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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6

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Quartile: search.filters.quartile.Q2Subject: search.filters.subject.Physics, condensed matter

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    PublicationOpen Access
    Spin-torque oscillation in a magnetic insulator probed by a single-spin sensor
    (American Physical Society (APS), 2020) Zhang, H.; Ku, M. J. H.; Casola, F.; Du, C. H.; van der Sar, T.; Ross, C. A.; Tserkovnyak, Y.; Yacoby, A.; Walsworth, R. L.; Department of Electrical and Electronics Engineering; Onbaşlı, Mehmet Cengiz; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 258783
    We locally probe the magnetic fields generated by a spin-torque oscillator (STO) in a microbar of ferrimagnetic insulator yttrium-iron-garnet using the spin of a single nitrogen-vacancy (NV) center in diamond. The combined spectral resolution and sensitivity of the NV sensor allows us to resolve multiple spin-wave modes and characterize their damping. When damping is decreased sufficiently via spin injection, the modes auto-oscillate, as indicated by a strongly reduced linewidth, a diverging magnetic power spectral density, and synchronization of the STO frequency to an external microwave source. These results open the way for quantitative, nanoscale mapping of the microwave signals generated by STOs, as well as harnessing STOs as local probes of mesoscopic spin systems.
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    PublicationOpen Access
    Unidirectional invisibility and PT symmetry with graphene
    (American Physical Society (APS), 2018) Taş, Murat; Department of Physics; Sarısaman, Mustafa; Researcher; Department of Physics; College of Sciences
    We investigate the reflectionlessness and invisibility properties of the transverse electric-mode solution of a linear homogeneous optical system which comprises PT-symmetric structures covered by graphene sheets. We derive analytic expressions, indicate the roles of each parameter governing the optical system with graphene, and prove that optimal conditions of these parameters give rise to broadband and wide-angle invisibility. The presence of graphene turns out to shift the invisible wavelength range and to reduce the required gain value considerably, based on its chemical potential and temperature. We substantiate that our results yield broadband reflectionless and invisible configurations for realistic materials of small refractive indices, usually around eta = 1, and of small thicknesses with graphene sheets of rather low temperatures and chemical potentials. Finally, we demonstrate that pure PT-symmetric graphene yields invisibility at low temperatures and chemical potentials.