Unconventional free charge in the correlated semimetal Nd2Ir2O7

TL;DR

This study reveals unconventional charge transport in Nd2Ir2O7, a correlated semimetal, showing non-Fermi liquid behavior and a decoupling of charge dynamics from single-particle excitations, challenging traditional band theory.

Contribution

It provides experimental evidence of non-Fermi liquid behavior and charge transport decoupling in Nd2Ir2O7, highlighting novel emergent properties in correlated topological semimetals.

Findings

Free carrier spectral weight scales as T^2 at low temperatures.

Absence of T^3 specific heat term indicates non-Fermi liquid state.

Momentum relaxation rate shows linear T dependence, suggesting Planckian dissipation.

Abstract

Nd2Ir2O7 is a correlated semimetal with the pyrochlore structure, in which competing spin-orbit coupling and electron-electron interactions are believed to induce a time-reversal symmetry broken Weyl semimetal phase characterized by pairs of topologically protected Dirac points at the Fermi energy. However, the emergent properties in these materials are far from clear, and exotic new states of matter have been conjectured. Here we demonstrate optically that at low temperatures the free carrier spectral weight is proportional to T^2 where T is the temperature, as expected for massless Dirac electrons. However, we do {\em not} observe the corresponding T^3 term in the specific heat. That the system is not in a Fermi liquid state is further corroborated by the "Planckian" T-linear temperature dependence of the momentum relaxation rate and the progressive opening of a correlation-induced gap at low temperatures. These observations can not be reconciled within the framework of band theory of electron-like quasiparticles and point toward the effective decoupling of the charge transport from the single particle sector.