M. B. Maple

University of Alabama at Birmingham, Birmingham, Alabama, United States

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Publications (875)1553.17 Total impact

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    ABSTRACT: Experimental contributors to the field of Superconducting Materials share their informal views on the subject.
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    ABSTRACT: We report results of zero-field muon spin relaxation experiments on the filled-skutterudite superconductors~Pr$_{1-x}$Ce$_{x}$Pt$_4$Ge$_{12}$, $x = 0$, 0.07, 0.1, and 0.2, to investigate the effect of Ce doping on broken time-reversal symmetry (TRS) in the superconducting state. In these alloys broken TRS is signaled by the onset of a spontaneous static local magnetic field~$B_s$ below the superconducting transition temperature. We find that $B_s$ decreases linearly with $x$ and $\to 0$ at $x \approx 0.4$, close to the concentration above which superconductivity is no longer observed. The (Pr,Ce)Pt$_4$Ge$_{12}$ and isostructural (Pr,La)Os$_4$Sb$_{12}$ alloy series both exhibit superconductivity with broken TRS, and in both the decrease of $B_s$ is proportional to the decrease of Pr concentration. This suggests that Pr-Pr intersite interactions are responsible for the broken TRS\@. The two alloy series differ in that the La-doped alloys are superconducting for all La concentrations, suggesting that in (Pr,Ce)Pt$_4$Ge$_{12}$ pair-breaking by Ce doping suppresses superconductivity. For all $x$ the dynamic muon spin relaxation rate decreases somewhat in the superconducting state. This may be due to Korringa relaxation by conduction electrons, which is reduced by the opening of the superconducting energy gap.
  • B.D. White, J.D. Thompson, M.B. Maple
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    ABSTRACT: Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion compounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. We conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.
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    ABSTRACT: We have used specific heat and neutron diffraction measurements on single crystals of URu$_{2-x}$Fe$_x$Si$_2$ for Fe concentrations $x$ $\leq$ 0.7 to establish that chemical substitution of Ru with Fe acts as "chemical pressure" $P_{ch}$ as previously proposed by Kanchanavatee et al. [Phys. Rev. B {\bf 84}, 245122 (2011)] based on bulk measurements on polycrystalline samples. Notably, neutron diffraction reveals a sharp increase of the uranium magnetic moment at $x=0.1$, reminiscent of the behavior at the "hidden order" (HO) to large moment antiferromagnetic (LMAFM) phase transition observed at a pressure $P_x\approx$ 0.5-0.7~GPa in URu$_2$Si$_2$. Using the unit cell volume determined from our measurements and an isothermal compressibility $\kappa_{T} = 5.2 \times 10^{-3}$ GPa$^{-1}$ for URu$_2$Si$_2$, we determine the chemical pressure $P_{ch}$ in URu$_{2-x}$Fe$_x$Si$_2$ as a function of $x$. The resulting temperature $T$-chemical pressure $P_{ch}$ phase diagram for URu$_{2-x}$Fe$_x$Si$_2$ is in agreement with the established temperature $T$-external pressure $P$ phase diagram of URu$_2$Si$_2$.
    Physical Review B 02/2015; 91:085122. DOI:10.1103/PhysRevB.91.085122 · 3.66 Impact Factor
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    ABSTRACT: La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$ were categorized as BCS superconductors. In a plot of the critical field $H_{c2}$ vs $T$, La$_3$Ru$_4$Sn$_{13}$ displays a second superconducting phase at the higher critical temperature $T_c^{\star}$, characteristic of inhomogeneous superconductors, while La$_3$Co$_4$Sn$_{13}$ shows bulk superconductivity below $T_c$. We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds with $\frac{dT_c^{\star}}{dP} > \frac{dT_c}{dP}$. The pressure dependences of $T_c$ are interpreted according to the McMillan theory and understood to be a consequence of lattice stiffening. The investigation of the superconducting state of La$_3$Co$_x$Ru$_{4-x}$Sn$_{13}$ shows a $T_c^{\star}$ that is larger then $T_c$ for $x<4$. This unique and unexpected observation is discussed as a result of the local disorder and/or the effect of chemical pressure when Ru atoms are partially replaced by smaller Co atoms.
