Comments on "Vortex phase diagram of HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ thin films from magnetoresistance measurements"

TL;DR

This paper critiques a previous study on vortex phase diagrams in HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ thin films, questioning their definitions and scaling relations, and supports an empirical activation energy model for better data agreement.

Contribution

It challenges the previous vortex region definitions and scaling relations, proposing the empirical activation energy form by Zhang extit{et al.} as a more accurate alternative.

Findings

The original vortex region definitions are questionable.

The empirical activation energy form aligns well with resistivity data.

The proposed model explains the apparent activation energy effectively.

Abstract

We make comments on the paper presented by Kim \textit{et al.} [Phys. Rev. B \textbf{61}, 11317 (2000)]. The authors analyzed activation energies of HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ thin films with a scaling relation, and defined four vortex regions for thin films. We find that the definitions of four vortex regions and the scaling relation are questionable when studying their definition of the resistivity range for thermally activated flux flow. Using the empirical activation energy form suggested by Zhang \textit{et al.} [Phys. Rev. B \textbf{71}, 052502 (2005)] for lower resistivity data, we find that the form is not only in good agreement with the resistivity $\rho(T,H)$, but also with the apparent activation energy $-\partial \ln \rho(T,H)/\partial T^{-1}$.