Europhysics News

Highlights

How to build doughnuts with Lego blocks (Vol. 43 No. 1)

A mix of two chemically discordant polymers with strong bonds creates previously unseen nanoscale assemblies

The present work reveals how nature minimises energy costs in rings of liquids with an internal nanostructure made of two chemically discordant polymers joined with strong bonds, or di-blocks, deposited on a silicon surface.

The authors first created rings of di-block polymers that they liken to building doughnuts from Lego blocks due to the nature of the material used, which has an internal structure discretised like Lego blocks, resulting in rings approximating the seamless shape of a doughnut (see photo).

The dynamics of interacting edges in ring structures that display asymmetric steps, i.e., different spacing inside and outside the ring, when initially created, has been measured. It is found that the interaction shaping the ring over time is the repulsion between edges. The source of this repulsion is intuitive: an edge is a defect which perturbs the surface profile with an associated cost to the surface energy.

These edges could be considered as defects in a material with an otherwise perfect order at the nanoscale. Thus, research based on the elucidation of defect interactions could help scientists trying to eliminate such defects by understanding how these materials self-assemble. Such systems could also provide an ideal basis for creating patterns on the nanoscale, data storage, and nanoelectronics.

Dynamics of interacting edge defects in copolymer lamellae
J. D. McGraw, I. D. W. Rowe, M. W. Matsen and K. Dalnoki-Veress, Eur. Phys. J. E, 34, 131 (2011)
[Abstract]

How to optimise an interface in spin-orbitronics? (Vol. 50, No. 1)

Spintronics is a rapidly developing field of applied physics seeking to exploit electron spins as a further degree of freedom, which is extremely appealing to numerous applications related to magnetic information processing and data storage. Creation of energy saving spintronic devices based on spin currents operated without magnetic fields is currently a key challenge in this domain. This fundamental problem can be resolved by making use of the effects related to Spin-Orbit Coupling (SOC), the approach adopted in a novel direction referred to as spin-orbitronics.

Such effects are typically of interfacial nature that take place in ferromagnetic metal/heavy metal bilayers, Pt being the most promising heavy metal candidate. In this paper the authors have investigated major tendencies in the behaviour of three of them, the Gilbert damping α, the magnetic anisotropy and the interfacial Dzyaloshinskii–Moriya interaction Ds, as a function of Pt concentration in Py (5 nm)/Cu1−xPtx bilayers. Although they demonstrate correlated general features as Pt is replaced by Cu, confirming their common physical nature, their behaviour is not identical. This opens up the possibility of creation of optimised interfaces with SOC-related parameters tuned independently for a specific application.

H. Bouloussa, R. Ramaswamy, Y. Roussigné, A. Stashkevich, H. Yang, M. Belmeguenai and S. M. Chérif, Pt concentration dependence of the interfacial Dzyaloshinskii–Moriya interaction, the Gilbert damping parameter and the magnetic anisotropy in Py/Cu_1-xPt_x systems, J. Phys. D: Appl. Phys. 52, 055001 (2019)
[Abstract]

How to stop diseases and forest fires from spreading (Vol. 50, No. 4)

A new model, exploring how epidemics spread, could help prevent infections and forest fires from getting out of hand

Recently, epidemics like measles have been spreading due to the lack of vaccinations, and forest fires have become increasingly frequent due to climate change. Understanding how both these things spread, and how to stop them, is more important than ever. Now, the authors, have studied the way epidemics spread in heterogeneous populations. Their findings were recently published in EPJ B.

A. B. Kolton and K. Laneri, Rough infection fronts in a random medium, Eur. Phys. J. B 92 ,126 (2019)
[Abstract]

Hydrodynamics of the fractional quantum Hall effect (Vol. 44 No. 6)

Many features of the Fractional Quantum Hall effect (FQHE) can be understood by considering electrons on the surface of semiconductors as a very peculiar, charged, two-dimensional fluid in the presence of a strong magnetic field. In this paper a classical hydrodynamic model of such a fluid is presented.

The model incorporates a relation between the vorticity and density of the fluid specific for FQHE and exhibits the Hall viscosity and Hall conductivity found in FQHE liquids. The relation of the model to previous effective models such as the Chern–Simons–Ginzburg– Landau theory of FQHE is explained. It is also shown how the Laughlin’s wavefunction is annihilated by the quantum velocity operator.

A. G. Abanov, ‘On the effective hydrodynamics of the fractional quantum Hall effect’ J. Phys. A: Math. Theor., 46, 292001 (2013)
[Abstract]

Hydrodynamics role in heavy-ion collisions (Vol. 45 No. 1)

The energy distribution of a random event

In ultra-relativistic nuclear collisions, hydrodynamics plays an important role in governing the system’s evolution. As various empirical evidence strongly points towards local thermalization or, at least, the validity of a certain kind of equation of state in the very early stages of the collisions, it is quite amazing that the resulting hot and dense system evolves more like a perfect fluid, rather than a collection of ‘hard’ binary collisions. Consequently, collectivity builds up inside the system, which can be measured by observables such as collective flow or multi-particle correlations.

