Momentum-resolved coherent phonon oscillations in cuprate superconductors.

Using time- and angle-resolved photoemission spectroscopy, we resolve coherent phonon modes on a cuprate superconductor Bi2212. Upon optical excitation, the electronic band dispersion near the node oscillates with a dominant mode at 3.94 THz. The amplitude of this mode weakly increases as a function of momentum away from the node. Comparing with phonon frequencies extracted from Raman spectroscopy and electron energy loss spectroscopy, we identify these coherent modes as A1g phonons involving the motion of Cu-O planes. Our study provides a new route to characterize the momentum-resolved electron-phonon coupling strength, which is essential to disentangle the competing interactions in cuprate superconductors.