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Author(s): Alexandru Florin Dobrin (corresponding author) [1] Our understanding of the world around us is summarized in the standard model of particle physics. This model describes the building blocks of [...]

Author(s): Bertram Blank Author Affiliations: Mirror symmetry broken for nuclear ground states Nature likes symmetry. Examples range across size scales from macroscopic objects, such as spiderwebs or honeycombs, to the [...], The principle of mirror symmetry, which states that nuclear structure remains the same when protons are swapped for neutrons and vice versa, has been found to be broken in the lowest-energy forms of a mirror pair of nuclei. Bromine-73 and strontium-73 have different ground-state configurations.

In the integer quantum Hall effect, the topology of the bulk Landaulevel energy bands requires the existence of gapless edge states at any interface with the vacuum. The metrological precision [...], Low-dimensional electronic systems have traditionally been obtained by electrostatically confining electrons, either in heterostructures or in intrinsically nanoscale materials such as single molecules, nanowires and graphene. Recently, a new method has emerged with the recognition that symmetry-protected topological (SPT) phases (1,2), which occur in systems with an energy gap to quasiparticle excitations (such as insulators or superconductors), can host robust surface states that remain gapless as long as the relevant global symmetry remains unbroken. The nature of the charge carriers in SPT surface states is intimately tied to the symmetry of the bulk, resulting in one- and two-dimensional electronic systems with novel properties. For example, time reversal symmetry endows the massless charge carriers on the surface of a three-dimensional topological insulator with helicity, fixing the orientation of their spin relative to their momentum (3,4). Weakly breaking this symmetry generates a gap on the surface (5), resulting in charge carriers with finite effective mass and exotic spin textures (6). Analogous manipulations have yet to be demonstrated in two-dimensional topological insulators, where the primary example of a SPT phase is the quantum spin Hall state (7,8). Here we demonstrate experimentally that charge-neutral monolayer graphene has a quantum spin Hall state (9,10) when it is subjected to a very large magnetic field angled with respect to the graphene plane. In contrast to time-reversal-symmetric systems (7), this state is protected by a symmetry of planar spin rotations that emerges as electron spins in a half-filled Landau level are polarized by the large magnetic field. The properties of the resulting helical edge states can be modulated by balancing the applied field against an intrinsic antiferro-magnetic instability (11-13), which tends to spontaneously break the spin-rotation symmetry. In the resulting canted antiferromagnetic state, we observe transport signatures of gapped edge states, which constitute a new kind of one-dimensional electronic system with a tunable bandgap and an associated spin texture (14).

Author(s): Premala Chandra [sup.1] , Piers Coleman [sup.1] [sup.2] , Rebecca Flint [sup.3] Author Affiliations: (1) Department of Physics and Astronomy, Center for Materials Theory, Rutgers University, 136 Frelinghuysen Road, [...], The development of collective long-range order by means of phase transitions occurs by the spontaneous breaking of fundamental symmetries. Magnetism is a consequence of broken time-reversal symmetry, whereas superfluidity results from broken gauge invariance. The broken symmetry that develops below 17.5 kelvin in the heavy-fermion compound URu.sub.2Si.sub.2 has long eluded such identification. Here we show that the recent observation of Ising quasiparticles in URu.sub.2Si.sub.2 results from a spinor order parameter that breaks double time-reversal symmetry, mixing states of integer and half-integer spin. Such 'hastatic' order hybridizes uranium-atom conduction electrons with Ising 5f.sup.2 states to produce Ising quasiparticles; it accounts for the large entropy of condensation and the magnetic anomaly observed in torque magnetometry. Hastatic order predicts a tiny transverse moment in the conduction-electron 'sea', a colossal Ising anisotropy in the nonlinear susceptibility anomaly and a resonant, energy-dependent nematicity in the tunnelling density of states. The formation of Ising quasiparticles in URu.sub.2Si.sub.2 results from 'hastatic' order, which breaks double time-reversal symmetry, mixing states of integer and half-integer spin, and accounts for the large entropy of condensation and the magnetic anomaly observed in torque magnetometry. Novel 'hastatic' order in condensed matter At temperatures below 17.5 K, the heavy-fermion uranium compound URu.sub.2Si.sub.2 exists in a mysterious 'hidden-order' phase that has eluded characterization for 25 years. In this study the authors have used various pieces of experimental evidence to establish the nature of the spontaneous phase transition that takes place at 17.5 K, and conclude that both single and double time-reversal symmetry occur, resulting in mixing of itinerant conduction electrons and localized 'Ising' states in the 5f.sup.2 orbital of uranium atoms. This is a fundamentally new type of order, which the authors dub hastatic (from the Latin hasta, a spear), and which they say could be a phenomenon that applies to other systems in which mixing with f-orbital states takes place.

