Fermi Surface Variation of Ce 4f-electrons in Hybridization Controlled Heavy-Fermion Systems

Ce 3d-4f resonant angle-resolved photoemission measurements on CeCoGe$_{1.2}$Si$_{0.8}$ and CeCoSi$_{2}$ have been performed to understand the Fermi surface topology as a function of hybridization strength between Ce 4$f$- and conduction electrons in heavy-fermion systems. We directly observe that the hole-like Ce 4$f$-Fermi surfaces of CeCoSi$_{2}$ is smaller than that of CeCoGe$_{1.2}$Si$_{0.8}$, indicating the evolution of the Ce 4$f$-Fermi surface with the increase of the hybridization strength. In comparision with LDA calculation, the Fermi surface variation cannot be understood even though the overall electronic structure are roughly explained, indicating the importance of strong correlation effects. We also discuss the relation between the Ce 4$f$-Fermi surface variation and the Kondo peaks.Comment: 7 pages, 3 figures, submitte

Existence of Heavy Fermions in the Antiferromagnetic Phase of CeIn3

We report the pressure-dependent optical conductivity spectra of a heavy fermion (HF) compound CeIn3 below the Neel temperature of 10 K to investigate the existence of the HF state in the antiferromagnetic (AFM) phase. The peak due to the interband transition in the hybridization gap between the conduction band and nearly localized 4f states (c-f hybridization) appears at the photon energy of about 20 meV not only in the HF regime but also in the AFM regime. Both the energy and intensity of the c-f hybridization peak continuously increase with the application of pressure from the AFM to the HF regime. This result suggests that the c-f hybridization, as well as the heavy fermions, exists even in the AFM phase of CeIn3.Comment: 5 pages, 3 figure

New State of Matter: Heavy Fermion Systems, Quantum Spin Liquids, Quasicrystals, Cold Gases, and High-Temperature Superconductors

International audienceWe report on a new state of matter manifested by strongly correlated Fermi systems including various heavy fermion (HF) metals, two-dimensional quantum liquids such as He films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds, we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their thermodynamic, transport, and relaxation properties. That is, the quantum physics of different HF compounds is found to be universal, emerging irrespective of the individual details of their symmetries, interactions, and microscopic structure. This observed universal behavior reveals the existence of a new state of matter manifest in HF compounds. We propose a simple, realistic model to study the appearance of flat bands in two-dimensional ensembles of ultracold fermionic atoms, interacting with coherent resonant light. It is shown that signatures of these flat bands may be found in peculiarities in their thermodynamic and spectroscopic properties. We also show that the FCQPT, in generating flat bands and altering Fermi surface topology, is an essential progenitor of the exotic behavior of the overdoped high-temperature superconductors represented by La$_{2+x}Sr$_x$xCuO$_4$, whose superconductivity differs from that predicted by the classical Bardeen–Cooper–Schrieffer theory. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen–Cooper–Schrieffer-like theories