384 research outputs found
Critical dynamics, duality, and the exact dynamic exponent in extreme type II superconductors
The critical dynamics of superconductors is studied using renormalization
group and duality arguments. We show that in extreme type II superconductors
the dynamic critical exponent is given exactly by . This result does not
rely on the widely used models of critical dynamics. Instead, it is shown that
follows from the duality between the extreme type II superconductor and
a model with a critically fluctuating gauge field. Our result is in agreement
with Monte Carlo simulations.Comment: 7 pages, no figures; version accepted for publication in PR
Specific heat of heavy fermion CePd2Si2 in high magnetic fields
We report specific heat measurements on the heavy fermion compound CePd2Si2
in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp
peak in the specific heat signals the antiferromagnetic transition at T_N ~ 9.3
K in zero field. The transition is found to shift to lower temperatures when a
magnetic field is applied along the crystallographic a-axis, while a field
applied parallel to the tetragonal c-axis does not affect the transition. The
magnetic contribution to the specific heat below T_N is well described by a sum
of a linear electronic term and an antiferromagnetic spin wave contribution.
Just below T_N, an additional positive curvature, especially at high fields,
arises most probably due to thermal fluctuations. The field dependence of the
coefficient of the low temperature linear term, gamma_0, extracted from the
fits shows a maximum at about 6 T, at the point where an anomaly was detected
in susceptibility measurements. The relative field dependence of both T_N and
the magnetic entropy at T_N scales as [1-(B/B_0)^2] for B // a, suggesting the
disappearance of antiferromagnetism at B_0 ~ 42 T. The expected suppression of
the antiferromagnetic transition temperature to zero makes the existence of a
magnetic quantum critical point possible.Comment: to be published in Journal of Physics: Condensed Matte
Observation of Magnetic Flux Generated Spontaneously During a Rapid Quench of Superconducting Films
We report observations of spontaneous formation of magnetic flux lines during
a rapid quench of YBaCuO films through T. This
effect is predicted according to the Kibble-Zurek mechanism of creation of
topological defects of the order parameter during a symmetry-breaking phase
transition. Our previous experiment, at a quench rate of 20K/sec, gave null
results. In the present experiment, the quench rate was increased to
\TEXTsymbol{>} 10 K/sec. Within experimental resolution, the dependence
of the measured flux on the cooling rate is consistent with the prediction
SO(5) superconductor in a Zeeman magnetic field: Phase diagram and thermodynamic properties
In this paper we present calculations of the SO(5) quantum rotor theory of
high-T superconductivity in Zeeman magnetic field. We use the spherical
approach for five-component quantum rotors in three-dimensional lattice to
obtain formulas for critical lines, free energy, entropy and specific heat and
present temperature dependences of these quantities for different values of
magnetic field. Our results are in qualitative agreement with relevant
experiments on high-T cuprates.Comment: 4 pages, 2 figures, to appear in Phys. Rev. B, see http://prb.aps.or
Magnetic resonance at 41 meV and charge dynamics in YBa_2Cu_3O_6.95
We report an Eliashberg analysis of the electron dynamics in YBa_2Cu_3O_6.95.
