Phase-resolved Higgs response in superconducting cuprates

Abstract

In high-energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be inferred from the decay product of the Higgs boson, i.e., the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a close analogy to the Higgs field. Interaction between the Cooper pairs and other degrees of freedom provides dissipation channels for the amplitude mode, which may reveal important information about the microscopic pairing mechanism. To this end, we investigate the Higgs (amplitude) mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG). In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above T c. These findings indicate coupling of the Higgs mode to other collective modes and potentially a nonzero pairing amplitude above T c .

Higgs-mode resonance in third harmonic generation in NbN superconductors: Multiband electron-phonon coupling, impurity scattering, and polarization-angle dependence

“…Interesting future applications include the THG resonance in MgB 2 , a multigap superconductor with multiple Higgs modes as well as the Leggett mode [54][55][56][57], and NbSe 2 , where superconductivity and charge density wave coexist. For unconventional superconductors such as cuprates [58][59][60][61][62][63] and iron-based superconductors, we need to extend the present formalism to take into account strong correlation effects beyond the BCS approximation in THG, which we leave as a future problem.…”

Geometry of variational methods: dynamics of closed quantum systems

“…We will see that this decomposition coincides exactly with the one of K µ ν in (128). To do this, we use the fact that a Kähler manifold of dimension 2n always admits 18 a parametrization…”

“…While the use of time-dependent variational methods is not so widespread as those for thermal equilibrium, the first have experienced a renewed interest thanks to the recent experimental progress in taming and studying the dynamics of many-body quantum systems in diverse setups. They include cold atoms in bulk or in optical lattices [11], trapped ions [12,13], boson-fermion mixtures [14], quantum impurity problems [15] and pump and probe experiments in condensed matter systems [16][17][18]. Recently, such methods have been used in the context of matrix product states to analyze a variety of phenomena, or with Gaussian states in the study of impurity problems [19,20], Holstein models [21], or Rydberg states in cold atomic systems [22,23].…”

Momentum-resolved analysis of condensate dynamic and Higgs oscillations in quenched superconductors with time-resolved ARPES

“…The first direct observation was performed in a THz pump-probe experiment on the s-wave superconductor Nb 1−x Ti x N [15], where Higgs oscillations of the order parameter, reflected in oscillations of the electromagnetic response, could be observed. Since then, only a few more experiments were reported [16][17][18][19][20], but theoretical works on the subject became more popular as it became clear that Higgs oscillations in nonequilibrium systems provide rich information about the superconducting ground state.…”

“…Excited in an asymmetric way, nontrivial gap symmetries can show additional oscillation frequencies as a result of an oscillation of the condensate in a different symmetry channel [28]. Finally, composite order parameters [29], excitations of subleading pairing channels [30] as well as coupling to other coexisting modes [20] might show up as additional frequencies.…”