Showing papers by "M. B. Maple published in 1996"
TL;DR: Experimentally, steps are observed only at multiples of {ital hf}/2{ital e}, suggesting that {ital s}-wave pairing is present in YBCO; however, the simultaneous presence of{ital d}- wave pairing is by no means ruled out.
Abstract: In heavily twinned crystals or films of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ (YBCO), ${d}_{{x}^{2}{\ensuremath{-}y}^{2}}$ pairing symmetry is expected to cause the cancellation of first-order Josephson tunneling through a YBCO-Pb tunnel junction grown on an a-b face; any residual tunneling is thus second order. As a result, microwaves at frequency f are predicted to induce steps on the current-voltage characteristic at voltages that are multiples of $\frac{1}{2}(hf/2e)$. Experimentally, steps are observed only at multiples of $hf/2e$, suggesting that s-wave pairing is present in YBCO; however, the simultaneous presence of d-wave pairing is by no means ruled out.
90 citations
TL;DR: In this paper, it was shown that the low-temperature physical properties in the NFL regime scale with the U concentration and T K, suggesting that single ion effects are responsible for the NFL behaviour.
Abstract: Certain chemically substituted Ce and U compounds have low-temperature physical properties that exhibit non-Fermi-liquid (NFL) characteristics and apparently constitute a new class of strongly correlated f-electron materials. The NFL behaviour takes the form of weak power law or logarithmic divergences in the temperature dependence of the physical properties that scale with a characteristic temperature T 0 , which, in some systems, can be identified with the Kondo temperature T K . These systems have complex temperature T-chemical substituent composition x phase diagrams, which contain regions displaying the Kondo effect, NFL behaviour, spin glass freezing, magnetic order, quadrupolar order, and, sometimes, even superconductivity. Possible origins of the NFL behaviour include a multichannel Kondo effect and fluctuations of an order parameter in the vicinity of a second-order phase transition at T = 0 K. Recent experiments on the systems Y 1-x U x Pd 3 and U 1-x M x Pd 2 Al 3 (M = Th, Y) are reviewed. In the Y 1-x U x Pd 3 and U 1-x Th x Pd 2 Al 3 systems, the low-temperature physical properties in the NFL regime scale with the U concentration and T K , suggesting that single-ion effects are responsible for the NFL behaviour.
56 citations
TL;DR: An investigation of superconductivity and magnetism in the series of compounds Pd{sub 2}Pb through measurements of electrical resistivity, magnetic susceptibility, specific heat, and lattice parameters.
Abstract: We report on an investigation of superconductivity and magnetism in the series of compounds {ital M}Pd{sub 2}Pb ({ital M}=rare earth, Th, U) through measurements of electrical resistivity, magnetic susceptibility, specific heat, and lattice parameters. Both single crystals and polycrystalline samples were studied. The compound UPd{sub 2}Pb was examined for possible heavy-fermion behavior, and found to exhibit antiferromagnetic order below {ital T}=35 K. {copyright} {ital 1996 The American Physical Society.}
33 citations
TL;DR: In this paper, low frequency ac electrical resistivity measurements were performed as a function of magnetic field H and temperature T on a polycrystalline sample of CeRu 2 with a zero field superconducting critical temperature T c of 6.1 K.
Abstract: Low frequency ac electrical resistivity ]g9 measurements were performed as a function of magnetic field H and temperature T on a polycrystalline sample of CeRu 2 with a zero field superconducting critical temperature T c of 6.1 K. These measurements revealed the development of a finite resistance anomaly in the superconducting state well below the upper critical field H c 2 ( T ). When H is increased at constant T , the anomaly takes the following form: ϱ ( H ) becomes finite at a field H 1 , increases slowly at first and then nearly linearly, drops abruptly to zero at a field H 2 , and remains zero until it increases to its normal state value around H c2 . The transition into the state with finite resistivity is reversible at H 1 but hystertic at H 2 , H 1 , and H c 2 approach each other with increasing T , while the hysteresis at H 2 decreases with increasing T and vanishes at T = 5.4 K. The anomaly is also observed in ϱ ( T ) measurements at constant H . In some regions of the H - T plane near H 1 ( T ), the resistivity exhibits transient behavior that could be due to flux jumps. The characteristic field H 2 corresponds to the field where the onset of irreversible behavior of the magnetization M ( H ) is observed. The anomaly is very sensitive to the transport current density and appears to be due to a decrease and subsequent increase of fluxoid pinning as H c 2 ( T ) is approached from within the mixed state.
