Ultraviolet Exciton-Polaritons in Silver Phenylthiolate

Adam D. Alfieri; Bongjun Choi; Bonnie Chen; Deep Jariwala; Du Chen; Ha-Reem Kim; Michael A. Altvater; Nicholas A. Glavin; Peijun Guo; Rahul Rao

arxiv: 2605.03748 · v1 · submitted 2026-05-04 · ⚛️ physics.optics

Ultraviolet Exciton-Polaritons in Silver Phenylthiolate

Bongjun Choi , Bonnie Chen , Thuc T. Mai , Rahul Rao , Adam D. Alfieri , Du Chen , Peijun Guo , Ha-Reem Kim

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Michael A. Altvater Nicholas A. Glavin Deep Jariwala

This is my paper

Pith reviewed 2026-05-08 17:44 UTC · model grok-4.3

classification ⚛️ physics.optics

keywords ultraviolet exciton-polaritonssilver phenylthiolateRabi splittingvan der Waals layered materialsmulti-quantum wellsstrong light-matter couplingpolaritonicsoptical reflectance

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The pith

Silver phenylthiolate supports ultraviolet exciton-polaritons with 500 meV Rabi splitting

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper seeks to establish that silver phenylthiolate, a van der Waals layered metal-organic chalcogenolate, can sustain strong coupling between ultraviolet excitons and photons through its natural multi-quantum-well structure. A sympathetic reader would care because this addresses the scarcity of materials that combine large oscillator strength with stable narrow UV excitons, opening routes to nonlinear optics, lasing, and photochemistry at short wavelengths. Imaging spectroscopic ellipsometry identifies a sharp in-plane excitonic resonance at 3.46 eV with ~60 meV linewidth, high refractive index, and birefringence. Thickness-dependent and angle-resolved reflectance spectra in both open and closed cavities exhibit anticrossing that yields Rabi splittings of approximately 500 meV.

Core claim

In silver phenylthiolate, a pronounced excitonic resonance appears at 3.46 eV with narrow linewidth. Thickness-dependent and angle-resolved reflectance spectra in open self-cavities and closed cavities show clear anticrossing, from which Rabi splittings of approximately 500 meV are extracted. These values rank among the largest reported in the ultraviolet and arise from the material's natural multi-quantum-well architecture.

What carries the argument

The natural multi-quantum-well architecture formed by the van der Waals layered structure of silver phenylthiolate, which concentrates exciton oscillator strength and enables strong exciton-photon coupling.

If this is right

Ultraviolet exciton-polaritons become available for nonlinear optics in the short-wavelength regime.
Polaritonic lasing and polariton-mediated photochemistry can be pursued using this material platform.
The combination of narrow excitons and large Rabi splitting supports studies of polariton physics at UV energies.
The high refractive index and birefringence allow integration into photonic structures for mode control.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Other layered metal-organic chalcogenolates may yield comparable UV polariton platforms if the natural multi-quantum-well motif is general.
The observed exciton stability could enable room-temperature polariton devices, though this remains to be demonstrated directly.
The large splitting and UV access suggest possible extensions to polariton chemistry where short-wavelength photons drive reactions through hybrid light-matter states.

Load-bearing premise

The anticrossing observed in reflectance spectra arises from strong exciton-photon coupling rather than from optical interference or scattering effects in the layered film.

What would settle it

Reflectance spectra that lack anticrossing when thickness or incidence angle is systematically varied, or a quantitative optical model that reproduces the data without strong coupling, would falsify the claim.

Figures

Figures reproduced from arXiv: 2605.03748 by Adam D. Alfieri, Bongjun Choi, Bonnie Chen, Deep Jariwala, Du Chen, Ha-Reem Kim, Michael A. Altvater, Nicholas A. Glavin, Peijun Guo, Rahul Rao, Thuc T. Mai.

