860 research outputs found
Low Temperature Superfluid Response of High-Tc Superconductors
We have reviewed our theoretical and experimental results of the low
temperature superfluid response function of high temperature superconductors
(HTSC). In clean high-Tc materials the in-plane superfluid density rho_s^{ab}
varies linearly with temperature. The slope of this linear T term is found to
scale approximately with 1/Tc which, according to the weak coupling BCS theory
for a d-wave superconductor, implies that the gap amplitude scales
approximately with Tc. A T^5 behavior of the out-of-plane superfluid density
rho_s^c for clean tetragonal HTSC was predicted and observed experimentally in
the single layer Hg-compound HgBa_2CuO_{4+delta}. In other tetragonal high-Tc
compounds with relatively high anisotropy, such as Hg_2Ba_2Ca_2Cu_3O_{8+delta},
rho_s^c varies as T^2 due to disorder effects. In optimally doped
YBa_2Cu_3O_{7-delta}, rho_s^c varies linearly with temperature at low
temperatures, but in underdoped YBa_2Cu_3O_{7-delta}, rho_s^c varies as T^2 at
low temperatures; these results are consistent with our theoretical
calculations.Comment: 26 pages, 8 figure
Effects of doping on thermally excited quasiparticles in the high- superconducting state
The physical properties of low energy superconducting quasiparticles in high-
superconductors are examined using magnetic penetration depth and
specific heat experimental data. We find that the low energy density of states
of quasiparticles of LaSrCuO scales with to the
leading order approximation, where is the critical doping concentration
below which . The linear temperature term of the superfluid density is
renormalized by quasiparticle interactions and the renormalization factor times
the Fermi velocity is found to be doping independent.Comment: 3 pages, 3 figures, minor change to the content, fig1 is reploted, to
appear in Phys Rev
The Lattice Free Energy with Overlap Fermions: A Two-Loop Result
We calculate the 2-loop partition function of QCD on the lattice, using the
Wilson formulation for gluons and the overlap-Dirac operator for fermions.
Direct by-products of our result are the 2-loop free energy and average
plaquette. Our calculation serves also as a prototype for further higher loop
calculations in the overlap formalism. We present our results as a function of
a free parameter entering the overlap action; the dependence on the
number of colors and fermionic flavors is shown explicitly.Comment: 10 pages, 5 figures. Final version to appear in Physical Review D. A
missing overall factor was inserted in Eq. 12; it affects also Eq. 1
Possible origin of 60-K plateau in the YBa2Cu3O(6+y) phase diagram
We study a model of YBa2Cu3O(6+y) to investigate the influence of oxygen
ordering and doping imbalance on the critical temperature Tc(y) and to
elucidate a possible origin of well-known feature of YBCO phase diagram: the
60-K plateau. Focusing on "phase only" description of the high-temperature
superconducting system in terms of collective variables we utilize a
three-dimensional semi microscopic XY model with two-component vectors that
involve phase variables and adjustable parameters representing microscopic
phase stiffnesses. The model captures characteristic energy scales present in
YBCO and allows for strong anisotropy within basal planes to simulate oxygen
ordering. Applying spherical closure relation we have solved the phase XY model
with the help of transfer matrix method and calculated Tc for chosen system
parameters. Furthermore, we investigate the influence of oxygen ordering and
doping imbalance on the shape of YBCO phase diagram. We find it unlikely that
oxygen ordering alone can be responsible for the existence of 60-K plateau.
Relying on experimental data unveiling that oxygen doping of YBCO may introduce
significant charge imbalance between CuO2 planes and other sites, we show that
simultaneously the former are underdoped, while the latter -- strongly
overdoped almost in the whole region of oxygen doping in which YBCO is
superconducting. As a result, while oxygen content is increased, this provides
two counter acting factors, which possibly lead to rise of 60K plateau.
Additionally, our result can provide an important contribution to understanding
of experimental data supporting existence of multicomponent superconductivity
in YBCO.Comment: 9 pages, 8 figures, submitted to PRB, see http://prb.aps.or
Multiple Broken Symmetries in Striped LaBaCuO detected by the Field Symmetric Nernst Effect
We report on a thermoelectric investigation of the stripe and superconducting
phases of the cuprate LaBaCuO near the doping known
to host stable stripes. We use the doping and magnetic field dependence of
field-symmetric Nernst effect features to delineate the phenomenology of these
phases. Our measurements are consistent with prior reports of time-reversal
symmetry breaking signatures above the superconducting , and
crucially detect a sharp, robust, field-invariant peak at the stripe charge
order temperature, . Our observations
suggest the onset of a nontrivial charge ordered phase at , and the subsequent presence of spontaneously
generated vortices over a broad temperature range before the emergence of bulk
superconductivity in LBCO
Universal optimal hole-doping concentration in single-layer high-temperature cuprate superconductors
We argue that in cuprate physics there are two types, hole content per
CuO plane () and the corresponding hole content per unit volume
(), of hole-doping concentrations for addressing physical properties
that are two-dimensional (2D) and three-dimensional (3D) in nature,
respectively. We find that superconducting transition temperature ()
varies systematically with as a superconducting \textquotedblleft
\textquotedblright with a universal optimal hole-doping concentration
= 1.6 10 cm for single-layer high
temperature superconductors. We suggest that determines the
upper bound of the electronic energy of underdoped single-layer high-
cuprates.Comment: 8 pages, 4 figures; added references ;accepted for the publication in
Supercond. Sci. Technol ; Ref. 13 is revise
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