共查询到20条相似文献,搜索用时 15 毫秒
1.
Guang-Hua Liu Xiao-Yan DengRui Wen 《Physica C: Superconductivity and its Applications》2012,472(1):10-14
Using the particle-hole version of the density-matrix renormalization-group technique, the pairing correlation and the quantum entanglement of the reduced BCS pairing model are investigated. Both of them behave smoothly from the weak to the strong coupling regimes. A convergence radius (∼1/ln Ω) of condensation energy is detected by the first order derivative of the block-block entanglement. Furthermore, the block-block entanglement in the strong coupling regime shows distinct size dependence, and a logarithmic volume law is suggested numerically. 相似文献
2.
Fermi gas with time-dependent pairing interaction hosts several different dynamical states. Coupling between the collective BCS pairing mode and individual Cooper pair states can make the latter either synchronize or dephase. We describe transition from phase-locked undamped oscillations to Landau-damped dephased oscillations in the collisionless, dissipationless regime as a function of coupling strength. In the dephased regime, we find a second transition at which the long-time asymptotic pairing amplitude vanishes. Using a combination of numerical and analytical methods we establish a continuous (type II) character of both transitions. 相似文献
3.
F. Matera A. Dellafiore 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):515-522
The pairing of fermionic atoms in a mixture of atomic fermion and boson gases at zero
temperature is investigated. The attractive interaction between fermions, that can be
induced by density fluctuations of the bosonic background, can give rise to a superfluid
phase in the Fermi component of the mixture. The atoms of both species are assumed to be
in only one internal state, so that the pairing of fermions is effective only in
odd-l channels. No assumption about the value of the ratio between the
Fermi velocity and the sound velocity in the Bose gas is made in the derivation of the
energy gap equation. The gap equation is solved without any particular ansatz
for the pairing field or the effective interaction. The p-wave
superfluidity is studied in detail. By increasing the strength and/or decreasing the range
of the effective interaction a transition of the fermion pairing regime, from the
Bardeen-Cooper-Schrieffer state to a system of tightly bound couples can be realized.
These composite bosons behave as a weakly-interacting Bose-Einstein condensate. 相似文献
4.
Motivated by recent efforts to achieve cold fermions pairing, we study the nonadiabatic regime of the Bardeen-Cooper-Schrieffer state formation. After the interaction is turned on, at times shorter than the quasiparticle energy relaxation time, the system oscillates between the superfluid and normal state. The collective nonlinear evolution of the BCS-Bogoliubov amplitudes u(p), v(p), along with the pairing function Delta, is shown to be an integrable dynamical problem which admits single soliton and soliton train solitons. We interpret the collective oscillations as Bloch precession of Anderson pseudospins, where each soliton causes a pseudospin 2pi Rabi rotation. 相似文献
5.
The treatment of a monopole pairing Hamiltonian, in the quasiparticle basis and with the inclusion of ground state correlations, is discussed. The theoretical procedure is based on the BCS method supplemented by a variational treatment of ground state correlations. A significant improvement in the results is found, for ground state energies, when the comparison between correlated, BCS and exact values is performed. Results are discussed for one and two level model configurations. 相似文献
6.
S. G. Magalhães F. M. Zimmer C. J. Kipper E. J. Calegari 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):209-218
The competition among spin glass (SG), antiferromagnetism (AF)
and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising spin glass model with a local BCS
pairing interaction in the presence of an applied magnetic transverse field Γ. In the present approach, spins in different
sublattices interact with a Gaussian random coupling with an antiferromagnetic mean J0 and standard deviation J.
The problem is formulated in the path integral formalism in which spin operators are represented by
bilinear combinations of Grassmann variables. The saddle-point Grand Canonical potential
is obtained within the static approximation and the replica symmetric ansatz. The results are analysed in phase diagrams in
which the AF and the SG phases can occur for small g (g is the strength of the local superconductor coupling written in units
of J), while the PAIR phase appears as unique solution for large g. However, there is a complex line transition separating
the PAIR phase from the others. It is second order at high temperature that ends in a tricritical point. The quantum fluctuations
affect deeply the transition lines and the tricritical point due to the presence of Γ. 相似文献
7.
We study a fermionic infinited-ranged Ising spin glass with a real space BCS interaction
in the presence of an applied transverse field. The problem is formulated in the integral
functional formalism where the SU(2) spins are given in terms of bilinear combinations of Grassmann fields.
The problem is solved within static approximation and the replica symmetry ansatz combined with previous approaches
used to study the critical behavior of the quantum Ising spin glass in a transverse field and the spin glass
Heisenberg model with BCS pairing.
Our results show that the transverse field has strong effect in the phase boundary of the spin glass phase and the
PAIR phase in which there is a long range order corresponding to formations of pairs. The location of the tricritical
point in the PAIR phase transition line is also affected. 相似文献
8.
M.E. Palistrant 《Physics letters. A》1978,67(4):303-304
The effect of the Peierls transition on superconductivity in a two-band system, where one of the bands is flat, is examined theoretically. We find that superconductivity appears at the background of the insulating phase (TP >; Tc). At Tc > TP only the superconducting transition is possible. 相似文献
9.
The problem of a two-component Fermi gas in a harmonic trap, with an imbalanced population and a pairing interaction of zero total momentum, is mapped onto the exactly solvable reduced BCS model. For a one-dimensional trap, the complete ground state diagram is determined with various topological features in ground state energy spectra. In addition to the conventional two-shell density profile of a paired core and polarized outer wings, a three-shell structure as well as a double-peak superfluid distribution are unveiled. 相似文献
10.
