Contrasting behavior of the 5/2 and 7/3 fractional quantum Hall effect in a tilted field

Using a tilted-field geometry, the effect of an in-plane magnetic field on the even denominator nu=5/2 fractional quantum Hall state is studied. The energy gap of the nu=5/2 state is found to collapse linearly with the in-plane magnetic field above approximately 0.5 T. In contrast, a strong enhancement of the gap is observed for the nu=7/3 state. The radically distinct tilted-field behavior between the two states is discussed in terms of Zeeman and magneto-orbital coupling within the context of the proposed Moore-Read Pfaffian wave function for the 5/2 fractional quantum Hall effect.     

Evidence of a first-order phase transition between Wigner-crystal and bubble phases of 2D electrons in higher Landau Levels

For filling factors nu in the range between 4.16 and 4.28, we simultaneously detect two resonances in the real diagonal microwave conductivity of a two-dimensional electron system (2DES) at low temperature T approximately 35 mK. We attribute the resonance to Wigner-crystal and Bubble phases of the 2DES in higher Landau Levels. For nu below and above this range, only single resonances are observed. The coexistence of both phases is taken as evidence of a first-order phase transition. We estimate the transition point as nu=4.22.     

Rovibrational Analysis of the nu(2) Band of Diazirine-d(2)

The gas-phase IR spectrum of the nu(2) (A(1), 1610.33 cm(-1)) band of the deuterated isotopomer of diazirine, D(2)CN(2), a three-membered ring compound which belongs to the molecular symmetry point group C(2v), has been studied at a resolution of about 0.005 cm(-1). This vibrational mode which can be approximately described as N&dbond;N stretching is widely perturbed. This is due to various interactions with the tetrad consisting of the binary combinations nu(6) + nu(7) (A(1)), nu(7) + nu(9) (A(2)), nu(5) + nu(6) (B(2)), and nu(5) + nu(9) (B(1)), which form a relatively isolated pentad together with nu(2) in the wavenumber region 1560-1610 cm(-1). A simultaneous upper state analysis of nu(2) from a pentad model including these resonances has been performed and a set of spectroscopic parameters has been obtained. Since the four combination bands of the pentad are dark states, only band centers could be determined; in addition for nu(5) + nu(9) and nu(7) + nu(9) also the term (B - C)/2 has been obtained. A number of Coriolis interaction constants and the vibrational resonance (with nu(6) + nu(7)) parameter have been calculated as well. Copyright 2001 Academic Press.     

Search for a W' boson decaying to a top and bottom quark pair in 1.8 TeV pp collisions

We report the results of a search for a W' boson produced in pp; collisions at a center-of-mass energy of 1.8 TeV using a 106 pb(-1) data sample recorded by the Collider Detector at Fermilab. We observe no significant excess of events above background for a W' boson decaying to a top and bottom quark pair. In a model where this boson would mediate interactions involving a massive right-handed neutrino (nu(R)) and have standard model strength couplings, we use these data to exclude a W' boson with mass between 225 and 536 GeV/c(2) at 95% confidence level for M(W')>M(nu(R)) and between 225 and 566 GeV/c(2) at 95% confidence level for M(W')相似文献   

High-Resolution Study of the Mid-Infrared Region of FNO(2)

Of the gas-phase IR spectrum of nitrylfluoride, FNO(2), between 1200 and 1900 cm(-1), the bands nu(4), 2nu(6), nu(2) + nu(3), and nu(1) have been studied at a resolution of ca. 0.003 cm(-1). Improved ground state rotational and centrifugal distortion constants have been obtained from a simultaneous analysis of the data from F. Hegelund, H. Bürger, and G. Pawelke [J. Mol. Spectrosc. 184, 350-361 (1997)] and the present data from nu(4) and nu(1). The nu(4) and 2nu(6) bands are free from local perturbations, and upper state spectroscopic constants have been obtained from the conventional Watson Hamiltonian. The bands nu(1) and nu(2) + nu(3) are strongly perturbed by Coriolis interactions with the nearby dark levels nu(5) + nu(6), nu(3) + nu(6), and nu(2) + nu(5). Upper state constants for nu(1) and nu(2) + nu(3) are obtained from triad and tetrad models, respectively, including Coriolis resonances within this system. In addition Coriolis interaction parameters and the vibrational energies for the three dark states together with some of their rotational constants are determined from the observed perturbation effects on nu(1) and nu(2) + nu(3). Copyright 2000 Academic Press.     

