Showing papers by "M. B. Maple published in 2007"
TL;DR: The electronic properties of a prototypical correlated insulator vanadium dioxide in which the metallic state can be induced by increasing temperature is reported, setting the stage for investigations of charge dynamics on the nanoscale in other inhomogeneous correlated electron systems.
Abstract: Electrons in correlated insulators are prevented from conducting by Coulomb repulsion between them. When an insulator-to-metal transition is induced in a correlated insulator by doping or heating, the resulting conducting state can be radically different from that characterized by free electrons in conventional metals. We report on the electronic properties of a prototypical correlated insulator vanadium dioxide in which the metallic state can be induced by increasing temperature. Scanning near-field infrared microscopy allows us to directly image nanoscale metallic puddles that appear at the onset of the insulator-to-metal transition. In combination with far-field infrared spectroscopy, the data reveal the Mott transition with divergent quasi-particle mass in the metallic puddles. The experimental approach used sets the stage for investigations of charge dynamics on the nanoscale in other inhomogeneous correlated electron systems.
1,283 citations
TL;DR: In this paper, a unique control parameter of T-linear scattering in heavy-fermion superconductors was found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sublattice.
Abstract: One of the most notorious non-Fermi-liquid properties of both archetypal heavy-fermion systems1,2,3,4 and the high-Tc copper oxide superconductors5 is an electrical resistivity that evolves linearly (rather than quadratically) with temperature, T. In the heavy-fermion superconductor CeCoIn5 (ref. 6), this linear behaviour was one of the first indications of the presence of a zero-temperature instability, or quantum critical point. Here, we report the observation of a unique control parameter of T-linear scattering in CeCoIn5, found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sublattice. We find that the evolution of inelastic scattering in Ce1−xRxCoIn5 is strongly dependent on the f-electron configuration of the R ion, whereas two other key properties—Cooper-pair breaking and Kondo-lattice coherence—are not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature of incoherent scattering centres in the Kondo lattice, which provides insight into the anomalous scattering rate synonymous with quantum criticality7.
61 citations
TL;DR: A persistent kink in the pressure dependence of the "hidden order" transition temperature of URu(2-x)RexSi2 is observed at a critical pressure P(c), accompanied by the destruction of superconductivity, a change in the magnitude of a spin excitation gap, determined from electrical resistivity measurements.
Abstract: A persistent kink in the pressure dependence of the "hidden order" (HO) transition temperature of URu(2-x)RexSi2 is observed at a critical pressure P(c)=15 kbar for 0
42 citations
TL;DR: In this article, a review of recent experiments on the Pr-based filled skutterudite arsenides and antimonides is presented, showing that the heavy fermion compound PrOs 4 Sb 12 exhibits unconventional strong-coupling superconductivity below T c = 1.85 K that breaks time reversal symmetry, and may involve triplet spin pairing of electrons.
40 citations
TL;DR: In this paper, an analysis of the optical properties of heavy fermion compounds is reported, focusing on the 1-1-5 series, where strong deviations of the spectra are seen from the predictions of the periodic Anderson model.
Abstract: An analysis of the optical properties of heavy fermion compounds is reported. We focus on the 1-1-5 series, where strong deviations of the spectra are seen from the predictions of the periodic Anderson model. Specifically we demonstrate that the differences between the experimental results and the theoretical predictions can be explained by accounting for the momentum dependence of the hybridization between the local moments and the conducting carriers. Furthermore we find correlations between the hybridization strength on a particular band and some properties of the 1-1-5 compounds. These correlations suggest that the momentum dependence of the hybridization has to be taken into account, for an understanding of the electronic properties of these heavy fermion compounds.
32 citations
TL;DR: In this paper, a review of the research carried out during the last several years on the heavy fermion superconductor PrOs4Sb12 is reviewed, and the determination of the Pr3+ energy level scheme in the crystalline electric field, as well as the discovery and characterization of the high field-ordered phase (HFOP), which has been identified with antiferroquadrupolar order, are summarized and compared.
Abstract: Research carried out during the last several years on the heavy fermion superconductor PrOs4Sb12 is reviewed. The compound PrOs4Sb12 exhibits unconventional strong coupling superconductivity below a superconducting critical temperature T
c = 1.85 K. The superconducting state breaks time reversal symmetry, apparently consists of several distinct superconducting phases, some of which may have point nodes in the energy gap, and may involve triplet spin pairing of electrons. The determination of the Pr3+ energy level scheme in the crystalline electric field, as well as the discovery and characterization of the high field-ordered phase (HFOP), which has been identified with antiferroquadrupolar order, are described. Studies of the substitutional systems Pr(Os1−x
Ru
x
)4Sb12, Pr1−x
La
x
Os4Sb12, and Pr1−x
Nd
x
Os4Sb12 are summarized and compared.
30 citations
TL;DR: In this paper, measurements made on the filled skutterudite CeRu_4As_{12] reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems.
Abstract: Electrical resistivity $\rho$, specific heat C, and magnetic susceptibility $\chi$ measurements made on the filled skutterudite CeRu_4As_{12} reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., $\rho$(T) $\sim$ T^{1.4} and weak power law or logarithmic divergences in C(T)/T and $\chi$(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3^+.
