Mr. Xinwei Li Profile

Xinwei Li

at Rice Univ

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Publications (2)

SPIE Journal Paper | 18 January 2023 Open Access

Terahertz spin dynamics in rare-earth orthoferrites

Xinwei Li, Dasom Kim, Yincheng Liu, Junichiro Kono

PI, Vol. 1, Issue 02, R05, (January 2023) https://doi.org/10.1117/12.10.3788/PI.2022.R05

KEYWORDS: Terahertz radiation, Magnetism, Magnons, Crystals, Iron, Erbium, Spin dynamics, Ultrafast phenomena, Phonons, Polarization

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Proceedings Article | 27 February 2019 Presentation + Paper

Terahertz strong-field physics without a strong external terahertz field

Motoaki Bamba, Xinwei Li, Junichiro Kono

Proceedings Volume 10916, 1091605 (2019) https://doi.org/10.1117/12.2512794

KEYWORDS: Iron, Erbium, Magnons, Magnetism, Terahertz radiation

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Traditionally, strong-field physics explores phenomena in laser-driven matter (atoms, molecules, and solids) that cannot be understood by treating the laser field as a small perturbation. Therefore, the presence of an extremely strong external field is usually a prerequisite for observing strong-field phenomena. However, even in the complete absence of an external electromagnetic field, strong-field phenomena can arise when matter strongly couples with the zero-point field of the quantum vacuum state, i.e., fluctuating electromagnetic waves whose expectation value is zero. This can occur in free space where the matter strongly interacts with a continuum of photon modes, but some of the most striking examples of strong-field physics without an external field occur in a cavity setting, in which an ensemble of two-level atoms resonantly interacts with a single photonic mode of vacuum fields, producing vacuum Rabi splitting. In particular, the nature of the matter-vacuum-field coupled system fundamentally changes when the coupling rate (equal to one half of the vacuum Rabi splitting) becomes comparable to, or larger than, the resonance frequency. In this so-called ultrastrong coupling regime, a non-negligible number of photons exist in the ground state of the coupled system. Furthermore, the coupling rate can be cooperatively enhanced (via so-called Dicke cooperativity) when the matter is comprised of a large number of identical two-level particles, and a quantum phase transition is predicted to occur as the coupling rate reaches a critical value. Low-energy electronic or magnetic transitions in many-body condensed matter systems with large dipole moments are ideally suited for searching for these predicted phenomena. Here, we discuss two condensed matter systems that have shown cooperative ultrastrong interactions in the terahertz frequency range: a Landau-quantized two-dimensional electron gas interacting with high-quality-factor cavity photons, and an Er³⁺ spin ensemble interacting with Fe³⁺ magnons in ErFeO₃.

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