Measuring particle-hole asymmetry in Bi2212 with time-resolved spectroscopy \newline*

One of the central questions in high-temperature superconductivity is the nature of the pseudogap state and its relation to superconductivity. Competing explanations of the pseudogap raise basic questions about its structure. The superconducting gap is known to have particle-hole symmetry, but it is not yet known whether the pseudogap shares this property. Here, we introduce a sensitive way to measure particle-hole symmetry in high-temperature superconductor Bi2212 by pumping it with laser pulses and measuring the ultrafast response of the chemical potential. By comparing samples with different doping, we discover new clues into the structure of the pseudogap.