Friday, May 3, 2013

1305.0381 (Ryusuke Matsunaga et al.)

The Higgs Amplitude Mode in BCS Superconductors Nb_{1-x}Ti_{x}N induced
by Terahertz Pulse Excitation

Ryusuke Matsunaga, Yuki I. Hamada, Kazumasa Makise, Yoshinori Uzawa, Hirotaka Terai, Zhen Wang, Ryo Shimano
We observed the collective amplitude mode of the BCS order parameter, namely the Higgs amplitude mode, in superconducting Nb1-xTixN films by using terahertz (THz) pump-THz probe spectroscopy. After a nonadiabatic excitation with the monocycle THz pump pulse, the transient oscillation of the order parameter emerges in the electromagnetic response in the BCS gap energy region. The oscillation frequency coincides with the asymptotic value of the BCS gap energy, showing an excellent agreement with the theoretical prediction. Our result opens a new pathway to the ultrafast manipulation of the superconducting order parameter by optical means.
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