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  • 11
    Electronic Resource
    Electronic Resource
    Fluctuation induced precriticality in heavy fermions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5140-5142 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nesting of the Fermi surfaces of an electron pocket and a hole pocket separated by a wave vector Q interacting via a repulsive potential gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as TN→0. The renormalization group flow leads to a strong coupling fixed point. We study the linear response to spin- and charge-density waves, to singlet and triplet superconducting fluctuations, the low-T specific heat, and the magnetic susceptibility. All quantities increase on a logarithmic scale when the temperature is lowered. The results are discussed in the context of non-Fermi-liquid behavior observed in some heavy fermion compounds. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373275
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  • 12
    Electronic Resource
    Electronic Resource
    Mean-field approach for the B phase of (La,Ca)MnO3 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6624-6626 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: I consider a simple cubic lattice of mixed valent Mn ions (Mn4+ and Mn3+) and calculate the ground state energy for the ferromagnetic B phase using a slave-boson mean-field approach. Each Mn ion has three localized t2g electrons with their spins ferromagnetically coupled to form a spin S=3/2. Ions in the Mn3+ configuration have an additional eg electron to form a total spin of (S+1/2). The eg electrons are allowed to hop between the Mn sites (giving rise to the double exchange), but the multiple occupancy of the eg levels is excluded at each site. Five slave bosons per site are introduced to take into account the correlations between the eg electrons. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357137
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  • 13
    Electronic Resource
    Electronic Resource
    Quantum critical points of an anisotropic multichannel Kondo impurity (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7183-7185 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-temperature behavior of a magnetic impurity of spin S interacting with an electron gas via an anisotropic spin exchange is studied via Bethe's ansatz. The multichannel Kondo model with U(1) invariance is integrable as a function of two continuous (the exchange and the anisotropy) and two discrete parameters, namely the impurity spin S and the number of channels n. As a function of S and n we distinguish: (i) the compensated case with n=2S, (ii) the overcompensated case if n〉2S, and (iii) the undercompensated case (n〈2S). While in case (i) the ground state is a singlet, the cases (ii), and (iii) yield quantum critical points. The undercompensated one is of a new type with the critical exponents depending on the anisotropy. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357846
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  • 14
    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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  • 15
    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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  • 16
    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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  • 17
    Electronic Resource
    Electronic Resource
    Perturbative approximation scheme for isolated impurity bonds in the two-dimensional spin-1/2 Heisenberg antiferromagnet : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5532-5534 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An isolated impurity bond of coupling−K replacing a link J in the spin-1/2 Heisenberg antiferromagnet on a square lattice is considered. A simple perturbative approximation scheme is deviced, in which the two-site cluster formed by the spins linked by the impurity bond is embedded into the linearized spin wave approximation for the antiferromagnet. The resolvent for the local states of the cluster is calculated in three successive levels of approximation. The ground state wave function, the magnetization at the impurity link, and the transverse correlation across the impurity link as a function of the coupling K are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355679
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  • 18
    Electronic Resource
    Electronic Resource
    Ground-state properties and excitations of an integrable one-dimensional model with δ-function interaction involving several bands : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6731-6733 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider an integrable model consisting of n parabolic bands of electrons of equal mass with a δ-function exchange interaction. The interaction is attractive or repulsive depending on whether the interacting particles are in a spin-singlet or triplet state. The structure of the Bethe ansatz and the classification of states is similar to that of the n-channel Kondo problem. The attractive interaction leads to Cooper-pair-like boundstates. Some ground-state properties and the excitation spectrum are discussed for the special situation of degenerate bands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356852
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  • 19
    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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  • 20
    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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