139 research outputs found
Phenomenological model for charge dynamics and optical response of disordered systems: application to organic semiconductors
We provide a phenomenological formula which describes the low-frequency
optical absorption of charge carriers in disordered systems with localization.
This allows to extract, from experimental data on the optical conductivity, the
relevant microscopic parameters determining the transport properties, such as
the carrier localization length and the elastic and inelastic scattering times.
This general formula is tested and applied here to organic semiconductors,
where dynamical molecular disorder is known to play a key role in the transport
properties. The present treatment captures the basic ideas underlying the
recently proposed transient localization scenario for charge transport,
extending it from the d.c. mobility to the frequency domain. When applied to
existing optical measurements in rubrene FETs, our analysis provides
quantitative evidence for the transient localization phenomenon. Possible
applications to other disordered electronic systems are briefly discussed.Comment: extended version with optical conductivity formulas for both
non-degenerate and degenerate electron system
Avoiding Stripe Order: Emergence of the Supercooled Electron Liquid
In the absence of disorder, electrons can display glassy behavior through
supercooling the liquid state, avoiding the solidification into a charge
ordered state. Such supercooled electron liquids are experimentally found in
organic - compounds. We present theoretical results that
qualitatively capture the experimental findings. At intermediate temperatures,
the conducting state crosses over into a weakly insulating pseudogap phase. The
stripe order phase transition is first order, so that the liquid phase is
metastable below . In the supercooled liquid phase the resistivity
increases further and the density of states at the Fermi level is suppressed,
indicating kinetic arrest and the formation of a glassy state. Our results are
obtained using classical Extended Dynamical Mean Field Theory.Comment: 4 pages, 4 figures, submitted to the proceedings of "Superstripes
2015", Journal of Superconductivity and Novel Magnetism (2015
Strange metal behavior from incoherent carriers scattered by local moments
We study metallic transport in an effective model that describes the coupling
of electrons to fluctuating magnetic moments with full SU(2) symmetry,
exhibiting characteristic behavior of metals at the approach of the Mott
transition. We show that scattering by fluctuating local moments causes a fully
incoherent regime of electron transport with linear T-dependent resistivities.
This strange metal regime is characterized by almost universal, "Planckian"
slope and a finite intercept at , that we can associate respectively to
the fluctuations in orientation and amplitude of the local moments. Our results
indicate a route for understanding the microscopic origin of strange metal
behavior that is unrelated to quantum criticality and does not rely on the
existence of quasiparticles.Comment: 5 pages, 3 figure
Glassy dynamics in geometrically frustrated Coulomb liquids without disorder
We show that introducing long-range Coulomb interactions immediately lifts
the massive ground state degeneracy induced by geometric frustration for
electrons on quarter-filled triangular lattices in the classical limit.
Important consequences include the stabilization of a stripe-ordered
crystalline (global) ground state, but also the emergence of very many
low-lying metastable states with amorphous "stripe-glass" spatial structures.
Melting of the stripe order thus leads to a frustrated Coulomb liquid at
intermediate temperatures, showing remarkably slow (viscous) dynamics, with
very long relaxation times growing in Arrhenius fashion upon cooling, as
typical of strong glass formers. On shorter time scales, the system falls out
of equilibrium and displays the aging phenomena characteristic of supercooled
liquids above the glass transition. Our results show remarkable similarity with
the recent observations of charge-glass behavior in ultra-clean triangular
organic materials of the -(BEDT-TTF) family.Comment: 5 pages,4 figure
Impact of quantized vibrations on the efficiency of interfacial charge separation in photovoltaic devices
We demonstrate that charge separation at donor-acceptor interfaces is a
complex process that is controlled by the combined action of Coulomb binding
for electron-hole pairs and partial relaxation due to quantized phonons. A
joint electron-vibration quantum dynamical study reveals that high energy
vibrations sensitively tune the charge transfer probability as a function of
time and injection energy, due to polaron formation. These results have
bearings for the optimization of energy transfer both in organic and quantum
dot photovoltaics, as well as in biological light harvesting complexes.Comment: 5 pages, 3 figures. v2 contains additional discussion of experiments,
and extra physical motivatio
Pinball liquid phase from Hund's coupling in frustrated transition metal oxides
