Production of kinks in an inhomogenous medium

TL;DR

This paper investigates how impurities in a medium influence the formation and persistence of kinks during phase transitions, modifying the standard Kibble-Zurek formalism to account for defect trapping near impurities.

Contribution

It introduces a mechanism showing that impurity gradients can lead to kink creation near imperfections, adding a new length scale to defect density predictions.

Findings

Kinks tend to form near impurity sites due to strong potential gradients.

Impurities can trap kinks, preventing their annihilation and leading to higher defect densities.

The impurity distribution influences the defect formation process and final density.

Abstract

The purpose of this report is presentation of the main modifications of the standard Kibble-Zurek formalism caused by the existence of the unperfections in the system. We know that the distribution of kinks created during a second order phase transition in pure systems is determined solely by the correlation length at freeze-out time. The correlation length at that instant of time intuitively describes the size of the defect and therefore the number density of defects is limited by the possibility of holding kinks in a unit volume. On the other hand if the system is populated by the impurities then kinks emerge mainly in knots of the force distribution which correspond to extremes of the impurity potential i.e. positions of imperfections. The purpose of this report is to show that, due to existence of the strong gradients of the impurity potential, kinks can be created mainly in the close vicinity of the impurities. It seems that this simple mechanism can be responsible for occurrence, in the number density formula, the additional length scale describing the impurity distribution. We know that in pure systems, as a consequence of kink-antikink annihilation, the number density of kinks decrease in time. In contradiction to pure systems, kinks produced in the systems populated by impurities could be confined by the impurity centers and therefore they may not disappear from the system and may remain above the level established by thermal nucleation of pairs.