Evidence for Dissipative Glauber Dynamics in the Charge Ordered Phase of La_1.875Ba_0.125CuO₄ studied with an X-ray Free-Electron Laser

Charge order (CO) is a ubiquitous feature of the phase diagrams of all the cuprate superconductor families that usually anticorrelates with superconductivity (SC). Despite recent studies of the structure of charge-order in the cuprates, little is known about its collective modes. Here, we investigate the collective dynamics of CO in La_1.875Ba_0.125CuO₄. By suddenly quenching the CO peak with an optical pulse and probing it with ultrafast X-rays at the LCLS free-electron laser, we find no evident signatures of coherent collective modes, at variance with other CO systems. Instead, we observe a surprising momentum-dependent relaxation time that implies a purely dissipative Glauber dynamics of CO. Our work suggests that the CO phase is strongly coupled to an incoherent continuum of states implying highly unconventional fluctuation dynamics of CO in cuprate superconductors.