bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of copper films deposited on H2-plasma-treated TaN substrate by chemical vapor deposition
Authors: Lin Cheng-Li , Chen Peng-Sen , Chang Chun-Li , Chen Mao-Chieh
Published: October 2002

This work investigates the chemical vapor deposition Cu films deposited on the TaN substrate with and without an H2-plasma treatment prior to Cu film deposition and the effect of postdeposition thermal annealing. The Cu films deposited on the H2-plasma-treated TaN substrate have a number of favorable properties over the films deposited on the TaN substrate without the plasma treatment. These include an increased (111)-preferred orientation, smoother film surface, and a larger effective deposition rate. However, the Cu films deposited on the H2-plasma-treated substrate have a higher electrical resistivity, presumably due to the smaller grain size. The postdeposition thermal annealing enhanced the (111)-preferred orientation and decreased the resistivity of the as-deposited Cu films. We presume that the H2-plasma treatment, resulted in a dense and uniform distribution of hydrogen radicals adsorbed on the substrate surface, leading to the shortening of incubation time and the formation of Cu films with a smoother surface and enhanced (100)-preferred orientation. A combined process including H2-plasma substrate treatment prior to Cu film deposition and postdeposition thermal annealing at an appropriate temperature in N2 ambient, is proposed for the advantage of low-resistivity and high (111)-oriented Cu film deposition.
Wet-etching selectivity of Ag-photodoped AsGeSeS thin films and the fabrication of a planar corrugated one-dimensional photonic crystal by a holographic method
Authors: Lee Hyun-Yong , Yao Takafumi
Published: October 2002

Characteristics of Ag photodoping into an amorphous As40Ge10Se15S35 thin film and its wet-etching selectivity containing edge-sharpening effect have been investigated. A planar corrugated one-dimensional photonic crystal (1D PC) has also been fabricated by a holographic method based on the Ag photodoping. Ag-doped films by an illumination of HeCd laser at 77 K (cooled Ag-doped films) exhibit a relatively uniformly distributed Ag profile over the entire depth of the chalcogenide and a strong resistance against an alkaline development solution. That is, the cooled Ag-doped film acts as a negative-type resist for wet-etching development using a solution of NaOH (selectivity >99%). In addition, its sensitivity and contrast, obtained from the exposure response curve, are very good to be approximately 3.3x1015 photons/cm2 and 6.46, respectively. Contrarily, Ag-doped films at 300 K (normally Ag-doped films) exhibit a Gaussian-formed Ag distribution, which has a peak at the interface (about 500 nm depth) between chalcogenide and substrate and a depletion at a depth of 0–400 nm. In particular, an edge-sharpening effect is observed in both developed films and this is discussed considering the model of photoinduced chemical modifications. This effect is thought to play an important role in fabricating a fine planar 1D PC structure by the holographic method. The fabricated 1D PC consisted of a space (s) of 350 nm and a linewidth (l) of 230 nm. For the holographic method based on Ag photodoping, a fabrication criterion for controlling the ratio s/l and the period Λ(=s+l) that are the important parameters in 1D PC structures is also proposed.
Effect of In and N incorporation on the properties of lattice-matched GaInNAs/GaAs grown by radio frequency plasma-assisted solid-source molecular beam epitaxy
Authors: Loke W. K. , Yoon S. F. , Ng T. K. , Wang S. Z. , Fan W. J.
Published: October 2002

We present the effect of nitrogen (N) and indium (In) incorporation on the structural and optical properties of Ga1−xInxNyAs1−y with low lattice mismatch to GaAs grown by solid-source molecular beam epitaxy using a radio frequency (rf) nitrogen plasma source. The results show that excessive introduction of nitrogen during the growth of GaInNAs may lead to greater incorporation of interstitial nitrogen and degradation in crystal quality. This effect is more significant in GaInNAs compared to GaNAs. A drastic 6× increase in x-ray diffraction full width at half maximum (XRD-FWHM) was observed in GaInNAs compared to 1.5× increase of the same in GaNAs when reactive nitrogen is introduced into the material. The more significant degradation in GaInNAs quality is believed to be due to greater incorporation of interstitial nitrogen in the presence of indium during growth. By changing the In content and fixing the N incorporation rate, a sample of Ga0.924In0.076N0.026As0.974/GaAs with relatively low lattice mismatch of −896 ppm (or ∼8.96×10−4) was grown. Low temperature (4 K) photoluminescence emission at 1518 nm was observed and XRD-FWHM of 118.2 arcsec was measured.
Improved TaN barrier layer against Cu diffusion by formation of an amorphous layer using plasma treatment
Authors: Ou Keng-Liang , Wu Wen-Fa , Chou Chang-Pin , Chiou Shi-Yung , Wu Chi-Chang
Published: October 2002

The thermal stability and electrical properties of plasma-treated TaN films have been investigated by Cu/TaN/Si systems. The properties of diffusion barrier were evaluated by sheet resistance, x-ray diffraction (XRD), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), energy-dispersive spectroscopy (EDS), Auger electron microscopy (AES), and reverse-biased junction leakage current. A new amorphous layer is found to form on the surface of TaN film after the plasma treatment. Plasma-treated TaN films show better barrier performance than untreated TaN films. The sheet resistance of Cu/TaN(10 nm)/Si increases apparently after annealing at 625 °C for 1 h, while the Cu/plasma-treated TaN(10 nm)/Si is fairly stable up to annealing at 750 °C. The resistance to copper diffusion in plasma-treated TaN film is more effective. This is attributed that an amorphous layer that forms on the surface of TaN film after the plasma treatment. The thermal stabilities of Cu/TaN/n+-p junction diodes are enhanced by plasma treatment. The Cu/TaN(10 nm)/n+-p and Cu/TaN(50 nm)/n+-p junction diodes result in large reverse-biased junction leakage currents after annealing at 525 and 575 °C, respectively. On the other hand, plasma-treated TaN diffusion barriers improve the integrity of junction diodes up to 650 °C. Nano crystallization and stuffing effects of plasma treatments are believed to impede Cu diffusion into the Si substrate and hence improve the barrier performance.
Influences of reaction products on etch rates and linewidths in a poly-Si/oxide etching process using HBr/O2 based inductively coupled plasma
Authors: Miwa K. , Mukai T.
Published: October 2002