  • Bulletin of the American Physical Society; 01/2015
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    ABSTRACT: Charge transport measurements under magnetic field and pressure on Ce 1- x Yb x CoIn 5 single crystalline alloys revealed that: (i) relatively small Yb substitution suppresses the field induced quantum critical point, with a complete suppression for Yb doping x > 0.07; (ii) the superconducting transition temperature ( T c ) and Kondo lattice coherence temperature ( T coh ) decrease with x , yet they remain finite over the wide range of Yb concentrations; (iii) both T c and T coh increase with pressure; (iv) there are two contributions to resistivity, which show different temperature and pressure dependences, implying that both heavy and light quasiparticles contribute to inelastic scattering. We also analyzed the pressure dependence of both T coh and T c within the composite pairing theory. In the purely static limit, we find that the composite pairing mechanism necessarily causes opposite behaviors of T coh and T c with pressure: if Tcoh grows with pressure, T c must decrease with pressure and vice versa.
    Journal of Physics Conference Series 01/2015; 592(1):012078.
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    ABSTRACT: Electrical resistivity, specific heat, and magnetization measurements on the URu [GRAPHICS] Os [GRAPHICS] Si [GRAPHICS] system suggest a phase transition from the 'hidden order' phase to another unidentified phase that is likely to be a large moment antiferromagnetic phase. It is noteworthy that the hidden order/large moment antiferromagnetic phase boundary [GRAPHICS] is enhanced from 17.5K at [GRAPHICS] = 0 to 50K at [GRAPHICS] = 1. However, as [GRAPHICS] increases, the gap opening in the Fermi surface due to the hidden order phase transition, deduced from electrical resistivity and specific heat measurements, decreases. This study reveals that both Fe and Os isoelectronic substitutions for Ru in URu [GRAPHICS] Si [GRAPHICS] yield an enhancement of [GRAPHICS] . In contrast to the URu [GRAPHICS] Fe [GRAPHICS] Si [GRAPHICS] system, where the unit cell volume decreases with [GRAPHICS] , in the URu [GRAPHICS] Os [GRAPHICS] Si [GRAPHICS] system, the unit cell volume increases with [GRAPHICS] . Thus the enhancement of the hidden order/large moment antiferromagnetic transition temperature cannot be solely due to an increase in chemical pressure.
    Philosophical Magazine 11/2014; 94(32-33):3681-3690. DOI:10.1080/14786435.2014.886022 · 1.43 Impact Factor
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    ABSTRACT: A quantum critical point (QCP) occurs upon chemical doping of the weak itinerant ferromagnet Sc_{3.1}In. Remarkable for a system with no local moments, the QCP is accompanied by non-Fermi liquid (NFL) behavior, manifested in the logarithmic divergence of the specific heat both in the ferro- and the paramagnetic states. Sc_{3.1}In displays critical scaling and NFL behavior in the ferromagnetic state, akin to what had been observed only in f-electron, local moment systems. With doping, critical scaling is observed close to the QCP, as the critical exponents, and delta, gamma and beta have weak composition dependence, with delta nearly twice, and beta almost half of their respective mean-field values. The unusually large paramagnetic moment mu_PM~1.3 mu_B/F.U. is nearly composition-independent. Evidence for strong spin fluctuations, accompanying the QCP at x_c = 0.035 +- 0.005, may be ascribed to the reduced dimensionality of Sc_{3.1}In, associated with the nearly one-dimensional Sc-In chains.
