Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides

TL;DR

This paper models quantum phase transitions in iron pnictides using a large-N approach, revealing concurrent magnetic and Ising-nematic transitions with broad quantum critical regions, relevant for understanding P-doped iron arsenides.

Contribution

It introduces a large-N effective model capturing magnetic and nematic order parameters, showing continuous transitions and quantum criticality in isoelectronically tuned iron pnictides.

Findings

Magnetic and Ising transitions are concurrent and nearly continuous.

Quantum criticality spans a wide dynamical range.

Results support further studies on quantum critical behavior in P-doped iron arsenides.

Abstract

Considerations of the bad-metal behavior led to an early proposal for a quantum critical point under a P for As doping in the iron pnictides, which has since been experimentally observed. We study here an effective model for the isoelectronically tuned pnictides using a large-$N$ approach. The model contains antiferromagnetic and Ising-nematic order parameters appropriate for $J_1$-$J_2$ exchange-coupled local moments on an Fe square lattice, and a damping caused by coherent itinerant electrons. The zero-temperature magnetic and Ising transitions are concurrent and essentially continuous. The order-parameter jumps are very small, and are further reduced by the inter-plane coupling; quantum criticality hence occurs over a wide dynamical range. Our results provide the basis for further studies on the quantum critical properties in the P-doped iron arsenides.