Variation of etch rates and linewidths due to various seasoning methods after plasma cleaning of an etch chamber in a poly-Si/oxide (SiO2) etching process are studied. An HBr/O2 based inductively coupled plasma (ICP) was investigated to determine the root cause and mechanisms of the variation. Poly-Si main-etch rates remain nearly constant after seasonings with bare-Si etching (hereafter, we denote the seasoning as Si seasoning) succeeding plasma cleaning of the chamber wall with an SF6 based ICP. Poly-Si over-etch rates increased and leveled off as the Si-seasoning time increased, whereas SiO2 etch rates drastically varied with increased Si-seasoning time. The optically estimated density of SiBr in the SiO2 etching plasma was found to increase with increased Si-seasoning time. SiO2 etch rates also varied as a function of O2 flow rate and bias power to the bottom electrode of the ICP etcher. These results suggest that etch rates of poly-Si and SiO2 are influenced by reaction products such as SiBrx (x=1,2,3) in the plasma. Critical-dimension (CD) shifts of poly-Si linewidths increased after Si seasonings. On the other hand, when short-time (about 10 s) plasma cleaning of the chamber was performed between etchings in the Si seasoning, CD shifts hardly increased or slightly decreased. Poly-Si over-etch rates also hardly increased with the short-time plasma cleaning. The results suggest that reaction products derived from deposition on the chamber wall would lead to the increase of CD shifts of poly-Si linewidths and poly-Si over-etch rates.
Ion flux composition in HBr/Cl2/O2 and HBr/Cl2/O2/CF4 chemistries during silicon etching in industrial high-density plasmas
Authors: Cunge G. , Inglebert R. L. , Joubert O. , Vallier L. , Sadeghi N.
Published: October 2002

Anisotropic etching of silicon gates is a key step in today’s integrated circuit fabrication. For sub-100 nm gate dimensions, one of the main issues is to precisely control the shape of the etched feature. This requires a detailed knowledge of the various physicochemical mechanisms involved in anisotropic plasma etching. Since silicon etching in high-density plasmas is strongly ion assisted, the identities of the ions bombarding the wafer is a key parameter that governs the etch rates and the etched profiles. In the present article, mass spectrometry has been used to investigate the chemical composition of the ion flux bombarding the reactor walls of an industrial inductively coupled plasma used for 200-mm-diam silicon wafer processing. The plasma chemistries investigated are HBr/Cl2/O2 and HBr/Cl2/O2/CF4 mixtures optimized for sub-100 nm gate processes. Quantitative ion mass spectra show that under those conditions the ion flux contains up to 50% of SiClXBrY+ (X,Y=0–2) ions, although Cl+, Cl2+, and Br+ ions were expected to be the predominant species. This observation can be explained by the combination of two well-accepted phenomena that are discussed in detail. The impact of the surprisingly large amount of ionized silicon-based etch products on silicon etching mechanisms are discussed.
QUANTUM HALL EFFECT IN AlAs 2D ELECTRON SYSTEMS
Authors: DE POORTERE E. P. , TUTUC E. , SHKOLNIKOV Y. P. , VAKILI K. , SHAYEGAN M. , PALM E. , MURPHY T.
Published: October 2002

We report on Fabrication of two-dimensional electrons in AlAs quantum wells with mobilities up to 31 m2/Vs. Magnetoresistance measurements reveal fractional quantum Hall states at high-order filling factors, and up to ν = 11/3. Shubnikov-de Haas oscillations of high-density samples suggest that electrons occupy two X-point valleys. We also study properties of hysteretic resistance spikes occurring at transitions between quantum Hall ferromagnets in AlAs quantum wells, and show that the spike hysteresis depends sensitively on the number of occupied energy levels involved in the transition.
TUNNELING IN A QUANTUM HALL EXCITONIC CONDENSATE
Authors: EISENSTEIN J. P. , SPIELMAN I. B. , PFEIFFER L. N. , WEST K. W.
Published: October 2002

Recent experiments on the tunneling conductance between parallel 2D electron gases at total Landau level filing ν tot = 1 are described. When the two layers are close enough together the ground state of the system may be viewed as a Bose condensate of excitons consisting of electrons in one layer paired with (conduction band) holes in the other. The measured tunneling conductance exhibits a spectacular resonance around zero bias which resembles the dc Josephson effect. This resonance is a signature of long wavelength Goldstone collective modes in the phase coherent ground state. Experiments performed with an added in-plane magnetic field have demonstrated the expected linear dispersion of this mode.
ULTRAFAST MANIPULATION OF ELECTRON SPIN COHERENCE IN QUANTUM WELLS
Authors: GUPTA J. A. , AWSCHALOM D. D. , KNOBEL R. , SAMARTH N.
Published: October 2002

