503 research outputs found
Sound Propagation in Nematic Fermi Liquid
We study the longitudinal sound propagation in the electronic nematic Fermi
liquid where the Fermi surface is distorted due to the spontaneously broken
rotational symmetry. The behavior of the sound wave in the nematic ordered
state is dramatically different from that in the isotropic Fermi liquid. The
collective modes associated with the fluctuations of the Fermi surface
distortion in the nematic Fermi liquid leads to the strong and anisotropic
damping of the sound wave. The relevance of the nematic Fermi liquid in doped
Mott insulator is discussed.Comment: 4 pages, no figur
GRB 190114C: from prompt to afterglow?
GRB 190114C is the first gamma-ray burst detected at Very High Energies (VHE,
i.e. >300 GeV) by the MAGIC Cherenkov telescope. The analysis of the emission
detected by the Fermi satellite at lower energies, in the 10 keV -- 100 GeV
energy range, up to ~ 50 seconds (i.e. before the MAGIC detection) can hold
valuable information. We analyze the spectral evolution of the emission of GRB
190114C as detected by the Fermi Gamma-Ray Burst Monitor (GBM) in the 10 keV --
40 MeV energy range up to ~60 sec. The first 4 s of the burst feature a typical
prompt emission spectrum, which can be fit by a smoothly broken power-law
function with typical parameters. Starting on ~4 s post-trigger, we find an
additional nonthermal component, which can be fit by a power law. This
component rises and decays quickly. The 10 keV -- 40 MeV flux of the power-law
component peaks at ~ 6 s; it reaches a value of 1.7e-5 erg cm-2 s-1. The time
of the peak coincides with the emission peak detected by the Large Area
Telescope (LAT) on board Fermi. The power-law spectral slope that we find in
the GBM data is remarkably similar to that of the LAT spectrum, and the GBM+LAT
spectral energy distribution seems to be consistent with a single component.
This suggests that the LAT emission and the power-law component that we find in
the GBM data belong to the same emission component, which we interpret as due
to the afterglow of the burst. The onset time allows us to estimate the initial
jet bulk Lorentz factor Gamma_0 is about 500, depending on the assumed
circum-burst density.Comment: 7 pages, 2 figures, in press, accepted for publication in A&
Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering
Nuclear inelastic scattering of synchrotron radiation has been used now since
10 years as a tool for vibrational spectroscopy. This method has turned out
especially useful in case of large molecules that contain a M\"ossbauer active
metal center. Recent applications to iron-sulfur proteins, to iron(II) spin
crossover complexes and to tin-DNA complexes are discussed. Special emphasis is
given to the combination of nuclear inelastic scattering and density functional
calculations
Cymantrene–Triazole "Click" Products: Structural Characterization and Electrochemical Properties
We report the first known examples of triazole-derivatized cymantrene complexes (η5-[4-substituted triazol-1-yl]cyclopentadienyl)tricarbonylmanganese(I), obtained via a “click” chemical synthesis, bearing a phenyl, 3-aminophenyl, or 4-aminophenyl moiety at the 4-position of the triazole ring. Structural characterization data using multinuclear NMR, UV–vis, ATR-IR, and mass spectrometric methods are provided, as well as crystallographic data for (η5-[4-phenyltriazol-1-yl]cyclopentadienyl)tricarbonylmanganese(I) and (η5-[4-(3-aminophenyl)triazol-1-yl]cyclopentadienyl)tricarbonylmanganese(I). Cyclic voltammetric characterization of the redox behavior of each of the three cymantrene–triazole complexes is presented together with digital simulations, in situ infrared spectroelectrochemistry, and DFT calculations to extract the associated kinetic and thermodynamic parameters. The trypanocidal activity of each cymantrene–triazole complex is also examined, and these complexes are found to be more active than cymantrene alone
Strongly coupled quantum criticality with a Fermi surface in two dimensions: fractionalization of spin and charge collective modes
We describe two dimensional models with a metallic Fermi surface which
display quantum phase transitions controlled by strongly interacting critical
field theories below their upper critical dimension. The primary examples
involve transitions with a topological order parameter associated with
dislocations in collinear spin density wave ("stripe") correlations: the
gapping of the order parameter fluctuations leads to a fractionalization of
spin and charge collective modes, and this transition has been proposed as a
candidate for the cuprates near optimal doping. The coupling between the order
parameter and long-wavelength volume and shape deformations of the Fermi
surface is analyzed by the renormalization group, and a runaway flow to a
non-perturbative regime is found in most cases. A phenomenological scaling
analysis of simple observable properties of possible second order quantum
critical points is presented, with results quite similar to those near quantum
spin glass transitions and to phenomenological forms proposed by Schroeder et
al. (cond-mat/0011002).Comment: 16 pages, 4 figures; (v2) additional clarifying remark
A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade
We provide a framework for analyzing the problem of interacting electrons in
a ballistic quantum dot with chaotic boundary conditions within an energy
(the Thouless energy) of the Fermi energy. Within this window we show that the