S.G. Magalhães A. Theumann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):5-13
We have examined the role of the BCS pairing mechanism in the formation of the magnetic moment and henceforth a spin glass
(SG) phase by studying a fermionic Sherrington-Kirkpatrick model with a local BCS coupling between the fermions. This model
is obtained by using perturbation theory to trace out the conduction electrons degrees of freedom in conventional superconducting
alloys. The model is formulated in the path integral formalism where the spin operators are represented by bilinear combinations
of Grassmann fields and it reduces to a single site problem that can be solved within the static approximation with a replica
symmetric ansatz. We argue that this is a valid procedure for values of temperature above the de Almeida-Thouless instability
line. The phase diagram in the T-g plane, where g is the strength of the pairing interaction, for fixed variance J
2
/N of the random couplings Jij, exhibits three regions: a normal paramagnetic (NP) phase, a spin glass (SG) phase and a pairing (PAIR) phase where there
is formation of local pairs.The NP and PAIR phases are separated by a second order transition line g=g
c
(T) that ends at a tricritical point T
3
=0.9807J, g
3
=5,8843J, from where it becomes a first order transition line that meets the line of second order transitions at T
c
=0.9570J that separates the NP and the SG phases. For T<T
c
the SG phase is separated from the PAIR phase by a line of first order transitions. These results agree qualitatively with
experimental data in .
Received 14 May 1998 相似文献
11.
12.
We have solved the coupled gap equations for a one dimensional electron gas which can undergo both a Peierls insulating and a BCS superconducting transition. We find that, except for a very special case, (i) only one of the order parameters can be non-vanishing and (ii) there is only one critical temperature. We conclude that, independent of the pairing interaction strength, if the Peierls transition occurs, there can be no BCS superconductivity, and conversely. 相似文献
13.
I. Z. Latypov A. A. Kalinkin A. V. Shkalikov A. A. Kalachev V. V. Samartsev 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(12):1659-1664
The problem of generating a narrow-band biphoton field during spontaneous parametric down conversion of light in a quadratic
nonlinear medium in a cavity is discussed. It is shown that, in the case of double resonance (for signal and idle fields),
the form of the single-photon wave packet is biexponential and has a half-width determined by the photon life time in the
cavity. An experiment is carried out on the generation of narrow-band biphotons in a crystal of lithium iodine with I-type
matching in a frequency degenerate collinear regime. The second-order correlation function of the cavity-enhanced biphotons
is measured using the electric nanosecond time delay line. 相似文献
14.
The problem of pairing in anisotropic electronic systems possessing patches of fermion condensate in the vicinity of the Van Hove points is analyzed. Attention is directed to opportunities for the occurrence of non-BCS pairing correlations between the states belonging to the fermion condensate. It is shown that the physical emergence of such pairing correlations would drastically alter the behavior of the single-particle Green function, the canonical pole of Fermi-liquid theory being replaced by a branch point. 相似文献
15.
We consider the effects of superfluidity on the light scattering properties of a two component gas of fermionic atoms, demonstrating that the scattered intensities of the Stokes and anti-Stokes lines exhibit a large maximum below the critical temperature when the gas is superfluid. This effect, the light scattering analog of the Hebel-Slichter effect in conventional superconductors, can be used to detect unambiguously the onset of pairing in an atomic gas in the BCS regime. 相似文献
16.
Z.-J. Ying M. Cuoco C. Noce H.-Q. Zhou 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(1):43-49
We study the phase separated state of an ultracold atomic Fermi
gas confined in a three-dimensional quantum harmonic trap with a
BCS pairing interaction. Examining various finite-temperature
phase diagrams, we investigate the interplay between the filling
of the quantum trap energy levels and the pairing energy. We find
that a low (high) filling leads to a large (small) critical
population imbalance for the superfluid/normal transition,
together with a fully (partially) polarized normal part. We also
show that the decrease of the density leads to a changeover of the
shape of the superfluid core from an equipotential form to a
deformed one. Moreover, we clarify the intrinsic mechanisms that
lead to the deformation, providing a unified scenario for phase
separation and deformation in a trapped Fermi gas, allowing for a
possible interpretation of the apparently controversial
experimental findings. 相似文献
17.
JETP Letters - Effect of two-particle correlations between impurities on the temperature of transition of a Fermi liquid in the superfluid or superconducting state is analyzed. It is shown, that... 相似文献
18.
I. A. Fomin 《JETP Letters》2011,92(9):585-589
Effect of two-particle correlations between impurities on the temperature of transition of a Fermi liquid in the superfluid
or superconducting state is analyzed. It is shown, that correlations with a radius, exceeding correlation length of the superconductor
can have a pronounced effect on the transition temperature. The equation for the transition temperature is corrected for correlations
of the impurities. Possible applications of the new equation are discussed. 相似文献
19.
Igor N. Karnaukhov 《Physics letters. A》2019,383(33):125951
A generalization of the Mattis-Nam model Mattis and Nam (1972) [7], which takes into account a correlated hopping and pairing of electrons, is proposed, its exact solution is obtained. In the framework of the model the stability of the zero energy Majorana fermions localized at the boundaries is studied in the chain in which electrons interact through both the on-site Hubbard interaction and the correlated hopping and pairing. The ground-state phase diagram of the model is calculated, the region of existence of topological states is determined. It is shown that low-energy excitations destroy bonds between electrons in the chain, leading to an insulator state. 相似文献
20.
Strutinsky calculations are used to investigate the shape and fission stability of rotating nuclei at finite temperature. Pairing correlations are described within a modified BCS approach which allows for the inclusion of both thermal and rotational degrees of freedom. Numerical results are discussed for the case of the deformed nucleus 240Pu up to angular momentum . The critical temperature T which characterizes the collapse of the pairing correlations is found to be of the order of Tc ≈ 0.40 MeV, for I = 0. 相似文献