A recently developed technique is reviewed with the potential for all-optical coherent control over electron spins in semiconductors. In these experiments, ultrafast laser pulses "tip" electron spins by generating effective magnetic fields via the optical Stark effect. Measurements of Stark shifts have provided estimates of the net tipping angle as a function of tipping pulse energy, intensity, and polarization. Background contributions to the measured tipping angle arise from the undesirable excitation of additional carriers by the tipping pulse.
SOME FRACTIONS ARE MORE SPECIAL THAN OTHERS: NEWS FROM THE FRACTIONAL QUANTUM HALL ZONE
Authors: PAN W. , STORMER H. L. , TSUI D. C. , PFEIFFER L. N. , BALDWIN K. W. , WEST K. W.
Published: October 2002

We report observation of new fractions: 4/11, 5/13, and 6/17 between ν=2/5 and ν=1/3, 4/3 and 5/17 between ν=1/3 and ν=2/7, and 4/19 between ν=2/9 and ν=1/5. The ν=4/11 state was studied in detail. The tilting magnetic field data show that its ground state is spin-polarized.
INTERFERENCE AND DECOHERENCE OF COMPOSITE FERMIONS IN THE QUANTUM HALL EFFECT
Authors: STERN A.
Published: October 2002

In this talk I will discuss quantum interference phenomena of composite fermions in quantum Hall systems. In particular, I will focus on huge mesoscopic fluctuations of non-linear response and of Coulomb drag in single and bi-layer systems. Finally, I will give a simple physical picture of dephasing (de-coherence) of composite fermions, with simple expressions for their coherence length.

Most of the talk will be based on work done in collaboration with I. Aleiner and B. Narozhny (Stony Brook).
HIGH MAGNETIC FIELD DEPENDENT DIAMAGNETIC SHIFTS IN AlxGa1-xAs SEMICONDUCTOR ALLOYS
Authors: JONES E. D. , RENO J. L. , CROOKER S. , BAJAJ K. K. , COLI G.
Published: October 2002

Low temperature diamagnetic shifts and FWHM linewidths of excitonic transitions in Al x Ga 1-x As alloys are reported as a function of magnetic field (50T maximum) at 4K using photoluminescence spectroscopy. Two samples with aluminum compositions of 5 and 20%, are discussed. The slope of the diamagnetic shift at high fields allows a direct measure of the excitonic reduced mass μ.
EFFECT OF STRONG TERAHERTZ RADIATION ON MAGNETOCONDUCTIVITY IN TWO DIMENSIONS
Authors: LEWIS R. A. , XU W. , KOENRAAD P. M. , BRADLEY I. V.
Published: October 2002

The interaction between strong THz radiation from a free electron laser and an electron sheet in a high-mobility, low-density, GaAs/AlGaAs structure has been investigated in magnetotransport experiments over a wide range of wavelengths, intensities, magnetic fields, and temperatures. Photovoltage and photocurrent effects are evident in both longitudinal and transverse potential differences. Broad cyclotron resonance is observed to high temperature and connected with a decrease in electron density. The change in electron temperature under THz radiation is estimated from changes in the magnitude of the magnetoresistivity oscillations at low lattice temperature. The effect of the magnetic field is to suppress the rise in electron temperature relative to the zero field case.
INCREASE OF QUANTUM HALL PLATEAU WIDTHS DUE TO ELECTRON-PHONON INTERACTION
Authors: RIESS J. , DUGUET T. , MAGYAR P. , BICOUT D.
Published: October 2002

We calculate the conductivities for a model system of the integer quantum Hall effect including electron-phonon interactions, with a substrate potential chosen such that microscopic processes can be understood in detail. We find that in general the macroscopic Hall current is not only composed of velocities arising from the Schrödinger time evolution but also of velocities generated by electron-phonon interactions and that the latter can contribute to the formation of the quantized Hall plateaus. We show for typical quantum Hall systems the phonon induced contributions lead to Hall plateaus which are somewhat larger than the plateaus of the dissipative conductivity. Experimentally this difference has been known for a long time, but it seemed unexplained so far. In the case where the substrate potential has no spatial fluctuations in the direction of the macroscopic electric field, all states are conducting and the dissipative conductivity vanishes only near integer filling factors. Nevertheless, the calculated Hall conductivity shows broad quantized plateaus, which here are entirely generated by velocities arising from phonon induced relaxation processes. These results show that absence of dissipation is not indispensable for the existence of quantized Hall plateaus.
SEARCH FOR SUPERLUMINAL PROPAGATION IN HIGH MAGNETIC FIELDS
Authors: RIESS J.
Published: October 2002

We investigate the possibility of superluminal propagation of massive particles in high magnetic fields. Formal arguments suggest that this could occur in the quantum Hall regime near zero temperature, since here a few conducting states in the center of a broadened Landau band carry a macroscopic Hall current. We investigate the microscopic processes which lead to the high velocities of conducting states in the quantum Hall effest and ask what are the highest possible velocities which can be generated in that way. Our analysis shows that in typical quantum Hall systems at the most a tiny fraction of a carrier wave function can describe superluminal behaviour but that the center of mass velocity is far below the velocity of light. On the other hand, on pure theoretical grounds we can construct special systems (with ≪exotic≫ parameters) where the Schrödinger equation does admit solutions with superluminal center of mass velocities. The described propagation has no analogy in classical physics. Einstein's causality is not violated. The time evolution of the corresponding wave function is similar to that of a recently observed superluminal light pulse.1 We discuss analogies and differences between the two phenomena.
RECONSTRUCTION OF FRACTIONAL QUANTUM HALL EDGES
Authors: WAN X. , YANG K. , REZAYI E. H.
Published: October 2002