28 citations
TL;DR: In this article, the authors assess the temperature and energy-dependences predicted by single-ion and disorder-dominated models and compare these results to experiments and conclude that the dynamics of isolated uranium ions are responsible for the observed temperature and frequency scaling, although inter-ion interactions may become important at lower temperatures and frequencies.
Abstract: We review the compiled measurements of the imaginary part of the dynamical magnetic susceptibility X(ω, T), static susceptibility χ(T), electrical resistivity ρ(T) and specific heat C(T) in the uranium intermetallics UCu 5-x Pd x (x = 1, 1.5). We assess the temperature- and energy-dependences predicted by single-ion and disorder-dominated models and compare these results to experiments. For temperatures T and excitation energies ω in the range 12 K < ω, T < 150 K, our analysis suggests that the dynamics of isolated uranium ions are responsible for the observed temperature and frequency scaling, although inter-ion interactions may become important at lower temperatures and frequencies.
21 citations
TL;DR: In this article, an overview of issues in the comparison of theory and experiment for actinide 5f electron spectra, with new experimental results on the photon energy dependence of 5f photoemission in UAl2 and the 4f core levels of the four phases of Pu metal.
16 citations
TL;DR: Critical scaling of the electrical resistivity is observed that is consistent with a vortex-glass transition for a film with an optimum superconducting transition temperature of {ital T}{sub {ital c}} of {approx_equal}22 K and {ital H}{parallel}{ital c}.
Abstract: We report measurements of the magnetoresistance of ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\ifmmode\pm\else\textpm\fi{}\mathrm{\ensuremath{\delta}}}$ epitaxial thin films with varying oxygen content in magnetic fields H applied parallel (H\ensuremath{\parallel}c) and perpendicular (H\ensuremath{\perp}c) to the tetragonal c axis. We have observed critical scaling of the electrical resistivity that is consistent with a vortex-glass transition for a film with an optimum superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ of \ensuremath{\approxeq}22 K and H\ensuremath{\parallel}c . The values of the zero-temperature upper critical field ${\mathit{H}}_{{\mathit{c}}_{2}}$(0)=80 kOe and the in-plane zero-temperature coherence length ${\ensuremath{\xi}}_{\mathit{ab}}$(0)=64 \AA{} were obtained from an analysis of the fluctuation conductivity. For an overoxygenated film with ${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}10 K, an anomaly develops with increasing field for H\ensuremath{\parallel}c and T\ensuremath{\lesssim}2 K that is characterized by a minimum in the temperature dependence of the resistivity followed by a second resistive transition at a lower temperature, which is nearly independent of H. This behavior is similar to that previously observed in ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ single crystals and may be associated with the magnetic ordering of the ${\mathrm{Nd}}^{3+}$ ions. \textcopyright{} 1996 The American Physical Society.
15 citations
TL;DR: In this paper, it was shown that the temperature dependence of the irreversibility line B(T*) of a vortex-solid phase transition triggered by vortex fluctuations can be explained in terms of a crossover from 3D to 2D vortex fluctuations.