In designing an optical system, nature demands that only a few basic 'ingredients' be used: refractive index, gain and loss. There is no doubt as to how useful index contrast [...], The development of new artificial structures and materials is today one of the major research challenges in optics. In most studies so far, the design of such structures has been based on the judicious manipulation of their refractive index properties. Recently, the prospect of simultaneously using gain and loss was suggested as a new way of achieving optical behaviour that is at present unattainable with standard arrangements. What facilitated these quests is the recently developed notion of 'parity-time symmetry' in optical systems, which allows a controlled interplay between gain and loss. Here we report the experimental observation of light transport in large-scale temporal lattices that are parity-time symmetric. In addition, we demonstrate that periodic structures respecting this symmetry can act as unidirectional invisible media when operated near their exceptional points. Our experimental results represent a step in the application of concepts from parity-time symmetry to a new generation of multifunctional optical devices and networks.

Colloidal particle dispersions feature a wide variety of attractive and repulsive interactions and mechanical packing constraints that have been exploited to assemble a diverse set of structures, including Pickering emulsions [...], The assembly of complex structures out of simple colloidal building blocks is of practical interest for building materials with unique optical properties (for example photonic crystals (1) and DNA biosensors (2)) and is of fundamental importance in improving our understanding of self-assembly processes occurring on molecular to macroscopic length scales (3-5). Here we demonstrate a self-assembly principle that is capable of organizing a diverse set of colloidal particles into highly reproducible, rotationally symmetric arrangements. The structures are assembled using the magnetostatic interaction between effectively diamagnetic and paramagnetic particles within a magnetized ferrofluid. The resulting multipolar geometries resemble electrostatic charge configurations such as axial quadrupoles ('Saturn rings'), axial octupoles ('flowers'), linear quadrupoles (poles) and mixed multipole arrangements ('two tone'), which represent just a few examples of the type of structure that can be built using this technique.

Author(s): F. Ronning [1]; T. Helm [2]; K. R. Shirer [2]; M. D. Bachmann [2]; L. Balicas [3]; M. K. Chan [4]; B. J. Ramshaw [4, 5]; R. D. McDonald [...]

Convective effects determine the pattern of electrodeposition of metals from solutions of their salt. Convective effects affect the electrodeposition of iron from FeSo4 solution and lead to the formation of a mesh-like pattern, as observed by interference contrast microscopy and transmission optical dark field microscopy. A reduction in pH reduces convection and shifts to dense branching pattern of deposition.

Mechanical motions and disturbances of growing branches of metal ions in solution modify morphology patterns between fractal and rectilinear states. A study of electrochemical deposition of ramified deposits reveals that high growth speeds break the symmetry of fanning in the growing branches and cause differential growth patterns. The experiment parameters also determine the final pattern detected.

Author(s): Johannes Hecker Denschlag [1] Quantum computers promise to solve problems that cannot be tackled by conventional computers [1]. But they make high demands on the machinery from which they [...]

The charge density wave behavior of ultra-thin films of lead adsorbed on germanium is accompanied by metal-nonmetal transition and periodic lattice distortion. The structural symmetry of the system is broken and the molecular orbits degenerate so that an electron can occupy a lower energy level. The lead-germanium system is non-metallic in the low temperature, distorted phase due to the band gap. This behavior can be used to produce specific electronic characteristics by tailoring interface and surface properties.

Spontaneous symmetry-breaking in magnets and soap films is discussed. Ferromagnetism is the most common type of spontaneous symmetry breaking and is related to the unpaired spin on each atom of iron. Chiral symmetry as demonstrated by the optical activity of sugars is another example of spontaneous symmetry breaking at the molecular level which is expressed in the macroscopic level. Understanding spontaneous symmetry breaking could help in engineering molecules to express useful patterns.

The fundamental asymmetry in the laws of physics called charge-parity (CP) violation is tiny, yet it looms large enough in physics to have led to Nobel prizes on three occasions. [...]

Exact symmetry fits into an outmoded mechanical model of molecular structure and may be replaced by a newly developed system of continuous symmetry measures. Continuous symmetry is a measure of degrees of deviation from a rotational or mirror symmetry. In two-dimensional cases, the measure is easily determined by comparison of a structure with its images in a hypothetical symmetrized set representing the nearest object with the desired symmetry. The situation is more complex in three-space. These measures should be of use in parametrizing property surfaces in anisotropic non-equilibrium geometries.