54 research outputs found
Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the c-axis
We studied a response of Bi-2212 mesa type structures to 100 GHz microwave
radiation. We found that applying magnetic field of about 0.1 T across the
layers enables to observe collective Shapiro step response corresponding to a
synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At
high microwave power we observed up to 10th harmonics of the fundamental
Shapiro step. Besides, we found microwave induced flux-flow step position of
which is proportional to the square root of microwave power and that can exceed
at high enough powers 1 THz operating frequency of IJJ oscillations.Comment: 11 pages including 5 figures, accepted for publication in JETP
Letter
Controlling high-frequency collective electron dynamics via single-particle complexity
We demonstrate, through experiment and theory, enhanced high-frequency
current oscillations due to magnetically-induced conduction resonances in
superlattices. Strong increase in the ac power originates from complex
single-electron dynamics, characterized by abrupt resonant transitions between
unbound and localized trajectories, which trigger and shape propagating charge
domains. Our data demonstrate that external fields can tune the collective
behavior of quantum particles by imprinting configurable patterns in the
single-particle classical phase space.Comment: 5 pages, 4 figure
Vortex fluctuations in underdoped Bi2Sr2CaCu2O8+d crystals
Vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d (Tc=69.4 K)
are studied using Josephson plasma resonance (JPR). From the data in zero
magnetic field, we obtain the penetration depth along the c-axis,
lambda_{L,c}(0) = 229 micrometers and the anisotropy ratio gamma(0) = 600. The
low plasma frequency allows us to study phase correlations over the whole
vortex solid (Bragg-glass) state. The JPR results yield a wandering length
r_{w} of vortex pancakes. The temperature dependence of r_{w} as well as its
increase with applied dc magnetic field can only be explained by the
renormalization of the tilt modulus by thermal fluctuations, and suggest the
latter is responsible for the dissociation of the vortices at the first order
transition.Comment: 4 pages, 5 figures. Submitted to Phys. Rev. Let
Modeling a Superconducting Triplet Spin Valve with Several Layers of a Superconductor
A matrix solution to Usadel linearized equations is used to obtain the critical temperature and distribution of singlet pairing components of a superconductor/ferromagnetic/superconductor/ferromagnetic structure with nonideal boundaries. There is a transition from the π- to the 0-phase state between the superconductor layers upon varying the angle between the magnetizations of ferromagnetic layers in such a structure.</p
Abrupt Change of Josephson Plasma Frequency at the Phase Boundary of the Bragg Glass in Bi_2Sr_2CaCu_2O_{8+\delta}
We report the first detailed and quantitative study of the Josephson coupling
energy in the vortex liquid, Bragg glass and vortex glass phases of
Bi_2Sr_2CaCu_2O_{8+\delta} by the Josephson plasma resonance. The measurements
revealed distinct features in the T- and H-dependencies of the plasma frequency
for each of these three vortex phases. When going across either
the Bragg-to-vortex glass or the Bragg-to-liquid transition line,
shows a dramatic change. We provide a quantitative discussion on the properties
of these phase transitions, including the first order nature of the
Bragg-to-vortex glass transition.Comment: 5pages, 4figure
Josephson Coupling, Phase Correlations, and Josephson Plasma Resonance in Vortex Liquid Phase
Josephson plasma resonance has been introduced recently as a powerful tool to
probe interlayer Josephson coupling in different regions of the vortex phase
diagram in layered superconductors. In the liquid phase, the high temperature
expansion with respect to the Josephson coupling connects the Josephson plasma
frequency with the phase correlation function. This function, in turn, is
directly related to the pair distribution function of the liquid. We develop a
recipe to extract the phase and density correlation functions from the
dependencies of the plasma resonance frequency and the
axis conductivity on the {\it ab}-component of the
magnetic field at fixed {\it c} -component. Using Langevin dynamic simulations
of two-dimensional vortex arrays we calculate density and phase correlation
functions at different temperatures. Calculated phase correlations describe
very well the experimental angular dependence of the plasma resonance field. We
also demonstrate that in the case of weak damping in the liquid phase,
broadening of the JPR line is caused mainly by random Josephson coupling
arising from the density fluctuations of pancake vortices. In this case the JPR
line has a universal shape, which is determined only by parameters of the
superconductors and temperature.Comment: 22 pages, 6 figures, to appear in Phys. Rev. B, December
Quasiparticle and Cooper Pair Tunneling in the Vortex State of Bi-2212
From measurements of the c-axis I-V characteristics of intrinsic Josephson
junctions in Bi_2Sr_2CaCu_2O_{8+delta} (Bi-2212) mesas we obtain the field
dependence (H || c) of the quasiparticle (QP) conductivity, sigma_q(H,T), and
of the Josephson critical current density, J_c(H,T). The quasiparticle
conductivity sigma_q(H) increases sharply with H and reaches a plateau at 0.05
T <H< 0.3 T. We explain such behavior by the dual effect of supercurrents
around vortices. First, they enhance the QP DOS, leading to an increase of
sigma_q with H at low H and, second, they enhance the scattering rate for
specular tunneling as pancakes become disordered along the c-axis at higher H,
leading to a plateau at moderate H.Comment: 4 pages, 4 figure
Effects of an in-plane magnetic field on c-axis sum rule and superfluid density in high- cuprates
In layered cuprates, the application of an in-plane magnetic field changes the c-axis optical sum rule and superfluid density . For
pure incoherent c-axis coupling, has no effect on either quantities
but it does if an additional coherent component is present. For the coherent
contribution, different characteristic variations on and on
temperature result from the constant part of the hopping matrix
element and from the part which has zero on the diagonal of the
Brillouin zone. Only the constant part leads to a dependence on
the direction of as well as on its magnitude.Comment: 3 figure
Evidence for LineLike Vortex Liquid Phase in TlBaCaCuO Probed by the Josephson Plasma Resonance
We measured the Josephson plasma resonance (JPR) in optimally doped
TlBaCaCuO thin films using terahertz time-domain
spectroscopy in transmission. The temperature and magnetic field dependence of
the JPR frequency shows that the c-axis correlations of pancake vortices remain
intact at the transition from the vortex solid to the liquid phase. In this
respect TlBaCaCuO films, withanisotropy parameter
, are similar to the less anisotropic
YBaCuO rather than to the most
anisotropic BiSrCaCuO single crystals ).Comment: Submitted to Physical Review Letter
Asymmetric Field Profile in Bose Glass Phase of Irradiated YBa2Cu3O7-d: Loss of Interlayer Coherence around 1/3 of Matching Field
Magneto-optical imaging in YBa2Cu3O7-d with tilted columnar defects (CD's)
shows an asymmetric critical-state field profile. The observed hysteretic shift
of the profile ridge (trough) from the center of the sample is explained by
in-plane magnetization originated from vortex alignment along CD's. The
extracted ratio of the in-plane to out-of-plane magnetization component has a
maximum at 1/5 of matching field () and disappears above ,
suggesting a reduction of interlayer coherence well bellow in the Bose
glass phase. Implications are discussed in comparison with the vortex liquid
recoupling observed in irradiated Bi2Sr2CaCu2O8+y.Comment: Revtex, 4 pages, 5 figures, also see a movie at
(http://www.ap6.t.u-tokyo.ac.jp/kitaka/Research/d-line/index_e.htm). This
manuscript will appear in Phys. Rev. Let
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