High-Resolution Infrared Spectra in the C-H Region of CH2F2: The nu6 and 2nu2 Bands

High-resolution, infrared absorption spectra of the nu6 (asymmetric C-H stretch) and 2nu2 (H-C-H symmetric bend overtone) bands of jet-cooled CH2F2 are reported with a sub-Doppler resolution of approximately 0.002 cm-1. More than 600 transitions were observed in the range of 3002-3036 cm-1, of which 268 were assigned the nu6 fundamental and 184 were assigned to the 2nu2 overtone. A fit of the nu6 band to the A-reduced Watson Hamiltonian yielded eight effective constants including nu0 = 3014.0503(1), A' = 1.62868(4), B' = 0.354165(5), and C' = 0.308852(3) cm-1. Similarly, the weaker 2nu2 band was fit to seven parameters including nu0 = 3026.2297(2), and A' = 1.63396(6), B' = 0.35367(1), and C' = 0.31183(1) cm-1. Numbers in parentheses are two standard deviations in units of the last digit. Anomalous values of the A rotational constant and the DeltaK centrifugal distortion constant are attributed to an a-axis Coriolis interaction between the 2nu2 and nu6 bands. The relative intensity of the 2nu2 band is used to estimate the stretch-bend anharmonic interaction with nu1. Copyright 1999 Academic Press.     

High-Resolution Fourier Transform Spectra of HDSe: The Interacting States (v(1) v(2) v(3))/(v(1) +/- 1 v(2) -/+ 2 v(3)) with 2v(1) + v(2) = 1, 2, 3, and 4

For the first time, high-resolution Fourier transform spectra of HDSe in the region of the three polyads, nu(1)/2nu(2), nu(1) + nu(2)/3nu(2), and 2nu(1)/nu(1) + 2nu(2)/nu(2) + nu(3), have been recorded and analyzed. Combined with an earlier investigation of the nu(2) band, and including estimates for the unobserved "dark" 4nu(2) band, these levels were subjected to a "Global Fit," which makes use of relations between parameters within the different polyads. Since there are five isotopic species present in natural HD(M)Se (M = 82, 80, 78, 77, 76), altogether 34 vibration-rotation bands have been studied in the present contribution. The parameters determined by the Global Fit reproduce upper vibrational-rotational energies of all these bands with accuracies close to experimental precision. Copyright 2000 Academic Press.     

New phase transition between partially and fully polarized quantum Hall states with charge and spin gaps at nu = 2/3

The average electron spin polarization Rho of a two-dimensional electron gas confined in GaAs/GaAlAs multiple quantum wells was measured by NMR near the fractional quantum Hall state with filling factor nu = 2/3. Above this filling factor (2/3< or = nu < 0.85), a strong depolarization is observed corresponding to two spin flips per additional flux quantum. The most remarkable behavior of the polarization is observed at nu = 2/3, where a quantum phase transition from a partially polarized (Rho approximately 3/4) to a fully polarized (Rho = 1) state can be driven by increasing the ratio between the Zeeman and the Coulomb energy above a critical value eta(c) = Delta(Z)/Delta(C) = 0.0185.     

Search for pi(0)-->nu(mu)nu(mu) decays in the LSND detector

We observe a net beam excess of 8.7+/-6.3(stat)+/-2.4(syst) events, above 160 MeV, resulting from the charged-current reaction of nu(micro) and/or nu;(mu) on C and H in the LSND detector. No beam-related muon background is expected in this energy regime. Within an analysis framework of pi(0)-->nu(mu)nu;(mu), we set a direct upper limit for this branching ratio of Gamma(pi(0)-->nu(mu)nu;(mu))/Gamma(pi(0)-->all)<1.6 x 10(-6) at 90% confidence level.     