Abstract: It is shown that the temperature dependence of the irreversibility line B(T*) of the ${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.97}$ (0\ensuremath{\le}x\ensuremath{\le}0.55) system, inferred from magnetoresistance measurements, can be described by a Lindemann-type model of a vortex-solid\char21{}vortex-fluid phase transition triggered by vortex fluctuations. In this model, the previously observed transition in B(T*) from a power-law temperature dependence near ${\mathit{T}}_{\mathit{c}}$ to a more rapid dependence below T*/${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}0.6 can be accounted for in terms of a crossover from three-dimensional (3D) to two-dimensional (2D) vortex fluctuations. For different x values, a lower limit for the anisotropy ratio \ensuremath{\gamma} and an upper limit for the crossover magnetic induction ${\mathit{B}}_{\mathrm{cr}}$ above which 2D vortex fluctuations dominate were determined. \textcopyright{} 1996 The American Physical Society.
11 citations
TL;DR: In this paper, the exchange coupling between Co and Cooxide in bilayer and trilayer thin-film structures has been studied using a recently developed ultrahigh vacuum SQUID magnetometer (UHVSQM) system.
Abstract: Exchange coupling between Co and Co‐oxide in bilayer and trilayer thin‐film structures has been studied using a recently developed ultrahigh vacuum SQUID magnetometer (UHVSQM) system. Using this novel technique, newly deposited Co films from a separate molecular beam epitaxy facility were transported into the UHVSQM without breaking vacuum and magnetically characterized before and after in situ room temperature oxidation. Field‐cooled hysteresis measurements performed at low temperatures indicate the presence of a complex antiferromagnetic Co‐oxide domain structure as a result of oxidation. The stability of the magnetic structure is determined by competition between frustration generated at the interface when the ferromagnetic Co moments are reversed and stabilizing antiferromagnetic anisotropy which becomes large only at low temperatures (<150 K).
11 citations
TL;DR: The frequency dependence of the scattering relaxation rate at various temperatures is evaluated, from which the evolution from a Fermi-liquid ground state for {ital x}{lt}0.2 to a non-Fermi -liquid groundState for 0.4{lt}{ital x},0.9 is characterized.
Abstract: We conducted optical investigations on the U{sub 1{minus}{ital x}}Th{sub {ital x}}Pd{sub 2}Al{sub 3} (0{lt}{ital x}{lt}09) system over a broad frequency range from 15 to 10{sup 5} cm{sup {minus}1} We evaluated the frequency dependence of the scattering relaxation rate at various temperatures, from which we have characterized the evolution from a Fermi-liquid ground state for {ital x}{lt}02 to a non-Fermi-liquid ground state for 04{lt}{ital x}{lt}09 {copyright} {ital 1996 The American Physical Society}
9 citations
TL;DR: A growing number of chemically substituted intermetallic compounds of Ce and U exhibit non-Fermi-liquid (NFL) behavior in their low temperature physical properties and apparently constitute a new class of strongly correlated f-electron materials.
Abstract: A growing number of chemically substituted intermetallic compounds of Ce and U exhibit non-Fermi-liquid (NFL) behavior in their low temperature physical properties and apparently constitute a new class of strongly correlated f-electron materials. In this paper, we update the experimental situation for the archetypal NFL f-electron system Y1−xUxPd3 and briefly describe recent experiments on the related systems M1−xUxPd3 (M Sc, La, Pr, Zr, Th).
TL;DR: In this paper, the Kondo effect with non-Fermi-liquid characteristics at low temperatures for high-purity samples with have been made as part of an effort to determine whether the non-fermi liquid behaviour persists to low U concentrations, i.e., whether it is a single ion effect.
Abstract: The system exhibits an unconventional Kondo effect with non-Fermi-liquid characteristics at low temperatures for . Measurements of the low-temperature electrical resistivity and magnetization of high-purity samples with have been made as part of an effort to determine whether the non-Fermi-liquid behaviour persists to low U concentrations, i.e., whether it is a single-ion effect. Irreversible behaviour in the magnetization, reminiscent of spin glass freezing, is observed for samples with , while long-range antiferromagnetic ordering has previously been established by neutron diffraction measurements for a sample with x = 0.45. Magnetic relaxation, ac magnetic susceptibility, and specific heat measurements were performed to investigate this unusual magnetic ordering.
