Get open-access full-text papers the legal way: Use Unpaywall

Using Unpaywall, anyone can now find freely available full-text of journal articles.

How does it work?
Step 1. Add the Unpaywall extension to your Chrome or Firefox browser
Step 2. When you view a research article (from publisher’s website), look out for the coloured tab on the right of the webpage.
a. Green tab: There is a free, legal full-text. Click on the green tab to read.
b. Gray tab: Unable to find a free legal full-text.

To get started, add Unpaywall extension and try to find full-text of this article:
Hennigar, R. A., Mann, R. B. and Tjoa, E. (2017). Superfluid Black Holes. Physical Review Letters, 118, 021301

Full-text from publisher costs US$25 but Unpaywall finds a free copy uploaded by the authors to arXiv.

Unpaywall was developed by Impactstory, an open-source website that helps researchers share the online impact of their research.