物理系学术报告       Physics Department Colloquium

 

1009周二16:00-17:0012-423

 

 

 

Condensation Energy of CeCu2Si2 and Theoretical Implications

 

Dr. Stefan Kirchner

 

 

Abstract

Unconventional superconductivity occurrs in a broad range of strongly correlated electron systems including the newly discovered iron pnictides and chalcogenides, various intermetallic rare earth metals, the cuprates and the organic superconductors. These systems are not only of varying effective dimensionality but their parent compounds out of which superconductivity emerges ranges from metals to bad metals and Mott insulators. The only unifying characteristic features seems that unconventional superconductivity occurs in close vicinity of zero-temperature instabilities which are most often magnetic in nature. Heavy fermion compounds represent prototype systems to address the interplay between quantum criticality and unconventional superconductivity [1]. In CeCu2Si2, the magnetic quantum phase transition and superconductivity occur at ambient pressure which allows for a detailed study of the energetics across the superconducting transition. Based on an in-depth study of the magnetic excitation spectrum of CeCu2Si2 in the normal and superconducting state we obtain a lower bound for the change in exchange energy [2]. The comparison with the superconducting condensation energy demonstrates that the built-up of magnetic correlations near the quantum critical point does drive superconductivity in CeCu2Si2. In addition, our comparison establishes a huge kinetic energy loss which we relate to the competition of Kondo screening and superconductivity as the opening of the gap weakens the Kondo effect [2,3]. We discuss the relation between kinetic energy loss and the nature of the underlying quantum critical point [1,3]. Our unexpected findings sheds further light on the emerging global phase diagram of heavy fermion compounds [4] and are believed to be relevant to other families of superconductivity which are also located in close proximity to magnetism.

[1] O. Stockert, S. Kirchner, F. Steglich, Q. Si, submitted to JPSJ (invited review paper).

[2] O. Stockert et al., Nature Physics, 7, 119–124 (2011).

[3] S. Kirchner and Q. Si, to be published.

[4] Q. Si, Phys. Status Solidi B247, 476 (2010).

Dr. Stefan Kirchner 简介:

Employment:

October 2010-February 2011:visiting professorship (’Vertretungsprofessur’) “Theoretische Physik II/Computational Physics”, TU Ilmenau

since February 2009: Head of the joint independent research group ’Collective Phenomena in Solid State and Materials Physics’ of the Max Planck Institute for the Physics of Complex Systems (MPIPKS) and the Max Planck Institute for Chemical Physics of Solids (MPI-CPfS), Dresden, Germany

April 2008-January 2009: Research Scientist, Department of Physics & Astronomy, Rice University, Houston, Texas

Spring 2003-2008:Postdoctoral Research Associate, Department of Physics & Astronomy, Rice University, Houston, Texas

Education:

Spring 2002-Spring 2003: Postdoctoral position at the TKM, Technical University of Karlsruhe, Germany

Spring 2002: PhD in physics, Technical University of Karlsruhe, Germany Dissertation Advisor: Professor P. Wolfle

Fall 1997: diploma degree in physics, University of W¨urzburg, Germany Diploma Advisor: Professor W. Hanke

Spring 1995: Master of Science, State University of New York at Albany Advisor: Professor A. Inomata

Fall 1993: Vordiplom Physik (equivalent to Bachelor of Science), University of W¨urzburg, Germany

Fellowships and Honors:

Spring DFG Research Fellowship

Robert A. Welch Foundation Postdoctoral Fellowship

Adjunct Assistant Professor, Department of Physics & Astronomy, Rice University, Texas (since June 2009)

Research Interests:

Theoretical condensed matter physics emphasizing strongly correlated electron systems

-Quantum phase transitions in strongly correlated electron systems

-Non-Fermi liquids and exotic excitations in correlated systems

-Heavy fermion systems

-Non-equilibrium dynamics and transport in correlated systems

-physics of periodically driven systems

-Unconventional superconductivity

-EDMFT and DMFT for strongly correlated electron systems

-Numerical methods

-Exotic ground states in quantum impurity systems; correlation effects in quantum dots