Response to tilted magnetic fields in Bi(2)Sr(2)CaCu(2)O(8) with columnar defects: evidence for transverse Meissner effect

The transverse Meissner effect (TME) in the highly layered superconductor Bi(2)Sr(2)CaCu(2)O(8+y) with columnar defects is investigated by transport measurements. We present evidence for the persistence of the Bose glass phase for H(perpendicular)H(+)(perpendicular c), moving kink chains consistent with a commensurate-incommensurate transition scenario are observed. These results show the existence of the TME for H(perpendicular)相似文献   

High Resolution FTIR Spectroscopy of DCCCl: Anharmonic Resonances in the nu(1) and nu(2) Bands

High-resolution infrared spectra of the nu(1) and nu(2) bands of DCCCl were observed using Bruker IFS 120HR Fourier transform spectrometers at resolutions of 0.0044 and 0.0035 cm(-1), respectively. For the DCC(35)Cl isotopomer, the nu(1) as well as the nu(2) band was found to be heavily perturbed. Detailed analyses revealed that the nu(1) state is in resonance with the l=0 substate of the nu(3)+4nu(4) state and that the nu(2) state is in resonance with the l=0 substate of the nu(3)+4nu(5) state. The rotational constants played a key role in identifying the perturbing states. In contrast, for the DCC(37)Cl isotopomer, the rotational structures of the nu(1) and nu(2) states are almost regular but slightly perturbed by interactions with the nu(3)+4nu(4) and nu(3)+4nu(5) states, respectively. The constants of resonances as well as the molecular constants for the nu(1), nu(2), nu(3)+4nu(4) and nu(3)+4nu(5) states were determined. Copyright 2001 Academic Press.     

Neutrino mass hierarchy and stepwise spectral swapping of supernova neutrino flavors

We examine a phenomenon recently predicted by numerical simulations of supernova neutrino flavor evolution: the swapping of supernova nu(e) and nu(mu,tau) energy spectra below (above) energy E(C) for the normal (inverted) neutrino mass hierarchy. We present the results of large-scale numerical calculations which show that in the normal neutrino mass hierarchy case, E(C) decreases as the assumed effective 2x2 vacuum nu(e)<==>nu(mu,tau) mixing angle (approximately theta13) is decreased. In contrast, these calculations indicate that E(C) is essentially independent of the vacuum mixing angle in the inverted neutrino mass hierarchy case. With a good neutrino signal from a future galactic supernova, the above results could be used to determine the neutrino mass hierarchy even if theta13 is too small to be measured by terrestrial neutrino oscillation experiments.     

Simultaneous Analysis of the nu(2) Raman and nu(2) + nu(6) Infrared Spectra of the SF(6) Molecule

High-resolution Raman spectra of the nu(2) band of SF(6) have been recorded at a temperature of 195 K (dry ice) and a pressure of 39 mbar. These spectra were analyzed using a new set of programs specially written for XY(6) molecules. These programs, called HTDS (highly spherical top data system) in reference to the set of programs called STDS (spherical top data system written for XY(4) molecules) can be freely accessible through ftp (user anonymous) at jupiter.u-bourgogne.fr or on the web at the URL http://www.u-bourgogne.fr/LPUB/shTDS.html. The study of nu(2) was made using a Hamiltonian developed through the third order. Four parameters were determined. The standard deviation obtained using about 559 data up to J < 61 is 0.0021 cm(-1). This result is used to refine by simultaneous analysis the nu(2) and nu(2) + nu(6) bands of SF(6). This new fit allows the determination for the first time of some nu(6) parameters. The values obtained for this band (forbidden in Raman and in infrared) will be used to study the infrared hot bands in the nu(3) and nu(4) regions. Copyright 2000 Academic Press.     

Vibrational–Rotational Analysis of the Hot 2ν2–ν2 Band of the 15NH2D and 15NHD2 Molecules

Optics and Spectroscopy - High-resolution spectra of the $$2{{\nu }_{2}}{-} {{\nu }_{2}}$$ hot band of the 15NH2D and 15NHD2 molecules are investigated for the first time. The analysis is carried...     

Evidence for superfluidity in a resonantly interacting Fermi gas

We observe collective oscillations of a trapped, degenerate Fermi gas of 6Li atoms at a magnetic field just above a Feshbach resonance, where the two-body physics does not support a bound state. The gas exhibits a radial breathing mode at a frequency of 2837(05) Hz, in excellent agreement with the frequency of nu(H) identical with sqrt[10nu(x)nu(y)/3]=2830(20) Hz predicted for a hydrodynamic Fermi gas with unitarity-limited interactions. The measured damping times and frequencies are inconsistent with predictions for both the collisionless mean field regime and for collisional hydrodynamics. These observations provide the first evidence for superfluid hydrodynamics in a resonantly interacting Fermi gas.     