The interplay of non-local Coulomb repulsion and Hund's coupling in the
d-orbital manifold in frustrated triangular lattices is analyzed by a mutliband
extended Hubbard model. We find a rich phase diagram with several competing
phases, including a robust pinball liquid phase, which is an unconventional
metal characterized by threefold charge order, bad metallic behavior and the
emergence of high spin local moments. Our results naturally explain the
anomalous charge-ordered metallic state observed in the triangular layered
compound AgNiO2. The potential relevance to other triangular transition metal
oxides is discussed.Comment: 4 pages, 4 figure
Emergent heavy fermion behavior at the Wigner-Mott transition
We study charge ordering driven by Coulomb interactions on triangular lattices relevant to the Wigner-Mott transition in two dimensions. Dynamical mean-field theory reveals the pinball liquid phase, a charge ordered metallic phase containing quasilocalized (pins) coexisting with itinerant (balls) electrons. Based on an effective periodic Anderson model for this phase, we find an antiferromagnetic Kondo coupling between pins and balls and strong quasiparticle renormalization. Non-Fermi liquid behavior can occur in such charge ordered systems due to the spin-flip scattering of itinerant electrons off the pins in analogy with heavy fermion compoundsJ. M. acknowledges financial support from MINECO (MAT2012-37263-C02-01). This work is supported by the French National Research Agency through Grant No. ANR-12-JS04-0003-01 SUBRISSYM
Pseudogap metal induced by long-range Coulomb interactions
In correlated electron systems the metallic character of a material can be
strongly suppressed near an integer concentration of conduction electrons as
Coulomb interactions forbid the double occupancy of local atomic orbitals.
While the Mott-Hubbard physics arising from such on-site interactions has been
largely studied, several unexplained phenomena observed in correlated materials
challenge this description and call for the development of new ideas. Here we
explore a general route for obtaining correlated behavior that is decidedly
different from the Mott-Hubbard mechanism and instead relies on the presence of
unscreened, long-range Coulomb interactions. We find a previously unreported
pseudogap metal phase characterized by a divergent quasiparticle mass and the
opening of a Coulomb pseudogap in the electronic spectrum. The destruction of
the Fermi liquid state occurs because the electrons move in a nearly frozen,
disordered charge background, as collective charge rearrangements are
drastically slowed down by the frustrating nature of long-range potentials on
discrete lattices. The present pseudogap metal realizes an early conjecture by
Efros, that a soft Coulomb gap should appear for quantum lattice electrons with
strong unscreened interactions due to self-generated randomness.Comment: 4 pages + 3 pages supplementary informatio
Royal Jelly: An ancient remedy with remarkable antibacterial properties
Royal Jelly (RJ), a honeybee hypopharyngeal gland secretion of young nurse and an exclusive nourishment for bee queen, has been used since ancient times for care and human health and it is still very important in traditional and folkloristic medicine, especially in Asia within the apitherapy. Recently, RJ and its protein and lipid components have been subjected to several investigations on their antimicrobial activity due to extensive traditional uses and for a future application in medicine. Antimicrobial activities of crude Royal Jelly, Royalisin, 10-hydroxy-2-decenoic acid, Jelleines, Major Royal Jelly Proteins against different bacteria have been reported. All these beehive products showed antimicrobial activities that lead their potential employment in several fields as natural additives. RJ and its derived compounds show a highest activity especially against Gram positive bacteria. The purpose of this Review is to summarize the results of antimicrobial studies of Royal Jelly following the timescale of the researches. From the first scientific applications to the isolation of the single components in order to better understand its application in the past years and propose an employment in future studies as a natural antimicrobial agent
Universal scaling near band-tuned metal-insulator phase transitions
We present a theory for band-tuned metal-insulator transitions based on the
Kubo formalism. Such a transition exhibits scaling of the resistivity curves,
in the regime where or , where is the scattering
time and the chemical potential. At the critical value of the chemical
potential, the resistivity diverges as a power law, .
Consequently, on the metallic side there is a regime with negative ,
which is often misinterpreted as insulating. We show that scaling and this
`fake insulator' regime is observed in a wide range of experimental systems. In
particular, we show that Mooij correlations in high-temperature metals with
negative can be quantitatively understood with our scaling theory in
the presence of -linear scattering.Comment: 10 pages, 7 figure
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