Edge reconstruction has been a well-known effect for integer quantum Hall liquids in the presence of both electron interactions and a confining potential generated by charged background. At more generic fractional fillings, we point out that confined two-dimensional interacting electrons can exhibit the similar reconstruction effect. Our exact diagonalization results show that, in a fractional quantum Hall system with a sharp cleaved edge potential, the electron density oscillation near the edge increases with the distance between the electron gas and the background charge layer. As a results, the outermost hump can detach from the bulk beyond certain point. We suggest that the edge reconstruction effect is relevant to the recent edge tunneling experiments,1 as well as the microwave absorption experiment on two-dimensional electrons in an antidot array.2 Calculating the finite-temperature density profiles, we estimate the temperature above which the edge reconstruction disappears to further discuss the relevance to the microwave absorption experiment.
SAMPLE COOLING AND ROTATION AT ULTRA-LOW TEMPERATURES AND HIGH MAGNETIC FIELDS
Authors: XIA J. S. , ADAMS E. D. , SULLIVAN N. S. , PAN W. , STORMER H. L. , TSUI D. C.
Published: October 2002

A rotator, made from polycarbonate and operated hydraulically using liquid helium, has been developed at the High B/T Facility of the National High Magnetic Field Laboratory (NHMFL) in Gainesville, It can be tilted more than 90 degrees by applying a pressure of several bars. The frictional heating was found to be negligible down to 8.0 mK. The sintered silver powder heat exchangers, specially designed for the cooling of the two-dimensional electron gas (2DEG) system in the fractional quantum Hall effect (FQHE) experiment,1,2 are also attached to the rotator. We have conducted an angular-dependent study of the even-denominator FQHE state at ν = 5/2. Our preliminary data showed that the rotator performed well at ultra-low temperatures and high magnetic fields. This technique should be applicable for other transport measurements at such extreme experimental conditions.
QUANTUM CRITICAL FLUCTUATIONS IN HEAVY FERMION COMPOUNDS
Authors: SCHROEDER A. , AEPPLI G. , COLEMAN P. , RAMAZASHVILI R. , COLDEA R. , ADAMS M. , BUCHER E. , MCMORROW D. F. , LÖHNEYSEN H. V. , STOCKERT O.
Published: October 2002

The electronic properties of heavy fermion alloys are dominated by spin fluctuations which are expected to become critical when tuned by pressure to a quantum critical point (QCP), entering a magnetic ordered state. Apart from the onset of exotic superconductivity, unexpected "normal conducting" behavior is found close to the QCP, which does not seem only to escape the conventional view of metals (Fermi liquids) but also the "conventional view" of an antiferromagnetic quantum phase transition in these f-metals. So far only few compounds have been investigated by neutron scattering to directly reveal the critical fluctuations spectrum. In CeCu 59 Au 01 the fluctuations develop an unusual energy dependence, characterized by an exponent α = 0.75, which persist over the entire Brillouin zone, provoking an unexpected local non Fermi liquid behavior. The same unusual exponent derived from E/T scaling determines the H/T scaling of the uniform magnetization. Recent neutron scattering data in magnetic fields further confirm this picture of nearly free local magnetic moments (modified by α) emerging at the antiferromagnetic QCP in this strongly correlated electron system.
ANISOTROPIC PROPERTIES OF SINGLE-CRYSTALLINE CeNiGe2
Authors: JUNG M. H. , HARRISON N. , LACERDA A. H. , PAGLIUSO P. G. , SARRAO J. L. , THOMPSON J. D.
Published: October 2002

The anisotropic properties of CeNiGe 2 with a layered crystal structure have been studied by measurements of electrical resistivity, magnetic susceptibility and magnetization. It is confirmed that CeNiGe 2 undergoes two-step antiferromagnetic transition at T N I = 4 K and T N II = 3 K as reported earlier on polycrystalline samples. CeNiGe 2 is found to exhibit highly anisotropic properties with an easy magnetization axis along the longest crystallographic b direction. The magnetization ratio M(H//b)/M(H⊥b) is estimated to be about 15 at 5 T. The in-plane resistivity ρ⊥b(T) shows double maxima typical of that expected when an interplay of crystal-field and Kondo effects plays a role. The low-T maximum at 4-K in ρ⊥b(T) is strongly suppressed with increasing magnetic field. This negative magnetoresistance is a result of the strong reduction of magnetic scattering by the ferromagnetic alignment of Ce magnetic moments.
HIGH FIELD PHASE DIAGRAM OF THE FIELD-INDUCED SUPERCONDUCTING STATE OF λ-(BETS)2FeCl4
Authors: BALICAS L. , BROOKS J. S. , STORR K. , UJI S. , TOKUMOTO M. , TANAKA H. , KOBAYASHI H. , KOBAYASHI A. , BARZYKIN V. , GOR'KOV L. P.
Published: October 2002

We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor λ- (BETS) 2 FeCl 4. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T, and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field compensates the exchange field of aligned Fe 3+ ions. We further argue that the Fe 3+ moments are essential to stabilize the resulting singlet, two-dimensional superconducting state. Here we provide experimental evidence indicating that this state, as well as the insulating antiferromagnetic ground state, is extremely sensitive to hydrostatic pressure.
ELECTRON MAGNETIC RESONANCE FERMI SURFACE IMAGING: APPLICATIONS TO ORGANIC CONDUCTORS AND Sr2RuO4
Authors: HILL S. , KOVALEV A. , MOLA M. M. , PALASSIS C. , MAO Z. Q. , MAENO Y. , QUALLS J. S.
Published: October 2002

