Research articles

Every metal has an underlying Fermi surface that gives rise to quantum oscillations. So far, quantum oscillation measurements in the superconductor YBCO have been inconclusive owing to the structural complexities of the material. Quantum oscillations in a Hg-based cuprate—with a much simpler structure—help to establish the origin and universality of the oscillations.

When a paramagnetic molecule is placed on a superconducting surface the lifetime of its spin excitations increases dramatically. This effect, caused by the depletion of the electronic states within the energy gap at the Fermi level, could find application in coherent spin manipulation.

In the band theory of solids, the topological properties of Bloch bands are characterized by geometric phases. For cold atoms moving in a one-dimensional optical potential the geometric phase can be measured directly using Bloch oscillations and Ramsey interferometry.

Femtosecond pulses from X-ray free-electron lasers offer a powerful method for observing the coherent dynamic of phonons in crystalline materials, it is now shown. This time-resolved spectroscopic tool could provide insight into low-energy collective excitations in solids and how they interact at a microscopic level to determine the material’s macroscopic properties.

Ultracold atoms in optical lattices are used to study various phenomena in condensed-matter physics, such as magnetism. A lattice-shaking technique can induce a strong effective spin-interaction, leading to the formation of ferromagnetic domains.

An action generates an equal and opposite reaction. If it were possible, however, for one of the two bodies to have negative mass, they would accelerate each other. A situation analogous to this is now realized in an optical system. Solitons moving in an optical mesh lattice exhibit either an effective positive or negative mass, thus enabling observation of self-acceleration.

The intensity of optically-pumped fluorescence generated from a single atomic defect in diamond can be reduced by 80% in just 100 ns by applying infrared laser light. This result demonstrates the possibility of using these so-called nitrogen–vacancy centres to create optical switches that operate at room temperature.

A combination of measurements from the Solar Dynamics Observatory and radiospectroscopy data from the Nançay Radioheliograph now details the mechanism that connects coronal mass ejections from the sun and the acceleration of particles to relativistic speeds. A spatial and temporal correlation between a coronal ‘bright front’ and radio emissions associated with electron acceleration demonstrates the fundamental relationship between the two.

Superparamagnetism (preferential alignment of spins along an easy axis) is a useful effect for spintronic applications as it prevents spin reversal. It is now shown that high-spin quantum dots can become magnetically anisotropic when coupled to nearby ferromagnets—‘artificial’ superparamagnets.

BiTeCl is a topological insulator with strong inversion asymmetry, which exhibits bulk charge polarization and pyroelectricity. Such a long-sought topological insulator paves the way for applications involving natural p–n junctions and spintronics.

Can Alice verify the result of a quantum computation that she has delegated to Bob without using a quantum computer? Now she can. A protocol for testing a quantum computer using minimum quantum resources has been proposed and demonstrated.

Emerging sensing and quantum-information technologies based on nitrogen–vacancy centres in diamond require a better understanding of the relaxation mechanisms. A two-dimensional spectroscopy study provides information about the effects of the vibrational bath on the electronic dynamics.

Real-world networks are rarely isolated. A model of an interdependent network of networks shows that an abrupt phase transition occurs when interconnections between independent networks are added. This study also suggests ways to minimize the danger of abrupt structural changes to real networks.

The Van Allen radiation belts are two rings of charged particles encircling the Earth. Therefore the transient appearance in 2012 of a third ring between the inner and outer belts was a surprise. A study of the ultrarelativistic electrons in this middle ring reveals new physics for particles above 2 MeV.

An ab initio study suggests that a known oxide superconductor, BaBiO₃, can be doped into a topological insulating state. This would simplify topological insulator–superconductor structures for applications.

Bulk vanadium dioxide undergoes a metal–insulator transition near room temperature. It is now shown that by putting a thin layer of vanadium dioxide on a buffer, and varying the buffer’s thickness, the orbital occupancy in the metallic state and the transition temperature can be tuned.

A quantum critical point associated with a carbon nanotube quantum dot that is in contact with dissipative leads exhibits striking non-Fermi-liquid properties and anomalous scaling. The dissipative environment enables the comparison of the system under thermal- and non-equilibrium conditions.

If correlations decay exponentially in a one-dimensional quantum many-body system, then entanglement satisfies an area law. The intuitive explanation for this turns out to be wrong, but the statement is nevertheless true, as demonstrated by a proof based on quantum information theory.

By growing a topological insulator on top of a high-temperature superconducting substrate it is possible to induce superconductivity in the surface states of the topological insulator. Moreover, the pairing symmetry of the induced superconductivity is s-wave, unlike the d-wave symmetry of the substrate.

A nanomechanical interface between optical photons and microwave electrical signals is now demonstrated. Coherent transfer between microwave and optical fields is achieved by parametric electro-optical coupling in a piezoelectric optomechanical crystal, and this on-chip technology could form the basis of photonic networks of superconducting quantum bits.