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    ABSTRACT: The formation of heavy fermion bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid renormalizations. Leggett predicted for liquid $^3$He that Fermi-liquid renormalizations change in the superconducting state, leading to a temperature dependence of the London penetration depth~$\Lambda$ quite different from that in the BCS theory. Using Leggett's theory, as modified for heavy fermions, it is possible to extract from the measured temperature dependence of $\Lambda$ in high quality samples both Landau parameters $F_0^s$ and $F_1^s$; this has never been accomplished before. A modification of the temperature dependence of the specific heat $C_\mathrm{el}$, related to that of $\Lambda$, is also expected. We have carefully determined the magnitude and temperature dependence of $\Lambda$ in CeCoIn$_5$ by muon spin relaxation rate measurements to obtain $F_0^s = 36 \pm 1$ and $F_1^s = 1.2 \pm 0.3$, and find a consistent change in the temperature dependence of electronic specific heat $C_\mathrm{el}$. This, the first determination of $F_1^s$ with a value~$\ll F_0^s$ in a heavy fermion compound, tests the basic assumption of the theory of heavy fermions, that the frequency dependence of the self-energy is much more important than its momentum dependence.
    Physical Review Letters 10/2014; 113(16). DOI:10.1103/PhysRevLett.113.166401 · 7.73 Impact Factor
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    Y. Fang, D. Yazici, B. D. White, M. B. Maple
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    ABSTRACT: The superconducting and normal-state properties of La$_{1-x}$Sm$_{x}$O$_{0.5}$F$_{0.5}$BiS$_{2}$ (0.1 $\leqslant$ $x$ $\leqslant$ 0.9) have been studied via electrical resistivity, magnetic susceptibility, and specific heat measurements. By using suitable synthesis conditions, Sm exhibits considerable solubility into the CeOBiS$_{2}$-type LaO$_{0.5}$F$_{0.5}$BiS$_{2}$ lattice. In addition to a considerable enhancement of the superconducting volume fraction, it is found that the superconducting transition temperature $T_{c}$ is dramatically enhanced with increasing Sm concentration to 5.4 K at $x$ = 0.8. These results suggest that $T_{c}$ for SmO$_{0.5}$F$_{0.5}$BiS$_{2}$ could be as high as $\sim$6.2 K and comparably high $T_{c}$ values might also be obtained in $Ln$O$_{0.5}$F$_{0.5}$BiS$_{2}$ ($Ln$ = Eu - Tm) if these compounds can be synthesized.
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    ABSTRACT: We present the effect of yttrium substitution on superconductivity in the La$_{1-\textit{x}}$Y$_{\textit{x}}$O$_{0.5}$F$_{0.5}$BiS$_{2}$ system. Polycrystalline samples with nominal Y concentrations up to 40% were synthesized and characterized via electrical resistivity, magnetic susceptibility, and specific heat measurements. Y substitution reduces the lattice parameter \textit{a} and unit cell volume \textit{V}, and a correlation between the lattice parameter \textit{c}, the La-O-La bond angle, and the superconducting critical temperature $T_c$ is observed. The chemical pressure induced by Y substitution for La produces neither the high-$T_c$ superconducting phase nor the structural phase transition seen in LaO$_{0.5}$F$_{0.5}$BiS$_{2}$ under externally applied pressure.
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    ABSTRACT: A crossover from a non-Fermi liquid to a Fermi liquid phase in Yb$_2$Ni$_{12}$P$_7$ is observed by analyzing electrical resistivity $\rho(T)$, magnetic susceptibility $\chi(T)$, specific heat $C(T)$, and thermoelectric power $S(T)$ measurements. The electronic contribution to specific heat, $C_{e}(T)$, behaves as $C_{e}(T)/T \sim -\ln(T)$ for 5 K $< T <$ 15 K, which is consistent with non-Fermi liquid behavior. Below $T \sim$ 4 K, the upturn in $C_{e}(T)/T$ begins to saturate, suggesting that the system crosses over into a Fermi-liquid ground state. This is consistent with robust $\rho(T) - \rho_0 = AT^2$ behavior below $T \sim$ 4 K, with the power-law exponent becoming sub-quadratic for $T >$ 4 K. A crossover between Fermi-liquid and non-Fermi liquid behavior suggests that Yb$_2$Ni$_{12}$P$_7$ is in close proximity to a quantum critical point, in agreement with results from recent measurements of this compound under applied pressure.
