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Event Number 3023
Monday, May 20th, 2013
 Condensed Matter Theory Group Seminar
 Critical quasiparticle theory and scaling near a Quantum Critical Point of Heavy Fermion metals.
 Time: 4:30 pm
 Place: 5310 Chamberlin
 Speaker: Peter Woelfle, Visiting Professor, UWMadison
 Abstract: We recently developed a theory of the critical properties of a heavy fermion metal near an antiferromagnetic (AFM) quantum phase transition governed by threedimensional spin fluctuations. The critical spin fluctuations induce critical behavior of the electron quasiparticles (qp) as seen in a diverging effective mass, leading, e.g., to a diverging specific heat coefficient. This in turn gives rise to a modification of the spin excitation spectrum [1]. We use that the concept of electron quasiparticles is welldefined as long as the qp width is less than their excitation energy, which is still the case in the socalled nonFermi liquid regime.
Impurity scattering [1,2] and/or higher order loop processes in the clean system [3] cause a redistribution of the critical scattering at the hot lines all over the Fermi surface, leading to a weakly momentum dependent critical selfenergy. We derive a selfconsistent equation for the qp effective mass which allows for two physical solutions: the usual weak coupling spin density wave solution and a strong coupling solution featuring a power law divergence of the effective mass as a function of energy scale. The resulting spin excitation spectrum obeys E/T scaling with dynamical exponent z=4 and correlation length exponent nu=1/3, in excellent agreement with data for YbRh2Si2 [1,2]. Results of our theory applied to threedimensional metals featuring quasitwodimensional spin fluctuations will be presented with the aim of explaining the observed properties of the AFM quantum critical point of CeCu(6x)Aux , in particular the E/T scaling exhibited by inelastic neutron scattering data. In that case we find z=8/3 and nu=3/7[3]. Finally, the microscopic underpinning of our theory will be addressed, including the issues of qp renormalization, vertex corrections, interaction of bosonic fluctuations in the renormalization group sense, and higher loop corrections [3].
[1] P. Woelfle, and E. Abrahams, Phys. Rev. B 84, 041101 (2011); Ann. Phys. (Berlin) 523, 591 (2011); Phys. Rev. B 80, 235112 (2009).
[2] E.Abrahams and P. Woelfle, PNAS , 3228 (2012).
[3] E. Abrahams, J. Schmalian, and P. Woelfle, to be published.
 Host: Perkins
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