# News / Highlights / Colloquia

## EPJ B Highlight - Investigating the role of random walks in particle diffusion

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- Published on 18 January 2024

Theoretical analysis reveals new insights into unusual patterns displayed by diffusing particles in recent experiments.

Several recent experiments identify unusual patterns in particle diffusion, hinting at some underlying complexity in the process which physicists have yet to discover. Through new analysis published in *EPJ B*, Adrian Pacheco-Pozo and Igor Sokolov at Humboldt University of Berlin show how this behaviour emerges through strong correlations between the positions of diffusing particles travelling along similar trajectories. Their results could help researchers to create better models of the diffusion process – ultimately drawing deeper insights into how fluids behave.

## EPJ B: Prof. Dr. Reinhold Egger new Editor-in-Chief for the Condensed Matter section as of 1 January 2024

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- Published on 15 December 2023

The publishers of *The European Physical Journal B* are pleased to announce the appointment of Prof. Dr. Reinhold Egger as new Editor-in-Chief for the Condensed Matter section of the journal as of January 1st, 2024.

Reinhold Egger has been a full professor of theoretical physics at Heinrich-Heine-Universität Düsseldorf since 2001. He has worked in many different areas of condensed matter physics, including nonequilibrium quantum transport, topological quantum matter, superconductivity and low-dimensional quantum field theory. He has been part of the board of EPJB since 2011 and he is recipient of the Gerhard-Hess-Preis of the DFG and of the Physics Prize of the Akademie der Wissenschaften zu Göttingen.

The publishers take the opportunity to thank wholeheartedly Dr. Eduardo Hernandez, for his dedicated work and leadership during his term as Editor-in-Chief of EPJB.

## EPJ B Highlight - Testing particle scattering and reflection in graphene

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- Published on 25 September 2023

Testing the quantum effects of Andreev reflection in the wonder material could have positive implications for quantum technology

Humanity stands on the verge of two major revolutions: the boom in 2-dimensional supermaterials like graphene with incredible properties and the introduction of quantum computers with processing power that vastly outstrips standard computers.

Understanding materials like graphene, made of single sheets of atoms, means better investigations of the properties they display at an atomic level. This includes how electrons behave around superconductors — materials that, when cooled to temperatures near absolute zero, can conduct electricity without energy loss.

When a superconductor is sandwiched between metal materials, a type of scattering called crossed Andreev reflection may appear, and in an s-wave superconductor junction, the Andreev reflection usually induces correlated opposite spin in electrons. This can be used to induce entanglement, a quantum phenomenon that is critical for quantum computers.

In a new paper in *EPJ B*, author Rui Shen, from the National Laboratory of Solid State Microstructures and School of Physics at Nanjing University, China, and his co-authors theoretically assess nonlocal transport and crossed Andreev reflection in a ferromagnetic s-wave superconductor junction composed of the gapped graphene lattices.

## EPJ B Colloquium - Density-matrix renormalization group: a pedagogical introduction

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- Published on 17 August 2023

The physical properties of a quantum many-body system can, in principle, be determined by diagonalizing the respective Hamiltonian, but the dimensions of its matrix representation scale exponentially with the number of degrees of freedom. Hence, only small systems that are described through simple models can be tackled via exact diagonalization. To overcome this limitation, numerical methods based on the renormalization group paradigm have been put forth, that restrict the quantum many-body problem to a manageable subspace of the exponentially large full Hilbert space. A striking example is the density-matrix renormalization group (DMRG), which has become the reference numerical method to obtain the low-energy properties of one-dimensional quantum systems with short-range interactions.

## EPJ B Highlight - How a transparent conductor responds to strain

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- Published on 02 August 2023

First-principles calculations show how to manipulate some transition metal oxides’ optical and electronic properties for use in thin-film devices.

Liquid crystal displays, touchscreens, and many solar cells rely on thin-film crystalline materials that are both electrically conductive and optically transparent. But the material most widely used in these applications, indium tin oxide (ITO), is brittle and susceptible to cracking. Researchers seeking alternatives have set their sights on strontium vanadate (SrVO_{3}), a material that ticks all the boxes for a transparent conductor. In a study published in *EPJ B*, Debolina Misra, of the Indian Institute of Information Technology, Design and Manufacturing, Kancheepuram, India, and her colleagues now calculate how SrVO_{3}‘s optical and electron transport properties vary in response to strain. Their simulations provide a detailed mechanism for tuning these properties to optimize the material’s utility in different devices and applications.

