La politique de transition vers une industrie des TIC sobre en carbone en Chine

International audienceSince 1997, Chongqing’s urban development model has been closely linked to the implementation of the central government’s strategy. After a first stage based on heavy industry, the government has encouraged a transition toward ICT industry limited to manufacturing. However, ICTs are an important part of the environmental problems faced by China and the world. Confronted with a growing environmentalist pressure, the government has decided to organize the transition to an ICT industry with low environmental impact, and to make of Chongqing the laboratory of this new industrial strategy. This article presents the first steps of this transition policy by highlighting the drivers and barriers to change.Depuis 1997, le modèle de développement urbain de Chongqing dépend étroitement de la mise en oeuvre de la stratégie du Gouvernement central. Après un premier stade basé sur l'industrie lourde, le gouvernement y a encouragé une première transition vers l'industrie des TIC, limitée aux départements de fabrication. Or l'industrie des TIC représente une part importante des problèmes environnementaux de la Chine et du monde. Face à une pression environnementaliste croissante, l'État a décidé d'organiser la transition vers une industrie des TIC à faible impact environnemental et de faire de Chongqing le laboratoire de cette nouvelle stratégie industrielle.Ce papier présente les premiers pas de cette politique de transition en mettant en évidence les leviers et les freins au changement

Quantum Anomalous Hall Effect in Hg1−y_{1-y}Mny_{y}Te Quantum Wells

The quantum Hall effect is usually observed when the two-dimensional electron gas is subjected to an external magnetic field, so that their quantum states form Landau levels. In this work we predict that a new phenomenon, the quantum anomalous Hall effect, can be realized in Hg$_{1-y}$Mn$_{y}$Te quantum wells, without the external magnetic field and the associated Landau levels. This effect arises purely from the spin polarization of the $Mn$ atoms, and the quantized Hall conductance is predicted for a range of quantum well thickness and the concentration of the $Mn$ atoms. This effect enables dissipationless charge current in spintronics devices.Comment: 5 pages, 3 figures. For high resolution figures see final published version when availabl

Model Hamiltonian for Topological Insulators

In this paper we give the full microscopic derivation of the model Hamiltonian for the three dimensional topological insulators in the $Bi_2Se_3$ family of materials ($Bi_2Se_3$, $Bi_2Te_3$ and $Sb_2Te_3$). We first give a physical picture to understand the electronic structure by analyzing atomic orbitals and applying symmetry principles. Subsequently, we give the full microscopic derivation of the model Hamiltonian introduced by Zhang {\it et al} [\onlinecite{zhang2009}] based both on symmetry principles and the ${\bf k}\cdot{\bf p}$ perturbation theory. Two different types of $k^3$ terms, which break the in-plane full rotation symmetry down to three fold rotation symmetry, are taken into account. Effective Hamiltonian is derived for the topological surface states. Both the bulk and the surface models are investigated in the presence of an external magnetic field, and the associated Landau level structure is presented. For more quantitative fitting to the first principle calculations, we also present a new model Hamiltonian including eight energy bands.Comment: 18 pages, 9 figures, 5 table

Active thermal metasurfaces for remote heating/cooling by mimicking negative thermal conductivity

Remote temperature control can be obtained by a long-focus thermal lens that can focus heat fluxes into a spot far away from the back surface of the lens and create a virtual thermal source/sink in the background material, around which the temperature field distribution can be remotely controlled by changing the parameters of the thermal lens. However, due to the lack of negative thermal conductivity, the existing thermal lenses have extremely short focal lengths and cannot be used to remotely control the temperature field around the virtual thermal source/sink. In this study, we theoretically propose a general approach to equivalently realize negative thermal conductivity by elaborately distributed active thermal metasurface (ATMS), then use the proposed ATMS to implement a novel thermal lens with long focal length designed by transformation thermodynamics, and experimentally verify the performance of the designed long-focus thermal lens with measured focal length f=19.8mm for remote heating/cooling. The proposed method expands the scope of the thermal conductivity and open up new ways to realize unprecedented thermal effects with effective negative thermal conductivity, such as "thermal surface plasmon polaritons", thermal superlens, thermal tunneling effect, and thermal invisible gateway