28 citations
TL;DR: In this paper, the authors used magnetometry and resonant soft x-ray magnetic reflectometry to determine the depth-dependent charge and magnetization density on an absolute scale across a Permalloy/CoO interface above the N'eel temperature of CoO.
Abstract: We have used magnetometry and resonant soft x-ray magnetic reflectometry to determine the depth-dependent charge and magnetization density on an absolute scale across a Permalloy/CoO interface above the N\'eel temperature of CoO. A thin magnetic layer of $1.0\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ forms at the interface. This layer has larger magnetization density and different temperature dependence of magnetization than Permalloy.
23 citations
TL;DR: In this paper, the de Haas-van Alphen effect has been investigated on single crystals of the filled skutterudites PrOs$_4$As$12}$ and LaO$_ 4$AsAs$ 12}$ using magnetic fields of up to 40~T.
Abstract: Comprehensive magnetic-field-orientation dependent studies of the susceptibility and de Haas-van Alphen effect have been carried out on single crystals of the filled skutterudites PrOs$_4$As$_{12}$ and LaOs$_4$As$_{12}$ using magnetic fields of up to 40~T. Several peaks are observed in the low-field susceptibility of PrOs$_4$As$_{12}$, corresponding to cascades of metamagnetic transitions separating the low-field antiferromagnetic and high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments show that the Fermi-surface topologies of PrOs$_4$As$_{12}$ in its PMM phase and LaOs$_4$As$_{12}$ are very similar. In addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs$_4$As$_{12}$ on the PrOs$_4$As$_{12}$ lattice. Both observations suggest that the Pr 4$f$ electrons contribute little to the number of itinerant quasiparticles in the PMM phase. However, whilst the properties of LaOs$_4$As$_{12}$ suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations are detected in the PMM phase of PrOs$_4$As$_{12}$. For example, the quasiparticle effective masses in PrOs$_4$As$_{12}$ are found to decrease with increasing field, probably reflecting the gradual suppression of magnetic fluctuations associated with proximity to the low-temperature, low-field antiferromagnetic state.
17 citations
TL;DR: In this paper, the de Haas-van Alphen effect has been investigated on single crystals of the filled skutterudites PrOs4As12 and LaOss 4As12 using magnetic fields of up to 40 T.
Abstract: Comprehensive magnetic-field-orientation dependent studies of the susceptibility and de Haas–van Alphen effect have been carried out on single crystals of the filled skutterudites PrOs4As12 and LaOs4As12 using magnetic fields of up to 40 T. Several peaks are observed in the low-field susceptibility of PrOs4As12, corresponding to cascades of metamagnetic transitions separating the low-field antiferromagnetic and high-field paramagnetic metal (PMM) phases. The de Haas–van Alphen experiments show that the Fermi-surface topologies of PrOs4As12 in its PMM phase and LaOs4As12 are very similar. In addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs4As12 on the PrOs4As12 lattice. Both observations suggest that the Pr 4f electrons contribute little to the number of itinerant quasiparticles in the PMM phase. However, while the properties of LaOs4As12 suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations are detected in the PMM phase of PrOs4As12. For example, the quasiparticle effective masses in PrOs4As12 are found to decrease with increasing field, probably reflecting the gradual suppression of magnetic fluctuations associated with proximity to the low-temperature, low-field antiferromagnetic state.
15 citations
TL;DR: The filled skutterudite compound PrOs₄P₁₂ was synthesized in single-crystal form using a molten metal flux growth technique but had features indicative of crystalline electric field (CEF) effects.
Abstract: The filled skutterudite compound PrOs₄P₁₂ was synthesized in single-crystal form using a molten metal flux growth technique Low-temperature magnetization, specific heat, and electrical resistivity measurements showed no indication of a phase transition down to 01 K but had features indicative of crystalline electric field (CEF) effects Analyses of these features in terms of a cubic CEF suggest a Γ₁ singlet or a Γ₃ doublet ground state separated by 30-50 K from a Γ₅ triplet first excited state
TL;DR: In this paper, it was shown that electronic spin fluctuations are not directly involved in the dynamic muon spin relaxation observed in these materials and the damping rate associated with this relaxation varies with temperature, applied magnetic field, and dopant concentrations.
Abstract: Zero- and longitudinal-field muon spin relaxation experiments have been carried out in the alloy series $\mathrm{Pr}{({\mathrm{Os}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x})}_{4}{\mathrm{Sb}}_{12}$ and ${\mathrm{Pr}}_{1\ensuremath{-}y}{\mathrm{La}}_{y}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$ to elucidate the anomalous dynamic muon spin relaxation observed in these materials. The damping rate $\ensuremath{\Lambda}$ associated with this relaxation varies with temperature, applied magnetic field, and dopant concentrations $x$ and $y$ in a manner consistent with the ``hyperfine enhancement'' of $^{141}\mathrm{Pr}$ nuclear spins first discussed by Bleaney [Physica (Utrecht) 69, 317 (1973)]. This mechanism arises from Van Vleck-like admixture of magnetic ${\mathrm{Pr}}^{3+}$ crystalline-electric-field-split excited states into the nonmagnetic singlet ground state by the nuclear hyperfine coupling, thereby increasing the strengths of spin-spin interactions between $^{141}\mathrm{Pr}$ and muon spins and within the $^{141}\mathrm{Pr}$ spin system. We find qualitative agreement with this scenario and conclude that electronic spin fluctuations are not directly involved in the dynamic muon spin relaxation.
