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Thursday, March 3rd @ 4pm – Fisher Hall 139 & Zoom
Hybrid-Mode: The students will give their talks in Fisher Hall 139. Please join in-person or by zoom.
Seth Nelson [Advisor: Miguel Levy]
Nonreciprocal Magneto-Optical Beam Splitters
Magneto-Optical materials are media in which the propagation of electromagnetic radiation is non-reciprocally modified by the presence of a magnetic field. This talk will report on recent results obtained in our group showing that optical beams in these media may be induced to generate quadruple reflection and triple refraction, each propagating with different phase velocities and polarizations. Separable elliptically and linearly polarized beams may be generated from linear or circularly polarized inputs. Moreover, these phenomena are nonreciprocal, meaning that reverse propagation does not restore the original inputs. We provide a theoretical explanation for these phenomena and have experimentally verified them in the visible and infrared wavelengths. These unique modes with separate reflection/refraction present the opportunity to create nonreciprocal polarization beam splitters, applicable to multi-functional photonic devices that may operate as classical or quantum photonic logic gates, beam steerers, and isolators.
Oindabi Mukherjee [Advisor: Robert Nemiroff]
Criteria to Detect a Gravitational Echo in the Light Curves of Gamma-Ray Bursts (GRBs)
To show a signature of gravitational lensing, two sections of the flux of a gamma-ray burst (GRB) must adhere to certain criteria. Here, I present a description of two straightforward similarity tests of these criteria: a hardness test and a light-curve test. Based on recent claims that pulse pairs in several GRBs are gravitationally millilensed images of the same parent pulse, our analyses indicate that none of those claims clearly satisfy both tests. A hardness similarity test performed on GRB 950830 found that the ratio between the second pulse and the first in channel 3 differed from the same ratio in all other channels with above 90% confidence. Also, a light curve similarity test performed on GRBs 090717, 200716C, and 210812A found that the two pulses differ at about 5 sigma, 3.1 sigma, and 2.8 sigma respectively. Hence, presently, no GRB of which we are aware can be confidently claimed to contain a signature of gravitational lensing.
Dharmendra Pant [Advisor: Ranjit Pati]
Emergence of Ferromagnetism in a Twisted Bilayer Graphene Nanoflex
When one layer of graphene is rotated on another layer, it exhibits many intriguing properties like superconductivity, Mott-like insulating phase, anomalous hall effect and ferromagnetism near the magic angle 1.1º. Here, using density functional theory we discovered ferromagnetism in a twisted bilayer graphene nanoflex (TBGNF) at several angles between 0 and 30º. Our results demonstrate that when the energy gap of TBGNF approaches zero, electronic instability happens, and the ferromagnetic phase emerges. In this talk, I will discuss the nonmagnetic to ferromagnetic phase transition in TBGNF caused by the spontaneous symmetry breaking of an unstable nonmagnetic phase to a low energy broken symmetry ferromagnetic phase.
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