Exploring Spin-Dependent Strong Light-Matter Coupling in a Quantum Hall 2D Hole Gas-Microcavity System - Novel Polaritonic Phenomena - Unveiling New Avenues in Polariton Physics

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Abstract:

The interplay between time-reversal symmetry breaking and strong light–matter coupling in two-dimensional (2D) gases brings intriguing aspects to polariton physics. This combination can lead to a polarization/spin-selective light–matter interaction in the strong coupling regime. Here we report such a selective strong light–matter interaction by harnessing a 2D gas in the quantum Hall regime coupled to a microcavity. Specifically, we demonstrate circular-polarization dependence of the vacuum Rabi splitting, as a function of magnetic field and hole density. We provide a quantitative understanding of the phenomenon by modelling the coupling of optical transitions between Landau levels to the microcavity. This method introduces a control tool over the spin degree of freedom in polaritonic semiconductor systems, paving the way for new experimental possibilities in light–matter hybrids.

**1. Introduction**

The field of strong light-matter coupling has captivated researchers for its ability to bridge the gap between quantum optics and condensed matter physics. In recent years, the combination of strong coupling with spin-selective interactions has brought about exciting new possibilities in the realm of polariton physics. This article presents a comprehensive exploration of a groundbreaking study that sheds light on the emergence of spin-selective strong light-matter coupling in a 2D hole gas-microcavity system.

**2. Background and Motivation**

The interaction between light and matter lies at the core of numerous technological applications, ranging from lasers to solar cells. Strong coupling occurs when the coupling strength between light and matter becomes comparable to the loss rates of both systems. This leads to the formation of hybrid light-matter states known as polaritons. These states exhibit a unique combination of properties, including mixed photon-exciton character, resulting in modified energy levels and enhanced light-matter interactions.

The study of strong coupling has extended to two-dimensional (2D) materials, offering a platform to investigate quantum phenomena in reduced dimensions. The quantum Hall regime, characterized by quantized conductance and strong magnetic fields, introduces a fertile ground for intriguing physical phenomena. The motivation behind the research lies in exploring how the interplay between time-reversal symmetry breaking and strong light-matter coupling can yield novel effects, specifically focusing on spin-selective interactions.

**3. Experimental Setup**

The experimental setup involves a 2D hole gas (2DHG) situated within a microcavity. The 2DHG is confined to a quantum well, and its response to external perturbations, such as magnetic fields, provides insights into its energy structure and interaction dynamics. The microcavity, on the other hand, enhances light-matter interactions by confining photons in a resonant structure. By precisely controlling the 2DHG properties, magnetic fields, and hole density, researchers aimed to observe and manipulate spin-selective strong coupling effects.

**4. Circular-Polarization Dependence of Vacuum Rabi Splitting**

One of the key findings of the study is the circular-polarization dependence of the vacuum Rabi splitting in the system. The vacuum Rabi splitting is a hallmark of strong coupling, representing the energy separation between the lower and upper polariton branches. The circular-polarization dependence indicates a strong correlation between the spin state of the 2DHG and the polariton states. This observation opens up the avenue for controlling light-matter interactions based on the spin degree of freedom.

**5. Theoretical Model and Quantitative Analysis**

To gain a deeper understanding of the observed phenomenon, researchers developed a comprehensive theoretical model. The model takes into account the Landau levels and their coupling to the microcavity, as well as the spin properties of the 2DHG. By comparing the experimental results with the theoretical predictions, researchers successfully quantified the spin-selective coupling effects. This modeling approach not only confirms the observed circular-polarization dependence but also provides insights into the underlying mechanisms.

**6. Implications and Future Directions**

The emergence of spin-selective strong light-matter coupling in the 2D hole gas-microcavity system carries significant implications for both fundamental physics and practical applications. The ability to control and manipulate the spin degree of freedom in polaritonic systems opens up new possibilities for quantum information processing, spintronic devices, and optoelectronic technologies. Moreover, the findings highlight the richness of 2D materials in exploring novel quantum phenomena.

**7. Conclusion**

In conclusion, the study of spin-selective strong light-matter coupling in a 2D hole gas-microcavity system unveils a fascinating interplay between quantum Hall physics, strong coupling, and spin properties. The observation of circular-polarization dependence of the vacuum Rabi splitting provides a clear manifestation of spin-selective interactions in the strong coupling regime. Theoretical modeling further elucidates the intricate mechanisms at play. This research not only deepens our understanding of polariton physics but also opens doors to a new era of spin-controllable light-matter interactions with broad implications across disciplines. As researchers continue to explore and harness the potential of this discovery, exciting new horizons await in the world of polaritonics and beyond.

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