ALBERT

Description: Nature Physics 12, 150 (2016). doi:10.1038/nphys3519 Authors: M. H. Hamidian, S. D. Edkins, Chung Koo Kim, J. C. Davis, A. P. Mackenzie, H. Eisaki, S. Uchida, M. J. Lawler, E.-A. Kim, S. Sachdev & K. Fujita Research on high-temperature superconducting cuprates is at present focused on identifying the relationship between the classic ‘pseudogap’ phenomenon and the more recently investigated density wave state. This state is generally characterized by a wavevector Q parallel to the planar Cu–O–Cu bonds along with a predominantly d-symmetry form factor (dFF-DW). To identify the microscopic mechanism giving rise to this state, one must identify the momentum-space states contributing to the dFF-DW spectral weight, determine their particle–hole phase relationship about the Fermi energy, establish whether they exhibit a characteristic energy gap, and understand the evolution of all these phenomena throughout the phase diagram. Here we use energy-resolved sublattice visualization of electronic structure and reveal that the characteristic energy of the dFF-DW modulations is actually the ‘pseudogap’ energy Δ1. Moreover, we demonstrate that the dFF-DW modulations at E  =   −Δ1 (filled states) occur with relative phase π compared to those at E  =  Δ1 (empty states). Finally, we show that the conventionally defined dFF-DW Q corresponds to scattering between the ‘hot frontier’ regions of momentum-space beyond which Bogoliubov quasiparticles cease to exist. These data indicate that the cuprate dFF-DW state involves particle–hole interactions focused at the pseudogap energy scale and between the four pairs of ‘hot frontier’ regions in momentum space where the pseudogap opens.

Description: Author(s): H. Naik, T. N. Nathaniel, A. Goswami, G. N. Kim, M. W. Lee, S. V. Suryanarayana, S. Ganesan, E. A. Kim, M.-H. Cho, and K. L. Ramakumar The postneutron yields of various fission products in the mass regions of 77–153 have been determined in the 50-, 60-, and 70-MeV bremsstrahlung-induced fission of 232 Th by using a recoil catcher and an off-line γ-ray spectrometric technique in the electron linac at the Pohang Accelerator Laboratory... [Phys. Rev. C 85, 024623] Published Mon Feb 27, 2012

Description: Author(s): H. Naik, T. N. Nathaniel, A. Goswami, G. N. Kim, M. W. Lee, S. V. Suryanarayana, S. Ganesan, E. A. Kim, M.-H. Cho, and K. L. Ramakumar [Phys. Rev. C 85, 039905] Published Tue Mar 27, 2012

Description: In the high-transition-temperature (high-T(c)) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a quantitative order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within each CuO(2) unit cell. We analyse spectroscopic-imaging scanning tunnelling microscope images of the intra-unit-cell states in underdoped Bi(2)Sr(2)CaCu(2)O(8 +) (delta) and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90 degrees -rotational symmetry within every CuO(2) unit cell.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lawler, M J -- Fujita, K -- Lee, Jhinhwan -- Schmidt, A R -- Kohsaka, Y -- Kim, Chung Koo -- Eisaki, H -- Uchida, S -- Davis, J C -- Sethna, J P -- Kim, Eun-Ah -- England -- Nature. 2010 Jul 15;466(7304):347-51. doi: 10.1038/nature09169.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, New York 13902-6000, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20631795" target="_blank"〉PubMed〈/a〉

Description: We study the coexisting smectic modulations and intra-unit-cell nematicity in the pseudogap states of underdoped Bi(2)Sr(2)CaCu(2)O(8+delta). By visualizing their spatial components separately, we identified 2pi topological defects throughout the phase-fluctuating smectic states. Imaging the locations of large numbers of these topological defects simultaneously with the fluctuations in the intra-unit-cell nematicity revealed strong empirical evidence for a coupling between them. From these observations, we propose a Ginzburg-Landau functional describing this coupling and demonstrate how it can explain the coexistence of the smectic and intra-unit-cell broken symmetries and also correctly predict their interplay at the atomic scale. This theoretical perspective can lead to unraveling the complexities of the phase diagram of cuprate high-critical-temperature superconductors.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mesaros, A -- Fujita, K -- Eisaki, H -- Uchida, S -- Davis, J C -- Sachdev, S -- Zaanen, J -- Lawler, M J -- Kim, Eun-Ah -- New York, N.Y. -- Science. 2011 Jul 22;333(6041):426-30. doi: 10.1126/science.1201082.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Instituut-Lorentz for Theoretical Physics, Universiteit Leiden, 2300 Leiden, Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21778393" target="_blank"〉PubMed〈/a〉

Description: Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x Nature 532, 7599 (2016). doi:10.1038/nature17411 Authors: M. H. Hamidian, S. D. Edkins, Sang Hyun Joo, A. Kostin, H. Eisaki, S. Uchida, M. J. Lawler, E.-A. Kim, A. P. Mackenzie, K. Fujita, Jinho Lee & J. C. Séamus Davis The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density. Such a state has been created in ultracold 6Li gas but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase of the copper oxide superconductors contains such a ‘pair density wave’ state. Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms and at the Bi2Sr2CaCu2O8+x crystal supermodulation. Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors QP ≈ (0.25, 0)2π/a0 and (0, 0.25)2π/a0 in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s′ symmetry. This phenomenology is consistent with Ginzburg–Landau theory when a charge density wave with d-symmetry form factor and wavevector QC = QP coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase.

