In cuprate superconductors, the charge order phase has been widely identified in the temperature region above the superconducting phase in their phase diagram. The elucidation of the interplay between the charge order and the superconductivity is anticipated to provide important insights into the understanding of high-T_c superconductivity. A representative example is the charge/spin stripe order that has been found in La-based cuprates, where charges and spins are aligned in a form of stripes in CuO₂ plane. The stripes are considered as competing order with the superconductivity. In fact, the initial studies of the light-induced superconductivity have been performed in the stripe phase of La_2−x−yEu_ySr_xCuO₄ (LESCO) [1] and La_2−xBa_xCuO₄ (LBCO) [2]. The phenomena have been understood primarily because of light-induced suppression of the stripe order which leads to the revival of initially prohibited c-axis interlayer Josephson couplings in equilibrium due to the geometric character of stripe orders between the adjacent CuO₂ planes. Yet, the nature of the interplay between the charge order and the superconductivity has remained to be resolved to date. In this work, we performed comprehensive studies of light-induced superconductivity in another representative stripe-ordered cuprate system, La_2-x-yNd_ySr_xCuO₄, by optical pump and terahertz (THz) probe spectroscopy. We found that the plasma edge appears in the c-axis THz reflectivity spectrum after the photo-excitation far above T_c up to around the onset temperature of the charge order, whereas the 1/ω-divergence of the imaginary part optical conductivity was absent in all the investigated doping samples [3]. Based on the experimental results, we discuss the interplay between the charge order and the superconductivity in La-based cuprates.

[1]D. Fausti, R. I. Tobey, N. Dean, S. Kaiser, A. Dienst, M. C. Hoffmann, S. Pyon, T. Takayama, H. Takagi, and A. Cavalleri, Science 331, 189 (2011).

[2] D. Nicoletti, E. Casandruc, Y. Laplace, V. Khanna, C. R. Hunt, S. Kaiser, S. S. Dhesi, G. D. Gu, J. P. Hill, and A. Cavalleri, Phys. Rev. B 90, 100503(R) (2014).

[3] M. Nishida, K. Katsumi , D. Song , H. Eisaki, and R. Shimano,Phys. Rev. B 107, 174523 (2023).