Comment on "Low Temperature Magnetic Instabilities in Triply Charged Fulleride Polymers" by D. Arcon et al., PRL 84, 562 (2000)

Recently, Arcon et al. reported ESR studies of the polymer phase (PP) of Na_{2}Rb_{0.3}Cs_{0.7}C_{60} fulleride. It was claimed that this phase is a quasi-one-dimensional metal above 45 K with a spin-gap below this temperature and has antiferromagnetic(AF) order below 15 K, that is evidenced by antiferromagnetic resonance(AFMR). For the understanding of the rich physics of fullerides it is important to identify the different ground states. ESR has proven to be a useful technique for this purpose. However, since it is a very sensitive probe, it can detect a multitude of spin species and it is not straightforward to identify their origin, especially in a system like Na_{2}Rb_{x}Cs_{1-x}C_{60} with three dopants, when one part of the sample polymerizes but the majority does not. The observation of a low dimensional instability in the single bonded PP would be a novel and important result. Nevertheless, in this Comment we argue that Na_{2}Rb_{0.3}Cs_{0.7}C_{60} is not a good choice for this purpose since, as we show, the samples used by Arcon et al. are inhomogeneous. We point out that recent results on the PP of Na_{2}CsC_{60} contradicts the observation of low dimensional instabilities in Na_{2}Rb_{0.3}Cs_{0.7}C_{60}.Comment: 1 pags, no figure

Bi2Te_xSe_y series studied by resistivity and thermopower

We study the detailed temperature and composition dependence of the resistivity, $\rho(T)$, and thermopower, $S(T)$, for a series of layered bismuth chalcogenides Bi$_2$Te$_{3-x}$Se$_x$, and report the stoichiometry dependence of the optical band gap. In the resistivity of the most compensated member, Bi$_2$Te$_{2.1}$Se$_{0.9}$, we find a low-temperature plateau whose onset temperature correlates with the high-temperature activation energy. For the whole series $S(T)$ can be described by a simple model for an extrinsic semiconductor. By substituting Se for Te, the Fermi level is tuned from the valence band into the conduction band. The maximum values of $S(T)$, bulk band gap as well the activation energy in the resistivity are found for $x \approx 0.9$

Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres

The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin–lattice and spin–spin relaxation times of electrons. Minimizing the effects of spin–orbit coupling and the local magnetic contributions of neighbouring atoms on spin–lattice and spin–spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin–lattice and spin–spin relaxation times of 175 ns at 300 K in 37±7 nm carbon spheres, which is remarkably long for any conducting solid- state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature

Polymeric alkali fullerides are stable in air

Infrared transmission, electron spin resonance, and X-ray diffraction measurements show unambiguously that RbC$_{60}$ and KC$_{60}$ are stable in air, in contrast to Rb$_{6}$C$_{60}$ which decomposes rapidly upon exposure. The specimens studied transform into pure C$_{60}$ and other byproducts when heated above 100\dd C, approximately the temperature of the orthorhombic-fcc phase transition. The stability of these compounds raises the possibility of applying them as protective layers for the superconducting fullerides.Comment: Scheduled for publication in Appl. Phys. Lett. 66, 20 Feb. 1995, typeset in REVTEX v3.0 in LaTeX. Postscript file including all figures is available on WWW http://insti.physics.sunysb.edu/~mmartin/ under my list of publications, or will be e-mailed by request

Rapid thickness reading of CH3NH3PbI3 nanowire thin films from color maps

Hybrid halide perovskite photovoltaic materials show a remarkable light conversion efficiency in various optoelectronic devices. In the fabrication of these solar cells, light emitting diodes, laser and photodetector prototypes the thickness of the perovskite is an important parameter since the light is absorbed within a thin layer of a few hundred nanometers. Nevertheless, making perovskite coatings with various solution-based and evaporation methods showing highly reproducible thickness and area coverage is still an issue. Therefore, rapid and reliable quality-control of the film morphology is needed. This report shows a simple, rapid, and calibration-free method for reading the thickness directly from the color map of nanowire perovskite films seen in standard optical microscope with visible light. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

CH3NH3PbI3: precise structural consequences of water absorption at ambient conditions

The crystal structure of the pristine (I) and aged (II) crystals of CH3NH3PbI3 (hereafter MAPbI(3)) hybrid organic-inorganic lead iodide has been studied at 293 K with high-precision single-crystal X-ray diffraction using a synchrotron light source. We show that (I) and (II) are characterized by an identical tetragonal unit cell but different space groups: I422 for (I) and P4(2)2(1)2 for (II). Both space groups are subgroups of I4/ mcm, which is widely used for MAPbI(3). The main difference between (I) and (II) comes from the difference in hydrogen bonds between the MA(+) cation and the PbI3 framework which is the direct consequence of H2O insertion in the aged crystal (II)