2017 Impact factor 1.536
Condensed Matter and Complex Systems

News / Highlights / Colloquia

EPJ B Highlight - Caffeine offers clues to ultra-transient positive charges' migration

A caffeine molecule

A new study investigates the extremely rapid changes in the density of electrons in specific sites of the caffeine molecules thanks to an ultra-fast laser pulse that persists long enough to be observed

Caffeine keeps physicists up at night. Particularly those concerned with the capacity of electrons to absorb energy. In a new study published in EPJ B, a Franco-Japanese team of physicists have used the caffeine molecule as a playground to test the effect of ionising radiation on its electrons as they approach excited states. Their model accounts for the ionisation phenomenon in electrons, which are in a site-specific, localised orbit in the caffeine molecule. The electron excitation leaves the door open to positive charge progression along a molecular backbone. Thomas Niehaus from Claude Bernard Lyon 1 University, France, and colleagues have now developed a method for quantifying this positive charge migration in line with the ultra-short laser impulse. The observed charge motion happens on an attosecond time scale charge rearrangements driven by nuclear motion.


EPJ B Highlight - Is the Bitcoin network an oligarchy?

Density of Bitcoin transaction where red crosses mark a specific community of owners.

New study of Bitcoin transactions reveals hidden owner communities and a high-concentration of wealth distributed between a few people

Cryptocurrencies like Bitcoin can be analysed because every transaction is traceable. This means that they are an attractive system for physicists to study. In a paper published in EPJ B, Leonardo Ermann from the National Commission for Atomic Energy in Buenos Aires, Argentina, and colleagues from the University of Toulouse, France, have examined the structure of the Bitcoin-owner community by looking at the transactions of this cryptocurrency between 2009 and 2013. The team’s findings reveal that Bitcoin owners are close to an oligarchy with hidden communities whose members are highly interconnected. This research has implications for our understanding of these emerging cryptocurrency communities in our society - as usual bank transactions are typically deeply hidden from the public eye. They could also be helpful to computer scientists, economists and politicians who could better understand handle them.


EPJ B Highlight - Futuristic data storage based on controlling the interactions between nanodots magnetic ‘mood’ twirls

Force microscopy image of the magnetisation structure for a part of the array of square elements.

Better understanding of the changing magnetic state of nanometric squares in an array could be the basis for future ultrahigh density data storage

The magnetisation of nanometric square material is not fixed. It moves around in a helical motion. This is caused by the electron whose degree of freedom, referred to as spin, which follows a precession motion centred on the middle of a square nano-magnet. To study the magnetisation of such material, physicists can rely on two-dimensional arrays of square nanomagnets. In a paper published in EPJ B, P. Kim from the Kirensky Institute of Physics, associated with the Russian Academy of Sciences, in Krasnoyarsk, Siberia, Russia, and colleagues have devised a new model taking into account the factors affecting the magnetic interaction between individual nanomagnets. Better controlling such nanomagnets arrays could have applications in ultrahigh density data storage,in an electronic application called spintronics exploiting electron spins and its magnetism, and in micro- and nanosurgery controlled by magnets.


EPJ B Colloquium - Laser and hot-electrons induced ultrafast magnetic phenomena in multilayers and nanostructures

Laser excited electrons transport in magnetic heterostructures

Understanding and controlling the magnetization dynamics in magnetic multilayers and nanostructures on the femtosecond timescale is becoming indispensable, both at the fundamental level and to develop future technological applications. While direct laser excitation of a ferromagnetic layer was commonly used during the past twenty years, laser-induced hot-electrons femtosecond pulses and subsequent transport in magnetic multilayers have attracted a lot of attention. Indeed, replacing photons by hot-electrons offers complementary information to improve our understanding of ultrafast magnetization dynamics and to provide new possibilities for manipulating the magnetization in a thin layer on the femtosecond timescale.


EPJ B Highlight - Unzipping graphene nanotubes into nanoribbons

Zigzag nanoribbon and armchair nanotube junction

New study shows elegant mathematical solution to understand how the flow of electrons changes when carbon nanotubes turn into zigzag nanoribbons

In a new study published in EPJ B, Basant Lal Sharma from the Indian Institute of Technology Kanpur provides a detailed analysis of how the flow of heat and electrons is affected at the interface between an ‘armchair’ shaped carbon nanotube and a zigzagging nanoribbon made up of a single-layer carbon honeycomb sheet of graphene. Applications of this method can help us understand the propagation of electrons and thermal flow in graphene and similar materials for electromagnetic devices. For example, a partially unzipped carbon nanotube could act as a device with varying electrical resistance depending on the strength of an external magnetic field applied to it. By contrast, these junctions can also act as perfect ‘valley filters’, allowing certain types of electrons through the junction with the maximum possible conductance, while other electrons can't pass through.


EPJ B Highlight - Physicists with green fingers estimate tree spanning rate in random networks

The diagram of the random network model.

