Optical response and Higgs mode excitationin s-wave superconductors using terahertz vortex beam
Hiroya Nagato1, Takeshi Mizushima1, Masahiro Sato2, Satoshi Fujimoto1
1Department of Materials Engineering Physics, Osaka University, Toyonaka, Osaka 560-8531
2Department of Physics, Chiba University, Chiba, Chiba 263-8522

Introduction

Calculation
Higgs mode is the amplitude mode ofthe order parameter . Its excitation
cost is about 2∆. (∆~𝑘! ~10"# Hz)※These calculations
and diagrams show only
the diamagnetic contribution. The paramagnetic contribution,
which is the constantterm, is neglected.

The Gaussian beam

One needs intense
terahertz lightthird order current response※Terahertz light is beginningto be used in condensed
matter research.

Difference of order

The vortex beam

[1] R.Shimano and N.Tsuji, Annu. Rev. Condens. Matter Phys.
11, 103 (2019).

Higgs mode andterahertz vortex beam
are linearly coupled. So,
the action has first order.

first order current response
Third Harmonic Generation

Response function

Peak is around

Scaling[2] R.Matsunaga, YI.Hamada,
K.Makise, Y.Uzawa, H.Terai, Z.Wang,
R.Shimano, Phys. Rev. Lett.
111,057002(2013)

0.003

0.008

40jΔ

0.004

2000

Current
Table1 taken from Rev [1]

0.002

χ x

|1/χΔΔ|

0.2

0.4

Frequency ω0.6

0.001

00

0.2

0.4

Frequency ω00

0.6

0.2

0.4

Frequency ω0.6

Vector potential[4] A. A. Peshkov, D. Seipt, A. Surzhykov, S. Fritzsche, Phys. Rev. 96, 023407 (2017),Background and Purpose

is Laguerre function

Previous experiments have revealed nonlinear coupling between Higgs
mode and the Gaussian beam. The goal of my research is to reveal linear
coupling between Higgs mode and light. I assume terahertz vortex beam aslight and consider current as the response of linear coupling.

Terahertz vortex beam

In the votex beam, a component of the vector
potential also appears in the direction of thelight propagetion. Therefore, surface plasmons
are excited when thin film superconductivity isconsidered. The OAM of terahertz vortex beamis translated to the phase fluctuation. As
follows below,

paramagnetic current-12(x1010)

8quasiparticle
Higgs mode

Current jx

Dirty limit is necessary. There isanother major excitation in SC, quasiparticle excitation. And the contribution of quasiparticle is much larger
than that of Higgs mode. In dirty limit,
the contribution of Higgs mode issame as that of quasiparticle.

Parameterpara〜3ω

peaks appear at ω = Δ
The current response is observed using pump-prove
spectroscopy.

jj
χ xx

pump:0.6 THz

64
200

When metamaterials is irradiated thevortex beam, multipole are excited.

Circular polarization

0.40.6Frequency ωThe contribution of Higgs mode is multiplied by 2,500 compared to quasipariticle. Higgs mode is not so visible.
[3] T.Arikawa et al., Sci. Adv. 6, eaay1977 (2020)

Orbital Argument Momentum
If lights can break inversion symmetry, we can see
the Higgs mode in linear coupling. Light that breaks
inversion symmetry is the vortex beam. As shown in
the above equation, the vortex beam has angularmomentum mh.

References

0.2

The vortex beam

Future WorkWe will take account of the following effects.
1. Phase fluctuations.
2. Rashba spin-orbit coupling(SOC) effect.
The SOC may enhance the linear coupling of terahertz
votex beam with Higgs.

[1] R.Shimano and N.Tsuji, Annu. Rev. Condens. Matter Phys. 11, 103 (2019).
[2] R.Matsunaga, YI.Hamada, K.Makise, Y.Uzawa, H.Terai, Z.Wang, R.Shimano, Phys. Rev. Lett. 111,057002(2013)[3] T.Arikawa et al., Sci. Adv. 6, eaay1977 (2020)[4] A. A. Peshkov, D. Seipt, A. Surzhykov, S. Fritzsche, Phys. Rev. 96, 023407 (2017)0.8