We report detailed angle dependent studies of the metallic state microwave (40 to 200 GHz) magneto-conductivity of single crystal samples of the α- (BEDT-TTF) 2 KHg(SCN) 4 organic charge density wave conductor, and the perovskite superconductor Sr 2 RuO 4. We observe series' of resonant absorptions which we attribute to periodic orbit resonances - a phenomenon closely related to cyclotron resonance. By performing measurements on several samples, and in different electromagnetic field configurations, we are able to couple to different orbital modes (+ harmonics), which derive from deformations (warpings) of the quasi-one and quasi-two-dimensional Fermi surfaces of these compounds. These studies provide vital information concerning interlayer dispersion which, in turn, affects the Fermi surface nesting characteristics which are believed to play a crucial role in the low temperature physics of these exotic materials.
FAR-INFRARED HALL EFFECT IN NORMAL STATE OF YBCO
Authors: GRAYSON M. , RIGAL L. , SCHMADEL D. C. , DREW H. D. , KUNG P.-J.
Published: October 2002

Cuprate superconductors in the normal state exhibit the "anomalous Hall effect",1ie., the longitudinal components of the current scattters linearly with T whereas the Hall angle obeys a T2 scattering, where T is temperature. To help resolve this anomaly, we have developed a technique to measure the Hall angle at far-infrared frequencies. Measuring the magnetotransmission spectrum of polarized light through thin film of YBCO, we are able to independently measure both the real and imaginary parts of the complex Hall response. With a spectral range from dc to 250 cm -1, a lineshape analysis of the Hall response reveals that the Hall angle spectrum has a non-Lorentzian from thereby ruling out Drude-like transport models of the Hall effect. Instead it shows a dominant Loretnzian-squared response, implying a square-scattering behavior with a scattering rate that is linear in T and which quantitatively fits the linear scattering rate of the longitudinal current. The experimental results strongly constrain the number of theories that can accurately describe transport in normal state cuprates.
LOW-TEMPERATURE NORMAL-STATE HALL EFFECT IN HIGH-TcBi2Sr2-xLaxCuO6+δ REVEALED BY 60 T MAGNETIC FIELDS
Authors: BALAKIREV F. F. , BETTS J. B. , BOEBINGER G. S. , ONO S. , ANDO Y. , MURAYAMA T.
Published: October 2002

We report low-temperature Hall coefficient in the normal state of the high-Tc superconductor Bi 2 Sr 2-x La x CuO 6+δ. The Hall coefficient was measured down to 0.5 K by suppressing superconductivity with a 60 T pulsed magnetic field. The carrier concentration was varied from overdoped to underdoped regimes by partially substituting Sr with La in a set of five samples. The observed saturation of the Hall coefficient at low temperatures suggests the ability to extract the carrier concentration of each sample. The most underdoped sample exhibits a diverging Hall coefficient at low temperatures, consistent with a depletion of carriers in the insulating ground state. The Hall number exhibits a sharp peak providing additional support for the existence of a phase boundary at the optimal doping.
MAGNETOTRANSPORT AND THE MAGNETIC PHASE DIAGRAM OF SUPERCONDUCTING ErNi2B2C
Authors: SCHMIEDESHOFF G. M. , TOUTON S. , BEYERMANN W. P. , LACERDA A. H. , BUD'KO S. L. , CANFIELD P. C.
Published: October 2002

We report magnetotransport measurements made on the anisotropic magnetic superconductor ErNi 2 B 2 C . We observe a minimum in the magnetoresistance with fields along the a-axis, a behavior consistent with the high field quenching of magnetic scattering. When the field is applied along the c-axis the magnetoresistance is positive. The temperature of the antiferromagnetic phase transition is depressed by magnetic fields applied along the c-axis (as it is along the a-axis) and is suppressed near 17 T. A feature in the first derivative of the temperature dependent resistivity may be related to the weak ferromagnetic phase. We find the temperature at which this feature occurs to be independent of magnetic fields to 18 T.
THEORETICAL OVERVIEW OF SUPERCONDUCTIVITY IN STRONTIUM RUTHENATE
Authors: AGTERBERG D. F.
Published: October 2002

An overview of the phenomenological and microscopic theory of the superconducting state in Sr 2 RuO 4 is presented. Existing experimental evidence will be used to demonstrate that the superconducting state is a 2D analogue of the Anderson Brinkman Morel superfluid 3 He state. A discussion of the microscopic theory will be presented that focuses on the recent experimental observations that line-nodes exist in superconducting Sr 2 RuO 4. These nodes come as a surprise since theory would predict a spin-triplet pairing state to be nodeless for this quasi-2D material. Finally, the consequences of magnetic fields on this pairing state will be described.
CRYSTAL-FIELD EFFECTS IN THE FIRST-ORDER VALENCE TRANSITION IN YbInCu4 INDUCED BY EXTERNAL MAGNETIC FIELD
Authors: DZERO M.
Published: October 2002

As it was shown earlier [Dzero, Gor'kov and Zvezdin, J. Phys.: Condens. Matt.12, L711 (1000)], the properties of the first-order valence phase transition in YbInCu4 in the wide range of magnetic fields and temperatures are perfectly described in terms of a simple entropy transition for free Yb ions. Within this approach, the crystal field effects have been taken into account and we show that the phase diagram in the B - T plane acquires some anisotropy with respect to the direction of an external magnetic field.
PHASE TRANSITIONS IN INSULATING VANADIUM OXIDE
Authors: JOSHI A. , MA M. , ZHANG F. C.
Published: October 2002

