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Experimentally accessible measurement of irreversibility in stochastic systems by categorizing single-molecule displacements
Authors:
Alvaro Lanza,
Inés Martínez-Martín,
Rafael Tapia-Rojo,
Stefano Bo
Abstract:
Quantifying the irreversibility and dissipation of non-equilibrium processes is crucial to understanding their behavior, assessing their possible capabilities, and characterizing their efficiency. We introduce a physical quantity that quantifies the irreversibility of stochastic Langevin systems from the observation of individual molecules' displacements. Categorizing these displacements into a fe…
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Quantifying the irreversibility and dissipation of non-equilibrium processes is crucial to understanding their behavior, assessing their possible capabilities, and characterizing their efficiency. We introduce a physical quantity that quantifies the irreversibility of stochastic Langevin systems from the observation of individual molecules' displacements. Categorizing these displacements into a few groups based on their initial and final position allows us to measure irreversibility precisely without the need to know the forces and magnitude of the fluctuations acting on the system. For short times, our model-free estimate of irreversibility is related to entropy production by a conditional fluctuation theorem. For short times and in general for stationary protocols, our estimate provides a lower bound to the average entropy production. We validate the method on single-molecule force spectroscopy experiments of proteins subject to force ramps. We show that irreversibility is sensitive to detailed features of the energy landscape underlying the protein folding dynamics and suggest how our methods can be employed to unveil key properties of protein folding processes.
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Submitted 8 July, 2026; v1 submitted 12 November, 2025;
originally announced November 2025.
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Recurrent neural network analysis of single trajectories switching between anomalous diffusion states
Authors:
Alvaro Lanza,
Xiang Qu,
Stefano Bo
Abstract:
Diffusive dynamics abound in nature and have been especially studied in physical, biological, and financial systems. These dynamics are characterised by a linear growth of the mean squared displacement (MSD) with time. Often, the conditions that give rise to simple diffusion are violated, and many systems, such as biomolecules inside cells, microswimmers, or particles in turbulent flows, undergo a…
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Diffusive dynamics abound in nature and have been especially studied in physical, biological, and financial systems. These dynamics are characterised by a linear growth of the mean squared displacement (MSD) with time. Often, the conditions that give rise to simple diffusion are violated, and many systems, such as biomolecules inside cells, microswimmers, or particles in turbulent flows, undergo anomalous diffusion, featuring an MSD that grows following a power law with an exponent $α$. Precisely determining this exponent and the generalised diffusion coefficient provides valuable information on the systems under consideration, but it is a very challenging task when only a few short trajectories are available, which is common in non-equilibrium and living systems. Estimating the exponent becomes overwhelmingly difficult when the diffusive dynamics switches between different behaviours, characterised by different exponents $α$ or diffusion coefficients $K$. We develop a method based on recurrent neural networks that successfully estimates the anomalous diffusion exponents and generalised diffusion coefficients of individual trajectories that switch between multiple diffusive states. Our method returns the $α$ and $K$ as a function of time and identifies the times at which the dynamics switches between different behaviours. We showcase the method's capabilities on the dataset of the 2024 Anomalous Diffusion Challenge.
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Submitted 25 July, 2025; v1 submitted 12 March, 2025;
originally announced March 2025.
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Charting the Skyrmion Free-Energy Landscape
Authors:
Juan Carlos Criado,
Peter D. Hatton,
Álvaro Lanza,
Sebastian Schenk,
Michael Spannowsky
Abstract:
Chiral magnets with Dzyaloshinskii-Moriya interactions feature a rich phase diagram with a variety of thermodynamical phases. These include helical and conical spin arrangements and topologically charged objects such as (anti)skyrmions. Crucially, due to hysteresis effects, the thermodynamical phases can co-exist at any given temperature and external magnetic field, typically leading to metastabil…
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Chiral magnets with Dzyaloshinskii-Moriya interactions feature a rich phase diagram with a variety of thermodynamical phases. These include helical and conical spin arrangements and topologically charged objects such as (anti)skyrmions. Crucially, due to hysteresis effects, the thermodynamical phases can co-exist at any given temperature and external magnetic field, typically leading to metastability of, e.g., the material's topological phase. In this work, we use Monte Carlo simulations to study these effects. We compute the relative free energies of co-existing states, enabling us to determine the ground state at all values of the external parameters. We also introduce a method to estimate the activation energy, i.e. the height of the energy barrier that separates the topological phase from the ground state. This is one of the key ingredients for the determination of the skyrmion lifetime, which is relevant for technological applications. Finally, we prescribe predicting the system's evolution through any path in the space of external parameters. This can serve as a guideline to prepare the magnetic material in any desired phase or even trigger a phase transition in an experimental setup.
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Submitted 9 May, 2024; v1 submitted 7 March, 2023;
originally announced March 2023.