In this paper, the authors explicitly decomposed and manipulated the initial conditions and studied the hydrodynamic evolution of individual cumulant components. In particular, they discussed to what extent linearity breaks down in hydrodynamics.

They found that, when expanding in azimuthal angles, each cumulant component possesses non-trivial radius dependence. Though in general linearity is approximately obtained, the authors found that flow harmonics of higher orders are produced, deviating from the linearity between eccentricities and flow coefficients. These results can be seen as a natural consequence of the non-linear nature of hydrodynamics, and they can be understood intuitively in terms of the peripheral-tube model.

W.-L. Qian, Ph. Motta, R. Andrade, F. Gardim, F. Grassi, Y. Hama and T. Kodama, “Decomposition of fluctuating initial conditions and flow harmonics” J. Phys. G: Nucl. Part. Phys. 41, 015103 (2014)
[Abstract]

Identifying ever-growing disturbances leading to freak waves (Vol. 46 No. 5-6)

A schematic one-dimensional illustration of the spatiotemporal evolution of the envelope of wave-train in the absolutely unstable case.

Physicists now better understand wave systems exhibiting unusual disturbances by identifying growing localised patterns as early indicators of such disturbances.

Physicists like to study unusual kinds of waves, like freak waves found in the sea. Such wave movements can be studied using models designed to describe the dynamics of disturbances. The authors have focused on finding ways of best explaining how wave disturbance occurs under very specific initial conditions that are key to the genesis of these disturbances. They looked for solutions to this puzzle by resolving a type of equation, called the nonlinear Schrödinger equation. It is solved by applying a method designed for studying instabilities tailored to these initial conditions. Their approach makes it possible to locate exactly where and how pertinent information used to identify disturbance patterns can be extracted from localised disturbances' characteristics. The findings have been published recently. They therefore contribute to a better understanding of the complex dynamics of systems subjected to such disturbances. For example, they could be used to better understand waves appearing on fluid surfaces, whose evolution is influenced by gravity, or light waves propagated in optical fibres.

S. Coulibaly, E. Louvergneaux, M. Taki and L. Brevdo, Spatiotemporal wave-train instabilities in nonlinear Schrödinger equation: revisited, Eur. Phys. J. D 69, 186 (2015)
[Abstract]

Image-guided restricted drug release in friendly implanted therapeutics (Vol. 49 No.5-6)

This review exposes a possible therapeutics scheme of using active implants for restricted drug release, accounting for friendly wellbeing and security of patient. Friendly therapeutics ought to use controlled drug release with minimally-invasive and non-ionizing techniques. The review of different issues elucidates that the strategy sought may use non-ionizing image-guided drug release embedded implant, which is powered and controlled wirelessly by an external source. The analysis of the principal biomedical imagers indicates the MR (magnetic resonance) imager as the most adequate non-ionizing solution.

The review of MRI (magnetic resonance imaging) technology suggests an optimization of performance versus biological effects, as well as of compatibility with hosting materials in its environment. For the sake of such compatibility, an EMC (electromagnetic compatibility) analysis has been performed considering the nature of different MRI fields and their conventional protections and corrections.

A possible future strategy would consist of an interactive system operating autonomously. Such a system is composed of the imager, the implant and its external wireless powering/control device. It integrates an AI (artificial intelligence) algorithm and has to operate under the supervision of the health-care team.

A. Razek, Towards an image-guided restricted drug release in friendly implanted therapeutics, Eur. Phys. J. Appl. Phys. 82, 31401 (2018)
[Abstract]

Imaging helps to spot fake ancient daggers (Vol. 48, No. 4)

Combining neutron and X-ray imaging gives clues to how ancient weapons were manufactured

Since the 19^th century, collectors have become increasingly interested in weapons from ancient Asia and the Middle East. In an attempt to fight forged copies, physicists are now adding their imaging power to better authenticate these weapons; the fakes can't resist the investigative power of X-rays combined with neutron imaging. In a study published recently, the authors have demonstrated the usefulness of such a combined imaging approach to help museum curators in their quest to ensure authenticity. They can now reliably tell first-class modern copies of early daggers and swords from authentic ones. In this study, the authors focus on a kris—the distinctive weapon of Malaysia and Indonesia—and a kanjar— a double-edged dagger with a slightly curved blade and a pistol-grip made of metal, ivory, jade or some other hard-stone found e.g. in Persia and India. The authors found the internal structure of the traditional kris examined in this study was inconsistent with descriptions of traditional forging methods to be found in the extant literature, thus suggesting the artefact was a fake. By contrast, the kanjar analysed in the study is most likely to be authentic, as the material distribution in the volume of the blade conforms to traditional metallurgical processes.

