Strange metal without magnetic criticality

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Science  31 Jul 2015:
Vol. 349, Issue 6247, pp. 506-509
DOI: 10.1126/science.1262054

A mysteriously misbehaving phase

Two electrons in a vacuum repel each other because they carry like charges. But in a metal, with a bunch of other electrons, in some ways they behave as if they didn't interact. This phenomenon, known as the Fermi liquid (FL) behavior, comes with a typical quadratic dependence of the solid's electrical resistance on temperature. Cases where the resistance deviates from the FL dependence are commonly associated with magnetic quantum criticality. Tomita et al. measured the resistivity of the heavy-fermion compound β-YbAlB4 over a range of pressures and temperatures to identify a non-FL phase removed from a magnetic phase by an intervening FL. Explaining the non-FL behavior in the absence of magnetism presents a challenge to theorists.

Science, this issue p. 506


A fundamental challenge to our current understanding of metals is the observation of qualitative departures from Fermi liquid behavior. The standard view attributes such non-Fermi liquid phenomena to the scattering of electrons off quantum critical fluctuations of an underlying order parameter. Although the possibility of non-Fermi liquid behavior isolated from the border of magnetism has long been speculated, no experimental confirmation has been made. Here, we report on the observation of a strange metal region away from a magnetic instability in an ultrapure single crystal. In particular, we show that the heavy-fermion superconductor β-YbAlB4 forms a possible phase with strange metallic behavior across an extensive pressure regime, distinctly separated from a high-pressure magnetic quantum phase transition by a Fermi liquid phase.

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