M. R. Norman

Paris Diderot University, Lutetia Parisorum, Île-de-France, France

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Publications (144)830.17 Total impact

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    ABSTRACT: Cuprates possess a large pseudogap that spans much of their phase diagram. The origin of this pseudogap is as debated as the mechanism for high-temperature superconductivity. In one class of theories, the pseudogap arises from some instability not related to pairing, typically charge, spin or orbital current ordering. Evidence of this has come from a variety of measurements indicating symmetry breaking. On the other side are theories where the pseudogap is associated with pairing. This ranges from preformed pairs to resonating valence bond theories where spin singlets become charge coherent. Here, we study pairing in the cuprates by constructing the pair vertex using spectral functions derived from angle-resolved photoemission data. Assuming that the pseudogap is not due to pairing, we find that the superconducting instability is strongly suppressed, in stark contrast to what is actually observed. We trace this suppression to the destruction of the BCS logarithmic singularity from a combination of the pseudogap and lifetime broadening. Our findings strongly support those theories of the cuprates where the pseudogap is instead due to pairing.
    04/2014; 10(5).
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    ABSTRACT: The energy gap for electronic excitations is one of the most important characteristics of the superconducting state, as it directly reflects the pairing of electrons. In the copper-oxide high-temperature superconductors (HTSCs), a strongly anisotropic energy gap, which vanishes along high-symmetry directions, is a clear manifestation of the d-wave symmetry of the pairing. There is, however, a dramatic change in the form of the gap anisotropy with reduced carrier concentration (underdoping). Although the vanishing of the gap along the diagonal to the square Cu-O bond directions is robust, the doping dependence of the large gap along the Cu-O directions suggests that its origin might be different from pairing. It is thus tempting to associate the large gap with a second-order parameter distinct from superconductivity. We use angle-resolved photoemission spectroscopy to show that the two-gap behavior and the destruction of well-defined electronic excitations are not universal features of HTSCs, and depend sensitively on how the underdoped materials are prepared. Depending on cation substitution, underdoped samples either show two-gap behavior or not. In contrast, many other characteristics of HTSCs, such as the dome-like dependence of Tc on doping, long-lived excitations along the diagonals to the Cu-O bonds, and an energy gap at the Brillouin zone boundary that decreases monotonically with doping while persisting above Tc (the pseudogap), are present in all samples, irrespective of whether they exhibit two-gap behavior or not. Our results imply that universal aspects of high-Tc superconductivity are relatively insensitive to differences in the electronic states along the Cu-O bond directions.
    Proceedings of the National Academy of Sciences 10/2013; · 9.81 Impact Factor
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    ABSTRACT: The mechanism of superconductivity is a long standing puzzle in the cuprates. Among various proposed models, pairing through the exchange of spin fluctuations is one of the leading candidates. Here we use spectral functions measured from angle resolved photoemission spectroscopy to calculate this pairing interaction within a random phase approximation, and then determine whether for a reasonable choice of the Hubbard parameter `U', we obtain a reasonable Tc.
    03/2013;
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    ABSTRACT: In order to understand the origin of high-temperature superconductivity in copper oxides, we must understand the normal state from which it emerges. Here, we examine the evolution of the normal state electronic excitations with temperature and carrier concentration in Bi2Sr2CaCu2O8 using angle-resolved photoemission. In contrast to conventional superconductors, where there is a single temperature scale Tc separating the normal from the superconducting state, the high- temperature superconductors exhibit two additional temperature scales. One is the pseudogap scale T*, below which electronic excitations exhibit an energy gap. The second is the coherence scale Tcoh, below which sharp spectral features appear due to increased lifetime of the excitations. We find that T* and Tcoh are strongly doping dependent and cross each other near optimal doping. Thus the highest superconducting Tc emerges from an unusual normal state that is characterized by coherent excitations with an energy gap.
    Proceedings of the National Academy of Sciences 02/2013; 108(23). · 9.81 Impact Factor
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    I Paul, C Pépin, M R Norman
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    ABSTRACT: Single band theories of quantum criticality successfully describe a single-particle lifetime with non-Fermi liquid temperature dependence, but they fail to obtain a charge transport rate with the same dependence unless the interaction is assumed to be momentum independent. Here we demonstrate that a quantum critical material, with a long-range mode that transmutes electrons between light and heavy bands, exhibits a quasilinear temperature dependence for both the single-particle and the charge transport lifetimes, despite the strong momentum dependence of the interaction.
