Ultrafast probing of collective mode of the charge order in La_1.875Ba_0.125CuO₄

The phase diagram of cuprate superconductors exhibits a plethora of intertwined orders, such as pseudogap, charge order and pair density wave. In particular, many cuprate families display a charge order near the 1/8 doping that coexist with superconductivity. Recent scattering studies have demonstrated that suppressing the superconductivity can increase the strength of coexisting charge order. However, little is known about the collective modes of the charge order and its interaction with other phases. Here, we perform time resolved transient reflectivity measurements on La_1.875Ba_0.125CuO₄ (LBCO) and La_1.885Ba_0.115CuO₄ (LBCO). We find a short-lived oscillatory signal, which turns on near the charge ordering temperature consistent with the amplitude mode of the charge order. We will comment on the implications of these measurements on the coupling between two dimensional superconductivity and stripe phase in LBCO.