Direct evidence of light-induced phase-fluctuations in cuprates via time-resolved ARPES

Light perturbation of the superconducting phase of cuprates typically promotes a non-thermal, superconducting-to-normal state phase transition. Although phase fluctuations are widely accepted as playing a primary role in disrupting long-range superconducting order, an experimental probe capable of unambiguously assessing their effect with momentum and time resolutions is still lacking. Here, by combining high-resolution time-resolved and temperature-dependent angle-resolved photoemission studies of optimally-doped Bi 2 Sr 2 CaCu 2 O 8+ δ , we demonstrate a new experimental strategy to directly probe light-induced changes in the order parameter’s phase with momentum resolution. To do so, we track the ultrafast response of a phase-sensitive hybridization gap that appears at the crossing between two bands with opposite superconducting gap signs. Supported by theoretical modeling, we establish phase fluctuations as the dominant factor defining the non-thermal response of the superconducting phase in cuprates, further corroborating the view that the density of phase fluctuations is enhanced by non-electronic, low-energy excitations.