bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric properties of random and 〈100〉 oriented SrTiO3 and (Ba,Sr)TiO3 thin films fabricated on 〈100〉 nickel tapes
Authors: Dawley J. T. , Clem P. G.
Published: October 2002

Properties are presented for random and enhanced 〈100〉 orientation SrTiO3 and BaxSr1−xTiO3 (x=0.33, 0.50, and 0.67) films fabricated on base-metal 〈100〉 Ni tapes using a chemical solution deposition approach. Films were crystallized in a reducing atmosphere, which prevented Ni oxidation, but permitted growth of SrTiO3 and BaxSr1−xTiO3 films with dielectric loss tan δ between 0.003 and 0.015. For randomly oriented BaxSr1−xTiO3 (x=0, 0.33, 0.5, and 0.67) films, zero-field 100 kHz dielectric constants ranged from 250 to 420. Films with enhanced 〈100〉 orientation exhibited zero-field dielectric constants of 980 to 1500, three times higher than random films. Development of such high dielectric constants on Ni suggests a future method for inexpensive, high performance base-metal electrode capacitor fabrication.
Temperature dependence of the photoluminescence of InGaAs/GaAs quantum dot structures without wetting layer
Authors: Sanguinetti S. , Mano T. , Oshima M. , Tateno T. , Wakaki M. , Koguchi N.
Published: October 2002

We analyze the photoluminescence temperature behavior of InGaAs/GaAs quantum dots grown by heterogeneous droplet epitaxy. Morphologically, these dots are nanocrystal InGaAs inclusions in the GaAs matrix, with a concave disk shape and, more important, no wetting layer is connecting the dots. The photoluminescence of the dots does not show any of the typical of the Stranski–Krastanov dots temperature properties, such as sigmoidal peak energy position and linewidth narrowing. We demonstrate that such behavior stems from the lacking of the thermally activated dot–dot coupling channel provided by the wetting layer thus preventing the establishment of a common quasiequilibrium in the whole dot ensemble.
Comparative ab initio prediction of gene
structures using pair HMMs
Authors: Meyer Irmtraud M. , Durbin Richard
Published: October 2002

We present a novel comparative method for the ab initio prediction of protein coding genes in eukaryotic genomes. The method simultaneously predicts the gene structures of two un-annotated input DNA sequences which are homologous to each other and retrieves the subsequences which are conserved between the two DNA sequences. It is capable of predicting partial, complete and multiple genes and can align pairs of genes which differ by events of exon-fusion or exon-splitting.

The method employs a probabilistic pair hidden Markov model. We generate annotations using our model with two different algorithms: the Viterbi algorithm in its linear memory implementation and a new heuristic algorithm, called the stepping stone, for which both memory and time requirements scale linearly with the sequence length.

We have implemented the model in a computer program called Doublescan. In this article, we introduce the method and confirm the validity of the approach on a test set of 80 pairs of orthologous DNA sequences from mouse and human.

More information can be found at: http://www.sanger.ac.uk/Software/analysis/doublescan/

Contact: im1@sanger.ac.ukrd@sanger.ac.uk

* To whom correspondence should be addressed.
GENIE: estimating demographic history from molecular phylogenies
Authors: Pybus O.G. , Rambaut A.
Published: October 2002

Summary: GENIE implements a statistical framework for inferring the demographic history of a population from phylogenies that have been reconstructed from sampled DNA sequences. The methods are based on population genetic models known collectively as coalescent theory.

Availability: GENIE is available from http://evolve.zoo.ox.ac.uk. All popular operating systems are supported.

Contact: oliver.pybus@zoo.ox.ac.uk

* To whom correspondence should be addressed.
Modeling the Al/Si rich oxide (SRO)/Si structure
Authors: Aceves M. , Glaenzer R. , Carrillo J. , Malik A. , Luna A.
Published: October 2002

Al/SRO/Si devices produced on N-type silicon are experimentally characterized to understand their behavior. Different values were used for the nitrous oxide/silane gas flow ratio (Ro) to control the excess silicon. Depending on the silicon excess, the devices could be operated in various modes; from surface accumulation to deep depletion or to a reverse biased PN junction. Modeling of the different devices is presented.
Correlation between the microstructures and the cycling performance of RuO2 electrodes for thin-film microsupercapacitors
Authors: Kim Han-Ki , Seong Tae-Yeon , Lim Jae Hong , Ok Young-Woo , Cho Won il , Shin Young Hwa , Yoon Young Soo
Published: October 2002

We have fabricated all solid-state thin-film microsupercapacitors (TFSCs) using RuO2 electrodes and LiPON electrolytes. The RuO2 electrodes were grown at oxygen gas flow ratios [O2/(O2+Ar)] of 10% and 30%. Room-temperature charge–discharge measurements show that specific capacitance is dependent on the oxygen gas flow ratio. Glancing angle x-ray diffraction (GXRD) and transmission electron microscopy (TEM) results show that the RuO2 electrodes grown at 10% contain nanocrystallites (0.7–10 nm across) embedded in the amorphous matrix, while the electrodes grown at 30% are polycrystalline (with grains of 0.7–15 nm in diameter). Based on the GXRD, TEM, Auger electron spectroscopy depth profile, and scanning electron microscopy results, the oxygen flow ratio dependence of the cycling performance of the RuO2-based TFSCs are discussed in terms of the combined effects of the microstructures of the electrodes, interfacial products, and the surface morphology of the electrodes.
Ag growth on Mo(112)–Oa and MoO2 surfaces
Authors: Santra A. K. , Min B. K. , Goodman D. W.
Published: October 2002