    Journal of Physics Condensed Matter 09/2014; 26(42). DOI:10.1088/0953-8984/26/42/425601 · 2.22 Impact Factor
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    ABSTRACT: Measurements of physical properties show that Yb enters the single crystals systematically and in registry with the nominal Yb concentration x of the starting material dissolved in the molten indium flux.
    Philosophical Magazine 07/2014; 94(36):4219. DOI:10.1080/14786435.2014.976287 · 1.43 Impact Factor
  • Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
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    ABSTRACT: Positive-muon ($\mu^+$) Knight shifts have been measured in the paramagnetic states of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloys, where $x =$ 0, 0.25, 0.45, 0.50, 0.55, 0.75, and 1.00. In Pr-substituted NdOs$_4$Sb$_{12}$ ($x \le$ 0.75), but not in NdOs$_4$Sb$_{12}$, Clogston-Jaccarino plots of $\mu^+$ Knight shift~$K$ versus magnetic susceptibility~$\chi$ exhibit an anomalous saturation of $K(\chi)$ at $\sim-$0.5% for large susceptibilities (low temperatures), indicating a reduction of the coupling strength between $\mu^+$ spins and $4f$ paramagnetism for temperatures $\lesssim$ 15~K. We speculate that itinerant Pr$^{3+}$ quadrupolar excitations, invoked to mediate the superconducting Cooper-pair interaction, might modify the $\mu^+$-$4f$ ion indirect spin-spin interaction.
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    ABSTRACT: Iridium-based 5d transition-metal oxides are attractive candidates for the study of correlated electronic states due to the interplay of enhanced crystal-field, Coulomb and spin-orbit interaction energies. At ambient pressure, these conditions promote a novel Jeff = 1/2 Mott-insulating state, characterized by a gap of the order of ~0.1 eV. We present high-pressure electrical resistivity measurements of single crystals of Sr2IrO4 and Sr3Ir2O7. While no indications of a pressure-induced metallic state up to 55 GPa were found in Sr2IrO4, a strong decrease of the gap energy and of the resistance of Sr3Ir2O7 between ambient pressure and 104 GPa confirm that this compound is in the proximity of a metal-insulator transition.
    Journal of Physics Condensed Matter 06/2014; 26(25):255603. DOI:10.1088/0953-8984/26/25/255603 · 2.22 Impact Factor
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    ABSTRACT: Muon spin rotation and relaxation ($\mu$SR) experiments have been carried out to characterize magnetic and superconducting ground states in the Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloy series. In the ferromagnetic end compound NdOs$_4$Sb$_{12}$ the spontaneous local field at positive-muon ($\mu^+$) sites below the ordering temperature $T_C$ is greater than expected from dipolar coupling to ferromagnetically aligned Nd$^{3+}$ moments, indicating an additional indirect RKKY-like transferred hyperfine mechanism. For 0.45 $\le x \le$ 0.75, $\mu^+$ spin relaxation rates in zero and weak longitudinal applied fields indicate that static fields at $\mu^+$ sites below $T_C$ are reduced and strongly disordered. We argue this is unlikely to be due to reduction of Nd$^{3+}$ moments, and speculate that the Nd$^{3+}$-$\mu^+$ interaction is suppressed and disordered by Pr doping. In an $x$ = 0.25 sample, which is superconducting below $T_c$ = 1.3 K, there is no sign of "spin freezing" (static Nd$^{3+}$ magnetism), ordered or disordered, down to 25 mK. Dynamic $\mu^+$ spin relaxation is strong, indicating significant Nd-moment fluctuations. The $\mu^+$ diamagnetic frequency shift and spin relaxation in the superconducting vortex-lattice phase decrease slowly below $T_c$, suggesting pair breaking and/or possible modification of Fermi-liquid renormalization by Nd spin fluctuations. For 0.25 $\le x \le$ 0.75, the $\mu$SR data provide evidence against phase separation; superconductivity and Nd$^{3+}$ magnetism coexist on the atomic scale.
