The role of oxygen in the electron-doped superconducting system Nd2−x Ce x CuO4

Mössbauer effect studies suggest the presence of extraneous oxygen in the whole family of title compounds. At certain concentrations of Ce, oxygen is rather tenaciously bound. Such oxygen causes superparamagnetism in the magnetically ordered material, and also brings about the formation of spin clusters in the metallic material.     

Existence and stability of global regular solutions for a dusty gas model

The initial and initial‐boundary value problems for the two‐phase model of ‘fluid‐solid particles’ media are considered. Existence, uniqueness and exponential decay of global strong solutions for small initial data are proved. Copyright © 2004 John Wiley & Sons, Ltd.     

Magnetic-field-induced Fermi-edge singularity in the tunneling current through an InAs self-assembled quantum dot

The results of the investigation of tunneling transport through a GaAs/(AlGa)As/GaAs single-barrier heterostructure containing InAs self-assembled quantum dots at low temperatures are reported. An anomalous increase in the tunneling current through the quantum dots has been observed in the presence of a magnetic field both parallel and perpendicular to the current. This increase is a manifestation of a Fermi-edge singularity appearing in the current due to the interaction of a tunneling electron with the electron gas in an emitter.     

Field dependence of the muon spin relaxation rate in MnSi

Muon spin rotation/relaxation measurements have been performed in the itinerant helical magnet MnSi at ambient pressure and at 8.3 kbar. We have found the following: (a) the spin-lattice relaxation rate 1/T(1) shows divergence as T1T proportional, variant (T-T(c))(beta) with the power beta larger than 1 near T(c); (b) 1/T(1) is strongly reduced in an applied external field B(L) and the divergent behavior near T(c) is completely suppressed at B(L)> or =4000 G. We discuss that (a) is consistent with the self-consistent renormalization theory and reflects a departure from "mean-field" behavior, while (b) indicates selective suppression of spin fluctuations of the q=0 component by B(L).     

Estimation of a non-negative function

It is pointed out that the problem of estimating a function from the values of a finite number of functionals is often posed, at least partially, as an aesthetic problem rather than as a mathematical one.A particular problem of interpretation of experimental results, arising in the study of radiation source distribution in a plasma, is formulated mathematically in two different ways. Although the two formulations are different in character, they both rely on the idea of imposing a relative likelihood distribution on an appropriate function space; this is particularly fruitful when observational errors are taken into account.     

Persistent current in superconducting nanorings

The superconductivity in very thin rings is suppressed by quantum phase slips. As a result, the amplitude of the persistent current oscillations with flux becomes exponentially small, and their shape changes from sawtooth to a sinusoidal one. We reduce the problem of low-energy properties of a superconducting nanoring to that of a quantum particle in a sinusoidal potential and show that the dependence of the current on the flux belongs to a one-parameter family of functions obtained by solving the respective Schr?dinger equation with twisted boundary conditions.     

Coulomb blockade with dispersive interfaces

What quantity controls the Coulomb blockade oscillations if the dot-lead conductance is essentially frequency dependent? We argue that it is the conductance at the imaginary frequency given by the effective charging energy. The latter may be very different from the bare charging energy due to the interface-induced capacitance (or inductance). These observations are supported by a number of examples, considered from the weak and strong coupling (perturbation theory versus instanton calculus) perspectives.     

Wigner function for highly convergent three-dimensional wave fields

The angle-impact Wigner function for highly convergent three-dimensional scalar wave fields is derived directly by use of the three-dimensional generalized optical transfer function rather than from a six-dimensional Wigner function. The angle-impact Wigner function is a real four-dimensional function from which the intensity at any point in space is readily determined.     

Spin freezing in geometrically frustrated β-Mn probed by muon spin relaxation

Muon spin relaxation was measured down to 0.05 K on a geometrically frustrated metallic system, β-Mn. The observed relaxation rate increases with decreasing temperature and unexpectedly makes a peak at 0.5 K indicating a spin freezing below the temperature. Actually the asymmetry is almost recovered by applying a longitudinal magnetic field of 0.1 T. But since the tail amplitude is more than half and the dynamical relaxation is still appreciable at the lowest temperature, it is likely that the frozen moments are associated with imperfection as oxygen impurity and the intrinsic ground state is fluctuating spin liquid. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase shifting algorithms for non-sinusoidal waveforms with phase shift errors

In phase shifting interferometry, phase errors due to harmonic components of a fringe signal can be minimized by applying synchronous phase shifting algorithms with more than four samples. However, when the phase shift calibration is inaccurate, these algorithms cannot eliminate the effects of a non-sinusoidal waveform. It is shown that by taking a number of samples beyond one period of the fringe pattern, phase errors due to the harmonic components of the fringe signal can be eliminated, even when there exists a constant error in the phase shift interval. A general procedure for constructing phase shifting algorithms that eliminate these errors is derived. A seven-sample phase shifting algorithm is derived as an example, in which the effect of the second harmonic component can be eliminated in the presence of a constant error in the phase shift interval.