From a single photon to a polariton
This project sits at the corner of magnetism, semiconductor physics and thin-film optics — a niche enough mix that the simulator alone won't explain itself. The pages below build the picture from the ground up, one floor at a time. Concepts will become clickable as their deep-dive pages come online; for now this is the static map of where we're heading.
- L6Putting it together— All five floors below in one breath: how a flipped spin on the left turns into a moving dip on the right.
- L5CrSBr & the experiment— The specific material at the heart of this project, and the sandwich we built around it.
- L4Light in layered structures— Stack a few thin films and light starts to bounce, interfere, and resonate in ways a single layer never could.
- L3Magnetism in layered materials— How spins arrange themselves between neighboring atomic planes — and what happens at the seams.
- L2How matter responds to light— Once we know what light and electrons are, we can describe how a chunk of material bends, slows, and absorbs a beam.
- L1Foundations— The raw ingredients: what light is, what atoms do with it, and what a 'spin' even means.
Foundations
The raw ingredients: what light is, what atoms do with it, and what a 'spin' even means.
Light comes in tiny packets. Each packet carries an energy in electron-volts (eV) that maps one-to-one to a wavelength in nanometers.
Electrons live on discrete energy ladders inside atoms. The gaps between rungs decide which colors of light a material can absorb or emit.
Every electron carries a tiny intrinsic magnet. Pointing them up or down is the seed of all the magnetic patterns in this project.
How matter responds to light
Once we know what light and electrons are, we can describe how a chunk of material bends, slows, and absorbs a beam.
A complex number that tells light how much to slow down (real part) and how much to fade (imaginary part) inside a material.
In crystals, electron levels merge into bands. The gap between the full and empty bands sets the lowest photon energy that can be absorbed.
When light kicks an electron out, the empty spot it leaves behind acts like a partner. The pair absorbs light at a very specific energy.
The full optical fingerprint of a material. Excitons show up here as bumps that turn into dips and peaks in the reflectance.
Magnetism in layered materials
How spins arrange themselves between neighboring atomic planes — and what happens at the seams.
All spins lined up the same way. A weak applied field locks the material into this 'all-aligned' mood.
Neighboring layers cancel each other out. CrSBr's natural ground state — calm, with no net magnetization.
The seam where AFM meets FM. A short transition window with optical properties of its own.
Patches of the sample where the spins all share the same pattern. Pushing the material with a field grows or shrinks these patches.
Above a critical magnetic field, AFM layers snap into the FM configuration. This is what re-paints the spin pattern in the simulator.
A whole family of materials where magnetism survives even when the crystal is just a few atoms thick. CrSBr is one of them.
Light in layered structures
Stack a few thin films and light starts to bounce, interfere, and resonate in ways a single layer never could.
Light reflects off both surfaces of a thin layer; the two echoes either reinforce or cancel each other depending on color.
The math trick we use to predict reflection through any 1D stack: hand the wave from layer to layer with a small matrix at every interface.
Many thin layers tuned so all their reflections add up. The result is a near-perfect mirror for one chosen color.
Two mirrors facing each other trap light between them. Only a few wavelengths fit — those become bright resonances we can measure.
Inside the cavity light freezes into a stripe pattern. The bright stripes are where the material can soak up energy most efficiently.
The fraction of light bounced back, plotted vs photon energy. Dips reveal cavity modes and excitons hiding inside the stack.
CrSBr & the experiment
The specific material at the heart of this project, and the sandwich we built around it.
A layered van der Waals semiconductor with strong in-plane FM order and AFM coupling between layers — a near-ideal magnetic 2D crystal.
The per-layer list of arrows the simulator hands to the physics engine. Editing it is how you sculpt the magnetic landscape.
A sliding 3-layer window classifies each spot as AFM, Mixed, or FM. This is the bridge from raw spins to optical refractive indices.
Top gold mirror, ~100 CrSBr monolayers in the middle, and a Bragg mirror at the bottom — the full sandwich the TMM solves.
Putting it together
All five floors below in one breath: how a flipped spin on the left turns into a moving dip on the right.
Spins → magnetic phases → per-layer dielectric → TMM → reflectance. Walk the pipeline once and the rest of the app becomes obvious.
When the cavity mode and the exciton meet, they fuse into a half-light, half-matter quasiparticle. The whole point of the experiment.
How to interpret the stack viewer, the R(E) curve, and the |E(z)|² profile — and which knob does what.
Each topic above will grow into its own page with diagrams, interactive components and worked examples — every concept finally getting the room it deserves. Want to suggest the next page to build, or rearrange the order? Open an issue or hop back to the simulator.