Charge and Spin Stripe Order: A New Phase of Condensed Matter Simultaneous Ordering of Holes and Spins in La 2 NiO 4.125, J.M. Tranquada et al., Phys.

Charge and Spin Stripe Order: A New Phase of Condensed Matter

Simultaneous Ordering of Holes and Spins in La2NiO4.125, J.M. Tranquada et al., Phys. Rev. Lett. 73, 1003 (1994). 205 citationsEvidence for stripe correlations of spins and holes in copper oxide superconductors, J.M. Tranquada et al., Nature 375, 561 (1995). 1245 citationsNeutron-scattering study of stripe-phase order of holes and spins in La1.48Nd0.4Sr0.12CuO4, J.M. Tranquada et al., Phys. Rev. B 54, 7489 (1996).

332 citationsCoexistence of, and Competition between, Superconductivity and Charge-Stripe Order in La 1.6-xNd0.4SrxCuO4, J.M. Tranquada et al., Phys. Rev. Lett. 78, 338

(1997). 390 citationsDoping dependence of the spatially modulated dynamical spin correlations and the superconducting-transition temperature in La 2-xSrxCuO4, K. Yamada, G.

Shirane, et al., Phys. Rev. B 57, 6165 (1998). 409 citations

A correlated (Mott) insulator with strong electron-electron repulsion typically exhibits antiferromagnetic order. By changing the charge density (doping) one can often obtain a metallic phase, which in some instances can exhibit high temperature superconductivity.

Neutron diffraction experiments on the layered superconducting compound, La1.48Nd0.4Sr0.12CuO4, and related isostructural La2NiO4.125 revealed a new type of intermediate order involving alternating stripes of antiferromagnetism and doped charges.

After a decade of research, new properties of the stripe-ordered state continue to be revealed. Evidence has also been obtained for phases of dynamic, fluctuating stripes. Such correlated states may play an important role in high-temperature superconductivity.

Tranquada et al., BNL

Antiferromagnetism and High-Temperature Superconductivity

Antiferromagnetism in La2CuO4-y, D. Vaknin, S. K. Sinha, D. E. Moncton, D. C. Johnston, J. M. Newsam, C. R. Safinya, and H. E. King, Jr., Phys. Rev. Lett. 58, 2802-5 (1987). 826 citationsTwo dimensional antiferromagnetic quantum fluid state in La2CuO4, G. Shirane et al., Phys. Rev. Lett. 59, 1613 (1987). 637 citationsNeutron diffraction determination of antiferromagnetic structure of Cu ions in YBa 2Cu3O6+x with x = 0.0 and 0.15, J. M. Tranquada et al., Phys. Rev. Lett. 60, 156-

9 (1988). 532 citationsStatic and dynamic spin correlations in pure and doped La2CuO4, Y. Endoh, J. M. Tranquada, G. Shirane et al., Phys. Rev. B 37, 7443 (1988).

396 citationsAntiferromagnetism in YBa2Cu3O6+x,” J. M. Tranquada et al., Phys. Rev. B 38, 2477 (1988). 272 citationsNeutron-scattering study of the dynamical spin susceptibility in YBa2Cu3O6+x, J. Tranquada et al. Phys. Rev. B 46, 5561 (1992). 252 citations

In 1986 superconductivity was discovered in the layered compound La2-xBaxCuO4 with a transition temperature much higher than the existing theory could explain. Relatively little was known about the copper oxides and, in particular, what unique properties could give rise to this remarkable phenomenon.

Neutron scattering studies on the parent material, La2CuO4 (see structure at right), and another superconducting parent, YBa2Cu3O6, demonstrated that the CuO2 planes exhibit antiferromagnetic order, typical of a correlated insulator. The antiferromagnetic correlations remain strong in the disordered phase due to a very large superexchange coupling between Cu spins.

This work initiated a continuing exploration of magnetic excitations in copper-oxide superconductors. Antiferromagnetic correlations are believed by many to be crucial to the mechanism of high-temperature superconductivity.

Shirane, Tranquada et al., BNL

Structural Phase Transitions

Lattice-Dynamical Study of the 110 K Phase Transition in SrTiO3, G. Shirane and Y. Yamada, Phys. Rev. 117, 858 (1969). 328 citationsCritical Neutron Scattering in SrTiO3 and KMnF3, S.M. Shapiro, J.D. Axe, G. Shirane, and T. Riste, Phys. Rev. B 6, 4332 (1972). 308 citations

In the late 1960’s and early 1970’s, Gen Shirane, John Axe, and Steve Shapiro used neutrons to study the mechanism of structural phase transitions in a large variety of compounds, many with the perovskite structure.

