Related Heavy Fermion Research Articles

Electronic structure of LaIrIn5 and f-electron character in its related Ce-115 compounds

LaIrIn$_5$ is a reference compound of the heavy-fermion superconductor CeIrIn$_5$.The lack of f electrons in LaIrIn$_5$ indicates that there should not be any f electron participatingin the construction of its Fermi surface. Thus the electronic structure comparison between LaIrIn$_5$and CeIrIn$_5$ provides a good platform to study the properties of f electrons. Here angle-resolvedphotoemission spectroscopy (ARPES) measurements and density functional theory (DFT)calculations are performed to study the electronic structures of LaIrIn$_5$ and CeIrIn$_5$.We find the valence band structures of the two materials are similar to each other, exceptfor the absence of f bands in LaIrIn$_5$. By analyzing the Fermi crossings of the threeconduction bands of the two materials quantitatively, we find the volumes of the electronpockets $\\upalpha$ and $\\upbeta$ around the M$'$ point become larger from LaIrIn$_5$ to CeIrIn$_5$,while the hole pocket $\\upgamma$ around the $\\Gamma'$ point becomes smaller. Together with thecalculation results, we confirm that this is mainly originated from the f-electron contribution,while the lattice-constant difference between LaIrIn$_5$ and CeIrIn$_5$only has a finite influence.We also give a summary of the f-electron character in its related Ce-115 heavy fermion compounds. Our results may be essential for the complete microscopic understandingof the 115 compounds and the related heavy-fermion systems.

Direct observation of heavy quasiparticles in the Kondo-lattice compound CeIn3

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.

A comparison of the structure and localized magnetism in Ce 2PdGa 12 with the heavy fermion CePdGa 6

Single crystals of Ce 2PdGa 12 have been synthesized in Ga flux and characterized by X-ray diffraction. This compound crystallizes in the tetragonal P 4 / nbm space group, Z = 2 with lattice parameters of a = 6.1040 ( 2 ) Å and c = 15.5490 ( 6 ) Å . It shows strongly anisotropic magnetism and orders antiferromagnetically at T N∼11 K. A field-induced metamagnetic transition to the ferromagnetic state is observed below T N. Structure–property relationships with the related heavy-fermion antiferromagnet CePdGa 6 are discussed.

Superconductors with charge- and spin-density waves: theory and experiment (Review)

The properties of existing superconductors with ejectron spectrum instabilities, namely charge-density waves (CDWs) and spin-density waves (SDWs), are reviewed. In such substances the superconducting gap exists over the whole Fermi surface, whereas the dielectric gap emerges only on its nested sections. In particular, CDW superconductors include layered dichalcogenides, NbSe3, compounds with the A15 and C15 structures, etc. There is a lot of evidence that high-Tc oxides also belong to this group of materials. SDW superconductors include, e.g., URu2Si2 and related heavy-fermion compounds, Cr–Re alloys and organic superconductors. The theoretical description given in this review is based mostly on the Bilbro-McMillan model of the partially dielectrized metal. Various thermodynamic and electrodynamic properties are calculated in the framework of this model. The main subject of the review is the nonstationary Josephson effect in tunnel junctions involving CDW or SDW superconductors. A new effect of symmetry breaking in symmetrical tunnel junctions is predicted by the authors. A comparison with experiment is given.

Quantum-phase transitions in CePd 2Si 2 and CeRh 2Si 2

We compare the cross-over from a magnetically ordered to a non-magnetic spin liquid state as a function of hydrostatic pressure in the related heavy-fermion antiferromagnets CePd 2Si 2 and CeRh 2Si 2. Both materials exhibit superconductivity at pressures close to the critical pressure p c at which their magnetic ordering temperatures extrapolate to zero. However, in CePd 2Si 2 the normal state resistivity varies according to ϱ ∼ T x (1.1 < x < 1.3) near p c, while CeRh 2Si 2 returns to the Fermi-liquid form ϱ ∼ T 2. This discrepancy between the two materials may be connected to the rapid destruction of the magnetic state in CeRh 2Si 2 with hydrostatic pressure.

Quantum critical behaviour in the CePd2Si2/CeNi2Ge2 system

We have explored the vicinity of the antiferromagnetic quantum critical point in the related heavy fermion metals CePd2Si2 and CeNi2Ge2 as a function of hydrostatic pressure. The normal state resistivity of the antiferromagnet CePd2Si2 near the critical pressure, at which magnetic order disappears, varies as ρ ∼ Tχ(1:1 < χ < 1:4) over nearly two orders of magnitude in temperature up to about 30 K. This anomalous form for the resistivity appears to defy not only Fermi-liquid theory, but also simple phenomenological models for the effect of spin fluctuations close to a quantum critical point. An analogous unconventional behaviour is observed in the ambient pressure resistivity of the electronically and structurally equivalent, non-magnetic metal CeNi2Ge2. At pressures above 15 kbar, a new and unexpected superconducting transition appears in CeNi2Ge2 below 220 mK, which rises to higher temperatures with increasing pressure, reaching 400 mK at 26 kbar.

Quasiparticle properties in ferromagnetic CeRu 2Ge 2

A detailed de Haas-van Alphen study of high-quality crystals of ferromagnetic CeRu 2Ge 2 ( T c ≈ 8 K) is presented. All expected Fermi surface sheets have been observed, including an extraordinarily large surface with a cross-sectional area bordering on the size of the Brillouin zone itself. A comparison to band structure calculations allows the formulation of a model for the Fermi surface consisting of five spin split sheets. For the first time in one of these systems the completeness of the de Haas-van Alphen data allows a rigorous analysis of the heat capacity and its accountability in terms of the observed quasiparticles. Analysis of the observed spin splitting yields values for the 4f to conduction electron interaction parameters for each sheet and enables a self-consistent understanding of the mass enhancement. A comparison to the related heavy-fermion system CeRu 2Si 2 provides new insight into the underlying nature of its quasiparticle properties.