Articles in 2015

The thermodynamic properties of artificial spin ice are strongly influenced by the manner in which its constituent nanomagnets are arranged. The so-called tetris lattice geometry is now shown to lead to emergent one-dimensional correlations.

Despite the simplicity of the Carnot cycle, realizing it at the microscale is complicated by the difficulty in implementing adiabatic processes. A clever solution subjects a charged particle to a noisy electrostatic force that mimics a thermal bath.

A detailed scanning tunnelling microscopy study of the cuprate superconductor Bi₂Sr₂CaCu₂O_8+x reveals the microscopic origin of the d-symmetry form factor density wave that exists in the pseudogap phase of this material.

Anharmonicity is a property of lattice vibrations governing how they interact and how well they conduct heat. Experiments on tin selenide, the most efficient thermoelectric material known, now provide a link between anharmonicity and electronic orbitals.

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.

Specific heat measurements up to 35 T provide thermodynamic evidence for a magnetic-field-driven phase transition within the superconducting dome of a copper-oxide-based superconductor.

Coupling two mechanical objects becomes tricky when they are quantum and can interact only through photons. An experiment now demonstrates such an optomechanical system with two separate atomic ensembles in the same optical cavity.

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.

Sr₂IrO₄ bears a striking electronic resemblance to the cuprate superconductors, except the iridate is an insulator. Introducing electrons into Sr₂IrO₄ leads to a d-wave gap, suggesting superconductivity or something equally exotic.

Topological protection can stabilize states of matter, but for how long? By creating metastable magnetic skyrmion lattices, the interplay between topological and thermodynamic stability has now been probed experimentally.

Magnetic atoms embedded in a niobium selenide superconductor are shown to give rise to a long-range coherent bound state extending tens of nanometres.

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.

The 2015 Nobel Prize in Physics has been awarded to Takaaki Kajita and Arthur B. McDonald "for the discovery of neutrino oscillations, which shows that neutrinos have mass".

An experiment with cold atoms confined in an isotropic three-dimensional harmonic potential confirms the long-predicted non-damping oscillations of the breathing mode.

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 cold-atom experiment confirms Boltzmann’s special case predicted more than a century ago: the ‘breathe’ mode of a gas in a perfectly isotropic three-dimensional harmonic potential is never damped by elastic collisions.

A switchable induced magnetic moment in a non-magnetic metal that is separated from a ferromagnet by a thick superconducting layer contradicts existing models.

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.