They used inelastic neutron scattering to study the temperature dependence of phonon dispersions. Of particular note were the first q-dependent study of the zone-boundary soft-mode transition in SrTiO3, and the first definitive characterization of the central mode typically seen in a soft-mode transition. The figures illustrate the variety of transition mechanisms studied: soft zone-center optical mode, soft zone-boundary mode, soft acoustic mode, and an order-disorder transition.

Shirane, Axe et al., BNL

Buckley Prize of the APS, Shirane Warren Award of the ACA, Axe and Shirane

X-ray Magnetic Scattering

Magnetic x-ray scattering studies of holmium using synchrotron radiation, D. Gibbs et al. Phys. Rev. Lett. 55 234 (1985) 201 citationsPolarization and resonance properties of magnetic x-ray scattering in holmium, D. Gibbs et al. Phys. Rev. Lett. 61 1241 (1988) 298 citationsX-ray resonance exchange scattering, J.P. Hannon et al. Phys. Rev. Lett. 61 1245 (1988) 348 citationsPolarization dependence of magnetic x-ray scattering, M. Blume and D. Gibbs, Phys. Rev. B 37 1779 (1988) 195 citationsX-ray resonant exchange scattering: polarization dependence and correlation functions, J.P. Hill and D.F. McMorrow Acta Cryst. A52 23 (1996) 95 citations

Researchers at BNL discovered a large resonant enhancement in the x-ray magnetic scattering cross-section. Subsequently, they took the lead in the experimental studies, theoretical understanding, and application of the resonant magnetic scattering technique. In particular, this work allowed high-resolution, element specific studies of magnetism in small volume samples.

This research has led to a new understanding of rare-earth magnetism and has had particular impact in the study of surface and interfacial magnetism, including applications to magnetic recording media. It also motivated general studies of resonant x-ray scattering phenomena, including the development of beamlines worldwide.

X-ray magnetic scattering from the spiral antiferromagnet, Ho. Large resonant enhancements are seen when the incident energy is tuned to the Ho LIII edge.

2003 Compton Award: Gibbs, Blume, McWhan, and Namikawa

Gibbs et al., BNL

Structure of Electrode Surfaces

In-situ x-ray diffraction and x-ray reflectivity of the Au(111) electrolyte interface- reconstruction and anion adsorption., J. Wang, et al. Phys. Rev. B. ,46, (1992). 155 citationsStructure and phases of the Au(001) surface I: in-plane structure, D. Gibbs et al. Phys. Rev. B42, 7330 (1990). 182 citations In situ x-ray reflectivity and diffusion studies of the Au(001) reconstruction in an electrochemcial cell, B.M. Ocko et al.., Phys. Rev. Lett. 65, 1466 (1990). 158 citationsThe structure and electrocompression of electrodeposited iodine monolayers on Au(111) , B.M. Ocko et al., J. Phys. Chem. 98, 897(1994). 106 citations

Au(111) surface reconstruction pattern

(a) Cyclic voltammetry and (b) x-ray intensity for Br adsorption on Ag(100)

X-ray cellOcko et al., BNL

In-situ structural studies at single crystal electrode surfaces using synchroton x-ray scattering techniques provided the first Angstrom resolution description of the potential-dependent structure. Results on metal, ion, and metal-ion adlayers and for “clean surfaces” which surface reconstruct provided the first direct structural basis for conventional electrochemical measurements. This structural basis could not be inferred from ex-situ studies.

Microscopic description of the electrode/electrolyte interfaces provided an unprecedented understanding of the electrical double layer structure, and revealed the initial stages of metal electrodeposition and the structure of catalytically active phases, which improved our understanding of electrode reaction kinetics, metal electrodeposition and electrocatalysis. Reliable theoretical treatments of these systems became feasible.

Phase Transitions in Low-Dimensional Antiferromagnets

Neutron scattering investigation of phase transitions and magnetic correlations in the two-dimensional antiferromagnets: K 2NiF4, Rb2NiF4, and Rb2FeF4, R. J.

Birgeneau, H. J. Guggenheim, and G. Shirane, Phys. Rev. B 1, 2211 (1970). 264 citations

Spin dynamics in one-dimensional antiferromagnet (CD3)4NMnCl3, M.T. Hutching, G. Shirane, R.J. Birgeneau, and S.L. Holt, Phys. Rev. B 5, 1999 (1972).

255 citations

The statistical mechanics of order-disorder phase transitions developed rapidly in the 1960’s and 1970’s. Magnetic systems were used as prototypes. More precise results were obtained for models of one- and two-dimensional systems.

