3,104 research outputs found
What can we learn from comparison between cuprates and He films ? : phase separation and fluctuating superfluidity
In the underdoped, overdoped, Zn-doped or stripe-forming regions of
high- cuprate superconductors (HTSC), the superfluid density
at shows universal correlations with . Similar
strong correlations exist between 2-dimensional superfluid density and
superfluid transition temperature in thin films of He in non-porous or
porous media, and He/He film adsorbed on porous media. Based on
analogy between HTSC and He film systems, we propose a model for cuprates
where: (1) the overdoped region is characterized by a phase separation similar
to He/He; and (2) pair (boson) formation and fluctuating
superconductivity occur at separate temperatures above in the
underdoped region.Comment: 8 pages, 5 figures. Invited paper presented at the third
international conference on stripes and high-Tc superconductivity
(STRIPE-2000), Sept. 25-30th, 2000, Rome, Italy. To be published in the
International Journal of Modern Physics
Magnetic Phase Diagram of the Hole-doped CaNaCuOCl Cuprate Superconductor
We report on the magnetic phase diagram of a hole-doped cuprate
CaNaCuOCl, which is free from buckling of CuO
planes, determined by muon spin rotation and relaxation. It is characterized by
a quasi-static spin glass-like phase over a range of sodium concentration
(), which is held between long range antiferromagnetic
(AF) phase () and superconducting phase where the system is
non-magnetic for . The obtained phase diagram qualitatively agrees
well with that commonly found for hole-doped high-\tc cuprates, strongly
suggesting that the incomplete suppression of the AF order for is an
essential feature of the hole-doped cuprates.Comment: 5 pages, submitted to Phys. Rev. Let
Superconducting Volume Fraction in Overdoped Regime of La_2-x_Sr_x_CuO_4_: Implication for Phase Separation from Magnetic-Susceptibility Measurement
We have grown a single crystal of La_2-x_Sr_x_CuO_4_ in which the Sr
concentration, x, continuously changes from 0.24 to 0.29 in the overdoped
regime and obtained many pieces of single crystals with different x values by
slicing the single crystal. From detailed measurements of the magnetic
susceptibility, chi, of each piece, it has been found that the absolute value
of chi at the measured lowest temperature 2 K, |chi_2K_|, on field cooling
rapidly decreases with increasing x as well as the superconducting (SC)
transition temperature. As the value of |chi_2K_| is regarded as corresponding
to the SC volume fraction in a sample, it has been concluded that a phase
separation into SC and normal-state regions occurs in a sample of
La_2-x_Sr_x_CuO_4_ in the overdoped regime.Comment: 4 pages, 3 figures, ver. 2 has been accepted in J. Phys. Soc. Jp
Inequivalent representations of commutator or anticommutator rings of field operators and their applications
Hamiltonian of a system in quantum field theory can give rise to infinitely
many partition functions which correspond to infinitely many inequivalent
representations of the canonical commutator or anticommutator rings of field
operators. This implies that the system can theoretically exist in infinitely
many Gibbs states. The system resides in the Gibbs state which corresponds to
its minimal Helmholtz free energy at a given range of the thermodynamic
variables. Individual inequivalent representations are associated with
different thermodynamic phases of the system. The BCS Hamiltonian of
superconductivity is chosen to be an explicit example for the demonstration of
the important role of inequivalent representations in practical applications.
Its analysis from the inequivalent representations' point of view has led to a
recognition of a novel type of the superconducting phase transition.Comment: 25 pages, 6 figure
Study of the in-plane magnetic penetration depth in the cuprate superconductor Ca_2-xNa_xCuO_2Cl_2: role of the apical sites
A study of the in-plane magnetic penetration depth \lambda_ab in a series of
the cuprate superconductors Ca_2-xNa_xCuO_2Cl_2 (Na-CCOC) with Na content
x=0.11, 0.12, 0.15, 0.18, and 0.19 is reported. The zero temperature values of
\lambda_ab(0) were obtained by means of the muon-spin rotation technique, as
well as from measurements of the intrinsic susceptibility \chi^int(0) by using
the procedure developed by Kanigel et al. [Phys.Rev.B 71, 224511 (2005)].
\lambda_ab at T=0K was found to increase with decreasing doping from
\lambda_ab(0)=316(19)nm for the x=0.19 sample to \lambda_ab(0)=430(26)nm for
the x=0.11 one. From a comparison of the present Na-CCOC data with those of
Bi2201 and La214 cuprate superconductors it is concluded that substitution of
the apical oxygen by chlorine decreases the coupling between the
superconducting CuO_2 planes, leading to an enhancement of the two-dimensional
properties of Na-CCOC.Comment: 8 pages, 7 figure
Enhancement of electronic anomalies in iron-substituted La_2-x_Sr_x_Cu_1-y_Fe_y_O_4_ around x=0.22
We have measured the temperature dependences of Rho and Chi for
Fe-substituted La_2-x_Sr_x_Cu_1-y_Fe_y_O_4_ in the overdoped regime, in order
to investigate Fe-substitution effects on electronic properties around x=0.22.
From the Rho measurements, it has been found around x=0.22 that the values of
Rho are large at room temperature and that Rho exhibits a pronounced upturn at
low temperatures. Moreover, from the Rho and Chi measurements, it has been
found that T_c_ is anomalously depressed around x=0.22. These results indicate
that the electronic anomalies around x=0.22 are enhanced by Fe substitution,
which might be related to the development of stripe correlations by Fe
substitution.Comment: 7 pages, 3 figure
Metallic mean-field stripes, incommensurability and chemical potential in cuprates
We perform a systematic slave-boson mean-field analysis of the three-band
model for cuprates with first-principle parameters. Contrary to widespread
believe based on earlier mean-field computations low doping stripes have a
linear density close to 1/2 added hole per lattice constant. We find a
dimensional crossover from 1D to 2D at doping followed by a breaking
of particle-hole symmetry around doping 1/8 as doping increases. Our results
explain in a simple way the behavior of the chemical potential, the magnetic
incommensurability, and transport experiments as a function of doping. Bond
centered and site-centered stripes become degenerate for small overdoping.Comment: submitted to PR
- …