# Quantum-critical scale invariance in a transition metal alloy

## TL;DR

This study reveals quantum-critical scale invariance in a non-superconducting iron-pnictide alloy, demonstrating non-Fermi liquid behavior and universal scaling near a quantum critical point, distinct from typical superconducting systems.

## Contribution

It provides experimental evidence of quantum-critical scale invariance in a non-superconducting alloy, highlighting unique properties of quantum criticality without pairing instability.

## Key findings

- Scale invariance of thermodynamic and transport quantities
- Universal scaling relation for scattering rate
- Absence of pairing instability near quantum critical point

## Abstract

Quantum-mechanical fluctuations between competing phases at $T=0$ induce exotic finite-temperature collective excitations that are not described by the standard Landau Fermi liquid framework. These excitations exhibit anomalous temperature dependences, or non-Fermi liquid behavior, in the transport and thermodynamic properties in the vicinity of a quantum critical point, and are often intimately linked to the appearance of unconventional Cooper pairing as observed in strongly correlated systems including the high-$T_c$ cuprate and iron pnictide superconductors. The presence of superconductivity, however, precludes direct access to the quantum critical point, and makes it difficult to assess the role of quantum-critical fluctuations in shaping anomalous finite-temperature physical properties. Here we report temperature-field scale invariance of non-Fermi liquid thermodynamic, transport, and Hall quantities in a non-superconducting iron-pnictide, Ba(Fe$_{1/3}$Co$_{1/3}$Ni$_{1/3}$)$_{2}$As$_{2}$, indicative of quantum criticality at zero temperature and zero applied magnetic field. Beyond a linear in temperature resistivity, the hallmark signature of strong quasiparticle scattering, we find the scattering rate that obeys a universal scaling relation between temperature and applied magnetic fields down to the lowest energy scales. Together with the dominance of hole-like carriers close to the zero-temperature and zero-field limits, the scale invariance, isotropic field response, and lack of applied pressure sensitivity suggests a unique quantum critical system that does not drive a pairing instability.