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Register a new userSuperconductivity and Superconductor-Insulator Transition in Single Crystal Sb2Te3 Nanoflakes
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Added by
Sergey Harutyunyan Ruben
Publication date
2016
fields
Physics
and research's language is
English
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We report on transport properties of the topological insulator single crystal $Sb2Te3$ nanoflakes with thickness about from 7 to 50nm. A steep drop of resistance is appeared near $3K$ in the ultrathin $Sb2Te3$ nanoflakes, manifesting a superconducting transition.The magnetic field induced superconductor insulator transition of disordered 2D superconductor system is observed in the nanoflakes.The results show that the existence of certain optimum degree of disorder is a necessary condition for emergence of superconductivity.Temperature dependence of magneto-resistance shows a consecutive transformation of weak antilocalization cusp into the superconducting transition at low field when $B < BC$.
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Andreev reflection spectroscopy with unpolarized and highly spin-polarized currents has been utilized to study an intermetallic single-crystal superconductor NiBi3. Magnetoresistance at zero bias voltage of point contacts shows the occurrence and suppression of Andreev reflection by unpolarized and polarized current, respectively. The gap value, its symmetry and temperature dependence have been determined using an unpolarized current. The spin state in the NiBi3 sample is determined to be antiparallel using a highly spin-polarized current. The gap value 2Delta/kBT, gap symmetry and its temperature dependence, combined with the antiparallel spin state show that the bulk NiBi3 is a singlet s-wave superconductor.
Superconductivity in the vicinity of a competing electronic order often manifests itself with a superconducting dome, centred at a presumed quantum critical point in the phase diagram. This common feature, found in many unconventional superconductors, has supported a prevalent scenario that fluctuations or partial melting of a parent order are essential for inducing or enhancing superconductivity. Here we present a contrary example, found in IrTe2 nanoflakes of which the superconducting dome is identified well inside the parent stripe charge ordering phase in the thickness-dependent phase diagram. The coexisting stripe charge order in IrTe2 nanoflakes significantly increases the out-of-plane coherence length and the coupling strength of superconductivity, in contrast to the doped bulk IrTe2. These findings clarify that the inherent instabilities of the parent stripe phaseare sufficient to induce superconductivity in IrTe2 without its complete or partial melting. Our study highlights the thickness control as an effective means to unveil intrinsic phase diagrams of correlated vdW materials.
The superconductor-insulator transition of ultrathin films of bismuth, grown on liquid helium cooled substrates, has been studied. The transition was tuned by changing both film thickness and perpendicular magnetic field. Assuming that the transition is controlled by a T=0 critical point, a finite size scaling analysis was carried out to determine the correlation length exponent v and the dynamical critical exponent z. The phase diagram and the critical resistance have been studied as a function of film thickness and magnetic field. The results are discussed in terms of bosonic models of the superconductor-insulator transition, as well as the percolation models which predict finite dissipation at T=0.
Experimental results of I-V characteristics near the superconductor-insulator transition observed for disorder-tuned YBaCuO thinfilms are presented. The I-V characteristics exibit new quasiperiodic structures as a function of the current. The current interval, the number of the dI/dV peaks, and the magnetic field dependence of the peaks are consistent with the theoretical predictions of the resonant tunneling of a phase particle ina tilted-cosine potential for asingle Josephson junction with small capacitance.
In high temperature cuprate superconductors, it is now generally agreed that the parent compound is a Mott insulator and superconductivity is realized by doping the antiferromagnetic Mott insulator. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. It has been proposed theoretically that the parent compound of the iron-based superconductors may be on the verge of a Mott insulator, but so far no clear experimental evidence of doping-induced Mott transition has been available. Here we report an electronic evidence of an insulator-superconductor transition observed in the single-layer FeSe films grown on the SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with the increasing doping. This observation represents the first example of an insulator-superconductor transition via doping observed in the iron-based superconductors. It indicates that the parent compound of the iron-based superconductors is in proximity of a Mott insulator and strong electron correlation should be considered in describing the iron-based superconductors.
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