The magnetic phase transition from the paramagnetic to antiferromagnetic state in insulating V2O3 shows some very interesting features. Not only is the magnetic order ng pattern anomalous, but the magnetic transition shows other surprises: I) the magnetic and orbital ordering occur at the same transition temperature; II) the transition is strongly first order; III) above the transition temperature, neutron scattering observes features in wave vectors different from the ordering wave vector. We study this system using the recently proposed S = 2 bond model (Phys. Rev. Lett.85, 1714 (2000)) for insulating V2O3. We show that this model not only explains the anomalous magnetic ordering, but also resolves the other questions associated with the magnetic phase transition (Phys. Rev. Lett.86, 5743 (2001)). We further point out the possibility of changes in the phase transition phenomenology in presence of a magnetic field, and another orbital phase transition at lower temperatures.
MAGNETIZATION CURVES OF QUASI-ONE-DIMENSIONAL HALDANE SYSTEMS
Authors: KAWAGUCHI A. , KOGA A. , KAWAKAMI N. , OKUNISHI K.
Published: October 2002

We study the magnetization process of a quasi-one-dimensional S=1 antiferromagnet with bond alternation by using the density matrix renormalization group method combined with interchain mean-field approximation. Particularly, we discuss how the interchain couplings affect the magnetization curve around a plateau structure in both of the Haldane phase and the dimer phase. It is shown that the antiferromagnetic correlation induced by the interchain couplings reduces the region of the plateau significantly, which will play an important role when the theoretical results are compared with actual measurements of the magnetization.
THE STUDY OF THE MAGNETIC BREAKDOWN EFFECT AS A FUNCTION OF ANGLE IN THE ORGANIC CONDUCTOR K- (BEDT-TTF)2Cu(NCS)2 IN HIGH MAGNETIC FIELDS
Authors: MIHUT I. , AGOSTA C. C. , MIELKE C. H. , TOKOMOTO M.
Published: October 2002

The magnetic breakdown effect can be seen by the growth of new frequencies in the quantum oscillations in clean metals as a function of magnetic field. We have studied the variation of the amplitudes in the quantum oscillations in the resistance (the Shubnikov-de Haas effect) as a function of angle in the quasi-two dimensional-organic conductor κ-(BEDT-TTF)2Cu(NCS)2. The measurements were made by means of a radio frequency (rf) tank circuit (~ 50 MHz) at very high magnetic fields(50T-60T) and low temperature(500 mK). The geometry of the rf excitation we used excited in-plane currents, and therefore we measured the in-plane resistivity. In contrast to conventional transport measurements that measure the inter-plane resistivity, the in-plane resistivity is dominated by the magnetic breakdown frequencies. As a result we measured much higher breakdown frequency amplitudes than conventional transport experiments. As is expected, the angular dependence of the Shubnikov-de Haas frequencies have a 1/cosθ behavior. This is due to the change of the cross sectional area of the tubular Fermi surface as the angle with respect to the magnetic field is changed. The amplitude of the oscillations changes due to the spin splitting factor which takes into account the ratio between the spin splitting and the energy spacing of the Landau levels which also has 1/cosθ behavior. We show that our data agree with the semi-classical theory (Lifshitz-Kosevich formula).
ELECTRONIC SCATTERING AND SPIN DISORDER IN 3d-FERROMAGNETS IN THE PARAPROCESS REGIME
Authors: RAQUET B. , BROTO J. M. , VIRET M. , SONDERGARD E. , CESPEDES O.
Published: October 2002

We determine the collective spin excitations and their contribution to the intrinsic resistivity in 3d-ferromagnets by high field magneto-transport experiments. In the paraprocess regime, the longitudinal magneto resistance has a non saturating negative slope of about 0.02-0.05μΩ.cm.T1 at 300 K for Fe, Co and Ni. We demonstrate its magnetic origin and assign the effect to a decrease of the electron-magnon scattering due to the damping of spin waves in high field. We provide a unique estimate of the pure magnetic resistivity in 3d-ferromagnets. Our analysis also gives an insight into the low energy spin waves, i.e. the theoretical magnon saturation field and the magnon mass renormalization.
ADVANCES IN MEGAGAUSS FIELD GENERATION AND APPLICATION AT ISSP
Authors: MIURA N. , MATSUDA Y. H. , UCHIDA K. , IKEDA S. , HERLACH F.
Published: October 2002

We report recent progress in the generation and application of megagauss fields at the new Megagauss Laboratory of ISSP in Kashiwa. New facilities for studying physics in ultra-high magnetic fields were built at the new campus of the University of Tokyo at Kashiwa, where pulsed high magnetic fields are produced by three different techniques: electromagnetic flux compression, the single-turn coil technique and non-destructive long pulse magnets. Considerable progress has been made in each of these techniques, as compared with the old facilities at Roppongi. For electromagnetic flux compression, the rise time of the primary current was reduced by decreasing the residual inductance of the capacitor bank. The cylindrical symmetry of the liner implosion was remarkably improved by inserting a "feed gap compensator" between the primary coil and the liner. So far, a maximum field of 622T has been achieved. By the single-turn coil technique, very high fields exceeding 300T have been obtained depending on the coil bore, in two systems with horizontal and vertical coil axes. These fields are successfully applied in many different kinds of experiments. Non-destructive long pulse fields up to 60T are available from wire-wound coils.
RECENT ADVANCES IN LOW TEMPERATURE THERMOMETRY IN HIGH MAGNETIC FIELDS
Authors: PALM E. C. , MURPHY T. P. , TOZER S. W. , HANNAHS S. T.
Published: October 2002

