Stephan Haas

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The photon scattering properties of aperiodic nanoscale dielectric structures can be tailored to closely match a desired response by using adaptive algorithms for device design. We show that broken symmetry of aperiodic designs provides access to device functions not available to conventional periodic photonic crystal structures.
We study field-induced magnetic order in cubic lattices of dimers with antiferromagnetic Heisenberg interactions. The thermal critical exponents at the quantum phase transition from a spin liquid to a magnetically ordered phase are determined from stochastic series expansion quantum Monte Carlo simulations. These exponents are independent of the interdimer(More)
Pancreatic ductal adenocarcinoma (PDAC) occurs mainly in people older than 50 years of age. Although great strides have been taken in treating PDAC over the past decades its incidence nearly equals its mortality rate and it was quoted as the 4th leading cause of cancer deaths in the U.S. in 2012. This review aims to focus on research models and scientific(More)
Adaptive quantum design identifies the best broken-symmetry configurations of atoms and molecules that enable a desired target function response. In this work, numerical optimization is used to design atomic clusters with specified quasiparticle densities of states. The dominant self-assembled building blocks of these engineered quantum systems are found to(More)
Adaptive design may be used to synthesize a conduction band potential profile to obtain desired nonequilibrium electron transmission-voltage characteristics. Our methodology is illustrated by designing a two-terminal linear element in which electron motion is limited by quantum mechanical transmission through a potential profile. The scaling of classical(More)
Using adaptive algorithms, the design of nanoscale dielectric structures for photonic applications is explored. Widths of dielectric layers in a linear array are adjusted to match target responses of optical transmission as a function of energy. Two complementary approaches are discussed. The first approach uses adaptive local random updates and(More)
Molecular squares, triangles, rectangles, and related structures , consisting of transition-metal corners and difunctional ligand edges, are the synthetic focus of a substantial segment of contemporary coordination chemistry. [1±4] The attraction of these structures, which typically feature molecule-sized cavities , is their ability to function as soluble(More)
We present a numerical study of a quantum phase transition from a spin-polarized to a topologically ordered phase in a system of spin-1 / 2 particles on a torus. We demonstrate that this non-symmetry-breaking topologi-cal quantum phase transition ͑TOQPT͒ is of second order. The transition is analyzed via the ground state energy and fidelity, block(More)
We use a stepwise pulling protocol in molecular dynamics simulations to identify how a G-quadruplex selects and conducts Na(+), K(+), and NH4(+) ions. By estimating the minimum free-energy changes of the ions along the central channel via Jarzynski's equality, we find that the G-quadruplex selectively binds the ionic species in the following order: K(+) >(More)
The ability of biological ion channels to conduct selected ions across cell membranes is critical for the survival of both animal and bacterial cells. Numerous investigations of ion selectivity have been conducted over more than 50 years, yet the mechanisms whereby the channels select certain ions and reject others are not well understood. Here we report a(More)