The growth of Ag clusters on preadsorbed oxygen and oxide-covered Mo(112) has been investigated using scanning tunneling microscopy (STM). The objective of these experiments is the synthesis of adjacent areas on a surface with distinctly different metal–support interactions in order to investigate the relationship between the morphology of a supported metal cluster and the strength of the cluster–support interaction. The STM results show that more highly dispersed Ag clusters with a greater number density are obtained on that surface that interacts to a greater extent with the metal. Heating leads to the formation of two-dimensional–Ag nanostructures on oxygen-free Mo(112) (strong metal–support interaction) and three-dimensional cluster growth on oxide-covered Mo(112) (relatively weak metal–support interaction).
Strategies for purging the pellicle space for 157 nm lithography
Authors: Burns Ryan L. , Punsalan David , Towidjaja Maria C. , Koros William J.
Published: October 2002

Current microlithography research is examining the viability of a 157 nm exposure wavelength in order to decrease the size of printed features. This wavelength shift is particularly challenging because many components of air strongly absorb at 157 nm, such as O2, H2O, and CO2. The particle barrier known as the pellicle presents a substantial resistance to mass transfer. In this project, a purge chamber has been devised that can decontaminate the reticle from these species. This work evaluates various purging strategies using polymeric and inorganic pellicle materials to attain acceptable contaminant levels. Results are presented that show the decline in O2 concentration over time within the pellicle space under an external N2 purge. Variables in the experiment include the pellicle material, the allotment of filters on the pellicle frame, and the flow rate of the purge gas. Furthermore, a model of the purging process was developed, which shows good agreement with experimental data.
Current gain degradation in SiGe HBTs by hot carriers
Authors: Gill C. R. , McAlister S. P. , Storey C. , McKinnon W. R. , Kovacic S.
Published: October 2002

The effects of open-collector and forward-collector reverse bias stressing on SiGe HBTs have been studied. Increases in the base current and degradation of the current gain, similar to those found in pure Si BJTs, were observed in the stressed devices. Short periods of severe reverse base-emitter bias stress cause random telegraph signals to occur in the base current. Damage is caused by hot holes, created by band-to-band tunneling in the base-emitter junction, during open-collector stressing and by hot holes and electrons, injected from the collector into the base, in forward-collector stressing. A comparison of the charge to failure as a function of stress voltage between the two hot carrier stressing methods suggests that, at a given kinetic energy, holes cause more damage than electrons.
Influence of parameters and substrates on the diameter of CuInSe2 nanoparticle thin films by rf reactive sputtering
Authors: Huang Shiyong , Zhang Lide , Dai Zhenhong , Zhu Xiaoguang , Qu Fenggin , Fu Shengqi
Published: October 2002

CuInSe 2 (CIS) nanoparticle thin films have been prepared by rf reactive magnetron sputtering from a fan-shaped ternary compound target on low temperature substrates with pure argon gas as the atmosphere. The stoichiometry of the thin films can be easily controlled by the ratios of the ternary elements and sputtering parameters. Regularly shaped and uniform CIS nanoparticle thin films can be deposited on substrates of soda-lime glass, indium-tin-oxide coated glass, monocrystalline silicon, etc. CIS samples have been investigated by atom force microscopy, optical absorption, x-ray photoelectron spectroscopy, x-ray diffraction, and spectrophotometer.
Synthesis of organically modified mesoporous silica as a low dielectric constant intermetal dielectric
Authors: Yu Suzhu , Wong Terence K. S. , Pita Kantisara , Hu Xiao
Published: October 2002

Silica mesoporous films with low dielectric constant were successfully fabricated by a multiple step sol-gel process. The employment of inorganic/organic precursors proved very useful in preventing the film from cracking. The acid/base two-step catalysis could adjust the refractive index or porosity of the silica films effectively and easily. The basic properties of the silica films were evaluated by transmission electron microscopy, specular x-ray reflectivity, Fourier transform infrared spectroscopy, and thermal gravimetric and differential thermal analysis. An inherently low dielectric constant of around 2.0 was realized for about 57% porosity in the silica film with a pore size less than 10 nm. The leakage current was at a level of 10−6 A/cm2 one month after fabrication. The dependencies of the dielectric properties of the films on the relative amount of the components in the starting solution and on the processing temperature were investigated in detail. Preliminary results of the silica films prepared here present a very positive prospective to an intermetal dielectric applications.
Influence of potential fluctuations on Landau quantization and spin splitting studied by low temperature scanning tunneling spectroscopy on InAs(110)
Authors: Morgenstern M. , Gudmundsson V. , Wiesendanger R.
Published: October 2002

The Landau quantization visible in dI/dV spectra on n-InAs(110) at B=6 T and T=8 K is studied with high spatial resolution. It is found that the dI/dV intensity is dominated by the Landau bands of the tip-induced quantum dot. The Landau band energies depend on the local surface potential provided by the ionized dopants. Comparison with Hartree–Fock calculations show that the energy shifts are accompanied by an enhanced spin splitting of the Landau bands induced by the spatially varying spin polarization of the dot. Imaging of the spin splitting demonstrates the nonsimple dependence of the spin polarization on the local potential.
Plasma surface modification for ion penetration barrier in organosiloxane polymer
Authors: Mallikarjunan A. , Yang G.-R. , Murarka S. P. , Lu T.-M.
Published: October 2002

