Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y36: Novel Superconductors III |
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Sponsoring Units: DCMP Chair: N. Peter Armitage, Johns Hopkins University Room: 344 |
Friday, March 22, 2013 8:00AM - 8:12AM |
Y36.00001: Spin incommensurability varies linearly with hole content in single-layer Bi2201 cuprate John Tranquada, M. Enoki, M. Fujita, T. Nishizaki, K. Yamada, S. Iikubo, D.K. Singh, S. Chang We have performed inelastic neutron scattering measurements on the single-layer cuprate Bi$_{2+x}$Sr$_{2-x}$CuO$_{6+y}$ (Bi2201) with $x=0.2$, 0.3, 0.4 and 0.5, a doping range that spans the spin-glass (SG) to superconducting (SC) phase boundary [1]. The doping evolution of low energy spin fluctuations ($\la 11$~meV) was found to be characterized by a change of incommensurate modulation wave vector from the tetragonal [110] to [100]/[010] directions, while maintaining a linear relation between the incommensurability and the hole concentration, $\delta\approx p$. In the SC regime, the spectral weight is strongly suppressed below $\sim4$~meV. Similarities and differences in the spin correlations between Bi2201 and the prototypical single-layer system La$_{2-x}$Sr$_x$CuO$_4$ will be discussed.\\[4pt] [1] M. Enoki {\it et al.}, arXiv:1205.3301. [Preview Abstract] |
Friday, March 22, 2013 8:12AM - 8:24AM |
Y36.00002: Strong coupling behavior of the neutron resonance mode in unconventional superconductors Patrik Hlobil, Boris Narozhny, Joerg Schmalian A number of unconventional superconductors are characterized by a resonance mode in the spin excitation spectrum, measured via inelastic neutron scattering, which emerges below the superconducting transition temperature and is sharp as function of momentum and energy. A promising theory for the resonance is based on the analysis of the particle-hole spectrum in the superconducting state and in the presence of antiferromagnetic fluctuations. In this theory, a resonance occurs in case of a sign change of the superconducting gap function for momenta on the Fermi surface that are coupled by the antiferromagnetic ordering vector. So far, the theory was analyzed without including higher order vertex corrections of the particle-hole spectrum. In this work we analyze such vertex correction and show that: i) the qualitative difference in the behavior between a gap that changes sign and that doesn't change sign remains if one includes higher order vertex corrections, ii) vertex corrections are of order unity and cannot be ignored. Thus, while the resonance mode does seem to be a reliable fingerprint for an unconventional, sign-changing order parameter, it is a strong coupling phenomenon and no reliable approach to determine its detailed behavior seems to exist. [Preview Abstract] |
Friday, March 22, 2013 8:24AM - 8:36AM |
Y36.00003: Distinct Fe-induced magnetic states in the underdoped and overdoped regimes of La$_{2-x}$Sr$_x$Cu$_{1-y}$Fe$_y$O$_4$ revealed by muon spin relaxation Kensuke Suzuki, Tadashi Adachi, Youichi Tanabe, Hidetaka Sato, Risdy Risdiana, Yasuyuki Ishii, Takao Suzuki, Isao Watanabe, Yoji Koike Zero-field muon-spin-relaxation measurements have been performed in partially Fe-substituted La$_{2-x}$Sr$_x$Cu$_{1-y}$Fe$_y$O$_4$ in a wide range of hole concentration, to investigate the magnetic state induced by the Fe substitution recently suggested from the neutron-scattering measurements [1]. It has been found that a static magnetic order is formed in 1\% Fe-substituted La$_{2-x}$Sr$_x$Cu$_{1-y}$Fe$_y$O$_4$ in a wide range of hole concentration where superconductivity appears in Fe-free La$_{2-x}$Sr$_x$CuO$_4$. In the underdoped regime, the Fe-induced magnetic order can be understood in terms of the concept of stripe pinning by Fe. In the overdoped regime, on the other hand, the Fe-induced magnetic order is short-ranged, which is distinct from the stripes. It is plausible that a spin-glass state of Fe spins derived from the RKKY interaction is realized in the overdoped regime. These results suggest a change of the electronic state from the strongly correlated electron state to the Fermi-liquid-like state with hole doping in La-214 high-$T_{\rm{c}}$ cuprates [2,3].\\[4pt] [1] R.-H. He et al., Phys. Rev. Lett. 107, 127002 (2011).\\[0pt] [2] K. Suzuki et al., Phys. Procedia 30, 275 (2012).\\[0pt] [3] K. M. Suzuki et al., Phys. Rev. B 86, 014522 (2012). [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 8:48AM |
