Abstract

The excitation spectrum of magnetic insulators is of central concern in condensed matter physics. Nonetheless, many properties of insulating copper oxides remain poorly understood, and the optical gap excitation near 2 eV is an important example. This excitation transfers electrons from oxygen to copper ions within the plane, creating electrons and holes which then interact with surrounding electronic states, with magnetic excitations, with phonons, and with each other. The relative significance of these interactions is not yet clear.

In this talk I will describe our efforts to characterise the photoexcited state of Sr2CuCl2O2, an undoped copper oxide. We create electrons and holes with a femtosecond laser pulse, and then use ultrafast, time-resolved spectroscopic probes to examine the non-equilibrium state as it decays. Measurements with THz pulses give the transient optical conductivity at low energies, from which we estimate the photocarrier contribution to long-range transport, as well as the characteristic energy scale for dynamical conductivity. Broadband measurements of optical transmission in the visible spectrum reveal the photo-production of low-energy bosons, whose energy and decay dynamics are in agreement with the THz measurements.