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- Shi-Wei Chu, Szu-Yu Chen, +4 authors Chi-Kuang Sun
- Biophysical journal
- 2004

Optical second- and third-harmonic generations have attracted a lot of attention in the biomedical imaging research field recently due to their intrinsic sectioning ability and noninvasiveness. Combined with near-infrared excitation sources, their deep-penetration ability makes these imaging modalities suitable for tissue characterization. In this article,… (More)

- Shi-Zeng Lin, Yoshitomo Kamiya, +9 authors Lars Onsager
- 2014

Lars Onsager and Richard Feynman envisaged that the three-dimensional (3D) superfluid-to-normal λ transition in 4He occurs through the proliferation of vortices. This process should hold for every phase transition in the same universality class. The role of topological defects in symmetry-breaking phase transitions has become a prime topic in cosmology and… (More)

- G W Chern, Avadh Saxena
- Optics letters
- 2015

The kagome lattice is a two-dimensional network of corner-sharing triangles and is often associated with geometrical frustration. In particular, the frustrated coupling between waveguide modes in a kagome array leads to a dispersionless flat band consisting of spatially localized modes. Here we propose a complex photonic lattice by placing PT-symmetric… (More)

- G W Chern, Muir J. Morrison, Cristiano Nisoli
- Physical review letters
- 2013

Although initially introduced to mimic the spin-ice pyrochlores, no artificial spin ice has yet exhibited the expected degenerate ice phase with critical correlations similar to the celebrated Coulomb phase in the pyrochlore lattice. Here we study a novel artificial spin ice based on a vertex-frustrated rather than pairwise frustrated geometry and show that… (More)

- G W Chern, Paula Mellado, Oleg Tchernyshyov
- Physical review letters
- 2011

Spin ice, a peculiar thermal state of a frustrated ferromagnet on the pyrochlore lattice, has a finite entropy density and excitations carrying magnetic charge. By combining analytical arguments and Monte Carlo simulations, we show that spin ice on the two-dimensional kagome lattice orders in two stages. The intermediate phase has ordered magnetic charges… (More)

- Sheng Zhang, Ian Gilbert, +7 authors Peter Schiffer
- Nature
- 2013

Artificial spin ice is a class of lithographically created arrays of interacting ferromagnetic nanometre-scale islands. It was introduced to investigate many-body phenomena related to frustration and disorder in a material that could be tailored to precise specifications and imaged directly. Because of the large magnetic energy scales of these nanoscale… (More)

- Oleg Tchernyshyov, G W Chern
- Physical review letters
- 2005

We provide a simple explanation of complex magnetic patterns observed in ferromagnetic nanostructures. To this end we identify elementary topological defects in the field of magnetization: ordinary vortices in the bulk and vortices with half-integer winding numbers confined to the edge. Domain walls found in experiments and numerical simulations in strips… (More)

- F. Q. Zhu, G W Chern, Oleg Tchernyshyov, Xian Can Zhu, J G Zhu, Chia-Ling Chien
- Physical review letters
- 2006

Magnetization reversals through the formation of a vortex state and the rotation of an onion state are two processes with comparable probabilities for symmetric magnetic nanorings with a radius of about 50 nanometers. This magnetic bistability is the manifestation of the competition between the exchange energy and the magnetostatic energy in nanomagnets.… (More)

- G W Chern, Oleg Tchernyshyov
- Philosophical transactions. Series A…
- 2012

We present a numerical study of magnetic ordering in spin ice on kagome, a two-dimensional lattice of corner-sharing triangles. The magnet has six ground states and the ordering occurs in two stages, as one might expect for a six-state clock model. In spin ice with short-range interactions up to second neighbours, there is an intermediate critical phase… (More)

- Oleg A. Tretiakov, David G. Clarke, G W Chern, Ya B Bazaliy, Oleg Tchernyshyov
- Physical review letters
- 2008

We express the dynamics of domain walls in ferromagnetic nanowires in terms of collective coordinates, generalizing Thiele's steady-state results. For weak external perturbations the dynamics is dominated by a few soft modes. The general approach is illustrated on the example of a vortex wall relevant to recent experiments with flat nanowires. A two-mode… (More)