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Understanding the nature and energy distribution of optical resonances is of central importance in low-dimensional materials$^{1-4}$ and its knowledge is critical for designing efficient optoelectronic devices. Ruddlesden-Popper halide perovskites are 2D solution-processed quantum wells with a general formula A$_2$A$_{n-1}$M$_n$X$_{3n+1}$, where optoelectronic properties can be tuned by varying the perovskite layer thickness (n value), and have recently emerged as efficient semiconductors with technologically relevant stability. However, fundamental questions concerning the nature of optical resonances (excitons or free-carriers) and the exciton reduced mass, and their scaling with quantum well thickness remains unresolved. Here, using optical spectroscopy and 60-Tesla magneto-absorption supported by modelling, we unambiguously demonstrate that the optical resonances arise from tightly bound excitons with unexpectedly high exciton reduced mass (0.20 m0) and binding energies varying from 470 meV to 125 meV with increasing thickness from n=1 to 5. Our work demonstrates the dominant role of Coulomb interactions in 2D solution-processed quantum wells and presents unique opportunities for next-generation optoelectronic and photonic devices.
Self-assembled hybrid perovskite quantum wells have attracted attention due to their tunable emission properties, ease of fabrication and device integration. However, the dynamics of excitons in these materials, especially how they couple to phonons
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A theoretical description of radiation-matter coupling for semiconductor-based photonic crystal slabs is presented, in which quantum wells are embedded within the waveguide core layer. A full quantum theory is developed, by quantizing both the electr
The optical properties of two-dimensional transition metal dichalcogenide monolayers such as MoS$_2$ or WSe$_2$ are dominated by excitons, Coulomb bound electron-hole pairs. Screening effects due the presence of hexagonal-BN surrounding layers have b