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Detection of structural and transport inhomogeneities in superconducting thin films using the standard four-probe method requires multiple measurements and may be inaccurate. A new approach to extract the information about the inhomogeneous transition into the superconducting state using van der Pauw technique is presented. The proposed method is applied to an electrochemically-reduced In-Sn-oxide (ITO) films known to be simultaneously transparent and superconducting. Relationship between the processing parameters and superconducting characteristics of the ITO films is considered, and prospects for using such samples in integrated photonic-superconducting chips for quantum-information processing are discussed. [ABSTRACT FROM AUTHOR]

A superconductor-insulator transition (SIT) in two dimensions is a prototypical quantum phase transition (QPT) with a clear quantum critical point (QCP) at zero temperature (T = 0). The SIT is induced by a field B and observed in disordered thin films. In some of weakly disordered or crystalline thin films, however, an anomalous metallic (AM) ground state emerges over a wide B range between the superconducting and insulating phases. It remains a fundamental open question how the QPT picture of the SIT is modified when the AM state appears. Here we present measurements of the Nernst effect N, which has great sensitivity to the fluctuations of the superconducting order parameter. From a thorough contour map of N in the B-T plane, we found a thermal-to-quantum crossover line of the superconducting fluctuations, a so-called ghost-temperature line associated with the QPT, as well as a ghost-field line associated with a thermal transition. The QCP is identified as a T = 0 intercept of the ghost-temperature line inside the AM state, which verifies that the AM state is a broadened critical state of the SIT. The authors present Nernst measurements on a 2D film of amorphous MoxGe1−x, which shows a magnetic-field-induced superconductor-metal-insulator transition. The intermediate metal phase is known as the "anomalous metal" (AM) state. The authors conclude that the AM state originates from broadening of the superconductor-insulator transition. [ABSTRACT FROM AUTHOR]

YBa2Cu3Ox (YBCO) thin films were deposited on 14°–22° tilted-axes NdGaO3 (NGO) substrates with pulsed laser deposition. Two orientations of the film are possible due to the presence of symmetrically equivalent (110) and (1 − 1 0) facets on the substrate surface. At high deposition rates, the pseudo-a grains, (100)YBCO||(110)NGO, gradually overgrow the pseudo-c grains, (001)YBCO||(110)NGO, forming high-tilted (tilt angle of the c axis 69°–74°) YBCO films. The substrate tilt angles in the vicinity of 18.43° promote formation of high-tilted films as a result of graphoepitaxial seeding of the pseudo-a grains on the (110) facets on the substrate surface due to the matching of the c lattice constant of the film with the length of the (110) terraces on the substrate surface. The effect of graphoepitaxial seeding was observed for the substrate tilt angles in the range 16°–21°, probably due to undulating edges of steps on the substrate surface. An increase of the deposition rate above a threshold level of ~ 3 nm/s results in a change of the growth mode with the formation of films with smooth surface morphology. The probable reason is a transition from vapor phase epitaxy to vapor–liquid–solid crystallization mechanism. The tilted-axes YBCO films demonstrate superconducting transition temperature superior to standard samples fabricated on (110) NGO substrates. The width of the superconducting transition for tilted-axes films increases due to the suppression of the critical current in the direction normal to the tilt axis. [ABSTRACT FROM AUTHOR]

A set of granular SmFeAsO1-xFx films were synthesized on LaAlO3 substrates with different percentage of the coverage of the substrate surface, and then their electrical properties were studied. At high temperatures, as the substrate coverage is increased, the films go from an insulating to a metallic behavior; and then, at low temperatures, the films that present a resistance RN of few kOhms in the normal state show a transition to the superconducting state with a width in the R(T) curves that changes with the coverage of the substrate surface. The line shape of these curves can be explained by the Ambegaokar-Halperin (AH) model of the resistance produced by the thermal activated phase slippage at the intergranular junctions if the dimensionality for the films is presumed appropriately. For the thicker films, that can be considered as a 3D network of the Josephson junctions, a temperature dependence of the AH parameter γ given by ∼ A(1 − t)3/2, fits the R(T) curve satisfactorily. However, for the films that cover the surface of the substrates only partially, the AH model fits the R(T) curves only if γ ~ A´(1 − t2)2, which is suitable for a 2D network of the Josephson junctions. [ABSTRACT FROM AUTHOR]

