title: Thermodynamics of phase formation in the quantum critical metal Sr3Ru2O7.
abstract: The behavior of matter near zero temperature continuous phase transitions, or "quantum critical points" is a central topic of study in condensed matter physics. In fermionic systems, fundamental questions remain unanswered: the nature of the quantum critical regime is unclear because of the apparent breakdown of the concept of the quasiparticle, a cornerstone of existing theories of strongly interacting metals. Even less is known experimentally about the formation of ordered phases from such a quantum critical "soup." Here, we report a study of the specific heat across the phase diagram of the model system Sr(3)Ru(2)O(7), which features an anomalous phase whose transport properties are consistent with those of an electronic nematic. We show that this phase, which exists at low temperatures in a narrow range of magnetic fields, forms directly from a quantum critical state, and contains more entropy than mean-field calculations predict. Our results suggest that this extra entropy is due to remnant degrees of freedom from the highly entropic state above T(c). The associated quantum critical point, which is "concealed" by the nematic phase, separates two Fermi liquids, neither of which has an identifiable spontaneously broken symmetry, but which likely differ in the topology of their Fermi surfaces.
authors.affiliation: Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St. Andrews, St Andrews KY16 9SS, United Kingdom. ar35@st-and.ac.uk
authors.forename: A W
authors.initials: AW
authors.lastname: Rost
authors.forename: S A
authors.initials: SA
authors.lastname: Grigera
authors.forename: J A N
authors.initials: JA
authors.lastname: Bruin
authors.forename: R S
authors.initials: RS
authors.lastname: Perry
authors.forename: D
authors.initials: D
authors.lastname: Tian
authors.forename: S
authors.initials: S
authors.lastname: Raghu
authors.forename: Steven Allan
authors.initials: SA
authors.lastname: Kivelson
authors.forename: A P
authors.initials: AP
authors.lastname: Mackenzie
mesh_terms: D003080:Cold Temperature; D019277:Entropy; D008956:Models, Chemical; D044367:Phase Transition; D011789:Quantum Theory; D017975:Ruthenium Compounds / Q000737:chemistry*; D013324:Strontium / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D017975:Ruthenium Compounds; D013324:Strontium