Low dielectric constant (low-κ) hybrid organosiloxane polymer (HOSP) displayed larger instability with Al compared to Cu capacitors when investigated using the bias temperature stressing (BTS) and triangular voltage sweep (TVS) techniques. We attributed this instability to ion penetration from the gate metal. As SiO2 is a well-known barrier against Al penetration, an attempt was made to create a SiO2-like surface on HOSP using different plasma treatments. The plasma conditions were selected to minimize bulk damage to the polymer. While N2O and O2 plasmas caused bulk electrical damage, N2 and Ar plasma treatments dramatically reduced ion penetration from the Al gate into HOSP. This was seen from the decrease in the BTS C–V shift as well as the TVS ion peak area. A short (1 min) low-power (30 W) N2 plasma treatment was effective as an aluminum ion penetration barrier, without significantly increasing the refractive index or dielectric constant value of HOSP. Formation of a SiO2-like surface was confirmed from x-ray photoelectron spectroscopy investigations. The above plasma-treatment approach reveals one possible route to attain the “zero barrier thickness” requirement for interconnect systems.
Simple and high-precision asymmetric gate-recess process for ultrafast InP-based high electron mobility transistors
Authors: Shinohara Keisuke , Matsui Toshiaki , Yamashita Yoshimi , Endoh Akira , Hikosaka Kohki , Mimura Takashi , Hiyamizu Satoshi
Published: October 2002

We present a simple and high-precision process technology for ultrafast InP-based high electron mobility transistors (HEMTs) having an asymmetrically recessed T-shaped gate. This technology is beneficial in fabricating high-performance InP-HEMTs because it enables us to independently optimize source- and drain-side recess lengths (Lrs, Lrd) while using a very short gate length (Lg). The process utilizes a conventional trilayer resist exposed by electron beam lithography, which has additional slit patterns beside a gate-foot pattern in the bottom layer. The gate metal is evaporated at a tilted angle to avoid evaporation through the slit patterns. The Lrs and Lrd can be precisely controlled by the etching time, and by the size and position of the slits, while keeping a constant recess depth. A 60 nm gate HEMT with a longer Lrd exhibits a much-enhanced maximum oscillation frequency (fmax) of 428 GHz mainly by reducing the drain conductance (gd) and the gate-to-drain capacitance (Cgd), as compared to that (244 GHz) for a conventional HEMT with a symmetric recess structure.
Kelvin probe force microscopy of beveled semiconductors
Authors: Ferguson R. S. , Fobelets K. , Cohen L. F.
Published: October 2002

For the first time, we present the results of Kelvin probe force microscope studies on beveled samples. The ease of sample preparation and simplicity of the measurement make this technique a good candidate for the rapid characterization of semiconductor multilayers. The GaSb/InAs and Ge/SiGe/Si samples presented demonstrate both the utility and the limits of the technique. Beveling has allowed us to easily image quantum wells of 7.5 nm thickness, which is well beyond the resolution available on cleaved samples. Bevel and sample roughness are shown to be the most critical parameters in obtaining good results.
Micromolar concentrations of base quenchers impact the apparent efficiency of photoacid generation in chemically amplified resists
Authors: Pawloski Adam R. , Christian  , Nealey Paul F.
Published: October 2002

The chemical composition of the base quencher added to chemically amplified photoresist formulations was found to influence the apparent efficiency of processes that lead to photoacid generation upon exposure to ionizing radiation. Resists formulated with the base quencher 1-piperidineethanol (1PE) required lower exposure doses to render development than resists containing 3-piperidino-1,2-propanediol (3P12PD) as the base. A standard addition technique was employed to determine the efficiency of photoacid generation in resist formulations consisting of one of the two base quenchers, the photoacid generator triphenylsulfonium triflate, and a matrix polymer composed of primarily p-hydroxystyrene and tert-butylacrylate monomers (environmentally stable chemically amplified photoresist type). The resist containing 1PE exhibited an apparently greater efficiency for photoacid generation than the formulation containing 3P12PD. Analysis of development processes showed that resists containing these bases exhibited identical dissolution behavior to that of a system without base quencher, verifying that resist dissolution could not explain the difference in exposure dose required for development of the 1PE and 3P12PD resists. Furthermore, the action of photoacid to deprotect the polymer, as interpreted from infrared spectroscopy, and the concentration of photoacid required to render development were the same for both resists. These results suggest that the small concentration of base in the resist may participate in the complicated chemical processes that produce photoacid from the decomposition of PAG upon exposure to ionizing radiation.
Microleveling mechanisms and applications of electropolishing on planarization of copper metallization
Authors: Chang Shih-Chieh , Shieh Jia-Min , Huang Chih-Chang , Dai Bau-Tong , Li Ying-Hao , Feng Ming-Shiann
Published: October 2002

The optimization of Cu electropolishing processes was explored to be in the mass-transfer-limited plateau with a stable limiting current density and in concentrated phosphoric acid by elucidating surface morphologies and potentiodynamic polarization. After electropolishing, the average roughness of polished surfaces achieved to 1.1 nm. Both the x-ray photoelectron spectroscopy and the electrochemical impedance spectroscopy suggest that the existence of a passivation film on the polished surface contributed to the microleveling effect of Cu electropolishing. Moreover, this passivation layer also induces an application of end point in electropolishing.
POSSIBLE NEW PHASES OF COMPOSITE FERMIONS
Authors: SCAROLA V. W. , LEE S. Y. , JAIN J. K.
Published: October 2002

When the effective filling factor of composite fermions is an integer, the residual interaction between them can often be neglected because the ground state of the non-interacting model is unique and incompressible. However, at non-integer composite fermion (CF) filling factors the ground state of composite fermions is enormously degenerate if the interaction between them is neglected, and consideration of the inter composite fermion interaction is necessary for determining the true ground state. In this article, we summarize certain results regarding what new states the inter composite fermion interaction can possibly produce. More details can be found in Refs. [11] and [12].
INTERSUBBAND MAGNETOPHONON RESONANCES IN QUANTUM CASCADE STRUCTURES
Authors: SMIRNOV D. , DRACHENKO O. , LEOTIN J. , PAGE H. , BECKER C. , SIRTORI C. , APALKOV V. , CHAKRABORTY T.
Published: October 2002