The recent discovery of superconductivity in infinite-layer nickelates generates tremendous research endeavors, but the ground state of their parent compounds is still under debate. Here, we report experimental evidence for the dominant role of Kondo scattering in the underdoped Nd1−xSrxNiO2 thin films. A resistivity minimum associated with logarithmic temperature dependence in both longitudinal and Hall resistivities are observed in the underdoped Nd1−xSrxNiO2 samples before the superconducting transition. At lower temperatures down to 0.04 K, the resistivities become saturated, following the prediction of the Kondo model. A linear scaling behavior |$\sigma _{{\boldsymbol{xy}}}^{{{\bf AHE}}}{\rm{\ }}\sim{\rm{\ }}{\sigma }_{{\boldsymbol{xx}}}$| between anomalous Hall conductivity |$\sigma _{{\boldsymbol{xy}}}^{{\bf{AHE}}}$| and conductivity |${\sigma }_{{\boldsymbol{xx}}}{\rm{\ }}$| is revealed, verifying the dominant Kondo scattering at low temperature. The effect of weak (anti-)localization is found to be secondary. Our experiments can help in clarifying the basic physics in the underdoped Nd1−xSrxNiO2 infinite-layer thin films. [ABSTRACT FROM AUTHOR]

The rising interest in increased manufacturing maturity of quantum processing units is pushing the development of alternative superconducting materials for semiconductor fab process technology. However, these are often facing CMOS process incompatibility. In contrast to common CMOS materials, such as Al, TiN, and TaN, reports on the superconductivity of other suitable transition-metal nitrides are scarce, despite potential superiority. Here, we demonstrate fully CMOS-compatible fabrication of HfN and ZrN thin films on state-of-the-art 300 mm semiconductor process equipment, utilizing reactive DC magnetron sputtering on silicon wafers. Measurement of mechanical stress and surface roughness of the thin films demonstrates process compatibility. We investigated the materials phase and stoichiometry by structural analysis. The HfN and ZrN samples exhibit superconducting phase transitions with critical temperatures up to 5.84 and 7.32 K, critical fields of 1.73 and 6.40 T, and coherence lengths of 14 and 7 nm, respectively. A decrease in the critical temperature with decreasing film thickness indicates mesoscopic behavior due to geometric and grain-size limitations. The results promise a scalable application of HfN and ZrN in quantum computing and related fields. [ABSTRACT FROM AUTHOR]

In the framework of the London model, a computer simulation has been performed and the magnetic field distribution in a thin film of type II superconductor has been found, taking into account changes in the magnetic field inhomogeneity of the irregular vortex lattice. It is shown that the line shape changes significantly depending on the vortex lattice irregularity. This change should be taken into account when interpreting the experimental data on the observation of the local magnetic field; consideration of this circumstance can change the conclusions regarding the type of vortex lattice and the parameters of the superconductor. [ABSTRACT FROM AUTHOR]

The evolution of the structural and transport properties of underdoped La 1.952 Sr 0.048 CuO 4 thin films under a compressive epitaxial strain has been studied. The films of different thicknesses d (from 26 nm to 120 nm) were deposited using an insulating target. The onset of superconductivity in the films is observed at temperatures as high as 26 K, while small residual resistance persists at low temperatures, indicating that superconductivity is inhomogeneous. The resistance measured under a perpendicular magnetic field saturates below about 0.65 K, suggesting a possible existence of nonconventional metallic state. The magnetic-field-tuned quasi-superconductor to insulator transition is observed at a magnetic field of about 32 T. [ABSTRACT FROM AUTHOR]

We report on electrical gating of superconducting bilayer NbSe2 using dual-gate field-effect transistors constructed by the van der Waals assembly of mechanically exfoliated NbSe2 and SrTiO3 thin films grown by molecular beam epitaxy. Charge carrier doping, but not a pure electric field, was found to induce changes to the superconducting resistive transition, reaching a 190 mK modulation of the critical temperature and excluding the Rashba effect. The phase space for the superconducting state beyond the Pauli limit under in-plane magnetic fields expands when the critical temperature is enhanced. Quantitative comparison with theory suggests the presence of intervalley scattering, which competes with Ising spin–orbit coupling to set the superconducting-normal phase boundary. The gating method demonstrated here may be applied to study other van der Waals layered superconductors. [ABSTRACT FROM AUTHOR]

