Volume 12 Issue 7, July 2016

An old branch of mathematics has paved the way for discovering new phases of matter.

Topological matter can host low-energy quasiparticles, which, in a superconductor, are Majorana fermions described by a real wavefunction. The absence of complex phases provides protection for quantum computations based on topological superconductivity.

Electronic topological insulators have inspired the design of new mechanical systems that could soon find real-life applications.

The topological state of matter depends on its dimension. Remarkably, topological properties of quasiperiodic systems are found to emerge from higher dimensions.

Optics played a key role in the discovery of geometric phase. It now joins the journey of exploring topological physics, bringing bosonic topological states that equip us with the ability to make perfect photonic devices using imperfect interfaces.

The topological degeneracy associated with Majorana edge states has been measured in a spin-1/2 chain of cobalt atoms, thereby opening new avenues in low-dimensional quantum magnetism.

A frequency comb technique used in NMR spectroscopy reveals the dynamics of the nuclear spin bath in self-assembled quantum dots.

When it comes to star formation, dwarf galaxies perform very poorly. A possible explanation for this behaviour involves photoelectric electrons heating the star-forming gas.

Radiation pressure noise from squeezed light constrains the precision of sensing devices such as improved gravitational wave interferometers.

Using optical lattices to trap ultracold atoms provides a powerful platform for probing topological phases, analogues to those found in condensed matter. But as these systems are highly tunable, they could be used to engineer even more exotic phases.

Aspects of the disordered Bose–Hubbard model, such as the Bose glass–superfluid transition, are still incompletely understood, but this can now be probed in an ultracold atomic gas in an optical lattice using controlled quantum quenches of disorder.

The stability of a large class of elemental knots and links to so-called reconnections is studied numerically using the Gross–Pitaevskii model for a superfluid, demonstrating that they universally untie.

Magnetic adatoms offer an appealing platform for building idealized spin models, but achieving sufficient control to do so is challenging. Now, arrays of Co atoms evaporated on a Cu₂N/Cu(100) surface are shown to behave like a spin-1/2 XXZ Heisenberg chain.

A magnetic analogue of the Poole–Frenkel effect shows that magnetic monopole quasiparticles in a spin ice behave similar to electrons in a semiconductor, with an attractive Coulomb force acting between positive and negative monopoles.

A combination of detailed photoelectron spectroscopy measurements and numerical simulations reveal the presence of so-called Dirac node arcs in the electronic structure of PtSn₄.

In analogy to fluids, electric currents can exhibit viscosity — albeit with effects difficult to observe experimentally. Now, vorticity is reported as a signature feature of electron viscosity in graphene, which leads to negative nonlocal resistance.

Coherent valley exciton dynamics are directly probed in a monolayer transition metal dichalcogenide, providing access to the valley coherence time and decoherence mechanisms — crucial for developing methods for manipulating the valley pseudospin.

Non-classical states of light, such as squeezed states, are used in quantum metrology to improve the sensitivity of mechanical motion sensing, but conversely mechanical oscillations can enhance the measurement of squeezed light.

Using a frequency-comb nuclear magnetic resonance spectroscopy technique it is possible to probe the fluctuations in the nuclear spin bath of a self-assembled quantum dot and reveal long nuclear spin correlation times over one second.

The magnetic response of nanoparticles made from wide-bandgap oxides that don’t contain any magnetic cations is somewhat of a mystery. Experiments with CeO₂ suggest that the origin may be due to vacuum fluctuations.

Multidimensional protein-folding dynamics are often probed experimentally by projecting into a single dimension. Single-molecule experiments now verify the idea that folding can be understood in terms of one-dimensional diffusion over a landscape.

Segregation between binding and non-binding proteins in the space between cells is critical for immune response. In vitro experiments show that size alone suffices to explain the exclusion of non-binding proteins from membrane interfaces.

Experiments combining dynamic and static light scattering have probed a colloidal hard-sphere system for the formation of dynamical and structural heterogeneities, which play a role in both forms of solidification: crystallization and vitrification.

Some concepts are useful but difficult to quantify, as Philip Ball illustrates with the property of hydrophobicity.