The accurate determination of the temperature of an experiment at low temperatures in high magnetic fields is difficult. We present the results of measurements made using a number of new techniques developed over the last few years. In particular we discuss the results of measurements made using a unique capacitor made with Kapton and copper in a cylindrical geometry.1 This capacitance thermometer, dubbed the "Kapacitor", is different from other low temperature thermometers in that the minimum in capacitance vs. temperature can be moved to lower temperatures (to below 20 mK) by changing the construction technique. In addition, we discuss measurements on Coulomb blockade thermometers (CBT's) that offer the possibility of true primary thermomemtry at low temperatures without any magnetic field dependence. Both of these new techniques will be compared to the standard technique of resistance thermometry using RuO chip resistors. The crucial issues of accuracy and precision, usefulness for control, and noise sensitivity will be discussed for each of these technologies. In addition, recent measurements on the magnetic behavior of RuO thermometers at low temperatures and its relationship to anomalous low field peaks in the resistance that develop at temperatures below 50 mK are also presented.
n-PARTICLE ENTANGLED STATES IN THE n-MODE FOCK SPACE
Authors: SONG TONG-QIANG , ZHU YUE-JIN
Published: October 2002

We introduce the n-particle entangled states in n-mode Fock space and examine their completeness relation, partly non-orthonormal property and Schmidt decomposition.
EGALITARIAN SETS FOR TU-GAMES
Authors: ARIN J. , IÑARRA E.
Published: October 2002

The paper introduces and studies egalitarian sets in the context of TU-games. Those solutions follow the idea that a payoff is egalitarian if it is bilaterally egalitarian.
ON THE COMPLEXITY OF COALITIONAL REASONING
Authors: PAULY MARC
Published: October 2002

Coalitional power in multistage processes is modeled using effectivity frames, which link an effectivity function to every possible state of the world. Effectivity frames are general enough to capture, e.g., what groups of agents can bring about in extensive games of perfect and almost perfect information. Coalition Logic is used to describe effectivity frames, and the question of generating an extensive game satisfying a given specification is formulated as a satisfiability problem in Coalition Logic. Using this logical reformulation, we show that the complexity of this implementation problem depends on two parameters: For coalitional specifications, the problem is shown to be PSPACE-complete. For individual specifications on the other hand, i.e., for specifications which only refer to the powers of individual agents, generating an implementation with perfect information is PSPACE-complete, whereas generating an implementation with almost perfect information is NP-complete.
CORES OF STOCHASTIC COOPERATIVE GAMES WITH STOCHASTIC ORDERS
Authors: FERNÁNDEZ F. R. , PUERTO J. , ZAFRA M. J.
Published: October 2002

In this paper we analyze cooperative games where the worth of a coalition is uncertain and the players only know their probability distribution. The novelty of our analysis is that the comparison among the uncertain values is done by stochastic orders among random variables. Thus, the classical concepts in cooperative game theory have to be revisited and redefined. This form of comparison leads to two-different notions of core. Conditions are given under which these cores are nonempty. The results are applied on three families of stochastic games.
HOUSEHOLD ECONOMIES WITH INFINITELY MANY AGENTS: A GAME-THEORETIC ANALYSIS
Authors: WIECZOREK ANDRZEJ
Published: October 2002

The paper presents a model of household economy with infinitely many anonymous agents producing, trading and consuming some goods. The model can be regarded as describing the behavior of an economy in one or two stages. Various solution concepts, such as competitive equilibrium, efficient production profiles, core and quasi-core are defined and studied. Numerical experience is briefly reported.
The local moduli ofSasakian 3‐manifolds
Authors: Guilfoyle Brendan S.
Published: October 2002

The Newman‐Penrose‐Perjes formalism is applied to Sasakian
3‐manifolds and the local form of the metric and contact
structure is presented. The local moduli space can be
parameterised by a single function of two variables and it is
shown that, given any smooth function of two variables, there
exists locally a Sasakian structure with scalar curvature equal
to this function. The case where the scalar curvature is
constant (η‐Einstein Sasakian metrics) is completely solved
locally. The resulting Sasakian manifolds include S 3, Nil,
and , as well as the Berger spheres. It
is also shown that a conformally flat Sasakian 3‐manifold is Einstein of positive scalar curvature.
Spaces whose only finite‐sheeted covers are themselves. Part I
Authors: Timm Mathew
Published: October 2002

This is a survey of results and open questions related to the
topology of spaces that have no nontrivial finite‐sheeted covers.
Simple Nonlinear Flexural Stiffness Model for Concrete Structural Walls
Authors: Adebar Perry , Ibrahim Ahmed M. M.
Published: October 2002

A trilinear bending moment–curvature model is proposed for the nonlinear static (pushover) analysis of concrete walls. To account for the effect of cracking on the flexural stiffness of concrete walls in a simple yet accurate way, the elastic portion of the bending moment–curvature relationship is modeled as bilinear. To account for the influence of cyclic loading on tension stiffening of cracked concrete, the concept of upper-bound response for a previously uncracked wall, and lower-bound response for a severely cracked wall is introduced. To validate the proposed model, the results of a large-scale test on a slender concrete wall are compared with predictions from the model. The application of the proposed model in a pushover analysis of a 131-m-(430-ft) high coupled-wall structure demonstrates the importance of accurately modeling the nonlinear flexural stiffness of concrete walls.
Elastic and Inelastic Seismic Response of Buildings with Damping Systems
Authors: Ramirez Oscar M. , Constantinou Michael C. , Whittaker Andrew S. , Kircher Charles A. , Chrysostomou Christis Z.
Published: October 2002

