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  • 2000-2004  (4)
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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Phase separation in inhomogeneous mixed-valence systems: Application to manganites (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5022-5024 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Manganites are inhomogeneous mixed-valence systems in which the Mn ions coexist in two magnetic configurations, Mn4+ and Mn3+. We consider a simple alloy-analogy model with a charge interaction between nearest neighbor Mn ions. In addition there is an antiferromagnetic (AF) (superexchange) interaction between nearest neighbor ions of equal valence, while ions of different valence are coupled ferromagnetically (FM) (double exchange). Assuming classical spins, we show that the system is unstable to phase separation, i.e., to the coexistence of AF and charge ordered FM domains. In a magnetic field the FM domains increase at the expense of the AF ones. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373235
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    Paper (German National Licenses)
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