Surface-stress-induced Mott transition and nature of associated spatial phase transition in single crystalline VO2 nanowires.

We demonstrate that the Mott metal-insulator transition (MIT) in single crystalline VO(2) nanowires is strongly mediated by surface stress as a consequence of the high surface area to volume ratio of individual nanowires. Further, we show that the stress-induced antiferromagnetic Mott insulating phase is critical in controlling the spatial extent and distribution of the insulating monoclinic and metallic rutile phases as well as the electrical characteristics of the Mott transition. This affords an understanding of the relationship between the structural phase transition and the Mott MIT.

Direct observation of the structural component of the metal-insulator phase transition and growth habits of epitaxially grown VO2 nanowires.

We have grown epitaxially orientation-controlled monoclinic VO2 nanowires without employing catalysts by a vapor-phase transport process. Electron microscopy results reveal that single crystalline VO2 nanowires having a [100] growth direction grow laterally on the basal c plane and out of the basal r and a planes of sapphire, exhibiting triangular and rectangular cross sections, respectively. In addition, we have directly observed the structural phase transition of single crystalline VO2 nanowires between the monoclinic and tetragonal phases which exhibit insulating and metallic properties, respectively, and clearly analyzed their corresponding relationships using in situ transmission electron microscopy.

Superradiance: exploiting quantum phase transition in the real world

Superradiance (SR), or cooperative spontaneous emission, has been predicted by R. Dicke before the invention of the laser. During the last few years one can see a renaissance of both experimental and theoretical studies of the superradiant phase transition in a variety of media, ranging from quantum dots and Bose condensates through to black holes. Until recently, despite of many years of research, SR has been considered as a phenomenon of pure scientific interest without obvious potential applications. However, recent investigations of the femtosecond SR emission generation from semiconductors have opened up some practical opportunities for the exploitation of this quantum optics phenomenon. Here we present a brief review of some features, advantages and potential applications of the SR generation from semiconductor laser structures

Intrinsic spin hall effect induced by quantum phase transition in HgCdTe quantum wells

The spin Hall effect can be induced by both extrinsic impurity scattering and intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. By tuning the Cd content, the well width, or the bias electric field across the quantum well, the intrinsic spin Hall effect can be switched on or off and tuned into resonance under experimentally accessible conditions.

Disentanglement of two qubits coupled to an XY spin chain: Role of quantum phase transition

We study the disentanglement evolution of two spin qubits which interact with a general XY spin-chain environment. The dynamical process of the disentanglement is numerically and analytically investigated in the vicinity of a quantum phase transition (QPT) of the spin chain in both weak and strong coupling cases. We find that the disentanglement of the two spin qubits may be greatly enhanced by the quantum critical behavior of the environmental spin chain. We give a detailed analysis to facilitate the understanding of the QPT-enhanced decaying behavior of the coherence factor. Furthermore, the scaling behavior in the disentanglement dynamics is also revealed and analyzed.

Electric field driven quantum phase transition between band insulator and topological insulator

We demonstrate theoretically that electric field can drive a quantum phase transition between band insulator to topological insulator in CdTe/HgCdTe/CdTe quantum wells. The numerical results suggest that the electric field could be used as a switch to turn on or off the topological insulator phase, and temperature can affect significantly the phase diagram for different gate voltage and compositions. Our theoretical results provide us an efficient way to manipulate the quantum phase of HgTe quantum wells.

Loschmidt echo and Berry phase of a quantum system coupled to an XY spin chain: Proximity to a quantum phase transition

We study the Loschmidt echo (LE) of a coupled system consisting of a central spin and its surrounding environment described by a general XY spin-chain model. The quantum dynamics of the LE is shown to be remarkably influenced by the quantum criticality of the spin chain. In particular, the decaying behavior of the LE is found to be controlled by the anisotropy parameter of the spin chain. Furthermore, we show that due to the coupling to the spin chain, the ground-state Berry phase for the central spin becomes nonanalytical and its derivative with respect to the magnetic parameter lambda in spin chain diverges along the critical line lambda=1, which suggests an alternative measurement of the quantum criticality of the spin chain.