Isotope Effect of Underdoped Cuprates in the Yang-Rice-Zhang Model

TL;DR

This paper uses the Yang-Rice-Zhang model to explain the doping-dependent isotope effect in underdoped cuprates, highlighting the role of spin fluctuations and a minor phonon contribution in their superconductivity.

Contribution

It extends the YRZ model to account for isotope effect variations with doping, providing a natural explanation for experimental observations.

Findings

Small isotope effect at optimal doping

Large isotope effect in underdoped cuprates

Supports spin fluctuation pairing with minor phonon role

Abstract

The underdoped region of the cuprate's phase diagram displays many novel electronic phenomena both in the normal and the superconducting state. Many of these anomalous properties have found a natural explanation within the resonating valence bond spin liquid phenomenological model of Yang-Rice-Zhang (YRZ) which includes the rise of a pseudogap. This leads to Fermi surface reconstruction and profoundly changes the electronic structure. Here we extend previous work to consider the shift in critical temperature on $^{16}$O to $^{18}$O substitution, The isotope effect has been found experimentally to be very small at optimal doping yet to rapidly increase to very large values with underdoping. The YRZ model provides a natural explanation of this behavior and supports the idea of a pairing mechanism which is mainly spin fluctuations with a subdominant $(\sim 10\%)$ phonon contribution.