T/B scaling of magnetization in the mixed valent compound \beta-YbAlB4

TL;DR

This study provides evidence of intrinsic quantum criticality in the valence fluctuating superconductor beta-YbAlB4 through T/B scaling of magnetization, indicating a breakdown of Fermi-liquid behavior at extremely low magnetic fields.

Contribution

It presents the first clear evidence of quantum criticality in an intermediate valence system without external tuning, using high-precision magnetization measurements.

Findings

T/B scaling observed over three decades in magnetization.

Critical magnetic field |B_c| < 0.2 mT, comparable to Earth's magnetic field.

Beta-YbAlB4 may be intrinsically quantum critical, without tuning parameters.

Abstract

Here we provide the first clear evidence of Fermi-liquid breakdown in an intermediate valence system. We employ high precision magnetization measurements of the valence fluctuating superconductor beta-YbAlB4 to probe the quantum critical free energy down to temperatures far below the characteristic energy scale of the valence fluctuations. The observed T/B scaling in the magnetization over three decades not only indicates unconventional quantum criticality, but places an upper bound on the critical magnetic field |B_c| < 0.2 mT, a value comparable with the Earth's magnetic field and six orders of magnitude smaller than the valence fluctuation scale. This tiny value of the upper bound on B_c, well inside the superconducting dome, raises the fascinating possibility that valence fluctuating beta-YbAlB4 is intrinsically quantum critical, without tuning the magnetic field, pressure, or composition: the first known example of such a phenomenon in a metal.