Advertisement for the post of Junior Research Fellow (JRF)
Applications are invited from eligible candidates for the position of Junior Research Fellow (JRF) in the SERB funded project entitled ‘Brownian dynamics studies on depinning, melting and dynamic phases of driven partially pinned vortex lattice’
Duration of the project: Three years
Eligibility criteria: M.Sc. in Physics or related subjects with a minimum of 60% marks or aggregate B+ grade. NET/GATE qualification is desirable.
Desirable quality: An interest in Statistical Physics and Computational Physics
Emolument: As per SERB norms
Principal Investigator: Dr. Toby Joseph, Department of Physics, BITS Pilani K K Birla Goa Campus, Zuarinagar, Goa. (Phone: 0832 2580145)
How to apply: Interested candidates may send their curriculum vitae to toby@goa.bits-pilani.ac.in
Deadline: 20th February, 2021
Project Summary:
The behavior of a collection of particles in two dimensions in the presence of a periodic substrate potential has been of interest in the context of varied systems. Vortices in thin film superconductors in the presence of regular array of pinning centers is one such system. For filling equals one, in the weak pinning regime, the existence of a partially pinned phase of vortices in the presence of a square substrate potential was seen in Monte Carlo simulations, density functional studies and in experiments. In this phase, vortex lattice exhibits only one of the basic periodicity (in x and y directions) of the underlying pinning potential. Preliminary simulation studies on driven partially pinned state by us has shown interesting properties including: (i) elastic depinning (ii) effective lattice pinning close to the solid to liquid transition (iii) anisotropic depinning threshold force and (iv) dependence of melting temperature on the drive direction and strength. The proposal is for a thorough study of depinning and dynamic phases of partially pinned solid by means of Brownian dynamics simulation. Driven vortex lattice for the partially pinned solid has not been thoroughly studied. The present study shall focus on characterizing the depinning transition, understanding the role of defects in the peak effect observed and study of various dynamic phases exhibited by the vortex system. The role of the symmetry of the substrate potential in the vortex lattice properties and peak effect seen will be studied. The proposed studies are to be carried out using Brownian dynamics simulations using large systems size (1600 particles and above) and large averaging times (1 million time steps and above). The depinning threshold for zero and finite temperature will be determined and the critical behavior above the threshold will be studied. With the help of Delaunay triangulation, the defect structures close to the transition will be studied to get a clearer understanding of the peak effect phenomena. For studying the equilibrium and driven steady state properties of the vortex lattice we shall be looking at structure factor, energy fluctuations and individual vortex trajectories. The nature of individual vortex trajectories will be also used to study the dynamics phases of the driven lattice as function of temperature and driving strength for various drive directions. This study will help in characterizing and understanding the weak pinning regime in vortex lattice studies. The comprehensive study of these phenomena would enhance our understanding, not only of the driven two dimensional vortex systems with periodic pinning, but similar two dimensional systems studied in varied contexts, in particular 2D colloidal systems in the presence of substrate potential and solid on solid friction models.