טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentFrischwasser Jacob
SubjectSpin Degeneracy Breaking in Coupled Thermal Antenna Lattices
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Erez Hasman
Full Thesis textFull thesis text - English Version


Abstract

According to quantum mechanics the spin is a fundamental internal degree of freedom, related to the intrinsic angular momentum of a particle. The spin state of elementary particles, atoms and molecules plays a key role in fundamental effects in physics. For instance, an external magnetic field causes energy separation of electrons due to the interaction with their spin (Zeeman effect) , inhomogeneous magnetic field causes a spin dependent spatial deflection of the electrons passing through it (Stern-Gerlach effect) and spin-dependent momentum separation of charge carriers (spin-orbit interaction) can occur due to structural inversion asymmetry in bulk materials (Rashba and Dresselhaus effects). The photonic analogy of spin-orbit interaction was recently presented, wherein, the spin of the photons (helicity state) plays the role of the spin of charge carriers. Spin-dependent deflection of light was obtained for propagation in gradient-index media and with the scattering of surface waves from metallic nanostructures. In the latter, only by changing the surface texture, the spin-dependent coupling of propagating light into surface modes is possible. A connection between the optical properties of a material and the surface texture is established by studying the excitation of surface waves: surface phonon-polaritons (SPhPs) in polar crystal and surface plasmon polaritons (SPPs) in metal. The underlying microscopic origin of the SPhPs is resonant collective lattice vibration whereas the origin of the SPPs is collective oscillation of the free electrons. A surface polariton has a longer wavevector than the light waves propagating along the surface at the same frequency. For this reason, they are called “nonradiative” surface waves. By coupling the surface waves with the propagating wave, by means of an additional prism or grating, one can produce either increased resonant absorption or emission. In this work, an observation of a spin degeneracy breaking in thermal radiation emitted from an inhomogeneous anisotropic lattice composed of coupled antennas supporting surface waves is presented. The spin degeneracy removal is manifested by a spin-dependent momentum splitting of the radiative mode which resembles the Rashba effect in electronics. The spin split dispersion arises from the inversion asymmetry of the lattice. Our experiment confirms that the spatial rate of the inhomogeneity determines the degree of the spin- dependent momentum redirection. The influence of the inversion asymmetry on the dispersion was studied by comparing the results to those produced by homogeneous lattices and characterizing the behavior of the isolated thermal antennas.