Quantum Criticality in Electron-doped BaFe_{2-x}Ni_xAs_2

TL;DR

This study identifies two quantum critical points in electron-doped BaFe_{2-x}Ni_xAs_2, revealing their association with magnetic and nematic transitions, and linking quantum criticality to superconductivity in iron-pnictides.

Contribution

First identification of two distinct quantum critical points in BaFe_{2-x}Ni_xAs_2, one magnetic and one nematic, using transport and NMR measurements, advancing understanding of quantum criticality in iron-based superconductors.

Findings

Two quantum critical points at x_{c1} = 0.10 and x_{c2} = 0.14.

Electrical resistivity shows linear and near-linear temperature dependence near critical points.

NMR indicates magnetic and nematic quantum criticality associated with the two points.

Abstract

A quantum critical point (QCP) is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently-discovered iron-pnictide high temperature superconductors, it is unknown whether a QCP exists or not in a carrier-doped system. Here we report transport and nuclear magnetic resonance (NMR) measurements on BaFe_{2-x}Ni_xAs_2 (0 =< x =< 0.17). We find two critical points at x_{c1} = 0.10 and x_{c2} = 0.14. The electrical resistivity follows \rho = \rho_0 + A*T^n, with n = 1 around x_{c1} and another minimal n = 1.1 at x_{c2}. By NMR measurements, we identity x_{c1} to be a magnetic QCP and suggest that x_{c2} is a new type of QCP associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.