    Physical Review Letters 02/2013; 110(6):066402. · 7.73 Impact Factor
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    T. Micklitz, A. Levchenko, M. R. Norman
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    ABSTRACT: Motivated by a recent experiment by Bergeal et al., we reconsider incoherent pair tunneling in a cuprate junction formed from an optimally doped superconducting lead and an underdoped normal metallic lead. We study the impact of the pseudogap on the pair tunneling by describing fermions in the underdoped lead with a model self-energy that has been developed to reproduce photoemission data. We find that the pseudogap causes an additional temperature dependent suppression of the pair contribution to the tunneling current. We discuss consistency with available experimental data and propose future experimental directions.
    Physical review. B, Condensed matter 11/2012; 87(2). · 3.66 Impact Factor
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    ABSTRACT: The doping dependence of the low-temperature spectral function is precisely determined from angle resolved photoemision (ARPES) measurements. It is found that, as the doping decreases, the maximum of the superconducting gap increases, but the slope of the gap near the nodes decreases. Though consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple cos(kx)-cos(ky) form. We suggest that this arises due to the increasing importance of long range interactions as one approaches the insulator. It is also shown that the shape of the spectral function at the (π, 0) point below Tc can be explained by the interaction of the electrons with a collective mode whose energy matches that of the magnetic resonance as obtained by inelastic neutron scattering data, and points to the intimate relation of magnetic correlatins to high Tc superconductivity.
    International Journal of Modern Physics B 01/2012; 14(29n31). · 0.46 Impact Factor
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    ABSTRACT: We report inelastic neutron scattering measurements of the resonant spin excitations in Ba(1-x)K(x)Fe(2)As(2) over a broad range of electron band filling. The fall in the superconducting transition temperature with hole doping coincides with the magnetic excitations splitting into two incommensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s(±)-symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight, caused by the weakening of electron-electron correlations.
    Physical Review Letters 10/2011; 107(17):177003. · 7.73 Impact Factor
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    ABSTRACT: We report inelastic neutron scattering measurements of the resonant spin excitations in Ba1-xKxFe2As2 over a broad range of electron band filling. The fall in the superconducting transi- tion temperature with hole doping coincides with the magnetic excitations splitting into two incom- mensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s+- symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight caused by the weakening of electron-electron correlations.
    Physical Review Letters 06/2011; 107. · 7.73 Impact Factor
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    Michael R Norman
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    ABSTRACT: During the past few decades, several new classes of superconductors have been discovered that do not appear to be related to traditional superconductors. The source of the superconductivity of these materials is likely different from the electron-ion interactions that are at the heart of conventional superconductivity. Developing a rigorous theory for any of these classes of materials has proven to be a difficult challenge and will remain one of the major problems in physics in the decades to come.
    Science 04/2011; 332(6026):196-200. · 31.20 Impact Factor
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    C Pépin, M R Norman, S Burdin, A Ferraz
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    ABSTRACT: We argue that near a Kondo breakdown critical point, a spin liquid with spatial modulations can form. Unlike its uniform counterpart, we find that this occurs via a second order phase transition. The amount of entropy quenched when ordering is of the same magnitude as for an antiferromagnet. Moreover, the two states are competitive, and at low temperatures are separated by a first order phase transition. The modulated spin liquid we find breaks Z4 symmetry, as recently seen in the hidden order phase of URu2Si2. Based on this, we suggest that the modulated spin liquid is a viable candidate for this unique phase of matter.
    Physical Review Letters 03/2011; 106(10):106601. · 7.73 Impact Factor
  • Stephen R. Julian, Michael R. Norman
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    ABSTRACT: Every metal has a Fermi surface, which gives rise to quantum oscillations in a magnetic field. But the nature of the Fermi surface in cuprate superconductors is a profound mystery that scientists are only starting to unravel.
    Nature Physics 03/2011; 7(3):191-192. · 19.35 Impact Factor
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    Ashot Melikyan, M. R. Norman
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    ABSTRACT: We derive and analyze an effective Ginzburg-Landau (GL) functional for a charge density wave (CDW) for a model of electrons on a tight binding square lattice with density-density interactions. We show, using realistic electronic dispersions for the cuprates, that for the simplest GL theory, the preferred symmetry is of the uni-directional (stripe) type, but upon inclusion of third-order terms, the CDW may exhibit a transition from a uni-directional to a checkerboard pattern depending on the strength and range of the interaction.
