musrfit: A free platform-independent framework for muSR data analysis

A free data-analysis framework for muSR has been developed. musrfit is fully written in C++, is running under GNU/Linux, Mac OS X, as well as Microsoft Windows, and is distributed under the terms of the GNU GPL. It is based on the CERN ROOT framework and is utilizing the Minuit optimization routines for fitting. It consists of a set of programs allowing the user to analyze and visualize the data. The fitting process is controlled by an ascii-input file with an extended syntax. A dedicated text editor is helping the user to create and handle these files in an efficient way, execute the fitting, show the data, get online help, and so on. A versatile tool for the generation of new input files and the extraction of fit parameters is provided as well. musrfit facilitates a plugin mechanism allowing to invoke user-defined functions. Hence, the functionality of the framework can be extended with a minimal amount of overhead for the user. Currently, musrfit can read the following facility raw-data files: PSI-BIN, MDU (PSI), ROOT (LEM/PSI), WKM (outdated ascii format), MUD (TRIUMF), NeXus (ISIS).Comment: 4 pages, 4 figure

Superconductivity in La(1.56)Sr(0.44)CuO(4)/La(2)CuO(4) superlattices

Superlattices of the repeated structure La(1.56)Sr(0.44)CuO(4)/La(2)CuO(4) (LSCO-LCO), where none of the constituents is superconducting, show a superconducting transition of T_c \simeq 25 K. In order to elucidate the nature of the superconducting state we have performed a low-energy muSR study. By applying a magnetic field parallel (Meissner state) and perpendicular (vortex state) to the film planes, we could show that superconductivity is sheet like, resulting in a very anisotropic superconducting state. This result is consistent with a simple charge-transfer model, which takes into account the layered structure and the difference in the chemical potential between LCO and LSCO, as well as Sr interdiffusion. Using a pancake-vortex model we could estimate a strict upper limit of the London penetration depth to 380 nm in these superlattices. The temperature dependence of the muon depolarization rate in field cooling experiments is very similar to what is observed in intercalated BSCCO and suggests that vortex-vortex interaction is dominated by electromagnetic coupling but negligible Josephson interaction.Comment: 4 pages, 3 figure

Zero-field spin depolarization of low-energy muons in ferromagnetic nickel and silver metal

We present zero-fieldmuon-spindepolarization measurements in nickel and silver performed using low-energymuon-spin relaxation technique.Ni or Ag are usually used in this depth-resolved technique as a backing material to enable background subtraction when studying small crystals or materials with weak magnetism. The depolarization rate of the asymmetry in silver and that of the slow relaxing part of the asymmetry in nickel are small(≤ 0.05 μs−1), and weakly temperature and energy-dependent

Nonlocal effect and dimensions of Cooper pairs measured by low-energy muons and polarized neutrons in type-I superconductors

The Pippard coherence length \u3be0 (the size of a Cooper pair) in two extreme type-I superconductors (In and Sn) was determined directly through high-resolution measurement of the nonlocal electrodynamic effect combining low-energy muon spin rotation spectroscopy and polarized neutron reflectometry. The renormalization factor Z=mcp*/2m (mcp* and m are the mass of the Cooper pair and the electron, respectively) resulting from the electron-phonon interaction, and the temperature-dependent London penetration depth \u3bbL(T) were determined as well. An expression linking \u3be0, Z, and \u3bbL(0) is introduced and experimentally verified. This expression allows one to determine experimentally the Pippard coherence length in any superconductor, independent of whether the superconductor is local or nonlocal, conventional or unconventional. \ua9 2013 American Physical Society.Peer reviewed: YesNRC publication: Ye