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  • 1
    Electronic Resource
    Electronic Resource
    Tb impurities in Th: A Kondo system with undercompensated magnetic moment? : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6417-6419 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dilute TbxTh1−x alloys have been thoroughly studied in the light of a possible valence instability and Kondo effect in Tb3+ and Tb4+ ions. We review the experimental data for the specific heat, magnetic susceptibility, magnetization, magnetoresistivity, and the change of the superconducting properties of Th. In analogy to Tm (Tm2+ and Tm3+) and Pr (Pr3+ and Pr4+) impurities in metals, Tb involves two electronic configurations each with a magnetic Hund's rule ground multiplet. Two classes of models for valence admixtures of two magnetic configurations have been investigated in the past. Depending on the form of the hybridization and the jj coupling within the 4f shell, the models either have a singlet or a magnetic ground state. As for Tm impurities the latter class of models, related to the undercompensated Kondo effect, appears to describe the system TbTh more appropriately. A qualitative explanation of the data is attempted within a scheme that combines Kondo screening with crystalline field splitting. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362015
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  • 2
    Electronic Resource
    Electronic Resource
    Low-temperature specific heat of the degenerate supersymmetric t-J model in one dimension : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6605-6607 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider the one-dimensional SU(N)-invariant t-J model, which consists of electrons with N spin components on a lattice with nearest-neighbor hopping t constrained by the excluded multiple occupancy of the sites and spin-exchange J between neighboring lattice sites. The model is integrable and has been diagonalized in terms of nested Bethe ansatze at the supersymmetric point t=J. The low-T specific heat is proportional to T. The γ-coefficient is extracted from the thermodynamic Bethe-ansatz equations and is expressed in terms of the spin wave velocities and the group velocity of the charges for arbitrary N, band filling, and splitting of the levels (magnetic and crystalline fields). Our results contain the following special cases: (i) For N=2 the traditional spin-1/2 supersymmetric t-J model, (ii) for exactly one electron per site the SU(N)-Heisenberg chain, and (iii) for N=4 the two-band supersymmetric t-J model with crystalline field splitting. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361897
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  • 3
    Electronic Resource
    Electronic Resource
    Metal-insulator transition in dirty Kondo insulators : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6414-6416 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider arbitrary clusters of Kondo holes in a Kondo insulator described by the nondegenerate symmetric Anderson lattice with a nearest-neighbor tight-binding conduction band on a simple cubic lattice. The f-electron self energy is considered within the local approximation. Each Kondo hole introduces a boundstate in the gap. The quantum interference in the scattering off the impurities gives rise to interactions among the Kondo holes. The spectral weight of the bound states is predominantly localized on the sites neighboring the Kondo holes. Clusters of impurities separated by more than one lattice site are disconnected for boundstates at the Fermi level. On a simple cubic lattice the metal-insulator transition in the impurity band then reduces to the site percolation of Kondo holes with first, second and fourth nearest neighbors. We use the low density mean cluster size expansion and a small cell renormalization to estimate the critical concentration. Hopping in the conduction band beyond nearest neighbors reduces the percolation threshold. Hence, 9.9% of Kondo holes is an upper bound for the insulator to become a metal. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362014
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  • 4
    Electronic Resource
    Electronic Resource
    Aharonov–Bohm oscillations at finite temperature : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5419-5421 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Aharonov–Bohm effect is the quantum interference of charged particles in mesoscopic rings enclosing a magnetic field. The wavefunction acquires a phase due to the field flux φ and gives rise to flux-dependent oscillations in persistent charge currents. The period and amplitude of the oscillations are associated with the properties of the Fermi surface of the elementary excitations. For systems with one Fermi surface the groundstate persistent current has the form of a saw-tooth. The temperature reduces the amplitudes of oscillation by smearing the Fermi surface. The amplitude of higher harmonics decreases faster with T than the fundamental one, changing the saw-tooth to a more sinusoidal form with much smaller amplitude. The controlling parameter is LT/zvF, where L is the length of the ring, vF is the Fermi velocity and z the dressed generalized charge. Our calculations are performed within the framework of Bethe's ansatz. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362325
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  • 5
    Electronic Resource
    Electronic Resource
    Some transport properties of the two-channel Kondo impurity : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4173-4175 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider conduction electrons moving along a ring in two different orbital channels interacting with a spin-1/2 impurity via isotropic spin exchange. The exchange is the same for both channels, but a crystalline field breaks the orbital symmetry. The tower structure of the finite size corrections to the ground state energy is derived from the Bethe ansatz equations and used to discuss the Aharonov–Bohm–Casher interference pattern in the persistent current and the magnetoresistivity. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365110
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  • 6
    Electronic Resource
    Electronic Resource
    Impurity model for Mn ions: Possibility of charge order and lattice distortions (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5423-5425 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mixed valent manganese ions play an important role in the magnetoresistance of LaMnO3-based systems. We consider a Mn impurity with the Mn4+ represented by a spin S=3/2 (three localized 3d-t2g electrons) and the Mn3+ configuration having an additional localized 3d-eg electron to form a total spin (S+1/2). The eg electron hybridizes with conduction electrons (representing the crystal), giving rise to a quadrupolar Kondo effect. The formation of the quadrupolar singlet interferes with the usual spin Kondo effect. Using the noncrossing diagram approximation, we calculate the ground state energy, valence, charge susceptibility, and the quadrupolar susceptibility as a function of the energy of the eg level for H→0 and compare it to results for H=0 and the ferromagnetic lattice. Both, the charge and quadrupolar susceptibilities, are larger in the spin-polarized limit, indicating that this state is more favorable for charge order and lattice distortions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369963
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  • 7
    Electronic Resource
    Electronic Resource
    Exact solution for a degenerate Anderson impurity in the limit embedded into a correlated host (1998)
    Springer
    The European physical journal 5 (1998), S. 325-335 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions - 75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena - 71.27.+a Strongly correlated electron systems; heavy fermions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We consider the one-dimensional t - J model, which consists of electrons with spin S on a lattice with nearest neighbor hopping t constrained by the excluded multiple occupancy of the lattice sites and spin-exchange J between neighboring sites. The model is integrable at the supersymmetric point, J = t. Without spoiling the integrability we introduce an Anderson-like impurity of spin S (degenerate Anderson model in the limit), which interacts with the correlated conduction states of the host. The lattice model is defined by the scattering matrices via the Quantum Inverse Scattering Method. We discuss the general form of the interaction Hamiltonian between the impurity and the itinerant electrons on the lattice and explicitly construct it in the continuum limit. The discrete Bethe ansatz equations diagonalizing the host with impurity are derived, and the thermodynamic Bethe ansatz equations are obtained using the string hypothesis for arbitrary band filling as a function of temperature and external magnetic field. The properties of the impurity depend on one coupling parameter related to the Kondo exchange coupling. The impurity can localize up to one itinerant electron and has in general mixed valent properties. Groundstate properties of the impurity, such as the energy, valence, magnetic susceptibility and the specific heat coefficient, are discussed. In the integer valent limit the model reduces to a Coqblin-Schrieffer impurity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510050450
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