We report on magnetotransport measurements of GaAs/GaAlAs quantum cascade structures in magnetic fields up to 62 T parallel to the current. We observe novel quantum oscillations series in tunneling current that are periodic in reciprocal magnetic field and have field positions independent of the applied bias. These oscillations are explained as intersubband magnetophonon resonance due to electron relaxation by emission of optical or acoustic phonons.
THEORY OF SURFACE-ACOUSTIC-WAVE PROPAGATION IN THE ν = 5/2 FRACTIONAL QUANTUM HALL STATE
Authors: FOSTER K. C. , BONESTEEL N. E. , SIMON S. H.
Published: October 2002

There is compelling theoretical evidence1 that the ν = 5/2 fractional quantum Hall state is a Moore-Read state2 - a state which can be viewed as a spin-polarized p-wave superconductor of composite fermions. The question remains, how can one test this hypothesis experimentally? To address this we have developed a semi-phenomenological description of this state in which the Halperin-Lee-Read3 theory of the half-filled Landau level is modified by adding a p-wave pairing interaction between composite fermions by hand. The electromagnetic response functions for the resulting mean-field p-wave superconducting state are then calculated and used in an RPA calculation of the physical electronic response. In particular, we predict the wave-vector and frequency dependence of the longitudinal conductivity σxx(q,ω) which can be measured in surface-acoustic-wave propagation experiments.4
HIGH MAGNETIC FIELD OPTICAL STUDIES OF CHARGED EXCITON IN CdTe 2D ELECTRON GASES
Authors: NEGRE N. , CROOKER S. A. , WOJS A. , KARCZEWSKI G.
Published: October 2002

Photoluminescence (PL) and reflectivity spectroscopy in magnetic fields up to 60 Tesla are used to investigate the excitonic optical transitions within CdTe/(Cd,Mg)Te 2D electron gases. The samples are 100 A and 200 A wide quantum well (QW) wherein the electron density is varied smoothly from 1 × 1011 to 4.5 × 1011 cm-3 across the wafer. This allows us to follow the energy diagram of the neutral exciton ( X 0) and the charged exciton singlet and triplet spin states ( X - s , X - t ) versus magnetic field and the electron density. We observe a weak PL peak above 12 T (15 T) for the 200 A QW (100 A) at the low energy side of the spectra in addition to the X -0 and X - s PL. This peak could be the signature of a fundamental dark triplet state recently predicted (Phys. Rev. B62, 4630). Moreover, for high density samples a balance of PL intensity between the X -s and an other X -t occurs in the 25T-30T range. These results are interpreted on the basis of the calculations by Wojs et al. (Phys. Rev. B62 4630) taking account the Zeeman energy of the charged exciton.
IMPURITIES IN A MAGNETIC-FIELD-INDUCED LUTTINGER LIQUID
Authors: TSAI S.-W. , MASLOV D. L. , GLAZMAN L. I.
Published: October 2002

We study the effect of dilute impurities on a system of interacting electrons subject to a quantizing magnetic field. For the case of point impurities, the calculation of the scattering cross section can be mapped onto a 1D problem of tunnelinng conductance through a barrier for interacting electrons. We find that the electron-electron interaction produces temperature-dependent corrections to the cross-section, and thus to the tensor of conductivities. Upon summation of the most diverging corrections in all orders of perturbation theory, a scaling behavior of the conductivities emerges. This behavior is similar to that of 1D Luttinger liquid. The scaling exponents depend on the magnetic field and are calculated explicitly in the weak-coupling limit. The limitations on the scaling behavior due to the formation of a charge-density wave are also discussed.
THE DE HAAS-VAN ALPHEN EFFECT IN CeMIn5 (Where M = Rh and Co)
Authors: HALL D. , MURPHY T. P. , PALM E. C. , TOZER S. W. , FISK Z. , HARRISON N. , GOODRICH R. G. , ALVER U. , SARRAO J. L.
Published: October 2002

To understand the electronic structure of the heavy fermion superconductors CeMIn 5, we have performed a comprehensive magnetic study of these materials.1-4 Our quantum oscillation studies reveal that the Fermi surface becomes systematically more 2-d (and displays heavier effective masses) as one progresses from M=Rh to M=Ir to M=Co, consistent with the observed increase in superconducting Tc. Furthermore, dilution studies show that the f-electrons in CeRhIn5 are substantially localized whereas in CeIrIn 5 and CeCoIn 5 a more itinerant character is observed.
SUPERCONDUCTING AND NORMAL STATE PROPERTIES OF THE HEAVY FERMION COMPOUND PrOs4Sb12
Authors: HO P.-C. , ZAPF V. S. , BAUER E. D. , FREDERICK N. A. , MAPLE M. B. , GIESTER G. , ROGL P. , BERGER S. T. , PAUL C. H. , BAUER E.
Published: October 2002

The filled skutterudite compound PrOs 4 Sb 12 displays superconductivity with a critical temperature T c ≈ 1.85 K which appears to involve heavy fermion quasiparticles with an effective mass m * ~ 50 - 100 m e as inferred from the slope of the upper critical field curve near T c and the specific heat. New measurements of electrical resistivity ρ(T) in applied magnetic fields, thermoelectric power, and X-ray diffraction are presented. A peak appears in the dρ/dT data for magnetic fields above 4 T that suggests the occurrence of a phase transition in the normal state of PrOs 4 Sb 12 below ~ 1K.
HIGH-FIELD MAGNETIZATION IN THE MOTT-HUBBARD SYSTEM (Y, Ca)VO3
Authors: NAKOTTE H. , ALSMADI A. M. , KAWANAKA H. , KINDO K. , GOTO K.
Published: October 2002