Odd-integer quantum Hall effect in graphene: interaction and disorder effects

We study the competition between the long-range Coulomb interaction, disorder scattering, and lattice effects in the integer quantum Hall effect (IQHE) in graphene. By direct transport calculations, both nu=1 and nu=3 IQHE states are revealed in the lowest two Dirac Landau levels. However, the critical disorder strength above which the nu=3 IQHE is destroyed is much smaller than that for the nu=1 IQHE, which may explain the absence of a nu=3 plateau in recent experiments. While the excitation spectrum in the IQHE phase is gapless within numerical finite-size analysis, we do find and determine a mobility gap, which characterizes the energy scale of the stability of the IQHE. Furthermore, we demonstrate that the nu=1 IQHE state is a Dirac valley and sublattice polarized Ising pseudospin ferromagnet, while the nu=3 state is an xy plane polarized pseudospin ferromagnet.     

Rovibrational Study of the CH(2) Wagging Fundamental of Monofluoroacetonitrile

The vapor-phase infrared spectrum of monofluoroacetonitrile (CH(2)FCN) has been recorded at high resolution in the nu(4) band region (1363-1398 cm(-1)) using a tunable diode laser spectrometer. A detailed assignment of the rotational structure of the expected a-/b-hybrid band has been made for a-type transitions with K(a)相似文献   

Analysis of Rovibrational Resonances Observed in the Microwave Spectrum of FCCCN

Microwave spectrum of fluorocyanoacetylene (FCCCN) produced by a glow discharge in pentafluorobenzonitrile (C6F5CN) was observed using a source modulation spectrometer with a free-space absorption cell. Rotational transitions in the range from J = 9-8 to 53-52 were observed for the vibrationally excited states of nu4 (C&sbond;C stretch), nu5 (CCN bend), nu6 (FCC bend), nu7 (CCC bend), and their associated overtone and combination states up to about 1000 cm-1. Most of the vibrational states above 500 cm-1 are perturbed by rovibrational resonances. The effective vibration-rotation constant of the nu4 state has a negative value (-0.4 MHz), although a vibration-rotation constant generally has a positive value in the excited state of the stretching vibrational mode in a linear molecule. This anomalous behavior is interpreted as due to the rovibrational resonances between the nu4 and several nearby states. By the simultaneous analysis of the states concerned, the unperturbed vibrational energy and rotational constant of the nu4 state are obtained to be 686.50(76) cm-1 and 2068.2387(21) MHz, respectively, where the uncertainties correspond to one standard deviation. Copyright 1999 Academic Press.     

Self-diffusion in core-shell composite 12CO2/13CO2 nanoparticles

A new technique for the generation of multilayered molecular nanoparticles is presented. Core-shell composite nanoparticles of CO(2) with varied composition have been investigated by Fourier-transform infrared spectroscopy over 600 s at 78 K. The isotopically different zones of the particles turned out to have completely different spectra in the nu(3) region: a tub structure (mantle) and a head-and-shoulders structure (core). From the aggregation behavior of both components the particle formation time was found to be 0.1 s. Low-temperature self-diffusion of airborne molecular nanoparticles has been monitored for the first time. The self-diffusion coefficient for (12)CO(2)/(13)CO2 nanocomposites at 78 K was determined from the time evolution of the nu(1) + nu(3) combination band to about 7 x 10(-20) m(2)/s. The work represents a major advance toward nanoengineering of molecular nanoparticles at low temperatures.     

High-Resolution Infrared and Millimeter-Wave Study of the Fermi-Coupled v(2) = 1 and v(3) = 2 States of DSiF(3)

The nu(2) (nu(eff.) 854.841 cm(-1)) and 2nu(3) infrared bands (nu(eff.) 840.083 cm(-1)) of DSiF(3) have been studied with a resolution of 2.5 x 10(-3) cm(-1). Moreover, millimeter-wave transitions in the v(2) = 1 and v(3) = 2 states up to J" = 33 have been measured. The assignments and fit of the poorly resolved, compressed cluster-type 2nu(3) IR transitions have been confirmed by a simultaneous study of the 2nu(3)-nu(3) band. The constant W = 5.116 cm(-1) of the Fermi interaction between the v(2) = 1 and v(3) = 2 levels has been determined from frequency effects which are in agreement with relative intensities of the nu(2) and 2nu(3) bands. The deperturbed (B(0) - B(v)) and (C(0) - C(v)) values of the states involved agree with their ab initio predictions within 7% in the worst case. Copyright 2001 Academic Press.