title: Thermopower evidence for an abrupt Fermi surface change at the quantum critical point of YbRh2Si2.
abstract: We present low-temperature thermopower results, S(T), on the heavy-fermion compound YbRh2Si2 in the vicinity of its field-induced quantum critical point (QCP). At B=0, a logarithmic increase of -S(T)/T between 1 and 0.1 K reveals strong non-Fermi-liquid behavior. A pronounced downturn of -S(T)/T below T{max}=0.1 K and a sign change from negative to positive S(T) values at T{0} approximately 30 mK are observed on the low-field side of the Kondo breakdown crossover line T{*}(B). In the field-induced, heavy Landau-Fermi-liquid regime, S(T)/T assumes constant, negative values below T{LFL}. A pronounced crossover in the -S(B)/T isotherms at T{*}(B) sharpens with decreasing T and seems to evolve toward a steplike function for T-->0. This is attributed to an abrupt change of the Fermi volume upon crossing the unconventional QCP of YbRh2Si2.
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, 01187 Dresden, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Hartmann
authors.forename: Niels
authors.initials: N
authors.lastname: Oeschler
authors.forename: Cornelius
authors.initials: C
authors.lastname: Krellner
authors.forename: Christoph
authors.initials: C
authors.lastname: Geibel
authors.forename: Silke
authors.initials: S
authors.lastname: Paschen
authors.forename: Frank
authors.initials: F
authors.lastname: Steglich