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Register a new userSuperconductivity in an almost localized Fermi liquid of quasiparticles with spin-dependent masses and effective field induced by electron correlations
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Paired state of nonstandard quasiparticles is analyzed in detail in two model situations. Namely, we consider the Cooper-pair bound state and the condensed phase of an almost localized Fermi liquid (ALFL) composed of quasiparticles in a narrow-band with the spin-dependent masses (SDM) and an effective field, both introduced earlier and induced by strong electronic correlations. Each of these novel characteristics are calculated in a self-consistent manner. We analyze the bound states as a function of Cooper-pair momentum q in applied magnetic field in the strongly Pauli limiting case (i.e. when the orbital effects of applied magnetic field are disregarded). The spin-direction dependence of the effective mass makes the quasiparticles comprising Cooper pair spin distinguishable in the quantum mechanical sense, whereas the condensed gas of pairs may still be regarded as composed of identical entities. The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) condensed phase of moving pairs is by far more robust in the applied field for the case with spin-dependent masses than in the situation with equal masses of quasiparticles. Relative stability of the Bardeen-Cooper-Schrieffer (BCS) vs. FFLO phase is analyzed in detail on temperature - applied field plane. Although our calculations are carried out for a model situation, we can conclude that the spin-dependent masses should play an important role in stabilizing high-field low-temperature (HFLT) unconventional superconducting phases (FFLO being an instance) in systems such as CeCoIn_5, organic metals, and possibly others.
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The in-plane resistivity, rho, and thermal conductivity, kappa, of a single crystal of Na_0.7CoO_2 were measured down to 40 mK. Verification of the Wiedemann-Franz law, kappa/T = L_0/rho as T -> 0, and observation of a T^2 dependence of rho at low temperature, rho = rho_0 + AT^2, establish the existence of a well-defined Fermi-liquid state. The measured value of coefficient A reveals enormous electron-electron scattering, characterized by the largest Kadowaki-Woods ratio, A/gamma^2, encountered in any material. The rapid suppression of A with magnetic field suggests a possible proximity to a magnetic quantum critical point. We also speculate on the possible role of magnetic frustration and proximity to a Mott insulator.
Spin dependence of quasiparticle mass has been observed recently in CeCoIn5 and other systems. It emerges from strong electronic correlations in a magnetically polarized state and was predicted earlier. Additionally, the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)phase has also been discovered in CeCoIn5 and therefore, the question arises as to what extent these two basic phenomena are interconnected, as it appears in theory. Here we show that the appearance of the spin-split masses essentially extends the regime of temperature and applied magnetic field, in which FFLO state is stable, and thus, it is claimed to be very important for the phase detectability. Furthermore, in the situation when the value of the spin z-component sigma differentiates masses of the particles, the fundamental question is to what extent the two mutually bound particles are indistinguishable quantum mechanically? By considering first the Cooper-pair state we show explicitly that the antisymmetry of the spin-pair wave function in the ground state may be broken when the magnetic field is applied.
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