We measured the magnetization of Y 1-x Ca x VO 3 compounds with 0 Ω × Ω, 0.6 in pulsed magnetic fields up to 56 T. YVO 3 exhibits a slightly S-shaped magnetization curve with an inflection point at B c = 42 T . the critical field B c was found to decrease with increasing calcium content, and no sign of an S-shape is seen for the compound with x = 0.6, which is at the boundary of the metal-to-insulator transition. Our data provide further evidence that the metal-to-insulator transition in this system coincides with the transition from a paramagnetic to a magnetic ground state.
INELASTIC NEUTRON SCATTERING FROM ANISOTROPIC SUPERCONDUCTORS
Authors: RISEBOROUGH P. S.
Published: October 2002

The magnetic fluctuation spectra are calculated for various phases of anisotropic superconductors. Both singlet and triplet superconducting phases can support antiferromagnetic fluctuations for small values of the Coulomb repulsion, the spectra show power law frequency dependencies due to the nodes in the superconducting order parameter. For larger strengths of the Coulomb interaction, low energy critically damped collective excitations develop from the quasi-particle density of states in the gap. The q and ω dependence of the spectra can be used to deduce the character of the superconducting order parameter.
NMR STUDY OF THE ANTIFERROMAGNETIC TO SUPERCONDUCTOR PHASE TRANSITION IN (TMTSF)2PF6
Authors: YU W. , BROWN S. E. , ZAMBORSZKY F. , LEE I. J. , CHAIKIN P. M.
Published: October 2002

The pressure-tuned quantum phase transition from spin-density wave (SDW) to Fermi Liquid (FL) ground states is studied in (TMTSF) 2 PF 6 by NMR relaxation and spectroscopy. As for recent transport measurements, we find evidence in the distribution of local hyperfine fields for phase segregation, from which we conclude the transition between normal and SDW phases is discontinuous. A tricritical point (TCP) is identified. A crossover to FL behavior identified by spin-lattice relaxation measurements intersects the normal to SDW phase boundary very close to the TCP.
THE FASCINATING NEW PHYSICS OF SOME OLD BCS SUPERCONDUCTORS
Authors: BARZYKIN V.
Published: October 2002

We consider the pairing state due to the usual Bardeen-Cooper-Schrieffer mechanism in substances where the Fermi surface forms pockets around several points of high symmetry. The symmetry imposed on the multiple pocket positions can give rise to a multidimensional nontrivial superconducting order parameter. A complicated mechanism is not required for unusual superconductivity to exist, just the usual phonon attraction and Coulomb repulsion. Time reversal symmetry is broken, so the superconducting state also has orbital magnetism. In some sense, these superconductors are similar to superfluid3 He, which is known to have an 18-dimensional order parameter and a complicated phase diagram. We suggest several candidate substances where ordering of this kind may appear and discuss how these phases may be identified. Superconductivity in these new materials is expected to be much less sensitive to impurities than in other non s-wave superconductors.1
PSEUDOGAP STATE OF HIGH Tc CUPRATES: A PREDOMINANT ROLE OF SPIN DEGREES OF FREEDOM
Authors: KRUSIN-ELBAUM L. , SHIBAUCHI T. , MALEY M. P. , LI M. , KES P. H.
Published: October 2002

We map the field-temperature (H-T) diagram of the pseudogap state in Bi 2 Sr 2 CaCu 2 O 8+y crystals in a wide range of hole doping. By probing the quasiparticle density-of-states with the c-axis interlayer resistivity measurements in fields up to 60 T we make a systematic evaluation of the pseudogap closing field Hpg that restores the superconductor to its ungapped state. In contrast to the characteristic fields of the superconducting state, Hpg(T) at low temperatures is temperature independent and scales with the pseudogap temperature T* by a simple Zeeman energy scale, indicating a predominant role of spins over the orbital effects in the formation of the pseudogap.
VORTEX MAGNETISM IN THE HIGH-TEMPERATURES SUPERCONDUCTOR La2-xSrxCuO4
Authors: LAKE B. , MASON T. E. , AEPPLI G. , LEFMANN K. , CHRISTENSEN N. B. , MCMORROW D. F. , CLAUSEN K. N. , RONNOW H. M. , VORDERWISCH P. , SMEIBIDL P. , MAGNKORNTONG N. , HUSSEY N. E. , SASAGAWA T. , NOHARA M. , TAKAGI H. , SCHRODER A.
Published: October 2002

There is strong evidence that magnetic interactions play a crucial role in the mechanism driving high-temperature superconductivity in cuprate superconductors. To investigate this further we have done a series of neutron scattering measurements on La 2-x Sr x CuO 4 (LSCO) in an applied magnetic field. Below Tc the field penetrates the superconductor via an array of normal state metallic inclusions or vortices. Phase coherent superconductivity characterized by zero resistance sets in at the lower field-dependent irreversibility temperature (Tirr). We have measured optimally doped LSCO (x = 0.16, Tc = 38.5 K ) and underdoped LSCO (x = 0.10, Tc = 29 K ); both have an enhanced antiferromagnetic response in a field. Measurements of the optimally doped system at H = 7.5 T show that sub-gap spin fluctuations first disappear with the loss of finite resistivity at Tirr, but then reappear at a lower temperature with increased lifetime and correlation length compared to the normal state. In the underdoped system elastic antiferromagnetism develops below Tc in zero field, and is significantly enhanced by application of a magnetic field. Phase coherent superconductivity is then established within the antiferromagnetic phase at Tirr; thus, the situation in underdoped LSCO is the reverse of that for the optimally doped LSCO where the zero-resistance state develops first before the onset of antiferromagnetism.
Mg AS A MAIN SOURCE FOR THE DIVERSE MAGNETOTRANSPORT PROPERTIES OF MgB2
Authors: KIM K. H. , BETTS J. B. , JAIME M. , LACERDA A. H. , BOEBINGER G. S. , JUNG C. U. , KIM H.-J. , KIM M.-S. , KIM J. Y. , DU Z. , LEE S.-I.
Published: October 2002

