78 research outputs found
Linear and field-independent relation between vortex core state energy and gap in Bi2Sr2CaCu2O8+d
We present a scanning tunneling spectroscopy study on quasiparticle states in vortex cores in Bi2Sr2CaCu2O8+δ. The energy of the observed vortex core states shows an approximately linear scaling with the superconducting gap in the region just outside the core. This clearly distinguishes them from conventional localized core states and is a signature of the mechanism responsible for their discrete appearance in high-temperature superconductors. The energy scaling of the vortex core states also suggests a common nature of vortex cores in Bi2Sr2CaCu2O8+δ and YBa2Cu3O7-δ. Finally, these states do not show any dependence on the applied magnetic field between 1 and 6 T
Ab-initio calculation of all-optical time-resolved calorimetry of nanosized systems: Evidence of nanosecond-decoupling of electron and phonon temperatures
The thermal dynamics induced by ultrashort laser pulses in nanoscale systems,
i.e. all-optical time-resolved nanocalorimetry is theoretically investigated
from 300 to 1.5 K. We report ab-initio calculations describing the temperature
dependence of the electron-phonon interactions for Cu nanodisks supported on
Si. The electrons and phonons temperatures are found to decouple on the ns time
scale at 10 K, which is two orders of magnitude in excess with respect to that
found for standard low-temperature transport experiments. By accounting for the
physics behind our results we suggest an alternative route for overhauling the
present knowledge of the electron-phonon decoupling mechanism in nanoscale
systems by replacing the mK temperature requirements of conventional
experiments with experiments in the time-domain.Comment: 5 pages, 3 figures. Accepted on Physical Review B
Ward identities for disordered metals and superconductors
This article revisits Ward identities for disordered interacting normal
metals and superconductors. It offers a simple derivation based on gauge
invariance and recasts the identities in a new form that allows easy analysis
of the quasiparticle charge conservation (as e.g. in a normal metal) or
non-conservation (as e.g. in a d-wave superconductor).Comment: Discussion of decoherence at T=0 remove
Evidence for field-induced excitations in low-temperature thermal conductivity of Bi_2Sr_2CaCu_2O_8
The thermal conductivity ,, of Bi_2Sr_2CaCu_2O_8 was studied as a
function of magnetic field. Above 5 K, after an initial decrease,
presents a kink followed by a plateau, as recently reported by Krishana et al..
By contrast, below 1K, the thermal conductivity was found to \emph{increase}
with increasing field. This behavior is indicative of a finite density of
states and is not compatible with the existence of a field-induced fully gapped
state which was recently proposed to describe the
plateau regime. Our low-temperature results are in agreement with recent works
predicting a field-induced enhancement of thermal conductivity by Doppler shift
of quasi-particle spectrum.Comment: 4 pages including 4 eps figures, submitted to Phys. Rev. Let
Thermo-mechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near infrared pump-probe diffraction experiments
The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of
metallic nano-disks has been studied by near infrared pump-probe diffraction
measurements, over a temporal range spanning from 100 fs to several
nanoseconds. The experiments demonstrate that, in these systems, a
two-dimensional surface acoustic wave (2DSAW), with a wavevector given by the
reciprocal periodicity of the array, can be excited by ~120 fs Ti:sapphire
laser pulses. In order to clarify the interaction between the nanodisks and the
substrate, numerical calculations of the elastic eigenmodes and simulations of
the thermodynamics of the system are developed through finite-element analysis.
