TY - JOUR
T1 - Infrared Activation of the Higgs Mode by Supercurrent Injection in Superconducting NbN
AU - Nakamura, Sachiko
AU - Iida, Yudai
AU - Murotani, Yuta
AU - Matsunaga, Ryusuke
AU - Terai, Hirotaka
AU - Shimano, Ryo
N1 - Publisher Copyright:
© 2019 American Physical Society.
PY - 2019/6/25
Y1 - 2019/6/25
N2 - The Higgs mode in superconductors, i.e., the collective amplitude mode of the order parameter, does not associate with charge nor spin fluctuations, therefore it does not couple to the electromagnetic field in the linear response regime. Contrary to this common understanding, here, we demonstrate that if the dc supercurrent is introduced into the superconductor, the Higgs mode becomes infrared active and is directly observed in the linear optical conductivity measurement. We observed a sharp resonant peak at ω=2Δ in the optical conductivity spectrum of a thin-film NbN in the presence of dc supercurrent, showing a reasonable agreement with the recent theoretical prediction. The method as proven by this work opens a new pathway to study the Higgs mode in a wide variety of superconductors.
AB - The Higgs mode in superconductors, i.e., the collective amplitude mode of the order parameter, does not associate with charge nor spin fluctuations, therefore it does not couple to the electromagnetic field in the linear response regime. Contrary to this common understanding, here, we demonstrate that if the dc supercurrent is introduced into the superconductor, the Higgs mode becomes infrared active and is directly observed in the linear optical conductivity measurement. We observed a sharp resonant peak at ω=2Δ in the optical conductivity spectrum of a thin-film NbN in the presence of dc supercurrent, showing a reasonable agreement with the recent theoretical prediction. The method as proven by this work opens a new pathway to study the Higgs mode in a wide variety of superconductors.
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U2 - 10.1103/PhysRevLett.122.257001
DO - 10.1103/PhysRevLett.122.257001
M3 - Article
C2 - 31347872
AN - SCOPUS:85068596508
SN - 0031-9007
VL - 122
JO - Physical review letters
JF - Physical review letters
IS - 25
M1 - 257001
ER -