Jan Zaanen (17 April 1957 – 18 January 2024) was a Dutch professor of theoretical physics at Leiden University.

He is best known for his contributions to the understanding of the quantum physics of the electrons in strongly correlated material, and in particular high temperature superconductivity.

Zaanen's areas of interest were in the search for novel forms of collective quantum phenomena realized in systems built from mundane constituents like electrons, spins, and atoms.

Zaanen introduced the so-called Zaanen-Sawatzky-Allen diagram, the LDA+U band structure method and he became particularly well known for his discovery of the stripe instability of the doped Mott insulator.

[3] Zaanen was one of the driving forces behind the scientific cooperation between the fields of string theory and high-temperature superconductivity.

In an interview with Dutch newspaper, De Volkskrant, he stated:[4] After winning the Spinoza Prize, it was no longer necessary to worry whether I was proving myself enough.

Zaanen and colleagues Cubrovic and Schalm applied string theory to explain a physical phenomenon.

Once it was realised that AdS/CFT could be applied to a broader spectrum of physical phenomena,[16] Zaanen was inspired to use these ideas for his own area of High-temperature superconductivity.