A team in China has just calculated the size of scale-free and small-world networks

Networks are often described as trees with spanning branches. How the tree branches out depends on the logic behind the network’s expansion, such as random expansion. However, some aspects of such randomly expanding networks are invariant; in other words, they display the same characteristics, regardless of the network’s scale. As a result, the entire network has the same shape as one or more of its parts. In a new study published in EPJ B, Fei Ma from Northwest Normal University in Lanzhou, Gansu Province, China, anc colleagues calculate the total number of spanning trees in randomly expanding networks. This method can be applied to modelling scale-free network models, which, as it turns out, are characterised by small-world properties. This means, for instance, that members of the network only exhibit six degrees of separation, like most people in our society.


EPJ B Highlight - Turning graphene into light nanosensors

Absorption on the plane of incident angle and wavelength.

Tuning the graphene embedded in a photonic crystal by varying the external temperature can transform it into a light-sensitive sensor

Graphene has many properties; it is e.g. an extremely good conductor. But it does not absorb light very well. To remedy this limiting aspect of what is an otherwise amazing material, physicists resort to embedding a sheet of graphene in a flat photonic crystal, which is excellent for controlling the flow of light. The combination endows graphene with substantially enhanced light-absorbing capabilities. In a new study published in EPJ B, Arezou Rashidi and Abdolrahman Namdar from the University of Tabriz, Iran demonstrate that, by altering the temperature in such a hybrid cavity structure, they can tune its capacity for optical absorption. They explain that it is the thermal expansion and thermo-optical effects which give the graphene these optical characteristics. Potential applications include light sensors, ultra-fast lasers, and systems capable of modulating incoming optical beams.


EPJ B Highlight - High-energy ions’ movement affected by silicon crystal periodicity

Simulated spatial and angular distributions for high-energy protons along a silicon axis.

Thinnest-ever silicon crystal enhances ion channelling performance in particle accelerators

The thinner the silicon crystal, the better. Indeed, thinner crystals provide better ways to manipulate the trajectories of very high-energy ions in particle accelerators. Further applications include materials analysis, semiconductor doping and beam transport in large particle accelerators. All of these rely on our understanding of how positively-charged high-energy particles move through crystals. This process, called ion channelling, is the focus of a new paper by Mallikarjuna Motapothula and Mark Breese working at the National University of Singapore. In a paper published in EPJ B, the authors study how the crystal periodicity affects the motion of ions whose energy belongs to a 1 to 2 MeV range, as they are transmitted through very thin crystals on the order of a few hundred nanometres, and how it impacts their angular distribution.


EPJ B Highlight - Predicting influencers has just been made simpler

Average epidemic size according to new theory.

Understanding the dynamics of message transmission in networks leads to identification of key individuals spreading news and viruses in epidemics

Social networks, such as Twitter, thrive on key influencers spreading news. Like information, epidemics also spread from key individuals. To identify the most influential actors in such networks, many studies have, until now, focused on ranking the influence of individual nodes. But these methods are not accurate enough to single out influential spreaders because they fail to take into account the spreading dynamics. Now, Byungjoon Min from the Institute of Interdisciplinary Physics and Complex Systems, Balearic Island University, Palma de Mallorca, Spain, has calculated for the first time the expected size of epidemic outbreaks when spreading originates from a single seed. In a study published in EPJ B, Min accurately predicts the influence of spreaders in such networks. Applications include viral marketing, efficient immunisation strategies, and identifying the most influential actors in our society.


EPJ B Highlight - Better mastery of heat flow leads to next-generation thermal cloaks

Janus thermal illusion.

Chinese physicists manipulate the transfer of thermal energy as a means of reducing heat waste, using thermal camouflage tactics

Ever heard of the invisibility cloak? It manipulates how light travels along the cloak to conceal an object placed behind it. Similarly, the thermal cloak is designed to hide heated objects from infrared detectors without distorting the temperature outside the cloak. Materials for such cloaks would need to offer zero thermal conductivity to help camouflage the heat. Now, Liujun Xu and colleagues from Fudan University, Shanghai, China, have explored a new mechanism for designing such materials. These findings published in EPJ B could have implications for manipulating the transfer of thermal energy as a way to ultimately reduce heat waste from fossil fuels and help mitigate energy crises.


Acting EiC: Eduardo Hernandez

Executive Editors:
B.K. Chakrabarti, W. Duan, E. Hernandez, H. Rieger
Thank you for the very fruitful and efficient collaboration. It has been a pleasure!!

Paul van Loosdrecht, Guest Editor Topical issue: Excitonic Processes in Condensed Matter, Nanostructured and Molecular Materials, 2013

ISSN (Print Edition): 1434-6028
ISSN (Electronic Edition): 1434-6036

© EDP Sciences, Società Italiana di Fisica and Springer-Verlag