Electronic structure of strongly correlated Ce 4f-electrons systems

Speaker: Dr. H. J. Im, UVSOR Facility, Institute for Molecular Science

Date + Time: November 12th, 11:30-12:05

Place: UVSOR Build. #304 (UVSOR Seminar room)

Abstract:
In heavy-fermion metals, the electronic structure of strongly correlated Ce 4f-electrons directly
influences on unusual physical properties such as heavy-fermion behavior and quantum criticality.
It is well established that localized Ce 4f-electrons form the large density of states at the Fermi
level (Kondo resonance peak) through the hybridization with conduction electrons. As a function
of this hybridization strength, their ground state changes from magnetic to non-magnetic heavy-
fermion via a quantum critical point (QCP). In order to clarify such physical properties in view of
electronic structure, we have performed angle-resolved photoemission measurements on Ce112
series (CeMX2 where M=Co, Ni and X=Ge, Si). For the first time, the dispersive Kondo resonance
peaks crossing the Fermi level in unoccupied regime were directly observed in non-magnetic heavy-
fermion CeCoGe1.2Si0.8 [1]. Furthermore, in both CeNiGe2 (antiferromagnetic) and CeNi0.7Co0.3Ge2
(QCP), the momentum dependence of Kondo peak intensity was found [2]. These results reveal the
periodicity and itinerancy of Ce 4f-electrons from magnetic to non-magnetic heavy-fermion via a
QCP. For the understanding of quantum criticality, the photoemission data are likely to prefer a spin-
density wave scenario [3] to a local quantum critical scenario [4].

[1] H. J. Im et al., Phys. Rev. Lett. 100, 176402 (2008).
[2] H. J. Im et al., (in preparation).
[3] A. J. Millis, Phys. Rev. B 48, 7183 (1993).
[4] Q. Si et al., Nature 413, 804 (2001).