Quantum-critical scale invariance in a transition metal alloy

Yasuyuki Nakajima,Christopher Eckberg,Nicholas P Butch,David Graf,Peter Y Zavalij,I-Lin Liu,Sergey V Borisenko,Kevin Kirshenbaum,Shanta R Saha,Johnpierre Paglione,Limin Wang,Yun Suk Eo,Alex Hughes,Renxiong Wang,Zhonghao Liu,Daniel Campbell,Tristin Metz

doi:10.1038/s42005-020-00448-5

Abstract

Quantum-mechanical fluctuations between competing phases induce exotic collective excitations that exhibit anomalous behavior in transport and thermodynamic properties, and are often intimately linked to the appearance of unconventional Cooper pairing. High-temperature superconductivity, however, 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(Fe1/3Co1/3Ni1/3)2As2, indicative of quantum criticality at zero temperature and applied magnetic field. Beyond a linear-in-temperature resistivity, the hallmark signature of strong quasiparticle scattering, we find a 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 unhindered by a pairing instability.

Highlights

Quantum-mechanical fluctuations between competing phases induce exotic collective excitations that exhibit anomalous behavior in transport and thermodynamic properties, and are often intimately linked to the appearance of unconventional Cooper pairing
Non-Fermi liquid (NFL) behavior ubiquitously appears in iron-based high-temperature superconductors with a novel type of superconducting pairing symmetry driven by interband repulsion[1, 2]
We show that NFL behavior is prevalent in the very low-temperature charge transport and thermodynamic properties of Ba(Fe1/3Co1/ 3Ni1/3)2As2, with temperature and magnetic energy scale invariance arising from a quantum critical (QC) ground state

Summary

Introduction

Quantum-mechanical fluctuations between competing phases induce exotic collective excitations that exhibit anomalous behavior in transport and thermodynamic properties, and are often intimately linked to the appearance of unconventional Cooper pairing. 20–23), and thereby modifying the electronic structure subtly, but significantly enough to tune in and out of different ground states and correlation types Utilizing this balance, counter-doping a system to achieve the same nominal d electron count as BaCo2As2 can realize a unique route to the same nearly FM system, while disrupting any specific spin correlation in the system. Counter-doping a system to achieve the same nominal d electron count as BaCo2As2 can realize a unique route to the same nearly FM system, while disrupting any specific spin correlation in the system We utilize this approach to stabilize a novel ground state in the counter-doped nonsuperconducting iron pnictide Ba(Fe1/ 3Co1/3Ni1/3)2As2, nearly FM but with a unique type of spin fluctuation that leads to very strong quasiparticle scattering. We show that NFL behavior is prevalent in the very low-temperature charge transport and thermodynamic properties of Ba(Fe1/3Co1/ 3Ni1/3)2As2, with temperature and magnetic energy scale invariance arising from a QC ground state

Methods

Results

Conclusion