Quantum-critical scale invariance in a transition metal alloy

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.

Sachdev-Ye-Kitaev Models and Beyond: A Window into Non-Fermi Liquids

“…It is found (Esterlis et al, 2021b) (11.27) along with factors which are slow logarithmic functions of temperature. This is remarkably similar to observations of Planckian dissipation in strange metals (Cao et al, 2020;Grissonnanche et al, 2021;Jaoui et al, 2021;Legros et al, 2019;Nakajima et al, 2020) even though the connection of the present models to the underlying microscopic models of these materials, if any, remains unclear.…”

“…Nevertheless, it is quite remarkable that for a number of metals exhibiting a broad regime of T −linear resistivity including the cuprates, pnictides, ruthenates, organics and rare-earth element materials, the above "operational" definition of a scattering rate leads to α ≈ 1 (Bruin et al, 2013). A similar analysis in magic-angle twisted bilayer graphene near half-filling of the electron and hole-like flat-bands (Cao et al, 2020;Jaoui et al, 2021), in twisted transition metal dichalcogenides (Ghiotto et al, 2021), several cuprates over an extended range of doping levels (Legros et al, 2019) and a nonsuperconducting iron-pnictide (Nakajima et al, 2020) have also found indication of a Planckian scattering rate with α ≈ 1. Recent measurements of angle-dependent magnetoresistance (ADMR) near the pseudogap critical point in Nd-LSCO also reveal a Fermi surface with an isotropic Planckian scattering set by α ≈ 1 (Grissonnanche et al, 2021).…”

Phenomenological classification of metals based on resistivity

“…The resistivity data of Ba(Fe 1/3 Co 1/3 Ni 1/3 ) 2 As 2 were obtained from the work of ref. [27]. The linear dependence of resistivity in this nonsuperconducting iron pnictide system has also been found to obey a universal scaling relation between temperature and applied magnetic fields down to the lowest energy scales [27].…”

“…1b. [6,9,27]. However, regardless of their different origin and classification, the resistivity of all the metallic systems in the intermediate region show many comparable features.…”

Planckian Dissipation in Metals

“…Explaining these phase diagrams in detail, taking advantage of simultaneous transport and thermodynamic data, and using de Haas-van Alphen oscillation data to carefully account for the multi-band nature of many of these systems, is likely to provide strong constraints on theories of the underlying scattering. In this review we have not touched upon the rich phenomenology of magnetotransport [201][202][203][204][205][206][207][208] and low temperature thermal [209] and thermoelectric [210,211] transport that has also been demonstrated experimentally in Planckian systems. These will likely also provide fruitful hunting ground for future theories.…”