TL;DR: In this paper, high temperature superconducting composite thin films on Ag substrates were prepared by cathodic arc deposition of alloy precursors, which employed a cathode comprised of a precursor alloy for the vacuum arc plasma source.
Abstract: High temperature superconducting composite thin films on Ag substrates were prepared by cathodic arc deposition of alloy precursors. The deposition technique employed a cathode comprised of a precursor alloy for the vacuum arc plasma source. The precursor alloy was prepared by multiple arc-melting of mixed metallic constituents of the high-temperature superconducting material Bi2Sr2CaCu2Oy (Bi2212) and 50 wt.% of Ag. The presence of silver in the precursor alloy film was expected to allow accommodation of the lattice and thermal expansion mismatch between the oxidized film and the silver substrate. The as-deposited film could be formed to practically any desirable shape before being subjected to heat treatments. Following deposition, controlled oxidation of the precursor alloy thin film on the Ag substrate was performed to produce the superconducting composite on the silver substrate. After the heat treatment, the composite film consisted of Bi2212 highly c-axis oriented normal to the Ag substrate.
TL;DR: In this article, electrical resistivity measurements under quasi-hydrostatic pressure up to 16 GPa on a (Tl,Pb,Bi) 1 (Sr,Ba) 2 Ca 2 Cu 3 O 9(Tl-1223) ceramic with a superconducting critical temperature T c of 116 K were reported.
Abstract: We report electrical resistivity measurements under quasi-hydrostatic pressure up to 16 GPa on a (Tl,Pb,Bi) 1 (Sr,Ba) 2 Ca 2 Cu 3 O 9 (Tl-1223) ceramic with a superconducting critical temperature T c of 116 K. The pressure, applied at room temperature, produces two different effects. (1) Initial application of a pressure of about 2.2 GPa results in a shift of the normal-state electrical resistivity ϱ n ( T ) by Δ ϱ n = −0.03 m ω ·cm. A subsequent pressure increase does not modify ϱ n ( T ). We interpret this behavior as a pressure-induced improvement of the contact between the Tl-1223 grains. (2) T c increases with pressure at the rate d T c /d P = + 0.13 K/GPa. Gaussian fluctuations are unable to explain the paraconductivity observed in the Tl-1223 ceramic sample investigated. One possible explanation could be the presence of structural defects which locally modify the Tl-1223 structure and, in turn, the superconducting properties.
TL;DR: In this article, the flux dynamics at low magnetic fields in UPt3 showed a clear distinction between the relaxation of bulk vortices and those close to the surface, indicating that an intrinsic, novel pinning mechanism exists in the low-temperature superconducting phase.
Abstract: The flux dynamics at low magnetic fields in UPt3 shows a clear distinction between the relaxation of bulk vortices and those close to the surface. In addition, in the high-temperature A-phase, vortices trapped in the bulk of the specimen after cycling it in a magnetic field creep out as expected, while bulk vortices in the B-phase remain strongly pinned, indicating that an intrinsic, novel pinning mechanism exists in the low-temperature superconducting phase of UPt3.
TL;DR: In this article, the influence of the Re substitution on the maximum as well as the temperature and magnetic field dependence of the zero bias structure of the antiferromagnetic superconductor URu 2 Si 2 is analyzed.
Abstract: On partially substituting Ru atoms by Re in the well-known antiferromagnetic superconductor URu 2 Si 2 an itinerant ferromagnetic state progressively develops. Simultaneously the partial gap at the Fermi surface, associated with the formation of a spin density wave ground state in the undoped material, is closed. We present point-contact measurements of the system URu 2− x Re x Si 2 with x in the range 0–0.8. A maximum around zero bias in the differential resistance of URu 2 Si 2 is assumed to represent the spin density wave gap on the Fermi surface. The influence of the Re substitution on the maximum as well as the temperature and magnetic field dependence of the zero bias structure are presented.
TL;DR: In this paper, the positron annihilation lifetime and Doppler broadening energy spectra have been measured in Dy-doped high-temperature YBCO superconductors as a function of temperature between 40 and 295 K.