Y36.00004: Test of Variational Methods for Electronic Structures of Solid State and Molecular Systems by Application to Atomic Systems R.H. Pink, S.R. Badu, R.H. Scheicher, T.P. Das The Linked Cluster Many-Body Perturbation Theory [1,2] uses energies and wave-functions obtained from the one-electron Hartree-Fock equations for the ground state to determine the occupied states' contribution to properties such as magnetic hyperfine interaction. Both the occupied and unoccupied bound and continuum state energies and wave-functions are then used to include many-body effects through perturbation theory. This method has been found to provide excellent agreement between theoretical and experimental values for hyperfine constants for atomic systems [3,4]. Due to their multi-center nature, one cannot solve the Hartree-Fock differential equations by numerical integration methods for solid state and molecular systems, and must instead use variational methods [5,6,7]. We shall present our assessment of the accuracy of the variational procedure by determining the hyperfine constants for the Phosphorous [3] and Lithium [2] atoms. [1] Hugh P. Kelly, Phys. Rev. 144, 39 (1966) [2] E.S. Chang, R.T. Pu and T.P. Das, Phys. Rev. 174, 1 (1968) [3] N.C. Dutta, C. Matsubara, R. T. Pu, and T.P. Das, Phys. Rev. Lett. 21, 1139 (1968) [4] J. Andriessen, K. Raghunathan, S.N. Ray and T.P. Das, Phys Rev. B15, 2533 (1977) [5] C.C.J. Roothaan, Rev. Mod. Phys. 23, 69 (1951) [6] J.E. Rodgers and T.P. Das, Phys. Rev. A8, 2195 (1973) [7] W.J. Hehre, R.F. Stewart, and J.A. Pople, J. Chem. Phys. 51, 2657 (1969) [Preview Abstract] |
Friday, March 22, 2013 8:48AM - 9:00AM |
Y36.00005: Understanding of Nuclear Quadrupole Interaction of $^{19}$F* and Binding Mechanism in Solid Fluorine at First-Principles Level D.R. Mishra, M.M. Aryal, N.P. Adhikari, R.H. Pink, T.P. Das We have carried out a theoretical study of the nuclear quadrupole interaction (NQI) parameters of $^{19}$F* excited nuclear state in solid fluorine as well as the intermolecular binding of fluorine molecules in the solid. This is in continuation of our investigation [1] of the properties of solid halogens using the first-principles Hartree-Fock (HF) cluster procedure combined with many-body perturbation theory (MBPT), implemented by the Gaussian 03 set of programs. For the NQI parameters, the value of ($e^{2}$\textit{qQ/h}) obtained from our investigation for the $^{19}$F* excited nuclear state in solid fluorine is 120.9 MHz, which agrees with the experimental value 127.2 MHz, quoted in [2], within 5{\%} and the asymmetry parameter, $\eta $ is essentially zero. For obtaining ($e^{2}$\textit{qQ/h}) the value of the quadrupole moment, $Q$ for $^{19}$F* is taken from [3] as 0.072 x 10$^{28}$ m$^{2}$. As regards the binding of fluorine molecules in solid fluorine, our quantitative binding energy results show that the binding arises mainly from the van der Waals interaction obtained from intermolecular many-body effects with the one electron HF contribution being weak and repulsive in nature.\\[4pt] [1] M.M. Aryal et al., Hyperfine Interact, 176, 51 (2007). \\[0pt] [2] K.C.Mishra et al.,Phys. Rev.B25, 3389(1982).\\[0pt] [3] H. Barfuss et al., Phys. Lett. 90A, 33(1982). [Preview Abstract] |
Friday, March 22, 2013 9:00AM - 9:12AM |
Y36.00006: Enhanced charge stripe order in superconducting La$_{\mathrm{2-x}}$Ba$_{\mathrm{x}}$CuO$_{4}$ in high magnetic fields M. Huecker, M. v. Zimmermann, Z.J. Xu, J.S. Wen, G.D. Gu, J.M. Tranquada There is mounting evidence for a proximity of the superconducting ground state in the cuprates to competing states with static spin and/or charge density modulations. One such competing state is the spin and charge stripe phase in La$_{\mathrm{2-x}}$Ba$_{\mathrm{x}}$CuO$_4$. By means of high energy (100 keV) x-ray diffraction we have studied the effect of a high magnetic field (H\textbar \textbar c) on the charge stripe order in a broad range of doping (0.095 $\le $ x $\le $ 0.155). We find that the field can significantly enhance the charge stripe order, but only at temperatures and dopings where it coexists with bulk superconductivity at zero field. The field also increases stripe correlations between the planes, which can result in an enhanced frustration of the interlayer Josephson coupling. Close to the famous x$=$1/8 compound, where zero field stripe order is pronounced and bulk superconductivity is suppressed, charge stripe order is independent of the field. The results imply that static stripe order and three-dimensionally coherent superconductivity are competing ground states. [Preview Abstract] |
Friday, March 22, 2013 9:12AM - 9:24AM |
Y36.00007: Lifetime of Skyrmions in Cuprates and Other Layered Materials Liufei Cai, Eugene Chudnovsky, Dmitry Garanin Collapse of a skyrmion due to the discreteness of a crystal lattice in isotropic two-dimensional ferro- and antiferromagnets has been studied analytically and by numerical solution of equations of motion for up to 2000$\times$2000 classical spins on a square lattice coupled via Heisenberg exchange interaction. Excellent agreement between analytical and numerical results has been achieved. The lifetime of the skyrmion scales with its initial size, $\lambda_0$, as $(\lambda_{0}/a)^{5}$ in ferromagnets and as $(\lambda_{0}/a)^{2.15}$ in antiferromagnets, with $a$ being the lattice parameter. This makes antiferromagnetic skyrmions significantly shorter lived than ferromagnetic skyrmions. [Preview Abstract] |
