Robert J. Birgeneau

Bio: Robert J. Birgeneau is an academic researcher from Lawrence Berkeley National Laboratory. The author has contributed to research in topics: Neutron scattering & Phase transition. The author has an hindex of 78, co-authored 587 publications receiving 22686 citations. Previous affiliations of Robert J. Birgeneau include Chalk River Laboratories & Tohoku University.

Doping dependence of the spatially modulated dynamical spin correlations and the superconducting-transition temperature in La 2-x Sr x CuO 4

Abstract: Systematic low-energy neutron-scattering studies have been performed on float-zone-grown single crystals of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ with $x$ extending from zero doping, $x=0$, to the overdoped, weakly superconducting regime, $x=025$ For $x$ beyond a critical doping value of ${x}_{c}\ensuremath{\approx}005$ the low-energy spin-fluctuation peak position shifts from ($\frac{1}{2}$, $\frac{1}{2}$) to ($\frac{1}{2}$\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}, $\frac{1}{2}$), and ($\frac{1}{2}$, $\frac{1}{2}$\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}); ${x}_{c}$ also represents the onset concentration for superconductivity For $006l~xl~012$ the incommensurability $\ensuremath{\delta}$ follows approximately the quantitative relation $\ensuremath{\delta}=x$ However, beyond $x\ensuremath{\approx}012$ the incommensurability tends to saturate around $\ensuremath{\delta}\ensuremath{\approx}1/8$ The superconducting-transition temperature ${T}_{c}(x)$ for stoichiometric samples at a given doping scales linearly with $\ensuremath{\delta}$ up to the optimal doping value of $x$ The peak momentum width of the spin fluctuations at low energies is small throughout the superconducting concentration region except in the strongly overdoped region An anomalously small width is observed for $x=\frac{1}{8}$ The incommensurate spatial modulation is found to be robust with respect to pair-breaking effects that lower ${T}_{c},$ such as deoxygenation of the sample or replacement of Cu by Zn

Magnetic, transport, and optical properties of monolayer copper oxides

Abstract: The authors review the results of a wide variety of experiments on materials such as ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ and ${\mathrm{Nd}}_{2}{\mathrm{CuO}}_{4}$ that contain weakly coupled ${\mathrm{CuO}}_{2}$ layers. These materials are antiferromagnetic insulators with very large Heisenberg exchange energies, which become high-temperature superconductors when charge carriers are added to the ${\mathrm{CuO}}_{2}$ layers. The growth of large single crystals has made it possible to carry out neutron scattering, as well as anisotropic optical, transport, and magnetization measurements. The properties of the undoped ${\mathrm{CuO}}_{2}$ layer are reviewed, and the evolution of magnetic, optical, and transport properties with the addition of charge carriers is discussed. The emphasis is on the pure and lightly doped materials, although the magnetism in the superconductors is discussed.

Two-dimensional antiferromagnetic quantum spin-fluid state in La2CuO

Abstract: Elastic, quasielastic, and inelastic neutron scattering measurements in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ reveal novel two-dimensional antiferromagnetic behavior. At high temperatures the spins are ordered instantaneously over long distances two dimensionally but there is no measurable time-averaged staggered moment. The energy scale of the spin fluctuations is large, corresponding to an effective dispersion of \ensuremath{\gtrsim}0.4 eV A\r{}. The relevance to the high-temperature superconductivity in this class of materials is noted.

Magnetic phase diagram and magnetic pairing in doped La2CuO

Abstract: We discuss the temperature-concentration phase diagram of doped ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. The addition of holes introduces a local ferromagnetic exchange coupling between Cu spins. The resulting frustration destroys the 3D N\'eel state characterizing pure ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, and generates a new 3D spin-glass phase. In the paramagnetic phase, strongly correlated Cu spins in the planes are canted by the holes, yielding an oscillating dipole-dipole attraction between holes. The possible relevance to superconductivity is discussed.

Magnetic excitations in pure, lightly doped, and weakly metallic La2CuO4.

Abstract: We report a comprehensive neutron-scattering study of the evolution of the magnetic excitations in La[sub 2[minus][ital x]]Sr[sub [ital x]]CuO[sub 4] for 0[le][ital x][le]0.04. We first present accurate measurements of the magnetic correlation length and the sublattice magnetization of a carrier-free La[sub 2]CuO[sub 4] crystal and analyze these in the context of recent theoretical predictions. We then systematically investigate the influence of different dopants on the magnetism: Our measurements indicate that static vacancies in the La[sub 2]Cu[sub 1[minus][ital y]]Zn[sub [ital y]]O[sub 4] system affect the magnetic correlations in a similar manner as electrons in Pr[sub 2[minus][ital x]]Ce[sub [ital x]]CuO[sub 4]. The magnetic correlation length is much more rapidly suppressed as a function of [ital x] in La[sub 2[minus][ital x]]Sr[sub [ital x]]CuO[sub 4], and for [ital x][le]0.04 we find that it obeys the empirical relation [xi][sup [minus]1]([ital x],[ital T])=[xi][sup [minus]1]([ital x],0)+[xi][sup [minus]1](0,[ital T]), where [xi](0,[ital T]) is the measured correlation length of the carrier-free sample. We also report an extensive set of measurements of the dynamical magnetic response function of a crystal of composition La[sub 1.96]Sr[sub 0.04]CuO[sub 4] for excitation energies 0.75[le][omega][le]45 meV and temperatures 1.5[le][ital T][le]500 K.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The Fractal Geometry of Nature

Abstract: "...a blend of erudition (fascinating and sometimes obscure historical minutiae abound), popularization (mathematical rigor is relegated to appendices) and exposition (the reader need have little knowledge of the fields involved) ...and the illustrations include many superb examples of computer graphics that are works of art in their own right." Nature

Phase Transitions and Critical Phenomena

Abstract: The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. It has moved into a central place in condensed matter studies. Statistical physics, and more specifically, the theory of transitions between states of matter, more or less defines what we know about 'everyday' matter and its transformations. The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable information on important recent developments.