Heavy-Mass Fermi Liquid near a Ferromagnetic Instability in Layered Ruthenates

Abstract

Low temperature magnetic, thermal, and transport measurements in Ca2-xSrxRuO4 clarify the appearance of a cluster glass phase, after the evolution of a nearly ferromagnetic heavy-mass Fermi liquid from the spin-triplet superconductor Sr2RuO4. As the Mott transition is approached across a 2nd-order structural transition, both the magnetization and specific heat decrease considerably while the transport scattering rate diverges. A metamagnetic transition to a highly spin polarized state, with a local moment S=1/2, is observed. We argue that an orbital rearrangement with Ca substitution changes itinerant ferromagnetism to antiferromagnetism of localized moments.

Origin of the heavy fermion behavior in Ca2−xSrxRuO4Arakawa1, Ogata2 2012Phys. Rev. B81220View full textAdd to dashboardCite

“…The largest value of γ e reaches 255 mJ/molRu K 2 at x = 0.5; this value is about 25 times of that obtained in the density-functional calculation for Sr 2 RuO 4 within local-density approximation (LDA). 13 A similar mass enhancement has been observed in the optical conductivity measurement by using the extended Drude model. 14 In addition, the spin susceptibility and Hall coefficient measured by applying the magnetic field perpendicular to ab plane show peak structures at T * ∼ 10 K for x = 0.3, 15 which are similar to those obtained for UPt 3 .…”

“…These results are consistent with the experimentally observed tendency of the effective mass in 0.5 ≤ x ≤ 2, i.e., monotonic increase of γ e towards x = 0.5. 13 Our calculation suggests that the HF behavior around x = 0.5 comes from the cooperative effects between moderately strong Coulomb interaction compared with the total bandwidth and the significant modification of the electronic structures for the Ru t 2g orbitals due to the rotation of RuO 6 octahedra; the latter includes both the variation of the dpπ hybridizations and the downward shift for the d xy orbital.…”

Nanoscale phase separation in colossal magnetoresistance materials: lessons for the cuprates?

“…In addition, large MR effects have been unveiled in bilayer Ruoxides [20]. Phase competition was also found in the single layer ruthenate [21]. It seems that (Ca,Sr)-based ruthenates may behave similarly as other materials mentioned here.…”

Magnetic excitations in the metallic single-layer ruthenates Ca2−xSrxRuOSteffens1, Friedt2, Sidis3 et al. 2011Phys. Rev. BSelf Cite

“…Moreover, for 0.2 < x < 0.5, a metamagnetic transition from a state with low susceptibility, reminiscent of antiferromagnetic correlations, to a state with high magnetic polarization is observed. 7,8 The metamagnetic transition is also observed in the closely related bilayer ruthenate Sr 3 Ru 2 O 7 , 9 where a discussion about its quantum-critical behavior has generated further interest. The high concentration dependence of the ground state in Ca 2−x Sr x RuO 4 points to a complex interplay of distinct magnetic correlations.…”

“…The γ -band width around the wave vectors associated with the van Hove singularity, (0.5,0,0), is remarkably small; it amounts to only a few meV, 41 similar to the values reported for Sr 3 Ru 2 O 7 . 30 The extreme reduction of the γ -band width results in a high electronic density of states at the Fermi level, which manifests itself in the heavy-mass states 6,7 as well as in the remarkably strong thermal expansion anomalies in Ca 2−x Sr x RuO 4 for 0.2 < x < 0.6. 44 Besides the signals at Q IC αβ , all magnetic correlations observed in our INS experiments should be attributed to the γ band.…”