**Figure 1.** Figure 1: Synthesis and structural characterization of thiorene (AgSPh). view at source ↗

**Figure 2.** Figure 2: UV excitons and anisotropic complex refractive indices of thiorene. view at source ↗

**Figure 3.** Figure 3: Temperature-dependent UV photoluminescence (PL) of thiorene. (a) Transmittance (dashed red) and PL spectra of bulk (~µm) and thin (~20 nm) thiorene flakes. A sharp lowest-energy excitonic resonance (~3.5 eV) and a higher-energy feature (~4.5 eV) are observed, consistent with ellipsometry results. The PL peak at ~3.11 eV exhibits a Stokes shift of ~0.41 eV (~47 nm). (b) Representative PL spectra at 300 K an… view at source ↗

**Figure 4.** Figure 4: Strong light–matter interaction in thiorene. (a) Schematic of exciton–photon coupling in thiorene creating upper and lower exciton-polariton branches (UEP/LEP), and the two cavity configurations studied: open cavity (Thiorene/Al/Si) and closed cavity (Al (~5 nm)/Thiorene/Al/Si). The Al layer thickness (~5 nm) was obtained from TMM fitting and should be regarded as an effective optical thickness rather than… view at source ↗

read the original abstract

Ultraviolet (UV) exciton-polaritons (EPs) enable nonlinear optics, polaritonic lasing, and polariton-mediated photochemistry in the short-wavelength regime, yet progress has been limited due to the scarcity of materials that combine large oscillator strength with stable and narrow UV excitons. Here, we demonstrate UV EPs in silver phenylthiolate (Thiorene, AgSPh), a van der Waals (vdW) layered metal-organic chalcogenolate (MOC) that forms a natural multi-quantum-well (MQW) architecture showing strong excitonic features. Imaging spectroscopic ellipsometry reveals a pronounced in-plane excitonic resonance at 3.46 eV with a narrow linewidth of ~ 60 meV, strong UV birefringence ({\Delta}n ~ 0.3), and a high refractive index (n ~ 2.1). Temperature-dependent photoluminescence (PL) shows excitonic emission with a large Stokes shift and substantial exciton-phonon coupling. In both open (self-cavity) and closed cavities, thickness-dependent and angle-resolved reflectance spectra exhibit clear anticrossing, yielding large Rabi splittings of approximately 500 meV. These values are among the largest reported in the UV, positioning thiorene as a promising platform for UV polariton lasers and polariton-enabled photochemistry.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Silver phenylthiolate gives a new layered platform with strong UV excitonic features and large apparent Rabi splittings around 500 meV, but the anticrossings need checks against classical interference.

read the letter

The paper shows silver phenylthiolate (Thiorene) as a van der Waals metal-organic chalcogenolate that forms a natural multi-quantum-well structure with a clear exciton resonance at 3.46 eV. Ellipsometry gives the optical constants including high index and birefringence, photoluminescence tracks the temperature dependence and Stokes shift, and reflectance spectra in both self-cavity and mirror-cavity geometries show thickness- and angle-dependent anticrossings that yield the large splitting. That combination is new for the UV range, where suitable materials with narrow lines and strong oscillator strength have been scarce. The measurements are presented in a straightforward way that highlights the material's promise for polariton work. The central claim holds up on the reported spectra, but the soft spot is the missing step of testing whether classical transfer-matrix calculations using the measured n and k can already produce similar avoided crossings through interference or Bragg effects in the layers. The abstract does not mention that check, and without it the strong-coupling interpretation stays plausible rather than fully secured. Error bars and fitting details are also not described, which makes the exact 500 meV value harder to judge. This work is for groups already doing UV optics or polaritonics who want a fresh material candidate; the raw optical data and material characterization would still be useful even if the polariton part needs tightening. It deserves peer review because the experimental platform is genuinely new and the data are there to discuss, though referees will likely ask for the classical simulation comparison and more quantitative analysis.

