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📰 From the beginnings of the universe to chains of atoms: cooling anomalies

Physicists have theoretically studied the cooling towards absolute zero of a series of magnetically interacting atoms. The system’s very slow dynamical behavior leads to persistence of defects, expressing similar physics to certain primordial universe expansion scenarios.

Perhaps one of the most fascinating phenomena in physics is the spontaneous emergence of phase transitions in complex systems: assemblies of particles interacting in a short range (a few molecular distances) can, if the temperature is lowered below a certain threshold, organize themselves over a macroscopic scale of distances. By automatically breaking symmetry.

Elchinator image from Pixabay

The most common example is undoubtedly the freezing of liquids, a transition beyond which a crystalline solid, made of an ordered assembly of superimposed molecular planes, does not displayproperties (distinguish the isotropic constants of the physical properties of the medium in …) that prevailed in the liquid. A different example of transition, called “continuous”, is provided by magnets: magnetization results from a direction (In a literal sense, direction indicates or embodies the direction of the east (sunrise…) A concerted action of the tiny magnets that certain atoms (such as iron) possess. These microscopic magnets (called spins) tend to align their magnets to create macroscopic magnetization (which we experience on our scale), a phenomenon frustrated byAccelerates (Stirring is the process that consists of mixing one or more phases…) thermal (Thermal is the science that deals with energy production and use…). If this exceeds a precise limit (770 degrees for iron), the magnetization disappears due to disorder Moving (The word dynamic is often used to designate or specify what is related to movement. It is…) So strong that the spins average out in all directions, and no macroscopic magnetization is shown anymore.

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From a dynamic point of view, continuous phase transitions are always accompanied by complex phenomena of competition between different orientations that appear in the different ordered regions that grow in the four corners of the macroscopic sample (liquid crystallinity differs from this scenario). Moreover, this competition becomes increasingly slow as the temperature approaches a phase change, which has consequences in any real experiment. In fact, the temperature reduction always occurs at a certain speed, and no matter how slow it is, it ends up “accelerating” the system which then tends to freeze into a formation with many defects (grains of irregular magnetic orientations of magnets).

The shape factor (the product of domain wall density and magnetic susceptibility) is a new tool for measuring distance to equilibrium.
Red dot: thermal equilibrium. Green dot: growth after immediate cooling.
Blue interval: a variety of infinitely slow cooling processes.
Credit: C. Godrèche and J.-M Luck

An important question, then, is how the intensity of these defects depends on the cooling rate. Unexpectedly, it was first put forward in 1976 by the British physicist Th. Cable in a completely different way Context (The context of the event includes the circumstances and conditions surrounding it; …) of condensed matter, that of Cosmology (Cosmology is the branch of astrophysics that studies the universe as a system…) For the early universe: according to Particle physics (Particle physics is the branch of physics that studies components…)the cooling that followed the expansion of the universe caused it to go through several continuous phase transitions (of quantum origin), which should leave so-called topological defects, which are likely to change in alive (The concept of neighborhood corresponds to an axiomatic approach equivalent to the concept of …) The usual laws of physics. So we understand Keble’s questioning, the intensity of these defects is a settings (A parameter in a broad sense is an element of information that must be considered…) Important for a complete description of the current universe.

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Keble’s ideas were applied to condensed matter by physicist W. Zurek a few years later, because the underlying mechanism is the same in both cases: a critical deceleration near Transitional phase (In physics, a phase transition is a transition of the studied system…) It continues to move the system out of equilibrium as it goes through this transition. These ideas gave rise to the Kibble-Zurek theory which established laws describing, among other things, the behavior of defect density as a function of cooling rate.

This theory has just been reviewed by researchers from the Institute for Theoretical Physics (IPhT, CNRS/CEA) in a recently published article. They consider a fully solvable one-dimensional model, the classical ferromagnetic series of Ising spins subject to random dynamics simulatinginteraction (An interaction is the exchange of information, influences, or energy between two agents within…) with one Thermostat (The thermostat is a system that ensures a constant temperature. It could be a device…) of compressive temperature, whose temporal change is arbitrary a priori. Due to its one-dimensional structure, this model has a continuous phase transition at absolute zero, which makes it possible to approach it “from above” and to study universally shared properties around critical points: critical hysteresis with insistence (insistence (statistics) insistence (computing) in drawing: …) defects, the emergence of larger and larger magnetic fields …

The authors comprehensively examine the different possible scenarios for cooling towards absolute zero, and introduce a new parameter, ‘form factor’, which compositionally accounts for the system’s distance from equilibrium caused by the cooling protocol. These results have been published in Journal of Physics a.

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Glauber-Ising series under low-temperature protocols, C. Godrèche, J.-M. Luck, Physics Journal A: Mathematics and Theorypublished on December 16, 2021.
DOI: 10.1088/1751-8121/aca84c
Open archive arXiv

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