Progress in the emergent field of topological superconductivity relies on synthesis of new material combinations, combining superconductivity, low density, and spin-orbit coupling (SOC). For example, theory [1][2][3][4] indicates that the interface between a one-dimensional (1D) semiconductor (Sm) with strong SOC and a superconductor (S) hosts Majorana modes with nontrivial topological properties [5][6][7][8]. Recently, epitaxial growth of Al on InAs nanowires was shown to yield a high quality S-Sm system with uniformly transparent interfaces [9] and a hard induced gap, indicted by strongly suppressed subgap tunneling conductance [10]. Here we report the realization of a two-dimensional (2D) InAs/InGaAs heterostructure with epitaxial Al, yielding a planar S-Sm system with structural and transport characteristics as good as the epitaxial wires. The realization of 2D epitaxial S-Sm systems represent a significant advance over wires, allowing extended networks via top-down processing. Among numerous potential applications, this new material system can serve as a platform for complex networks of topological superconductors with gate-controlled Majorana zero modes [1][2][3][4]. We demonstrate gateable Josephson junctions and a highly transparent 2D S-Sm interface based on the product of excess current and normal state resistance.The recent focus on topological states in solid state systems has revealed new directions in condensed matter physics with potential applications in topological quantum information [11,12]. In an exciting development, it was realized one could readily engineering an effective one-dimensional (1D) spinless superconductor using the proximity effect from conventional superconductors (Al, Nb) in nanowires with strong SOC (InAs, InSb), and that Majorana zero modes would naturally emerge at the ends of the wire [1][2][3][4]. First experiments on nanowires grown by chemical vapor deposition (CVD) revealed striking evidence of Majorana zero modes states [13][14][15][16][17][18]. In order to eventually move beyond demonstrations of braiding [19][20][21], to larger-scale Majorana networks [22] it is likely that a top-down patterning approach will be needed. Molecular beam epitaxy (MBE) growth of large-area 2D SSm systems can form the basis for such an approach, but to date have not been available.Narrow bandgap semiconductors such as InAs and InSb are natural choices for the Sm component due to large g factors and strong SOC, which are important for the stability of an emergent topological phase in S-Sm heterostructures, with the topological gap proportional to the SOC strength [23]. There are, however, significant challenges in growing high quality quantum wells in these systems. The lack of insulating latticematched substrates and difficulty in device fabrication, compared to well-developed GaAs material system, has restricted their use in mesoscopic devices. Nevertheless, it has long been known [24] that surface level pinning in InAs could allow for fabrication of transparent contact to superconduct...

We theoretically obtain the phase diagram of localized magnetic impurity spins arranged in a one-dimensional chain on top of a one-or two-dimensional electron gas. The interactions between the spins are mediated by the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism through the electron gas. Recent work predicts that such a system may intrinsically support topological superconductivity without spin-orbit coupling when a helical spin-density wave is spontaneously formed in the spins, and superconductivity is induced in the electron gas. We analyze, using both analytical and numerical techniques, the conditions under which such a helical spin state is stable in a realistic situation in the presence of disorder. We show that (i) it appears only when the spins are coupled to a (quasi-) 1D electron gas, and (ii) it becomes unstable towards the formation of (anti) ferromagnetic domains if the disorder in the impurity spin positions δR becomes comparable with the Fermi wave length. We also examine the stability of the helical state against Gaussian potential disorder in the electronic system using a diagrammatic approach. Our results suggest that in order to stabilize the helical spin state and thus the emergent topological superconductivity under realistic experimental conditions, a sufficiently strong Rashba spin-orbit coupling, giving rise to Dzyaloshinskii-Moriya interactions, is required.PACS numbers: 73.21. Hb, 71.10.Pm, 74.78.Fk Magnetism originating from interactions between magnetic atoms mediated by delocalized electrons (the so-called RKKY interaction) represents an important problem in modern condensed matter physics [1] and has been a subject of intense research [2][3][4][5][6][7]. In this Letter, we consider the specific case of a helical spin density wave (SDW) that might appear in a one-dimensional chain of magnetic atoms that are coupled to a metal or a superconductor. The issue of RKKY-induced magnetism has recently taken on a new and unexpected interesting perspective in the physics of non-Abelian Majorana bound states (Majoranas) [8,9], with the recent claims of the natural (i.e. self-tuned) emergence of Majorana modes in a chain of states induced by magnetic atoms at the surface of a superconductor, see Fig. 1. A Majorana-carrying topological superconducting phase should emerge in this system without the tuning of any external parameters due to the existence of an RKKY-stabilized helical order in conjunction with s-wave superconductivity [13][14][15][16]. If correct, this is a breakthrough in the prospective realization of non-Abelian topological phases of matter, and hence of great importance. A helical spin texture is a crucial ingredient also in most other proposals for topological superconductivity [17][18][19][20][21][22].In these recent Majorana proposals, the presence of the helical order was either assumed a priori [13,[23][24][25][26][27][28] or shown to exist in rather limited situations [14][15][16]. In this Letter, we revisit the claims of the emergent self-tuned topological supercon...

