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First Direct Observation of Fermi Surfaces Formed by �Heavy Electrons�
-Clue to the Mechanism of Superconductivity Coexisting with Magnetism-
May. 26, 2009
In f electron systems such as Cerium (Ce) compounds, it is considered that �heavy electrons�, which have an extraordinary large effective mass of 10-1000 m0 (m0: free electron mass), are formed through hybridization between f and conduction electrons. This means that originally localized f electrons acquire an itinerant character and carry such a heavy mass. In many Ce compounds, exotic physical properties e.g., non-Fermi liquid behaviors, unconventional superconductivity, etc., are observed around a boundary called �quantum critical point�, where a magnetic order emerges at low temperature. It is vitally important to clarify the nature of heavy f electrons around the quantum critical point, since it is expected that the f electrons turn from itinerant to localized ones at around the quantum critical point and their nature should be closely related to the mechanism of the unconventional superconductivity. The observation of the variation in Fermi surfaces is most decisive experimental evidence for the itinerant-to-localized transition of f electrons. However, it has been difficult to observe experimentally the Fermi surfaces formed by the heavy f electrons.
In this study, we have succeeded in the direct observation of the Fermi surfaces formed by the heavy f electrons for the first time by performing resonant angle-resolved photoelectron spectroscopy (resonant ARPES) on CeRu2(SixGe1-x)2 at the Ce 3d-4f absorption edge. The measurement was carried out at the JAEA beamline BL23SU of SPring-8. By the observation of the Fermi surfaces of heavy 4f electrons of Ce atoms, we have confirmed that the nature of the 4f electrons in the paramagnetic states of CeRu2(SixGe1-x)2 varies continuously around the quantum critical point. In future, the resonant ARPES study will play an indispensable role in clarifying the relation between the nature of f electrons and the mechanism of the superconductivity coexisting with magnetism around the quantum critical point.
This work has been published in Physical Review Letters 102, 216401 (2009). This work was supported by the Grant-in-Aid for Scientific Research on Innovative Areas "Emergence of Heavy Electrons and Their Ordering" (No.20102003) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.
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