Multi-loop arrays of Josephson junctions (JJs) with non-uniform area distributions, which are known as superconducting quantum interference filters (SQIFs), are the most highly sensitive sensors of changes in applied magnetic field as well as the absolute magnitude of magnetic fields. The non-uniformity of the loop sizes allows the array to produce a unique collective voltage response that has a pronounced single peak with a large voltage swing around zero magnetic field. To obtain high linear dynamic range, which is critical for a wide variety of applications, the linearity of the slope of the anti-peak response must be improved. We propose a novel scheme for enhancing linearity—a new configuration combining the SQIF array concept with the recently introduced bi-superconductive quantum interference device (SQUID) configuration, in which each individual SQUID loop is made up of three JJs as opposed to using two JJs per loop in standard dc SQUIDs. We show, computationally, that the additional junction offers a viable linearization method for optimizing the voltage response and dynamic range of SQIF arrays. We have realized SQIF arrays based on bi-SQUID cells and present first experimental results.

We report a smectic-A-smectic-Csmectic-C" (ACC') multicritical point in mixtures of chiral DOBAMBC [p-(n-decyloxy-benzylidene)-p-amino-(2-methyl-butyl)] cinnamate and achiral 100.8 (4decyloxybenzylidene-4-octylaniline).Studies of the phase diagram, tilt angle, polarization, and helix pitch indicate an AC| ' Lifshitz point describable by the extended Landau theory. Specifically, TA, c and the maximum polarization (P ) exhibit quadratic composition dependence while the helical pitch length (p = 2z'/q) varies linearly. Both q and P vanish discontinuously at the C-C' boundary revealing its first order nature, consistent with a possible Lifshitz point. PACS numbers: 64.70.Md, 61.20.p A Lifshitz point [1] represents an anomaly in a phase diagram along a second order phase transition line () line) where the coefficient of the gradient term(s) (A) vanishes. Emanating from the Lifshitz point (LP) is a line of first order transition that separates a modulated

We develop a two-dimensional (2D) Superconducting Quantum Interference Filter (SQIF) array based on recently introduced high-linearity tri-junction bi-SQUIDs. Our bi-SQUID SQIF array design is based on a tight integration of individual bi-SQUID cells sharing inductances with adjacent cells. We provide extensive computer simulations, analysis and experimental measurements, in which we explore the phase dynamics and linearity of the array voltage response. The non-uniformity in inductances of the bi-SQUIDs produces a pronounced zero-field single antipeak in the voltage response. The anti-peak linearity and size can be optimized by varying the critical current of the additional junction of each bi-SQUID. The layout implementation of the tight 2D array integration leads to a distinct geometrical diamond shape formed by the merged dual bi-SQUID cells. Different size 2D arrays are fabricated using standard HYPRES niobium 4.5 kA/cm 2 fabrication process. The measured linearity, power gain, and noise properties will be analyzed for different array sizes and the results will be compared with circuit simulations. We will discuss a design approach for the electrically small magnetic field antenna and low-noise amplifiers with high bandwidth based on these 2D bi-SQUID SQIF arrays. The results from this work will be used to design chips densely and completely covered in bi-SQUIDs that has optimized parameters such as linearity and power gain.

Measured intermodulation distortion ͑IMD͒ power at 1.5 GHz in a series of YBa 2 Y 3 O 7−␦ stripline resonators of varying strip widths is compared to the predictions of two qualitatively distinct theories of the nonlinear Meissner effect. The stripline resonators are patterned from a single wafer to ensure uniformity of the material properties. According to the first theory ͓T. Dahm and D. J. Scalapino, Phys. Rev. B 60, 13125 ͑1999͔͒, the IMD power is dominated by contributions from the strip edges, while according to the second theory ͓D. Agassi and D. E. Oates, Phys. Rev. B 72, 014538 ͑2005͔͒ it is dominated by contributions from the body of the strip. The parameter-free comparison of the measured data with the theoretical predictions clearly favors the latter theory. We conclude that the nonlinear component of the penetration depth must be treated with nonlocal electrodynamics. The origins of this outcome are discussed briefly in the framework of a Green's-function approach.

Ferroelectric liquid crystals (FLCs) find many applications in display devices, waveguide switching and optical computing. These applications exploit the electrically alignable polarization of FLCs in the Smectic C* (SmC*) phase. In the absence of an electrical field, the SmC* phase exhibits helical modulation of the polarization vector resulting in no net bulk polarization. Pitch length and polarization properties of the phase are associated with the tilted structure and chirality of FLCs. Fundamentally, these physical properties constitute secondary order parameters of the SmASmC* (AC*) phase transitions. In this paper, we report a unique and startling ACC* multicritical point in mixtures of chiral DOBAMBC (p-(n-decyloxybenzylidene)-p-amino-(2-methyl-butyl) cinnamate and achiral 100.8 (4-decyloxybenzylidene-4' octylaniline) where the SmA, C, and C* (ACC* point) phases meet. Studies of the phase diagram, tilt angle (6), polarization (P) and helix pitch (p) reveal an ACC* Lifshitz point that can be described in terms of the extended Landau theory. Specifically, the TAC* and maximum polarization (Pm) exhibit quadratic composition dependence while the helical pitch length (p = 2ir/q) varies linearly. Both q and Pm vanish discontinuously at the CC* phase boundary revealing its first order nature. Significantly, the composition dependence (x) of Pm and 0 can be explained using percolation and thermodynamic scaling theories, respectively.