Birgeneau and Shirane performed some of the first neutron scattering studies of magnetic ordering and correlations in 1D and 2D antiferromagnets. That work initiated a line of study that continues to yield fascinating results. In particular, the model system K2NiF4 has the same structure as the high-temperature superconductor La2-xSrxCuO4, which also shows 2D antiferromagnetism. The figure at right shows superlattice intensity and critical scattering in K2NiF4.

In his 1982 Nobel-prize lecture, Ken Wilson cited the work of Birgeneau and Shirane.

Shirane et al., BNL

Surface Freezing

Kiessig fringes monolayer

surface liquid

bulksolid

C20

C20

Surface freezing was first observed in long-chain molecules at NSLS/BNL. This occurs when the surface forms a frozen molecular crystalline phase at the vapor interface with the molten bulk.

Surface crystallization of liquid normal-alkanes, X.Z. Wu, et. Al, Phys. Rev. Lett. 70 , 958--61 (1993). 167 citationsSurface tension measurements of surface freezing in liquid normal-alkanes, X.Z. Wu et al.,, Science 261 , 1018--21 (1993). 126 citations

Surface freezing in chain molecules , B.M. Ocko et al., Phys. Rev. E , 55 , 3164- (1997) 126 citations

The existing predictions suggested that the opposite phenomenon, surface melting, would occur. The insights gained from these series of experiment are relevant to surface induced nucleation and surface phase separation in mixtures. Surface freezing was recently observed in polymers and this may have technological implications

N-alkane x-ray reflectivity and density profiles (insert)

Temperature dependence:first order phase transition

Ocko et al., BNL

Electronic Order in Doped Manganites

Exhibiting colossal magnetoresistance (CMR), the nature of the electronic ground states of strongly correlated transition metal oxides need to be understood.

A series of neutron and x-ray scattering studies were carried out on CMR manganites. In particular, resonant x-ray scattering studies revealed that the ground state of the half-doped manganite consists of a checkerboard pattern of inequivalent Mn sites with varying orbital occupancy (orbital order) but the same valence (no charge order).

This work overturned a 50-year old picture of ionic charge ordering in doped manganites, and has broader implications for other charge-transfer insulators.

Charge and magnetic order in La0.5Sr1.5MnO4, B. Sternlieb, J.P. Hill et al., Phys. Rev. Lett. 76 2169 (1996) 170 citationsResonant X-ray scattering from orbital ordering in LaMnO3, Y. Murakami, J.P. Hill et al., Phys. Rev. Lett. 81 582 (1998) 268 citationsAn X-ray-induced insulator-metal transition in a magnetoresistive manganite, Kiryukhin, Casa, Hill et al., Nature 386 813 (1997) 185 citationsInterplay between charge, orbital, and magnetic order in Pr1-xCax/MnO3, M. v. Zimmermann, J.P. Hill et al., Phys. Rev. Lett. 83 4872 (1999) 72 citations

Resonant x-ray scattering from orbital order in LaMnO3. Data were taken at the Mn K-edge.

Revised picture of half-doped ground state, which exhibits orbital order, but not charge order.

Hill et al., BNL

High Resolution Powder Diffraction with Synchrotron X-Rays

Rietveld refinement of Debye-Scherrer synchrotron X-ray data from Al2O3, P. Thompson, D.E. Cox, and J.B. Hastings, J. Appl. Cryst.

20, 79 (1987). 540 citationsA correction for powder diffraction peak asymmetry due to axial divergence, L.W. Finger, D.E. Cox, and A.P. Jephcoat, J. Appl. Cryst. 27, 892 (1994). 296 citationsStructural phase-transformations and superconductivity in La2-xBaxCuO4, J.D. Axe et al., Phys. Rev. Lett. 62, 2751 (1989).

484 citationsOrientational ordering transition in solid C60, P.A. Heiney, …, and D.E. Cox, Phys. Rev. Lett. 66, 2911 (1991). 991 citationsCharge, orbital, and magnetic ordering in La0.5Ca0.5MnO3, P.G. Radaelli, D.E. Cox, M. Marezio, and S.W. Cheong, Phys. Rev. B 55,

3015 (1997). 421 citations

X-ray powder diffraction using laboratory diffractometers has long been an important technique for structure determination; however, the advantages of using synchrotron X-rays was not immediately apparent to many.

Dave Cox was the first to show that one could exploit the highly collimated X-ray beam from a synchrotron source to obtain high-resolution diffraction data for structural refinement using the Rietveld method. He went on to build the X-7A powder diffraction beam line at the NSLS, which has been extremely productive.

X-ray powder diffraction with high angular resolution has been essential to studies identifying new ordered states in important new materials, from high-temperature superconductors to colossal magneto-resistive compounds.

