Conversion of glassy antiferromagnetic-insulating phase to equilibrium ferromagnetic-metallic phase by devitrification and recrystallization in Al substituted Pr0.5{_{0.5}}Ca0.5_{0.5}MnO3{_3}

We show that Pr${_{0.5}}$Ca$_{0.5}$MnO${_3}$ with 2.5% Al substitution and La${_{0.5}}$Ca$_{0.5}$MnO${_3}$ (LCMO) exhibit qualitatively similar and visibly anomalous M-H curves at low temperature. Magnetic field causes a broad first-order but irreversible antiferromagnetic (AF)-insulating (I) to ferromagnetic (FM)-metallic (M) transition in both and gives rise to soft FM state. However, the low temperature equilibrium state of Pr$_{0.5}$Ca$_{0.5}$Mn$_{0.975}$Al$_{0.025}$O$_3$ (PCMAO) is FM-M whereas that of LCMO is AF-I. In both the systems the respective equilibrium phase coexists with the other phase with contrasting order, which is not in equilibrium, and the cooling field can tune the fractions of the coexisting phases. It is shown earlier that the coexisting FM-M phase behaves like `magnetic glass' in LCMO. Here we show from specially designed measurement protocols that the AF-I phase of PCMAO has all the characteristics of magnetic glassy states. It devitrifies on heating and also recrystallizes to equilibrium FM-M phase after annealing. This glass-like AF-I phase also shows similar intriguing feature observed in FM-M magnetic glassy state of LCMO that when the starting coexisting fraction of glass is larger, successive annealing results in larger fraction of equilibrium phase. This similarity between two manganite systems with contrasting magnetic orders of respective glassy and equilibrium phases points toward a possible universality.Comment: Highlights potential of CHUF (Cooling and Heating in Unequal Fields), a new measurement protoco

Coexisting tuneable fractions of glassy and equilibrium long-range-order phases in manganites

Antiferromagnetic-insulating(AF-I) and the ferromagnetic-metallic(FM-M) phases coexist in various half-doped manganites over a range of temperature and magnetic field, and this is often believed to be an essential ingredient to their colossal magnetoresistence. We present magnetization and resistivity measurements on Pr(0.5)Ca(0.5)Mn(0.975)Al(0.025)O(3) and Pr(0.5)Sr(0.5)MnO(3) showing that the fraction of the two coexisting phases at low-temperature in any specified measuring field H, can be continuously controlled by following designed protocols traversing field-temperature space; for both materials the FM-M fraction rises under similar cooling paths. Constant-field temperature variations however show that the former sample undergoes a 1st order transition from AF-I to FM-M with decreasing T, while the latter undergoes the reverse transition. We suggest that the observed path-dependent phase-separated states result from the low-T equilibrium phase coexisting with supercooled glass-like high temperature phase, where the low-T equilibrium phases are actually homogeneous FM-M and AF-I phases respectively for the two materials

T invariance of Higgs interactions in the standard model

In the standard model, the Cabibbo-Kobayashi-Maskawa matrix, which incorporates the time-reversal violation shown by the charged current weak interactions, originates from the Higgs-quark interactions. The Yukawa interactions of quarks with the physical Higgs particle can contain further complex phase factors, but nevertheless conserve T, as shown by constructing the fermion T transformation and the invariant euclidean fermion measure.Comment: LaTeX, 4 pages; presented at PASCOS'0

Near infra-red spectroscopy of V838 Monocerotis

Near IR, multi-epoch, spectroscopic and photometric observations of the enigmatic, eruptive variable V838 Mon in JHK bands are reported. One of the unusual features is the detection of several strong neutral TiI lines in emission in the K band. From the strength of these lines, the mass of the ejected envelope is estimated to be in the range 10e-7 to 10e-5 M(sun). The spectra also show the strong presence of the first and second overtones of 12CO bands seen in the K and H bands. The CO bands show a complex evolution. Deep water bands at 1.4 and 1.9 micron are also seen later in the object's evolution. Blackbody fits to the JHK photometric data show that V838 Mon has evolved to temperatures between 2400 - 2600 K by approximately 130 days after outburst. The spectra at this stage have the general characteristics of a very cool M giant.Comment: 7 pages, 5 figures, to appear in Astronomy and Astrophysic