M. v. Zimmermann

Deutsches Elektronen-Synchrotron, Hamburg, Hamburg, Germany

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Publications (162)392.92 Total impact

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    ABSTRACT: Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3O6.54 at its superconducting transition temperature ∼60 K. We find that the CDWs in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO2 planes, and are out of phase with each other. The planar oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For instance, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.
    Preview · Article · Dec 2015 · Nature Communications
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    ABSTRACT: The application of large magnetic fields ($B \sim B_{c2}$) to layered cuprates suppresses their high temperature superconducting behaviour and reveals competing ground states. In the widely-studied material YBa$_2$Cu$_3$O$_{6+x}$ (YBCO), underdoped ($p \sim 1/8$) samples show signatures of field-induced electronic and structural changes at low temperatures. However, the microscopic nature of the field-induced reconstruction and the high-field state are unclear. Here we report an x-ray study of the high-field charge density wave (CDW) in YBCO, for doping, $0.1 \lesssim p \lesssim 0.13$. For $p \sim 0.123$, we find that a field ($B \sim 10$~T) induces new CDW correlations along the CuO chain ($b$) direction only, leading to a 3-D ordered state along this direction at $B \sim 15$~T. The CDW signal along the $a$-direction is also enhanced by field, but does not develop a new pattern of correlations. We find that field modifies the coupling between the CuO$_2$ bilayers in the YBCO structure, and causes the sudden appearance of 3D CDW order. The mirror symmetry of individual bilayers is broken by the CDW at low and high fields, allowing recently suggested Fermi surface reconstruction.
    Preview · Article · Nov 2015
  • K. Dey · A. Karmakar · A. Indra · S. Majumdar · U. Rütt · O. Gutowski · M. v. Zimmermann · S. Giri
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    ABSTRACT: We report appearance of polar order with a ordering temperature (TC) at 28 K, which is well below the ferrimagnetic order at 225 K (TN) for CoCr2S4. Intriguingly, the value of spontaneous electric polarization (P) is ∼ 122 μC/m2 at 15 K, which is the second largest value in Cr octahedra-based spinels after CdCr2S4. Incidentally, the P value is ∼ 60 times larger than the value of P for the oxide counterpart CoCr2O4. The significant magnetoelectric coupling is verified from the magnetodielectric response and magnetic field dependent enhancement of P. We note that the field-dependent dielectric permittivity scales linearly to the squared magnetization in the low field regime below ∼ 10 kOe as described by the Ginzburg-Landau theory. Synchrotron diffraction studies over a wide temperature range, 15-300 K, illustrate strong magnetoelastic coupling at TN and isostructural distortion at TC. Analyses of the diffraction patterns reveal that the occurrence of polar order involves expansion of Co tetrahedra and contraction of Cr octahedra of the spinel structure and these distortions are further enhanced driven by the magnetic field. The delicate interplay between magnetoelastic, magnetoelectric, and electroelastic couplings in CoCr2S4 proposes the system as a potential candidate in multiferroics.
    No preview · Article · Jul 2015 · Physical Review B
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    ABSTRACT: Underdoped high-temperature cuprate superconductors now appear to ubiquitously exhibit charge density wave (CDW) order. For hole doping near $^1/_8$ per planar copper atom, the CDW order develops above the superconducting transition temperature, $T_c$, and competes with the superconductivity below $T_c$. Experiments show that the modulations of the CDW order are aligned with both CuO directions in the CuO$_2$ planes with a period of 3-5 lattice spacings. However, the microscopic symmetry breaking corresponding to the CDW order has remained unclear. Here we use X-ray diffraction to determine the ionic displacements associated with the CDW order in the archetypical material YBa$_2$Cu$_3$O$_{7-x}$ (YBCO). We find that major components of the CDW are shear displacements perpendicular to the CuO$_2$ planes. These remove the mirror symmetry of the CuO$_2$ bilayers and have important implications for understanding the signals from other probes of the CDW order. For example, our results for the copper and oxygen displacement patterns give an explicit explanation of how signals described as "$s$- and/or bond $d$-density waves" can appear in scanning tunnelling microscopy (STM) and soft X-ray measurements. The CDW symmetry that we discover has implications for Fermi surface reconstruction observed by quantum oscillation (QO) measurements. Finally, we measure the $a/b$ anisotropy of the CDWs and find that the amplitudes of the $a$ and $b$-axis components are of the same order.
