Browsing by Subject "Anderson Localization"

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    Heat Assisted Magnetic Recording: Light-Matter Interaction in the Deep Subwavelength Regime
    (2019-01) Ghoreyshi, Ali
    The necessity for low price data storage in emerging Cloud technologies suggests that the Hard Disk Drives (HDDs) will continue to remain the dominant storage technology. To keep up with demands, the hard disk drive industry provided ∼ 40% annual average areal density growth rate over the past 60 years. However, the areal density of current perpendicular magnetic recording technology tends to saturate at ∼ 1.5 Tb/in2. Heat Assisted Magnetic Recording (HAMR) has been considered as the most promising candidate to increase the areal density of HDDs up to 10 Tb/in2. This improvement in the areal density requires employing several aspects of physics - optics, thermal conduction, magnetism, and mechanical control - simultaneously at the smallest regime that a device could operate with the current fabrication technologies. In addition to technological aspects, HAMR provides the opportunity to investigate physical phenomena at the length scale that was rarely investigated before. In this thesis, the light-matter interaction is investigated at the deep subwavelength regime: near the validity limits of macroscopic Maxwell’s equations. First, it is demonstrated that, using plasmonic near-field transducers, light can be focused in an area much smaller than diffraction limit (/100). At this regime, it is demonstrated that the ubiquitous Effective Medium Theory (EMT) breaks down and cannot be used for modeling the interaction between a localized beam and composite structures such as HAMR media. Indeed, the fundamental assumptions of EMT are only valid when the size of the optical beam is much larger than the feature size of composite structures. Instead, by assuming a constant field inside the inhomogeneous phase and neglecting hot spots, an impedance model is proposed for modeling and designing patterned recording media. For the case of the granular recording layer, it is demonstrated that randomness in shape, size, and position of recording grains can lead to localization of depolarization fields. This localization is similar to Anderson localization of electronic wavefunctions in a random potential. In addition, it is demonstrated that for the case of plasmonic particles, random hopping of photons between Localized Surface Plasmonic Polaritons (LSPPs) modes of the system can lead to Anderson localization of the light in the deep subwavelength regime. Finally, the resulting impacts of these localized modes are investigated on the randomness in the absorption of different recording grains. In fact, random absorption can lead to ∼ 3% variation in the temperature of the grains (σT ≈ 3%), which is comparable to the effect of σTc: the common source of transition noise in the recording process.