共查询到20条相似文献,搜索用时 15 毫秒
1.
We present in this work an exact renormalization group (RG) treatment of a one-dimensional p-wave superconductor. The model proposed by Kitaev consists of a chain of spinless fermions with a p-wave gap. It is a paradigmatic model of great actual interest since it presents a weak pairing superconducting phase that has Majorana fermions at the ends of the chain. Those are predicted to be useful for quantum computation. The RG allows to obtain the phase diagram of the model and to study the quantum phase transition from the weak to the strong pairing phase. It yields the attractors of these phases and the critical exponents of the weak to strong pairing transition. We show that the weak pairing phase of the model is governed by a chaotic attractor being non-trivial from both its topological and RG properties. In the strong pairing phase the RG flow is towards a conventional strong coupling fixed point. Finally, we propose an alternative way for obtaining p-wave superconductivity in a one-dimensional system without spin–orbit interaction. 相似文献
2.
We use the bosonization approach to investigate quantum phases of boson-fermion mixtures (BFM) of atoms confined to one dimension by an anisotropic optical lattice. For a BFM with a single species of fermions we find a charge-density wave phase, a fermion pairing phase, and a phase separation regime. We also obtain the rich phase diagram of a BFM with two species of fermions. We demonstrate that these phase diagrams can be understood in terms of polarons, i.e., atoms "dressed" by screening clouds of the other atom species. Techniques to detect the resulting quantum phases are discussed. 相似文献
3.
We study a mixture of fermionic and bosonic cold atoms on a two-dimensional optical lattice, where the fermions are prepared in two isospin states and the bosons have Bose-Einstein condensed. Number density fluctuations of the condensate form delocalized bosonic modes which couple to the fermionic atoms similarly to the electron-phonon coupling in crystals. We study the phase diagram for this system at fixed fermion density of one per site. We find that tuning of the lattice parameters and interaction strengths drives the system to undergo antiferromagnetic ordering, s-wave and d-wave pairing superconductivity, or a charge density-wave phase. We use functional renormalization group analysis where retardation effects are fully taken into account. We calculate response functions and also provide estimates of the energy gap associated with the dominant order, and how it depends on different parameters of the problem. 相似文献
4.
Using a renormalization group approach, we determine the phase diagram of an extended quasi-one-dimensional electron gas model that includes interchain hopping, nesting deviations, and both intrachain and interchain repulsive interactions. We find a close proximity of spin-density- and charge-density-wave phases and singlet d-wave and triplet f-wave superconducting phases. There is a striking correspondence between our results and recent puzzling experimental findings in the Bechgaard salts, including the coexistence of spin-density-wave and charge-density-wave phases and the possibility of a triplet pairing in the superconducting phase. 相似文献
5.
6.
G. Roux S. Capponi P. Lecheminant P. Azaria 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):293-308
We study spin 3/2 fermionic cold atoms with attractive interactions confined in a one-dimensional optical lattice. Using numerical
techniques, we determine the phase diagram for a generic density. For the chosen parameters, one-particle excitations are
gapped and the phase diagram is separated into two regions: one where the two-particle excitation gap is zero, and one where
it is finite. In the first region, the two-body pairing fluctuations (BCS) compete with the density ones. In the other one,
a molecular superfluid (MS) phase, in which bound-states of four particles form, competes with the density fluctuations. The
properties of the transition line between these two regions is studied through the behavior of the entanglement entropy. The
physical features of the various phases, comprising leading correlations, Friedel oscillations, and excitation spectra, are
presented. To make the connection with experiments, the effect of a harmonic trap is taken into account. In particular, we
emphasize the conditions under which the appealing MS phase can be realized, and how the phases could be probed by using the
density profiles and the associated structure factor. Lastly, the consequences on the flux quantization of the different nature
of the pairing in the BCS and MS phases are studied in a situation where the condensate is in a ring geometry. 相似文献
7.
We present an analytical strong-disorder renormalization group theory of the quantum phase transition in the dissipative random transverse-field Ising chain. For Ohmic dissipation, we solve the renormalization flow equations analytically, yielding asymptotically exact results for the low-temperature properties of the system. We find that the interplay between quantum fluctuations and Ohmic dissipation destroys the quantum critical point by smearing. We also determine the phase diagram and the behavior of observables in the vicinity of the smeared quantum phase transition. 相似文献
8.
A mixture of ultracold bosons and fermions placed in an optical lattice constitutes a novel kind of quantum gas, and leads to phenomena, which so far has been discussed neither in atomic physics, nor in condensed matter physics. We discuss the phase diagram at low temperatures, and in the limit of strong atom-atom interactions, and predict the existence of quantum phases that involve pairing of fermions with one or more bosons, or, respectively, bosonic holes. The resulting composite fermions may form, depending on the system parameters, a normal Fermi liquid, a density wave, a superfluid liquid, or an insulator with fermionic domains. We discuss the feasibility for observing such phases in current experiments. 相似文献
9.
10.
H.-J. Lee R. Bulla 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):199-203
We consider a quantum impurity model in which a bosonic impurity
level is coupled to a non-interacting bosonic bath, with the bosons
at the impurity site subject to a local Coulomb repulsion U. Numerical
renormalization group calculations for this bosonic single-impurity
Anderson model reveal a zero-temperature phase diagram where
Mott phases with reduced charge fluctuations are separated from a
Bose-Einstein condensed phase by lines of quantum critical
points. We discuss possible realizations of this model, such as
atomic quantum dots in optical lattices. Furthermore, the bosonic
single-impurity Anderson model appears as an effective impurity model
in a dynamical mean-field theory of the Bose-Hubbard model. 相似文献
11.