We have investigated the correlation between structural and transport properties in sputtered β -FeSe films grown onto SrTiO 3 (100). The growth parameters, such as substrate temperature and thickness, have been varied in order to explore different regimes. In the limit of textured thick films, we found promising features like an enhanced T c ∼ 12 K, a relatively high H c 2 , and a low anisotropy. By performing magnetoresistance and Hall coefficient measurements, we investigate the influence of the disorder associated with the textured morphology on some features attributed to subtle details of the multiband electronic structure of β -FeSe. Regarding the superconductor-insulator transition induced by reducing the thickness, we found a nontrivial evolution of the structural properties and morphology associated with a strained initial growth and the coalescence of grains. Finally, we discuss the origin of the insulating behavior in high-quality stressed epitaxial thin films. We found that a lattice distortion, described by Poisson's coefficient associated with the lattice parameters a and c, may play a key role. [ABSTRACT FROM AUTHOR]

Superconducting high entropy alloys (HEAs) may combine extraordinary mechanical properties with robust superconductivity. They are suitable model systems for the investigation of the interplay of disorder and superconductivity. Here, we report on the superconductivity in (TaNb)1-x(ZrHfTi)x thin films. Beyond the near-equimolar region, the films comprise hundreds-of-nanometer-sized crystalline grains and show robust bulk superconductivity. However, the superconducting transitions in these nanocomposites are dramatically suppressed in the near-equimolar configurations, i.e., 0.45 < x < 0.64, where elemental distributions are equivalently homogeneous. Crystal/glass high entropy alloy nanocomposite phase separation was observed for the films in the near-equimolar region, which yields a broadened two-step normal to superconducting transition. Furthermore, the diamagnetic shielding in these films is only observed far below the onset temperature of superconductivity. As these unusual superconducting transitions are observed only in the samples with the high mixing entropy, this compositional range influences the collective electronic properties in these materials. High entropy alloys are multielement materials exhibiting enhanced properties compared to their binary or ternary equivalents. Here, the authors investigate the influence of microstructure and elemental distribution on the transport and superconducting properties of (TaNb)1-x(ZrHfTi)x thin films. [ABSTRACT FROM AUTHOR]

The possible connection between superconductivity and polar order in SrTiO3 has been discussed extensively in the recent literature. Here, the thickness dependence of the superconducting and ferroelectric transitions in strained, epitaxial films of SrTiO3 films is studied. Both superconductivity and ferroelectricity are absent in thinner films (25 nm and below). We discuss the possible origins of the thickness dependence of both phenomena. [ABSTRACT FROM AUTHOR]

We report the effect of the ab-plane magnetic field B up to 8 T on the resistivity ρ(T) and fluctuation conductivity σ′'(T) in YBa2Cu3O7-δ thin films. As expected, up to ∼ 2.5 T the magnetic field monotonously increases ρ, the width of the resistive transition, ΔTc, and coherence length along the c axis, ξC(0), but decreases both Tc and the range of superconducting (SC) fluctuations ΔTfl. The fluctuation conductivity exhibits a crossover at characteristic temperature T0 from the 3D Aslamasov-Larkin (AL) theory near Tc to the 2D fluctuation theory of Maki-Thompson (MT). However, at B = 3 T, the MT term is completely suppressed, and above T0 σ′'(T) is unexpectedly described by the fluctuation contribution of 2D AL, suggesting the formation of a 2D vortex lattice in the film under the action of a magnetic field. At the same time, ΔTf sharply increases by a factor of about 7, and ξC(0) demonstrates a very unusual dependence on Tc when B increases above 3 T. Our results demonstrate the possibility of the formation of a vortex state in YBCO and its evolution with increasing B. [ABSTRACT FROM AUTHOR]

Herein, DC magnetization measurements of high‐quality single crystals of optimally doped YBa2Cu3O7−δ(YBCO) superconductor are reported on. The temperature and orientation dependence of the magnetic penetration depth λ(T,θ) for single‐crystal YBCO is estimated from the slope of the linear M(lnH) dependence in the London regime. The penetration depth is strongly anisotropic. Also, the electrical resistivity as a function of temperature in YBCO thin film deposited by laser ablation on the SrTiO3 substrate face is investigated around the superconducting transition region under various values of the magnetic field up to 14 T. In this work, based on the resistivity measurements, the upper critical magnetic field for both directions B∥c‐axis and B⊥c‐axis is determined with a DC weak transport current density by using 90% criteria of the normal‐state resistivity value. According to the relations Bc2∥c=ϕ02πξ∥2 and Bc2⊥c=ϕ02πξ∥ξ⊥, the coherence length ξ∥(0) and ξ⊥(0) is determined, where ϕ0 is the magnetic flux quantum. The anisotropy parameter is calculated and analyzed within the frame of Ginzburg–Landau theory. This result indicates that anisotropy is more evident in YBCO. [ABSTRACT FROM AUTHOR]

Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7âˆ' x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (∼130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of ∼180Âş with the layer plane. The value of the Curie temperature T Curie estimated using the Curieâ€"Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect. [ABSTRACT FROM AUTHOR]

Herein, DC magnetization measurements of high‐quality single crystals of optimally doped YBa2Cu3O7−δ(YBCO) superconductor are reported on. The temperature and orientation dependence of the magnetic penetration depth λ(T,θ) for single‐crystal YBCO is estimated from the slope of the linear M(lnH) dependence in the London regime. The penetration depth is strongly anisotropic. Also, the electrical resistivity as a function of temperature in YBCO thin film deposited by laser ablation on the SrTiO3 substrate face is investigated around the superconducting transition region under various values of the magnetic field up to 14 T. In this work, based on the resistivity measurements, the upper critical magnetic field for both directions B∥c‐axis and B⊥c‐axis is determined with a DC weak transport current density by using 90% criteria of the normal‐state resistivity value. According to the relations Bc2∥c=ϕ02πξ∥2 and Bc2⊥c=ϕ02πξ∥ξ⊥, the coherence length ξ∥(0) and ξ⊥(0) is determined, where ϕ0 is the magnetic flux quantum. The anisotropy parameter is calculated and analyzed within the frame of Ginzburg–Landau theory. This result indicates that anisotropy is more evident in YBCO. [ABSTRACT FROM AUTHOR]

Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7âˆ' x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (∼130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of ∼180Âş with the layer plane. The value of the Curie temperature T Curie estimated using the Curieâ€"Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect. [ABSTRACT FROM AUTHOR]

Controlling the perpendicular magnetic anisotropy (PMA) in thin films has received considerable attention in recent years due to its technological importance. PMA based devices usually involve heavy-metal (oxide)/ferromagnetic-metal bilayers, where, thanks to interfacial spin-orbit coupling (SOC), the in-plane (IP) stability of the magnetisation is broken. Here we show that in V/MgO/Fe(001) epitaxial junctions with competing in-plane and out-of-plane (OOP) magnetic anisotropies, the SOC mediated interaction between a ferromagnet (FM) and a superconductor (SC) enhances the effective PMA below the superconducting transition. This produces a partial magnetisation reorientation without any applied field for all but the largest junctions, where the IP anisotropy is more robust; for the smallest junctions there is a reduction of the field required to induce a complete OOP transition ( H OOP ) due to the stronger competition between the IP and OOP anisotropies. Our results suggest that the degree of effective PMA could be controlled by the junction lateral size in the presence of superconductivity and an applied electric field. We also discuss how the H OOP field could be affected by the interaction between magnetic stray fields and superconducting vortices. Our experimental findings, supported by numerical modelling of the ferromagnet-superconductor interaction, open pathways to active control of magnetic anisotropy in the emerging dissipation-free superconducting spin electronics. [ABSTRACT FROM AUTHOR]

We describe an experimental setup designed for transport measurement of thin disordered superconducting films as a function of pressure up to several GPa. We use a specially designed single screw diamond anvil cell that allows the gradual increase of high pressure at cryogenic temperatures. By depositing amorphous films of disordered superconducting indium oxide directly on the diamond, we avoid the effect of pressure-induced structural changes in the substrate. Using this technique, we are able to drive thin films through a pressure tuned superconductor–insulator transition. [ABSTRACT FROM AUTHOR]

