Dynamics of a Pair of Interacting Spins Coupled to an Environmental Sea

We solve for the dynamics of a pair of spins, coupled to each other and also to an environmental sea of oscillators. The environment mediates an indirect interaction between the spins, causing both mutual coherence effects and dissipation. This model describes a wide variety of physical systems, ranging from 2 coupled microscopic systems (eg., magnetic impurities, bromophores, etc), to 2 coupled macroscopic quantum systems. We obtain analytic results for 3 regimes, viz., (i) The locked regime, where the 2 spins lock together; (ii) The correlated relaxation regime (mutually correlated incoherent relaxation); and (iii) The mutual coherence regime, with correlated damped oscillations. These results cover most of the parameter space of the system.Comment: 49 pages, To appear in Int J. Mod. Phys.

Correlated random fields in dielectric and spin glasses

Both orientational glasses and dipolar glasses possess an intrinsic random field, coming from the volume difference between impurity and host ions. We show this suppresses the glass transition, causing instead a crossover to the low $T$ phase. Moreover the random field is correlated with the inter-impurity interactions, and has a broad distribution. This leads to a peculiar variant of the Imry-Ma mechanism, with 'domains' of impurities oriented by a few frozen pairs. These domains are small: predictions of domain size are given for specific systems, and their possible experimental verification is outlined. In magnetic glasses in zero field the glass transition survives, because the random fields are disallowed by time-reversal symmetry; applying a magnetic field then generates random fields, and suppresses the spin glass transition.Comment: minor modifications, final versio

Quantum spin glass in anisotropic dipolar systems

The spin-glass phase in the \LHx compound is considered. At zero transverse field this system is well described by the classical Ising model. At finite transverse field deviations from the transverse field quantum Ising model are significant, and one must take properly into account the hyperfine interactions, the off-diagonal terms in the dipolar interactions, and details of the full J=8 spin Hamiltonian to obtain the correct physical picture. In particular, the system is not a spin glass at finite transverse fields and does not show quantum criticality.Comment: 6 pages, 2 figures, to appear in J. Phys. Condens. Matter (proceedings of the HFM2006 conference

Characterization and Optimization of a Bi-Layer BARC

Standing wave effects have been seen throughout the history of microlithography. Due to standing wave effects, the line width control of imaged lines in photoresist is compromised. A technology that has emerged as strong solution for the reduction of standing wave effects is a Bottom Antireflective Coating (BARC) that is deposited onto the wafer before the photoresist deposition. By reducing the substrate reflectivity, the standing wave effects can also be reduced dramatically. The 193 nm photoresist and the bi-layer BARC films were characterized and then optimized to reduce standing wave effects within the 193 nm photoresist. A bi-layer BARC film configuration that reduces the reflectivity to less than 1% for both of the experimental numerical aperture settings of 1.05NA and 1.3NA is the goal of this project and was achieved in the RIT SMFL cleanroom. Also, a single-layer BARC system was designed to reduce substrate reflectivity to less than 1% at a setting of 1.05NA. This single-layer design was used as the control experiment or baseline to prove that a bi-layer BARC design is much more efficient than a single-layer BARC system. Simulations were conducted for the design of the multi-layer lithography systems using ILSim 1.0, an interferometric lithography simulation software as well as a simulation program on the JA Woolam Co., Inc. Variable Angle Spectroscopic Ellipsometer (VASE), which was also used to characterize the 193nm DUV resist. The simulations are run by utilizing the refractive indexes (n) and the extinction coefficients (k) of the films being used, which are the optical characteristics of the films. Imaged lines and spaces were then exposed for each of the two designed film stacks and at the two NA settings as stated above. Imaged lines of 45 nm and 35 nm were obtained at 1.05 NA and 1.3NA, respectively, for the bi-layer system, while only 45 nm lines could be obtained with the single-layer BARC system. Since the project objectives and goals were reached, a brief proposal to push the limits of the bi-layer BARC system to 1.5NA is suggested

Theory of single-particle properties of the Hubbard model

It is shown that it is possible to quantitatively explain quantum Monte Carlo results for the Green's function of the two-dimensional Hubbard model in the weak to intermediate coupling regime. The analytic approach includes vertex corrections in a paramagnon-like self-energy. All parameters are determined self-consistently. This approach clearly shows that in two dimensions Fermi-liquid quasiparticles disappear in the paramagnetic state when the antiferromagnetic correlation length becomes larger than the electronic thermal de Broglie wavelength.Comment: 5 pages, latex, uuencoded figures, REVTEX Also available by direct request to [email protected]