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Quantum Critical Matter and Phase Transitions Chapter 280 323 experimental data for the temperature dependences, that is, whether there is NFL behavior or if the various coexistence phases are homogeneous or disor- dered. Nevertheless, Park et al. (2006) attempt to draw similarities with the high-Tc cuprates even though the putative QPT’s are undefined. An interest- ing experiment here is the de Haas–van Alphen studies of the Fermi surface as a function of pressure (Shishido et al., 2005). The authors observed an increase in the cyclotron mass above 1.6 GPa, where SC sets in. Above 2.4 GPa a drastic reconstruction of the Fermi surface occurs that indicates a change from localized to itinerant behavior thereby giving a TcS maximum. Finally and most recently very high magnetic fields (H to 70 T) have been applied to investigate the quantum oscillations, specific heat, and Hall effect of CeRhIn5 (Jiao et al., 2015). These authors observe field-induced modifica- tions of the phase coincident with sharp reconstructions of the Fermi surface (FS) in all the high-field measurements. Especially dramatic are the changes in the quantum oscillation as a function of field H, spanning 10–30 and 45–70 T. Based on the data an experimental phase diagram (T H) may be constructed as shown in Fig. 18—contrast with Fig. 17. Although the lowest temperature of measurement is only % 0.4 K, when extrapolated to T 1⁄4 0, two QCPs are proposed: the transition from an AFM with a small Fermi sur- face (AFMS) to one with a large Fermi surface (AFML) at % 30 T; and a tran- sition from an antiferromagnet to a paramagnet (PL) at % 50 T. The authors speculate further with a “schematic” pressure–field phase diagram at T1⁄40 for CeRhIn5. Here, there are intersecting quantum critical lines between SC, AFMS, AFML, and PL phases as illustrated in the bottom half of Fig. 18. These conjectures of quantum critical lines warrant their experimental proof. The last in this cerium-troika, CeIrIn5, is a heavy-fermion unconventional superconductor with TcS 1⁄4 0:4 K lacking any coexisting magnetic order (Petrovic et al., 2001a). Accordingly, the SC was thought to be mediated by valence fluctuations rather than by spin fluctuations. Thermal conduc- tivity and penetration depth studies indicate a dx2y2—type gap symmetry Movshovich et al. (2001) and Vandervelde et al. (2009). Recent doping inves- tigations of Hg and Sn on In sites, and Pt on Ir sites were performed using C(T) and r(T) (Shang et al., 2014). The results indicated hole doping via Hg caused AFM while electron doping via Sn or Pt favored a paramagnetic Fermi-liquid. Again the microprobe-determined concentrations are signifi- cantly different from the nominal concentrations. So disorder and clustering could be the main cause of the AFM and FL behavior. All of which appears out of a NFL regime. There was no evidence of QPT or QCP for CeIrIn5 or its various doping. 4.2 Hidden Order in URu2Si2 There is a particular uranium-based heavy fermion intermetallic compound, URu2Si2, that has been studied in-detail regarding a possible QPT. URu2Si2PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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