Cox et al., BNL

Inelastic X-ray Scattering

J.P. Hill et al., Phys. Rev. Lett. 80 4967 (1998) 80 citations

Recent publications utilizing IXSY.-J. Kim, J.P. Hill et al., Phys. Rev. Lett. 92 137402 (2004)

S. Grenier, J.P. Hill et al., Phys. Rev. Lett. 94 47203 (2005)

Recent research has led to the development of resonant inelastic x-ray scattering (IXS) as a useful probe of electronic excitations in strongly correlated systems.

Momentum-resolved studies of the excitation spectrum provide new information on the electron dynamics and provide challenging tests of the various theoretical descriptions of strongly correlated systems.

The large resonant enhancements have allowed both resolutions and count rates to improve, allowing detailed studies of the low energy dynamics of strongly correlated systems. A beamline dedicated to such studies is currently being commissioned at the Advanced Photon Source.

IXS-CDT

Advanced Photon Source

Hill et al., BNL

First IXS spectrum from a high-Tc cuprate, Nd2CuO4..

Data were taken at the Cu K-edge at the NSLS, 1998.

Spin-polarised Quantum Well States

Magnetic Interface States and Finite Size Effects, N. B. Brookes, Y. Chang and P. D. Johnson, Phys. Rev .Lett. 67, 354 (1991). 86 CitationsOn the Spin Polarization of Quantum Well States in Copper Thin Films deposited on a Co(001) substrate, K. Garrison, Y. Chang and P.D. Johnson, Phys. Rev. Lett. 71, 2801 (1993). 130 CitationsQuantum-Well and Tight-Binding Analyses of Spin-Polarized Photoemission from Ag/Fe(001) Overlayers, N.V. Smith, N.B. Brookes, Y. Chang and P.D. Johnson, Phys.Rev. B 49, 332 (1994). 130 Citations

The Giant Magnetoresistance effect (GMR) and related oscillatory magnetic coupling in magnetic multilayers were discovered in 1988. In the early 90’s the Electron Spectroscopy group at BNL provided the first evidence that the quantum well states in the non-magnetic layers were spin-polarized, as a result of the exchange-split band gaps in the magnetic layers.

The minority spin states are reflected at the interface because of the presence of the minority spin gap but the majority spin states pass through the interface and disappear.

It is the quantum well states in the non-magnetic layer that mediate the oscillatory coupling between the adjacent magnetic layers.

P.D. Johnson et al. BNLFe Ag

Ag/Fe(001)

Minority Spin

Majority Spin

“Many-body effects in angle-resolved photoemission: quasiparticle energy and lifetime of a Mo(110) surface state,” T. Valla, A.V. Fedorov, P.D.

Johnson and S.L. Hulbert. Phys. Rev. Lett. 83(10), 2085-2088 (1999). 100 Citations“Evidence for quantum critical behavior in a photoemission study of optimally doped Bi2Sr2CaCu2O8+,” T. Valla, A.V. Fedorov, P.D. Johnson, B.O.

Wells, S.L. Hulbert, Q. Li, G.D. Gu, and N. Koshizuka. Science 285, 2110-2113 (1999). 212 Citations

First Measurements of Mass Renormalization in Photoemission Electron Spectroscopy

T. Valla. P.D. Johnson et al. BNL

The self-energy corrections reflecting electron-boson coupling result in a mass or velocity renormalization in the immediate vicinity of the Fermi level.

In 1999 new high resolution electron spectrometers allowed the first direct observations of these mass renormalizations in photoemission spectra. The observation in the High Tc superconductors has promoted considerable controversy as to the origin, phonons or spin excitations.

The BNL group introduced the new technique of measuring Momentum Distribution Curves to extract self energies. The imaginary component of the self energy is directly derived from the width of the MDC, the real component is derived from the dispersion.

Momentum DistributionCurve

Energy DistributionCurve

Renormalized velocity Bare velocity

Electron-phonon coupling in Molybdenum

Liquid metals have a strong variation in the interaction in going across the surface from conductor (bulk) to insulator (vapor). On the other hand, dielectric liquids have no such variation and no layering is expected.

The quasi-Bragg peak observed in synchrotron X-ray reflectivity studies showed for the first time the existence of surface induced layering. More recently this same phenomenon was observed in Ga, In, Bi, and K. However, as expected, it was not observed in simple dielectric liquids (water).

These x-ray studies were the first to show a high degree of order at liquid surfaces. Recent results in alloys show surface segregation or demixing phenomenon (Shpyrko, PRL, 95, 106103, 2005). Surface demixing predicted in 1950, but eluded experimentalists for more than 50 years.

