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Akiho T.,Solid State Group
NTT Technical Review | Year: 2017

Two-dimensional topological insulators (2DTIs) pave the way to explore novel quasiparticles for fault-tolerant quantum computing and to create devices utilizing spin degree of freedom. However, host materials that realize 2DTIs have so far been limited to two systems. In this article, we propose a strained quantum well structure as a new 2DTI candidate and demonstrate that strain enhances the energy gap and leads to superior bulk insulation properties.

Kumada N.,Solid State Group
NTT Technical Review | Year: 2017

N-type and p-type regions in graphene can adjoin without a gap in between. This article explains how such characteristic p-n junctions can serve as beam splitters of electrons. Utilizing the long coherence length of electrons in graphene may make it possible to carry out an electron version of quantum optics.

Silva M.R.,University of Coimbra | Martin-Ramos P.,University of Coimbra | Coutinho J.T.,Solid State Group | Pereira L.C.J.,Solid State Group | Martin-Gil J.,University of Valladolid
Dalton Transactions | Year: 2014

Erbium complexes featuring β-diketonate ligand 2,4-hexanedione (Hh) and N,N-donor-ligands 2,2′-bipyridine (bipy), 5-nitro-1,10-phenanthroline (5NO2phen) and bathophenanthroline (bath) have been synthesized. The structures of the ternary complexes [Er(h)3(bipy)], [Er(h) 3(5NO2phen)] and [Er(h)3(bath)] have been determined by single crystal X-ray diffraction. Excitation of the complexes in the ultraviolet region (337 nm) led to near infrared (NIR) luminescence at 1532 nm characteristic of the trivalent erbium ion in the three compounds, with an improved antenna effect in the 5-nitro-1,10-phenanthroline complex. The AC susceptibility studies conducted at frequencies ranging from 33 to 9995 Hz and at temperatures in the 1.7 to 10 K range revealed that the application of a static magnetic field induces a slow magnetic relaxation in all three compounds. The complex with the bulkier capping ligand (bathophenanthroline) exhibits the highest energy barrier U/kB = 23 K. This journal is © the Partner Organisations 2014.

Kourtis S.,Solid State Group | Neupert T.,Solid State Group | Chamon C.,Solid State Group | Mudry C.,Solid State Group
Physical Review Letters | Year: 2014

We study two models for spinless fermions featuring topologically nontrivial bands characterized by Chern numbers C=±1 at fractional filling. Using exact diagonalization, we show that, even for infinitely strong nearest-neighbor repulsion, the ground states of these models belong to the recently discovered class of quantum liquids called fractional Chern insulators (FCI). Thus, we establish that FCI states can arise even if interaction strengths are arbitrarily larger than the noninteracting band gap, going beyond the limits in which FCI states have been previously studied. The strong-coupling FCI states, therefore, depart from the usual isolated-band picture that parallels the fractional quantum Hall effect in Landau levels and demonstrate how a topologically ordered state can arise in a truly multiband system. © 2014 American Physical Society.

Ba0.6Sr0.4Ti0.99Fe0.01O 3 films were deposited by Pulsed Laser Deposition (PLD) technique on two different substrates viz. Pt/Si and quartz, which were ex situ annealed at 700 °C in normal air atmosphere. The formation of single phase with perovskite structure and nanosize surface morphology of the films was ascertained by X-ray Diffraction studies and Atomic Force Microscopy (AFM) respectively. The detailed electrical properties like dielectric constant, loss tangent and tunability at low frequency were measured. The dielectric properties at microwave frequencies are also investigated in order to find suitability of the films for microwave tunable device applications. With the substitution of Fe3+ at B-site (1 mol%), the dielectric loss has been brought down due to better compensation of charges in the composition to 0.003 (measured at 11.06 GHz) in BST system. The optical properties of the film were also measured and the band gap of the films was calculated to ascertain the dielectric insulating properties. P-E hysteresis loop confirms its paraelectric behavior, which is one of the essential criterion for the films in tunable applications. © 2013 Elsevier B.V. All rights reserved.

Kashyap R.,University of Delhi | Thakur O.P.,Solid State Group | Tandon R.P.,University of Delhi
Ceramics International | Year: 2012

Effect of Gd on microstructural, dielectric and electrical properties has been studied over wide temperature (300-500 K) and frequency range (100 Hz-1 MHz). Gd substitution in CCTO system results in decrease in the grain size and increase of Schottky potential barrier which causes lower value of dielectric constant. The dielectric constant remains nearly constant in temperature range 300-350 K. Doped samples show lower dielectric loss in middle frequency range (∼10 kHz-1 MHz) at room temperature. The AC conductivity (σ ac) obeys a power law, σ ac = Af n, where n is temperature dependent frequency exponent. The AC conductivity behaviour can be divided into three regions depending on conduction processes and the relevant charge transport mechanisms have been discussed. © 2011 Elsevier Ltd and Techna Group S.r.l.

Ashiri R.,Islamic Azad University at Dezful | Nemati A.,Sharif University of Technology | Sasani Ghamsari M.,Solid State Group
Ceramics International | Year: 2014

In this report, crack-free nanostructured barium titanate thin films are prepared by a sol-gel processing method. Glacial acetic acid, barium acetate, titanium tetraisopropyl alkoxide, 2-propanol and deionized water are used as precursors for preparing stable precursor solution. Then very thin films (thickness=26 nm) are deposited on fused silica substrates. In order to prepare crack-free thin films of BaTiO3, much attention is given to solvent evaporation process and a controlled pre-drying process is developed. It is found that the control of the process, especially in the initial stage of drying process is crucial and important for preparation of the crack-free ultrathin nanostructured BaTiO3 films. In our proposed method, as-deposited thin films undergo a slow drying process in saturated vapor pressure of the precursor solution. The above process leads to the formation of crack-free nanostructured BaTiO3 thin films. Structure and morphology of the thin films are characterized by XRD, SEM and AFM characterization methods. Results indicate that the thin films are crack-free with a dense nanogranular structure. © 2014 Elsevier Ltd and Techna Group S.r.l.

