Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A26: Materials at High Pressure: Methods and Superconductors |
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Sponsoring Units: DCOMP DMP GSCCM Chair: Christopher Seagle, Sandia National Laboratories Room: 502 |
Monday, March 3, 2014 8:00AM - 8:12AM |
A26.00001: Improvements on the Murnaghan Equation of State Michael Mehl Formulas for interpolating the equation of state of a material are useful to consolidate both experimental and computational data. A good equation of state can reduce the computational effort needed to determine the equilibrium energy and to prediction phase transitions. The Murnaghan equation of state, which starts from the simple approximation that the bulk modulus of a system is linear in the pressure, is popular because it yields analytic expressions for V(P), P(V), E(V), and H(P) = E + P V. However, it has unphysical behavior as the bulk modulus approaches zero, predicting this to occur only at infinite volume, and at high pressure, where it misses the softening of B'(P). This paper presents a simple, analytic modification of B(P) which properly accounts for both regimes, and which still yields analytic behavior of the volume, pressure, energy, and enthalpy. The accuracy of the resulting equation of state is compared to the Murnaghan, Birch, and ``Universal'' equation of state for both simple and complex systems. [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A26.00002: Towards an accurate dissociative potential for water Omololu Akin-Ojo Most models of water describe the molecule as rigid, i.e., with fixed bond angles and bond lengths, or as flexible in which the bond angles and bond lengths vary but the chemical bonds cannot be broken. In this work we present our progress in the development of a water model which allows for the breaking and formation of chemical bonds. The force field was obtained by fitting {\it ab initio} (not DFT) energies, forces, and molecular properties. The ability of the model to predict properties of water at ambient and extreme conditions will be presented. We will also report on the modeling of small clusters of water using the dissociative force field. [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A26.00003: Emergence of charge density wave domain walls above the superconducting dome in TiSe$_2$ Y.I. Joe, X.M. Chen, P. Ghaemi, K.D. Finkelstein, G.A. de la Pe\~na, Y. Gan, J.C.T. Lee, S. Yuan, J. Geck, G.J. MacDougall, T.C. Chiang, S.L. Cooper, E. Fradkin, P. Abbamonte Superconductivity (SC) in so-called ``unconventional superconductors'' is nearly always found in the vicinity of another ordered state, such as antiferromagnetism, charge density wave (CDW), or stripe order. This suggests a fundamental connection between SC and fluctuations in some other order parameter. 1$T$-TiSe$_2$ is a prototypical CDW material in the transition-metal dichalcogenide family and was previously shown to exhibit SC when the CDW is suppressed by hydrostatic pressure or intercalation of Cu atoms. Here, we present detailed high pressure x-ray scattering study on 1$T$-TiSe$_2$. We found that the CDW phase of 1$T$-TiSe$_2$ is completely suppressed on the application of hydrostatic pressure and established the existence of a quantum critical point (QCP). Unexpectedly, we observed a weakly first order, incommensurate CDW phase, suggesting the presence of a Lifshitz tricritical point somewhere above the superconducting dome. Our study suggests that SC in 1$T$-TiSe$_2$ may not be directly connected to the QCP of the CDW order, but to the formation of CDW domain wall. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A26.00004: High-pressure neutron scattering of Prussian blue analogue magnets D.M. Pajerowski, S.E. Conklin, J. Leao Pressure sensitive magnetism is known to be useful in sensors, and while applications tend to use metallic alloys, molecule based magnets (MBMs) have been shown to have large inverse magnetostrictive (IMS) response. A promising group of MBMs are the Prussian blue analogues (PBAs), in which magnetic ordering can be tuned by external stimuli such as light, electric field, and pressure. Two IMS active PBAs are KFe$_{\mathrm{3}}$[Cr(CN)$_{\mathrm{6}}$]$_{\mathrm{2}}$ (Fe-Cr) and KNi$_{\mathrm{3}}$[Cr(CN)$_{\mathrm{6}}$]$_{\mathrm{2}}$ (Ni-Cr), and there are open questions about the details of the observed effects. Presently, it is believed that under applied pressure, Fe-Cr undergoes a linkage isomerism (LI) that changes carbon coordination of the CN from Cr to Fe, resulting in a change in magnetic configuration of the Fe cation from high-spin (HS) S $=$ 4 to low-spin (LS) S $=$ 0, thus reducing the observed magnetization. On the other hand, Ni-Cr is thought to undergo random spin-canting due to either bond-deformation or LI. We utilize neutron diffraction to test these theories. Polarized beam experiments are also performed to test a contrary hypothesis of domain wall movement providing the pressure sensitive magnetism. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A26.00005: P-V-T equation of state of SiC-3C: implications for primary pressure scale Kirill Zhuravlev, Alexander F. Goncharov, Sergey Tkachev, Przemyslaw Dera, Vitali Prakapenka We present a new primary pressure scale based on concomitant measurements of the density and elastic parameters of the single crystal samples of cubic silicon carbide (3C-SiC) under quasi-hydrostatic pressures up to 65 GPa and 773 K. The established pressure scale has precision of 2{\%}--4{\%} up to 65 GPa and will allow more accurate pressure determination in that range than the previously used pressure scales. We also report x-ray diffraction data and Raman spectroscopy on 3C-SiC up to 75 GPa. We determined the P-V-T equation of state (EOS) of 3C-SiC and pressure and temperature dependencies of the zone-center phonons, elastic tensor, and mode Gruneisen parameters. Cubic SiC lattice was found to be stable up to 75 GPa, but there is a tendency for destabilization above 40 GPa, based on softening of a transverse sound velocity. We proposed corrections to the existing ruby and neon pressure scales, and~also calibrated cubic SiC as an optical pressure~marker using Raman spectroscopy. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A26.00006: Mercury Fluorides under high pressure: Hg as a pressure-induced transition metal Jorge Botana, Xiaoli Wang, Dadong Yang, Haiqing Ling, Yangming Ma, Mao-Sheng Miao Hg has recently been found experimentally to be capable of forming a chemical compound, HgF$_4$, where it behaves as a transition metal, with an oxidation number of IV, but this molecule is very short lived. In this work we present theoretical evidence obtained through \textit{ab initio} calculations that higher oxidation states than II can be stabilized in crystalline form for Hg, under extreme pressure. We have performed a structural search and optimization by means of Particle Swarm Optimization and Density Functional Theory for the crystalline series of HgF$_n$ (n=3,4,5,6), and then used those data to draw the phase diagram of the equilibrium among those stoichiometries and HgF$_2$ and F$_2$. We have found that from $0$ to $38$ $GPa$ only the mixture of HgF$_2$ and F$_2$ phases is thermodynamically stable. HgF$_3$ and HgF$_4$ have been found to be thermodynamically stable in different pressure ranges (from $73$ $GPa$ to at least $500$ $GPa$ and from $38$ $GPa$ to $200$ $GPa$, respectively). We have also found that the HgF$_3$ crystal shows a very interesting band structure that suggests it could be a transparent conductor. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A26.00007: Electrical resistivity study of Magnetite under high pressure Takaki Muramatsu, Viktor Struzhkin, Lev Gasparov Magnetite is known as one of the oldest magnetic materials and crystallizes in the inversed spinel structure. At about 120 K magnetite undergoes a structural phase transition called Verway transition where electrical resistivity abruptly increases with decreasing temperature. Pressure effects of Verway transition studied by magnetic susceptibility and electrical resistivity by several groups revealed Verway transition decreased with pressure and the precise pressure effects depend on the pressure condition i.e., pressure transmitting media. In this work, electrical resistivity measurements were made to revisit the property of magnetite under pressure. Both metallization observed in precedent work using cubic anvil press and the higher pressure properties beyond metallization are examined by diamond anvil cell. [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A26.00008: Observation of antiferromagnetic order collapse in the pressurized insulator LaMnPO Jing Guo, Jack Simonson, Liling Sun, Qi Wu, Peiwen Guo, Chao Zhang, Dachun Gu, Gabriel Kotliar, Meigan Aronson, Zhongxian Zhao The emergence of superconductivity in the iron pnictide or cuprate high temperature superconductors usually accompanies the suppression of a long-ranged antiferromagnetic (AFM) order state in a