363 research outputs found
Thermodynamic evidence for valley-dependent density of states in bulk bismuth
Electron-like carriers in bismuth are described by the Dirac Hamiltonian,
with a band mass becoming a thousandth of the bare electron mass along one
crystalline axis. The existence of three anisotropic valleys offers electrons
an additional degree of freedom, a subject of recent attention. Here, we map
the Landau spectrum by angle-resolved magnetostriction, and quantify the
carrier number in each valley: while the electron valleys keep identical
spectra, they substantially differ in their density of states at the Fermi
level. Thus, the electron fluid does not keep the rotational symmetry of the
lattice at low temperature and high magnetic field, even in the absence of
internal strain. This effect, reminiscent of the Coulomb pseudo-gap in
localized electronic states, affects only electrons in the immediate vicinity
of the Fermi level. It presents the most striking departure from the
non-interacting picture of electrons in bulk bismuth.Comment: 6 pages, 3 Figure
Low-temperature thermopower study of YbRh2Si2
The heavy-fermion compound YbRh2Si2 exhibits an antiferromagnetic (AFM) phase
transition at an extremely low temperature of TN = 70 mK. Upon applying a tiny
magnetic field of Bc = 60 mT the AFM ordering is suppressed and the system is
driven toward a field-induced quantum critical point (QCP). Here, we present
low-temperature thermopower S(T) measurements of high-quality YbRh2Si2 single
crystals down to 30 mK. S(T) is found negative with comparably large values in
the paramagnetic state. In zero field no Landau-Fermi-liquid (LFL) like
behavior is observed within the magnetically ordered phase. However, a sign
change from negative to positive appears at lowest temperatures on the magnetic
side of the QCP. For higher fields B > Bc a linear extrapolation of S to zero
clearly evidences the recovery of LFL regime. The crossover temperature is
sharply determined and coincides perfectly with the one derived from
resistivity and specific heat investigations.Comment: LT25 conference proceedings in Journal of Physics: Conference Serie
Intelligent controlling microbubble radial oscillations by using Slave-Master Feedback control
Dynamics of acoustically driven microbubbles in ultrasonic fields are known to be complex and uncontrollable phenomena indicative of a highly active nonlinear as well as chaotic behavior. In this paper, a method based on Slave-Master Feedback (SMF) to suppress unstable radial oscillations of contrast agents is presented. In the proposed control process, the encapsulated microbubbles as the slave system is coupled with a dynamical system as the master, so that the output of the coupled system is able to produce a stable oscillation. A great virtue of this control technique is its flexibility. In comparison with existing techniques, the present dynamical chaos control method does not need to know more than one variable. The numerical results show its strong impact on reducing the chaotic oscillations to regular ones. © 2014 Elsevier Inc. All rights reserved
Effect of controlled disorder on quasiparticle thermal transport in BiSrCaCuO
Low temperature thermal conductivity, , of optimally-doped Bi2212 was
studied before and after the introduction of point defects by electron
irradiation. The amplitude of the linear component of remains
unchanged, confirming the universal nature of heat transport by zero-energy
quasiparticles. The induced decrease in the absolute value of at
finite temperatures allows us to resolve a nonuniversal term in due to
conduction by finite-energy quasiparticles. The magnitude of this term provides
an estimate of the quasiparticle lifetime at subkelvin temperatures.Comment: 5 pages including 2 .eps figuer
Chaotic behavior of gas bubble in non-Newtonian fluid: A numerical study
In the present paper, the nonlinear behavior of bubble growth under the excitation of an acoustic pressure pulse in non-Newtonian fluid domain has been investigated. Due to the importance of the bubble in the medical applications such as drug, protein or gene delivery, blood is assumed to be the reference fluid. Effects of viscoelasticity term, Deborah number, amplitude and frequency of the acoustic pulse are studied. We have studied the dynamic behavior of the radial response of bubble using Lyapunov exponent spectra, bifurcation diagrams, time series and phase diagram. A period-doubling bifurcation structure is predicted to occur for certain values of the effects of parameters. The results show that by increasing the elasticity of the fluid, the growth phenomenon will be unstable. On the other hand, when the frequency of the external pulse increases the bubble growth experiences more stable condition. It is shown that the results are in good agreement with the previous studies. © 2013 Springer Science+Business Media Dordrecht
