Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

Graphene is a two-dimensional carbon material with a honeycomb lattice and Dirac-like low-energy excitations. When Zeeman and spin-orbit interactions are neglected, its Landau levels are fourfold degenerate, explaining the 4e2/h separation between quantized Hall conductivity values seen in recent experiments. In this Letter we derive a criterion for the occurrence of interaction-driven quantum Hall effects near intermediate integer values of e2/h due to charge gaps in broken symmetry states.

Quantum Hall Ferromagnetism in Graphene

The control and manipulation of the electron spin in semiconductors is central to spintronics, which aims to represent digital information using spin orientation rather than electron charge. Such spin-based technologies may have a profound impact on nanoelectronics, data storage, and logic and computer architectures. Recently it has become possible to induce and detect spin polarization in otherwise non-magnetic semiconductors (gallium arsenide and silicon) using all-electrical structures, but so far only at temperatures below 150 K and in n-type materials, which limits further development. Here we demonstrate room-temperature electrical injection of spin polarization into n-type and p-type silicon from a ferromagnetic tunnel contact, spin manipulation using the Hanle effect and the electrical detection of the induced spin accumulation. A spin splitting as large as 2.9 meV is created in n-type silicon, corresponding to an electron spin polarization of 4.6%. The extracted spin lifetime is greater than 140 ps for conduction electrons in heavily doped n-type silicon at 300 K and greater than 270 ps for holes in heavily doped p-type silicon at the same temperature. The spin diffusion length is greater than 230 nm for electrons and 310 nm for holes in the corresponding materials. These results open the way to the implementation of spin functionality in complementary silicon devices and electronic circuits operating at ambient temperature, and to the exploration of their prospects and the fundamental rules that govern their behaviour.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-008352.pdf

Electrical creation of spin polarization in silicon at room temperature

The unrelated discoveries of quasicrystals and topological insulators have in turn challenged prevailing paradigms in condensed-matter physics. We find a surprising connection between quasicrystals and topological phases of matter: (i) quasicrystals exhibit nontrivial topological properties and (ii) these properties are attributed to dimensions higher than that of the quasicrystal. Specifically, we show, both theoretically and experimentally, that one-dimensional quasicrystals are assigned two-dimensional Chern numbers and, respectively, exhibit topologically protected boundary states equivalent to the edge states of a two-dimensional quantum Hall system. We harness the topological nature of these states to adiabatically pump light across the quasicrystal. We generalize our results to higher-dimensional systems and other topological indices. Hence, quasicrystals offer a new platform for the study of topological phases while their topology may better explain their surface properties.

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Topological States and Adiabatic Pumping in Quasicrystals

The Li–Co–O and Li–Ni–O systems, used as cathodes in lithium ion batteries, have been investigated by means of ab initio calculations and empirical methods. An approach based on ab initio calculati...

Thermodynamic and Electrochemical Properties of the Li–Co–O and Li–Ni–O Systems

Quantum pump in a system with both Rashba and Dresselhaus spin–orbit couplings

Bose-Einstein condensation of finite number of confined particles

Structural stability and magnetic properties of Co-doped or adsorbed polar-ZnO surface

Ballistic transport in extended Datta–Das spin field effect transistors

The study of topological states in electric circuits is developing rapidly recently and forming the field of topoelectrical circuits. As both the loss and gain can be easily introduced and tuned in electric circuits, it permits flexible and accurate fabrications of non-Hermitian systems. Loss is generally considered negative in electric circuits, as it weakens the electrical signals. However, we show here that a non-Hermitian second-order topological phase can be realized in electric circuits by taking advantage of loss. We observe the gapped edge states and in-gap corner states in experiment. Our system provides a readily accessible platform to explore the non-Hermitian-induced topological phases. 

Wen-Ji Deng

Papers

Quantum pump in a system with both Rashba and Dresselhaus spin–orbit couplings

Bose-Einstein condensation of finite number of confined particles

Structural stability and magnetic properties of Co-doped or adsorbed polar-ZnO surface

Ballistic transport in extended Datta–Das spin field effect transistors

Non-Hermitian second-order topology induced by resistances in electric circuits