Optical Control of Superconductivity
Strong transient laser fields at terahertz frequencies can be used to control the response of high-temperature superconductors on ultrafast time scales. In a series of experiments, we have demonstrated that the superconducting response of high-Tc cuprates and of some alkali-doped fullerides can be transiently enhanced via tailored optical stimulation. In addition to that, resonant excitation of Josephson Plasma modes at longer wavelengths, in the terahertz regime, has turned out to be very effective in driving highly nonlinear dynamics and probing new excitations in layered superconductors.
Phase control in complex oxides
The ground states of strongly correlated electron systems are stabilized by the complex interaction of electronic, magnetic and lattice degrees of freedom. Their nonlinear physics promote a large susceptibility of their macroscopic electronic and magnetic to external perturbations.
The stimulation with light can perturb a stable ground state and induce transient metastable phases - with dramatic rearrangements in the structural, electronic and magnetic properties. These optically driven states are typically ´hidden´ phases, not found in the equilibrium phase diagram. Of particular interest for our group is the selective excitation of one single (vibrational) degree of freedom on low energy scales, in stark contrast to excitation at visible or near-IR wavelengths mostly heating up the electronic systems.