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High harmonic spectroscopy retrieves electronic structure of high-pressure superconductors

Date:31-01-2024 Print

High pressure has revealed surprising physics and creates novel states in condensed matter. Exciting examples include near-room-temperature superconductivity (Tc > 200 K) in highly-pressured hydrides such as H3S and LaH10.

Although the superconducting transition temperature of high-pressure superconductors is constantly increasing, the mechanism of superconductivity under such high pressure remains an open question. Knowledge regarding the properties and ultrafast dynamics of electrons and quasiparticles in high-pressure quantum states is lacking.

High harmonic generation (HHG) is the up-conversion of laser light to radiation carried at multiples of the laser frequency. As the poster child of nonlinear optics, HHG in solids originates from the nonlinear driving of electrons within and between electronic bands by strong-field light-matter interactions. Therefore, HHG spectroscopy naturally contains fingerprints of intrinsic atomic and electronic properties of materials. A lot of excitement emerges around learning about the material's properties through this nonlinear, non-perturbative laser-matter interaction.

With the help of state-of-the-art first-principles time-dependent density-functional theory simulations, Prof. MENG Sheng's group from the Institute of Physics at the Chinese Academy of Sciences have studied the ultrafast HHG dynamics in the high-pressure superconductor H3S.

The researchers found that HHG in high-pressure superconductors is strongly dependent on the electronic structures and electron-phonon coupling (EPC). Via HHG spectroscopy, they retrieved the band dispersion and EPC, and revealed the significant influence of many-body EPC on electron behavior near the Fermi level. Their results support the phonon-mediated mechanism based on EPC of high-pressure superconductivity, providing an all-optical approach to probe the band dispersion and EPC of high-pressure quantum states.

This study entitled “Solid-state high harmonic spectroscopy for all-optical band structure probing of high-pressure quantum states” was published on Proceedings of the National Academy of Sciences (PNAS). The study was supported by the National Science Foundation, the Ministry of Science and Technology of China, and the Chinese Academy of Sciences.

Fig.1 The high harmonic generation (HHG) spectra in high-pressure superconductor H3S. (Image by Institute of Physics)

Fig.2 Band structure reconstruction via HHG spectra. (Image by Institute of Physics)

Fig.3 Electron-phonon coupling reconstruction via HHG spectra. (Image by Institute of Physics)

Institute of Physics
MENG Sheng

Key words:
High harmonic generation; High-pressure superconductor; Electronic structure; Electron-phonon coupling;

The electronic structure and superconducting mechanism of the high-pressure superconductor are issues under continued investigation. A first-principles theoretical study of high harmonic generation in high-pressure H3S reveals the influence of electronic structure and many-body interaction on the ultrafast dynamics, providing an all-optical approach to probe the band dispersion and electron-phonon coupling of high-pressure quantum states.