Light quantum control of persisting Higgs modes in iron-based superconductors

• Published in: Nature communications Vol. 12; no. 1; p. 258
• Main Authors: Vaswani, C., Kang, J. H., Mootz, M., Luo, L., Yang, X., Sundahl, C., Cheng, D., Huang, C., Kim, R. H. J., Liu, Z., Collantes, Y. G., Hellstrom, E. E., Perakis, I. E., Eom, C. B., Wang, J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11.01.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/1003; 639/766/400/561; 639/766/400/584; Amplitudes; Antimatter; Broken symmetry; Charge density; Coherence; Complex systems; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Dark energy; Equilibrium; High temperature; Humanities and Social Sciences; Hybridization; Iron; Laboratories; Lasers; Magnetism; multidisciplinary; Order parameters; Quantum entanglement; Quantum mechanics; Science; Science (multidisciplinary); Spectroscopy; Spectrum allocation; Spectrum analysis; superconducting properties and materials; Superconductivity; terahertz optics; ultrafast photonics; Unconventional superconductors
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-20350-6

The Higgs mechanism, i.e., spontaneous symmetry breaking of the quantum vacuum, is a cross-disciplinary principle, universal for understanding dark energy, antimatter and quantum materials, from superconductivity to magnetism. Unlike one-band superconductors (SCs), a conceptually distinct Higgs amplitude mode can arise in multi-band, unconventional superconductors  via strong interband Coulomb interaction, but is yet to be accessed. Here we discover such hybrid Higgs mode and demonstrate its quantum control by light in iron-based high-temperature SCs. Using terahertz (THz) two-pulse coherent spectroscopy, we observe a tunable amplitude mode coherent oscillation of the complex order parameter from coupled lower and upper bands. The nonlinear dependence of the hybrid Higgs mode on the THz driving fields is distinct from any known SC results: we observe a large reversible modulation of resonance strength, yet with a persisting mode frequency. Together with quantum kinetic modeling of a hybrid Higgs mechanism, distinct from charge-density fluctuations and without invoking phonons or disorder, our result provides compelling evidence for a light-controlled coupling between the electron and hole amplitude modes assisted by strong interband quantum entanglement. Such light-control of Higgs hybridization can be extended to probe many-body entanglement and hidden symmetries in other complex systems. A collective excitation called Higgs mode may arise in multi-band superconductors via strong interband interaction, but it is yet to be accessed. Here, the authors observe a tunable coherent amplitude oscillation of the order parameter in Ba(Fe 1− x Co x ) 2 As 2 , suggesting appearance and control of the Higgs mode by light tuning interband interaction.