F. Salvemini, F. Grazzi, N. Kardjilov, F. Wieder, I. Manke, D. Edge, A. Williams and M. Zoppi, Combined application of imaging techniques for the characterization and authentication of ancient weapons, Eur. Phys. J. Plus 132, 228 (2017)
[Abstract]

Improved quantum information motion control (Vol. 43 No. 5)

Sketch map of the double quantum dot (two horizontal lines) coupled with the nanomechanical resonator (rectangle).

A new model simulates closer control over the transport of information carrying electrons under specific external vibration conditions. The present article developes a new method for handling the effect of the interplay between vibrations and electrons on electronic transport, which could have implications for quantum computers due to improvements in the transport of discrete amounts of information, known as qubits, encoded in electrons.

The authors create an electron transport model to assess electrons’ current fluctuations based on a double quantum dot (DQD) subjected to quantized modes of vibration, also known as phonons, induced by a nanomechanical resonator. Unlike previous studies, this work imposes arbitrary strong coupling regimes between electrons and phonons.

They successfully control the excitations of the phonons without impacting the transport of quantum information. They decouple the electron-phonon interaction by inducing resonance frequency of phonons. When the energy excess between the two quantum dots of the DQD system is sufficient to create an integer number of phonons, electrons can reach resonance and tunnel from one quantum dot to the other.

As electron-phonon coupling becomes even stronger, the phenomenon of phonon scattering represses electron transport and confines them, suggesting that tuning the electron-phonon coupling, could make a good quantum switch to control the transport of information in quantum computers.

C. Wang, J. Ren, B. Li and Q-H. Chen, ‘Quantum transport of double quantum dots coupled to an oscillator in arbitrary strong coupling regime’, Eur. Phys. J. B (2012) 85, 110
[Abstract]

Improvement in 3D device performance (Vol. 43 No. 4)

SEM image of a device cross sectional view

Microelectronics researchers and engineers are finally running into the fundamental physical limits of silicon and are trying to find innovative ways around these limits. Three-dimensional (3D) integration technology is emerging and has drawn attention as a viable solution to extend the fundamental limits of complementary metal–oxide–semiconductor (CMOS) scaling because 3D technologies allow reduction in chip size, delay time in interconnections and power dissipation. In order to fully benefit from the 3D architecture, the development of vertical MOS field-effect transistors (FETs) is essential, especially for memory and radio frequency applications.

In this work, the authors investigated a vertical MOSFET incorporating an epitaxial channel and a drain junction in a stacked silicon-insulator structure. An oxide layer near the drain junction edge (referred to as a junction stop) acts as a dopant diffusion barrier and consequently a shallow drain junction is formed to suppress short channel effects. A simulation study in the sub-100 nm regime calibrated to measured results on the fabricated devices was carried out. The use of an epitaxial channel delivers 50% higher drive current due to the higher mobility of the retrograde channel and the junction stop structure delivers improvements of threshold voltage roll-off and drain induced barrier lowering compared with a conventional vertical MOSFET. These results suggest that this device architecture allows CMOS scaling to be extended.

Improved vertical MOSFET performance using an epitaxial channel and a stacked silicon-insulator structure
T. Uchino, E. Gili, L. Tan, O. Buiu, S. Hall and P. Ashburn, Semicond. Sci. Technol. 27, 062002 (2012)
[Abstract]

Improving heat recycling with the thermodiffusion effect (Vol. 50, No. 5-6)

Numerical simulations of the thermodiffusion effect within falling film absorbers reveal that thin films composed of liquid mixtures with negative thermodiffusion coefficients enhance the efficiency of heat recycling.

Absorption heat transformers can effectively reuse the waste heat generated in various industries. In these devices, specialised liquids form thin films as they flow downward due to gravity. These liquid films can absorb vapour, and the heat is then extracted by a coolant so that it can be used in future processes. So far, however, there has been little research into how the performance of these films is influenced by the thermodiffusion effect – a behaviour seen in mixtures, where different types of mixture respond differently to the same temperature gradient. In a study recently published, researchers from the Fluid Mechanics group at Mondragon University and Tecnalia, pooled their expertise in transport phenomena and absorption technology. Together, they explored for the first time the influence of the thermodiffusion property on the absorption, temperature and concentration profiles of falling films.

P. Fernandez de Arroiabe, A. Martinez-Urrutia, X Peña, M. Martinez-Agirre, M. M. Bou-Ali, On the thermodiffusion effect in vertical plate heat exchangers, Eur. Phys. J. E 42, 85 (2019)
[Article]

Improving insulation materials, down to wetting crossed fibres (Vol. 46 No. 5-6)

Evolution of the morphology of a drop of silicone oil on two touching crossed fibres.

