Light Induces Magnetization in Quantum Hall Fluids via Inverse Faraday and Cotton-Mouton

The interplay of light and quantum materials reveals surprising phenomena, and recent work explores how light can directly induce magnetism in two-dimensional electron systems known as Hall fluids. Gabriel Cardoso, Erlend Syljůasen, and colleagues at Nordita, Stockholm University, and affiliated institutions, demonstrate two distinct light-induced effects that generate static magnetization within these fluids. Their research reveals a dominant contribution to the inverse Faraday effect, where circularly polarized light stirs the electrons, and a novel inverse Cotton-Mouton effect, where linearly polarized light directly probes the fluid’s chiral properties. Importantly, the predicted magnetization, reaching up to 10 Bohr magnetons per charge carrier in materials like graphene and transition-metal dichalcogenides, opens possibilities for optically controlling and patterning these systems, potentially enabling the “printing” of density profiles with light.

Magnetization effects in quantum Hall (QH) fluids arise from their response to external stimuli, particularly light. Researchers have discovered that shining light onto these fluids generates magnetization, an alignment of internal magnetic moments, through two distinct mechanisms: the inverse Faraday effect and the inverse Cotton-Mouton effect. These effects offer complementary methods for controlling the fluid’s magnetic properties.

Perturbative Calculation of Magnetization and Density Profiles

A detailed theoretical calculation has explored the density of states, magnetization, and density profiles within a two-dimensional electron system, relevant to the Quantum Hall Effect. This work employs a perturbative approach, refining calculations to higher orders to accurately determine the system’s behavior and predict its response to external electromagnetic fields. The calculation connects the density of electrons to the magnetic field and magnetization, a fundamental relationship in the Quantum Hall Effect.

Light Controls Magnetism in Quantum Hall Fluids

Researchers have demonstrated a novel way to manipulate quantum Hall fluids using light. These fluids exhibit unique responses to polarized light, allowing for unprecedented control over their internal magnetic properties and even their density. The inverse Faraday effect, where circularly polarized light stirs the charged fluid, and the inverse Cotton-Mouton effect, where linearly polarized light also generates magnetization, both contribute to this control. The magnitude of these induced magnetizations is substantial, estimated to be between 0. 5 and 10 Bohr magnetons per charge carrier in materials like graphene and transition-metal dichalcogenides.

Beyond simply inducing magnetization, the research reveals that light can also locally alter the density of the quantum Hall fluid, creating a “quantum Hall printing” effect. This allows for the creation of patterned density profiles within the material, opening possibilities for creating complex structures and devices. Detailed theoretical work extends existing hydrodynamic models to describe these unusual fluid behaviors and confirms that the observed effects are intrinsic to the quantum Hall state itself.

Light Induces Magnetization in Transverse Fluids

Researchers have identified two distinct light-induced orbital magnetization effects within transverse fluids, such as those found in quantum Hall systems. These effects stem from the way these fluids respond to light, specifically through the inverse Faraday effect and a newly discovered orbital inverse Cotton-Mouton effect. The inverse Cotton-Mouton effect reveals information about the fluid’s chiral properties. The resulting magnetization can reach 0. 5 to 10 Bohr magnetons per charge carrier in materials like graphene and transition-metal dichalcogenides. Furthermore, the induced magnetization alters the static particle density within the fluid, creating a pathway for “quantum Hall printing,” where light can be used to imprint density profiles onto the electronic fluid. Future research should focus on experimental verification of these predicted effects, particularly in quantum Hall states with strong field gradients, potentially opening new avenues for optical control and manipulation of topological phases of matter.