Negative refraction in ferromagnet-superconductor superlattices.

Area of Science:

• Condensed Matter Physics
• Metamaterials
• Optics

Background:

• Negative refraction, a phenomenon reversing classical optics, requires materials with both negative dielectric permittivity and negative magnetic permeability.
• Achieving these properties simultaneously in a single material or engineered system is a significant challenge in optics and materials science.

Purpose of the Study:

• To experimentally realize negative refraction at millimeter wave frequencies.
• To demonstrate the use of a multilayer stack of ferromagnetic and superconducting thin films for achieving tunable negative refractive index.

Main Methods:

• Fabrication of a multilayer superlattice composed of superconducting YBa2Cu3O7 (YBCO) and ferromagnetic (La:Sr)MnO3 (LSMO) thin films.
• Experimental measurements at millimeter wave frequencies under finite magnetic fields and cryogenic temperatures.
• Tuning the magnetic properties of the LSMO layers near ferromagnetic resonance to achieve negative magnetic permeability.

Main Results:

• Demonstrated negative dielectric permittivity from the superconducting YBCO layers.
• Achieved negative magnetic permeability from the ferromagnetic LSMO layers near ferromagnetic resonance.
• Observed negative refraction in the fabricated superlattice structures.

Conclusions:

• The study successfully demonstrates experimental realization of negative refraction using engineered metamaterials.
• The refractive index of the superlattice can be dynamically tuned between positive and negative values by an external magnetic field.
• This work opens possibilities for novel optical devices operating at millimeter wave frequencies.