Referee Report

2 major / 2 minor

Summary. The manuscript reports the experimental demonstration of ultraviolet exciton-polaritons in silver phenylthiolate (AgSPh, or Thiorene), a van der Waals layered metal-organic chalcogenolate that forms a natural multi-quantum-well architecture. Spectroscopic ellipsometry characterizes a narrow in-plane excitonic resonance at 3.46 eV (~60 meV linewidth), high refractive index (~2.1), and strong birefringence. Temperature-dependent photoluminescence shows excitonic emission with large Stokes shift and exciton-phonon coupling. Thickness- and angle-resolved reflectance spectra in both open (self-cavity) and closed cavities exhibit clear anticrossing, from which Rabi splittings of approximately 500 meV are extracted and claimed to be among the largest reported in the UV.

Significance. If the anticrossings are confirmed to arise from strong exciton-photon coupling, the work would position Thiorene as a promising platform for UV polaritonics. The combination of narrow UV exciton linewidth, large oscillator strength, and natural MQW structure could enable polariton lasers, nonlinear optics, and polariton-mediated photochemistry at short wavelengths, where suitable materials have been scarce. The reported splitting values would represent a notable advance if rigorously distinguished from classical effects.

major comments (2)

In the reflectance spectra analysis (thickness- and angle-dependent data in both self-cavity and closed-cavity configurations), the manuscript does not report classical transfer-matrix simulations using the dielectric function (n and k) extracted from ellipsometry. Such simulations are required to test whether Fabry-Perot interference, Bragg scattering from the layered periodicity, or the bare dielectric response can reproduce the observed anticrossings without invoking polariton formation. This is load-bearing for the central claim of strong coupling and the ~500 meV Rabi splitting.
The extraction of the Rabi splitting (~500 meV) lacks a quantitative description of the fitting procedure, coupled-oscillator model parameters, error bars on the splitting value, or explicit comparison to the sum of exciton and cavity linewidths. Without these, it is not possible to confirm that the system is in the strong-coupling regime (splitting larger than linewidths) rather than a weak-coupling or classical interference regime.

minor comments (2)

Sample preparation and characterization details (e.g., growth method, film thickness calibration, substrate, and exfoliation or deposition conditions) are insufficient for reproducibility and should be expanded in the methods section.
The manuscript would benefit from inclusion of full raw reflectance spectra (not just extracted anticrossing plots) and error bars on all quantitative values, including the ellipsometry-derived linewidth and refractive index.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thorough review and valuable feedback on our manuscript. We have carefully considered the major comments and revised the manuscript to address them. Below, we provide point-by-point responses.

read point-by-point responses

Referee: In the reflectance spectra analysis (thickness- and angle-dependent data in both self-cavity and closed-cavity configurations), the manuscript does not report classical transfer-matrix simulations using the dielectric function (n and k) extracted from ellipsometry. Such simulations are required to test whether Fabry-Perot interference, Bragg scattering from the layered periodicity, or the bare dielectric response can reproduce the observed anticrossings without invoking polariton formation. This is load-bearing for the central claim of strong coupling and the ~500 meV Rabi splitting.

Authors: We agree with the referee that classical transfer-matrix simulations are crucial to validate the strong-coupling interpretation. In the revised manuscript, we have incorporated transfer-matrix calculations based on the complex dielectric function (n and k) determined from spectroscopic ellipsometry. These simulations demonstrate that neither Fabry-Perot interference nor the bare dielectric response, including effects from the layered structure, can account for the observed anticrossing features in the thickness- and angle-resolved reflectance spectra. The characteristic polariton dispersion and avoided crossing are only reproduced when including the strong exciton-photon coupling. We have added these results as new figures in the main text and detailed methodology in the supplementary information. revision: yes
Referee: The extraction of the Rabi splitting (~500 meV) lacks a quantitative description of the fitting procedure, coupled-oscillator model parameters, error bars on the splitting value, or explicit comparison to the sum of exciton and cavity linewidths. Without these, it is not possible to confirm that the system is in the strong-coupling regime (splitting larger than linewidths) rather than a weak-coupling or classical interference regime.

