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Register a new userCeNiAsO: an antiferromagnetic dense Kondo lattice
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A cerium containing pnictide, CeNiAsO, crystallized in the ZrCuSiAs type structure, has been investigated by measuring transport and magnetic properties, as well as specific heat. We found that CeNiAsO is an antiferromagnetic dense Kondo lattice metallic compound with Kondo scale $T_K sim$ 15 K and shows an enhanced Sommerfeld coefficient of $gamma_0 sim$ 203 mJ/mol$cdot$K$^{2}$. While no superconductivity can been observed down to 30 mK, Ce ions exhibit two successive antiferromagnetic (AFM) transitions. We propose that the magnetic moment of Ce ion could align in the G type AFM order below the first transition at $T_{N1}$=9.3 K, and it might be modified into the C type AFM order below a lower transition at $T_{N2}$=7.3 K. Our results indicate that the 3$d-4f$ interlayer Kondo interactions play an important role in Ni-based Ce-containing pnictide.
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In this paper we introduce an exactly solvable Kondo lattice model without any fine-tuning local gauge symmetry. This model describes itinerant electrons interplaying with a localized magnetic moment via only longitudinal Kondo exchange. Its solvability results from conservation of the localized moment at each site, and is valid for arbitrary lattice geometry and electron filling. A case study on square lattice shows that the ground state is a N{e}el antiferromagnetic insulator at half-filling. At finite temperature, paramagnetic phases including a Mott insulator and correlated metal are found. The former is a melting antiferromagnetic insulator with a strong short-range magnetic fluctuation, while the latter corresponds to a Fermi liquid-like metal. Monte Carlo simulation and theoretical analysis demonstrate that the transition from paramagnetic phases into the antiferromagnetic insulator is a continuous $2D$ Ising transition. Away from half-filling, patterns of spin stripes (inhomogeneous magnetic order) at weak coupling, and phase separation at strong coupling are predicted. With established Ising antiferromagnetism and spin stripe orders, our model may be relevant to a heavy fermion compound CeCo(In$_{1-x}$Hg$_{x}$)$_{5}$ and novel quantum liquid-crystal order in a hidden order compound URu$_{2}$Si$_{2}$.
The previous theoretical study has shown that pulse irradiation to the Mott insulating state in the Hubbard model can induce the enhancement of superconducting correlation due to the generation of $eta$ pairs. Here, we show that the same mechanism can be applied to the Kondo lattice model, an effective model for heavy electron systems, by demonstrating that the pulse irradiation indeed enhances the $eta$-pairing correlation. As in the case of the Hubbard model, the non-linear optical process is essential to increase the number of photoinduced $eta$ pairs and thus the enhancement of the superconducting correlation. We also find the diffusive behavior of the spin dynamics after the pulse irradiation, suggesting that the increase of the number of $eta$ pairs leads to the decoupling between the conduction band and the localized spins in the Kondo lattice model, which is inseparably related to the photodoping effect.
Ternary iron phosphide EuFe$_2$P$_2$ with ThCr$_2$Si$_2$-type structure has been systematically studied by the measurements of crystal structure, magnetization, M{o}ssbauer effect, transport properties and specific heat. The structural refinement result confirms no direct P-P covalent bonding. The M{o}ssbauer spectra indicate no magnetic moment for the Fe atoms and, that the Eu ions are divalent in the whole temperatures, carrying local moments of $S$=7/2. The Eu$^{2+}$ spins order ferromagnetically at $T_C$=29.5 K, followed by a possible helimagnetic ordering below $T_{HM}$=26 K, where the Eu$^{2+}$ moments tilt a little from the c-axis. External magnetic field increases $T_C$ gradually, but suppresses $T_{HM}$ rapidly. (Magneto)resistivity data indicate characteristic dense Kondo behaviour above the Curie temperature. The result is discussed in terms of the interplay between intersite RKKY and intrasite Kondo interactions.
One of the most notorious non-Fermi liquid properties of both archetypal heavy-fermion systems [1-4] and the high-Tc copper oxide superconductors [5] is an electrical resistivity that evolves linearly with temperature, T. In the heavy-fermion superconductor CeCoIn5 [5], this linear behaviour was one of the first indications of the presence of a zero-temperature instability, or quantum critical point. Here, we report the observation of a unique control parameter of T-linear scattering in CeCoIn5, found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sub-lattice. We find that the evolution of inelastic scattering in Ce1-xRxCoIn5 is strongly dependent on the f-electron configuration of the R ion, whereas two other key properties -- Cooper-pair breaking and Kondo-lattice coherence -- are not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature of incoherent scattering centers in the Kondo lattice, which provides insight into the anomalous scattering rate synonymous with quantum criticality [7].
In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. These excitations are fundamental to the appearance of unconventional superconductivity and non-Fermi-liquid behaviour observed in actinide- and lanthanide-based compounds. Here we use spectroscopic mapping with the scanning tunnelling microscope to detect the emergence of heavy excitations with lowering of temperature in a prototypical family of cerium-based heavy-fermion compounds. We demonstrate the sensitivity of the tunnelling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons. Scattering and interference of the composite quasiparticles is used to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy-temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system.
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