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Non-Fermi-liquid states in FeCrAs and Sr3Ru2O7


In the first half of this presentation, the novel non-Fermi-liquid state in the iron-pnictide FeCrAs will be discussed. The resistivity shows an unusual
“non-metallic” dependence on temperature T over a huge temperature range. Below 10 K the resistivity follows a non-Fermi-liquid power law, rho(T) = rho 0
AT x with x < 1. The specific heat, on the other hand, shows typical Fermi liquid behaviour with a linear temperature dependence and a large Sommerfeld
coefficient, gamma ~ 30 mJ/molK 2 . The magnetic susceptibility is also Fermi-liquid like. The high temperature properties of FeCrAs are reminiscent of those of the
parent compounds of the new layered iron-pnictide superconductors, however the T ->0 K properties suggest a new class of non-Fermi liquid.
In the second half, I will talk about the quantum criticality of the bilayer ruthenate Sr 3 Ru 2 O 7 . It is a exchange-enhanced paramagnet, exhibiting a firstorder
metamagnetic transition (MMT) that bifurcates to enclose an anomalous phase with intriguing properties for field along c-axis. Despite many studies,
the emergent phase is still not well understood. We investigated the quantum criticality in ultrapure crystals of Sr 3 Ru 2 O 7 for fields in the ab-plane using
hydrostatic pressure instead of field angle. Our ac susceptibility measurements show that the critical point of MMT is continuously suppressed by hydrostatic
pressure, going to zero near 13.4 kbar without any clear sign of MMT splitting or new phase.