Models for enhanced absorption in inhomogeneous superconductors

Barabash, S. V.; Stroud, D.

doi:10.1103/physrevb.67.144506

Cited by 16 publications

(9 citation statements)

References 21 publications

(26 reference statements)

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“…This appears to be a manifestation of a more general tendency where disorder allows optical absorption by 'forbidden' collective modes. Similar phenomena have been observed 117 along the ab-planes of the cuprates in the THz regime and explained with a model of a planar disordered array of Josephson junctions 118 .…”

Section: Transverse Optical Plasmon and Bi-layer Splitting In Hisupporting

confidence: 73%

Optical Spectroscopy of Plasmons and Excitons in Cuprate Superconductors

Marel

2004

J Supercond

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An introduction is given to collective modes in layered, high Tc superconductors. An experimental demonstration is treated of the mechanism proposed by Anderson whereby photons travelling inside the superconductor become massive, when the U(1) gauge symmetry is broken in the superconductor to which the photons are coupled. Using the Ferrell-Tinkham sumrule the photon mass is shown to have a simple relation to the spectral weight of the condensate. Various forms of Josephson plasmons can exist in single-layer, and bi-layer cuprates. In the bi-layer cuprates a transverse optical plasma mode can be observed as a peak in the c-axis optical conductivity. This mode appears as a consequence of the existence of two different intrinsic Josephson couplings between the CuO2 layers. It is strongly related to a collective oscillation corresponding to small fluctuations of the relative phases of the two condensates, which has been predicted in 1966 by A.J. Leggett for superconductors with two bands of charge carriers. A description is given of optical data of the high Tc cuprates demonstrating the presence of these and similar collective modes. Superconductivity Electroweak symmetry breakingSpontaneous symmetry breaking of the pairing order parameter, ¡.Spontaneous symmetry breaking of the Higgs field, ¢. Amplitudon Higgs particleThe Goldstone mode of the phase of the order parameter has a gapless sound-dispersionThe electromagnetic field, Aµ, has a gapless sound-like dispersion.The W +/− and Z gauge fields have a gapless sound-like dispersion.Coupling between the order-parameter and the EM-field: (∂µ+iqAµ)ψCoupling between the Higgs-field and the W +/− ,Z fields: (2∂µ+igτ⋅Wµ+ig'BµY)ΦThe coupling makes the gauge particles massive Massive photons Massive W +/− ,Z particles

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Section: Transverse Optical Plasmon and Bi-layer Splitting In Hisupporting

confidence: 73%

Optical Spectroscopy of Plasmons and Excitons in Cuprate Superconductors

Marel

2004

J Supercond

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“…In particular, in [24,25,26] even the values of the coupling constants for the system of equations (22) for the two-gap and two-band model of MgB 2 were given.…”

Section: Implications For Mgb2mentioning

confidence: 99%

Effective action approach to the Leggett's mode in two-band superconductors

2002

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We investigate a collective excitation (Leggett's mode) corresponding to small fluctuations of the relative phase of two condensates in two-band superconductor using the effective "phase only" action. We consider the possibility of observing Leggett's mode in MgB2 superconductor and conclude that for the known at present values of the two-band model parameters for MgB2 Leggett's mode arises above the two-particle threshold.

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“…In principle, both collective modes and quasiparticle excitations may contribute. It has been pointed out that, in systems with a spatial modulation of the superfluid density, one may find absorptions far below 2∆ [14,20,21]. Cea et al give a similar scenario where the spectral weight may be exhibited at finite frequency [22].…”

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confidence: 98%

Anomalous gap-edge dissipation in disordered superconductors on the brink of localization

Cheng

Laurita

et al. 2016

Phys. Rev. B

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Superconductivity in disordered systems close to an incipient localization transition has been an area of investigation for many years. It has been noted that in such highly disordered superconductors, anomalous spectral weight develops in their conductivity near and below the superconducting gap energy. In this work we investigate the low frequency conductivity in disordered superconducting NbN thin films close to the localization transition with time-domain terahertz spectroscopy. In the normal state, strong deviations from the Drude form due to incipient localization are found. In the superconducting state we find substantial spectral weight at frequencies well below the superconducting gap scale derived from tunneling. We analyze this spectral weight in the context of a model of disorder induced broadening of the quasiparticle density of states and effective pair-breaking. We find that although aspects of the optical and tunneling data can be consistently modeled in terms of this effect of mesoscopic disorder, the optical conductivity returns to the normal state value much faster than any model predicts. This points to the non-trivial interplay of superconductivity and disorder close to localization.The manifestation of superconductivity in systems close to a disorder-driven localization transition has been an area of investigation for many years, yet many even central topics are not understood. The electrodynamic response of such systems is a fundamental probe of their low-energy physics but wide-open issues exist here as well. The optical conductivity corresponding to the mean-field Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity was worked out in the context of the celebrated Matthis-Bardeen (MB) theory [1]. A central prediction of the MB theory is the presence of a zero-frequency delta function and a gap 2∆ of a form that depends non-trivially on the BCS coherence factors in the real part of optical conductivity (σ 1 ). This theory works exceptionally well for many superconductors in the "dirty" limit, where the normal state scattering rate (1/τ ) is much larger than the gap, but which are still far from a localization transition [2][3][4]. The MB theory predicts that in the limit of zero temperature, e.g. the gap is clean, there is no spectral weight in σ 1 for frequencies below 2∆. However, it has been noticed for many years that in highly disordered superconductors, for instance in thin-film systems near the superconductor-insulator transition, anomalous spectral weight develops near and below the expected gap edge. This has been observed in many different systems including granular superconductors [5][6][7][8][9], amorphous thin films [10][11][12], and high-temperature superconductors with intrinsic disorder [13,14].In this work we studied the low-frequency conductivity of strongly disordered superconducting NbN thin films close to the localization transition. In the normal state, strong deviations from the Drude form are found, which are indicative of incipient localization in these film...

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Models for enhanced absorption in inhomogeneous superconductors

Cited by 16 publications

References 21 publications

Optical Spectroscopy of Plasmons and Excitons in Cuprate Superconductors

Optical Spectroscopy of Plasmons and Excitons in Cuprate Superconductors

Effective action approach to the Leggett's mode in two-band superconductors

Anomalous gap-edge dissipation in disordered superconductors on the brink of localization

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