9 research outputs found
Binary matrices of optimal autocorrelations as alignment marks
We define a new class of binary matrices by maximizing the peak-sidelobe
distances in the aperiodic autocorrelations. These matrices can be used as
robust position marks for in-plane spatial alignment. The optimal square
matrices of dimensions up to 7 by 7 and optimal diagonally-symmetric matrices
of 8 by 8 and 9 by 9 were found by exhaustive searches.Comment: 8 pages, 6 figures and 1 tabl
Multimode One-Way Waveguides of Large Chern Numbers
Current experimental realizations of the quantum anomalous Hall phase in both electronic and photonic systems have been limited to a Chern number of one. In photonics, this corresponds to a single-mode one-way edge waveguide. Here, we predict quantum anomalous Hall phases in photonic crystals with large Chern numbers of 2, 3, and 4. These new topological phases were found by simultaneously gapping multiple Dirac and quadratic points. We demonstrate a continuously tunable power splitter as a possible application of multimode one-way waveguides. All our findings are readily realizable at microwave frequencies.MIT Tom Frank FellowshipNational Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Grant DMR-0819762)United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center Grant DE-SC0001299)United States. Army Research Office (Contract W911NF-13-D-0001
Experimental Observation of Large Chern numbers in Photonic Crystals
Despite great interest in the quantum anomalous Hall phase and its analogs,
all experimental studies in electronic and bosonic systems have been limited to
a Chern number of one. Here, we perform microwave transmission measurements in
the bulk and at the edge of ferrimagnetic photonic crystals. Bandgaps with
large Chern numbers of 2, 3, and 4 are present in the experimental results
which show excellent agreement with theory. We measure the mode profiles and
Fourier transform them to produce dispersion relations of the edge modes, whose
number and direction match our Chern number calculations.Comment: This experimental work was accepted to PRL on Oct. 13, 2015. Our
theoretical work from PRL http://dx.doi.org/10.1103/PhysRevLett.113.11390
Quantum \v{C}erenkov Radiation: Spectral Cutoffs and the Role of Spin and Orbital Angular Momentum
We show that the well-known \v{C}erenkov Effect contains new phenomena
arising from the quantum nature of charged particles. The \v{C}erenkov
transition amplitudes allow coupling between the charged particle and the
emitted photon through their orbital angular momentum (OAM) and spin, by
scattering into preferred angles and polarizations. Importantly, the spectral
response reveals a discontinuity immediately below a frequency cutoff that can
occur in the optical region. Specifically, with proper shaping of electron
beams (ebeams), we predict that the traditional \v{C}erenkov radiation angle
splits into two distinctive cones of photonic shockwaves. One of the shockwaves
can move along a backward cone, otherwise considered impossible for
\v{C}erenkov radiation in ordinary matter. Our findings are observable for
ebeams with realistic parameters, offering new applications including novel
quantum optics sources, and open a new realm for \v{C}erenkov detectors
involving the spin and orbital angular momentum of charged particles.Comment: 27 pages, 3 figure
Viscoelasticity of stepped interfaces
Using molecular dynamics modeling, we show that interfaces in sputter deposited Cu-Nb superlattices exhibit time-dependent elasticity, i.e., viscoelasticity, under shear loading. In the high temperature and small strain rate limit, the interfacial shear modulus approaches a value proportional to the density of steps in the interface. It may therefore be possible to tailor the low-frequency shear moduli of interfaces by controlling their step densities.National Science Foundation (U.S.) (Grant 1150862)MIT International Science and Technology Initiatives (MISTI-Chile Seed Grant)MIT Energy Initiative (Summer Fellowship
The role of thermal spike compactness in radiation-induced disordering and Frenkel pair production in Ni[subscript 3]Al
We show that the shape of the kinetic energy distribution in radiation-induced thermal spikes may be described using a dimensionless number, proportional to (volume)[superscript 2/3]/(surface area), known as compactness. The disorder produced in thermal spikes in Ni[subscript 3]Al increases with compactness because the thermal spike cooling rate, which determines the time available for thermal disordering, decreases with compactness. On the other hand, Frenkel pair production is inversely correlated to compactness because longer thermal spike lifetimes enhance vacancy–interstitial recombination
Planar-lens Enabled Beam Steering for Chip-scale LIDAR
© 2018 OSA. A lens-enabled chip-scale beam steering device for LIDAR is theoretically analyzed and experimentally demonstrated with azimuthal, φrange = 38.8°, and polar, θrange = 12.0°, beam-steering. The device allows for beam-steering at low power and low cost