8,111 research outputs found
Homotopy Method for the Large, Sparse, Real Nonsymmetric Eigenvalue Problem
A homotopy method to compute the eigenpairs, i.e., the eigenvectors and eigenvalues, of a given real matrix A1 is presented. From the eigenpairs of some real matrix A0, the eigenpairs of
A(t) ≡ (1 − t)A0 + tA1
are followed at successive "times" from t = 0 to t = 1 using continuation. At t = 1, the eigenpairs of the desired matrix A1 are found. The following phenomena are present when following the eigenpairs of a general nonsymmetric matrix:
• bifurcation,
• ill conditioning due to nonorthogonal eigenvectors,
• jumping of eigenpaths.
These can present considerable computational difficulties. Since each eigenpair can be followed independently, this algorithm is ideal for concurrent computers. The homotopy method has the potential to compete with other algorithms for computing a few eigenvalues of large, sparse matrices. It may be a useful tool for determining the stability of a solution of a PDE. Some numerical results will be presented
FeAs-based superconductivity: a case study of the effects of transition metal doping on BaFe2As2
The recently discovered FeAs-based superconductors are a new, promising set
of materials for both technological as well as basic research. They offer
transition temperatures as high as 55 K as well as essentially isotropic and
extremely large upper, superconducting critical fields in excess of 40 T at 20
K. In addition they may well provide insight into exotic superconductivity that
extends beyond just FeAs-based superconductivity, perhaps even shedding light
on the still perplexing CuO-based high-Tc materials. Whereas superconductivity
can be induced in the RFeAsO (R = rare earth) and AEFe2As2 (AE = Ba, Sr, Ca))
families by a number of means, transition metal doping of BaFe2As2, e.g.
Ba(Fe1-xTMx)2As2, offers the easiest experimental access to a wide set of
materials. In this review we present an overview and summary of the effect of
TM doping (TM = Co, Ni, Cu, Pd, and Rh) on BaFe2As2. The resulting phase
diagrams reveal the nature of the interaction between the structural, magnetic
and superconducting phase transitions in these compounds and delineate a region
of phase space that allows for the stabilization of superconductivity.Comment: edited and shortened version is accepted to AR:Condensed Matter
Physic
An increase in under hydrostatic pressure in the superconducting doped topological insulator NbBiSe
We report an unexpected positive hydrostatic pressure derivative of the
superconducting transition temperature in the doped topological insulator \NBS
via SQUID magnetometry in pressures up to 0.6 GPa. This result is contrary
to reports on the homologues \CBS and \SBS where smooth suppression of is
observed. Our results are consistent with recent Ginzburg-Landau theory
predictions of a pressure-induced enhancement of in the nematic
multicomponent state proposed to explain observations of rotational
symmetry breaking in doped BiSe superconductors.Comment: 5 pages, 5 figure
Signature of the matching field in Bose-glass melting of untwinned YBa_2Cu_3O_(7-δ) single crystals
We map out the phase boundary separating the Bose-glass and vortex-liquid phases in an irradiated twin-free YBa_2Cu_3O_(7-δ) single crystal. We take the phase boundary to be the temperature T_g and magnetic field H at which the crystal begins to screen a small ac magnetic field, h_(ac). There is a significant change in slope dT_g/dH of the phase boundary at the matching field B_Φ (≃0.5 T) indicating that interstitial vortices significantly weaken pinning in the Bose-glass state. There is also a pronounced peak in the slope dT_g/dH just below B_Φ at higher h_(ac). Both features disappear when the field is tilted away from the columns
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