Microwave investigation of Higgs Mode in a superconducting wire

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 can be tuned with the sample thickness. 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 BCS 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.

This experiment is the first step toward the integration of Higgs mode in electronic circuit.​

[1] Phys. Rev. 112,1900 (1958)

[2] PRL 118, 047001 (2017)

[3] PRL 111, 057002 (2013)