the static dielectric constant ε(0) has been measured as ∼ 10 4 in the temperature range where superconductivity occurs [4]. In addition to these two materials, Weger and collaborators have recently proposed that in the high temperature cuprate superconductors, a new multicritical point occurs due to an underlying nearly-ferroelectric instability which renormalizes the electron-phonon and electronelectron interaction and enhances T c [5,6].…”

Section: Introductionmentioning

confidence: 99%

Electrodynamics of nearly ferroelectric superconductors

Birman

Zimbovskaya

2001

We report here the frequency-dependent optical response of a nearly ferroelectric superconductor (NFE-SC), like NaxWO3, or n-SrTiO3. From ω = 0, up to a critical frequency ωc1, Meissner-like field extinction occurs as in a usual superconductor. In the "anomalous" region ωc1 < ω < ωT O (the TO frequency of the NFE) the field propagates as in a dielectric. For ω > ωT O Meissner damping recurrs, then at higher ω, dielectriclike propagation is found. New optical anomalies (peaks in transmission) are predicted for a film of NFE-SC below the soft mode frequency ωT O . These effects are due to including the contribution of the NFE displacement current in the solution of the coupled Maxwell, lattice and London equations. Quantitative calculations are given for the NFE-SC n-SrTiO3 to illustrate this.

“…In very recent work Fay and Weger [60] discuss the renormalization of the electronphonon vertex in media with large dielectric constant near the ferroelectric phase transition.…”

Section: Interaction Terms; Double Mean Field Approximation A) Imentioning

confidence: 99%

Theory of coexistence of superconductivity and ferroelectricity: A dynamical symmetry model

Birman

Weger

2001

We propose and investigate a model for the coexistence of Superconductivity (SC) and Ferroelectricity (FE) based on the dynamical symmetries su(2) for the (pseudo-spin) SC sector , h(4) for the (displaced oscillator) FE sector and su(2) ⊗ h(4) for the composite system. We assume a minimal symmetryallowed coupling ,and simplify the hamiltonian using a double mean-field approximation (DMFA). A variational coherent-state (VCS) trial wave-function is used for the ground state : the energy, and the relevant order parameters for SC and FE are obtained . For positive sign of the SC-FE coupling coefficient, a non-zero value of either order parameter can suppress the other one (FE polarization suppresses SC , and vice versa). This gives some support to "Matthias' Conjecture" [1964] , that SC and FE tend to be mutually exclusive. For such a Ferroelectric Superconductor we predict: a) the SC gap ∆ (and T c ) will increase with increasing applied pressure when pressure 1