94,805 research outputs found

    Photoemission Spectroscopy of Magnetic and Non-magnetic Impurities on the Surface of the Bi2_2Se3_3 Topological Insulator

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    Dirac-like surface states on surfaces of topological insulators have a chiral spin structure that suppresses back-scattering and protects the coherence of these states in the presence of non-magnetic scatterers. In contrast, magnetic scatterers should open the back- scattering channel via the spin-flip processes and degrade the state's coherence. We present angle-resolved photoemission spectroscopy studies of the electronic structure and the scattering rates upon adsorption of various magnetic and non-magnetic impurities on the surface of Bi2_2Se3_3, a model topological insulator. We reveal a remarkable insensitivity of the topological surface state to both non-magnetic and magnetic impurities in the low impurity concentration regime. Scattering channels open up with the emergence of hexagonal warping in the high-doping regime, irrespective of the impurity's magnetic moment.Comment: 5 pages, 4 figure

    Superconducting energy gap in MgCNi3 single crystals: Point-contact spectroscopy and specific-heat measurements

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    Specific heat has been measured down to 600 mK and up to 8 Tesla by the highly sensitive AC microcalorimetry on the MgCNi3 single crystals with Tc ~ 7 K. Exponential decay of the electronic specific heat at low temperatures proved that a superconducting energy gap is fully open on the whole Fermi surface, in agreement with our previous magnetic penetration depth measurements on the same crystals. The specific-heat data analysis shows consistently the strong coupling strength 2D/kTc ~ 4. This scenario is supported by the direct gap measurements via the point-contact spectroscopy. Moreover, the spectroscopy measurements show a decrease in the critical temperature at the sample surface accounting for the observed differences of the superfluid density deduced from the measurements by different techniques

    Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals

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    The lower (Hc1H_{c1}) and upper (Hc2H_{c2}) critical fields of Mg1−x_{1-x}Alx_{x}B2_2 single crystals (for x=0x = 0, 0.1 and ≳0.2\gtrsim 0.2) have been deduced from specific heat and local magnetization measurements, respectively. We show that Hc1H_{c1} and Hc2H_{c2} are both decreasing with increasing doping content. The corresponding anisotropy parameter ΓHc2(0)=Hc2ab(0)/Hc2c(0)\Gamma_{H_{c2}}(0) = H^{ab}_{c2}(0)/H^c_{c2}(0) value also decreases from ∌5\sim 5 in pure MgB2_2 samples down to ∌1.5\sim 1.5 for x≳0.2x \gtrsim 0.2 whereas ΓHc1(0)=Hc1c(0)/Hc1ab(0)\Gamma_{H_{c1}}(0)=H^c_{c1}(0)/H^{ab}_{c1}(0) remains on the order of 1 in all samples. The small and large gap values have been obtained by fitting the temperature dependence of the zero field electronic contribution to the specific heat to the two gap model for the three Al concentrations. Very similar values have also been obtained by point contact spectroscopy measurements. The evolution of those gaps with Al concentration suggests that both band filling and interband scattering effects are present

    Soliton Resonances for MKP-II

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    Using the second flow - the Derivative Reaction-Diffusion system, and the third one of the dissipative SL(2,R) Kaup-Newell hierarchy, we show that the product of two functions, satisfying those systems is a solution of the modified Kadomtsev-Petviashvili equation in 2+1 dimension with negative dispersion (MKP-II). We construct Hirota's bilinear representation for both flows and combine them together as the bilinear system for MKP-II. Using this bilinear form we find one and two soliton solutions for the MKP-II. For special values of parameters our solution shows resonance behaviour with creation of four virtual solitons. Our approach allows one to interpret the resonance soliton as a composite object of two dissipative solitons in 1+1 dimensions.Comment: 11 pages, 2 figures, Talk on International Conference "Nonlinear Physics. Theory and Experiment. III", 24 June-3 July, 2004, Gallipoli(Lecce), Ital

    Integrable model of interacting XX and Fateev-Zamolodchikov chains

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    We consider the exact solution of a model of correlated particles, which is presented as a system of interacting XX and Fateev-Zamolodchikov chains. This model can also be considered as a generalization of the multiband anisotropic t−Jt-J model in the case we restrict the site occupations to at most two electrons. The exact solution is obtained for the eigenvalues and eigenvectors using the Bethe-ansatz method.Comment: 10 pages, no figure
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