36 research outputs found
Existence of nuclei with unusual neutron excess?
AbstractA realistic model is suggested based on the quasiparticle Lagrange version of the self-consistent Finite Fermi Systems theory supplemented with the microscopically calculated surface parameters of the Landau–Migdal interaction amplitude. The latter are expressed in terms of the off-shell T-matrix of free NN-scattering and show a strong dependence on the chemical potential of a nucleus under consideration in the drip line vicinity. This effect could result in shifting the neutron drip line position to very large values of the neutron excess
- Pairing in Dense Neutron Matter: The Spectrum of Solutions
The - pairing model is generally considered to provide an
adequate description of the superfluid states of neutron matter at densities
some 2-3 times that of saturated symmetrical nuclear matter. The problem of
solving the system of BCS gap equations expressing the - model is
attacked with the aid of the separation approach. This method, developed
originally for quantitative study of S-wave pairing in the presence of strong
short-range repulsions, serves effectively to reduce the coupled, singular,
nonlinear BCS integral equations to a set of coupled algebraic equations. For
the first time, sufficient precision becomes accessible to resolve small energy
splittings between the different pairing states. Adopting a perturbative
strategy, we are able to identify and characterize the full repertoire of real
solutions of the - pairing model, in the limiting regime of small
tensor-coupling strength. The P-F channel coupling is seen to lift the striking
parametric degeneracies revealed by a earlier separation treatment of the pure,
uncoupled pairing problem. Remarkably, incisive and robust results are
obtained solely on the basis of analytic arguments. Unlike the traditional
Ginzburg-Landau approach, the analysis is not restricted to the immediate
vicinity of the critical temperature, but is equally reliable at zero
temperature. Interesting connections and contrasts are drawn between triplet
pairing in dense neutron matter and triplet pairing in liquid He.Comment: 23 pages, 1 figur
Entropy paradox in strongly correlated Fermi systems
A system of interacting, identical fermions described by standard Landau
Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if
the correlations grow sufficiently strong, as occurs at a quantum critical
point where the effective mass diverges. As yet, this phenomenon defies full
understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior
observed beyond the quantum critical point are still accessible within the
general framework of the Landau quasiparticle picture. Self-consistent
solutions of the coupled Landau equations for the quasiparticle momentum
distribution and quasiparticle energy spectrum are shown
to exist in two distinct classes, depending on coupling strength and on whether
the quasiparticle interaction is regular or singular at zero momentum transfer.
One class of solutions maintains the idempotency condition of
standard FL theory at zero temperature while adding pockets to the Fermi
surface. The other solutions are characterized by a swelling of the Fermi
surface and a flattening of the spectrum over a range of momenta
in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The
latter, non-idempotent solution is revealed by analysis of a Poincar\'e mapping
associated with the fundamental Landau equation connecting and
and validated by solution of a variational condition that yields
the symmetry-preserving ground state. Paradoxically, this extraordinary
solution carries the burden of a large temperature-dependent excess entropy
down to very low temperatures, threatening violation of the Nernst Theorem. It
is argued that certain low-temperature phase transitions offer effective
mechanisms for shedding the entropy excess. Available measurements in
heavy-fermion compounds provide concrete support for such a scenario.Comment: 34 pages, 6 figure
Fermi surface properties of the bifunctional organic metal κ-(BETS)2Mn[N(CN)2]3 near the metal-insulator transition
We present detailed studies of the high-field magnetoresistance of the layered organic metal κ-(BETS)2Mn- [N(CN)2]3 under a pressure slightly above the insulator-metal transition. The experimental data are analyzed in terms of the Fermi surface properties and compared with the results of first-principles band structure calculations. The calculated size and shape of the in-plane Fermi surface are in very good agreement with those derived from Shubnikov-de Haas oscillations as well as the classical angle-dependent magnetoresistance oscillations. A comparison of the experimentally obtained effective cyclotron masses with the calculated band masses reveals electron correlations significantly dependent on the electron momentum. The momentum- or band-dependent mobility is also reflected in the behavior of the classical magnetoresistance anisotropy in a magnetic field parallel to layers. Other characteristics of the conducting system related to interlayer charge transfer and scattering mechanisms are discussed based on the experimental data. Besides the known high-field effects associated with the Fermi surface geometry, new pronounced features have been found in the angle-dependent magnetoresistance, which might be caused by coupling of the metallic charge transport to a magnetic instability in proximity to the metal-insulator phase boundary