corresponding parent compound by doping or pressurizing. A great deal of effort by doping has been made to find superconductivity in Mn-based compounds, which are thought to bridge the gap between the two families of high temperature superconductors, but the AFM order was not successfully suppressed. Here we report the first observations of the pressure-induced elimination of long-ranged AFM order at $\sim$ 34 GPa and a crossover from an AFM insulating to an AFM metallic state at $\sim$ 20 GPa in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor by \textit{in-situ} high pressure resistance and \textit{ac} susceptibility measurements. These findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A26.00009: Study electron-phonon interactions under high pressures by ultrafast time-resolved spectroscopy Xiaojing Tan, Alexander Goncharov, Viktor Struzhkin, Xiaojia Chen We study the electron-phonon interactions in Al under high pressures by ultrafast time-resolved spectroscopy. We observe dramatic change of the pump-probe signals with pressure between 3.0 and 7.5 GPa: a fast decay in order of picosecond, followed by a bump that evolves with pressure. The change can be explained as competitions between electron-phonon coupling, hot electron diffusion and non-Fermi distribution of hot electrons. It's the decrease of electron-phonon coupling with pressure that cause hot electron diffusion play the main role for the fast decay, and the change of the non-Fermi electrons distribution results the evolution of the bump with pressure. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A26.00010: Fermi-surface reconstruction under pressure in the cuprate superconductors YBCO and Nd-LSCO Sophie Dufour-Beaus\'ejour, Olivier Cyr-Choini\`ere, Ga\"el Grissonnanche, Marcin Matusiak, Fazel Fallah Tafti, Elena Hassinger, Samuel Ren\'e de Cotret, Nicolas Doiron-Leyraud, Louis Taillefer, Brad Ramshaw, Ruixing Liang, Doug Bonn, Walter Hardy, Jianshi Zhou, John Goodenough, David Graf It is well established by now that the Fermi surface of hole-doped cuprates such as YBCO [1], Eu-LSCO [2], Nd-LSCO [3] and Hg1201 [4] undergoes a reconstruction caused by the emergence of charge order at low temperature. Here we show how the process of Fermi-surface reconstruction evolves as a function of applied hydrostatic pressure in both YBCO and Nd-LSCO, via measurements of the resistivity and Hall coefficient as a function of temperature and magnetic field. \\[4pt] [1] D. LeBoeuf \textit{et al}., Physical Review B \textbf{83}, 054506 (2011). \\[0pt] [2] F. Lalibert\'{e} \textit{et al}., Nature Communications \textbf{2}, 432 (2011). \\[0pt] [3] R. Daou \textit{et al}., Nature Physics \textbf{5}, 31 (2009). \\[0pt] [4] N. Doiron-Leyraud \textit{et al}., Physical Review X \textbf{3}, 021019 (2013). [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A26.00011: High Pressure study of Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O with x = 0, 0.10, and 0.15 Melissa Gooch, Phuong Doan, Zhongjia Tang, Bernd Lorenz, Arnold Guloy, Ching Wu Paul Chu Here we report a systematic study of the effects of pressure on the resistivity for the superconducting and spin/charge density wave (SDW/CDW) transitions of Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O (x = 0, 0.10, and 0.15). With increasing pressure no measurable change is observed for the SDW/CDW transition temperature (T$_S$) for x = 0.15; however, for x = 0 and 0.10 a decrease of the SDW/CDW transition temperature T$_S$ is observed. With respect to the superconducting transition temperature T$_c$, the effects of pressure effect on the three samples are different. The T$_c$ of BaTi$_2$Sb$_2$O increases linearly from 1.2 K to ~ 2.9 K at 16.1 kbars. In contrast, T$_c$ of Ba$_{0.90}$Na$_{0.10}$Ti$_2$Sb$_2$O only initially increases to 4.2 K and then saturates at higher pressure values. For Ba$_{0.85}$Na$_{0.15}$Ti$_2$Sb$_2$O, T$_c$ continuously decreases with increasing pressure. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A26.00012: Large enhancement of $T_{c}$ of Sr$_{2}$RuO$_{4}$ under uni-axial strain Daniel O. Brodsky, Clifford W. Hicks, Edward A. Yelland, Alexandra S. Gibbs, Jan A.N. Bruin, Mark E. Barber, Stephen D. Edkins, Keigo Nishimura, Shingo Yonezawa, Yoshiteru Maeno, Andrew P. Mackenzie We present AC magnetic susceptibility data taken on samples of the spin-triplet superconductor Sr$_{2}$RuO$_{4}$ under uni-axial strain. To do this, we built a probe that enables us to vary the strain applied to our samples continuously from compression to tension, whilst at cryogenic temperatures. We found that $T_{c}$ changes dramatically with in-plane strain: strain along the crystallographic [100] direction leads to a strong strain-symmetric response of $T_{c}$, which is pushed up from 1.35 K to 1.9 K for 0.23{\%} strain. Conversely, the response along the [110] direction is weak and mostly linear in strain. We discuss these results in the context of the predicted p$_{x} + i$p$_{y}$ topological order parameter. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A26.00013: The Strain Derivatives of $T_c$ in HgBa$_2$CuO$_{4+\delta}$: CuO$_2$ Plane Alone Is Not Enough Shibing Wang, Jianbo Zhang, Xiao-Jia Chen, Viktor Struzhkin, Wojciech Tabis, Neven Barisic, Mun Chan, Chelsey Dorow, Xudong Zhao, Martin Greven, Wendy Mao, Ted Geballe The strain derivatives of $T_c$ along the $a$ and $c$ axes have been determined for HgBa$_2$CuO$_{4+\delta}$ (Hg1201), the simplest monolayer cuprate with the highest $T_c$ of all monolayer cuprates ($T_c$ = 97 K at optimal doping). The underdoped compound with the initial $T_c$ of 65~K has been studied as a function of pressure up to 20 GPa by magnetic susceptibility and X-ray diffraction (XRD). The observed linear increase in $T_c$ with pressure is the same as previously been found for the optimally-doped compound. The above results have enabled the investigation of the origins of the significantly different $T_c$ values of optimally doped Hg1201 and the well-studied compound La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO), the latter value of $T_c$ = 40 K being only about 40\% of the former. Hg1201 can have almost identical CuO$_6$ octahedra as LSCO if specifically strained. When the apical and in-plane CuO$_2$ distances are the same for the two compounds, a large discrepancy in their $T_c$ remains. Differences in crystal structures and interactions involving the Hg-O charge reservoir layers of Hg1201 may be responsible for the different $T_c$ values exhibited by the two compounds. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A26.00014: A DFT investigation of pressure effects in the infinite-layer ACuO$ _{2} $ cuprate superconductor for A=\{Mg, Ca, Sr, Ba\} Ben Mallett, Nicola Gaston, James Storey, Grant Williams, Alan Kaiser, Jeffery Tallon We use density functional theory to investigate external-pressure and ``internal-pressure'' effects in the infinite-layer cuprate ACuO$_2$ for A=\{Mg, Ca, Sr, Ba\}, where internal-pressure is induced by ion-size substitution. Where these materials have been synthesised we find good agreement between our calculated structural parameters and the experimental ones. We find that these non-hydrostatic pressure-effects can have a significant effect on the superconducting energy gap via modifications to the electronic dispersion. Furthermore, pressure alters the dispersion independently of how it is applied (internal or external) so that the superconducting energy gap correlates with the unit-cell volume. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A26.00015: Pressure-induced insulator to metal transitions in potential 3D topological insulators Ag$_{2}$Se and Ag$_{2}$Te Zhao Zhao, Shibing Wang, Artem Oganov, Pengcheng Chen, Haijun Zhang, Zhenxian Liu, Wendy Mao Silver chalcogenides Ag$_{2}$Se and Ag$_{2}$Te are non-magnetic compounds exhibiting interesting physics like linear magnetoresistance and dimensionality tunable band gap. To explore their behaviors under high pressure, we performed synchrotron X-ray diffraction and infrared experiments combined with evolutionary algorithm structure predictions and \textit{ab-initio} band structure calculations. For Ag$_{2}$Se, the unusual increase of phase I's band gap and topologically nontrivial features of its band structure support $\beta -$Ag$_{2}$Se as a potential 3D topological insulator. The bulk insulating phase I first transforms to a bulk metallic phase II with 2.4 percent volume drop, marked by the appearance of the distinctive Se(Ag1)-Ag2-Se(Ag1) triple layers stacking pattern. At higher pressure, a transition from the phase II to a completely metallic phase III was observed. And for Ag$_{2}$Te, our study shows that the bulk insulating phase I first transforms into a semi-metallic phase II with the perseverance of its topologically non-trivial nature, and then to a bulk metallic phase III. Our study highlights pressure's role in tuning the electronic structures of Ag$_{2}$Se and Ag$_{2}$Te. [Preview Abstract] |
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