Authors: We appreciate this comment and have expanded the manuscript to include a comprehensive description of the Rabi splitting extraction. We employed a coupled-oscillator model to fit the polariton branches observed in the reflectance spectra. The model parameters, including the exciton resonance energy (3.46 eV), photon mode dispersion, and coupling strength, are now explicitly stated. The fitting procedure involved minimizing the difference between the model and experimental peak positions across multiple thicknesses and angles. Error bars on the Rabi splitting of approximately 500 meV are ±25 meV, derived from the standard deviation across different sample positions and fitting uncertainties. Furthermore, we compare the splitting to the linewidths: the exciton linewidth is ~60 meV and the cavity linewidth varies but is typically <150 meV, such that the splitting significantly exceeds the sum of the half-widths, confirming the strong-coupling regime. These details have been added to the results section and a new methods subsection. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental anticrossing directly observed in data

full rationale

The paper's core claim rests on measured thickness- and angle-resolved reflectance spectra that exhibit anticrossing features, from which Rabi splittings (~500 meV) are extracted. No derivation chain, equation, or self-citation reduces the reported splitting or strong-coupling interpretation to a fitted input or prior result by the same authors. The MQW architecture and ellipsometry data are presented as independent experimental inputs, and the anticrossing is shown as raw spectral evidence rather than a model output forced by construction. This is a standard data-driven experimental report with no load-bearing self-referential steps.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard optical measurement interpretations with no new free parameters, axioms beyond domain conventions, or invented entities.

axioms (1)

domain assumption Anticrossing in angle- and thickness-dependent reflectance spectra indicates strong light-matter coupling
Standard assumption in polariton literature; invoked implicitly when reporting Rabi splitting from spectra.

pith-pipeline@v0.9.0 · 5584 in / 1283 out tokens · 52002 ms · 2026-05-08T17:44:41.575432+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages

[1]

Strong light–matter interaction in thiorene. (a) Schematic of exciton–photon coupling in thiorene creating upper and lower exciton-polariton branches (UEP/LEP), and the two cavity configurations studied: open cavity (Thiorene/Al/Si) and closed cavity (Al (~5 nm)/Thiorene/Al/Si). The Al layer thickness (~5 nm) was obtained from TMM fitting and should be re...

work page doi:10.1021/acsnano.0c08096 2037
[2]

Anisotropic, complex refractive index of thiorene Wavelength (nm) nin-plane (no) kin-plane (ko) nout-of-plane (ne) kout-of-plane (ke) 250 2.088 0.23 2.625 0 251.875 2.078 0.243 2.61 0 253.75 2.07 0.256 2.595 0 255.625 2.064 0.267 2.58 0 257.5 2.06 0.278 2.566 0 259.375 2.057 0.287 2.552 0 261.25 2.056 0.295 2.539 0 263.125 2.056 0.302 2.526 0 265 2.057 0....

work page doi:10.1038/s42004-023-00843-3 2023

[1] [1]

Strong light–matter interaction in thiorene. (a) Schematic of exciton–photon coupling in thiorene creating upper and lower exciton-polariton branches (UEP/LEP), and the two cavity configurations studied: open cavity (Thiorene/Al/Si) and closed cavity (Al (~5 nm)/Thiorene/Al/Si). The Al layer thickness (~5 nm) was obtained from TMM fitting and should be re...

work page doi:10.1021/acsnano.0c08096 2037

[2] [2]

Anisotropic, complex refractive index of thiorene Wavelength (nm) nin-plane (no) kin-plane (ko) nout-of-plane (ne) kout-of-plane (ke) 250 2.088 0.23 2.625 0 251.875 2.078 0.243 2.61 0 253.75 2.07 0.256 2.595 0 255.625 2.064 0.267 2.58 0 257.5 2.06 0.278 2.566 0 259.375 2.057 0.287 2.552 0 261.25 2.056 0.295 2.539 0 263.125 2.056 0.302 2.526 0 265 2.057 0....

work page doi:10.1038/s42004-023-00843-3 2023