THz time-domain spectroscopy of mixed CO2–CH3OH interstellar ice analogs

The icy mantles of interstellar dust grains are the birthplaces of the primordial prebiotic molecular inventory that may eventually seed nascent solar systems and the planets and planetesimals that form therein. Here, we present a study of two of the most abundant species in these ices after water: carbon dioxide (CO2) and methanol (CH3OH), using TeraHertz (THz) time-domain spectroscopy and mid-infrared spectroscopy. We study pure and mixed-ices of these species, and demonstrate the power of the THz region of the spectrum to elucidate the long-range structure (i.e. crystalline versus amorphous) of the ice, the degree of segregation of these species within the ice, and the thermal history of the species within the ice. Finally, we comment on the utility of the THz transitions arising from these ices for use in astronomical observations of interstellar ices

55Mn NMR and magnetization studies of La0.67Sr0.33MnO3 thin films

55Mn nuclear magnetic resonance and magnetization studies of the series of La0.67Sr0.33MnO3 thin films have been performed at low temperature. Two distinct lines were observed, at 322 MHz and 380 MHz, corresponding to two different phases, the former located at the interface, with localized charges, and the latter corresponding to the film bulk, with itinerant carriers (as it was also found in Ca manganite films). The spin-echo amplitude was measured as a function of a dc magnetic field applied either in the film plane or perpendicular to it. The field dependence of both the main NMR signal intensity and frequency shift is quite consistent with that calculated in a simple single domain model. The best fit to the model shows that magnetization rotation processes play a dominant role when the applied field exceeds the effective anisotropy field. Distinctly different magnetic anisotropies are deduced from the interface NMR signal.Comment: 7 pages, 8 figure

Modification of magnetic and transport properties of manganite layers in Au/La_0.67Sr_0.33MnO_3/SrTiO_3 interfaces

The effect of gold capping on magnetic and transport properties of optimally doped manganite thin films is studied. An extraordinary suppression of conductivity and magnetic properties occurs in epitaxial (001) La_0.67Sr_0.33MnO_3 (LSMO) films grown on SrTiO_3 upon deposition of 2 nm of Au: in the case of ultrathin films of LSMO (4 nm thick) the resistivity increases by four orders of magnitude while the Curie temperature decreases by 180 K. Zero-field 55Mn nuclear magnetic resonance reveals a significant reduction of ferromagnetic double-exchange mechanism in manganite films upon the gold capping. We find evidence for the formation of a 1.9-nm thick magnetic "dead-layer" at the Au/LSMO interface, associated with the creation of interfacial non double-exchange insulating phases.Comment: 4 figure

Critical chain length and superconductivity emergence in oxygen-equalized pairs of YBa2Cu3O6.30

The oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is studied, for the first time in a comparative way, on pair samples having the same oxygen content and thermal history, but different Cu(1)Ox chain arrangements deriving from their intercalated and deintercalated nature. Structural and electronic non-equivalence of pairs samples is detected in the critical region and found to be related, on microscopic scale, to a different average chain length, which, on being experimentally determined by nuclear quadrupole resonance (NQR), sheds new light on the concept of critical chain length for hole doping efficiency.Comment: 7 RevTex pages, 2 Postscript figures. Submitted to Phys. Rev.

Nonlinear terahertz coherent excitation of vibrational modes of liquids

We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detection with an optical pulse. The spectrometer reported here has broader terahertz frequency coverage, and an increased sensitivity relative to previously reported terahertz Kerr effect experiments. Vibrational coherences are observed in liquid diiodomethane at 3.66 THz (122 cm^(−1)), and in carbon tetrachloride at 6.50 THz (217 cm^(−1)), in exact agreement with literature values of those intramolecular modes. This work opens the door to 2D spectroscopies, nonlinear in terahertz field, that can study the dynamics of condensed-phase molecular systems, as well as coherent control at terahertz frequencies

Hydrogen bonding in the ethanol–water dimer

We report the first rotational spectrum of the ground state of the isolated ethanol–water dimer using chirped-pulse Fourier transform microwave spectroscopy between 8–18 GHz. With the aid of isotopic substitutions, and ab initio calculations, we identify the measured conformer as a water-donor/ethanol-acceptor structure. Ethanol is found to be in the gauche conformation, while the monomer distances and orientations likely reflect a cooperation between the strong (O–H⋯O) and weak (C–H⋯O) hydrogen bonds that stabilizes the measured conformer. No other conformers were assigned in an argon expansion, confirming that this is the ground-state structure. This result is consistent with previous vibrationally-resolved Raman and infrared work, but sheds additional light on the structure, due to the specificity of rotational spectroscopy

Effect of two gaps on the flux lattice internal field distribution: evidence of two length scales from muSR in Mg1-xAlxB2

We have measured the transverse field muon spin precession in the flux lattice (FL) state of the two gap superconductor MgB2 and of the electron doped compounds Mg1-xAlxB2 in magnetic fields up to 2.8T. We show the effect of the two gaps on the internal field distribution in the FL, from which we determine two coherence length parameters and the doping dependence of the London penetration depth. This is an independent determination of the complex vortex structure already suggested by the STM observation of large vortices in a MgB2 single crystal. Our data agrees quantitatively with STM and we thus validate a new phenomenological model for the internal fields.Comment: now in press Phys. Rev. Lett., small modifications required by the edito

Influence of Nd on the magnetic properties of Nd1-xCaxMnO3

The role played by the Nd ions in the magnetic properties of Nd0.5Ca0.5MnO3 and Nd0.7Ca0.3MnO3 is studied using static magnetization, neutron diffraction and high frequency (9.4-475GHz) Electron Spin Resonance. We show that the Nd ions are weakly coupled to the Mn ions via ferromagnetic exchange and are responsible for the peculiar ferromagnetic resonance observed in the FM phase of both compounds (ground state below 120K for x=0.3, high field state for x=0.5). We then use ESR to look for magnetic phase separation in the low field, CO phase of Nd0.5Ca0.5MnO3. We show that there is no trace of the FM phase imbedded in the CO phase, contrary to what is observed in La0.5Ca0.5MnO3 or Pr0.5Sr0.5MnO3.Comment: to be published in phys.Rev.B as a Rapid Com

Correlated trends of coexisting magnetism and superconductivity in optimally electron-doped oxy-pnictides

We report on the recovery of the short-range static magnetic order and on the concomitant degradation of the superconducting state in optimally F-doped SmFe_(1-x)Ru_(x)AsO_0.85F_0.15 for 0.1< x<0.6. The two reduced order parameters coexist within nanometer-size domains in the FeAs layers and finally disappear around a common critical threshold x_c=0.6. Superconductivity and magnetism are shown to be closely related to two distinct well-defined local electronic environments of the FeAs layers. The two transition temperatures, controlled by the isoelectronic and diamagnetic Ru substitution, scale with the volume fraction of the corresponding environments. This fact indicates that superconductivity is assisted by magnetic fluctuations, which are frozen whenever a short-range static order appears, and totally vanish above the magnetic dilution threshold x_c.Comment: Approved for publication in Phys. Rev. Letter