title: Fermi-surface collapse and dynamical scaling near a quantum-critical point.
abstract: Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh(2)Si(2), a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems.
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, 01187 Dresden, Germany. Sven.Friedemann@cpfs.mpg.de
authors.forename: Sven
authors.initials: S
authors.lastname: Friedemann
authors.forename: Niels
authors.initials: N
authors.lastname: Oeschler
authors.forename: Steffen
authors.initials: S
authors.lastname: Wirth
authors.forename: Cornelius
authors.initials: C
authors.lastname: Krellner
authors.forename: Christoph
authors.initials: C
authors.lastname: Geibel
authors.forename: Frank
authors.initials: F
authors.lastname: Steglich
authors.forename: Silke
authors.initials: S
authors.lastname: Paschen
authors.forename: Stefan
authors.initials: S
authors.lastname: Kirchner
authors.forename: Qimiao
authors.initials: Q
authors.lastname: Si
mesh_terms: D000465:Algorithms; D055598:Chemical Phenomena; D007700:Kinetics; D008280:Magnetics; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D044367:Phase Transition; D012413:Rubidium / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D044366:Transition Temperature; D015018:Ytterbium / Q000737:chemistry
chemical_list: D008670:Metals; D012822:Silicon Dioxide; D012413:Rubidium; D015018:Ytterbium