Spin current can be used to control the magnetization dynamics of a nano-magnet. There are various ways to generate spin current. Electrical current or heat current passing through a ferromagnet can generate spin current due to the spin dependent conductivity or spin-dependent Seebeck effect. Electrical current passing through a non-magnetic material with high spin-orbit coupling can generate spin current via the spin-Hall effect. Heat current passing through a non-magnet can also generate spin current due the spin-orbit coupling. This effect known as the spin-Nernst effect (SNE), has been shown recently by measuring thermally driven spin-Hall magneto-resistance [1-3]. We have shown that the spin-Nernst effect can be measured directly via a multi-terminal device with ferromagnetic Ni contacts on Pt . We generated heat current in the Pt and the resultant spin current was then detected by Ni contacts. The same multi-terminal device was used to measure the spin-Hall angle for comparison with spin-Nernst angle. In a further work, we have shown that the spin current generated via spin-Nernst effect can be injected into an adjacent FM layer to exert spin-transfer torque (spin-Nernst torque) . We could change the effective damping of the ferromagnet via spin-Nernst torque.
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In this paper, we discuss the setup of a confocal nanoscope in reflection using a super-oscillatory lens (SOL)which offers a sub-diffracted focal spot with an ultra-short depth of focus (≈100 nm). A tolerance of 20 nm defocussing in a 10 μm travel range is thus necessary, translating to an alignment requirement of the stage, with respect to the optical axis, below 2 mrad. We discuss an iterative procedure to fine tune the stage movement to achieve this requirement. We also demonstrate the necessity of the alignment by imaging a 5μm long 1D array of rectangular shaped Au nanostructures with a periodicity of 500 nm
Dipole induced quadrupole resonance leads to transmission peak within the broad dipole absorption as shown in plasmonic metamaterials. We show quadrupolar interactions as a new paradigm to control this classical analogue of electromagnetically induced transparency (i.e. plasmon induced transparency, PIT) in metamaterials. While the asymmetry factor of the resultant Fano line shape of a EIT spectrum limits the quality factor (Q) of the resonance and thus the sensing application, we show that quadrupolar interactions give a handle on the Q factor. A Q as high as 600 is seen in simulations at about 0.977 THz. Limited by the experimental resolution, a Q of about 100 is observed. Further plasmonic structures can be designed to make use of the quadrupolar interactions for high sensitive devices at THz frequencies.
Plasmonic quasicrystals stand out as the center of cynosure behind the many potential applications which emerges due to the quasi-periodic structure and metal dielectric patterns. The rotational symmetry elicits the optical properties resembling like crystals and and the metal dielectric nanostructure are being probed and explored in various disciplines of science and even in engineering also. Plasmonic quasicrystals composed of quasi- periodic and metal-dielectric patterns furnish efficacious benefits in improving the efficiency of solar cells, broadband transmission enhancement, and bio-sensing applications etc. Due to the intriguing properties of plasmonic crystals such as periodicity and short range ordering, the excitation of the surface Plasmon polaritons is restricted by a few fewer techniques such as polarization, launch angle dependence. Polarization contains wealth of information and holds the potential to control the interaction of light with metal Nano particles. Therefore, an exhaustive and thorough information regarding incident and scattered light is necessary for the examining the spectral response of the quasi crystal. Here, we report to the best of our knowledge the first ever quantitative polarimetric studies on the extremely complex plasmonic quasicrystal by recording a full 4x4 spectral Mueller matrix from the same and tried to explore the fascinating and interesting properties of quasi crystals. A homebuilt comprehensive Mueller Matrix platform (integrated with dark field microscope) is utilized to record the conventionally weak, intermixed polarization signal from plasmonic quasicrystals. These studies probed the enthralling phenomena of Fano resonance, explored and probed the presence of phase anisotropy in the plasmonic quasicrystals using the Mueller matrix derived retardance (δ) parameter. Additionally polarization mediated tuning of Fano Resonance is achieved too. Moreover it is demonstrated that the Mueller matrix derived diattenuation, retardance parameters probes the Fano resonance, phase and amplitude anisotropy from such complex plasmonic nanostructure and proved instrumental in polarization controlled tuning of Fano resonance.
We have dramatically improved the optical properties of extremely thin QWs required for ISBT devices operating at optical communication wavelengths using novel InGaAs/AlAs/AlAsSb QW structures with 4-7 monolayers (MLs) of AlAs. The intersubband saturation intensity (Is) was reduced to 3fj/μm2. This represented an Is reduction of nearly 3 orders of magnitude relative to the previous samples whether or not such sample featured 1 ML of AlAs interface layer. This paper reviews the recent results of novel InGaAs/AlAs/AlAsSb quantum well properties grown by molecular beam epitaxy, and discusses the linear and nonlinear optical responses of ISBT.
Based on our line shape analysis of temperature dependent absorption spectra on InGaAs/AlAsSb single quantum wells, we expect a fast carrier redistribution with in the broad inhomogeneous intersubband absorption spectrum from a wavelength as short as 1.72 micrometers . In addition, due to large resonant 3rd order susceptibility but weak absorption, we expect small saturation intensity (Is) at this short wavelength. We present wavelength dependent saturation measurements to show that the Is is, indeed, lower by more than an order of magnitude compared to that at the main peak (1.88 micrometers ). We also show from the figure of merit estimates that the carrier relaxation time at 1.72 micrometers is expected to be faster at 1.72 micron, consistent with the line shape analysis predictions.