The electronic properties of graphene have received wide recognition, most notably the award of the 2010 physics Nobel Prize. In graphene's two-dimensional hexagonal lattice, the electrons behave as massless chiral Fermions obeying the Dirac equation. The exotic nature of these quasi-particles and their low carrier density is at the heart of several interesting phenomena, including the unconventional quantum Hall effect and Klein tunneling. Raising the density of charge carriers in graphene can have several implications including the possibility for van Hove singularity driven high-Tc superconductivity. From a fundamental point of view, the high carrier densities substantially modify the interactions between quasi-particles in this two-dimensional crystal.

In this report, graphene devices in Hall-bar geometry are gated with a polymer electrolyte to realize carrier densities an order of magnitude higher than achieved by conventional methods. At these densities, the carriers sufficiently screen the long-range interactions. This allows fully appreciating the importance of various neutral defects on the graphene lattice. In contrast to metals, the temperature scale for quantum suppression of acoustic-phonon scattering in graphene is significantly gate-tunable. The phenomenon is readily observed to high temperatures at high carrier densities.

The soaring demands on non-volatile memory for ultra-portable electronic devices have grown NAND flash into a multi-billion dollar business. As a Si-CMOS based technology, NAND flash provides the most aggressive scalability, closely following the-state-of-art semiconductor manufacturing process. NAND flash also takes advantage of its relatively simple floating-gate structure and seamless integration with Si-CMOS logics, leading to significant lower production cost over other competing non-volatile technologies such as FeRAM and MRAM.

Graphene, with its ultra-high mobility and almost unlimited scalability down to atomic scale, is considered now as one of the most promising candidates for replacing Si. Graphene-based non-volatile memory has also been demonstrated very recently. However, a seamless solution for integrating graphene transistors and non-volatile memory remains a challenge.

Here, Zheng et al. demonstrate the wafer-scale patterning and device operations of Cu-CVD graphene-ferroelectric field effect transistors (GFeFETs) on ferroelectric Pb(Zr_0.3Ti_0.7)O₃ (PZT) substrates, integrating both transistor and non-volatile memory functionalities on the same chip.

In the linear regime of PZT, ultra-low-voltage operations of GFeFETs within +/-1V can be used as controlling transistors for addressing and reading/writing of memory unit cells. After polarizing PZT, the hysteretic switching of GFeFETs is ideal for ultra-fast non-volatile data storage. The combination of high-quality Cu-CVD graphene and functional substrates will not only greatly speed up the studies of all graphene-based electronics but also open up a new route in exploring new graphene physics and functionalities.

A new manipulation tool exploits the fact that when light interacts with matter, it creates a force that produces material properties in macromolecules and biological cells.

Romanian scientists have discovered a novel approach for the optical manipulation of macromolecules. The authors had the idea to use green photon beams. With them, it is possible to perform optical manipulation of macrostructures, such as biological proteins, with greater precision than with optical tweezers.

The authors used high-density green photon beams (HDGP) capable of inducing a polarisation effect within complex macrostructures. They found that the effect of the beam leads to ‘biological optical matter’. This includes newly-organised material structures, such as molecular aggregates and micro-particles, and can feature new characteristics such as antioxidant properties. The authors realised that this approach covers a larger area than focused tweezers and is capable of organising mesoscopic matter into a new 3D molecular architecture.

Nanomaterials are promising platforms for testing fundamental heat transport theories. The present review article outlines anomalous heat transport in nanometric scale materials from the latest developments in experimental, theoretical and numerical studies of heat conduction. It shows that the standard laws governing conduction at macroscopic scale no longer apply in nanostructures, which has implications in electronic, optoelectronic, and thermal devices.

Nanostructures are low-dimensional materials such as single carbon atom layers of graphene, nanowires or nanotubes. Laws governing heat transport through what are known as phonons, representing the vibrational modes of lattices, are different in such materials compared to the macroscopic scale. This is because the phonon characteristic lengths are comparable to the characteristic lengths of these nanostructures. Particularly, heat carriers diffuse faster than in a random walk but slower than in a straight trajectory motion.

This paper outlines the recent experiments on quasi-one-dimensional nanostructures and two-dimensional graphene that display a thermal conductivity with this anomalous behaviour, linked to heat diffusion’s size dependency. Such studies present a dual challenge in that the technique associated with measuring heat flux in nanosystems is combined with the complexity of accurately controlling object at nanoscale.

Due to these measurement challenges, experimental results need to be complemented by theoretical studies. Hence, this paper also accounts for numerical studies on heat conduction of nanotubes, nanowires and graphene, concentrating particularly on atomic-level simulations.

In addition, the latest theories explaining the mechanisms of such anomalous heat conduction are presented. But these are by no means complete. Further systematic investigations are needed for better thermal energy management and control in nanoscale devices.

Equilibrium statistical mechanics provides general expressions for probability distributions from which thermodynamics can be deduced. A long-standing question concerns the possibility of describing by general principles also non-equilibrium fluctuations. Important progress in this direction has been made with the development of fluctuation theorems and macroscopic fluctuation theory for non-equilibrium steady states. However, fluctuations in non-stationary systems remain poorly understood.

