共查询到20条相似文献,搜索用时 15 毫秒
1.
Given the spectrum of a Hamiltonian, a methodology is developed which employs the Landau-Ginsburg theory for characterizing
phase transitions in infinite systems to identify phase transition remnants in finite fermion systems. As a first application
of our appproach we discuss pairing in finite nuclei. 相似文献
2.
We analyze the possibilities of pairing between two different fermion species in asymmetric matter at low density. While the direct interaction allows pairing only for very small asymmetries, the pairing mediated by polarization effects is always possible, with a pronounced maximum at finite asymmetry. We present analytical results up to second order in the low-density parameter kFa. 相似文献
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Fermion systems with more than two components can exhibit pairing condensates of a much more complex structure than the well-known single BCS condensate of spin-up and spin-down fermions. In the framework of the exactly solvable SO(8) Richardson-Gaudin (RG) model with SU(4)-symmetric Hamiltonians, we show that the BCS approximation remains valid in the thermodynamic limit of large systems for describing the ground-state energy and the canonical and quasiparticle excitation gaps. Correlations beyond BCS pairing give rise to a spectrum of collective excitations, but these do not affect the bulk energy and quasiparticle gaps. 相似文献
7.
Y. nuki R. Settai F. Honda T. Takeuchi N. Tateiwa T.D. Matsuda E. Yamamoto Y. Haga H. Harima 《Physica C: Superconductivity and its Applications》2009,469(15-20):868-873
The heavy fermion state in the f-electron systems is due to competition between the RKKY interaction and the Kondo effect. The typical compound is CeCu6. To understand the electronic state, we studied the Fermi surface properties via the de Haas–van Alphen (dHvA) experiment and energy band calculation for CeSn3,CeRu2Si2,UPt3, and nowadays, transuranium compounds. Pressure is also an important technique to control the electronic state. The Néel temperature TN decreases with increasing pressure P and becomes zero at the critical pressure for . The typical compound is an antiferromagnet CeRhIn5, which we studied from the dHvA experiment under pressure. A change of the 4f-electronic state from localized to itinerant is realized at , revealing the first-order phase transition, together with a divergent tendency of the cyclotron mass at Pc. It is stressed that appearance of superconductivity in CeRhIn5 is closely related to the heavy fermion state. It is also noted that the parity-mixed novel superconducting state might be realized in a pressure-induced superconductor CeIrSi3 without inversion symmetry in the crystal structure. 相似文献
8.
We show explicitly that the hydrodynamic density modes of a heavy fermion system in the presence of long range Coulomb interactions can be reduced to those of an effective Hamiltonian used previously. Outside the hydrodynamic regime one finds acoustic plasmon (or zero sound) excitations as well as high energy plasmons. When the Fermi level intersects more than one heavy quasiparticle band, a situation which is expected to occur in most cases, then also a low-energy optical plasmon excitation should exist. The latter can be overdamped under special conditions. 相似文献
9.
A theory of hydrodynamic fluctuations in heavy fermion systems is presented. It is used to compute the attenuation and velocity of longitudinal ultrasound. The attenuation is dominated by the coupling of phonons to electronic density fluctuations. A discrepancy is resolved between theory and experiments on UPt3, which has been existing with respect to the absolute magnitude of the temperature dependent attenuation. The latter provides direct proof for a large Fermi liquid parameterF
0
s
. The phonon Green's function is found to have a four-pole structure, resulting in two diffusive modes. One is the conventional one due to heat diffusion while the other is due to electron density diffusion and is a characteristic feature of heavy fermion systems. The two modes are coupled at finite temperatures. With the help of a model Hamiltonian (slave boson mean-field formulation of the Anderson lattice Hamiltonian) the ultrasound attenuation is calculated for low temperatures. 相似文献
10.
We discuss an approach for the treatment of correlations in finite nuclear systems. The approach is based on a boson formalism, the basic boson operators representing elementary particle-hole excitations. We show an application of the method within an exactly solvable multilevel pairing model. We calculate the correlation energy of the system and compare it with the exact results as well as with results obtained within other approaches. 相似文献
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《Journal of magnetism and magnetic materials》1999,192(3):553-563
The crystal field of valence fluctuating systems is time dependent due to f-electron transfers to the conduction band. We show how these fluctuations influence the line shapes of inelastic neutron scattering spectra. The numerical analysis is performed for CePb3 and CeAl2. 相似文献
13.
