Microwave investigation of Higgs Mode in a superconducting wires.

Higgs mode in superconductors is an analogous of the Higgs boson in high energy physics that has been predicted by Anderson in the late 50s [1]. Its detection is usually difficult because of its weak coupling with electromagnetic fields. However, a recent theory predicted a huge increase of this coupling in the presence of a DC current, which translates into an anomaly in the complex conductivity at frequencies of the order of 2Δ [2].

Observation of Higgs modes in superconductors have been performed in the THz

range [3]. A study in the microwave range could enable new measurement such as non-local conductivity to probe its propagation.

We studied Titanium samples for which 2Δ is of the order of 10-30 GHz and we studied different samples corresponding to different limits of superconductivity.

In this experiment we present a precise and quantitative measurement of the high frequency complex impedance of a

superconducting wire in the microwave range. In the absence of DC current, we compare our results with Mattis Bardeen theory at equilibrium. With current we observe a feature at frequency 2Δ which behaves as predicted in [2] with a width much larger than expected.

Furthermore, in the spirit of integrating Higgs mode in electronic circuit, we designed an experiment where a measurement in tranmission is made; the Higgs mode is propagated/stopped when the current is turned on/off.

[1] Anderson PW. 1958. Phys. Rev. 112:1900–16

[2] A. Moor and al., Amplitude Higgs Mode and Admittance in Superconductors with

a Moving Condensate, PRL 118, 047001 (2017)).

[3] Matsunaga R, Hamada YI, Makise K, Uzawa Y, Terai H, et al. 2013. Phys. Rev. Lett. 111:057002