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Magnetism and spintronics

Can magnetic order switch how excitons behave in a crystal?

Liebich M, Florian M, Nilforoushan N, et al. · Nature materials · 2025

Open access · cc by · source: Europe PMC

In the layered magnet CrSBr, antiferromagnetic order traps excitons in single layers as nearly one-dimensional, tightly bound pairs, and destroying that order by heating or a small magnetic field lets them spread and weakens their binding.

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Study at a glance

Design
Other — Near-infrared pump, phase-locked mid-infrared probe spectroscopy of a bulk CrSBr flake across temperature and with a small magnetic field, compared with anisotropic many-body calculations.
N
One main 620-nm-thick bulk sample measured across temperatures; no statistical sample size.
Population
Bulk flake of the layered van der Waals antiferromagnet CrSBr
Outcome
Intra-excitonic 1s-2p transition energy and linewidth, anisotropy, exciton decay dynamics versus temperature and magnetic field

Structured fields used in claim comparison tables when every cited study has a complete layer.

Key findings

The 1s-2p transition sat at 62 meV for light polarised along the chain (b) axis, while along the a axis it was redshifted by 13 meV and much weaker, showing strongly anisotropic, nearly one-dimensional excitons. At the magnetic transition the transition energy switched from about 50 meV (tightly bound) to about 15 meV (weakly bound) and the damping jumped more than sixfold. A slow decay component above 60 ps appeared alongside the 13 ps decay, and a 200 mT field shifted these changes to roughly 50 K lower temperature.

Methodology

The authors excited electron-hole pairs in a 620-nm-thick CrSBr flake with 20-femtosecond near-infrared pulses and probed internal exciton transitions with mid-infrared pulses polarised along either crystal axis. They repeated the measurements from low temperature through the Néel temperature of 132 K, and with a 200 mT field, interpreting spectra with a many-body theory that includes anisotropic masses and screening.

Limitations

Only bulk samples were studied; the authors note that few-layer and monolayer flakes, with larger binding energies, remain to be tested. Assigning spectral features and binding energies depends on the many-body model, so the quantities are inferred rather than directly measured. Separating magnetic from purely thermal effects rests on a single applied field value.

How this study connects

Role on claims

Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.

  • SupportsMagnetismconcept

    Spins shape excitons and the lattice, not only magnetisation.

    Magnetic order feeds back on other degrees of freedom: in CrSBr the excitonic 1s-2p transition shifted from about 50 to 15 meV across the magnetic transition, and in granular FePt films laser demagnetisation caused a transient lattice contraction that returned only after remagnetisation (about 100 ps).

    Evidence for the claim as stated.

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