Coherent control of nonequilibrium BCS state by intense THz pulse

2014 Fiscal Year Final Research Report

• Project/Area Number: 25800175
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Condensed matter physics I
• Research Institution: The University of Tokyo
• Principal Investigator: MATSUNAGA Ryusuke 東京大学, 理学(系)研究科(研究院), 助教 (50615309)
• Project Period (FY): 2013-04-01 – 2015-03-31
• Keywords: テラヘルツ分光 / ヒッグスモード / 超伝導

Outline of Final Research Achievements

We realized nonadiabatic excitation to an s-wave superconductor NbTiN by using an intense monocycle THz pulse, and reported time-resolved observation of the Higgs mode as a free oscillation of the order parameter amplitude after the nonadiabatic perturbation. This collective mode is a condensed matter analog of the Higgs bosons in particle physics. We also examined the dynamics of the order parameter during the irradiation of the strong THz electric field, and showed that strong sub-gap electric field induces forced oscillation of the order parameter with twice the pump frequency, accompanied by third harmonics generation (THG). We found that the forced oscillation and THG are strongly enhanced when the nonlinear driving frequency is equal to the Higgs mode frequency. This result is the first discovery of the resonance between light and Higgs mode in nonlinear response regime and paves a way for ultrafast control of macroscopic quantum condensates by light.

Free Research Field

光物性