Extreme magneto-transport of bulk carbon nanotubes in sorted electronic concentrations and aligned high performance fiber

We explored high-field (60T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classical MR involving electronic mobility. Subtracting high-field fits from the aligned fiber's MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber's room temperature resistance, appears to lack MR field dependence

Spin noise spectroscopy to probe quantum states of ultracold fermionic atomic gases

Ultracold alkali atoms provide experimentally accessible model systems for probing quantum states that manifest themselves at the macroscopic scale. Recent experimental realizations of superfluidity in dilute gases of ultracold fermionic (half-integer spin) atoms offer exciting opportunities to directly test theoretical models of related many-body fermion systems that are inaccessible to experimental manipulation, such as neutron stars and quark-gluon plasmas. However, the microscopic interactions between fermions are potentially quite complex, and experiments in ultracold gases to date cannot clearly distinguish between the qualitatively different microscopic models that have been proposed. Here, we theoretically demonstrate that optical measurements of electron spin noise -- the intrinsic, random fluctuations of spin -- can probe the entangled quantum states of ultracold fermionic atomic gases and unambiguously reveal the detailed nature of the interatomic interactions. We show that different models predict different sets of resonances in the noise spectrum, and once the correct effective interatomic interaction model is identified, the line-shapes of the spin noise can be used to constrain this model. Further, experimental measurements of spin noise in classical (Boltzmann) alkali vapors are used to estimate the expected signal magnitudes for spin noise measurements in ultracold atom systems and to show that these measurements are feasible

A quantitative study of spin noise spectroscopy in a classical gas of 41^{41}K atoms

We present a general derivation of the electron spin noise power spectrum in alkali gases as measured by optical Faraday rotation, which applies to both classical gases at high temperatures as well as ultracold quantum gases. We show that the spin-noise power spectrum is determined by an electron spin-spin correlation function, and we find that measurements of the spin-noise power spectra for a classical gas of $^{41}$K atoms are in good agreement with the predicted values. Experimental and theoretical spin noise spectra are directly and quantitatively compared in both longitudinal and transverse magnetic fields up to the high magnetic field regime (where Zeeman energies exceed the intrinsic hyperfine energy splitting of the $^{41}$K ground state)

Zeeman-effect studies of the electronic absorption spectrum of octachlorodirhenate(2-) (Re(Strictly equivalent to)Re) in pulsed 50-Tesla magnetic fields

Electronic absorption spectra have been measured for crystals of (Bu4N)2[Re2Cl8] at 3.8 K in pulsed magnetic fields (pulse duration ca. 10 ms; field strength to 50 T). Spectra were measured in the 530-600 nm (\u27Band I\u27) and 435-500 nm (\u27Band II\u27) regions, where well resolved vibrational fine structure had been noted in previous spectroscopic studies. Application of magnetic fields up to 50 T caused no measurable splittings or shifts in these two absorption bands. This indicates that both bands are attributable to spin-allowed electronic transitions, since spin-forbidden transitions would be expected to show Zeeman splitting. Possible assignments for Bands I and II include transitions to two 1Eg excited states [1(π,δ*) and 1(δ,π*)], as previously suggested by Bursten et al. (B.E. Bursten, F.A. Cotton, P.E. Fanwick and G.G. Stanley, J. Am. Chem. Soc., 105 (1983) 3082), and to two formally doubly excited states, 1A1g [1(δδ,δ*δ*)] and 1Eu [1(πδ,δ*δ*)]

Some aspects of data processing for an optical absorption experiment in a pulsed 1000-tesla magnet

A procedure is given for the analysis of optical absorption data acquired in the hostile environment of a pulsed 1000-Tesla magnet. © 1998 John Wiley & Sons, Inc