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Hybrid improper dipolar density wave in NaLaCoWO$_6$
Authors:
Andrea Griesi,
Enrico Mugnaioli,
Arianna E. Lanza,
Valentina Vit,
Lara Righi,
Mauro Gemmi,
Fabio Orlandi
Abstract:
Hybrid Improper Ferroelectricity (HIF) allows the generation of an electrical polarization in the AA'BB'O$_6$ double perovskite materials thanks to the combination of two non-polar octahedral distortions. Nevertheless, for selected combination of the A/A' cations a non-polar incommensurate phase is observed with average symmetry $C2/m$. Thanks to a detailed crystallographic description of the inco…
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Hybrid Improper Ferroelectricity (HIF) allows the generation of an electrical polarization in the AA'BB'O$_6$ double perovskite materials thanks to the combination of two non-polar octahedral distortions. Nevertheless, for selected combination of the A/A' cations a non-polar incommensurate phase is observed with average symmetry $C2/m$. Thanks to a detailed crystallographic description of the incommensurate phase, based on electron, neutron and x-ray diffraction data, we show that the incommensurate modulation is related to an abrupt change of the out-of-phase tilting along the a- and c-axis whereas the tilting along the b-axis remain constant across the structure. By using group theory and symmetry analysis we show that we observe an incommensurate analog of HIF which induces a hybrid improper dipolar density wave in NaLaCoWO$_6$. The dipolar ordering is due also in this case to a trilinear invariant involving the commensurate and incommensurate octahedra tilting's.
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Submitted 28 March, 2022; v1 submitted 28 October, 2021;
originally announced October 2021.
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The structure of the superconducting high-pressure phase of Sc$_3$CoC$_4$
Authors:
Jan Langmann,
Marcel Vöst,
Dominik Schmitz,
Christof Haas,
Georg Eickerling,
Anton Jesche,
Michael Nicklas,
Arianna Lanza,
Nicola Casati,
Piero Macchi,
Wolfgang Scherer
Abstract:
We investigate pressure-induced structural changes to the Peierls-type distorted low-temperature phase of the low-dimensional Sc$_3$CoC$_4$ as a possible origin of its pressure-enhanced superconductivity. By means of cryogenic high-pressure x-ray diffraction experiments we could reveal subtle, but significant structural differences between the low-temperature phase at ambient and elevated pressure…
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We investigate pressure-induced structural changes to the Peierls-type distorted low-temperature phase of the low-dimensional Sc$_3$CoC$_4$ as a possible origin of its pressure-enhanced superconductivity. By means of cryogenic high-pressure x-ray diffraction experiments we could reveal subtle, but significant structural differences between the low-temperature phase at ambient and elevated pressures. We could thus establish the structure of the superconducting phase of the title compound which interestingly still shows the main features of the Peierls-type distorted low-temperature phase. This indicates that in contrast to other low-dimensional materials a suppression of periodic structural distortions is no prerequisite for superconducitivity in the transition metal carbide.
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Submitted 2 February, 2021;
originally announced February 2021.
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Giant pressure dependence and dimensionality switching in a metal-organic quantum antiferromagnet
Authors:
Björn Wehinger,
Christoph Fiolka,
Arianna Lanza,
Rebecca Scatena,
Mariusz Kubus,
Audrey Grockowiak,
William A. Coniglio,
David Graf,
Markos Skoulatos,
Jyong-Hao Chen,
Jan Gukelberger,
Nicola Casati,
Oksana Zaharko,
Piero Macchi,
Karl W. Krämer,
Stan Tozer,
Christopher Mudry,
Bruce Normand,
Christian Rüegg
Abstract:
We report an extraordinary pressure dependence of the magnetic interactions in the metal-organic system [(CuF$_2$(H$_2$O)$_2$)$_2$pyrazine]. At zero pressure, this material realizes a quasi-two-dimensional (Q2D) spin-1/2 square-lattice Heisenberg antiferromagnet. By high-pressure, high-field susceptibility measurements we show that the dominant exchange parameter is reduced continuously by a facto…
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We report an extraordinary pressure dependence of the magnetic interactions in the metal-organic system [(CuF$_2$(H$_2$O)$_2$)$_2$pyrazine]. At zero pressure, this material realizes a quasi-two-dimensional (Q2D) spin-1/2 square-lattice Heisenberg antiferromagnet. By high-pressure, high-field susceptibility measurements we show that the dominant exchange parameter is reduced continuously by a factor of 2 upon compression. Above 18 kbar, a phase transition occurs, inducing an orbital re-ordering that switches the dimensionality, transforming the Q2D lattice into weakly coupled chains (Q1D). We explain the microscopic mechanisms for both phenomena by combining detailed x-ray and neutron diffraction results with quantitative modeling using spin-polarized density functional theory.
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Submitted 8 February, 2018; v1 submitted 27 June, 2016;
originally announced June 2016.