Friday, March 22, 2013 9:24AM - 9:36AM |
Y36.00008: Fractional Flux Quantization in Loops of Unconventional Superconductors Florian Loder, Arno Kampf, Thilo Kopp The magnetic flux threading a conventional superconducting ring is typically quantized in units of $\Phi_0=hc/2e$. The factor 2 in the denominator of $\Phi_0$ originates from the existence of two different types of pairing states with minima of the free energy at even and odd multiples of $\Phi_0$. Here we show that spatially modulated pairing states exist with energy minima at fractional flux values, in particular at multiples of $\Phi_0/2$. In such states condensates with different center-of-mass momenta of the Cooper pairs coexist. The proposed mechanism for fractional flux quantization is discussed in the context of cuprate superconductors, where $hc/4e$ flux periodicities as well as uniaxially modulated superconducting states were observed. [Preview Abstract] |
Friday, March 22, 2013 9:36AM - 9:48AM |
Y36.00009: Magnetic structures in YBCO single crystals under tilted magnetic fields Vitalii Vlasko-Vlasov, Ulrich Welp, Alexei Koshelev, Wai Kwok We study magnetic flux distributions in YBCO single crystals remagnetized by magnetic fields of different orientations using the magneto-optic indicator technique. Application of the perpendicular field to the crystals cooled in the in-plane magnetic field, application of the in-plane field to the crystals cooled in the normal magnetic field, and remagnetization by magnetic field tilted to the sample surface result in unusual quasiperiodic vortex structures. These strongly inhomogeneous vortex patterns can be associated with the flux cutting and strong anisotropy of the vortex kink motion depending on the trapped flux and external field orientations. We discuss the effect of resulting inhomogeneous current distributions on the current carrying ability of the YBCO coated conductors. Work supported by the US DoE-BES funded Energy Frontier Research Center and by Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357. [Preview Abstract] |
Friday, March 22, 2013 9:48AM - 10:00AM |
Y36.00010: Vortex lock-in transition coinciding with the 3D to 2D crossover in YBa$_2$Cu$_3$O$_7$ Saskia Bosma, Stephen Weyeneth, Roman Puzniak, Andreas Erb, Hugo Keller Dimensionality is essential to understand the behavior of vortices in layered cuprate superconductors. A 3D (three-dimensional) to 2D (two-dimensional) crossover takes place when the out-of-plane coherence length becomes smaller than the interplane distance. We directly detected a vortex lock-in transition by torque magnetometry in an overdoped YBa$_2$Cu$_3$O$_{7-\delta}$ single crystal of low anisotropy. The locked-in state was observed below the 3D to 2D crossover temperature, independently of extrinsic pinning effects thanks to a high quality clean crystal and the use of a vortex shaking technique. The lock-in is enhanced by decreasing temperature and increasing magnetic field. The shape of the torque signal is in very good agreement with the model developped by Feinberg and Ettouhami [Int. J. Mod. Phys. B {\bf 7}, 2085 (1993)] for quasi-2D superconductors, despite the low anisotropy of the material. Additionally, we present a new torque magnetometer design featuring vortex shaking, and compatible with the {\it Quantum Design} PPMS system. [Preview Abstract] |
Friday, March 22, 2013 10:00AM - 10:12AM |
Y36.00011: Investigating the low-field vortex lattice phase diagram in CeCoIn$_5$ with $H \parallel c$ P. Das, M. R. Eskildsen, E. M. Forgan, H. Kawano-Furukawa, C. Petrovic Here we present small angle neutron scattering studies of the vortex lattice (VL) phase diagram in CeCoIn$_5$ in the low-field high-temperature regime with $H \parallel c$ which remained unexplored. While previous studies [A. D. Bianchi $et. al.$ Science {\bf{319}}, 177 (2008)] reported the phase boundary between the high-field square $\rightarrow$ rhombic $\rightarrow$ hexagonal VLs, the lower boundary between hexagonal $\rightarrow$ rhombic $\rightarrow$ square remained unexplored at higher temperatures where only estimates were provided. We have investigated this regime and mapped out these VL transitions. Interestingly, at the base temperature, no rhombic phase is observed but a direct transition from hexagonal to square phase. A possible explanation for this deviation from earlier reports may be that the current measurements were done following a field-ramp at base temperature rather than field-cool used in previous measurements. This indicates a slight hysteresis associated with this transition. While the measured hexagonal to rhombic phase transition agrees with the earlier estimates, the square VL phase occupies a larger region at higher temperatures than previously estimated. [Preview Abstract] |