Employing the density matrix renormalization group method and strong-coupling perturbation theory, we study the phase diagram of the SU(2)xSU(2) Kondo lattice model in one dimension. We show that, at quarter filling, the system can exist in two phases depending on the coupling strength. The weak-coupling phase is dominated by RKKY exchange correlations, while the strong-coupling phase is characterized by strong antiferromagnetic correlations of the channel degree of freedom. These two phases are separated by a quantum critical point. For conduction-band fillings of less than one-quarter, we find a paramagnetic metallic phase at weak coupling and a ferromagnetic phase at moderate to strong coupling. 相似文献
12.
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
13.
The ground state phase diagram of the one-dimensional Bose-Fermi Hubbard model is studied in the canonical ensemble using a quantum Monte Carlo method. We focus on the case where both species have half filling in order to maximize the pairing correlations between the bosons and the fermions. In case of equal hopping we distinguish among phase separation, a Luttinger liquid phase, and a phase characterized by strong singlet pairing between the species. True long-range density waves exist with unequal hopping amplitudes. 相似文献
14.
Incommensurate quantum systems with two competing periodicities exhibit metallic (with Bloch-type extended wave functions),
insulating (with exponentially localized wave functions) as well ascritical (with fractal wave functions) phases. An exact renormalization method, which takes into account the inherent incommensurability,
is used to obtain the phase diagram of various quantum models for the two-dimensional electron gas and for quantum spin chains
in a magnetic field. In this approach, the scaling properties of the fractal eigenstates are characterized by a fixed point
or a strange invariant set of the renormalization flow. One of our novel results is the existence of self-similar fluctuations
in the localized states once the exponentially decaying envelope is factorized out. In almost all cases under investigation
here, the universality classes can be broadly classified as those of the nearest-neighbor square or triangular lattices. 相似文献
15.
R. Duprat C. Bourbonnais 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):219-228
The interference between spin-density-wave and superconducting instabilities in quasi-one-dimensional correlated metals is
analyzed using the renormalization group method. At the one-loop level, we show how the interference leads to a continuous
crossover from a spin-density-wave state to unconventional superconductivity when deviations from perfect nesting of the Fermi
surface exceed a critical value. Singlet pairing between electrons on neighboring stacks is found to be the most favorable
symmetry for superconductivity. The consequences of non uniform spin-density-wave pairing on the structure of phase diagram
within the crossover region is also discussed.
Received 3 January 2001 and Received in final form 1st March 2001 相似文献
16.
Sanner C Su EJ Keshet A Huang W Gillen J Gommers R Ketterle W 《Physical review letters》2011,106(1):010402
Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in?situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices. 相似文献
17.
V. E. Sinitsyn A. S. Boyarchenkov A. S. Ovchinnikov I. G. Bostrem 《Journal of Experimental and Theoretical Physics》2005,101(3):472-480
An anisotropic Heisenberg spin S = 1 model on a two-dimensional hexagonal lattice (formed from interacting chains) with antiferromagnetic nearest-neighbor interactions of two types is analyzed by the real space renormalization group method. The problem of the influence of interchain pairing on the critical properties of the model is studied, and the phase diagram of the model is constructed. The two-dimensional density matrix renormalization group algorithm is used to calculate the ground state energy for the isotropic case as a function of the ratio between interchain and intrachain interactions. 相似文献
18.
Ejima S Bhaseen MJ Hohenadler M Essler FH Fehske H Simons BD 《Physical review letters》2011,106(1):015303
We investigate the phase diagram of bosons interacting via Feshbach-resonant pairing interactions in a one-dimensional lattice. Using large scale density matrix renormalization group and field theory techniques we explore the atomic and molecular correlations in this low-dimensional setting. We provide compelling evidence for an Ising deconfinement transition occurring between distinct superfluids and extract the Ising order parameter and correlation length of this unusual superfluid transition. This is supported by results for the entanglement entropy which reveal both the location of the transition and critical Ising degrees of freedom on the phase boundary. 相似文献
19.
We consider a magnetic impurity coupled to both fermionic quasiparticles with a pseudogap density of states and bosonic spin fluctuations. Using renormalization group and large-N calculations we investigate the phase diagram of the resulting Fermi-Bose Kondo model. We show that the Kondo temperature is strongly reduced by low-energy spin fluctuations, and make connections to experiments in cuprate superconductors. Furthermore, we derive an exact exponent for the critical behavior of the conduction electron T matrix, and propose our findings to be relevant for certain scenarios of local quantum criticality in heavy-fermion metals. 相似文献
20.
R. M. Noack S. R. White D. J. Scalapino 《Physica C: Superconductivity and its Applications》1996,270(3-4):281-296
We present density-matrix renormalization group results for the ground state properties of two-leg Hubbard ladders. The half-filled Hubbard ladder is an insulating spin-gapped system, exhibiting a crossover from a spin liquid to a band insulator as a function of the interchain hopping matrix element. When the system is doped, there is a parameter range in which the spin gap remains. In this phase, the doped holes from singlet pairs and the pair field and the “4kF” density correlations associated with pair-density fluctuations decay as power laws, while the “2kF” charge density wave correlations decay exponentially. We discuss the behavior of the exponents of the pairing and density correlations within this spin-gapped phase. Additional one-band Luttinger liquid phases which occur in the large interband hopping regime are also discussed. 相似文献