TL;DR: The double superconducting transition in PrOs4Sb12 was first observed in specific heat C(T) measurements on single crystal samples by means of specific heat measurements as discussed by the authors.
Abstract: The double superconducting transition in PrOs4Sb12, first observed in specific heat C(T) measurements on single crystal samples, was studied by means of specific heat measurements on PrOs4Sb12 crystals that had been subjected to applied magnetic fields, substitution of up to 4 Ru for Os, and annealing. The double superconducting transitions of a batch of single crystals were measured before and after annealing for 5 days at 500°C, to remove strains and promote homogeniety, with no observed change. Measurements of C(T) near Tc for PrOs4Sb12 in several magnetic fields are also presented, detailing the evolution of the double transition up to 1 T. Samples of Pr(Os1-x Rux)Sb12 with 0.01 ≤ x ≤ 0.04 also appear to display a double superconducting transition in specific heat. In addition, samples with the smallest Ru concentration measured (x = 0.01) may even display a more isotropic type of superconductivity than pure PrOs4Sb12 (x = 0).
TL;DR: Magnetization and torque measurements were performed on single crystals to study the mixed-state thermodynamics as discussed by the authors, which allowed the determination of both paramagnetic and vortex responses in the mixed state magnetization.
Abstract: Magnetization and torque measurements were performed on ${\mathrm{CeCoIn}}_{5}$ single crystals to study the mixed-state thermodynamics. These measurements allow the determination of both paramagnetic and vortex responses in the mixed-state magnetization. The paramagnetic magnetization is suppressed in the mixed state with the spin susceptibility increasing with increasing magnetic field. The dependence of spin susceptibility on magnetic field is due to the fact that heavy electrons contribute both to superconductivity and paramagnetism and a large Zeeman effect exists in this system. No anomaly in the vortex response was found within the investigated temperature and field range.
TL;DR: In this article, Ru doping was shown to be considerably more efficient than La doping in suppressing TRS-breaking superconducting pairing in the PrOs 4 Sb 12 alloy system.
TL;DR: In this paper, Andreev spectroscopy data, taken with ballistic point contacts on single crystals of the heavy-fermion superconductor PrOs 4 Sb 12, were studied to track how the order-parameter symmetry evolves and thus map out the H-T phase diagram.
Abstract: We present Andreev spectroscopy data, down to 80 mK and up to 2.5 T, taken with ballistic point contacts on single crystals of the heavy-fermion superconductor PrOs 4 Sb 12 . Spectral dependences on magnetic field H and temperature T were studied to track how the order-parameter symmetry evolves and thus map out the H – T phase diagram. We observe a field-driven change in the nodality of the order-parameter suggesting that there are multiple superconducting phases, with different pairing symmetries, in PrOs 4 Sb 12 .
Journal Article•
TL;DR: In this article, a unique control parameter of T-linear scattering in heavy-fermion superconductors was found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sublattice.
Abstract: One of the most notorious non-Fermi-liquid properties of both archetypal heavy-fermion systems1,2,3,4 and the high-Tc copper oxide superconductors5 is an electrical resistivity that evolves linearly (rather than quadratically) with temperature, T. In the heavy-fermion superconductor CeCoIn5 (ref. 6), this linear behaviour was one of the first indications of the presence of a zero-temperature instability, or quantum critical point. Here, we report the observation of a unique control parameter of T-linear scattering in CeCoIn5, found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sublattice. We find that the evolution of inelastic scattering in Ce1−xRxCoIn5 is strongly dependent on the f-electron configuration of the R ion, whereas two other key properties—Cooper-pair breaking and Kondo-lattice coherence—are not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature of incoherent scattering centres in the Kondo lattice, which provides insight into the anomalous scattering rate synonymous with quantum criticality7.
Journal Article•
TL;DR: In this paper, the dynamic behavior of vortices in the high T c cuprates YBa 2 Cu 3 O 6.5 and Y 1− x Pr x Ba 2 Co 2 Co 6.97 has been investigated over an unprecedented temperature range by means of electrical transport measurements in magnetic fields up to 45 tla.
Abstract: The dynamic behavior of vortices in the high- T c cuprates YBa 2 Cu 3 O 6.5 and Y 1− x Pr x Ba 2 Cu 3 O 6.97 have been investigated over an unprecedented temperature – field range by means of electrical transport measurements in magnetic fields up to 45 tesla. The magnitude of the displacement of a single flux line due to quantum fluctuations of the vortex core in each system has been found and is seen to increase with temperature along the vortex-glass melting transition.