Friday, March 22, 2013 10:12AM - 10:24AM |
Y36.00012: Vortices in superconducting MoGe pentagon Takekazu Ishida, Ho Thanh Huy, Masaru Kato, Masahiko Hayashhi Vortices in bulk prefer to form a triangular lattice while a mesoscopic superconductor with a size comparable to coherence length $\xi $ or the magnetic penetration depth $\lambda $ is quite different so as to create particular configuration of vortices. The behavior of such structures in an external magnetic field is strongly influenced by the boundary conditions. Vortex states in superconducting disk, triangle and square pattern have been extensively studied both theoretically and experimentally [B. J. Baelus et al., Phys. Rev. B 69, 064506 (2004)]. We present vortex structures in MoGe pentagon disks imaged by means of a scanning quantum interference device (SQUID) microscopy [Ho Thanh Huy et al., Physica C, in press; DOI 10.1016/j.physc.2012.03.037.] Systematic measurements allow us to reveal how vortex arrangement evolves with the applied magnetic field. Moreover, we found that shell filling rule is subjected to change when a pinning center is introduced. Numerical calculations of vortex structure in pentagon disks on the basis of the nonlinear Ginzburg-Landau theory reveal that there are good agreement between experimental data and theoretical calculations. [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 10:36AM |
Y36.00013: Unconventional Vortex States in Nanoscale Superconductors Due to Shape-Induced Resonances in the Inhomogeneous Cooper-pair Condensate Ling-Feng Zhang, Lucian Covaci, Milorad Milosevic, Golibjon Berdiyorov, Francois Peeters Vortex matter in mesoscopic superconductors is known to be strongly affected by the geometry of the sample. Here we show that in nanoscale superconductors with coherence length comparable to the Fermi wavelength the shape resonances of the order parameter results in an additional contribution to the quantum topological confinement leading to unconventional vortex configurations. Our Bogoliubov de Gennes calculations in a square geometry reveal a plethora of asymmetric, giant multivortex, and vortex antivortex structures, stable over a wide range of parameters and which are very different from those predicted by the Ginzburg Landau theory. By modifying the size of the system and the Fermi energy we show that ground states with different symmetries can be obtained. By increasing the temperature we observe first-order transitions from multivortex to giant vortex states. These unconventional states are relevant for high Tc nanograins, confined Bose Einstein condensates, and graphene flakes with proximity induced superconductivity. [Preview Abstract] |
Friday, March 22, 2013 10:36AM - 10:48AM |
Y36.00014: Competition between covalent bonding and charge transfer tendencies at complex-oxides interfaces J. Salafranca, J. Tornos, J. Garc\'Ia-Barriocanal, C. Le\'on, J. Santamaria, J. Rinc\'on, G. \'Alvarez, S.J. Pennycook, E. Dagotto, M. Varela Interfaces alter the subtle balance among different degrees of freedom responsible for exotic phenomena in complex oxides, such as cuprate-manganite interfaces. We study these interfaces by means of scanning transmission electron microscopy and theoretical calculations. Microscopy and EEL spectroscopy indicate that the interfaces are sharp, and the chemical profile is symmetric with two equivalent interfaces. Spectroscopy also allows us to establish an oxidation state profile with sub-nanometer resolution. We find an anomalous charge redistribution: a non-monotonic behavior of the occupancy of d orbitals in the manganite layers as a function of distance to the interface. Relying on model calculations, we establish that this profile is a result of the competition between standard charge transfer tendencies involving materials with different chemical potentials and strong bonding effects across the interface. The competition can be tuned by different factors (temperature, doping, magnetic fields...). As examples, we report different charge distributions as a function of doping of the manganite layers. ACKNOWLEDGEMENTS ORNL:U.S. DOE-BES, Material Sciences and Engineering Division \& ORNL's ShaRE. UCM:Juan de la Cierva, Ramon y Cajal, \& ERC Starting Investigator Award programs. [Preview Abstract] |
Friday, March 22, 2013 10:48AM - 11:00AM |
Y36.00015: ABSTRACT WITHDRAWN |
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