Browsing by Author "Haenel, Rafael"

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Open Access
Collective modes of the superconducting condensate
(2023) Haenel, Rafael; Daghofer, Maria (Prof. Dr.)
When a continuous symmetry is spontaneously broken, collective modes emerge. Usually, their spectrum is dominated by the low-energy physics of massless Goldstone modes. Superconductors, that break U(1) symmetry, are different. Here, the Goldstone boson is gapped out due to the Anderson-Higgs mechanism. The superconducting condensate can therefore host a zoo of massive collective excitations that are stable for lack of a gapless decay channel. The most prominent of them is the Higgs mode. Spectroscopy of collective modes can serve as a probe to reveal the nature of the superconducting state. In this thesis, we study the signatures of collective modes in nonlinear optical experiments. We explore the theoretical description of a new spectroscopic excitation scheme. We show how impurity scattering significantly enhances the optical Higgs mode response. We apply group theoretical methods to multi-order-parameter theories and investigate microscopic signatures of coupled modes in third harmonic generation experiments. We study the phenomenology and collective mode spectrum of an exotic system of twisted cuprate bilayers that supports topological superconductivity. Finally, we propose a novel device implementation of the superconducting diode effect. These results contribute to the emerging field of collective mode spectroscopy.
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Fano interference between collective modes in cuprate high-Tc superconductors
(2023) Chu, Hao; Kovalev, Sergey; Wang, Zi Xiao; Schwarz, Lukas; Dong, Tao; Feng, Liwen; Haenel, Rafael; Kim, Min-Jae; Shabestari, Parmida; Hoang, Le Phuong; Honasoge, Kedar; Dawson, Robert David; Putzky, Daniel; Kim, Gideok; Puviani, Matteo; Chen, Min; Awari, Nilesh; Ponomaryov, Alexey N.; Ilyakov, Igor; Bluschke, Martin; Boschini, Fabio; Zonno, Marta; Zhdanovich, Sergey; Na, Mengxing; Christiani, Georg; Logvenov, Gennady; Jones, David J.; Damascelli, Andrea; Minola, Matteo; Keimer, Bernhard; Manske, Dirk; Wang, Nanlin; Deinert, Jan-Christoph; Kaiser, Stefan
Cuprate high-Tc superconductors are known for their intertwined interactions and the coexistence of competing orders. Uncovering experimental signatures of these interactions is often the first step in understanding their complex relations. A typical spectroscopic signature of the interaction between a discrete mode and a continuum of excitations is the Fano resonance/interference, characterized by the asymmetric light-scattering amplitude of the discrete mode as a function of the electromagnetic driving frequency. In this study, we report a new type of Fano resonance manifested by the nonlinear terahertz response of cuprate high-Tc superconductors, where we resolve both the amplitude and phase signatures of the Fano resonance. Our extensive hole-doping and magnetic field dependent investigation suggests that the Fano resonance may arise from an interplay between the superconducting fluctuations and the charge density wave fluctuations, prompting future studies to look more closely into their dynamical interactions.