Letters in 2013

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.

The relaxation mechanisms of isolated quantum many-body systems are insufficiently understood, but a one-dimensional quantum gas experiment uncovers the local emergence of thermal correlations and their cone-like propagation through the system.

Measurements of the spin heat accumulation at the ferromagnetic/non-magnetic interface in nanopillar spin valves show that spin-up and spin-down electrons have different temperatures. This observation is important for the design of magnetic thermal switches and the study of inelastic spin scattering.

The interface between two non-magnetic band insulators, LaAlO₃ and SrTiO₃, can exhibit conductivity, superconductivity and magnetism. These interfacial phenomena can be reconciled by a theory that predicts a spiral magnetic ground state.

Ensembles of nuclear spins display thermal fluctuations—spin noise—that interfere with nuclear magnetic resonance measurements of samples below a threshold size. Experiments on nanowires show that by monitoring spin noise in real time and applying instantaneously adjusted radiofrequency pulses, spin polarization distributions that are narrower than the thermal distribution can be obtained.

The interaction between light and a relativistic electron beam can be used to generate optical vortices in a free electron laser, providing a way to engineer bright orbital angular momentum light at shorter X-ray wavelengths.

The fluctuation relations are a central concept in thermodynamics at the microscopic scale. These relations are experimentally verified by measuring the entropy production in a single-electron box coupled to two heat baths.

Patchy colloidal systems consist of particles with attractive patches on them. If the bonds between particles are allowed to be flexible, a colloidal liquid state may be observed as the system approaches zero temperature.

Schrodinger’s cat paradox embodies the open question of whether quantum effects can survive at macroscopic scales. A quantum optics experiment explores this question by creating entanglement between a microscopic and a macroscopic system.

Does quantum theory still apply at macroscopic scales? Looking for new insights into this open problem, an experiment in the spirit of Schroedinger’s cat gedanken experiment investigates the entanglement between microscopic and macroscopic domains.

By means of low-temperature scanning tunnelling spectroscopy, a heavy fermion material in its superconducting and mixed states can be imaged. Besides probing the superconducting gap symmetry, the measurements also reveal a pseudogap.

By pushing scanning tunnelling spectroscopy down to millikelvin temperatures, it is now possible to image a heavy fermion superconductor and measure the superconducting gap symmetry, with gap nodes in unexpected momentum-space locations.

Extreme ultraviolet and X-ray imaging of a solar flare with unprecedented clarity now provide visual evidence that magnetic reconnection plays a fundamental role in generating solar flares. The Atmospheric Imaging Assembly on NASA’s Solar Dynamics Observatory is able to observe a ’cold’ plasma moving into the reconnection point and the simultaneous acceleration of a hot-flare-heated plasma away from it.

Buckling is often regarding as a form of mechanical failure to be avoided. High-speed video microscopy and mechanical stability theory now show, however, that bacteria use such processes to their advantage. Cells propelled with a single flagellum change direction with a flick-like motion that exploits a buckling instability.

Coherent control of two flexural modes of a nanoscale oscillator using radiofrequency signals is now demonstrated. This oscillator is analogous to quantum two-level systems such as superconducting circuits and quantum dots, and therefore this technique raises the possibility of information processing using nanomechanical resonators.

Gamma-ray bursts are the most energetic sources of radiation in the Universe, and half are followed by afterglows that include X-ray flares of mysterious origin. A statistical study of such X-ray flares reveals the same power-law behaviour as solar flares, which suggests a common underlying magnetic reconnection process.

It is now shown that phonons can be coherently transferred between two nanomechanical resonators. The technique of controlling the coupling between nanoscale oscillators using a piezoelectric transducer is useful for manipulating classical oscillations, but if extended to the quantum regime it could also enable entanglement of macroscopic mechanical objects.

Magnetic reconnection in the Earth's magnetosphere accelerates electrons. And yet energetic electrons are not created during reconnection in the solar wind. Observations from the Cluster spacecraft now suggest that electron acceleration is caused by repeated bursts of plasma flow, which only occur in situations where the magnetic reconnection is unsteady.

The quantum phase transition from a topological to a conventional insulator in In-doped Bi₂Se₃ occurs when the topological phase is destroyed by the hybridization of states on opposite surfaces. This is characterized by a sudden change in the transport lifetime, measured by means of optical spectroscopy.