Search Results - (Author, Cooperation:M. R. Norman)

2018-05-23

National Academy of Sciences

0027-8424

1091-6490

Biology

Medicine

Natural Sciences in General

2018-08-22

American Physical Society (APS)

1098-0121

1095-3795

Physics

Magnetism

2011-04-09

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2015-02-13

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

One of the most controversial topics in condensed matter physics concerns the nature of the electronic structure of transition metal oxides. Unpolarized band structure calculations predict metallic ground states for these oxides, whereas experimentally they are insulating. This led to the development of the Mott insulator picture for these materials fifty years ago. Later, though, Slater's group showed that by taking into account spin polarization, one could produce insulating gaps from band theory for MnO and NiO. The gaps are too small, the size of the gap actually being determined by the Mott-Hubbard U, but this led to a hope that on symmetry grounds one could also obtain gaps for the other two metal oxides, FeO and CoO. In these two cases, there is an unquenched orbital moment, which might be important for this purpose. Recently, a theory has been developed by Erickson, Brooks, and Johansson for including an orbital polarization correction to local spin density theory.1 The author in turn showed that such a correction can lead to insulating gaps for CoO and FeO.2 A discussion of these results, including the calculated sizes of the moments, as well as related work on insulating mixed valent TmSe, will be presented in this paper.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The Eliashberg equations for magnetic fluctuations are solved for heavy fermion superconductors. The susceptibility is taken from neutron data, and the Fermi surface from band calculations. For the case of UPt3, mass renormalizations of about 16 are found consistent with de Haas–van Alphen data. A superconducting transition temperature of the order of 0.12 K is calculated, due to the momentum dependence of the susceptibility, with the gap function having lines of zeros in parts of the zone. The transition temperature can be boosted up to experimental values by crude incorporation of interband matrix elements. Extensions of these calculations to other heavy fermion superconductors will be reported.

Electronic Resource

1365-2036

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Background : Steroid resistance represents a major clinical problem in the treatment of ulcerative colitis. In vitro, interleukin-2 renders lymphocytes steroid resistant.Aim : To explore the therapeutic potential of interleukin-2 receptor blockade in steroid-resistant ulcerative colitis with both in vitro measures and a pilot in vivo study.Methods : Ten patients with steroid-resistant ulcerative colitis received a single bolus of 40 mg of intravenous basiliximab plus steroid treatment in an open-label, uncontrolled, 24-week study. The outcome was assessed using the Ulcerative Colitis Symptom Score, rectal biopsy and Inflammatory Bowel Disease Questionnaire. Lymphocyte steroid sensitivity was measured in vitro in 39 subjects in the presence or absence of basiliximab.Results : Nine of the 10 patients achieved clinical remission within 8 weeks. At 24 weeks, seven patients were in clinical remission. Marked improvement in the Ulcerative Colitis Symptom Score was seen by 1 week (P = 0.004) and on rectal biopsy and Inflammatory Bowel Disease Questionnaire by 2 weeks (both P 〈 0.05). Improvements persisted to 24 weeks (Ulcerative Colitis Symptom Score, Inflammatory Bowel Disease Questionnaire, both P 〈 0.005). Eight of the nine responders relapsed (median, 9 weeks), but remission was re-achieved with further corticosteroids and the addition of azathioprine. At 24 weeks, seven patients were in full clinical remission, five off all steroid therapy. In vitro measurement of lymphocyte steroid sensitivity demonstrated steroid resistance in 22% of subjects. All were rendered steroid sensitive in the presence of basiliximab.Conclusions : Basiliximab appears to be effective at inducing remission in steroid-resistant ulcerative colitis. In vitro, basiliximab also produced a dramatic increase in lymphocyte steroid sensitivity in healthy subjects. Confirmation in randomized controlled studies is required.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] In ARPES, photons incident upon a sample cause electrons to be ejected, whose energies and momenta are measured. From this one obtains the electronic excitation spectrum of the sample. Our experiments were carried out at the Synchrotron Radiation Center, Wisconsin, following procedures described ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The Fermi surface—the set of points in momentum space describing gapless electronic excitations—is a central concept in the theory of metals. In this context, the normal ‘metallic’ state of the optimally doped high-temperature superconductors is not very unusual: above ...

Electronic Resource

1573-7357

Springer Online Journal Archives 1860-2000

Physics

Abstract We use the gradient of the energy-integrated angle resolved photoemission (ARPES) intensity in order to define precisely the Fermi surface (FS) in BSCCO superconductors. We show that, independent of the photon energy, the FS is a hole barrel centered at (π, π). Then, the superconducting gap along the FS is precisely determined from ARPES measurements on overdoped and underdoped samples of Bi2212. As the doping decreases, the maximum 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(k x) − cos(k y) form. A comparison of our ARPES results with available penetration depth data indicates that the renormalization of the linear T suppression of the superfluid density at low temperatures due to quasiparticle excitations around the d-wave nodes is large and doping dependent.

Electronic Resource

1572-9605

Spin dynamics ; d-Wave pairing ; Eliashberg theory ; high-temperature superconductors ; impurities

Springer Online Journal Archives 1860-2000

Electrical Engineering, Measurement and Control Technology

Physics

Abstract We review the spin dynamics of the normal state of the cuprates with special emphasis on neutron data in both the YBa2Cu3O7−δ and La2−x Sr x CuO4 systems. When realistic models of the Fermi surface shapes are incorporated, along with a moderate degree of spin fluctuations, we find good semiquantitative agreement with experiment for both cuprates. Building on the success of this Fermi-liquid-based scheme, we explore the implications ford-wave pairing from a number of vantage points. We conclude that our present experimental and theoretical understanding is inadequate to confirm or refute thed-wave scenario.

Electronic Resource

0020-7608

Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

An orbital polarization (Hund's second rule) correction to local spin density (LSD) theory is developed in both a spherical harmonic basis and in a crystal field basis, and applied to the electronic band structure of FeO, CoO, NiO, and La2CuO4, resulting in a substantial enhancement of the LSD insulating band gap for NiO, and the creation of insulating band gaps for FeO, CoO, and La2CuO4.

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Electronic Resource