Gauge field and the confinement-deconfinement transition in hydrogen-bonded ferroelectrics.

Quantum melting of a ferroelectric moment in the frustrated hydrogen-bonded system with the "ice rule" is studied theoretically by using quantum Monte Carlo simulation. The large number of nearly degenerate configurations are described as the gauge degrees of freedom; i.e., the model is mapped to a lattice gauge theory, which shows the confinement-deconfinment transition (CDT). The dipole-dipole interaction J(2), on the other hand, explicitly breaks the gauge symmetry leading to the ferroelectric transition at finite temperature T. It is found that the crossover from the FT to CDT manifests itself in the reduced correlation length of the polarization ξ(FT)∼Δ(K-K(c))(-ν), with Δ∝√J(2) while K(c) and ν remains finite in the limit J(2)→0. In contrast, the Curie-Weiss-like law for the susceptibility χ and the spontaneous polarization behaves smoothly and the length scale ξ(CDT), related to the molecular symmetry and volume for CDT, does not reduce in this limit.

Proposed nonmagnetic Stern-Gerlach experiment using electron diffraction.

We demonstrate that a transverse spin current can be generated simply by diffraction through a single slit in the spin-orbit coupling system of the two-dimensional electron gas. In the regime of spin-orbit coupling ~10(-13) eV·m, an out-of-plane component of the electron spin of up to 0.42h can be generated. Based on this effect, a novel device consisting of a grating to distill spin is designed. Two first diffraction peaks of electron carry different spins, providing a nonmagnetic version of the Stern-Gerlach experiment. The direction of the spin current can be controlled by the gate voltage with low energy cost.

New family of models for incompressible quantum liquids in d>/=2.

Through Haldane's construction, the fractional quantum Hall states on a two-sphere were shown to be the ground states of one-dimensional SU(2) spin Hamiltonians. In this Letter we generalize this construction to obtain a new class of SU(N) spin Hamiltonians. These Hamiltonians describe center-of-mass-position conserving pair hopping fermions in space dimension d>/=2.

Disorder-enhanced dielectric response of nanoscale and mesoscopic insulators.

Enhancement of the dielectric response of insulators by disorder is theoretically proposed, where the quantum interference of electronic waves through the nanoscale or mesoscopic system and its change due to external perturbations control the polarization. In the disordered case with all the states being localized, the resonant tunneling, which is topologically protected, plays a crucial role, and enhances the dielectric response by a factor 30-40 compared with the pure case. The realization of this idea with accessible materials or structures is also discussed.