Volume 5 Issue 12, December 2009

It has been 20 years since the fall of the Berlin Wall. In the wake of the upheaval, the East German society was radically remodelled. For physicists, it brought new opportunities — and fresh challenges.

A demonstration of a 'two terminal' single-electron transistor governed by the magnetic anisotropy of ferromagnetic electrodes connected to a metal quantum dot could give birth to a new field of single-electron spintronics.

Quantum computers can outperform their classical counterparts at some tasks, but the full scope of their power is unclear. A new quantum algorithm hints at the possibility of far-reaching applications.

The observation of Hall quantization and complete lifting of the degeneracy in bilayer graphene at magnetic fields an order of magnitude lower than previously reported has important implications for an understanding of the role of many-body interactions in the exotic behaviour of bi- and monolayer graphene.

The metal–insulator Mott transition, which has been extensively studied by means of charge transport, is now detected through the electron spins in a two-dimensional organic conductor.

A study of a one-dimensional system may have finally resolved the long-standing discrepancy between the expected and measured inelastic neutron scattering intensities in the high-temperature cuprate superconductors.

A comprehensive survey of the cuprate, heavy-fermion and iron-based superconductors shows a universal linear relationship between their magnetic resonance energy and superconducting gap. This result suggests that antiferromagnetic fluctuations might have a similar role in the unconventional superconductivity of these seemingly different classes of materials.

Single-molecule transistors have enabled studies of magnetism and other correlated nanoscale behaviour, but superconductivity has not been observed with this approach. It is now shown that superconducting junctions on both sides of a C₆₀ molecule induce superconductivity across the whole device.

The Mott transition between an insulator and a metal can be tuned by applying pressure, which affects the electronic correlations. In an insulating organic salt, NMR studies reveal that the spin fluctuations are suppressed whereas the conductance is enhanced by the same critical exponent as pressure drives the insulator into a bad metal.

Complex oxide films are highly anisotropic in the way they conduct electricity, which is due to phase separation. However, the origin of this metal–insulator phase coexistence has been unclear. Transport measurements now show that strain, rather than chemical inhomogeneity, is mainly responsible.

The presence of disorder makes it difficult to determine the intrinsic properties of graphene in its ideal form. Measurements of high-quality bilayer graphene flakes suspended above a substrate identify the persistence of quantum Hall behaviour at magnetic fields an order of magnitude lower than seen before, and previously unseen symmetry breaking of the lowest Landau level is also observed.

Graphene is expected to possess characteristics that are particularly useful for transporting and manipulating electronic spin. The discovery of spin-dependent interference features in its electrical characteristics could be useful in the development of graphene spintronics.

Spin-transfer torque allows the magnetization of nanopillar devices to be switched electrically. Incorporating asymmetries into the design of such a device generates a linear out-of-plane torque component that could help prevent the unwanted spontaneous reversal of the nanopillar’s magnetization.

The spin state of two electrons in a double well is a promising qubit. Now, such qubits can be arbitrarily rotated around two different axes by applying a magnetic field of different magnitude to each electron. This can be done in nanoseconds, before the stored information is lost.

Coupling a nanometre-scale oscillator to a micrometre-scale optical resonator provides a way of measuring the small-amplitude motion. The scheme is applied to silicon nitride ’strings’, but it could be extended to many other types of tiny vibrating structures.

Optical tweezers use the forces exerted by light to manipulate objects at the micrometre scale. An approach in which the target particle itself plays an active part now achieves this using a lower light intensity. This reduction means that heat-sensitive targets such as viruses could be manipulated directly.

Anisotropies in the response of ferromagnetic electrodes attached to a gold nanoparticle lead to Coulomb blockade and spin-valve-like magnetoresistance phenomena. Such behaviour could allow the development of magnetically gated single-electron transistors composed of just two terminals.