Articles in 2015

Exploiting lasers for accelerating charged particles to relativistic velocities has long been theoretically considered. Now, applying a plasma mirror for injecting electrons into an intense laser field in vacuum is shown to lead to such acceleration.

The dynamic susceptibility of the quantum spin ice material Yb₂Ti₂O₇ is probed by means of time-domain spectroscopic techniques, providing a handle on the conductivity of monopole excitations in this system.

A series of transport experiments on lanthanum antimonide reveal a plateau in its resistivity and an extremely large magnetoresistance that are consistent with topologically protected electronic states.

Thouless introduced the idea of a topological charge pump: the quantized motion of charge due to the slow cyclic variation of a periodic potential. This topologically protected transport has now been realized with ultracold bosonic atoms.

A study of robots jumping on granular media reveals that performance depends on an added-mass effect born of grains solidifying on impact. Techniques that are optimized for launching off hard surfaces are shown to be compromised by the effect.

Using an artificial three-level lambda system realized in a superconducting transmon qubit in a microwave cavity one can observe coherent population trapping, electromagnetically induced transparency and superluminal pulse propagation.

What happens to correlated electronic phases—superconductivity and charge density wave ordering—as a material is thinned? Experiments show that both can remain intact in just a single layer of niobium diselenide.

Determining—and defining—the size of an atomic nucleus is far from easy. First-principles calculations now provide accurate information on the neutron distribution of the neutron-rich ⁴⁸Ca nucleus—and constraints on the size of a neutron star.

Hydrostatic pressure is used as a means to tune the two-dimensional electron gas hosted in a GaAs/AlGaAs crystal from a topologically ordered to a spontaneously broken symmetry phase.

For small twist angles, electrons can resonantly tunnel between graphene layers in a van der Waals heterostructure. It is now shown that the tunnelling not only preserves energy and momentum, but also the chirality of electronic states.

Heat transport is well described by the Green–Kubo formalism. Now, the formalism is combined with density-functional theory, enabling simulations of thermal conduction in systems that cannot be adequately modelled by classical interatomic potentials.

Tin selenide is at present the best thermoelectric conversion material. Neutron scattering results and ab initio simulations show that the large phonon scattering is due to the development of a lattice instability driven by orbital interactions.

Exchange interactions are typically short-ranged as they depend on wavefunction overlap, but a long-ranged exchange is now seen in a hybrid ferromagnet–semiconductor system, which may be mediated by elliptically polarized phonons.

Tunable interactions in quantum many-body systems have practical applications in quantum technologies. The effective spin-dependent long-range interaction known as Rydberg dressing is now exploited to entangle a pair of ultracold neutral atoms.

A study of a composite soft-matter nanomechanical system consisting of a rotating ring of optically trapped colloidal particles confining a set of untrapped colloids demonstrates the possibility of gearwheel-like torque transmission on the nanoscale.

A theoretical study uncovers the role of entanglement in the relaxation dynamics of a one-dimensional Bose gas following coherent splitting, a relevant scenario for recent ultracold atom experiments.

Using a superconducting circuit analogue of an atom in front of a mirror it is possible to shape the modes of the quantum vacuum and hide the atom from the vacuum fluctuations.

A combination of nonlinear optical experiments, piezoresponse force microscopy and Monte Carlo simulations resolves the correlation between polarization, topology and temperature for the hexagonal manganite YMnO₃—a persistent ferroelectrics puzzle.

Cells moving in a tissue undergo a rigidity transition resembling that of active particles jamming at a critical density—but the tissue density stays constant. A new type of rigidity transition implicates the physical properties of the cells.

Nematic phases with broken crystal rotation symmetry are as ubiquitous in superconductors as they are puzzling. One model shows that frustrated magnetism alone can account for the nematicity in FeSe, which shows no measurable magnetic order.