Direct visualization of local interaction forces in Bi2Sr2CaCu2O8+δ vortex matter

Abstract

We study the local vortex-vortex interaction force fi of the structure frozen during a field-cooling process in an electron-irradiated Bi2Sr2CaCu2O8+d sample. We compute this magnitude from snapshots of the vortex structure obtained via magnetic decoration experiments at various fields H in the same sample. Since the observed structures correspond to the equilibrium ones frozen at T∼Tirr(H)[1], at this temperature the local modulus of fi roughly equals the local pinning force at the decorated surface of the sample. We estimate the most probable local pinning force from the mode value of the fi(r)distribution, fp m. We found that fp m grows algebraically with H and in electron-irradiated samples is 50-20% smaller than for samples with columnar defects.