Magnetotransport properties of pure Mg metal and MgB 2 samples with varying amounts of excess Mg were systematically studied in magnetic fields up to 18 T. It is found that the both the Mg and inhomogeneous MgB 2 samples show large low temperature conductivity, residual resistance ratio (RRR) and magnetoresistance (MR) under high fields. Calculations of the generalized effective medium theory show that the large RRR and MR of the inhomogeneous MgB 2 samples can be explained by unusual magnetotransport properties of pure Mg metal.
FIELD-INDUCED ANTIFERROMAGNETISM IN THE HIGH-TEMPERATURE SUPERCONDUCTOR La2-xSrxCuO4
Authors: LAKE B. , MASON T. E. , AEPPLI G. , LEFMANN K. , CHRISTENSEN N. B. , MCMORROW D. F. , CLAUSEN K. N. , RONNOW H. M. , VORDERWISCH P. , SMEIBIDL P. , MANGKORNTONG N. , HUSSEY N. E. , SASAGAWA T. , NOHARA M. , TAKAGI H. , SCHRÖDER A.
Published: October 2002

There is strong evidence that magnetic interactions play a crucial role in the mechanism driving high-temperature superconductivity in cuprate superconductors. To investigate this we have done a series of neutron scattering measurements on La 2-x Sr x CuO 4 (LSCO) in an applied magnetic field. Below Tc the field penetrates the superconductor via an array of normal state metallic inclusions or vortices. Phase coherent superconductivity characterized by zero resistance sets in at the lower field-dependent irreversibility temperature (Tirr). We have measured optimally doped LSCO (x = 0.16, Tc = 38.5 K ) and under-doped LSCO ( x = 0.10, Tc = 29 K ); both have an enhanced antiferromagnetic response in a field. Measurements of the optimally doped system at H = 7.5 T show that sub-gap spin fluctuations first disappear with the loss of finite resistivity at Tirr, but then reappear at a lower temperature with increased lifetime and correlation length compared to the normal state. In the under-doped system elastic antiferromagnetism develops below Tc in zero field, and is significantly enchanced by application of a magnetic field. Phase coherent superconductivity is then established within the antiferromagnetic phase at Tirr; thus, the situation in under-doped LSCO is the reverse of that for the optimally doped LSCO where the zero-resistance state develops first before the onset of antiferromagnetism.
MAGNETIC PROPERTIES OF HEAVY FERMION SUPERCONDUCTORS CeRhIn5 AND Ce2RhIn8
Authors: BAO WEI , AEPPLI G. , CHRISTIANSON A. D. , FISK Z. , HUNDLEY M. F. , LACERDA A. H. , LYNN J. W. , PAGLIUSO P. G. , SARRAO J. L. , THOMPSON J. D.
Published: October 2002

Some recent neutron scattering works on CeRhIn5 and Ce2RhIn8, together with related resistivity and specific heat measurements, are summarized. In spite of its layered crystal structure, CeRhIn5 is shown to be 3 dimensional both magnetically and in transport. We also find that the Fisher-Langer behavior is closely followed in CeRhIn5. This may circumvent the Kondo lattice model and support applying established Fermi-liquid superconductivity theory to heavy fermion superconductors.
SPIN CORRELATIONS IN MAGNETIZED HALDANE CHAINS
Authors: BROHOLM C. L.
Published: October 2002

Neutron scattering experiments have been carried out in high magnetic fields to understand the magnetized state of the uniform spin-1 antiferromagnetic chain. In zero field this system has a cooperative singlet ground state with a gap to a propagating triplet excitation. The quasi-one-dimensional uniform spin-1 antiferromagnets NENP (Ni(C2D8N2)2NO2CIO4) and NDMAP (Ni(C5D14N2)2N3PF6) were examined. NENP has an alternating g-tensor such that staggered magnetization is induced for arbitrarily small fields and there is no finite field phase transition. In the high field phase the lowest energy mode has a field dependent gap and an unusually small effective spin wave velocity. NDMAP has only one spin per unit cell and hence a uniform g-tensor. This system has a critical transition at a finite field. Surprisingly the high field phase has quasi-two-dimensional or three-dimensional long-range order depending on the direction of the applied field. In the paramagnetic high field phase immediately above the ordering transition of NDMAP, there are gapless magnetic excitations that are broader in Q than the higher energy gap mode. The data is compared to theoretical predictions of a gapless incommensurate phase above the critical field.
QUANTUM OSCILLATIONS, TUNNELING MAGNETORESISTANCE AND ANGULAR DEPENDENCE OF MAGNETIZATION IN Ca3Ru2O7
Authors: CAO G.
Published: October 2002

Ca3Ru2O7 has a double Ru-O layered orthorhombic structure. It is a "bad" metal characterized by various abrupt magnetic and electronic transitions that are highly anisotropic. Ca3Ru2O7 undergoes antiferromagnetic ordering at TN = 56 K and a metal to poorer metal transition at TM = 48 K with a unique antiferromagnetic metallic phase intermediate between the paramagnetic and antiferromagnetic phases. Our recent study reveals a few more striking features: (1) Quantum oscillations, i.e., the Shubnikov-de Haas effect, of which the fast Fourier transform shows two frequencies F1 = 23.4 and F2 = 41 tesla, respectively; (2) Inter-plane tunneling magnetoresistance, whose ratio is more than 90% [ρ(0) - ρ(H)/ρ(0)]; (3) Anomalous angular dependence of magnetization, which leads to similar angular dependence of resistivity due to a strong spin-charge coupling. Ca3Ru2O7 is a rare system that possesses a wide range of interesting yet complex physical properties that very often do not coexist in other materials. The results and discussions will be presented along with comparisons with other related systems.
A METAMAGNETIC QUANTUM CRITICAL ENDPOINT IN Sr3Ru2O7
Authors: GRIGERA S. A. , MACKENZIE A. P. , SCHOFIELD A. J. , JULIAN S. R. , LONZARICH G. G.
Published: October 2002

