High-order nonlinear terahertz probing of the two-band superconductor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">MgB</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>: Third- and fifth-order harmonic generation
C. Reinhoffer, Patrick Pilch, Anneke Reinold, P. Derendorf, Sergey Kovalev, Jan‐Christoph Deinert, I. Ilyakov, A. Ponomaryov, Min Chen, Tiequan Xu, Yue Wang, Zizhao Gan, Desheng Wu, Jianlin Luo, S. Germanskiy, E. A. Mashkovich, P. H. M. van Loosdrecht, I. M. Eremin, Zhe Wang
Abstract
We report on high-order harmonic generation in the two-band superconductor ${\mathrm{MgB}}_{2}$ driven by intense terahertz electromagnetic pulses. Third- and fifth-order harmonics are resolved in time domain and investigated as a function of temperature and in applied magnetic fields crossing the superconducting phase boundary. The high-order harmonics in the superconducting phase reflects nonequilibrium dynamics of the superconducting order parameter in ${\mathrm{MgB}}_{2}$, which is probed via nonlinear coupling to the terahertz field. The observed temperature and field dependence of the nonlinear response allows to establish the superconducting phase diagram.