Deformation behavior of undoped and In-doped GaAs in the temperature range 700–1100 °C

Compressive deformation of undoped and In‐doped GaAs single crystals has been carried out in [001] and [123] orientations in the temperature range 700–1100 °C. Indium additions, at levels of 1–2×10^(20) atoms cm^(−3), result in critical resolved shear stress (CRSS) values that are about twice as large as the undoped crystals in the temperature range of 700–1100 °C. The CRSS was weakly dependent on temperature in the temperature range investigated as expected for a model of athermal solid solution hardening. The CRSS value of 3.3 MPa for the In‐doped crystal is sufficient to eliminate profuse dislocation formation in a 75‐mm‐diam crystal on the basis of current theories for the magnitude of the thermal stress experienced during growth. The results also suggest that the process of dislocation climb is slowed appreciably by In doping

K-matrices for non-abelian quantum Hall states

Two fundamental aspects of so-called non-abelian quantum Hall states (the q-pfaffian states and more general) are a (generalized) pairing of the participating electrons and the non-abelian statistics of the quasi-hole excitations. In this paper, we show that these two aspects are linked by a duality relation, which can be made manifest by considering the K-matrices that describe the exclusion statistics of the fundamental excitations in these systems.Comment: LaTeX, 12 page

Influence of solute doping on the high-temperature deformation behavior of GaAs

The role of isovalent dopants in the high‐temperature deformation of GaAs has been studied in the temperature range 500–1150 °C. Additions of In, Sb, and B increase the critical resolved shear stress for deformation at a given strain rate and result in lowering the dislocation density of as‐grown liquid‐encapsulated Czochralski GaAs crystals. Phosphorus, because of its minor influence on the lattice strain, shows little enhancement of the yield stress. These results are consistent with a solute hardening model, in which the solute atom surrounded tetrahedrally by four Ga or As atoms comprise the hardening cluster. Codoping with In and Si hardens GaAs, but codoping with Si is less effective than the isovalent solutes In, Sb, and B, and produces softening at high temperatures. The effect of solutes on both dislocation nucleation and multiplication are reviewed here

The Haldane-Rezayi Quantum Hall State and Magnetic Flux

We consider the general abelian background configurations for the Haldane-Rezayi quantum Hall state. We determine the stable configurations to be the ones with the spontaneous flux of $(\Z+1/2) \phi_0$ with $\phi_0 = hc/e$. This gives the physical mechanism by which the edge theory of the state becomes identical to the one for the 331 state. It also provides a new experimental consequence which can be tested in the enigmatic $\nu=5/2$ plateau in a single layer system.Comment: RevTex, 5 pages, 2 figures. v2:minor corrections. v4: published version. Discussion on the thermodynamic limit adde

Site-specific fluorescence dynamics in an RNA 'thermometer' reveals the role of ribosome binding in its temperature-sensitive switch function

RNA thermometers control the translation of several heat shock and virulence genes by their temperature-sensitive structural transitions. Changes in the structure and dynamics of MiniROSE RNA, which regulates translation in the temperature range of 20–45°C, were studied by site specifically replacing seven adenine residues with the fluorescent analog, 2-aminopurine (2-AP), one at a time. Dynamic fluorescence observables of 2-AP-labeled RNAs were compared in their free versus ribosome-bound states for the first time. Noticeably, position dependence of fluorescence observables, which was prominent at 20°C, was persistent even at 45°C, suggesting the persistence of structural integrity up to 45°C. Interestingly, position-dependent dispersion of fluorescence lifetime and quenching constant at 45°C was ablated in ribosome-bound state, when compared to those at 20°C, underscoring loss of structural integrity at 45°C, in ribosome-bound RNA. Significant increase in the value of mean lifetime for 2-AP corresponding to Shine–Dalgarno sequences, when the temperature was raised from 20 to 45°C, to values seen in the presence of urea at 45°C was a strong indicator of melting of the 3D structure of MiniROSE RNA at 45°C, only when it was ribosome bound. Taken all together, we propose a model where we invoke that ribosome binding of the RNA thermometer critically regulates temperature sensing functions in MiniROSE RNA

Quasi-Spin-Charge Separation and the Spin Quantum Hall Effect

We use quantum field theory methods to study the network model for the spin quantum hall transition. When the couplings are fine tuned in a certain way, the spin and charge degrees of freedom, corresponding to the supercurrent algebras su(2) and osp(2|2) respectively, decouple in the renormalization group flow. The infrared fixed point of this simpler theory is the coset osp(4|4)/su(2) which is closely related to the current algebra osp(2|2) but not identical. Some critical exponents are computed and shown to agree with the recent predictions based on percolation.Comment: 20 pages, two figures, Some subtleties in implementing the coset are pointed out, so that the resulting fixed point theory is not precisely the osp(2|2) current algebra. This modifies the comparison with percolatio

Singular Density of States of Disordered Dirac Fermions in the Chiral Models

The Dirac fermion in the random chiral models is studied which includes the random gauge field model and the random hopping model. We focus on a connection between continuum and lattice models to give a clear perspective for the random chiral models. Two distinct structures of density of states (DoS) around zero energy, one is a power-law dependence on energy in the intermediate energy range and the other is a diverging one at zero energy, are revealed by an extensive numerical study for large systems up to $250\times 250$. For the random hopping model, our finding of the diverging DoS within very narrow energy range reconciles previous inconsistencies between the lattice and the continuum models.Comment: 4 pages, 4 figure

Spin-singlet hierarchy in the fractional quantum Hall effect

We show that the so-called permanent quantum Hall states are formed by the integer quantum Hall effects on the Haldane-Rezayi quantum Hall state. Novel conformal field theory description along with this picture is deduced. The odd denominator plateaux observed around $\nu=5/2$ are the permanent states if the $\nu=5/2$ plateau is the Haldane-Rezayi state. We point out that there is no such hierarchy on other candidate states for $\nu=5/2$. We propose experiments to test our prediction.Comment: RevTex,4 pages, v2:typo,one reference adde