- Published on 04 February 2020
The phase transitions of an ultracold gas under a fluctuating magnetic field show interesting patterns, particularly a loss of symmetry in the energy spectrum that is well observed in the disappearance of the ‘Hofstadter’s butterfly’ effect.
It is now technically possible to hold groups of atoms at temperatures that are only a few hundredths of a degree above absolute zero. This so-called ‘ultracold gas’ loaded in an optical lattice is an extremely powerful platform to study quantum mechanical phenomena including phase transitions, due to the excellent control of experimental parameters, such as potential depths, inter-particle interaction strengths and lattice parameters. Sk Noor Nabi from Zhejiang University in Hangzhou, China and colleagues in the Indian Institute of Technology, Guwahati, India, have studied the phase transition between the Mott insulating (MI) and superfluid (SF) states of such a gas in a time-dependent synthetic magnetic field. Their results, published in EPJ B, show that the energy spectrum of the gas loses symmetry in the fluctuating magnetic field. This is observed in the disappearance of the striking ‘Hofstadter’s butterfly’ effect seen in the energy spectrum under a constant magnetic field.
EPJ B Topical Review - Electronic structure and optical properties of semiconductor nanowires polytypes
- Published on 29 January 2020
Advances in the fabrication and characterization of nanowires polytypes have made crystal phase engineering a well-established tool to tailor material properties. In a new review article published in EPJB, Luiz Galvão Tizei and Michele Amato (Université Paris-Saclay, CNRS, LPS, France) describe recent progress in the field, with special focus on the central role that crystal phase has in modulating the electronic and optical properties of nanowires.
- Published on 15 January 2020
A theoretical analysis of electron spins in slowly moving quantum dots suggests these can be controlled by electric fields.
The name ‘quantum dots’ is given to particles of semiconducting materials that are so tiny – a few nanometres in diameter – that they no longer behave quite like ordinary, macroscopic matter. Thanks to their quantum-like optical and electronic properties, they are showing promise as components of quantum computing devices, but these properties are not yet fully understood. Physicists Sanjay Prabhakar of Gordon State College, Georgia, USA and Roderick Melnik of Wilfrid Laurier University, Waterloo, Canada have now described the theory behind some of these novel properties in detail. This work is published in EPJ B.
- Published on 10 January 2020
The new year sees big changes for EPJ B, with two new Editors-in-Chief appointed from January 2020. Prof Dr Heiko Rieger (Saarland University, Germany) and Prof Eduardo Hernandez (ICMM-CSIC, Spain) take on joint EiC roles, with broad responsibility for papers in statistical physics and condensed matter physics respectively. At the same time, Prof Bikas Chakrabarti (Saha Institute of Nuclear Physics, Kolkata, India) and Prof Wenhui Duan (Tsinghua University, China) step down from their roles as Executive Editors on the journal.
- Published on 02 December 2019
An existing technique is better suited to describing superconductivity in pure, single-layer graphene than current methods.
Made up of 2D sheets of carbon atoms arranged in honeycomb lattices, graphene has been intensively studied in recent years. As well as the material’s diverse structural properties, physicists have paid particular attention to the intriguing dynamics of the charge carriers its many variants can contain. The mathematical techniques used to study these physical processes have proved useful so far, but they have had limited success in explaining graphene’s ‘critical temperature’ of superconductivity, below which its’ electrical resistance drops to zero. In a new study published in EPJ B, Jacques Tempere and colleagues at the University of Antwerp in Belgium demonstrate that an existing technique is better suited for probing superconductivity in pure, single-layer graphene than previously thought.
- Published on 16 October 2019
By considering the crystal structures of atomic clusters in new ways, researchers may be able to better assess whether the groups have distinctive shapes, or whether they are amorphous.
Too large to be classed as molecules, but too small to be bulk solids, atomic clusters can range in size from a few dozen to several hundred atoms. The structures can be used for a diverse range of applications, which requires a detailed knowledge of their shapes. These are easy to describe using mathematics in some cases; while in others, their morphologies are far more irregular. However, current models typically ignore this level of detail; often defining clusters as simple ball-shaped structures. In research published in EPJ B, José M. Cabrera-Trujillo and colleagues at the Autonomous University of San Luis Potosí in Mexico propose a new method of identifying the morphologies of atomic clusters. They have now confirmed that the distinctive geometric shapes of some clusters, as well as the irregularity of amorphous structures, can be fully identified mathematically.
- Published on 18 September 2019
A new agent-based computer modelling technique has been applied to the growth and sliding movement of colonies of bacteria
As many people will remember from school science classes, bacteria growing on solid surfaces form colonies that can be easily visible to the naked eye. Each of these is a complex biological system in its own right; colonies display collective behaviours that indicate a kind of 'social intelligence' and grow in fractal patterns that can resemble snowflakes. Despite this complexity, colony growth can be modelled using principles of basic physics. Lautaro Vassallo and his co-workers in Universidad Nacional de Mar del Plata, Argentina have modelled such growth using a novel method in which the behaviour of each of the bacteria is simulated separately. This work has now been published in the journal EPJ B.
- Published on 11 September 2019
The conductivity of dual layers of graphene greatly depends on the states of carbon atoms at their edges; a property which could have important implications for information transmissions on quantum scales.
Made from 2D sheets of carbon atoms arranged in honeycomb lattices, graphene displays a wide array of properties regarding the conduction of heat and electricity. When two layers of graphene are stacked on top of each other to form a ‘bilayer’, these properties can become even more interesting. At the edges of these bilayers, for example, atoms can sometimes exist in an exotic state of matter referred to as the ‘quantum spin Hall’ (QSH) state, depending on the nature of the interaction between their spins and their motions, referred to as their ‘spin-orbit coupling’ (SOC). While the QSH state is allowed for ‘intrinsic’ SOC, it is destroyed by ‘Rashba’ SOC. In an article recently published in EPJ B, Priyanka Sinha and Saurabh Basu from the Indian Institute of Technology Guwahati showed that these two types of SOC are responsible for variations in the ways in which graphene bilayers conduct electricity.
- Published on 02 August 2019
Mathematical analysis reveals that the exponential patterns in RNA diffusion rates linked to small-scale diffusive behaviours
Recent studies have revealed that within cells of both yeast and bacteria, the rates of diffusion of RNA proteins – complex molecules that convey important information throughout the cell – are distributed in characteristic exponential patterns. As it turns out, these patterns display the highest possible degree of disorder, or ‘entropy’, of all possible diffusion processes within the cell. In new research published in EPJ B, Yuichi Itto at Aichi Institute of Technology in Japan explores this behaviour further by zooming in to study local fluctuations in the diffusion rates of RNA proteins. By associating these small-scale diffusion rates with time-varying values for entropy, he finds that the rates of change of entropy in certain time intervals are larger in areas with higher RNA diffusion rates.
- Published on 24 July 2019
New study explains why it is not possible to couple nano-scale microwave generators known as spin-torque oscillators together in series to generate a macroscopic strength signal
Spin-torque oscillators (STOs) are nanoscale devices that generate microwaves using changes in magnetic field direction, but those produced by any individual device are too weak for practical applications. Physicists have attempted - and, to date, consistently failed - to produce reliable microwave fields by coupling large ensembles. Michael Zaks from Humboldt University of Berlin and Arkady Pikovsky from the University of Potsdam in Germany have now shown why connecting these devices in series cannot succeed, and, at the same time, suggested other paths to explore. Their work was recently published in EPJ B.