An antisite defect mechanism for room temperature ferroelectricity in orthoferrites

Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of YFe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications.

Scan Chain Fault Isolation using Single Event Upsets Induced by a Picosecond 1064nm Laser

We present the first experimental demonstration of stuck-at scan chain fault isolation through the exploitation of Single Event Upsets (SEU) in a Laser-Induced Fault Analysis (LIFA) system. By observing a pass/fail flag, we can spatially map all flops after a defect in a failing scan chain through induced SEU sites produced by a fiber-amplified 25 ps 1064 nm diode laser. In addition, a custom fault isolation methodology is presented in which the result highlights only the first working flop immediately after the defect mechanism causing the stuck-at chain failure. This work demonstrates a novel method for rapid scan chain fault isolation that significantly improves localization efficacy over conventional best-known methods (BKM) based on frequency mapping. Moreover, experimental results are presented to demonstrate that LIFA can be extended to interrogate the data state of flip flops in a scan chain. Results are also presented to establish that LIFA can be configured as a hardware-based diagnostics platform.

A twist defect mechanism for ATP-dependent translocation of nucleosomal DNA

As superfamily 2 (SF2)-type translocases, chromatin remodelers are expected to use an inchworm-type mechanism to walk along DNA. Yet how they move DNA around the histone core has not been clear. Here we show that a remodeler ATPase motor can shift large segments of DNA by changing the twist and length of nucleosomal DNA at superhelix location 2 (SHL2). Using canonical and variant 601 nucleosomes, we find that the Saccharomyces cerevisiae Chd1 remodeler decreased DNA twist at SHL2 in nucleotide-free and ADP-bound states, and increased twist with transition state analogs. These differences in DNA twist allow the open state of the ATPase to pull in ~1 base pair (bp) by stabilizing a small DNA bulge, and closure of the ATPase to shift the DNA bulge toward the dyad. We propose that such formation and elimination of twist defects underlie the mechanism of nucleosome sliding by CHD-, ISWI-, and SWI/SNF-type remodelers.