Localized bosonic modes in superconductors

Abstract

We show that a localized bosonic mode acts as a new type of "defect" in s-and d x 2 −y 2 -wave superconductors. The mode induces bound or resonance states, whose spectral signature are peaks in the superconductor's density of states (DOS). We study the peaks' shape and energy as a function of temperature and the mode's frequency and lifetime. We identify several characteristic signatures of the localized mode that qualitatively distinguishes its effects from those of magnetic or nonmagnetic impurities.PACS numbers: 72.10. 72.10.Fk, 74.25.Jb The study of local defects or impurities in superconductors has attracted significant experimental [1, 2] and theoretical [3,4,5] interest over the last few years. These studies have proven particularly important for further elucidating the nature of the superconducting (SC) pairing mechanism in unconventional superconductors. In particular, recent scanning tunnelling microscopy (STM) experiments provided a detailed picture of the frequency and spatial dependence of defect induced resonance states in the high-temperature superconductor (HTSC) Bi 2 Sr 2 CaCu 2 O 8+δ [2], and the triplet superconductor Sr 2 RuO 4 [6]. Several theoretical scenarios for the physical origin of these impurity states have been proposed, ranging from electronic scattering off classical impurities [3,5] to the onset of .

Impurity-induced states in conventional and unconventional superconductors

“…For more detailed analysis see (Morr and Nyberg, 2003). The proposed extension of the inelastic tunneling spectroscopy on the strongly correlated electrons states, such as a d-wave superconductor and pseudogap normal state would open up possibilities to study the dynamics of local spin and vibrational excitations.…”

Inelastic magnetic scattering effect on local density of states of topological insulators

“…If we neglect the warping term in the Dirac Hamiltonian and denote k by its polar coordinates (k,φ), then in Eqs. (15) and (13) G 0 (k,ω) and G 0 (k ,ω) depend only on the moduli, andŨ t (φ,φ ,ω) depends only on the angles of the wave vectors. Then the summation in these equations may be done separately for the Green's functions and the T matrix.…”

Role of Inelastic Tunneling through the Insulating Barrier in Scanning-Tunneling-Microscope Experiments on Cuprate Superconductors

“…In our model, unlike those of Refs. [9,10,11,12], such an explanation does not apply. However it is known empirically that the positions of the apical O-ions influences the transition temperature T c of BSSCO superconductors [26] and more generally that materials with longer Cu-apical O bonds have higher values of T c [27].…”

“…Lee et al [1] report further that isotope substitution on the O-ions shifts this energy consistent with a phonon origin for this peak. This raises the question whether these spectra should be interpreted analogously to those of conventional superconductors or if these peaks have another source.A series of works explain the appearence of side peaks in the DOS of d-wave superconductors in terms of localized bosonic modes [9], resonant spin modes [10,11] or the breathing mode phonons [12]. All these proposals consider inelastic processes that happen directly in the superconducting plane.…”

“…A series of works explain the appearence of side peaks in the DOS of d-wave superconductors in terms of localized bosonic modes [9], resonant spin modes [10,11] or the breathing mode phonons [12]. All these proposals consider inelastic processes that happen directly in the superconducting plane.…”