At this light, we unambiguously show that the observed 2DSAW velocity shift
originates from the mechanical interaction between the 2DSAWs and the
nano-disks, while the correlated 2DSAW damping is due to the energy radiation
into the substrate.Comment: 13 pages, 10 figure
Dirac quasiparticles in the mixed state
Energies and wave functions are calculated for d-wave quasiparticles in the
mixed state using the formalism of Franz and Tesanovic for the low-lying energy
levels. The accuracy of the plane-wave expansion is explored by comparing
approximate to exact results for a simplified one-dimensional problem, and the
convergence of the plane- wave expansion to the two-dimensional case is
studied. The results are used to calculate the low-energy tunneling density of
states and the low-temperature specific heat, and these theoretical results are
compared to semiclassical treatments and to the available data. Implications
for the muon spin resonance measurements of vortex core size are also
discussed.Comment: 13 pages, 15 figures, RevTeX. References corrected. A factor of 2 in
the results has been corrected, and the conclusions have been update
Order parameter of MgB_2: a fully gapped superconductor
We have measured the low-temperature specific heat C(T) for polycrystalline
MgB_2 prepared by high pressure synthesis. C(T) below 10 K vanishes
exponentially, which unambiguously indicates a fully opened superconducting
energy gap. However, this gap is found to be too small to account for Tc of
MgB_2. Together with the small specific heat jump DeltaC/gamma_nTc=1.13,
scenarios like anisotropic s-wave or multi-component order parameter are called
for. The magnetic field dependence of gamma(H) is neither linear for a fully
gapped s-wave superconductor nor H^1/2 for nodal order parameter. It seems that
this intriguing behavior of gamma(H) is associated with the intrinsic
electronic properties other than flux pinning.Comment: 7 pages, 5 figures; revised text and figures; references updated,
Phys. Rev. Lett., in pres
Singularity of the Vortex Density of States in d-wave Superconductors
In d-wave superconductors, the electronic density of states (DOS) induced by
a vortex exhibits 1/|E| divergency at low energies. It is the result of gap
nodes in the excitations spectrum outside the vortex core. The heat capacity in
two regimes, (T/T_c)^2 >> B/B_{c2} and (T/T_c)^2 << B/B_{c2}, is discussed.Comment: LaTeX file, 8 pages, no figures, submitted to JETP Letter
Transport Properties, Thermodynamic Properties, and Electronic Structure of SrRuO3
SrRuO is a metallic ferromagnet. Its electrical resistivity is reported
for temperatures up to 1000K; its Hall coefficient for temperatures up to 300K;
its specific heat for temperatures up to 230K. The energy bands have been
calculated by self-consistent spin-density functional theory, which finds a
ferromagnetic ordered moment of 1.45 per Ru atom. The measured
linear specific heat coefficient is 30mJ/mole, which exceeds the
theoretical value by a factor of 3.7. A transport mean free path at room
temperature of is found. The resistivity increases nearly
linearly with temperature to 1000K in spite of such a short mean free path that
resistivity saturation would be expected. The Hall coefficient is small and
positive above the Curie temperature, and exhibits both a low-field and a
high-field anomalous behavior below the Curie temperature.Comment: 6 pages (latex) and 6 figures (postscript, uuencoded.) This paper
will appear in Phys. Rev. B, Feb. 15, 199
Supercooled vortex liquid and quantitative theory of melting of the flux line lattice in type II superconductors
A metastable homogeneous state exists down to zero temperature in systems of
repelling objects. Zero ''fluctuation temperature'' liquid state therefore
serves as a (pseudo) ''fixed point'' controlling the properties of vortex
liquid below and even around melting point. There exists Madelung constant for
the liquid in the limit of zero temperature which is higher than that of the
solid by an amount approximately equal to the latent heat of melting. This
picture is supported by an exactly solvable large Ginzburg - Landau model
in magnetic field. Based on this understanding we apply Borel - Pade
resummation technique to develop a theory of the vortex liquid in type II
superconductors. Applicability of the effective lowest Landau level model is
discussed and corrections due to higher levels is calculated. Combined with
previous quantitative description of the vortex solid the melting line is
located. Magnetization, entropy and specific heat jumps along it are
calculated. The magnetization of liquid is larger than that of solid by irrespective of the melting temperature. We compare the result with
experiments on high cuprates , , low material and with Monte Carlo simulations.Comment: 28 pages and 4 figures. Enlarged version of paper cond-mat/0107281
with many new content
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