Nb3Sn is considered as a potential candidate for superconducting radiofrequency cavities for particle acceleration due to its higher transition temperature of 18.3 K and higher superheating field of 400 mT. Nb3Sn films can be grown inside the surface of a Nb cavity by sequentially sputtering multiple layers of Nb and Sn thin films followed by annealing at 950 °C for 3 h. We report on the properties of Nb3Sn films grown on Nb substrates by magnetron sputtering. The films’ crystal structure, surface morphology, and composition were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The films had a polycrystalline Nb3Sn structure with a fine-grain surface and an atomic Sn composition of ∼23%. The RF surface resistance of the films was measured for different temperatures at 7.4 GHz to understand the feasibility of this method for the SRF application. The RF surface resistance of the films was 5 mΩ at 12 K, which is about 2 orders of magnitude higher than 60 μΩ previously measured in Nb3Sn films grown by Sn vapor diffusion. The sputtered film had a superconducting transition at 17.2 K, which is also lower than 17.9 K observed in Nb3Sn film prepared by vapor diffusion. [ABSTRACT FROM AUTHOR]

We are currently developing transition edge sensors (TES) for the gamma-ray spectroscopy using a single gold bump post to connect the bulk metal absorber to the superconducting thin film. In order to develop a multi-pixel TES array for the gamma-ray spectroscopy, a stable and feasible method of mounting gamma-ray absorbers is indispensable. However, mounting gamma-ray absorbers on a single gold bump post is difficult from a structural stability and process development perspective. To overcome this problem, we have established a method to improve the structural stability in mounting gamma-ray absorbers by using 4 gold bump posts. We developed a TES array coupled with a Sn absorber which was mounted with our newly established method and used it to collect gamma-ray spectrum from an Am241 source. The rise time of the signal waveform was shorter than 200 μs and showed a favorable energy resolution considering the high transition temperature of the Ir/Au superconducting film. This new method to mount gamma-ray absorbers on TES will contribute to the development of multi-pixel TES arrays using bulk metal for gamma-ray absorbers. [ABSTRACT FROM AUTHOR]

The newly discovered superconductivity in infinite-layer nickelate superconducting films has attracted much attention, largely because their crystalline and electronic structures are similar to those of high-Tc cuprate superconductors. The upper critical field can provide a great deal of information on the subject of superconductivity, but detailed experimental data are still lacking for these films. We present the temperature- and angle-dependence of resistivity, measured under different magnetic fields H in Nd0.8Sr0.2NiO2 thin films. The onset superconducting transition occurs at about 16.2 K at 0 T. Temperature-dependent upper critical fields, determined using a criterion very close to the onset transition, show a clear negative curvature near the critical transition temperature, which can be explained as a consequence of the paramagnetically limited effect on superconductivity. The temperature-dependent anisotropy of the upper critical field is obtained from resistivity data, which yields a value decreasing from 3 to 1.2 with a reduction in temperature. This can be explained in terms of the variable contribution from the orbital limit effect on the upper critical field. The angle-dependence of resistivity at a fixed temperature, and at different magnetic fields, cannot be scaled to a curve, which deviates from the prediction of the anisotropic Ginzburg–Landau theory. However, at low temperatures, the resistance difference can be scaled via the parameter Hβ |cosθ| (β = 6–1), with θ being the angle enclosed between the c-axis and the applied magnetic field. As the first detailed study of the upper critical field of nickelate thin films, our results clearly indicate a small anisotropy, and a paramagnetically limited effect, in terms of superconductivity, in nickelate superconductors. [ABSTRACT FROM AUTHOR]

The impact of film thickness to the electron–phonon coupling and the critical temperature of the superconducting transition, as well as to the structural, phonon and electronic properties of Al films in the ultrathin regime, was studied by means of ab initio calculations. The presence of the inevitable quantum fluctuations in the regime of 5 to 9 atomic layers was found not to be detrimental for the transition critical temperature, as quantum confinement was found to have a monotonically positive impact. As calculations were performed on perfect crystalline films, results of this work give further indirect evidence of the impact of the experimentally observed defects on the superconducting transition. The reduction of the dimensions of materials in the critically low regime of quantum effects can unlock new prospects for high Tc superconducting devices, such as cryogenic light detectors and superconducting single-electron transistors; hence, the understanding of the underlying mechanisms is required for the deterministic tailoring of their properties. [ABSTRACT FROM AUTHOR]

Normal-state properties of some epitaxial YBa2Cu3O7-δ thin films which were derived from the metal-organic deposition route were studied through the context of Aslamazov and Larkin theory of fluctuation conductivity. Six samples with various superconducting properties were selected for this purpose. Resistivity vs. temperature analysis showed that the general normal-state behavior of the samples can be described by 3D, 2D, and 1D Aslamazov and Larkin model of fluctuation conductivity. Samples with the higher superconducting transition temperatures showed the higher Josephson interlayer coupling. Moreover, a linear behavior has been found between Josephson interlayer coupling constant and critical current density. In addition, fitting excess conductivity with Lawrence-Doniach (LD) and Maki-Thompson (MT) models revealed that the LD term dominates in 3D region near the superconducting transition. However, the MT term gains an important role in 2D region far away superconducting transition. [ABSTRACT FROM AUTHOR]