Abstract: Positron annihilation lifetime and Doppler broadening energy spectra have been measured in Dy-doped high-temperature YBCO superconductors as a function of temperature between 40 and 295 K. The defect-related lifetime component τ 2 was approximately constant from room temperature to above T c at about 90 K and then showed a step-like decrease. These results indicated that the electronic structure changed below T c . It was also found that a transition in the positron Doppler line-shape parameter S occurred at the superconducting transition temperature. These results show that the average electron momentum at the annihilation sites increases as temperature is lowered across the superconducting transition range.
TL;DR: In this article, the authors performed measurements of acmagnetic susceptibility χac as a function of temperature and magnetic field on polycrystalline specimens of Sm2−x Ce x CuO4−y (0.15≤x≤0.18) prepared from a sol‐gel precursor.
Abstract: We have performed measurements of acmagnetic susceptibility χac as a function of temperature and magnetic field on polycrystalline specimens of Sm2−x Ce x CuO4−y (0.15≤x≤0.18) prepared from a sol‐gel precursor. All the samples studied show a striking double resistive superconducting transition. One of the resistive transitions occurs at a higher temperatureT ci and the other one at a lower Josephson‐coupling temperatureT cj . Magnetic measurements reveal the appearance of superconductivity below T cj which is evident from the resistive component χ″ which peaks only at T cj . Measurements made on pellets and crushed samples with average grain size ∼1 μm show essentially the same features. This suggests that Josephson coupling occurs inside physical grains with dimensions close to 5 μm. We have also utilized the behavior of the peak in the χ″ component as a function of applied magnetic fields to build a H vs Tphase diagram for these compounds. Some interesting features were observed in this H vs Tphase diagram: (1) a H α, α=2/3, dependence at low applied magnetic fields (H≤2 kOe) and high temperatures, and (2) an abrupt increase in the magnitude of the exponent at high fields and low temperatures. The behavior at low fields and high temperatures suggests that the magnetic response of the system is mainly controlled by a disordered Josephson network. Possible connections between these two different behaviors are discussed.
TL;DR: In this paper, the influence of substitution of Ce for Hg on the structural and superconducting properties of the mercury-based high-temperature super-conducting compound HgBa 2 CuO 4+δ (Hg-1201) was investigated for samples subjected to various annealing procedures.
TL;DR: In this article, the evolution of the magnetic rare-earth ordering under the influence of oxygen reduction with be discussed and strong indications for an inhomogeneous distribution of charge carriers in the CuO3-planes were found.
Abstract: In this paper the evolution of the magnetic rare-earth ordering under the influence of oxygen reduction with be discussed. Strong indications for an inhomogeneous distribution of charge carriers in the CuO3-planes were found.
TL;DR: In this article, the experimental situation for the archetypal Y 1− x U x Pd 3 system and briefly describe recent experiments on the U 1 − x Th x pd 2 Al 3 system are discussed.
Abstract: Certain chemically substituted f-electron compounds exhibit non-Fermi liquid behavior in their low-temperature physical properties and appear to constitute a new class of strongly correlated f-electron materials. In this paper, we update the experimental situation for the archetypal Y 1− x U x Pd 3 system and briefly describe recent experiments on the U 1− x Th x Pd 2 Al 3 system.
10 Jun 1996
TL;DR: In this article, the overlap of the pair wavefunction of a conventional superconductor with that of a high Tc cuprate was investigated, and it was shown that the order parameter in YBCO is not strictly of dx2-y2 symmetry.
Abstract: Investigation of the overlap of the pair wavefunction of a conventional superconductor with that of a high Tc cuprate should reveal the symmetry of the superconducting order parameter of the cuprate. We have been studying this overlap by Josephson tunneling (tunneling as opposed to SNS or weak link) between conventional superconductors (Pb, Sn) and YBCO. The observation of Josephson coupling in the c direction implies that the order parameter in YBCO is not strictly of dx2-y2 symmetry. We have carried out studies on YBCO in the form of twinned and detwinned single crystals and thin films on various substrates. The magnetic field dependence of the Josephson current Ic(B) allows a direct, dc, and low field measurement of the low temperature penetration depth (lambda) ab. Measurements of (lambda) a and (lambda) b in detwinned single crystals of YBCO give the value of in-plane anisotropy ratio in this material.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, the authors conducted optical investigations on the URu 2− x Re x Si 2 (0 x x is varied) in the antiferromagnetic phase ( x x > 0.4).
