Studies of quantum matter driven out-of-equilibrium by light irradiation have gained growing interest over decades. In particular, with the recent advance of coherent and intense terahertz (THz) light sources, it has become possible to drive the system into a prethermalized nonequilibrium state with avoiding the heating effect. The perspectives of these studies are the elucidation of hidden phases, controlling the competing phases, excitation of collective modes, the manipulation of Chern numbers in topological materials by light, etc. For instance, it has been shown that the amplitude oscillation of superconducting order parameter, termed as the Higgs mode from its analogy to the Higgs boson in particle physics, is induced by quantum quench  or coherent driving  of the order parameter by THz pulses. A new functionality of quantum matter is expected to emerge under the strong AC field driving. In this project, we are offering experiments on the THz field induced phenomena in unconventional superconductors aiming at the observation of new collective modes and the optical manipulation of superconductivity.
 "Higgs Amplitude Mode in the BCS Superconductors Nb1-xTixN induced by Terahertz Pulse Excitation", R. Matsunaga, Y. I. Hamada, K. Makise, Y. Uzawa, H. Terai, Z. Wang, and R. Shimano,
Phys. Rev. Lett. 111, 057002 (2013).
 "Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor"
R. Matsunaga, N. Tsuji, H. Fujita, A. Sugioka, K. Makise, Y. Uzawa, H. Terai, Z. Wang, H. Aoki, and R. Shimano, Science 345, 1145 (2014).