An Innovative Perspective on Light-Matter Interaction: Exploring the Photon Conductivity

When we place a conductor in a magnetic field, the current it generates flows perpendicularly to the electric field in what is known as the Hall effect. This conventional understanding changes when we consider the behavior of electrons at low temperatures, where quantum-mechanical effects come into play, leading to the discovery of the quantum Hall effect. Researchers have long wondered if light, which follows a similar wave equation as electrons, exhibits a quantum Hall effect as well. While aspects of an optical quantum Hall effect have been observed, the analogy between photons and electrons has remained incomplete.

Now, Mário Silveirinha from the University of Lisbon offers a new perspective on light-matter interaction by introducing the concept of “photon conductivity.” This innovative approach seeks to characterize the flow of light in response to the motion of matter, bridging the gap between the physics of electrons and that of photons [6]. Silveirinha’s theoretical study opens up exciting possibilities for understanding motion-induced wave effects.

The quantum Hall effect can be understood through topology, specifically through the link between Hall conductance and topological invariants known as Chern numbers. These integers determine whether different sets of wave functions attached to a torus surface can smoothly transition into each other. Silveirinha’s work demonstrates that the quantum Hall effect is not exclusive to electrons in magnetic fields but can also apply to other types of waves propagating through periodic structures [7].

While previous research has explored the emergence of edge states for classical light waves, electron-like behavior is absent due to the differences in spin and the absence of a clearly defined conductance. Silveirinha’s work addresses these limitations by considering the inverse scenario, where the acceleration of matter induces a flow of electromagnetic energy. By defining a “photon conductivity,” he establishes a direct analog of the Hall effect for light confined in an accelerating optical cavity containing a nonreciprocal material [6].

Silveirinha’s theoretical predictions open up avenues for experimental investigations into motion-induced wave effects and may contribute to the development of advanced photonic devices and technologies.


Q: What is the Hall effect?
The Hall effect describes the behavior of electrical currents in a conductor placed in a magnetic field. The current flows perpendicular to both the electric field and the magnetic field.

Q: What is the quantum Hall effect?
The quantum Hall effect is a phenomenon observed in low-temperature conditions where the conductivity exhibits discrete jumps as the magnetic field varies. This effect arises due to the quantum-mechanical behavior of electrons.

Q: Can light exhibit a quantum Hall effect?
While aspects of an optical quantum Hall effect have been observed, the complete analogy between light and electrons remains incomplete. However, theoretical work by Mário Silveirinha suggests a new perspective by defining a “photon conductivity” that characterizes the flow of light in response to the motion of matter.

Q: How does Silveirinha’s work contribute to our understanding of light-matter interaction?
Silveirinha’s innovative viewpoint allows researchers to bridge the gap between the physics of electrons and photons. By introducing the concept of “photon conductivity,” he offers a fresh perspective on how light behaves in the presence of matter motion, potentially uncovering a wealth of motion-induced wave effects.