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SUMMARY:Quantum criticality and dynamical scaling in YbRh2Si2 - Sven Fried
 emann\, QM group
DTSTART:20100526T101500Z
DTEND:20100526T111500Z
UID:TALK24968@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:The heavy fermion compound YbRh2Si2 exhibits antiferromagnetic
  ordering at 70 mK. Suppressing this transition to zero temperature by a t
 iny magnetic field leads to the quantum critical point. Conventionally\, a
 \nquantum critical point is described by the quantum generalization of fin
 ite-temperature phase transitions. In this talk I present high-precision H
 all effect measurements which are at variance with the predictions of the 
 standard theory for both the static and dynamic\nbehaviour.\n\nOn the one 
 hand\, the data suggest a reconstruction of the Fermi surface and on the o
 ther hand\,  they allow to exclude the dynamical scaling predicted by the 
 conventional theory. The results rather suggest a\nbreakdown of the Kondo 
 effect as the dominant mechanism.\nIn addition\, I show results revealing 
 the global phase diagram of YbRh2Si2 under positive and negative chemical 
 pressure as realized by Co and Ir substitution on the Rh side. Surprisingl
 y\, this leads to a detachment of the antiferromagnetic quantum critical p
 oint from the Fermi surface reconstruction. In particular\, negative press
 ure induces a separation of the two with an intermediate non-Fermi-liquid 
 ground state emerging in an extended field range. These results indicate a
  new quantum phase arising from the interaction of the Kondo breakdown and
  the AF QCP.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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