In this paper, we discuss the concept of a metamagnetic quantum critical end-point, consequence of the depression to zero temperature of a critical end-point terminating a line of first order first transitions. This new type of quantum critical point (QCP) is interesting both from a fundamental point of view: a study of a symmetry conserving QCP, and because it opens the possibility of the use of symmetry breaking tuning parameters, notably the magnetic field. In addition, we discuss the experimental evidence for the existence of such a QCP in the bilayer ruthenate Sr3Ru2O7.
HIGH FIELD NMR IN STRONGLY CORRELATED LOW-DIMENSIONAL FERMIONIC SYSTEMS
Authors: HORVATIĆ M. , BERTHIER C.
Published: October 2002

We review some recent NMR results obtained in Grenoble High Magnetic Field Laboratory on magnetic field induced phenomena in strongly correlated low-dimensional fermionic systems: i) magnetic field dependence of the soliton lattice in the IC phase of the spin-Peierls system CuGeO3, ii) NMR study of the complete H-T phase diagram of the organo-metallic spin ladder Cu2(C5H12N2)2Cl4, and iii) the first "standard" NMR measurements (i.e., without optical pumping) on 2D electrons in Quantum wells, providing a detailed description of the fractional quantum Hall effect state at ν = 1/2 with the first determination of the corresponding effective polarization mass of composite fermions. Latest study of the ν = 2/3 state revealed, among other features, an unexpected phase transition.
TRIPLET SUPERCONDUCTIVITY ORDER PARAMETER IN AN ORGANIC SUPERCONDUCTOR (TMTSF)2PF6
Authors: LEBED A. G.
Published: October 2002

We argue that an organic superconductor (TMTSF)2PF6 under pressure P = 6 kbar is a triplet superconductor1,2 with a spin part of the triplet order parameter being d(k) = (dx (k) ≠ 0, dy (k) = 0, dz (k) = 0). We obtain these results by means of an analysis of the anisotropic experimental critical fields H c2 (see I. J. Lee et al., Phys. Rev. Lett.78, 3555 (1997)). By using symmetry arguments, we also discuss the most probably orbital part of the triplet order parameter in (TMTSF)2PF6. Our analysis is in accordance with the very recent Knight shift data obtained on (TMTSF)2PF6.
EFFECTS OF IN-PLANE STRAIN ON MAGNETISM IN LaMnO3 THIN FILMS
Authors: AHN K. H. , MILLIS A. J.
Published: October 2002

The effects of the in-plane strain on the magnetic properties of LaMnO3 thin films are calculated using an elastic energy expression and a tight binding Hamiltonian with electron-lattice coupling. Tensile uniaxial strain of the order of 2%, which is the order of the magnitude of those induced in thin films by lattice mismatch with substrates, is found to change the magnetic ground state from A-type antiferromagnetic state to purely antiferromagnetic state.
COLOSSAL EFFECTS IN TRANSITION METAL OXIDES CAUSED BY INTRINSIC INHOMOGENEITIES
Authors: BURGY J. , MAYR M. , MARTIN-MAYOR V. , MOREO A. , DAGOTTO E.
Published: October 2002

The general aspects of the influence of quenched disorder on the competition between ordered states separated by a first-order transition are investigated. A phase diagram with features resembling quantum-critical behavior is observed. The paramagnetic phase at low temperature consists of coexisting ordered clusters, with a random orientation of the order parameter. Specializing to manganites, this state is shown to have a colossal magnetoresistance effect. A new scale T* for cluster formation is predicted. It is argued that cuprates have similar features, compatible with the large proximity effect of the very underdoped regime.1
HIGH FIELD NMR STUDIES OF NaV2O5 to 44.7 T
Authors: CALDWELL T. , KUHNS P. L. , MOULTON W. G. , REYES A. P. , ROGERS P. N. , SHELTON R. N.
Published: October 2002

23Na NMR studies have been carried out to map the uniform to dimerized phase boundary up to 44.7 T in the NHMFL hybrid. The transition is observed by the splitting of the NMR line ( H //a axis) by the lattice distortion. The field dependence of Tc up to 44.7 T, in agreement with previous magnetization data to 30 T, is very small (α = 0.092) compared to 0.4 for conventional SP systems and shows no deviation within experimental error from the h2 dependence, while optical data show a decrease of the slope in the H-T phase diagram beginning around 40 T. The region of an anomaly near T 33 T and 32 K observed in optical data taken in the long pulse magnet at LANL1 was also explored. The only evidence in the NMR of the observed optical anomaly near 33 T and 32 K was line broadening over a 2 T interval.
LARGE EFFECTS OF MAGNETIC FIELD ON JOSEPHSON CURRENTS THROUGH ANTIFERROMAGNETIC BARRIERS
Authors: GOR'KOV L. P. , KRESIN V. Z.
Published: October 2002

Ferromagnetism being known to have a detrimental effect on superconductivity, we consider the Josephson current amplitude for junctions built up of antiferromagnetic metallic weak links. It is assumed that the latter consist of ferromagnetic layers with magnetizations aligned alternatively along perpendicular-to-the-layers direction. Currents between two superconducting electrodes flow along the layers. Such antiferromagnetic structure realizes itself in mixed valence manganites (the so-called A-phase), in an array of parallel ferromagnetic domains, or even in artificial GMR heterostructures. It is shown that even minor canting of magnetic moments in the presence of magnetic fields causes remarkable oscillations in the value of the Josephson current amplitude.
FERROMAGNETIC RESONANCES IN POLYCRYSTALLINE La0.8Li0.2MnO3
Authors: LEWIS R. A. , WANG X. L. , DOU S. X. , BISKUP N. , BROOKS J. S.
Published: October 2002