interactions can be characterized by Landau Fermi liquid parameters. When ,
the dimensionless conductance of the dot, is large, we find that the disordered
interacting problem can be solved in a saddle-point approximation which becomes
exact as (as in a large-N theory). The infinite theory shows a
transition to a strong-coupling phase characterized by the same order parameter
as in the Pomeranchuk transition in clean systems (a spontaneous
interaction-induced Fermi surface distortion), but smeared and pinned by
disorder. At finite , the two phases and critical point evolve into three
regimes in the plane -- weak- and strong-coupling regimes separated
by crossover lines from a quantum-critical regime controlled by the quantum
critical point. In the strong-coupling and quantum-critical regions, the
quasiparticle acquires a width of the same order as the level spacing
within a few 's of the Fermi energy due to coupling to collective
excitations. In the strong coupling regime if is odd, the dot will (if
isolated) cross over from the orthogonal to unitary ensemble for an
exponentially small external flux, or will (if strongly coupled to leads) break
time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we
are treating charge-channel instabilities in spinful systems, leaving
spin-channel instabilities for future work. No substantive results are
change
pi+ + d --> p + p reaction between 18 and 44 MeV
A study of the reaction pi+ + d --> p + p has been performed in the energy
range of 18 - 44 MeV. Total cross sections and differential cross sections at
six angles have been measured at 15 energies with an energy increment of 1 - 2
MeV. This is the most systematic data set in this energy range. No structure in
the energy dependence of the cross section has been observed within the
accuracy of this experiment.Comment: 20 pages, 7 Postscript figure
The renormalization group for interacting fermions: from Fermi liquids to quantum dots
The renormalization group approach as developed by the author for Fermi
liquids is applied to clean Fermi liquids and ballistic quantum dots. In the
former case Landau theory is shown to be a fixed point and in the latter the
Universal Hamiltonian is shown to be a fixed point for weak coupling. The
strong coupling phase is analyzed using large N and Random Matrix methods.Comment: Lectures given at the Fifteenth Chris Engelbrecht Summer School South
Africa, January 2004. 6 eps figs and springer style file (svmult
How to detect fluctuating order in the high-temperature superconductors
We discuss fluctuating order in a quantum disordered phase proximate to a
quantum critical point, with particular emphasis on fluctuating stripe order.
Optimal strategies for extracting information concerning such local order from
experiments are derived with emphasis on neutron scattering and scanning
tunneling microscopy. These ideas are tested by application to two model
systems - the exactly solvable one dimensional electron gas with an impurity,
and a weakly-interacting 2D electron gas. We extensively review experiments on
the cuprate high-temperature superconductors which can be analyzed using these
strategies. We adduce evidence that stripe correlations are widespread in the
cuprates. Finally, we compare and contrast the advantages of two limiting
perspectives on the high-temperature superconductor: weak coupling, in which
correlation effects are treated as a perturbation on an underlying metallic
(although renormalized) Fermi liquid state, and strong coupling, in which the
magnetism is associated with well defined localized spins, and stripes are
viewed as a form of micro-phase separation. We present quantitative indicators
that the latter view better accounts for the observed stripe phenomena in the
cuprates.Comment: 43 pages, 11 figures, submitted to RMP; extensively revised and
greatly improved text; one new figure, one new section, two new appendices
and more reference
Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor
Despite twenty years of research, the phase diagram of high transition-
temperature superconductors remains enigmatic. A central issue is the origin of
the differences in the physical properties of these copper oxides doped to
opposite sides of the superconducting region. In the overdoped regime, the
material behaves as a reasonably conventional metal, with a large Fermi
surface. The underdoped regime, however, is highly anomalous and appears to
have no coherent Fermi surface, but only disconnected "Fermi arcs". The
fundamental question, then, is whether underdoped copper oxides have a Fermi
surface, and if so, whether it is topologically different from that seen in the
overdoped regime. Here we report the observation of quantum oscillations in the
electrical resistance of the oxygen-ordered copper oxide YBa2Cu3O6.5,
establishing the existence of a well-defined Fermi surface in the ground state
of underdoped copper oxides, once superconductivity is suppressed by a magnetic
field. The low oscillation frequency reveals a Fermi surface made of small
pockets, in contrast to the large cylinder characteristic of the overdoped
regime. Two possible interpretations are discussed: either a small pocket is
part of the band structure specific to YBa2Cu3O6.5 or small pockets arise from
a topological change at a critical point in the phase diagram. Our
understanding of high-transition temperature (high-Tc) superconductors will
depend critically on which of these two interpretations proves to be correct
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