Solution of the microscopic gap equation for a slab of nuclear matter with the Paris NN-potential
The gap equation in the -channel is solved for a nuclear slab with the
separable form of the Paris potential. The gap equation is considered in the
model space in terms of the effective pairing interaction which is found in the
complementary subspace. The absolute value of the gap turned out to be
very sensitive to the cutoff in the momentum space in the equation
for the effective interaction. It is necessary to take to guarantee 1% accuracy for . The gap equation itself is
solved directly, without any additional approximations. The solution reveals
the surface enhancement of the gap which was earlier found with an
approximate consideration. A strong surface-volume interplay was found also
implying a kind of the proximity effect. The diagonal matrix elements of
turned out to be rather close to the empirical values for heavy atomic
nuclei.Comment: 17 pages, 12 figure
Shubnikov–de Haas oscillations and electronic correlations in the layered organic metal κ-(BETS)₂Mn[N(CN)₂]₃
We present magnetoresistance studies of the quasi-two-dimensional organic conductor κ-(BETS)₂Mn[N(CN)₂]₃, where BETS stands for bis(ethylenedithio)tetraselenafulvalene. Under a moderate pressure of 1.4 kbar, required for stabilizing the metallic ground state, Shubnikov–de Haas oscillations, associated with a classical and a magnetic-breakdown cyclotron orbits on the cylindrical Fermi surface, have been found at fields above 10 T. The effective cyclotron masses evaluated from the temperature dependence of the oscillation amplitudes reveal strong renormalization due to many-body interactions. The analysis of the relative strength of the oscillations corresponding to the different orbits and of its dependence on magnetic field suggests an enhanced role of electron-electron interactions on flat parts of the Fermi surface
Magnetic quantum oscillations in the charge-density-wave state of the organic metals α-(BEDT-TTF)₂MHg(SCN)₄ with M = K and Tl
The low-temperature charge-density-wave (CDW) state in the layered organic metals α-(BEDT-TTF)₂MHg(SCN)₄
has been studied by means of the Shubnikov–de Haas and de Haas–van Alphen effects. In addition to the dominant
α-frequency, which is also observed in the normal state, both the magnetoresistance and magnetic torque possess a
slowly oscillating component. These slow oscillations provide a firm evidence for the CDW-induced reconstruction
of the original cylindrical Fermi surface. The α-oscillations of the interlayer magnetoresistance exhibit an anomalous
phase inversion in the CDW state, whereas the de Haas–van Alphen signal maintains the normal phase. We argue
that the anomaly may be attributed to the magnetic-breakdown origin of the α-oscillations in the CDW state.
A theoretical model illustrating the possibility of a phase inversion in the oscillating interlayer conductivity in the
presence of a spatially fluctuating magnetic breakdown gap is proposed
Adaptation of the Landau-Migdal Quasiparticle Pattern to Strongly Correlated Fermi Systems
A quasiparticle pattern advanced in Landau's first article on Fermi liquid
theory is adapted to elucidate the properties of a class of strongly correlated
Fermi systems characterized by a Lifshitz phase diagram featuring a quantum
critical point (QCP) where the density of states diverges. The necessary
condition for stability of the Landau Fermi Liquid state is shown to break down
in such systems, triggering a cascade of topological phase transitions that
lead, without symmetry violation, to states with multi-connected Fermi
surfaces. The end point of this evolution is found to be an exceptional state
whose spectrum of single-particle excitations exhibits a completely flat
portion at zero temperature. Analysis of the evolution of the temperature
dependence of the single-particle spectrum yields results that provide a
natural explanation of classical behavior of this class of Fermi systems in the
QCP region.Comment: 26 pages, 14 figures. Dedicated to 100th anniversary of A.B.Migdal
birthda
Interaction of the single-particle and collective degrees of freedom in non-magic nuclei: the role of phonon tadpole terms
A method of a consistent consideration of the phonon contributions to mass
and gap operators in non-magic nuclei is developed in the so-called g^2
approximation, where g is the low-lying phonon creation amplitude. It includes
simultaneous accounting for both the usual non-local terms and the phonon
tadpole ones. The relations which allow the tadpoles to be calculated without
any new parameters are derived. As an application of the results, the role of
the phonon tadpoles in the single-particle strength distribution and in the
single-particle energies and gap values has been considered. Relation to the
problem of the surface nature of pairing is discussed.Comment: 22 pages, 7 figure