The effect of damping on the response of elastic and inelastic single-degree-of-freedom systems was studied by nonlinear response-history analysis using earthquake histories that matched on average a 2000 NEHRP spectrum on a stiff soil site for a region of high seismic risk. New displacement reduction factors for levels of damping greater than 5% of critical are presented. New equations to relate inelastic and elastic displacements in the short-period range, for levels of damping greater than 5% of critical, are presented. The technical basis for reducing the minimum design base shear in damped buildings by a maximum of 25%, from that required for the corresponding undamped building, is derived based on comparable levels of damage in both the damped and undamped buildings.
Evaluation of Simplified Methods of Analysis of Yielding Structures with Damping Systems
Authors: Ramirez Oscar M. , Constantinou Michael C. , Gomez Juan D. , Whittaker Andrew S. , Chrysostomou Christis Z.
Published: October 2002

The 2000 NEHRP Provisions include simplified methods of analysis of inelastic buildings equipped with linear viscous, nonlinear viscous, and hysteretic damping devices. These methods are based in part on the data presented in the paper. Nonlinear response-history analysis was used to validate the methods. The derivation of the 2000 NEHRP simplified methods for calculating the maximum acceleration and maximum velocity in damped framing systems are presented. These simplified methods produce exact or conservative estimates of peak displacement and peak acceleration, and reasonable estimates of peak velocities. The estimated velocities are within 25% of the average values obtained from response-history analysis for a broad range of periods and damping ratios. Velocity correction factors are provided to calculate peak velocity given the pseudo-velocity.
Performance-Based Evaluation of Reinforced Concrete Building Exterior Joints for Seismic Excitation
Authors: Pantelides Chris P. , Clyde Chandra , Reaveley Lawrence D.
Published: October 2002

Beam-column joints of nonductile reinforced concrete buildings that were built prior to the current seismic code provisions have been investigated using several performance-based criteria. Four half-scale reinforced concrete exterior joints were tested to investigate their behavior in a shear-critical failure mode. The joints were subjected to quasi-static cyclic loading, and their performance was examined in terms of lateral load capacity, drift ratio, axial load reduction in the column at high drift ratios, joint shear strength, ductility, shear deformation angle of the joint, and residual strength. Two levels of axial compressive column load were investigated to determine how this variable might influence the performance of the joint. Specific performance levels for this type of reinforced concrete joint were established and a comparison was made to current design and rehabilitation standards. A limit states model was established, which could be used for performance evaluation or seismic rehabilitation.
Risk of Alopecia Areata After COVID-19
Authors: Kim Jong-Seung , Lee Geon-Jong , Jeong Cho-Yun , Yeom Sang-Woo , Nam Kyung-Hwa , Yun Seok-Kweon , Park Jin
Published: January 2024

This cohort study examines the incidence, prevalence, and risk of alopecia areata after COVID-19.
Concordance in Medical Urgency Classification of Discharge Diagnoses and Reasons for Visit
Authors: Giannouchos Theodoros V. , Ukert Benjamin , Wright Brad
Published: January 2024

Importance

Current policies to divert emergency department (ED) visits for less medically urgent conditions to more cost-effective settings rely on retrospective adjudication of discharge diagnoses. However, patients present to the ED with concerns, making it challenging for clinicians.

Objective

To characterize ED visits based on the medical urgency of the presenting reasons for visit and to explore the concordance between discharge diagnoses and reasons for visit.

Design, Setting, and Participants

In this retrospective, cross-sectional study, a nationwide sample of ED visits by adults (aged ≥18 years) in the US from the 2018 and 2019 calendar years’ ED data of the National Hospital Ambulatory Medical Care Survey was used. An algorithm to probabilistically assign ED visits into medical urgency categories based on the presenting reason for visit was developed. A 3-step, look-back method was applied using an updated version of the New York University ED algorithm, and a map of all possible discharge diagnoses to the same reasons for visit was developed. Analyses were conducted in July and August 2023.

Main Outcomes and Measures

The main outcome was probabilistic medical urgency classification of reasons for visits and discharge diagnoses and their concordance.

Results

We analyzed 27 068 ED visits (mean age, 48.2% years [95% CI, 47.5%-48.9% years]) representing 190.7 million visits nationwide. Women (mean, 57.0% [95% CI, 55.9%-58.1%]) and patients with public health insurance coverage, including Medicare (mean, 24.9% [95% CI, 21.9%-28.0%]) and Medicaid (mean, 25.1% [95% CI, 21.0%-29.2%]), accounted for the largest share of ED visits, and a mean of 13.2% (95% CI, 11.4%-15.0%) of all visits resulted in a hospital admission. Overall, about 38.5% and 53.9% of all ED visits were classified with 100% and 75% probabilities, respectively, as injury related, emergency care needed, emergent but primary care treatable, nonemergent, or mental health or substance use disorders related based on discharge diagnosis compared with 0.4% and 12.4%, respectively, of all encounters based on patients’ reason for visit. Among discharge diagnoses assigned with high certainty to only 1 urgency category using the New York University ED algorithm, between 38.0% (95% CI, 36.3%-39.6%) and 57.4% (95% CI, 56.0%-58.8%) aligned with the probabilistic categorical assignments of their corresponding reasons for visit.

Conclusions and Relevance

In this cross-sectional study of 190.7 million ED visits among adults aged 18 years or older, a smaller percentage of reasons for visit could be prospectively categorized with high accuracy to a specific medical urgency category compared with all visits based on discharge diagnoses, and a limited concordance between reasons for visit and discharge diagnoses was found. Alternative methods are needed to identify the medical necessity of ED encounters more accurately.