Experimental realization of SQUIDs with topological insulator junctions

We demonstrate topological insulator (Bi$_2$Te$_3$) dc SQUIDs, based on superconducting Nb leads coupled to nano-fabricated Nb-Bi$_2$Te$_3$-Nb Josephson junctions. The high reproducibility and controllability of the fabrication process allows the creation of dc SQUIDs with parameters that are in agreement with design values. Clear critical current modulation of both the junctions and the SQUID with applied magnetic fields have been observed. We show that the SQUIDs have a periodicity in the voltage-flux characteristic of $\Phi_0$, of relevance to the ongoing pursuit of realizing interferometers for the detection of Majorana fermions in superconductor- topological insulator structures

Optimizing the Majorana character of SQUIDs with topologically non-trivial barriers

We have modeled SQUIDs with topologically non-trivial superconducting junctions and performed an optimization study on the Majorana fermion detection. We find that the SQUID parameters beta_L, and beta_C can be used to increase the ratio of Majorana tunneling to standard Cooper pair tunneling by more than two orders of magnitude. Most importantly, we show that dc SQUIDs including topologically trivial components can still host strong signatures of the Majorana fermion. This paves the way towards the experimental verification of the theoretically predicted Majorana fermion.Comment: accepted by Physical Review

Josephson supercurrent in a topological insulator without a bulk shunt

A Josephson supercurrent has been induced into the three-dimensional topological insulator Bi1.5Sb0.5Te1.7Se1.3. We show that the transport in Bi1.5Sb0.5Te1.7Se1.3 exfoliated flakes is dominated by surface states and that the bulk conductivity can be neglected at the temperatures where we study the proximity induced superconductivity. We prepared Josephson junctions with widths in the order of 40 nm and lengths in the order of 50 to 80 nm on several Bi1.5Sb0.5Te1.7Se1.3 flakes and measured down to 30 mK. The Fraunhofer patterns unequivocally reveal that the supercurrent is a Josephson supercurrent. The measured critical currents are reproducibly observed on different devices and upon multiple cooldowns, and the critical current dependence on temperature as well as magnetic field can be well explained by diffusive transport models and geometric effects

Higher levels of CO2 during late incubation alter the hatch time of chicken embryos

status: publishe

Person-Specific Non-shared Environmental Influences in Intra-individual Variability : A Preliminary Case of Daily School Feelings in Monozygotic Twins

Most behavioural genetic studies focus on genetic and environmental influences on inter-individual phenotypic differences at the population level. The growing collection of intensive longitudinal data in social and behavioural science offers a unique opportunity to examine genetic and environmental influences on intra-individual phenotypic variability at the individual level. The current study introduces a novel idiographic approach and one novel method to investigate genetic and environmental influences on intra-individual variability by a simple empirical demonstration. Person-specific non-shared environmental influences on intra-individual variability of daily school feelings were estimated using time series data from twenty-one pairs of monozygotic twins (age = 10 years, 16 female pairs) over two consecutive weeks. Results showed substantial inter-individual heterogeneity in person-specific non-shared environmental influences. The current study represents a first step in investigating environmental influences on intra-individual variability with an idiographic approach, and provides implications for future behavioural genetic studies to examine developmental processes from a microscopic angle

Vortex trapping and expulsion in thin-film YBCO strips

A scanning SQUID microscope was used to image vortex trapping as a function of the magnetic induction during cooling in thin-film YBCO strips for strip widths W from 2 to 50 um. We found that vortices were excluded from the strips when the induction Ba was below a critical induction Bc. We present a simple model for the vortex exclusion process which takes into account the vortex - antivortex pair production energy as well as the vortex Meissner and self-energies. This model predicts that the real density n of trapped vortices is given by n=(Ba-BK)/Phi0 with BK = 1.65Phi0/W^2 and Phi0 = h/2e the superconducting flux quantum. This prediction is in good agreement with our experiments on YBCO, as well as with previous experiments on thin-film strips of niobium. We also report on the positions of the trapped vortices. We found that at low densities the vortices were trapped in a single row near the centers of the strips, with the relative intervortex spacing distribution width decreasing as the vortex density increased, a sign of longitudinal ordering. The critical induction for two rows forming in the 35 um wide strip was (2.89 + 1.91-0.93)Bc, consistent with a numerical prediction

Optics-less smart sensors and a possible mechanism of cutaneous vision in nature

Optics-less cutaneous (skin) vision is not rare among living organisms, though its mechanisms and capabilities have not been thoroughly investigated. This paper demonstrates, using methods from statistical parameter estimation theory and numerical simulations, that an array of bare sensors with a natural cosine-law angular sensitivity arranged on a flat or curved surface has the ability to perform imaging tasks without any optics at all. The working principle of this type of optics-less sensor and the model developed here for determining sensor performance may be used to shed light upon possible mechanisms and capabilities of cutaneous vision in nature