Amplitude Mode in a Multigap Superconductor MgB2 Investigated by Terahertz Two-Dimensional Coherent Spectroscopy
Kota Katsumi, Jiahao Liang, Ralph Romero, III, Ke Chen, Xiaoxing Xi, N. P. Armitage
DOI 10.1103/g5rp-6vb1 · Physical Review Letters
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Abstract
We have investigated the terahertz (THz) nonlinear response of the multigap superconductor MgB2, using THz two-dimensional coherent spectroscopy (THz 2DCS). With broadband THz drive fields, we identified a nonlinear response at twice the lower superconducting gap energy 2Δπ at the lowest temperatures. Using narrow-band THz driving pulses, we observed first (FH) and third harmonic responses. The FH intensity shows a monotonic increase with decreasing temperature when properly normalized by the driving field strength. This is distinct from the single-gap superconductor NbN, where the FH signal exhibited a resonant enhancement at temperatures when twice the gap energy 2Δ was resonant with the driving photon energy, which was interpreted to originate from the superconducting amplitude mode. Our results in MgB2 are consistent with a well-defined amplitude mode only at the lowest temperatures and indicate strong damping as temperature increases. This likely indicates the importance of interband coupling in MgB2 and its influence on the nature of the amplitude mode and its damping.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 38 | Pressure not reported | unknown |
| NbN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
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