Szalay S.,Solid State Group
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

The main concern of this paper is how to define proper measures of multipartite entanglement for mixed quantum states. Since the structure of partial separability and multipartite entanglement is getting complicated if the number of subsystems exceeds two, one cannot expect the existence of an ultimate scalar entanglement measure, which grasps even a small part of the rich hierarchical structure of multipartite entanglement, and some higher-order structure characterizing that is needed. In this paper we make some steps in this direction. First, we reveal the lattice-theoretic structure of the partial separability classification, introduced earlier [Sz. Szalay and Z. Kökényesi, Phys. Rev. A 86, 032341 (2012)PLRAAN1050-294710.1103/PhysRevA.86.032341]. It turns out that, mathematically, the structure of the entanglement classes is the up-set lattice of the structure of the different kinds of partial separability, which is the down-set lattice of the lattice of the partitions of the subsystems. It also turns out that, physically, this structure is related to the local operations and classical communication convertibility: If a state from a class can be mapped into another one, then that class can be found higher in the hierarchy. Second, we introduce the notion of multipartite monotonicity, expressing that a given set of entanglement monotones, while measuring the different kinds of entanglement, shows also the same hierarchical structure as the entanglement classes. Then we construct such hierarchies of entanglement measures and propose a physically well-motivated one, being the direct multipartite generalization of the entanglement of formation based on the entanglement entropy, motivated by the notion of statistical distinguishability. The multipartite monotonicity shown by this set of measures motivates us to consider the measures to be the different manifestations of some "unified" notion of entanglement. © 2015 American Physical Society.

News Article | December 5, 2011

Britain is relying on the technology sector to drive innovation, attract foreign investment, and get the UK economy back on track. This was the message from the Mayor of London's digital advisor, Kulveer Ranger, speaking at an event held in London's 'Tech City' today. Ranger said the IT community needs to use the opportunity of the London 2012 Olympics, when the spotlight will be turned on the UK, to “set up a shop window and demonstrate our wares”. “London is the engine of the UK economy, but there has been a need to diversify our economy,” said Ranger. “We all know there have been issues in terms of financial institutions; our manufacturing hasn't quite taken off; growth is very small. Technology is the sector. It's not the nice to have, it's a must. “From the Mayor's perspective, we must encourage more business to come here,” he added. “London is such a great city, but sometimes it's hard to get a key message across about why you should be here. Tech City has been a way of conveying that message, of saying look at all the opportunities here, all the infrastructure, all the development that's happening without us doing anything.” While the government is keen to encourage growth and help promote London as a place for technological innovation, it must also be careful not to interfere too much in what is already a competitive, collaborative and self-sustaining ecosystem. “One of the most important things central government is doing is staying out of the way and not messing it up,” said Eric Van Der Kleij, chief executive of the UK government's Tech City Investment Organisation. He added that one of the few things government could usefully do is throw a spotlight on what is happening. “We do have a terrific convening power to be able to do that,” he said. Government is also trying to remove financial barriers for entrepreneurs setting up businesses in the UK. At the beginning of this year it introduced lifetime capital gains tax relief for entrepreneurs, meaning that the first £10 million of capital gain is taxed at just 10 percent. The R&D tax credit also means that companies get 225 percent in tax credit for the investments they make in R&D. Meanwhile, the government is sending out a message to investors with the Enterprise Investment Scheme (EIS), designed to help smaller higher-risk trading companies to raise finance by offering a range of tax reliefs to investors who purchase new shares in those companies. Moreover, all the investments made in 2012 will be free of capital gains tax for one year. “This is one of the most attractive angel investment tax policies globally,” said Van Der Kleij. On the flip side, however, the government's decision to pinpoint Shoreditch as the epicentre of technological innovation in the UK has led to a number of large companies, such as Cisco and Google, setting up offices there. This will inevitably prompt a rise in rental prices and a gentrification of the area – which attracted startups in the first place because of the low cost of office space. Matt Evans, founder of Solid State Group and an “incubator” at office space provider Hoxton Mix, warned that if the area becomes too commercial, startups will move further east and the area will lose its “cool vibe”. But Ranger said the Mayor prefers to think of this development as “regeneration”. “At what point do you become a victim of your own success?” he asked. “At what point is it that an area starts improving and the money is drawn to it because people want to see things improve, they want to see new coffee shops, new bars, better infrastructure. If that helps lift this sector then I wouldn't want to call it gentrification, I'd want to call it regeneration.” For now at least, the area is still attracting startups. Last month the Prime Minister unveiled an interactive map of East London's technology cluster, created by Trampoline Systems and Playgen, revealing more than 600 firms in the area. That number has since grown to over 1,000. “The Tech City map supports the renaissance that is already underway in the Shoreditch area infusing technology, investment and talent into startups in East London”, says Bob Schukai, Global Head of Mobile Technology for Thomson Reuters, which partnered on the map along with Mother, LinkedIn, Cisco and Atos. Meanwhile TechHub, the high-profile shared workspace for technology startups, is growing in another direction. The company recently announced its first development outside of London's ‘Silicon Roundabout’, with TechHub Riga, and has today opened a third office in Prague. “While the TechHub London has been enthusiastically welcomed by the community here and abroad, we want to ensure that this community spirit and support is accessible to technology startups all over the world,” says TechHub co-founder, Elizabeth Varley.

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