Angular position of nodes in the superconducting gap of YBCO
The thermal conductivity of a YBCO single crystal has been studied as a
function of the relative orientation of the crystal axes and a magnetic field
rotating in the Cu-O planes. Measurements were carried out at several
temperatures below T_c and at a fixed field of 30 kOe. A four-fold symmetry
characteristic of a superconducting gap with nodes at odd multiples of 45
degrees in k-space was resolved. Experiments were performed to exclude a
possible macroscopic origin for such a four-fold symmetry such as sample shape
or anisotropic pinning. Our results impose an upper limit of 10% on the weight
of the s-wave component of the essentially d-wave superconducting order
parameter of YBCO.Comment: 10 pages, 4 figure
Skutterudite Results Shed Light on Heavy Fermion Physics
Only few selected examples among the great diversity of anomalous rare earth
skutterudite are reviewed. Focus is first given on PrFe4P12 in comparison with
URu2Si2. For PrFe4P12, great progress has been made on determining the nature
of the order parameter (OP). A non magnetic order parameter with a multipolar
component emerges here while for URu2Si2 the nature of the so-called hidden
order remains mysterious. The two systems have several similarities in their
temperature--pressure (T, P) and magnetic field--temperature (H, T) phase
diagrams, in their spin dynamics, in their nesting character and in their high
sensitivity to impurities. Advances on one side must stimulate new views on the
other. Besides general considerations on the choice of the OP, a simple basic
problem is the treatment of the Kondo coupling in a system with low charge
carrier number for the cases of uncompensated and compensated semi-metal. An
interesting problem is also the possible decoupling between exciton modes and
itinerant carriers.Comment: 8 pages, 10 figures, proceedings of International Conference on "New
Quantum Phenomena in Skutterudite and Related Systems
High-field muSR studies of superconducting and magnetic correlations in cuprates above Tc
The advent of high transverse-field muon spin rotation (TF-muSR) has led to
recent muSR investigations of the magnetic-field response of cuprates above the
superconducting transition temperature T_c. Here the results of such
experiments on hole-doped cuprates are reviewed. Although these investigations
are currently ongoing, it is clear that the effects of high field on the
internal magnetic field distribution of these materials is dependent upon a
competition between superconductivity and magnetism. In La_{2-x}Sr_xCuO_4 the
response to the external field above Tc is dominated by heterogeneous spin
magnetism. However, the magnetism that dominates the observed inhomogeneous
line broadening below x ~ 0.19 is overwhelmed by the emergence of a completely
different kind of magnetism in the heavily overdoped regime. The origin of the
magnetism above x ~ 0.19 is currently unknown, but its presence hints at a
competition between superconductivity and magnetism that is reminiscent of the
underdoped regime. In contrast, the width of the internal field distribution of
underdoped YBa_2Cu_3O_y above Tc is observed to track Tc and the density of
superconducting carriers. This observation suggests that the magnetic response
above Tc is not dominated by electronic moments, but rather inhomogeneous
fluctuating superconductivity.Comment: 28 pages, 11 figures, 104 reference
Insulator-Metal Transition in One Dimension Induced by Long-Range Electronic Interactions
The effects of a long range electronic potential on a one dimensional
commensurate Charge Density Wave (CDW) state are investigated. Using numerical
techniques it is shown that a transition to a metallic ground state is reached
as the range of the electron-electron repulsion increases. In this metallic
state, the optical conductivity exhibits a large Drude weight. Possible
interpretations of our results are discussed.Comment: 5 pages, Revtex, minor misprints corrected and a reference to earlier
work by V. Emery and C. Noguera adde
Hierarchy of piecewise non-linear maps with non-ergodicity behavior
We study the dynamics of hierarchy of piecewise maps generated by
one-parameter families of trigonometric chaotic maps and one-parameter families
of elliptic chaotic maps of and types, in detail.
We calculate the Lyapunov exponent and Kolmogorov-Sinai entropy of the these
maps with respect to control parameter. Non-ergodicity of these piecewise maps
is proven analytically and investigated numerically . The invariant measure of
these maps which are not equal to one or zero, appears to be characteristic of
non-ergodicity behavior. A quantity of interest is the Kolmogorov-Sinai
entropy, where for these maps are smaller than the sum of positive Lyapunov
exponents and it confirms the non-ergodicity of the maps.Comment: 18 pages, 8 figure
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