## EPJ B Highlight - How a molecular motor moves in a network

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- Published on 24 July 2023

A new study determines the efficiency of a single-molecule heat engine by considering a series of ratchets that transfer energy along a network.

From internal combustion engines to household refrigerators, heat engines are a ubiquitous component of daily life. These machines convert heat into usable energy which can then be used to do work. Heat engines can be as small as a single molecule whose random movements exchange energy with the environment. But determining the efficiency of a molecular heat engine is no simple task. In a study published in *EPJ B*, Mesfin Asfaw Taye, of West Los Angeles College, California, USA now calculates the performance of a molecular heat engine in terms of a series of molecular ratchets that transfer energy, step-wise, in one direction. He shows and discusses how to manipulate such a system for transporting a particle along a complex path.

## EPJ B Highlight - Calculating thermal properties from phonon behaviours

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- Published on 21 July 2023

A new study determines the thermal properties of advanced solid materials, based on first-principles calculations of quantum vibrations.

As the energy demands of our modern world continue to grow, there is a crucial need to understand how heat flows through the materials we use to build our technology. Through new research published in *EPJ B*, Vinod Solet and Sudhir Pandey at the Indian Institute of Technology Mandi have accurately estimated the thermal properties of a particularly promising alloy, based on first-principles calculations of phonons. Composed of scandium (Sc), silver (Ag), and carbon (C), this alloy could soon become a key component of devices which convert heat into electricity, while its low reflectivity and strong photon absorption would make it especially well-suited for highly efficient solar cells.

## EPJ B Highlight - Investigating the use of noise to solve inverse physical problems

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- Published on 19 June 2023

New research looks at the problem of solving a physics problem starting with observational data and working backwards

The early success of physics comes mainly from solving direct or forward problems in which the physical state of a system can be described from a well-defined physical model and from governing equations. Yet, there exists a different type of problem, inverse problems, that are trickier to solve but are crucial to fields such as engineering, astrophysics and geophysics.

Solving these inverse problems requires taking a set of observational data and then working backwards, or inverting the problem, to arrive at the causal factors that gave rise to the data.

A new paper in *EPJ B* by Universidade Federal do Rio researchers Gilberto Corso and João Medeiros de Araujo, considers the possibility of solving inverse problems in physics by using statistical information from noise statistics.

## EPJ B Highlight - Uncovering spin ladders in real compounds

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- Published on 19 June 2023

Low-dimensional quantum systems named ‘spin ladders’ are strongly linked to superconductivity. A new theoretical approach has accurately predicted the nature of the spin ladder which appears in real chemical compound – possibly paving the way for new discoveries of advanced superconductors.

When fabricated in 1 or 2 dimensions, systems of particles whose quantum spins interact with each other can display some unique quantum properties. Through new research published in *EPJ B*, Asif Iqbal and Baidur Rahaman at Aliah University in Kolkata, India, developed a new theoretical technique for calculating the structures and interactions taking place in these unique materials. Their approach could pave the way for advanced new superconductors – which allow electric currents to flow through them with zero resistance.

## EPJ B Highlight - Statistical physics reveals how languages evolve

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- Published on 27 April 2023

Models based on the principles of statistical physics can provide useful insights into how languages change through contact between speakers of different languages. In particular, the analysis reveals how unusual linguistic forms are more likely to be replaced by more regular ones over time.

The field of historical linguistics explores how languages change over time, with a particular focus on the evolution of sounds, meanings, and structures in words and sentences. So far, however, it hasn’t been widely studied from the viewpoint of statistical physics – which uses mathematical models to explain patterns and behaviours in complex, evolving systems. Through a series of models described in *EPJ B*, Jean-Marc Luck at Université Paris-Saclay, together with Anita Mehta at the Clarendon Institute in Oxford, use statistical physics to show how exceptions to well-established grammatical rules are linked to the influence of neighbouring languages.