    Preview · Article · Apr 2015
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    Full-text · Article · Mar 2015 · Nature Physics
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    ABSTRACT: Low-dimensional electron systems, as realized in layered materials, often tend to spontaneously break the symmetry of the underlying nuclear lattice by forming so-called density waves; a state of matter that at present attracts enormous attention. Here we reveal a remarkable and surprising feature of charge density waves, namely their intimate relation to orbital order. For the prototypical material 1T-TaS 2 we not only show that the charge density wave within the two-dimensional TaS 2 layers involves previously unidentified orbital textures of great complexity. We also demonstrate that two metastable stackings of the orbitally ordered layers allow manipulation of salient features of the electronic structure. Indeed, these orbital effects provide a route to switch 1T-TaS 2 nanostructures from metallic to semiconducting with technologically pertinent gaps of the order of 200 meV. This new type of orbitronics is especially relevant for the ongoing development of novel, miniaturized and ultrafast devices based on layered transition metal dichalcogenides.
    Full-text · Article · Mar 2015 · Nature Physics
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    Full-text · Article · Jan 2015 · Nature Physics
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    Full-text · Article · Jan 2015 · Nature Physics
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    ABSTRACT: Low-dimensional electron systems, as realized naturally in graphene or created artificially at the interfaces of heterostructures, exhibit a variety of fascinating quantum phenomena with great prospects for future applications. Once electrons are confined to low dimensions, they also tend to spontaneously break the symmetry of the underlying nuclear lattice by forming so-called density waves; a state of matter that currently attracts enormous attention because of its relation to various unconventional electronic properties. In this study we reveal a remarkable and surprising feature of charge density waves (CDWs), namely their intimate relation to orbital order. For the prototypical material 1T-TaS2 we not only show that the CDW within the two-dimensional TaS2-layers involves previously unidentified orbital textures of great complexity. We also demonstrate that two metastable stackings of the orbitally ordered layers allow to manipulate salient features of the electronic structure. Indeed, these orbital effects enable to switch the properties of 1T-TaS2 nanostructures from metallic to semiconducting with technologically pertinent gaps of the order of 200 meV. This new type of orbitronics is especially relevant for the ongoing development of novel, miniaturized and ultra-fast devices based on layered transition metal dichalcogenides.
    Full-text · Article · Sep 2014
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    ABSTRACT: To explore the doping dependence of the recently discovered charge density wave (CDW) order in YBa2Cu3Oy, we present a bulk-sensitive high-energy x-ray study for several oxygen concentrations, including strongly underdoped YBa2Cu3O6.44. Combined with previous data around the so-called 1/8 doping, we show that bulk CDW order exists at least for hole concentrations (p) in the CuO2 planes of 0.078 <~ p <~ 0.132. This implies that CDW order exists in close vicinity to the quantum critical point for spin density wave (SDW) order. In contrast to the pseudogap temperature T*, the onset temperature of CDW order decreases with underdoping to T_CDW ~ 90K in YBa2Cu3O6.44. Together with a weakened order parameter this suggests a competition between CDW and SDW orders. In addition, the CDW order in YBa2Cu3O6.44 shows the same type of competition with superconductivity as a function of temperature and magnetic field as samples closer to p = 1/8. At low p the CDW incommensurability continues the previously reported linear increasing trend with underdoping. In the entire doping range the in-plane correlation length of the CDW order in b-axis direction depends only very weakly on the hole concentration, and appears independent of the type and correlation length of the oxygen-chain order. The onset temperature of the CDW order is remarkably close to a temperature T^\dagger that marks the maximum of 1/(T_1T) in planar 63^Cu NQR/NMR experiments, potentially indicating a response of the spin dynamics to the formation of the CDW. Our discussion of these findings includes a detailed comparison to the charge stripe order in La2-xBaxCuO4.
