Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session U7: CM.3 Transport Properties |
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Chair: James Schilling, Washington University in St. Louis Room: Grand Crescent |
Thursday, July 11, 2013 11:00AM - 11:15AM |
U7.00001: Hydrostatic High-Pressure Studies to 25 GPa on the Model Superconducting Pnictide LaRu$_{2}$P$_{2}$ Neda Foroozani, Jinhyuk Lim, James Schilling, Roxanna Fotovat, Chong Zheng, Roald Hoffmann Prior to the discovery of the Fe-pnictides in 2008, the ruthenium phosphide LaRu$_{2}$P$_{2}$ possessed the highest value of the superconducting transition temperature $T_{c\, }\approx $ 4 K in the entire pnictide family. Recently, there has been renewed interest in this compound in an effort to understand why its $T_{c}$ value is as much as 15x lower than for some Fe-pnictides. Recent soft x-ray angle-resolved photoemission spectroscopy studies [1] have revealed that LaRu$_{2}$P$_{2}$ exhibits Fermi liquid behavior with weak electron-electron correlations. The superconducting properties of LaRu$_{2}$P$_{2}$ are also more isotropic than those of the Fe-pnictides. Unfortunately, the dependence of $T_{c}$ on hydrostatic pressure has not yet been determined, although such studies have an excellent track record for uncovering valuable systematics and pointing the way to higher $T_{c}$ values. We report the first measurement for LaRu$_{2}$P$_{2}$ of the dependence of $T_{c}$ on hydrostatic pressure. In these studies a He-gas system provides pressures to 1 GPa followed by a He-loaded diamond-anvil cell to higher pressures. $T_{c}$ initially increases under pressure, but exhibits a relatively sharp downturn above 2 GPa, indicating a possible structural phase transition. The results of these studies are compared to related work on the Fe-pnictides. [1] Razzoli \textit{et al.,} Phys. Rev. Lett. 108, 257005 (2012). [Preview Abstract] |
Thursday, July 11, 2013 11:15AM - 11:30AM |
U7.00002: A NiCrAl pressure cell up to 4.6 GPa and its application to cuprate and pnictide superconductors Naoki Fujiwara, Yoshiya Uwatoko, Takehiko Matsumoto A NiCrAl-CuBe hybrid cell has been paid much attention because its maximum pressure goes beyond 3 GPa despite its large sample space. In the previous pressurizing trials for this pressure cell, we reached 4.0 GPa under a steady load of 15 ton. In the present trial, we have succeeded in reaching 4.6 GPa by using a short Teflon capsule as a pressure-mediation-liquid container. The pressure efficiency at 15 ton was 75$\%$. The maximum expansion of the inner diameter of the NiCrAl cylinder was 5$\%$, suggesting that 4.6 GPa is the upper limit of pressure. To keep high pressure above 4 GPa, a steady load control is needed: a pressure of 4.0 GPa under a steady load decreased to 3.7 GPa after the pressure cell was clamped and the steady load was released. The pressure cell is available to various experiments that need a large sample space. We have applied this pressure cell to nuclear magnetic resonance (NMR) measurements on cuprate and pnictide superconductors, such as Sr$_2$Ca$_{12}$Cu$_{24}$O$_{41}$, LaFeAsO$_{1-x}$F$_x$, and CaFe$_{1-x}$Co$_x$AsF. These compounds have superconducting layers, and $T_c$s of these compounds are enhanced by pressure application. We review what happens at optimal pressure in electric and/or magnetic properties on a microscopic level. [Preview Abstract] |
Thursday, July 11, 2013 11:30AM - 11:45AM |
U7.00003: Effect of large uniaxial strain on carrier recombination mechanisms in GaAs P. Grivickas, M.D. McCluskey, Y.M. Gupta Carrier transport properties govern the operating characteristics of semiconductor devices. Strains are known to have a profound effect on carrier recombination processes, but details of these effects are not well understood due to the inherent limitations of common compression techniques. In this work, carrier lifetime measurements were obtained in shock-compressed GaAs using time- and spectrally-resolved photoluminescence measurements. Linear lifetime reduction was observed for different doping concentrations and for different crystal orientations. These experimental findings do not support previous hypothesis that emphasize recombination center formation in highly strained GaAs. A numerical carrier dynamics model, based on the continuity equation, was constructed to relate the experimental findings to the underlying material properties. It is shown that uniaxial strain primarily affects the non-radiative recombination mechanism and is consistent with the loss of quantum efficiency observed in GaAs. Work supported by DOE/NNSA. [Preview Abstract] |
Thursday, July 11, 2013 11:45AM - 12:00PM |
U7.00004: High temperature bulk diffusion in GaN B. Sadovyi, I. Grzegory, J. Weyher, I. Dziecielewski, A. Khachapuridze, S. Porowski, I. Petrusha, V. Turkevich, D. Statiichuk, V. Kapustianyk, M. Albrecht Surprisingly, gallium nitride single crystals grown by High Nitrogen Pressure Solution method at temperature as high as 1750~K show non uniformities in distribution of impurities which suggests still slow bulk diffusion and very high melting temperature of GaN. In this work, GaN single crystals have been annealed at temperature up to 3350~K at pressure up to 9~GPa in order to induce homogeneization of crystal properties by bulk diffusion. For this purpose the crystals with intentional patterns of impurity distribution were used. The crystals before and after annealing were characterized by PL and CL mapping, photochemical etching sensitive to free electron concentration. It was established, that the bulk diffusion starts at temperature as high as 3300~K. It is reflected in uniformization of both optical and electrical properties of the crystals. This estimation suggests then melting temperature of GaN is significantly higher than current belief [1]. \\[4pt] [1] W.~Utsumi et al. Nature Materials \textbf{2}, 735 (2003). [Preview Abstract] |
Thursday, July 11, 2013 12:00PM - 12:30PM |
U7.00005: Measurement and interpretation of shear viscosities at high pressures Invited Speaker: Evan Abramson High pressures employed in the study of fluids allow density and temperature to be used as independent, experimental variables, providing extensive and clear comparison with theory. Measurements of the viscosities of simple fluids in the diamond-anvil cell have allowed confirmation of a hypothesized relation between viscosity and entropy, and a more general exploration of ``isomorphs'' as well as fluid-mixing rules. Densities and temperatures at which viscosities can be measured statically overlap those achievable by dynamic compression; inferences of viscosity from observations using, e.g., shock compression can thus be tested for accuracy. [Preview Abstract] |
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