    02/2011;
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    Alex Levchenko, M. R. Norman
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    ABSTRACT: We develop a theory of the rectification effect in a double-layer system where both layers are superconductors, or one of the layers is a normal metal. The Coulomb interaction is assumed to provide the dominant coupling between the layers. We find that superconducting fluctuations strongly enhance the drag conductivity, with rectification most pronounced when both layers are superconductors. In view of their distinct dependence on temperature near Tc and layer separation, drag measurements based on a Giaever transformer could distinguish whether rectification occurs due to fluctuating pairs or inductively coupled fluctuating vortices.
    01/2011;
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    ABSTRACT: The observation of a large Nernst signal in cuprates above the superconducting transition temperature has attracted much attention. A potential explanation is that it originates from superconducting fluctuations. Although the Nernst signal is indeed consistent with Gaussian fluctuations for overdoped cuprates, Gaussian theory fails to describe the temperature dependence seen for underdoped cuprates. Here, we consider the vertex correction to Gaussian theory resulting from the pseudogap. This yields a Nernst signal in good agreement with the data.
    Physical review. B, Condensed matter 01/2011; 83. · 3.66 Impact Factor
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    ABSTRACT: We present an angle-resolved photoelectron spectroscopy study of YBa2Cu3O7-δ films in situ grown by pulsed laser deposition. We have successfully produced underdoped surfaces with ordered oxygen vacancies within the CuO chains resulting in a clear ortho-II band folding of the Fermi surface. This indicates that order within the CuO chains affects the electronic properties of the CuO2 planes. Our results highlight the importance of having not only the correct surface carrier concentration, but also a very well ordered and clean surface in order that photoemission data on this compound be representative of the bulk.
    Physical review. B, Condensed matter 01/2011; 83(14). · 3.66 Impact Factor
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    M. R. Norman
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    ABSTRACT: A brief overview is given of the problem of high temperature superconductivity in the cuprates, with emphasis on theoretical ideas.
    Journal of Superconductivity and Novel Magnetism 01/2011; 25(7). · 0.93 Impact Factor
  • Alex Levchenko, M. R. Norman
    [Show abstract] [Hide abstract]
    ABSTRACT: We develop a theory of the rectification effect in a double-layer system where both layers are superconductors or one of the layers is a normal metal. The Coulomb interaction is assumed to provide the dominant coupling between the layers. We find that superconducting fluctuations strongly enhance the drag conductivity, with rectification most pronounced when both layers are superconductors. In view of their distinct dependence on temperature near Tc and layer separation, drag measurements based on a Giaever transformer could distinguish whether rectification occurs due to fluctuating pairs or inductively coupled fluctuating vortices.
    Physical review. B, Condensed matter 01/2011; 83(10). · 3.66 Impact Factor
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    ABSTRACT: A Comment on the Letter by V. Arpiainen, A. Bansil, and M. Lindroos, Phys Rev. Lett. 103, 067005 (2009). The authors of the Letter offer a Reply.
    Physical Review Letters 10/2010; 105(18):189701; author reply 189702. · 7.73 Impact Factor
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    A. Levchenko, M. R. Norman, A. A. Varlamov
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    ABSTRACT: The observation of a large Nernst signal in cuprates above the superconducting transition temperature has attracted much attention. A potential explanation is that it originates from superconducting fluctuations. Although the Nernst signal is indeed consistent with gaussian fluctuations for overdoped cuprates, gaussian theory fails to describe the temperature dependence seen for underdoped cuprates. Here, we consider the vertex correction to gaussian theory resulting from the pseudogap. This yields a Nernst signal in good agreement with the data.
    09/2010;

Publication Stats

5k Citations
830.17 Total Impact Points

Institutions

  • 2013
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
  • 2000–2013
    • University of Illinois at Chicago
      • Department of Physics
      Chicago, IL, United States
  • 1997–2011
    • Argonne National Laboratory
      • Division of Materials Science
      Lemont, Illinois, United States
  • 2006
    • Iowa State University
      • Department of Physics and Astronomy
      Ames, IA, United States
  • 2005
    • Freie Universität Berlin
      • Institute of Theoretical Physics
      Berlin, Land Berlin, Germany
    • University of Wisconsin, Madison
      • Department of Physics
      Madison, MS, United States
  • 2003
    • Karlsruhe Institute of Technology
      • Institute for Theoretical Solid State Physics
      Karlsruhe, Baden-Wuerttemberg, Germany
  • 2002
    • Los Alamos National Laboratory
      Los Alamos, California, United States
  • 1995
    • Tsukuba Research Institute
      Edo, Tōkyō, Japan