Theory of the Transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8

TL;DR

This paper proposes a theoretical explanation for a phase transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8, attributing it to spin density wave formation caused by impurity-electron interactions, which affects thermal conductivity.

Contribution

It introduces a new theory linking impurity-induced spin density waves to the observed phase transition and thermal conductivity change in Ni-doped Bi2Sr2CaCu2O8.

Findings

The phase transition is due to spin density wave formation.

A small gap opens at two nodes of the superconducting gap.

Thermal conductivity is reduced by a factor of two.

Abstract

A theory is put forward that the electronic phase transition at 0.2 K in Ni-doped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ is result of the formation of a spin density wave in the system of Ni impurities. The driving force for the transition is the exchange interaction between the impurity spins and the spins of the conduction electrons. This creates a small gap at two of the four nodes of the superconducting gap. The effect is to reduce the thermal conductivity by a factor of two, as observed.