    Preview · Article · May 2014 · Physical Review B
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    ABSTRACT: We present a volume-sensitive high-energy x-ray diffraction study of the underdoped cuprate high temperature superconductor La2-xSrxCuO4 (x = 0.12, Tc=27 K) in applied magnetic field. Bulk short-range charge stripe order with propagation vector q_ch = (0.231, 0, 0.5) is demonstrated to exist below T_ch = 85(10) K and shown to compete with superconductivity. We argue that bulk charge ordering arises from fluctuating stripes that become pinned near boundaries between orthorhombic twin domains.
    Preview · Article · Apr 2014
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    J.-C. Grivel · Y. Zhao · X. Tang · P.G.P.A. Pallewatta · A. Watenphul · M. v. Zimmermann
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    ABSTRACT: The thermal decomposition of yttrium(III) valerate (Y(C4H9CO2)3) was studied in argon by means of thermogravimetry, differential thermal analysis, IR-spectroscopy, X-ray diffraction, in-situ synchrotron diffraction and hot-stage microscopy as well as room temperature optical microscopy. Melting takes place around 90 °C and evidence was found for solidification of the melt at 260 °C–300 °C, i.e. close to the onset of decomposition. Between 300 °C and 450 °C, Y(C4H9CO2)3 decomposes in a single step into Y2O2CO3 with release of gaseous CO2 and C4H9COC4H9 (5-nonanone). Final conversion to Y2O3 takes pace with release of CO2. The carbonaceous residue, which is left as a by-product during this last decomposition step is finally slowly burned by the residual oxygen present in the Ar atmosphere between 700 °C and 900 °C.
    Full-text · Article · Mar 2014 · Journal of Analytical and Applied Pyrolysis
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    ABSTRACT: MgB2 bulk and wire samples were prepared using cheap, low grade amorphous boron powders. Based on chemical analysis performed on the starting reagents, three nominal stoichiometries were studied. It was found that the structural and superconducting properties of the bulk samples were not affected by the composition, but that residual Mg was left in the wires for the nominal MgB2 composition. In contrast, slightly Mg-deficient compositions were free from residual Mg and exhibited higher critical current densities. The MgB2 phase formation kinetics was not influenced by the variations in the nominal powder composition.
    Full-text · Article · Feb 2014 · Journal of Superconductivity and Novel Magnetism
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    ABSTRACT: We present a detailed 7Li- and 31P-NMR study on single crystalline LiMnPO4 in the paramagnetic and antiferromagnetic phase (AFM, TN∼34 K). This allows us to determine the spin directions in the field-induced spin-flop phase. In addition, the anisotropic dipolar hyperfine coupling tensor of the 7Li and 31P nuclei is also fully determined by orientation and temperature-dependent NMR experiments and compared to the calculated values from crystal structure data. Deviations of the experimental values from the theoretical ones are discussed in terms of Mn disorder which is induced by Li disorder. In fact, the disorder in the Mn sublattice is directly revealed by diffuse x-ray scattering data. The present results provide experimental evidence for the Li diffusion strongly coupling to structural distortions within the MnPO4 host, which is expected to significantly affect the Li mobility as well as the performance of batteries based on this material.
    Full-text · Article · Aug 2013 · Physical Review B
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    ABSTRACT: The thermal decomposition of La(C3H7CO2)3·xH2O (x ≈ 0.82) was studied in argon during heating at 5 K/min. After the loss of bound H2O, the anhydrous butyrate presents at 135 °C a phase transition to a mesophase, which turns to an isotropic liquid at 180 °C. The decomposition of the anhydrous butyrate is associated to a solidification process. The final decomposition to La2O3 takes place via two intermediate products: La2O(C3H7CO2)4 and La2O2CO3 with release of CO2 and the symmetrical ketone C3H7COC3H7.
    Full-text · Article · Aug 2013 · Thermochimica Acta