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    ABSTRACT: The London penetration depth, $\lambda (T)$ was measured in single crystals of Ce$_{1-x}R_x$CoIn$_5$, $R$=La, Nd and Yb down to 50~mK ($T_c/T \sim$50) using a tunnel-diode resonator. In the cleanest samples $\Delta \lambda (T)$ is best described by the power law, $\Delta \lambda (T) \propto T^{n}$, with $n \sim 1$, consistent with line nodes. Substitutions of Ce with La, Nd and Yb lead to similar monotonic suppressions of $T_c$, however the effects on $\Delta \lambda(T)$ differ. While La and Nd doping results in an increase of the exponent to $n \sim 2$, as expected for a dirty nodal superconductor, Yb doping leads to $n > 3$, inconsistent with nodes, suggesting a change from nodal to nodeless superconductivity where Fermi surface topology changes were reported, implying that the nodal structure and Fermi surface topology are closely linked.

Publication Stats

14k Citations
1,553.17 Total Impact Points

Institutions

  • 2012–2014
    • University of Alabama at Birmingham
      • Department of Physics
      Birmingham, Alabama, United States
    • University of Silesia in Katowice
      • Institute of Physics
      Catowice, Silesian Voivodeship, Poland
  • 1970–2014
    • University of California, San Diego
      • Department of Physics
      San Diego, California, United States
  • 2010
    • General Atomics
      San Diego, California, United States
  • 1979–2009
    • Applied Physical Sciences
      Groton, Connecticut, United States
  • 2006
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
  • 2003
    • University of Campinas
      Conceição de Campinas, São Paulo, Brazil
  • 2000
    • Universidad Nacional Autónoma de México
      Ciudad de México, Mexico City, Mexico
    • Himeji Institute of Technology
      • Faculty of Science
      Himezi, Hyōgo, Japan
    • Kent State University
      • Department of Physics
      Кент, Ohio, United States
  • 1999–2000
    • Chonnam National University
      Gwangju, Gwangju, South Korea
  • 1998
    • Indiana University Bloomington
      • Department of Chemistry
      Bloomington, Indiana, United States
  • 1987–1995
    • Los Alamos National Laboratory
      • • Materials Physics and Applications Division
      • • Materials Science and Technology Division
      Лос-Аламос, California, United States
  • 1994
    • Universidad Autónoma de Madrid
      Madrid, Madrid, Spain
    • Hankuk University of Foreign Studies
      Sŏul, Seoul, South Korea
    • Whittier College
      Whittier, California, United States
    • Iowa State University
      Ames, Iowa, United States
  • 1975–1994
    • Tufts University
      • Department of Physics and Astronomy
      Бостон, Georgia, United States
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, California, United States
  • 1993
    • Lomonosov Moscow State University
      • Division of Physics
      Moskva, Moscow, Russia
    • University of São Paulo
      San Paulo, São Paulo, Brazil
  • 1991–1993
    • University of San Diego
      • Department of Physics
      San Diego, California, United States
    • Kyoto University
      • Division of Chemistry
      Kioto, Kyōto, Japan
  • 1988–1992
    • CSU Mentor
      Long Beach, California, United States
  • 1990
    • The University of Texas at Austin
      • Department of Physics
      Texas City, TX, United States
    • San Diego State University
      • Department of Physics
      San Diego, California, United States
  • 1985–1989
    • Stanford University
      Palo Alto, California, United States
  • 1983
    • TRIUMF
      Vancouver, British Columbia, Canada
  • 1982
    • Palo Alto Research Center
      Palo Alto, California, United States
    • University of Kentucky
      • Department of Physics & Astronomy
      Lexington, Kentucky, United States
    • Oak Ridge National Laboratory
      • Solid State Division
      Oak Ridge, Florida, United States