411 research outputs found
Reply to the comment of Chudnovsky&Garanin on "Spin relaxation in Mn12-acetate"
Reply to the comment of E.M. Chudnovsky and D.A. Garanin on Europhys. Lett.
46, 692 (1999).Comment: 2 pages, Latex (europhys.sty
Degradation of polycrystalline HfO2-based gate dielectrics under nanoscale electrical stress
The evolution of the electrical properties of HfO2/SiO2/Si dielectric stacks under electrical stress has been investigated using atomic force microscope-based techniques. The current through the grain boundaries (GBs), which is found to be higher than thorough the grains, is correlated to a higher density of positively charged defects at the GBs. Electrical stress produces different degradation kinetics in the grains and GBs, with a much shorter time to breakdown in the latter, indicating that GBs facilitate dielectric breakdown in high-k gate stacks
Nuclear Tunnelling and Dynamical Jahn-Teller Effect in Graphene with Vacancy
We show that the substitutional vacancy in graphene forms a dynamical
Jahn-Teller center. The adiabatic potential surface resulting from the
electron-lattice coupling was computed using density-functional methods and
subsequently the Schr\"odinger equation was solved for the nuclear motion. Our
calculations show a large tunnelling splitting of about 86
cm. %, which is large as compared to the typical strain splitting. The
effect results in a large delocalization of the carbon nuclear wave functions
around the vacancy leading to a significant broadening of the Jahn-Teller
active electron states. The tunnelling splitting should be
observable in electron paramagnetic resonance and two-photon resonance
scattering experiments.Comment: 5 pages, 4 figure
A possible mechanism of ultrafast amorphization in phase-change memory alloys: an ion slingshot from the crystalline to amorphous position
We propose that the driving force of an ultrafast crystalline-to-amorphous
transition in phase-change memory alloys are strained bonds existing in the
(metastable) crystalline phase. For the prototypical example of GST, we
demonstrate that upon breaking of long Ge-Te bond by photoexcitation Ge ion
shot from an octahedral crystalline to a tetrahedral amorphous position by the
uncompensated force of strained short bonds. Subsequent lattice relaxation
stabilizes the tetrahedral surroundings of the Ge atoms and ensures the
long-term stability of the optically induced phase.Comment: 6 pages, 3 figure
Quasi-degenerate self-trapping in one-dimensional charge transfer exciton
The self-trapping by the nondiagonal particle-phonon interaction between two
quasi-degenerate energy levels of excitonic system, is studied. We propose this
is realized in charge transfer exciton, where the directions of the
polarization give the quasi-degeneracy. It is shown that this mechanism, unlike
the conventional diagonal one, allows a coexistence and resonance of the free
and self-trapped states even in one-dimensional systems and a quantitative
theory for the optical properties (light absorption and time-resolved
luminescence) of the resonating states is presented. This theory gives a
consistent resolution for the long-standing puzzles in quasi-one-dimensional
compound A-PMDA.Comment: accepted to Phys. Rev. Letter
Analysis of effective mobility and hall effect mobility in high-k based In0.75Ga0.25As metal-oxide-semiconductor high-electron-mobility transistors
We report an In0.75Ga0.25As metal-oxide-semiconductor high-electron-mobility transistor with a peak Hall mobility of 8300 cm(2)/Vs at a carrier density of 2 x 10(12) cm(-2). Comparison of split capacitance-voltage (CV) and Hall Effect measurements for the extracted electron mobility have shown that the split-CV can lead to an overestimation of the channel carrier concentration and a corresponding underestimation of electron mobility. An analysis of the electron density dependence versus gate voltage allows quantifying the inaccuracy of the split-CV technique. Finally, the analysis supported by multi-channel conduction simulations indicates presence of carriers spill over into the top InP barrier layer at high gate voltages. (C) 2011 American Institute of Physics. (doi: 10.1063/1.3665033
Generalized "Quasi-classical" Ground State for an Interacting Two Level System
We treat a system (a molecule or a solid) in which electrons are coupled
linearly to any number and type of harmonic oscillators and which is further
subject to external forces of arbitrary symmetry. With the treatment restricted
to the lowest pair of electronic states, approximate "vibronic"