We report on magnetic resonances observed in the doped lanthanum manganite La0.8Li0.2MnO3 (LLMO) below the Curie temperature Tc ~ 235 K. Fields up to 30 T were employed. The data are compared with that from the archetypal colossal magnetoresistance perovskite La0 7Ca0 3MnO3 (LCMO) taken under similar conditions. In contrast to LCMO, LLMO exhibits two resonances, one above and one below the LCMO resonant field. These are attributed to a ferromagnetic interaction and a canted ferromagnetic interaction.
DEVELOPMENT OF ADVANCED INSTRUMENTATION FOR STATIC AND PULSED FIELDS
Authors: MIGLIORI A. , BALAKIREV F. F. , BETTS J. B. , BOEBINGER G. S. , MIELKE C. H. , RICKEL D.
Published: October 2002

The DC and pulsed magnets now available at the NHMFL provide routine access to high magnetic fields in cryogenic environments (down to even dilution refrigerator levels), that are world-record unique. This uniqueness comes with a price that reflects constraints of the magnets and the low temperatures, including limited volume and time at peak magnetic field, cryogenic power limits on electronics, and, particularly for pulsed magnets, increased noise. In effect, the instrumentation constraints are similar for NHMFL superconducting, resistive and pulsed magnets. An NHMFL experimentalist therefore has a simple goal: acquisition of all the information produced by a measurement in the shortest time permitted by information theory, with minimum sensitivity to noise and interference. To assist with this, we propose here to eliminate commercial general-purpose lock-in amplifiers, preamplifiers and digitizers and replace them with commercial-quality custom building blocks optimized for NHMFL measurements, that are faster, quieter, more versatile, and cheaper. We will use these new instruments to support users by improving present measurements as well as adding new capabilities, including specific heat for materials that suffer adiabatic effects in pulsed fields, and thermal conductivity in both dc and pulsed magnets based on 3rd harmonic methods. We will use these techniques to measures the thermal conductivity of high Tc superconductors at high field in the normal state, and to test the Weideman-Franz relationship between electronic thermal conductivity and electrical conductivity in the extreme high-field limit.
THOMPSON's METHOD APPLIED TO THE BROWNIAN AND NON-BROWNIAN DIFFUSION-CONTROLLED REACTIONS OF TYPE kA → lA (l < k)
Authors: NASSIF CLÁUDIO , SILVA P. R.
Published: October 2002

The diffusion-controlled reactions of type kA → lA, with l < k, including the case of the annihilation reaction kA → 0, are studied by using Thompson's method, both in the case of Brownian (γ = 2) as in the case of anomalous (γ ≠ 2) diffusion conditions. These reactions are known to be strongly dependent on fluctuations below some critical dimension dc. We find dc = γ/(k-1) and the asymptotic behavior of density [Formula: see text]. At d = dc, the density goes as <∊> ~ ( ln t/t)1/k-1. For γ = 2, the scaling results obtained here are in agreement with the renormalization group calculations of Lee15 and a more recent work of Oliveira.8 We go further by also studying the case of an external homogeneous source (h) of single species particles A in the case of the stationary regime. Then we obtain the critical exponent δ in [Formula: see text], the dynamical exponent for the relaxation time Δ′ in (τh ~ hΔ′) and the exponent for the concentration decay ξ in (∊ ~ τ- ξ), with all these quantities evaluated in the limit h → 0. We get relations of scaling among critical indexes, and, in the special case of γ = 2, we recover those results previously obtained by Rácz.30 Thompson's method is a simple alternative way to the renormalization group scheme and has been shown to be a good description for the long-time (long wave-length) regime.
The generalized Turner‐Bradley‐Kirk‐Pruitt equation
Authors: Redheffer Ray
Published: October 2002

Several recent results pertaining to nonlinear equations of
ecology are applied to a generalization of the
Turner‐Bradley‐Kirk‐Pruitt (TBKP) equation, which illustrates a
variety of interesting possibilities as regards persistence and
extinction. The chief novelty consists in exploiting the value set
of the equation, that is, the set of values taken on by the
solution as t
increases from 0
to ∞. This aspect of
the subject depends on a new formulation of a condition that was
first introduced by Vance and Coddington in 1989.
Geotechnical Engineering Aspects of the June 1999 Central Mexico Earthquakes
Authors: Pestana J. M. , Sancio R. B. , Bray J. D. , Romo M. P. , Mendoza M. J. , Moss R. E. S. , Mayoral J. M. , Seed R. B.
Published: October 2002

An earthquake of moment magnitude (Mw) 7.0 struck the central region of Mexico on 15 June 1999 between the states of Puebla and Oaxaca. A second event with a moment magnitude 6.3 occurred on June 21, also affecting the central region of Mexico but with minor consequences. Attenuation relationships of peak ground acceleration with hypocentral distance for the June 15th event were compared with strong-motion recordings over a variety of geologic site conditions. Significant site amplification was observed and was correlated with deep soil conditions. The June 15th event caused significant damage of unreinforced masonry structures, such as churches and houses, including more than 500 historical buildings. Puebla City and the towns of Tehuacán and Acatlán de Osorio were the urban areas hardest hit by the earthquake. Although the earthquake was felt in Mexico City, the damage was light and mostly restricted to nonstructural elements. Comparison with observations obtained during the September 1985 earthquake suggest that significant soil nonlinearity, resulting in increased amplification at larger periods, can be observed for soft soil sites.