We study origin of Rashba spin-orbit interaction at SrTiO3 surfaces and LaAlO3/SrTiO3 interfaces by considering the interplay between atomic spin-orbit coupling and inversion asymmetry at the surface or interface. We show that, in a simple tight-binding model involving 3d t2g bands of Ti ions, the induced spin-orbit coupling in the dxz and dyz bands is cubic in momentum whereas the spin-orbit interaction in the dxy band has linear momentum dependence. We also find that the spinorbit interaction in one-dimensional channels at LaAlO3/SrTiO3 interfaces is linear in momentum for all bands. We discuss implications of our results for transport experiments on SrTiO3 surfaces and LaAlO3/SrTiO3 interfaces. In particular, we analyze the effect of a given spin-orbit interaction term on magnetotransport of LaAlO3/SrTiO3 by calculating weak anti-localization corrections to the conductance and to universal conductance fluctuations.

Various industry forecasts project that, by 2020, there will be around 50 billion devices connected to the Internet of Things (IoT), helping to engineer new solutions to societalscale problems such as healthcare, energy conservation, transportation, etc. Most of these devices will be wireless due to the expense, inconvenience, or in some cases, the sheer infeasibility of wiring them. Further, many of them will have stringent size constraints. With no cord for power and limited space for a battery, powering these devices (to achieve several months to possibly years of unattended operation) becomes a daunting challenge. This paper highlights some promising directions for addressing this challenge, focusing on three main building blocks: (a) the design of ultra-low power hardware platforms that integrate computing, sensing, storage, and wireless connectivity in a tiny form factor, (b) the development of intelligent system-level power management techniques, and (c) the use of environmental energy harvesting to make IoT devices self-powered, thus decreasing -in some cases, even eliminating -their dependence on batteries. We discuss these building blocks in detail and illustrate case-studies of systems that use them judiciously, including the QUBE wireless embedded platform, which exploits the characteristics of emerging non-volatile memory technologies to seamlessly and efficiently enable long-running computations in systems that experience frequent power loss (i.e., intermittently powered systems).

The stress produced by the coupling of reactive oxygen species (ROS) and endoplasmic reticulum (ER) has been explored extensively, but little is known regarding their roles in the early development of mammalian embryos. Here, we demonstrated that the early development of in vitro-produced (IVP) bovine embryos was governed by the cooperative action between ROS and ER stress. Compared with the tension produced by 5% O2, 20% O2 significantly decreased the blastocyst formation rate and cell survival, which was accompanied by increases in ROS and in levels of sXBP-1 transcript, which is an ER stress indicator. In addition, treatment with glutathione (GSH), a ROS scavenger, decreased ROS levels, which resulted in increased blastocyst formation and cell survival rates. Importantly, levels of sXBP-1 and ER stress-associated transcripts were reduced by GSH treatment in developing bovine embryos. Consistent with this observation, tauroursodeoxycholate (TUDCA), an ER stress inhibitor, improved blastocyst developmental rate, trophectoderm proportion, and cell survival. Moreover, ROS and sXBP-1 transcript levels were markedly decreased by supplementation with TUDCA, suggesting a possible mechanism governing the mutual regulation between ROS and ER stress. Interestingly, knockdown of XBP-1 transcripts resulted in both elevation of ROS and decrease of antioxidant transcripts, which ultimately reduced in vitro developmental competence of bovine embryos. Based on these results, in vitro developmental competence of IVP bovine embryos was highly dependent on the coupled response between oxidative and ER stresses. These results increase our understanding of the mechanism(s) governing early embryonic development and may improve strategies for the generation of IVP embryos with high developmental competence.

The nucleotide sequence around the translational initiation site is an important cis-acting element for post-transcriptional regulation. However, it has not been fully understood how the sequence context at the 5′-untranslated region (5′-UTR) affects the translational efficiency of individual mRNAs. In this study, we provide evidence that the 5′-UTRs of Arabidopsis genes showing a great difference in the nucleotide sequence vary greatly in translational efficiency with more than a 200-fold difference. Of the four types of nucleotides, the A residue was the most favourable nucleotide from positions −1 to −21 of the 5′-UTRs in Arabidopsis genes. In particular, the A residue in the 5′-UTR from positions −1 to −5 was required for a high-level translational efficiency. In contrast, the T residue in the 5′-UTR from positions −1 to −5 was the least favourable nucleotide in translational efficiency. Furthermore, the effect of the sequence context in the −1 to −21 region of the 5′-UTR was conserved in different plant species. Based on these observations, we propose that the sequence context immediately upstream of the AUG initiation codon plays a crucial role in determining the translational efficiency of plant genes.

Electrical energy is a high quality form of energy that can be easily converted to other forms of energy with high efficiency and, even more importantly, it can be used to control lower grades of energy quality with ease. However, building a cost-effective electrical energy storage (EES) system is a challenging task despite steady advances in the design and manufacturing of EES elements including various battery and supercapacitor technologies. As of today, no single type of EES element fulfills high energy density, high power delivery capacity, low cost per unit of storage, long cycle life, low leakage, and so on at the same time.Unlike conventional EES systems, we introduce a HEES (hybrid EES) system comprising heterogeneous EES elements. Our proposed HEES system builds on the concepts of computer memory system architecture and management in order to achieve the attributes of an ideal EES system through appropriate allocation and organization of various types of EES elements. We also introduce a HEES design considerations which should be taken into account to optimize the amortized cost for the system, including the initial cost (cost per capacity), the operating cost (efficiency), the maintenance cost (cycle life and disposal cost), and so forth.

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