Description: Magnetic devices are a leading contender for the implementation of memory and logic technologies that are non-volatile, that can scale to high density and high speed, and that do not wear out. However, widespread application of magnetic memory and logic devices will require the development of efficient mechanisms for reorienting their magnetization using the least possible current and power. There has been considerable recent progress in this effort; in particular, it has been discovered that spin-orbit interactions in heavy-metal/ferromagnet bilayers can produce strong current-driven torques on the magnetic layer, via the spin Hall effect in the heavy metal or the Rashba-Edelstein effect in the ferromagnet. In the search for materials to provide even more efficient spin-orbit-induced torques, some proposals have suggested topological insulators, which possess a surface state in which the effects of spin-orbit coupling are maximal in the sense that an electron's spin orientation is fixed relative to its propagation direction. Here we report experiments showing that charge current flowing in-plane in a thin film of the topological insulator bismuth selenide (Bi2Se3) at room temperature can indeed exert a strong spin-transfer torque on an adjacent ferromagnetic permalloy (Ni81Fe19) thin film, with a direction consistent with that expected from the topological surface state. We find that the strength of the torque per unit charge current density in Bi2Se3 is greater than for any source of spin-transfer torque measured so far, even for non-ideal topological insulator films in which the surface states coexist with bulk conduction. Our data suggest that topological insulators could enable very efficient electrical manipulation of magnetic materials at room temperature, for memory and logic applications.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mellnik, A R -- Lee, J S -- Richardella, A -- Grab, J L -- Mintun, P J -- Fischer, M H -- Vaezi, A -- Manchon, A -- Kim, E-A -- Samarth, N -- Ralph, D C -- England -- Nature. 2014 Jul 24;511(7510):449-51. doi: 10.1038/nature13534.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Cornell University, Ithaca, New York 14853, USA. ; Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. ; 1] Cornell University, Ithaca, New York 14853, USA [2] Weizmann Institute of Science, Rehovot 76100, Israel. ; King Abdullah University of Science and Technology, Physical Sciences and Engineering Division, Thuwal 23955-6900, Saudi Arabia. ; 1] Cornell University, Ithaca, New York 14853, USA [2] Kavli Institute at Cornell, Ithaca, New York 14853, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25056062" target="_blank"〉PubMed〈/a〉

Description: The existence of electronic symmetry breaking in the underdoped cuprates and its disappearance with increased hole density p are now widely reported. However, the relation between this transition and the momentum-space (k-space) electronic structure underpinning the superconductivity has not yet been established. Here, we visualize the Q = 0 (intra-unit-cell) and Q not equal 0 (density-wave) broken-symmetry states, simultaneously with the coherent k-space topology, for Bi(2)Sr(2)CaCu(2)O(8+delta) samples spanning the phase diagram 0.06 〈/= p 〈/= 0.23. We show that the electronic symmetry-breaking tendencies weaken with increasing p and disappear close to a critical doping p(c) = 0.19. Concomitantly, the coherent k-space topology undergoes an abrupt transition, from arcs to closed contours, at the same p(c). These data reveal that the k-space topology transformation in cuprates is linked intimately with the disappearance of the electronic symmetry breaking at a concealed critical point.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fujita, K -- Kim, Chung Koo -- Lee, Inhee -- Lee, Jinho -- Hamidian, M H -- Firmo, I A -- Mukhopadhyay, S -- Eisaki, H -- Uchida, S -- Lawler, M J -- Kim, E-A -- Davis, J C -- New York, N.Y. -- Science. 2014 May 9;344(6184):612-6. doi: 10.1126/science.1248783.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24812397" target="_blank"〉PubMed〈/a〉

Description: Author(s): D. E. Shai, M. H. Fischer, A. J. Melville, E. J. Monkman, J. W. Harter, D. W. Shen, D. G. Schlom, M. J. Lawler, E.-A. Kim, and K. M. Shen Chemical substitution plays a key role in controlling the electronic and magnetic properties of complex materials. For instance, in EuO, carrier doping can induce a spin-polarized metallic state and colossal magnetoresistance, and significantly enhance the Curie temperature. Here, we employ a combin… [Phys. Rev. B 94, 195102] Published Tue Nov 01, 2016

Description: Author(s): Papa B. Ndiaye, C. A. Akosa, M. H. Fischer, A. Vaezi, E.-A. Kim, and A. Manchon We address the nature of spin-orbit torques at the magnetic surfaces of topological insulators using the linear-response theory. We find that the so-called Dirac torques in such systems possess a different symmetry compared to their Rashba counterpart, as well as a high anisotropy as a function of t… [Phys. Rev. B 96, 014408] Published Thu Jul 06, 2017