Signature of charge density wave excitations in Bi2212 via ultrahigh resolution RIXS*

Low energy excitations in heavily underdoped Bi$_2$Sr$_2$CaCu$_2$O$_8$ crystals were investigated using resonant inelastic soft x-ray scattering (RIXS) measurement at the Cu L3-edge with an ultrahigh energy resolution of 40 meV. In the quasi-elastic region, an incommensurate charge density wave (CDW) with a wavevector of 0.3 reciprocal lattice units are observed, confirming the existence of a CDW in this compound. Importantly, we observe signatures of dispersive CDW excitations that emanate from the CDW wavevector and intersect with bond-stretching phonons, causing an intensity anomaly at a wavevector away from the CDW wavevector. Temperature dependent measurement will also be discussed.