Divergence of the Grüneisen Ratio at Quantum Critical Points in Heavy Fermion Metals

Abstract

We present low-temperature volume thermal expansion, β, and specific heat, C, measurements on high-quality single crystals of CeNi 2 Ge 2 and YbRh 2 (Si 0.95 Ge 0.05 ) 2 which are located very near to quantum critical points. For both systems, β shows a more singular temperature dependence than C, and thus the Grüneisen ratio Γ ∝ β/C diverges as T → 0. For CeNi 2 Ge 2 , our results are in accordance with the spin-density wave (SDW) scenario for three-dimensional critical spinfluctuations. By contrast, the observed singularity in YbRh 2 (Si 0.95 Ge 0.05 ) 2 cannot be explained by the itinerant SDW theory but is qualitatively consistent with a locally quantum critical picture.

Strong electron correlations in magnetic systems

“…This agrees well with the prediction for the 3D-SDW scenario [17]. By contrast, recent investigations ofYbRh 2 Sh revealed f"'(T) -'1 x with x = 0.7 [18] as expected in the presence of local AF quantum critical fluctuations (Fig. 3b).…”

“…As these authors argue, ['(T) must diverge at any QCP [17]. This has indeed been observed [18] for both paramagnetic CeNhGe2 (inset of Fig. 3a) and the isostructural weakly antiferromagnetically ordered compound YbRh2Sh (TN = 70 mK).…”

Non-Fermi Liquid Regimes and Superconductivity in the Low Temperature Phase Diagrams of Strongly Correlated d- and f-Electron Materials

“…By analogy to CeCu 6−x Au x , these results were taken as evidence for 2D antiferromagnetic critical fluctuations near the QCP [47,236], although it should be pointed out that this conclusion remains an open issue. Subsequently, several other unusual phenomena were observed near the QCP including divergent Grüneisen ratios for YbRh 2 (Si 0.95 Ge 0.05 ) 2 [240] and further evidence for ferromagnetic quantum critical fluctuations (inferred from 29 Si NMR and ESR measurements [241,242]). In order to further probe the low T NFL behavior, extensive studies in applied magnetic fields have been performed.…”

Influence of chemical composition on the X-ray photoemission, thermopower, specific heat, and magnetic properties of CeNi2(Si1-yGey)2

“…While CeNi 2 Si 2 is a well confirmed fluctuating valence (FV) system [2,6,7], the behaviour of the HF CeNi 2 Ge 2 indicates on exotic behaviours like NFL and superconductivity [8][9][10][11][12][13][14][15]. It is due to the proximity of this compound to the antiferromagnetic Quantum Critical Point (QCP).…”