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Register a new userDirect observation of heavy quasiparticles in the Kondo lattice CeIn3
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The electronic structure of the Kondo lattice CeIn3 has been studied by on-resonant angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. A weakly dispersive quasiparticle band has been observed directly with an energy dispersion of 4 meV by photoemission, implying the existence of weak hybridization between the f electrons and conduction electrons. The hybridization is further confirmed by the formation of the hybridization gap revealed by temperature-dependent scanning tunneling spectroscopy. Moreover, we find the hybridization strength in CeIn3 is much weaker than that in the more two-dimensional compounds CeCoIn5 and CeIrIn5. Our results may be essential for the complete microscopic understanding of this important compound and the related heavy-fermion systems.
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We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the {Gamma}-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical meanfield theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds.
Numerous phenomenological parallels have been drawn between f- and d- electron systems in an attempt to understand their display of unconventional superconductivity. The microscopics of how electrons evolve from participation in large moment antiferromagnetism to superconductivity in these systems, however, remains a mystery. Knowing the origin of Cooper paired electrons in momentum space is a crucial prerequisite for understanding the pairing mechanism. Of especial interest are pressure-induced superconductors CeIn3 and CeRhIn5 in which disparate magnetic and superconducting orders apparently coexist - arising from within the same f-electron degrees of freedom. Here we present ambient pressure quantum oscillation measurements on CeIn3 that crucially identify the electronic structure - potentially similar to high temperature superconductors. Heavy pockets of f-character are revealed in CeIn3, undergoing an unexpected effective mass divergence well before the antiferromagnetic critical field. We thus uncover the softening of a branch of quasiparticle excitations located away from the traditional spin-fluctuation dominated antiferromagnetic quantum critical point. The observed Fermi surface of dispersive f-electrons in CeIn3 could potentially explain the emergence of Cooper pairs from within a strong moment antiferromagnet.
It is a long-standing important issue in heavy fermion physics whether $f$-electrons are itinerant or localized when the magnetic order occurs. Here we report the {it in situ} scanning tunneling microscopy observation of the electronic structure in epitaxial thin films of CeRhIn$_5$, a prototypical heavy fermion compound with antiferromagnetic ground state. The conductance spectra above the Neel temperature $T_N$ clearly resolve the energy gap due to the hybridization between local 4$f$ electrons and conduction bands as well as the crystal electric field excitations. These structures persist even below $T_N$. Moreover, an additional dip in the conductance spectra develops due to the antiferromagnetic order. These results provide direct evidence for the presence of itinerant heavy $f$-electrons participating in the Fermi surface even in the magnetically ordered state of CeRhIn$_5$.
Resolving the heavy fermion band in the conduction electron momentum resolved spectral function of the Kondo lattice model is challenging since, in the weak coupling limit, its spectral weight is exponentially small. In this article we consider a composite fermion operator, consisting of a conduction electron dressed by spin fluctuations that shares the same quantum numbers as the electron operator. Using approximation free auxiliary field quantum Monte Carlo simulations we show that for the SU(2) spin-symmetric model on the square lattice at half filling, the composite fermion acts as a magnifying glass for the heavy fermion band. In comparison to the conduction electron residue that scales as $e^{-W/J_k}$ with $W$ the bandwidth and $J_k$ the Kondo coupling, the residue of the composite fermion tracks $J_k$. This result holds down to $J_k/W = 0.05$, and confirms the point of view that magnetic ordering, present below $J_k/W = 0.18$, does not destroy the heavy quasiparticle. We furthermore investigate the spectral function of the composite fermion in the ground state and at finite temperatures, for SU($N$) generalizations of the Kondo lattice model, as well as for ferromagnetic Kondo couplings, and compare our results to analytical calculations in the limit of high temperatures, large-$N$, large-$S$, and large $J_k$. Based on these calculations, we conjecture that the composite fermion operator provides a unique tool to study the destruction of the heavy fermion quasiparticle in Kondo breakdown transitions. The relation of our results to scanning tunneling spectroscopy and photoemission experiments is discussed.
Heavy fermion materials gain high electronic masses and expand Fermi surfaces when the high-temperature localized f electrons become itinerant and hybridize with the conduction band at low temperatures. However, despite the common application of this model, direct microscopic verification remains lacking. Here we report high-resolution angle-resolved photoemission spectroscopy measurements on CeCoIn5, a prototypical heavy fermion compound, and reveal the long-sought band hybridization and Fermi surface expansion. Unexpectedly, the localized-to-itinerant transition occurs at surprisingly high temperatures, yet f electrons are still largely localized at the lowest temperature. Moreover, crystal field excitations likely play an important role in the anomalous temperature dependence. Our results paint an comprehensive unanticipated experimental picture of the heavy fermion formation in a periodic multi-level Anderson/Kondo lattice, and set the stage for understanding the emergent properties in related materials.
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