G. M. Luke A. Keren L. P. Le Y. J. Uemura W. D. Wu D. Bonn L. Taillefer J. D. Garrett Y. Ōnuki 《Hyperfine Interactions》1994,85(1):397-409
Heavy fermion systems have received a great deal of study by a wide variety of techniques, includingSR. In a number of systems, coexisting superconducting and magnetic states have been reported, leading to speculation of an intimate connection between magnetism and superconductivity in these compounds. We observe a spontaneous magnetic field in the superconducting phase of UPt3. In addition, the broadening of the transverse field muon precession signal only onsets approximately 60 mK below the superconductingT
c. Our results provide evidence that the lower superconducting phase in theH-T phase diagram of UPt3 is characterised by broken time-reversal symmetry. Measurements of URu2Si2 and CeCu2.2Si2 indicate that the magnetically ordered volume fraction is temperature dependent in both systems. 相似文献
14.
The half-space boundary value problem for fermions near zero temperature in plane geometry is solved for diffuse boundary scattering by numerically constructing the spatial propagator in terms of the eigenfunctions of a generalized eigenvalue problem for the linearized Uehling-Uhlenbeck collision integral. The slip length is calculated for several interparticle scattering laws and compared with a relaxation time ansatz result and the experimental values for normal fluid3He. It is shown that the nonsingular part of the collision operator is relatively compact to the singular part. 相似文献
15.
The heavy fermion system (HFS) is described by the periodic Anderson model (PAM), treating the Coulomb correlation between
the f-electrons in the meanfield Hartree-Fock approximation. Superconductivity is introduced by a BCS-type pairing term among the
conduction electrons. Within this approximation the equation for the superconducting gap is derived, which depends on the
effective position of the energy level of the f-electrons relative to the Fermi level. The latter in turn depends on the occupation probability n
f of the f-electrons. The gap equation is solved self-consistently with the equation for n
f; and their temperature dependences are studied for different positions of the bare f-electron energy level, with respect to the Fermi level. The dependence of the superconducting gap on the hybridization leads
to a re-entrant behaviour with increasing strength. The induced pairing between the f-electrons and the pairing of mixed conduction and f-electrons due to hybridization are also determined. The temperature dependence of the hybridization parameter, which characterizes
the number of electrons with mixed character and represents the number of heavy electrons is studied. This number is shown
to be small. The quasi-particle density of states (DOS) shows the existence of a pseudo-gap due to superconductivity and the
signature of a hybridization gap at the Fermi level. For the choice of the model parameters, the DOS shows that the HFS is
a metal and undergoes a transition to the gap-less superconducting state.
相似文献
16.
O. D. Timofeevskaya 《Physics of Particles and Nuclei Letters》2009,6(7):608-611
In this communication we consider the zero temperature properties of entanglement in free and interacting fermion systems
following Bogoliubov’s excitation approach. We investigate spin biparticle entanglement in BCS superconductor ground state
of electron gas and in EPS state of 3He atoms. The relation between pair-distribution functions and biparticle quantum entanglement is discussed. 相似文献
17.
The derivation of gap equations and Ginzburg-Landau free energies for relativistic fermion systems is reviewed. The cases of superfluid neutron matter, superconducting electrons and superconducting and colour superconducting quark matter are described in detail. 相似文献
18.
Heavy fermion systems are described by the periodic Anderson Model (PAM), i.e. a lattice of localized, highly correlatedf-electron states hybridized with the delocalized states of a conduction band. We treat the PAM within the second orderU perturbation theory around the non-magnetic Hartree-Fock solution (U on site Coulomb correlation between thef-electrons). This treatment has the advantage that Fermi liquid relations (Luttinger theorem) are automatically fulfilled. Thef-electron selfenergy and spectral function are calculated for different temperatures, and, for the symmetric PAM, we obtain single-particle peaks near toE
f andE
f
+U and in addition many-particle (Kondo) resonance peaks near to the chemical potential (E
f baref-electron energy). The resonance peaks are strongly temperature dependent and vanish on a characteristic temperature scaleT
K. For the symmetric PAM and a constant on-site hybridization the Fermi energy falls into a hybridization gap. A second, smaller characteristic temperature scaleT
coh (coherence temperature), on which the hybridization gap vanishes, is observed within this approach. For the non-symmetric PAM (i.e.E
f andE
f
+U not symmetric around the chemical potential) we obtain a similar behaviour, but the single-particle peaks are no longer at the correct positionsE
f andE
f
+U. The proper behaviour for the symmetric PAM but less satisfactory behaviour for the non-symmetric PAM can be understood from the fact that only for the symmetric PAM the exactly solvable limit of a vanishing hybridization is reproduced within this approach. 相似文献
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Critical modes of one-dimensional fermion systems are examined by use of the renormalization group technique. Both strongly incommensurate and commensurate bands are treated. Both frequency and momentum dependence and the analytic property of the response functions are determined. It is stressed that for some region of coupling constants the model has anomalous dimensions, i.e. it has critical indices dependent on the coupling constants. The results are applied to predict the temperature dependence of the shift and relaxation of the nuclear magnetic resonances. 相似文献