The fundamental principle for electrophoresis, the motion of a charged particle in solution driven by an applied electric field, is well understood. But experimental measurements of the electrophoretic retardation force, one of those responsible for electrophoresis, have been scarce and equivocal. Now a Belgian group develops a creative new approach to control the source of the retardation—the counterion cloud surrounding the charged particle—by gradual depletion and makes unambiguous measurement of the retardation force.

A study of the thermoelectric properties of the doped insulator, strontium titanate, shows that it superconducts with the lowest charge density ever observed.

A study of the two-dimensional version of a topological insulator, the quantum spin Hall (QSH) system, finds that the current flow in the one-dimensional edge channels of the QSH state is affected by small puddles of electrons that lift the protection against backscattering.

An analytical statistical-physical approach that is low in computational complexity, but high in accuracy is now available for theoretical studies of how behaviors, opinions, and infectious diseases spread among human populations.

Slow oscillations in neuronal activity in the human brain are the defining feature of scalp-measured electroencephalography taken under general anesthesia. A theoretical investigation of a model for the human cortex reveals that slow spatiotemporal patterns emerge spontaneously as the result of a chemically modified balancing act between two instabilities in cortical dynamics—one to spatial organizations and the other to temporal bifurcation. Long-range interneuronal communication across the cortex is shown to be crucial to the pattern formation.

What cultural and social processes determine the size and growth of the vocabulary of a natural language? Does such a vocabulary grow forever? From large text databases, such as the Google Ngram, that have become available only recently, researchers tease out new and systematic insights into these fundamental questions and develop a mathematical model with predictive power that describes vocabulary growth as a simple stochastic process.

While the tracks of the elusive Majorana fermion have been seen in semiconductor nanowires in contact with superconductors, this exotic particle is also predicted to appear in nanostructures made of three-dimensional topological insulators, such as HgTe, with induced superconducting surface current. Researchers show that such supercurrent can indeed be induced in HgTe Josephson junctions and offer insights into the underlying mechanism.

In sensing-feedback control of a quantum system, optimizing the timing of the sensing measurements turns out to be a key to getting around the fundamental difficulty that a measurement can randomly change the system’s state. Achieving optimal timing by combining technical advances with conceptual physical insight, researchers demonstrate, for the first time, high-fidelity control of a superconducting qubit along time-dependent trajectories.

So far two mechanisms, time-reversal symmetry and chirality, have been known to “protect” conducting edge states in a bulk insulator. Now Michael Levin of University of Maryland reveals “fractional statistics” of bulk particle-like excitations as the third (and final) mechanism of edge-state protection in two-dimensional insulators.

Whether polarization catastrophe or oxygen vacancies is responsible for the remarkable emergence of a two-dimensional electron gas at the interface of the insulating oxides, polar LaAlO${}_3$ and nonpolar SrTiO${}_3$, has been hotly debated. Using a series of experiments that compare the electrical properties of amorphous and crystalline LaAlO${}_3$/SrTiO${}_3$ heterostructures, researchers discover that the answer depends on the structure of the LaAlO${}_3$ overlayer.

Establishing the strength of the electron-phonon interaction, which plays an important role in superconductivity, has proven difficult with current experimental and theoretical techniques. Theorists now propose a reliable first-principles method and also use it to explain the extraordinarily high superconducting temperatures seen in bismuthates and transition-metal chloronitrides.

The ampere, the basic measurement standard for electric current, is still defined based on the electromagnetic force between two parallel current-carrying wires. To achieve a quantum standard of current based on electron counting, an extremely accurate electron pump with a high current yield in the nanoampere range is required. Researchers now present a proof-of-principle demonstration of such a pump.

An innovative wiring of two familiar superconducting circuits, a microwave LC resonator containing a small mass on a spring and a microwave amplifier that measures the motion of the mass, feeds the output of the amplifier directly back to the first circuit, creating a quantum-devices-based network that can be continuously and dynamically tuned to optimize control and measurement capabilities.

The optical properties of graphene previously used to probe its electronic structure are its optical dispersion and absorption coefficients. Now, scientists report the third-harmonic generation of light in graphene and demonstrate the promise of this nonlinear optical response as a technically versatile microscopic imaging approach of the physical structure of graphene.

Many conventional quantum information-processing proposals fix data spatially and use temporally sequenced operations to carry out a computation. Researchers now propose a different approach, relying on connected modular elements—quantum transistors—that could enable clock-controlled quantum information processing similar to present-day classical integrated circuits.

Traditional models for the growth of complex networks rely on a positive-feedback mechanism—nodes with the most existing connections get the most new connections. Theorists now present a new growth model involving a negative-feedback mechanism that may explain the prevalence of small, densely connected groups of nodes seen in real-world networks.

When sound waves travel through a disordered solid, vibrational modes above a certain threshold frequency can become localized and stop propagating. Theorists present a minimal model that predicts the critical frequency separating the localized and propagating modes in dimensions above two and explores how the transition relates to the level of disorder in the solid and its dimensionality.

Calculations show that topological states induced by structural defects may be responsible for the well-known subgap conduction in multilayer graphene that limits its use in applications.

A key to understanding high-temperature superconductivity in cuprates lies in the identification of competing electronic phases in these materials. In YBa${}_2$Cu${}_3$O${}_y$, an important cuprate with distorted CuO${}_2$ planes, the electronic phase is characterized by charge density-wave order. New measurements indicate that charge density-wave order is also present in HgBa${}_2$CuO${}_{4+\delta }$, a cuprate with undistorted CuO${}_2$ planes, suggesting that the charge order is a generic property of cuprates.