Domain Wall Patterning and Giant Response Functions in Ferrimagnetic Spinels.

The manipulation of mesoscale domain wall phenomena has emerged as a powerful strategy for designing ferroelectric responses in functional devices, but its full potential is not yet realized in the field of magnetism. This work shows a direct connection between magnetic response functions in mechanically strained samples of Mn3 O4 and MnV2 O4 and stripe-like patternings of the bulk magnetization which appear below known magnetostructural transitions. Building off previous magnetic force microscopy data, a small-angle neutron scattering is used to show that these patterns represent distinctive magnetic phenomena which extend throughout the bulk of two separate materials, and further are controllable via applied magnetic field and mechanical stress. These results are unambiguously connected to the anomalously large magnetoelastic and magnetodielectric response functions reported for these materials, by performing susceptibility measurements on the same crystals and directly correlating local and macroscopic data.

Asymmetric Fraunhofer spectra in a topological insulator-based Josephson junction.

Josephson junctions with topological insulators as their weak link (S-TI-S junctions) are predicted to host Majorana fermions, which are key to creating qubits for topologically protected quantum computing. But the details of the S-TI-S current-phase relation and its interplay with magnetic fields are not well understood. We fabricate a Bi2Se3junction with NbTi leads and measure the Fraunhofer patterns of the junction with applied in-plane fields. We observe that asymmetric Fraunhofer patterns appear in the resistance maps ofBzvsBx,y, with aperiodic node spacings. These asymmetric patterns appear even at zero parallel field and for temperatures up to 1 K. The anomalous features are compared to asymmetric Fraunhofer patterns expected for finite Cooper pair momentum shifts as well as geometric effects. We show that the geometric effects can dominate, independent of in-plane field magnitude. These results are important for differentiating geometrical phase shifts from those caused by Cooper pair momentum shifting, Majorana mode signatures, or other unconventional superconducting behavior.

Finite momentum Cooper pairing in three-dimensional topological insulator Josephson junctions.

Unconventional superconductivity arising from the interplay between strong spin-orbit coupling and magnetism is an intensive area of research. One form of unconventional superconductivity arises when Cooper pairs subjected to a magnetic exchange coupling acquire a finite momentum. Here, we report on a signature of finite momentum Cooper pairing in the three-dimensional topological insulator Bi2Se3. We apply in-plane and out-of-plane magnetic fields to proximity-coupled Bi2Se3 and find that the in-plane field creates a spatially oscillating superconducting order parameter in the junction as evidenced by the emergence of an anomalous Fraunhofer pattern. We describe how the anomalous Fraunhofer patterns evolve for different device parameters, and we use this to understand the microscopic origin of the oscillating order parameter. The agreement between the experimental data and simulations shows that the finite momentum pairing originates from the coexistence of the Zeeman effect and Aharonov-Bohm flux.

A simple chemical vapor deposition method for the production of highly conductive polymer poly(3,4-ethylenedioxythiophene).

Conductive thin films of Poly(3,4-ethylenedioxythiophene) (PEDOT) have been successfully deposited on a variety of substrates by a simple chemical vapor deposition (CVD) method starting from the liquid monomer (EDOT) and using FeCl3 as a catalyst. Resistivity measurements indicated very good conductivity of the material, comparable with other previously reported values for PEDOT deposited by CVD. Further cyclic voltammetry measurements indicated a value of around -4.7 eV for the HOMO level of PEDOT in the deposited films, in agreement with other reported values. This value is within the bandgap of most semiconductors, and together with the relative low internal resistance makes our material an ideal candidate as a solid-state hole transport material for dye sensitized solar cells.