The first report that doping a Mott insulator reveals a first-order transition between the pseudogap
and a correlated Fermi liquid [1] has triggered intensive research. It was predicted that this transition
could be at the origin of many of the surprising properties of doped cuprates, such as the fall in the
Knight shift.
However, this transition has never been directly observed experimentally. Furthermore, many have
suggested that the transition might be an artifact of numerical methods, such as the small clusters in
cluster dynamical mean field theory, or of clusters that favor antiferromagnetic fluctuations.
Following the recent proofs that the transition still exists with larger clusters without
antiferromagnetic fluctuations [2,3], we used the dynamical cluster approximation to propose
experiments for the 11% doped organic superconductor κ-(BEDT-TTF)₄Hg_2.89Br₈ [4]. Using the
concept of Widom lines, namely of crossover lines originating from the Sordi transition, we predicted
that both the resistivity and the Seebeck coefficient should exhibit detectable signals of the transition
at 11% doping, representing the first-ever observation of a consequence of the Sordi transition in a
doped spin liquid.
In collaboration with Prof. Kazushi Kanoda and Dr. Hiroshi Oike, we now report preliminary
evidence consistent with this scenario, including a resistivity crossover and a Seebeck coefficient
feature that may correspond to the predicted Widom line. These results suggest that
κ-(BEDT-TTF)₄Hg_2.89Br₈, could provide a unique platform to observe the fingerprints of the
Mott-driven Sordi transition in real materials.
References
[1]. G. Sordi et al. Phys. Rev. Letters, 104, 226402, 2010.
[2]. P.-O. Downey et al. Phys. Rev. B, 107, 125159, 2023.
[3]. P.-O. Downey et al. Phys. Rev. B, 110, L121109, 2024.
[4]. H. Oike et al. Nat. Comm. 8, 756, 2017.