The magnetic resonance at 41 meV couples to charge carriers and defines the
characteristic shape in energy of the scattering rate \tau^{-1}(T,\omega) which
allows us to construct the charge-spin spectral density I^2\chi(\omega,T) at
temperature T. The T dependence of the weight under the resonance peak in
I^2\chi(\omega,T) agrees with experiment as does that of the London penetration
depth and of the microwave conductivity. Als, at T=0 condensation energy, the
fractional oscillator strength in the condensate, and the ratio of gap to
critical temperature agree well with the data.Comment: 7 Pages, 3 Figures, accepted for publication in Europhysics Letter
In-plane optical spectral weight transfer in optimally doped BiSrCaCuO
We examine the redistribution of the in-plane optical spectral weight in the
normal and superconducting state in tri-layer \bbb (Bi2223) near optimal doping
( = 110 K) on a single crystal via infrared reflectivity and spectroscopic
ellipsometry. We report the temperature dependence of the low-frequency
integrated spectral weight for different values of the cutoff
energy . Two different model-independent analyses consistently show
that for = 1 eV, which is below the charge transfer gap,
increases below , implying the lowering of the kinetic
energy of the holes. This is opposite to the BCS scenario, but it follows the
same trend observed in the bi-layer compound \bb (Bi2212). The size of this
effect is larger in Bi2223 than in Bi2212, approximately scaling with the
critical temperature. In the normal state, the temperature dependence of
is close to up to 300 K
Differential-thermal analysis around and below the critical temperature Tc of various low-Tc superconductors: A comparative study
We present specific-heat data on the type-II superconductors V3Si, LuNi2B2C
and NbSe2 which were acquired with a low-temperature thermal analysis (DTA)
technique. We compare our data with available literature data on these
superconductors. In the first part we show that the DTA technique allows for
fast measurements while providing a very high resolution on the temperature
scale. Sharp features in the specific heat such as at the one at the transition
to superconductivity are resolved virtually without instrumental broadening. In
the second part we investigate the magnetic-field dependence of the specific
heats of V3Si and LuNi2B2C at a fixed temperature T=7.5K to demonstrate that
DTA techniques also allow for sufficiently precise measurements of absolute
values of cp even in the absence of a sharp phase transition. The corresponding
data for V3Si and LuNi2B2C are briefly discussed
Thermal fluctuations and vortex melting in the classical superconductor Nb3Sn from high-resolution specific-heat measurements
The range of critical thermal fluctuations in classical bulk superconductors
is extremely small and especially in low fields hardly experimentally
inaccessible. With a new type of calorimeter we have been able to resolve a
small lambda anomaly within a narrow temperature range around the Hc2 line. We
show that the evolution of the anomaly as a function of magnetic field follows
scaling laws expected in the presence of critical fluctuations. The lower onset
of the fluctuation regime shows many characteristics of a continuous
solid-to-liquid transition in the vortex matter. It can be driven into a
first-order vortex melting transition by a small AC field which helps the
vortex matter to reach equilibrium.Comment: 12 pages, 5 figures new extended version, more figures added, more
detailed discussion about the vortex melting transitio
Superconductivity-Induced Transfer of In-Plane Spectral Weight in Bi2Sr2CaCu2O8: Resolving a Controversy
We present a detailed analysis of the superconductivity-induced
redistribution of optical spectral weight in Bi2Sr2CaCu2O8 near optimal doping.
It confirms the previous conclusion by Molegraaf et al. (Science 66, 2239
(2002)), that the integrated low-frequency spectral weight shows an extra
increase below Tc. Since the region, where the change of the integrated
spectral weight is not compensated, extends well above 2.5 eV, this transfer is
caused by the transfer of spectral weight from interband to intraband region
and only partially by the narrowing of the intraband peak. We show that the
opposite assertion by Boris et al. (Science 304, 708 (2004)) regarding this
compound, is unlikely the consequence of any obvious discrepancies between the
actual experimental data.Comment: ReVTeX, 9 pages, 8 encapsulated postscript figures, several typo's
correcte
Phase fluctuations and the pseudogap in YBa2Cu3Ox
The thermodynamics of the superconducting transition is studied as a function
of doping using high-resolution expansivity data of YBa2Cu3Ox single crystals
and Monte-Carlo simulations of the anisotropic 3D-XY model. We directly show
that Tc of underdoped YBa2Cu3Ox is strongly suppressed from its mean-field
value (Tc-MF) by phase fluctuations of the superconducting order parameter. For
overdoped YBa2Cu3Ox fluctuation effects are greatly reduced and Tc ~ Tc-MF . We
find that Tc-MF exhibits a similar doping dependence as the pseudogap energy,
naturally suggesting that the pseudogap arises from phase-incoherent Cooper
pairing.Comment: 9 pages, 3 Figure
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