Signatures of quantum criticality in hole-doped and chemically pressurized EuFe_2As_2 single crystals

TL;DR

This study investigates quantum criticality in EuFe_2As_2-based crystals through doping and chemical pressure, revealing electronic transitions and signatures of quantum critical behavior in thermopower and resistivity measurements.

Contribution

It provides experimental evidence of quantum critical signatures in hole-doped and chemically pressurized EuFe_2As_2, highlighting electronic configuration changes and Lifshitz transition points.

Findings

Suppression of spin-density-wave transition at critical doping levels.

Emergence of superconductivity near critical doping points.

Observation of quantum critical signatures in thermopower and resistivity.

Abstract

We study the effect of hole-doping and chemical pressure (isovalent doping) in single crystals of K$_x$Eu$_{1-x}$Fe$_2$As$_2$ and EuFe$_2$(As$_{1-y}$P$_y$)$_2$, respectively, by measurements of the thermopower, $S(T)$, and electrical resistivity, $\rho(T)$. The evolution of $S(T)$ upon doping indicates drastic changes of the electronic configuration at critical values $x_{\mathrm{cr}}=0.3$ and $y_{\mathrm{cr}}=0.21$, respectively, as the spin-density-wave transition is completely suppressed and superconductivity (SC) emerges. For the case of chemical pressure, the comparison with published ARPES measurements indicates a Lifshitz transition at $y_{cr}$. The temperature dependences $S(T)/T\propto \log T$ and $\Delta\rho\propto T$ observed in the normal state above the SC transition suggest quantum criticality in both systems.