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

Abstract

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.

Light-induced enhancement of superconductivity in iron-based superconductor FeSe0.5Te0.5

“…41 ). The experimental scheme has been extended to d-wave cuprate superconductors 42,43 and multiband superconductors 44,45 . Here we investigated THz-THG in FeSe 0.5 Te 0.5 to extract the dynamics of the superconducting order parameter upon the photoexcitation.…”

Visualization and quantum control of light-accelerated condensates by terahertz multi-dimensional coherent spectroscopy

“…We recently showed that purely electronic processes in iron-based superconductors with strong interband Coulomb coupling lead to a controllable hybrid-Higgs collective mode. This mode was observed as THz four-wave-mixing signal coherent oscillations, whose field and temperature dependences are clearly distinguished from those observed in single-band or weakly-coupled multi-band superconductors 21 .…”

“…superconducting states requires quantum sensing of their collective modes and underlying order parameters. Such characterization is challenging with ultrafast PP THz spectroscopy [20][21][22][23] . First, the collective excitations of superconducting states couple linearly to electromagnetic fields only in the presence of a finite Cooper-pair center-of-mass momentum p S .…”

“…Higgs-mode excitation thus competes with the excitation of quasi-particles. Depending on the strength of electronphonon, electron-impurity, or interband Coulomb coupling in multi-band superconductors, either the Higgs-mode or the quasiparticle excitation process dominates the third-order nonlinear response 21,[28][29][30] .…”

Add a Pinch of Tetrel: The Transformation of a Centrosymmetric Metal into a Nonsymmorphic and Chiral Semiconductor

“…Symmetry-driven physical phenomena, such as second harmonic generation and topological non-trivial properties are only a sliver of the applications for new NCS materials. [1][2][3][4][5][6][7][8][9] Ternary silicon phosphides, such as Ba 2 Si 3 P 6 , MnSiP 2 , and RuSi 4 P 4 have shown promising nonlinear optical properties, [10][11][12][13][14] and have prompted the investigation of other metal tetrel pnictides. [15] Generally, NCS structures are rare in intermetallics (< 10 %) but are much more prevalent (up to 95 %) among transition metal silicon phosphides where M/(Si + P) < 1.…”