Scientists model the manner in which a liquid wets fibres, gaining useful insights for improving glass wool properties

Sandcastles are a prime example of how adding a small amount of liquid to a granular material changes its characteristics. But understanding the effect of a liquid wetting randomly oriented fibres in a fibrous medium remains a mystery. Relevant to the building industry, which uses glass wool, for instance, this phenomenon can be better understood by studying the behaviour of a liquid trapped between two parallel fibres. It can either remain in the shape of a drop or spread between the fibres into a long and thin column of liquid. Now, the authors have demonstrated that the spreading of the liquid is controlled by three key parameters: the amount of liquid on the fibres, the fibres’ orientation and the minimum distance between them. These findings, based on experimental and modelling work, were published recently.

A. Sauret, F. Boulogne, B. Soh, E. Dressaire and H. A. Stone, Wetting morphologies on randomly oriented fibers, Eur. Phys. J. E 38, 62 (2015)
[Abstract]

Improving safety of neutron sources (Vol. 47 No. 5-6)

Sampling of Lead-Bismuth-eutectic material/cover gas-interface sample consisting of solid material forming a powdery crust onto the steel wall

Testing liquid metals as target material bombarded by high-energy particles

There is a growing interest in the scientific community in a type of high-power neutron source that is created via a process referred to as spallation. This process involves accelerating high-energy protons towards a liquid metal target made of material with a heavy nucleus. The issue here is that scientists do not always understand the mechanism of residue nuclei production, which can only be identified using spectrometry methods to detect their radioactive emissions. In a new study examining the radionuclide content of lead-bismuth-eutectic (LBE) targets, the authors found that some of the radionuclides do not necessarily remain dissolved in the irradiated targets. Instead, they can be depleted in the bulk LBE material and accumulate on the target's internal surfaces. These findings have recently been published. The results improve our understanding of nuclear data related to the radionuclides stemming from high-power targets in spallation neutron sources. They contribute to improving the risk assessment of future high-power spallation neutron beam facilities --including, among others, the risk of erroneous evaluation of radiation dose rates.

B. Hammer-Rotzler, J. Neuhausen, V. Boutellier, M. Wohlmuther, L. Zanini, J.-C. David, A. Türler and D. Schumann, Distribution and surface enrichment of radionuclides in lead-bismuth eutectic from spallation target, Eur. Phys. J. Plus 131, 233 (2016)
[Abstract]

Improving the signal-to-noise ratio in quantum chromodynamics simulations (Vol. 50, No. 5-6)

A new Monte Carlo based simulation method enables more precise simulation for ensembles of elementary particles.

Over the last few decades, the exponential increase in computer power and accompanying increase in the quality of algorithms has enabled theoretical and particle physicists to perform more complex and precise simulations of fundamental particles and their interactions. If you increase the number of lattice points in a simulation, it becomes harder to tell the difference between the observed result of the simulation and the surrounding noise. A new study recently published in EPJ Plus, describes a technique for simulating particle ensembles that are 'large' (at least by the standards of particle physics). This improves the signal-to-noise ratio and thus the precision of the simulation; crucially, it also can be used to model ensembles of baryons: a category of elementary particles that includes the protons and neutrons that make up atomic nuclei.

M. Cè, Locality and multi-level sampling with fermions. Eur. Phys. J. Plus 134, 299 (2019)
[Article]

In the thermopower of underdoped cuprates (Vol. 44 No. 4)

Comparison of calculated (line) and measured (symbols) thermopower of Bi₂Sr₂CuO_6+d. The undulations (arrowed) arise from electron-like Fermi-surface pockets.

In recent years the possibility of electron-like Fermi-surface pockets in the high-Tc cuprates has become an area of intense experimental and theoretical interest. What is the origin of these pockets? Are they connected to the mysterious pseudogap, a depletion in the density of states that dominates thermodynamic and transport properties over a wide range of temperature and doping? Until now, experimental support for these pockets has been confined to samples which, in addition to pseudogap effects, exhibit a separate spin/charge stripe correlation, making their connection to the pseudogap unclear.

In the present paper we calculate the thermopower of high-Tc cuprates from the resonating-valence-bond spin-liquid model developed by Yang, Rice and Zhang, achieving an excellent match with experimental data. A key result of this work is the identification of features in the observed thermopower corresponding to electron pockets in the Fermi-surface appearing with the opening of the pseudogap. These results link the pseudogap with Fermi-surface reconstruction and will be of considerable interest to researchers using photoemission, quantum oscillations and other techniques presently engaged in efforts to detect these pockets directly.

J. G. Storey, J. L. Tallon and G. V. M. Williams, ‘Electron pockets and pseudogap asymmetry observed in the thermopower of underdoped cuprates’, EPL, 102 (2013) 37006
[Abstract]

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