M. R. Norman

Argonne National Laboratory, Lemont, Illinois, United States

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Publications (185)1032.17 Total impact

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    ABSTRACT: The loss of single-particle coherence going from the superconducting state to the normal state in underdoped cuprates is a dramatic effect that has yet to be understood. Here, we address this issue by performing angle resolved photoemission spectroscopy (ARPES) measurements in the presence of a transport current. We find that the loss of coherence is associated with the development of an onset in the resistance, in that well before the midpoint of the transition is reached, the sharp peaks in the ARPES spectra are completely suppressed. Since the resistance onset is a signature of phase fluctuations, this implies that the loss of single-particle coherence is connected with the loss of long-range phase coherence.
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    ABSTRACT: Understanding the underlying mechanism and phenomenology of colossal magnetoresistance in manganites has largely focused on atomic and nanoscale physics such as double exchange, phase separation, and charge order. Here we consider a more macroscopic view of manganite materials physics, reporting on the ferromagnetic domain behavior in a bilayer manganite sample with a nominal composition of La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ with $x=0.38$, studied using in-situ Lorentz transmission electron microscopy. The role of magnetocrystalline anisotropy on the structure of domain walls was elucidated. On cooling, magnetic domain contrast was seen to appear first at the Curie temperature within the $a-b$ plane. With further reduction in temperature, the change in area fraction of magnetic domains was used to estimate the critical exponent describing the ferromagntic phase transition. The ferromagnetic phase transition was accompanied by a distinctive nanoscale granular contrast close to the Curie temperature, which we infer to be related to the presence of ferromagnetic nanoclusters in a paramagnetic matrix, which has not yet been reported in bilayer manganites.
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    ABSTRACT: A charge-density wave (CDW) state has a broken symmetry described by a complex order parameter with an amplitude and a phase. The conventional view, based on clean, weak-coupling systems, is that a finite amplitude and long-range phase coherence set in simultaneously at the CDW transition temperature Tcdw. Here we investigate, using photoemission, X-ray scattering and scanning tunnelling microscopy, the canonical CDW compound 2H-NbSe2 intercalated with Mn and Co, and show that the conventional view is untenable. We find that, either at high temperature or at large intercalation, CDW order becomes short-ranged with a well-defined amplitude, which has impacts on the electronic dispersion, giving rise to an energy gap. The phase transition at Tcdw marks the onset of long-range order with global phase coherence, leading to sharp electronic excitations. Our observations emphasize the importance of phase fluctuations in strongly coupled CDW systems and provide insights into the significance of phase incoherence in 'pseudogap' states.
    Nature Communications 02/2015; 6:6313. DOI:10.1038/ncomms7313 · 11.47 Impact Factor
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    Vivek Mishra · M. R. Norman ·
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    ABSTRACT: Charge order has emerged as a generic feature of doped cuprates, leading to important questions about its origin and its relation to superconductivity. Recent experiments on two classes of hole doped cuprates indicate a novel d-wave symmetry for the order. These were motivated by earlier spin fluctuation theoretical studies based on an expansion about hot spots in the Brillouin zone that indicated such order would be competitive with d-wave superconductivity. Here, we reexamine this problem by solving strong coupling equations in the full Brillouin zone. Our results find that bond-oriented order, as seen experimentally, is strongly suppressed, indicating that the charge order must have a different origin.
    Physical Review B 02/2015; 92(6). DOI:10.1103/PhysRevB.92.060507 · 3.74 Impact Factor
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    Vivek Mishra · U. Chatterjee · J. C. Campuzano · M. R. Norman ·
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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.
    Nature Physics 04/2014; 10(5). DOI:10.1038/nphys2926 · 20.15 Impact Factor
  • Michael R. Norman · Cyril Proust ·
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    ABSTRACT: Almost three decades after the discovery of high temperature cuprate superconductors, the origin of their high critical temperature remains an enigma. But it is now possible to discuss the ‘fermiology’ of the cuprates thanks to the discovery of quantum oscillations, which give valuable information about the Fermi surface and therefore the physical properties of a metal. The aim of this ‘focus on’ collection is to bring together experimentalists and theorists in order to provide new insights into the Fermi surface of cuprate superconductors. This new direction of research has definitely stimulated further progress in the field of high temperature superconductivity.
    New Journal of Physics 03/2014; 16(4). DOI:10.1088/1367-2630/16/4/045004 · 3.56 Impact Factor
  • Michael R. Norman ·
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    ABSTRACT: Small Fermi surfaces have been observed by quantum oscillations in the YBCO family of copper oxide superconductors, but until now it has been unclear whether they are specific to YBCO or universal to all underdoped cuprates.
    Nature Physics 12/2013; 9(12):757-758. DOI:10.1038/nphys2822 · 20.15 Impact Factor
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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; 110(44). DOI:10.1073/pnas.1302932110 · 9.67 Impact Factor
  • Vivek Mishra · U. Chatterjee · J. C. Campuzano · M. R. Norman ·
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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.
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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). DOI:10.1073/pnas.1101008108 · 9.67 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 quasi-linear temperature dependence for {\it 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. DOI:10.1103/PhysRevLett.110.066402 · 7.51 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). DOI:10.1103/PhysRevB.87.024503 · 3.66 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. DOI:10.1103/Physrevlett.107.177003 · 7.51 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. Most of these do not appear to be related to traditional superconductors. As a consequence, it is felt by many that for these materials, superconductivity arises from a different source than 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 continue to be one of the major problems in physics in the decades to come.
    Science 04/2011; 332(6026):196-200. DOI:10.1126/science.1200181 · 33.61 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 04/2011; 83(14). DOI:10.1103/PhysRevB.83.140511 · 3.66 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. DOI:10.1038/nphys1930 · 20.15 Impact Factor
  • 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.
    Physical review. B, Condensed matter 03/2011; 83(10). DOI:10.1103/PhysRevB.83.100506 · 3.66 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. DOI:10.1103/PhysRevLett.106.106601 · 7.51 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.
    Physical Review B 02/2011; 89(2). DOI:10.1103/PhysRevB.89.024507 · 3.74 Impact Factor
  • Alex Levchenko · M. R. Norman · A. A. Varlamov · SPIN-CNR ·
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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(2). DOI:10.1103/PhysRevB.83.020506 · 3.66 Impact Factor

Publication Stats

8k Citations
1,032.17 Total Impact Points


  • 1991-2015
    • Argonne National Laboratory
      • Division of Materials Science
      Lemont, Illinois, United States
  • 2011
    • University of Duisburg-Essen
      Essen, North Rhine-Westphalia, Germany
  • 2006-2010
    • The Ohio State University
      • Department of Physics
      Columbus, Ohio, United States
  • 2005
    • University of Wisconsin, Madison
      • Department of Physics
      Madison, MS, United States
  • 1999-2003
    • University of Illinois at Chicago
      • Department of Physics
      Chicago, IL, United States
  • 1996-1999
    • Tata Institute of Fundamental Research
      Mumbai, Maharashtra, India
  • 1995
    • Tohoku University
      Miyagi, Japan