Recently, the off-equilibrium probability distribution of the heat exchanged with the thermal bath by a ferromagnet quenched below the critical point (a paradigm of phase separation and, more generally, of non-equilibrium aging systems) has been calculated analytically in an exactly solvable limit. Surprisingly, the distribution shows the existence of a singular threshold (see figure), beyond which fluctuations undergo a condensation transition. Namely, macroscopic amounts of heat are released to the thermal bath through a single microscopic mode.

The mechanism driving this novel dynamical feature is reminiscent of the one underlying the Bose-Einstein condensation. The remarkable difference is that the Bose-Einstein condensation is about average properties, while in this case the condensation transition involves fluctuations remote from typical properties. The occurrence of this phenomenon in an out of equilibrium context still needs to be fully understood.

From the explicit knowledge of the heat distribution a fluctuation relation, connecting the probabilities of released and absorbed heat, has been derived. This is the first analytical expression of this kind found for non-stationary systems. In this relation two characteristic energy scales appear, formally playing the same role of the reservoir temperatures in stationary fluctuation relations. The interpretation of these energy scales in terms of non-equilibrium effective temperatures and its consequences is an open question currently under investigation.

Presently, laser diodes are mainly used to convert electronic signals into optical signals in fast communication systems. They are manufactured with a wide variety of semiconductors different from silicon and the incorporation of these lasers in silicon layers leads to distortion of the signals, degradation of sensitivity, and limits the reliability. Silicon, with more than 95% of the international market share, dominates other semiconductors. A silicon laser source would provide the ideal improvement for future high-speed electronics. The structure of silicon limits its light-emitting efficiency and, despite the very fast development of silicon based electronics, optical applications of silicon devices have not been conducted thoroughly.

The question “which silicon device will be useful for transforming electronic signals into optical signals?” is still relevant today. This paper presents an advance in optoelectronic silicon devices since it introduces and formulates a process for the creation of an optical active layer inside silicon devices. A degradation of the structure is induced by hot carriers injection. The process has been controlled by the analysis of the junction characteristic. The authors suggest that the created defects disturb the lattice periodicity by creating energy states in the band gap of the silicon. The model is based on a population inversion associated with a defect layer for carrier confinement and an electrical stimulation of light is demonstrated. The emitted light is localized is an area close the emitter-base junction. The authors measure the amplification of emitted light, and they showed that defect layer appears as an optical cavity. This groundwork introduces practical ways for improving the optical properties of silicon devices for optoelectronic applications.

Nuclear structures of short-lived radioisotopes are nowadays investigated in large scale facilities based on in-flight fragmentation or isotope separation online (ISOL) methods. The ISOL technique has been constantly extended at CERN-ISOLDE, where 1.4GeV protons are exploited by physicists to create radioisotopes in thick materials; these exotic nuclei are released and pumped online into an ion source, producing a secondary beam which is further selected in a magnetic mass spectrometer before post-acceleration.

Ten years ago a proposal to inject suitable ISOL beams into the CERN accelerator complex and to store these isotopes in a decay ring with straight sections was proposed for a ”Β-beam facility”; intense sources of pure electron neutrinos - emitted when such isotopes decay - are directed towards massive underground detectors for fundamental studies such as observation of neutrino flavour oscillations and CP violation.

Our paper reports on the experimental production of the anti-neutrino emitter 6He. We use a two-step reaction in which the proton beam interacts with a tungsten neutron spallation source. The emitted neutrons intercept a BeO target to produce ⁹Be(n,a)⁶He reactions. The neutron field was simulated by Monte-Carlo codes such as Fluka and experimentally measured. The large predicted ⁶He production rates were also experimentally verified. Fast 6He diffusion, driven by the selection of a suitable BeO material, could be demonstrated, leading to the highest ⁶He beam rates ever achieved at ISOLDE. These results provide a firm experimental confirmation that the Β-beam will be able to deliver enough anti-neutrino rates using a neutron spallation source similar to ISIS-RAL (UK). This work is now being completed by the experimental validation of the ¹⁸Ne neutrino source design.

Many quantum technologies—such as cryptography, quantum computing and quantum networks—hinge on the use of single photons. In the present paper, the authors have identified the extent to which photon detector characteristics shape the preparation of a photon source designed to reliably generate single photons. They determined the value of key source parameters that are necessary to generate high-fidelity single photons.

The problem with photon detectors is that they can be noisy or have a limited ability to detect single photons. Some cannot identify the number of photons; they can only detect their presence. Given the influence of these factors, improving the fidelity of single-photon generation is very challenging.

Single photons are typically generated using two laser beams that are correlated at the quantum level. This means that the detection of a single photon in the first beam heralds the generation of a single photon in the second one.

The authors simulated which photons would be obtained from different initial sources. This led to outline the conditions under which the heralding detector can deliver good resolution of the number of photons, as a means of improving the reliability in obtaining single photons. Using two experimental detectors checked these findings.