(vibration-electronic) ground state wave functions are constructed having the
form of simple, closed expressions. The basis of the method is to regard
electronic density operators as classical variables. It extends an earlier
"guessed solution", devised for the dynamical Jahn-Teller effect in cubic
symmetry, to situations having lower (e.g., dihedral) symmetry or without any
symmetry at all. While the proposed solution is expected to be quite close to
the exact one, its formal simplicity allows straightforward calculations of
several interesting quantities, like energies and vibronic reduction (or Ham)
factors. We calculate for dihedral symmetry two different -factors (""
and "") and a -factor. In simplified situations we obtain . The formalism enables quantitative estimates to be made for the dynamical
narrowing of hyperfine lines in the observed ESR spectrum of the dihedral
cyclobutane radical cation.Comment: 28 pages, 4 figure
Role of Orbitals in the Physics of Correlated Electron Systems
Rich properties of systems with strongly correlated electrons, such as
transition metal oxides, is largely connected with an interplay of different
degrees of freedom in them: charge, spin, orbital ones, as well as crystal
lattice. Specific and often very important role is played by orbital degrees of
freedom. In this comment I will shortly summarize the main concepts and discuss
some of the well-known manifestations of orbital degrees of freedom, but will
mostly concentrate on a recent development in this field.Comment: To be published in "Comments on Solid State Physics", part of
"Physica Scripta
The CoQ oxidoreductase FSP1 acts parallel to GPX4 to inhibit ferroptosis.
Ferroptosis is a form of regulated cell death that is caused by the iron-dependent peroxidation of lipids1,2. The glutathione-dependent lipid hydroperoxidase glutathione peroxidase 4 (GPX4) prevents ferroptosis by converting lipid hydroperoxides into non-toxic lipid alcohols3,4. Ferroptosis has previously been implicated in the cell death that underlies several degenerative conditions2, and induction of ferroptosis by the inhibition of GPX4 has emerged as a therapeutic strategy to trigger cancer cell death5. However, sensitivity to GPX4 inhibitors varies greatly across cancer cell lines6, which suggests that additional factors govern resistance to ferroptosis. Here, using a synthetic lethal CRISPR-Cas9 screen, we identify ferroptosis suppressor protein 1 (FSP1) (previously known as apoptosis-inducing factor mitochondrial 2 (AIFM2)) as a potent ferroptosis-resistance factor. Our data indicate that myristoylation recruits FSP1 to the plasma membrane where it functions as an oxidoreductase that reduces coenzyme Q10 (CoQ) (also known as ubiquinone-10), which acts as a lipophilic radical-trapping antioxidant that halts the propagation of lipid peroxides. We further find that FSP1 expression positively correlates with ferroptosis resistance across hundreds of cancer cell lines, and that FSP1 mediates resistance to ferroptosis in lung cancer cells in culture and in mouse tumour xenografts. Thus, our data identify FSP1 as a key component of a non-mitochondrial CoQ antioxidant system that acts in parallel to the canonical glutathione-based GPX4 pathway. These findings define a ferroptosis suppression pathway and indicate that pharmacological inhibition of FSP1 may provide an effective strategy to sensitize cancer cells to ferroptosis-inducing chemotherapeutic agents
Macroscopic nucleation phenomena in continuum media with long-range interactions
Nucleation, commonly associated with discontinuous transformations between
metastable and stable phases, is crucial in fields as diverse as atmospheric
science and nanoscale electronics. Traditionally, it is considered a
microscopic process (at most nano-meter), implying the formation of a
microscopic nucleus of the stable phase. Here we show for the first time, that
considering long-range interactions mediated by elastic distortions, nucleation
can be a macroscopic process, with the size of the critical nucleus
proportional to the total system size. This provides a new concept of
"macroscopic barrier-crossing nucleation". We demonstrate the effect in
molecular dynamics simulations of a model spin-crossover system with two
molecular states of different sizes, causing elastic distortions.Comment: 12 pages, 4 figures. Supplementary information accompanies this paper
at http://www.nature.com/scientificreport
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