Possible inhomogeneous high temperature superconductiity in FeSe at ambient pressure

Sinchenko, A.A.; Grigoriev, P.D.; Orlov, A.P.; Frolov, A.V.; Shakin, A.; Chareev, D.A.; Volkova, O.S.; Vasiliev, A.N.

Авторы: Sinchenko A.A., Grigoriev P.D., Orlov A.P., Frolov A.V., Shakin A., Chareev D.A., Volkova O.S., Vasiliev A.N.
Сборник: MSU-IFW-ILTPE Joint Workshop: Synthesis, Theoretical Examination and Experimental Investigation of Emergent Materials. Book of Abstracts. ISBN 978-5-9909981-3-1
Тезисы
Год издания: 2017
Место издания: ООО "КЛУБ ПЕЧАТИ" Москва
Первая страница: 10
Последняя страница: 10
Аннотация: Based on high quality FeSe single-crystals the micro-bridges oriented parallel and transverse to the layer direction have been fabricated by the focused ion beam (FIB) technique and the measurements of electrical resistance and of current-voltage (IV) characteristics have been done in the conventional 4-probe configuration. The intralayer electronic transport demonstrates conventional behavior: at high current the differential resistance is a square function of voltage because of small Joule heating at all measured temperatures, but close to Tc=8 K we observed excess conductivity (deviation from square law) at low current corresponding the superconducting fluctuations which disappear rapidly and completely absent above T≈13 K. Quite different behavior is observed in the interlayer electronic transport: at high current IV curves follow square dependence but the excess conductivity observed at low current is much more pronounced and, more importantly, observed up to T≈40 K which is near 5 times higher than its zero-resistance superconducting transition temperature. The temperature dependence of the real part of magnetic susceptibility demonstrates appearance additional diamagnetic contribution below the same temperature. Both magnetic and transport measurements indicate the existing inhomogeneous superconductivity in FeSe, most probably in the form of small superconducting inclusions. To explain this effect the theoretical model has been proposed. We show that in a layered conductor with the anisotropy parameter η = σzz/σxx<<1 and small superconducting islands of volume ratio φ<<1 there are two parallel ways of interlayer current: jz ≈ j1+j2 (see Fig. 1), so that the total conductivity σzz tot ≈ σzz (1)+σzz (2). The first, standard way is with almost uniform current density and direction j1(r) perpendicular to the conducting layers. The rare superconducting inclusions then only slightly increase corresponding interlayer conductivity σzz (1) proportionally to their volume ratio, and σzz (1) ~ ησxx. The second way of interlayer current is via superconducting islands. Since these islands are rare, the major part of the current path goes in the normal phase. But instead of flowing along the external field Ez, the current j2 between the superconducting islands flows along the highly conducting layers until it comes to another island which allows next lift in the interlayer direction. Using Maxwell approximation the expression for interlayer conductivity has been obtained. We show that if inhomogeneous superconductivity in an anisotropic conductor first appears in the form of isolated superconducting islands, it reduces electric resistivity anisotropically with maximal effect along the least conducting axis [1]. This property provides a simple and very general tool to detect inhomogeneous superconductivity in various anisotropic compounds and this method may be applicable to almost all high-temperature superconductors, which have layered anisotropic crystal structure.
Добавил в систему: Чареев Дмитрий Александрович

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