Nature of the two quantum critical points in Ce„Ru1−xRhx...2Si2 (x=0.4 and 0.6)

The magnetic phase diagram of Ce Ru1−xRhx 2Si2 contains a spin-density-wave SDW magnetic ordering temperature approaching T=0 at both x 0.03 and 0.35–0.4 i.e., a dome-shaped phase boundary and long range, local moment antiferromagnetism, TN=36 K, in pure CeRh2Si2 suppressed with Ru doping to T=0 at x 0.6–0.65. This latter possible second quantum critical point QCP , and the possible interplay between the fluctuations caused at each of the two QCP’s, are investigated here using specific heat, resistivity, and dcmagnetic susceptibility data over a broad range of composition, from x=0.04 to 0.8. One principal result is that the specific heat divided by temperature, C /T, for x=0.6 0.65 near Tlocal moment→0 is proportional to log T over 2 1/2 decades of temperature down to the lowest temperature of measurement, 0.04 0.3 K, indicative of strong fluctuations near a QCP. For the region in the phase diagram x=0.4–0.5, i.e., near the reported TSDW →0 composition, C /T measured down to 0.08 K in the present work, as well as literature data, show a distinctly different behavior with temperature, a saturation in C /T which can be fit by −a T. Such a temperature dependence is consistent with a nearby QCP with weakly interacting spin fluctuations as proposed, e.g., in the theory of Moriya. In the region between the two QCP’s, at x=0.55, specific heat data down to 0.1 K are not well fit by C /T= −a T and are consistent with C /T log T only down to 0.6 K, i.e., this composition displays intermediate behavior. The residual resistivity, 0, vs x shows two strong peaks, at x=0.4 and 0.65, consistent with the existence of two quantum critical points. The exponent in = 0+AT indicates nonFermi liquid behavior, with varying monotonically—in contrast to 0—from 1.5 to 0.9 between x=0.3 and 0.65. The Fermi liquid exponent, =2, is recovered at x=0.8. These results taken together indicate two distinct quantum critical points in the phase diagram of Ce Ru1−xRhx 2Si2, with different fluctuation strengths at x TSDW→0 =0.4 and x Tlocal moment→0 0.6–0.65.