Volume 12 Issue 11, November 2016

A wire moving at constant speed through superfluid helium can considerably exceed the Landau critical velocity.

Although Dirac fermions in graphene can tunnel through potential barriers without reflection, two experiments show how they can temporarily be trapped inside nanoscale graphene quantum dots.

Intuition informs a widespread policy of epidemic response, replacing infected workers in classrooms or hospitals with healthy substitutes. But modelling now suggests that this mechanism may be a key factor in the accelerated spread of an epidemic.

The physical properties of ice are governed by its tetrahedral network of hydrogen bonds and the ice rules that determine the distribution of the protons. Deviations from the tetrahedral structure and violations of these rules can lead to surprising phenomena, such as the ferroelectric state now reported for thin films of epitaxial ice.

Solar eruptions are triggered by magnetic stress building up in the corona due to the motion of the Sun's dense surface. New observations reveal that these eruptions can, in turn, induce the rotational motion of sunspots.

Using a technique inspired by Ramsey spectroscopy it is now possible to coherently control free electrons in an electron microscope.

Condensed-matter physics meets quantum optics in a study of light–matter interaction in the strong-coupling regime using a two-dimensional electron gas in a high-quality-factor terahertz cavity.

Josephson plasma waves — electromagnetic waves propagating between layered superconductors — lie at the basis of a broad variety of phenomena. Now, parametric amplification of such waves has been shown by tuning the phase between pump and seed waves.

An experiment reports the unexpected behaviour of an object in uniform motion in superfluid helium-3 above the Landau critical velocity — the limit above which it can generate excitations at no energy cost.

Two distinct valleys in the electronic band structure of graphene provide an additional degree of freedom that could be exploited for devices. Conservation of this valley symmetry can now be seen in the quantized conductance of graphene nanoribbons.

The spin–momentum locking of Dirac surface states offers intriguing possibilities for converting between charge and spin currents. Experiments show that fine tuning of the Fermi level is critical for maximizing the efficiency of such conversions.

Relativistic Dirac fermions can be locally confined in nanoscale graphene quantum dots using electrostatic gating, and directly imaged using scanning tunnelling microscopy before escaping via Klein tunnelling.

The realization of a quantum kicked top provides evidence for ergodic dynamics and thermalization in a small quantum system consisting of three superconducting qubits.

The common policy of replacing infected individuals with healthy substitutes can have the effect of accelerating disease transmission. A dynamic network model suggests that standard modelling approaches underplay the effect of network structure.

A scanning tunnelling spectroscopy study focuses on the lightly doped region of the phase diagram of a cuprate superconductor to reveal the microscopic evolution of a high-temperature superconductor from a charge-ordered insulator.

A method for analysing STM data enables the recovery of information about quasiparticle scattering in the form of holographic maps. The approach is verified for superconducting cuprates, but may find applications in heavy-fermion materials research.

Studies of supercurrent phenomena, such as superconductivity and superfluidity, are usually restricted to cryogenic temperatures, but evidence suggests that a magnon supercurrent can be excited in a Bose–Einstein magnon condensate at room temperature.

Ice is a frustrated system: many ground states are possible due to the structure of a water molecule and the geometry of the ice lattice. Now, this frustration is shown to lead to high-T_c ferroelectric proton ordering in a heteroepitaxial ice film.

Relativistic Dirac fermions can be locally confirmed in nanoscale graphene quantum dots using electrostatic gating, and directly imaged using scanning tunnelling microscopy before escaping via Klein tunnelling.

Multiplex networks are shown to harbour significant correlations between layers. A framework describing the correlations enables multilayer community and link detection, and reveals that they improve navigation — but only when they’re strong.

Nick van Remortel demystifies natural unit systems — and advises what to do when you see a mass expressed in GeV.