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    ABSTRACT: X-ray diffraction measurements show that the high-temperature superconductor YBa_{2}Cu_{3}O_{6.54}, with ortho-II oxygen order, has charge-density-wave order in the absence of an applied magnetic field. The dominant wave vector of the charge density wave is q_{CDW}=(0,0.328(2),0.5), with the in-plane component parallel to the b axis (chain direction). It has a similar incommensurability to that observed in ortho-VIII and ortho-III samples, which have different dopings and oxygen orderings. Our results for ortho-II contrast with recent high-field NMR measurements, which suggest a commensurate wave vector along the a axis. We discuss the relationship between spin and charge correlations in YBa_{2}Cu_{3}O_{y} and recent high-field quantum oscillation, NMR, and ultrasound experiments.
    No preview · Article · Mar 2013 · Physical Review Letters
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    Full-text · Article · Mar 2013 · Physical review. B, Condensed matter
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    ABSTRACT: We present a state-of-the-art x-ray diffraction study of the charge density wave order in 1T-TaS2 as a function of temperature and pressure. Our results prove that the charge density wave, which we characterize in terms of wave vector, amplitude and the coherence length, indeed exists in the superconducting region of the phase diagram. The data further imply that the ordered charge density wave structure as a whole becomes superconducting at low temperatures, i. e, superconductivity and charge density wave coexist on a macroscopic scale in real space. This result is fundamentally different from a previously proposed separation of superconducting and insulating regions in real space and, instead, provides evidence that the superconducting and the charge density wave gap exist in separate regions of reciprocal space.
    Full-text · Article · Feb 2013 · Physical review. B, Condensed matter
  • Hucker M. · M.v. Zimmermann · Z.J. Xu · J.S. Wen · G.D. Gu · J.M. Tranquada
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    ABSTRACT: The effect of a magnetic field on the charge stripe order in La2−xBaxCuO4 has been studied by means of high-energy (100 keV) x-ray diffraction for charge carrier concentrations ranging from strongly underdoped to optimally doped. We find that charge stripe order can be significantly enhanced by a magnetic field applied along the c axis, 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 a magnetic field. The results for La2−xBaxCuO4 resemble recent observations in YBa2Cu3O6+δ and, independent of potential differences in the microscopic origin of charge order in these two compounds, imply a very similar competition with three-dimensionally coherent superconductivity.
    No preview · Article · Jan 2013 · Physical Review B
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    ABSTRACT: The formation of the FeSe0.5Te0.5 phase was studied by means of high energy synchrotron x-ray diffraction. The precursors consisted of Fe, Se and Te or Se0.5Te0.5 powder mixtures and were encased in a metal (Cu/Nb) composite sheath to prevent evaporation of Se and Te during high temperature processing. In all cases (Fe - Se - Te ternary mixture; Fe - Se0.5Te0.5 binary mixtures with two different Fe particle sizes) the ternary alloy forms via Fe(Se,Te)(2) and Fe-3(Se,Te)(4) intermediate phases. When unreacted Se and Te powders are used in the precursor, partial Se1-xTex alloying takes place during heating prior and during the formation of the intermediate phases. As the alloying is incomplete, the resulting Fe(Se, Te) phase is not homogeneous. Using pre-alloyed Se0.5Te0.5 allows a better control of the reaction although homogeneisation also occurs in the Fe(Se, Te) phase as a consequence of the phase equilibria of the Se - Te system. The grain size of the starting Fe powder has no influence on the reaction path for the grain sizes used in the present study. However, the reaction rate for Fe(Se, Te) formation is clearly sensitive to this parameter. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of the Guest Editors.
    Full-text · Article · Dec 2012

Publication Stats

2k Citations
392.92 Total Impact Points

Institutions

  • 1995-2015
    • Deutsches Elektronen-Synchrotron
      • • Hamburger Synchrotronstrahlungslabor
      • • DESY Photon Science
      Hamburg, Hamburg, Germany
  • 2012
    • Technical University of Denmark
      • National Laboratory for Sustainable Energy
      Lyngby, Capital Region, Denmark
  • 1999-2003
    • Brookhaven National Laboratory
      • Physics Department
      New York City, NY, United States
  • 2001
    • Keio University
      • Department of Physics
      Edo, Tokyo, Japan