Abstract: We have conducted optical investigations on the URu 2− x Re x Si 2 (0 x x is varied. In the antiferromagnetic phase ( x x > 0.4).
TL;DR: In this article, the frequency dependence of the scattering relaxation rate at various temperatures was evaluated and it was shown that the relaxation rate increases linearly with decreasing frequency and temperature for U 0.2 Y 0.8 Pd 3 and for U 1− x Th x Pd 2 Al 3 with Th-doping x > 0.4.
Abstract: We conducted optical investigations on the U 0.2 Y 0.8 Pd 3 and U 1− x Th x Pd 2 Al 3 (0 x 5 cm −1 . We evaluated the frequency dependence of the scattering relaxation rate at various temperatures and find it to increase linearly with decreasing frequency and temperature for U 0.2 Y 0.8 Pd 3 and for U 1− x Th x Pd 2 Al 3 with Th-doping x > 0.4. We interpret this as a manifestation of a non-Fermi-liquid ground state of these alloys.
TL;DR: In this article, the authors report on the evolution of the resistivities of fully oxygenated Y1−xPrxBa2Cu3O7−δ single crystals.
Abstract: We report on the systematic study of the evolution of the in-plane (ρab) and out-of-plane (ρc) resistivities of fully oxygenatedY1−xPrxBa2Cu3O7−δ single crystals. ρc(x) exhibits a non-monotonic behavior: at low to moderatex, ρc(x) and the anisotropy ρc(x) increase, reaching a maximum at x≈0.42; for higherx,x, ρc and ρc/ρcab decrease, while ρab continues to increase monotonically. These results, along with the coexistence of metallic ρab(T) and semiconducting ρc(T), are consistent with the presence of a gap in the energy spectrum of the chains, leading to tunneling through both valence and conduction bands of theCuO chains.
TL;DR: In this paper, an investigation of the flux dynamics in UPt3 at low fields shows a clear distinction between the relaxation of bulk vortices and vortice close to the surface, indicating that quantum motion is involved.
Abstract: An investigation of the flux dynamics in UPt3 at low fields shows a clear distinction between the relaxation of bulk vortices and vortices close to the surface. The vortices close to the surface show large creeping rates (up to 40% in the first 104s) which are nearly independent of temperature, indicating that quantum motion is involved. Bulk vortices on the other hand creep in the high-temperature A-phase but they show practically no creep from a metastable mageetization in the low-temperature B-phase. This behaviour indicates an intrinsic, strong pinning mechanism not present in the A-phase. As domain walls between domains of degenerate superconducting phases can act as additional pinning centers, the dramatic reduction is a strong evidence that the B-phase of UPt3 breaks time-reversal symmetry.
TL;DR: In this article, the authors observed the development of a resistive anomaly in the magnetic fieldH and temperatureT dependences of the electrical resistivity ρ of polycrystalline CeRu2.
Abstract: We observed the development of a resistive anomaly in the magnetic fieldH and temperatureT dependences of the electrical resistivity ρ of polycrystalline CeRu2. The transition into this resistive region, which is observed in the superconducting state well below the upper critical fieldH
c2(T), is hysteretic in bothT andH. The intermediate field interval where ρ=0 corresponds to the field region in which an irreversible anomaly is observed in the magnetization curvesM(H). In some regions of theH-T plane, the resistivity exhibits transient behavior that could be due to flux jumps. The anomaly is very sensitive to the transport current density and appears to be due to a decrease and subsequent increase of fluxoid pinning asH
c2(T) is approached from within the mixed state.