Abstract:We report the structural and superconducting properties of FeSe0.3Te0.7 (FST) thin films with different thicknesses grown on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the FST films undergo biaxial tensile strains which are fully relaxed for films with thicknesses above 200 nm. Electrical transport measurements reveal that the ultrathin films exhibit an insulating behavior and superconductivity appears for thicker films with Tc saturated above 200 nm. The current-voltage curves around… Show more
“…Since a is inversely proportional to the square root of the density of states at the Fermi energy, this behaviour is expected for systems with very small Fermi energy, as found in FeSe 22 . The Cooper-law is commonly used to describe superconducting thin films but the trends observed in our data are in qualitative agreement with those found in thin films of FeSe 12 , thin flakes of FeSe 0.3 Te 0.7 27 and nanoflakes devices of FeSe fabricated using alternate device fabrication techniques 17,20 .…”
Section: Thickness Dependence Of the Transport Behaviour Of Fese Thinsupporting
FeSe is a unique superconductor that can be manipulated to enhance its superconductivity using different routes, while its monolayer form grown on different substrates reaches a record high temperature for a two-dimensional system. In order to understand the role played by the substrate and the reduced dimensionality on superconductivity, we examine the superconducting properties of exfoliated FeSe thin flakes by reducing the thickness from bulk down towards 9 nm. Magnetotransport measurements performed in magnetic fields up to 16 T and temperatures down to 2 K help to build up complete superconducting phase diagrams of different thickness flakes. While the thick flakes resemble the bulk behaviour, by reducing the thickness the superconductivity of FeSe flakes is suppressed. The observation of the vortex-antivortex unbinding transition in different flakes provide a direct signature of a dominant two-dimensional pairing channel. However, the upper critical field reflects the evolution of the multi-band nature of superconductivity in FeSe becoming highly two-dimensional and strongly anisotropic only in the thin limit. Our study provides detailed insights into the evolution of the superconducting properties of a multi-band superconductor FeSe in the thin limit in the absence of a dopant substrate.
“…Since a is inversely proportional to the square root of the density of states at the Fermi energy, this behaviour is expected for systems with very small Fermi energy, as found in FeSe 22 . The Cooper-law is commonly used to describe superconducting thin films but the trends observed in our data are in qualitative agreement with those found in thin films of FeSe 12 , thin flakes of FeSe 0.3 Te 0.7 27 and nanoflakes devices of FeSe fabricated using alternate device fabrication techniques 17,20 .…”
Section: Thickness Dependence Of the Transport Behaviour Of Fese Thinsupporting
FeSe is a unique superconductor that can be manipulated to enhance its superconductivity using different routes, while its monolayer form grown on different substrates reaches a record high temperature for a two-dimensional system. In order to understand the role played by the substrate and the reduced dimensionality on superconductivity, we examine the superconducting properties of exfoliated FeSe thin flakes by reducing the thickness from bulk down towards 9 nm. Magnetotransport measurements performed in magnetic fields up to 16 T and temperatures down to 2 K help to build up complete superconducting phase diagrams of different thickness flakes. While the thick flakes resemble the bulk behaviour, by reducing the thickness the superconductivity of FeSe flakes is suppressed. The observation of the vortex-antivortex unbinding transition in different flakes provide a direct signature of a dominant two-dimensional pairing channel. However, the upper critical field reflects the evolution of the multi-band nature of superconductivity in FeSe becoming highly two-dimensional and strongly anisotropic only in the thin limit. Our study provides detailed insights into the evolution of the superconducting properties of a multi-band superconductor FeSe in the thin limit in the absence of a dopant substrate.
“…Instability in the form of the voltage jumps was observed recently in FeSeTe thin film on Pb(MgNb)TiO substrate 11 . Only the current drive was used, so that the S-shaped I-V curved cannot be determined.…”
Section: Comparison With Experiments and Discussionmentioning
confidence: 70%
“…The experimental data of FeSeTe in a current driving setup from ref. 11 are fitted best by the following values of parameters: T c0 = 7 K , k = σ n / σ GL = 0.07 and the fluctuation strength parameter ω = 0.01.Figure 3The I-V curves of FeSeTe thin film 11 at different temperatures. The points are the experimental data and the solid lines are the theoretical fitting results.…”
Section: Comparison With Experiments and Discussionmentioning
confidence: 99%
“…The I-V curves of FeSeTe thin film 11 at different temperatures. The points are the experimental data and the solid lines are the theoretical fitting results.…”
Section: Comparison With Experiments and Discussionmentioning
We develop a nonlinear theory of the electronic transport in superconductors in the framework of the time-dependent Ginzburg-Landau (TDGL) equation. We utilize self-consistent Gaussian approximation and reveal the conditions under which the current-voltage V(I) dependence (I-V characteristics) acquires an S-shape form leading to switching instabilities. We demonstrate that in two-dimensions the emergence of such an instability is a hallmark of the Berezinskii-Kosterlitz-Thouless (BKT) transition that we have detected by transport measurements of titanium nitride (TiN) films. Our theoretical findings compare favorably with our experimental results.
“…The effects of biaxial strain have been frequently explored due to the surprising responses obtained when it comes to properties' modulation, which ranges from induction of dielectric anomalies 19 to bandgap engineering 20 . To control the amount of induced strain, substrates with different mismatches with the films are usually employed 21 . The application of an electric field to a piezoelectric substrate has also been used to induce biaxial strain and modulate specific properties 22 .…”
Ultrathin films of perovskites have attracted considerable attention once they fit in numerous applications. Over the years, controlling and tuning their properties have been attainable when biaxial strain is applied. Through ab initio DFT calculations, (110) ultrathin (Na,K)TaO 3 films were submitted to biaxial tensile and compressive strain. Intrinsically, surface Ta shallow states emerge into the bandgap since the (110) cleavage breaks its octahedral symmetry to create TaO 4 units. Removal of ligands along the x-y plane stabilizes d x 2-y 2 orbitals, which decrease in energy due to lower electrostatic repulsion. Such stabilization is maximized when biaxial tensile increases the TaO 4 planarity towards a square planar symmetry. Accordingly, the corresponding electronic levels move further into the bandgap. Conversely, compressive biaxial strain intensifies electrostatic repulsion, closing the TaO 4 tetrahedra, and surface states move to higher energy zones. The reported strain-driven modulation might be applied in different applications, as photocatalysis, ferroelectricity, and spintronics.
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