Metallic Dielectric

X-ray reflectivity measurements of surface layering in liquid mercury, O.M. Magnussen et al., Phys. Rev. Lett. 74 , 4444 (1995) 146 citationsCapillary wave roughening of surface induced layering in liquid gallium, M.J. Regan et al., Phys. Rev. B 54, 9730 (1996). 111 citations

mercury

Ocko et al., BNL

Surface Induced Layering in Liquid Metals

US - Japan Triple Axis Spectrometer for Neutron Scattering

The US-Japan Program grew out of a 1980 government-to-government agreement on cooperation in scientific R&D. One part of the agreement signed in 1983 established a program between the Institute for Solid State Physics (ISSP) at the University of Tokyo and Brookhaven. Japan provided funding for construction of the H4M triple-axis spectrometer (shown at right, behind a group of eminent physicists and designers) while DOE provided half of the funds for its operation at the High Flux Beam Reactor. The instrument is presently being relocated to a cold-neutron beam line at Oak Ridge’s High Flux Isotope Reactor.

In 23 years, the program has produced more than 350 collaborative peer-reviewed papers, including many on high temperature superconductors.

Long-term visitors at BNL who have gone on to significant positions include:

H. Yoshizawa (ISSP, U. Tokyo) K. Kakurai (ASRC, JAEA)K. Yamada (IMR, Tohoku U.) K. Hirota (ISSP, U. Tokyo)M. Matsuda (JAEA)

Vic Emery, Yasusada Yamada, Marty Blume, Sadao Hoshino, Hideki Yoshizawa, John Axe, Andy Kevey, Frank Langdon, and Gen Shirane (1985)

Shirane, Axe et al., BNL

Low Symmetry Yields High Polarization in Ferroelectrics

“A monoclinic ferroelectric phase in the Pb(Zr1-xTix)O3 solid solution,” B. Noheda, D.E. Cox, G. Shirane, J.A. Gonzalo, L.E. Cross, and S.E. Park, Appl. Phys.

Lett. 74, 2059 (1999). 197 citations“Tetragonal-to-monoclinic phase transition in a ferroelectric perovskite: The structure of PbZr 0.52Ti0.48O3,” B. Noheda, J.A. Gonzalo, L.E. Cross, R. Guo, S.E.

Park, D.E. Cox, and G. Shirane, Phys. Rev. B 61, 8687 (2000). 153 citations“Polarization rotation via a monoclinic phase in the piezoelectric 92% PbZn1/3Nb2/3O3-8% PbTiO3,” B. Noheda, D.E. Cox, G. Shirane, S.E. Park, L.E. Cross,

and Z. Zhong, Phys. Rev. Lett. 86, 3891 (2001). 145 citations

Ferroelectrics are crucial components in applications such as medical imaging, telecommunications, and ultrasonic devices. Some of the best materials are solid solutions, such as combinations of PbZrO3 and PbTiO3. The strongest response occurs near a structural phase boundary, but the reason was not understood.

X-ray powder diffraction studies at the NSLS on extremely homogeneous samples demonstrated that the strong polarization results from a lowering of the symmetry to monoclinic just below the phase boundary (hatched area in figure).

This fundamental insight points the way to improving materials for practical applications. A theoretical group has proposed reducing the symmetry in thin films by making artificial multilayers.

Shirane et al., BNL

Incommensurate-Commensurate Transitions and Charge-Density-Wave Order

“Neutron scattering study of the 38 K and 54 K phase transitions in deuterated TTF-TCNQ,” R. Comès, S.M. Shapiro, G. Shirane, A.F. Garito, and A.J. Heeger, Phys. Rev. Lett. 35, 1518 (1975). 186 citations“Structural phase transformations in K2SeO4,” M. Iizumi, J.D. Axe, G. Shirane, and K. Shimaoka, Phys. Rev. B 15, 4392 (1977). 444 citations“A neutron scattering study of the charge-density wave transitions in 2H-TaSe 2 and 2H-NbSe2,” D.E. Moncton, J.D. Axe, and F.J. DiSalvo, Phys. Rev. B 16,

801 (1977). 270 citations

Many one- and two-dimensional metallic systems are unstable towards charge-density-wave order at low temperatures. The study of such systems grew rapidly in the mid 1970’s.

Pioneering neutron scattering studies showed that the ordering often starts out with a modulation wave vector that is incommensurate with respect to the crystal lattice, locking into a commensurate wave vector at lower temperature. In the dielectric K2SeO4, the ordering developed through a soft-mode transition, as indicated at the right.

Shirane, Axe et al., BNL