Letters in 2017

Ensuring topological protection of the edge states in candidate topological insulators is complicated by the need to break time-reversal symmetry. Polar active liquids present an innovative solution to this problem, as a new metamaterial design shows.

In different applications the Gouy phase is used to describe broadband lasers, but new 3D measurements of the spatial dependence of a focused laser pulse show serious deviations from the Gouy phase.

An experimental study of the rare-earth intermetallic system LuPt₂In reveals a strong enhancement of superconductivity near the charge density wave quantum critical point. This represents an unusual counter-example to cuprates, in which superconductivity and charge density waves tend to compete.

The presence of a Higgs amplitude mode is revealed in a two-dimensional spin-half quantum antiferromagnet, C₉H₁₈N₂CuBr₄ by means of neutron scattering.

Deformable polygons are shown to form fibres when the energies associated with attraction and deformation are comparable. The fibres constitute a kinetically trapped metastable state, reminiscent of irreversible protein assembly in living systems.

Atomic interferometry measurements of the gravitational force on free-falling atoms provide improved constraints on certain scalar field theories trying to explain dark energy.

A combination of photoemission and scanning tunnelling spectroscopy measurements provide compelling evidence that single layers of 1T'-WTe₂ are a class of quantum spin Hall insulator.

Bragg spectroscopy shows the evolution of gapless Goldstone modes and single-particle-like excitations in an atomic Fermi superfluid as it crosses from a Bardeen–Cooper–Schrieffer superfluid to the Bose–Einstein condensate regime.

A decades-old proposal that all distinct packings are equally probable in granular media has gone unproven due to the sheer number of packings involved. Numerical simulation now demonstrates that it holds — precisely at the jamming threshold.

The amplification of waves reflected from a rotating obstacle, or superradiance, has been predicted in hydrodynamics and black-hole physics. An experiment with rotating vortex flows confirms this phenomenon.

Ultrahigh-resolution resonant inelastic X-ray scattering shows how dispersive charge density wave excitations influence the charge and lattice degrees of freedom in a high-T_c cuprate, pointing to a connection to the mysterious pseudogap state.

Superfluidity is a phenomenon usually restricted to cryogenic temperatures, but organic microcavities provide the conditions for a superfluid flow of polaritons at room temperature.

Measuring the photocurrent response to circularly polarized mid-infrared light provides direct access to the chirality of Weyl fermions in Weyl semimetals — the property responsible for a range of exotic phenomena.

Attosecond streaking is used to study the dynamics of electron scattering in dielectric nanoparticles in real time. Revealing the mechanisms involved is the first step towards understanding electron scattering in more complex dielectrics.

An electronic double layer, subjected to a high magnetic field, can form an exciton condensate: a Bose–Einstein condensate of Coulomb-bound electron–hole pairs. Now, exciton condensation is reported for a graphene/boron-nitride/graphene structure.

Strongly interacting bosons have been predicted to display a transition into a superfluid ground state, similar to Bose–Einstein condensation. This effect is now observed in a double bilayer graphene structure, with excitons as the bosonic particles.

Strong plasmonic hotspots can facilitate ultrafast energy transfer between metallic nanoparticles with almost no energy loss.

The emergence of Efimov states in ultracold atomic systems is expected to have a universal behaviour, but a new experimental study defies this expectation, reporting a clear deviation around a narrow Feshbach resonance.

Thermal-expansion measurements of CeCu_6−xAu_x reveal the thermodynamic landscape of this material’s entropy, offering insights into the behaviour of quantum critical fluctuations as the system approaches its quantum critical point.

A detailed experimental investigation on the spin excitations in SrCu₂(BO₃)₂ under an external magnetic confirms the existence of topological triplon modes in this experimental realization of the Shastry–Sutherland model.