We report a successful observation of pressure-induced superconductivity in a topological compound Bi 2 Te 3 with T c of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the holetype carrier in the pressure-induced superconducting Bi 2 Te 3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi 2 Te 3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor.high-pressure effects | pressure-tuned conductivity | topological superconductors U tilizing high pressure can be a very powerful method to generate new materials states, as demonstrated by either highpressure synthesis of new compounds, or pressure-tuned unique electronic states, such as insulator metal transitions. High pressure is particularly effective in tuning superconductivity as it is well documented that the record high superconducting transition temperature T c for either elements (1) or compounds (2) is created with the application of pressure. Recently, topological insulators (TIs) have generated great interest in the area of condensed matter physics (3-8). These materials have an insulating gap in the bulk, while also possessing conducting gapless edges or surface states in the boundaries that are protected by the timereversal symmetry (8, 9). Similar to TIs, topological superconductors have a full pairing gap in the bulk and gapless Majorana states on the edge or surface (10-13, 18). Majorana Fermions (14), half of ordinary Dirac fermions, could be very useful in topological quantum computing (15-17), which is proscriptive for new concept information technology.

Shape memory and ferromagnetic shape memory effects in single-crystal Ni 2 MnGa thin films Heusler alloy Mn 2 NiGa has been developed by synthesizing a series of ferromagnetic shape memory alloys Mn 25+x Ni 50−x Ga 25 ͑x = 0-25͒. Mn 2 NiGa exhibits a martensitic transformation around room temperature with a large thermal hysteresis up to 50 K and a lattice distortion as large as 21.3% and has a quite high Curie temperature of 588 K. The martensite shows a high-saturated field up to 2 T. The excellent two-way shape memory behavior with a strain of 1.7% was observed in the single crystal Mn 2 NiGa. The magnetic-field-controlled effect created a total strain up to 4.0% and changed the sign of the shape deformation effectively.

Both experimental and theoretical studies have been carried out to study the structure and magnetic properties of Mn 2 NiGa alloys. We have found, instead of forming L2 1 structure where both A and C sites are occupied by Mn atoms, the alloy favor a structure where the C site is occupied by Ni atoms and Mn atoms at A and B sites. The electronic structures of both cubic austenite and tetragonal martensite Mn 2 NiGa were calculated by self-consistent full-potential linearized-augmented plane-wave ͑FP-LAPW͒ method. Austenite Mn 2 NiGa materials show ferrimagnetism due to antiparallel but unbalanced magnetic moments of Mn atoms at A and B sublattices. The magnetic moment of Mn atoms decrease greatly upon martensitic transformation to a tetragonal structure with a 50% reduction in Mn moments at the A site and almost completely suppressed Mn moments at B sites. Consequently, martensite Mn 2 NiGa alloys show ferromagnetic coupling. Different magnetic orderings in martensite and austenite also lead to very different temperature dependence, with which the abnormal behavior of magnetization upon martensitic transformation can be understood. In the offstoichiometric samples with composition between Ni 2 MnGa and Mn 2 NiGa, we show that additional Mn atoms that substitute for Ni atoms in Ni 2 MnGa have the same magnetic behaviors as Mn in Mn 2 NiGa phase, which successfully explains the dependence of the magnetization on Mn composition.