Detection of collective modes in unconventional superconductors using tunneling spectroscopy

Abstract

We propose using tunneling spectroscopy with a superconducting electrode to probe the collective modes of unconventional superconductors. The modes are predicted to appear as peaks in dI/dV at voltages given by eV = ωi/2 where ωi denotes the mode frequencies. This may prove to be a powerful tool to investigate the pairing symmetry of unconventional superconductors. The peaks associated with the collective modes appear at fourth order in the single particle tunneling matrix element. At the same fourth order, multiple Andreev reflection (MAR) leads to peaks at voltage equal to the energy gaps, which, in BCS superconductors, coincides with the expected position of the amplitude (Higgs) mode. The peaks stemming from the collective modes of unconventional superconductors do not suffer from this coincidence. For scanning tunneling microscopes (STM), we estimate that the magnitude of the collective mode contribution is smaller than the MAR contribution by the ratio of the energy gap to the Fermi energy. Moreover, there is no access to the mode dispersion. Conversely, for planar tunnel junctions the collective mode peak is expected to dominate over the MAR peak, and the mode dispersion can be measured. We discuss systems where the search for such collective modes is promising.

Post-peer review version of the article

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Cited by in corpus (6)

• Evidence of a distinct collective mode in Kagome superconductors
• Linear spectroscopy of collective modes and the gap structure in two-dimensional superconductors
• Spatially-resolved dynamics of the amplitude Schmid-Higgs mode in disordered superconductors
• Quantum Fluctuations and Multifractally-Enhanced Superconductivity in Disordered Thin Films
• Signatures of superconducting Higgs mode in irradiated Josephson junctions
• AC Josephson Signatures of the Superconducting Higgs Mode