The majority of thin film studies that were devoted to Fe-oxyarsenides has focused so far on F-substituted (i.e. indirectly electron doped) LnOFeAs (Ln = La, Nd, Sm). Here we turn our attention towards Co-substituted (i.e. directly electron doped) LaOFeAs and SmOFeAs in order to investigate its growth on different substrate materials by using pulsed laser deposition (PLD). We detected dominant LnOFeAs phase formation and discuss the occurrence of minor impurity phases in the different films on different substrates. The lack of a superconducting transition in LnOFe0.85Co0.15As films on MgO(100) could be due to strain, since we observe an onset of superconductivity in SmOFe1 − xCoxAs (x = 0.07, 0.15) films on other oxide substrates. In addition, Co-substitution (i.e. within the Fe2As2 layers) and F-substitution (i.e. within the Ln2O2 layers) leading to direct and indirect electron doping respectively, appears for films deposited on CaF2 substrates. In contrast to the F-substituted but Co-free Fe-oxyarsenides, the co-doped SmO1 − xFxFe0.85Co0.15As film has experimentally accessible upper critical fields down to the lowest temperatures and may serve as an ideal test bed for further theoretical modeling of Fe-oxyarsenides. [ABSTRACT FROM AUTHOR]

We report experimental investigation of the resistivity and Nernst effect in two-dimensional (2D) NbSe2 crystals. A strongly enhanced Nernst effect, 100 times larger than that in bulk NbSe2, caused by moving vortices is observed in thin film. It is found that in the low temperature, high magnetic field regime, pinning effects show little dependence on the thickness and resistivity of the superconductor films. Strong Nernst signals persist above the superconducting transition, suggesting that the Nernst effect is a sensitive probe to superconducting fluctuations. A magnetic field induced superconductor--insulator transition (SIT) is evident, which is surprising in that such a SIT usually takes place in disordered dirty superconductors, while our samples are highly crystalline and close to the clean limit. Hence, our results expand the scope of SIT into 2D crystal clean superconductors. [ABSTRACT FROM AUTHOR]

We report experimental investigation of the resistivity and Nernst effect in two-dimensional (2D) NbSe2 crystals. A strongly enhanced Nernst effect, 100 times larger than that in bulk NbSe2, caused by moving vortices is observed in thin film. It is found that in the low temperature, high magnetic field regime, pinning effects show little dependence on the thickness and resistivity of the superconductor films. Strong Nernst signals persist above the superconducting transition, suggesting that the Nernst effect is a sensitive probe to superconducting fluctuations. A magnetic field induced superconductor--insulator transition (SIT) is evident, which is surprising in that such a SIT usually takes place in disordered dirty superconductors, while our samples are highly crystalline and close to the clean limit. Hence, our results expand the scope of SIT into 2D crystal clean superconductors. [ABSTRACT FROM AUTHOR]

We report experimental investigation of the resistivity and Nernst effect in two-dimensional (2D) NbSe2 crystals. A strongly enhanced Nernst effect, 100 times larger than that in bulk NbSe2, caused by moving vortices is observed in thin film. It is found that in the low temperature, high magnetic field regime, pinning effects show little dependence on the thickness and resistivity of the superconductor films. Strong Nernst signals persist above the superconducting transition, suggesting that the Nernst effect is a sensitive probe to superconducting fluctuations. A magnetic field induced superconductor--insulator transition (SIT) is evident, which is surprising in that such a SIT usually takes place in disordered dirty superconductors, while our samples are highly crystalline and close to the clean limit. Hence, our results expand the scope of SIT into 2D crystal clean superconductors. [ABSTRACT FROM AUTHOR]

We report experimental investigation of the resistivity and Nernst effect in two-dimensional (2D) NbSe2 crystals. A strongly enhanced Nernst effect, 100 times larger than that in bulk NbSe2, caused by moving vortices is observed in thin film. It is found that in the low temperature, high magnetic field regime, pinning effects show little dependence on the thickness and resistivity of the superconductor films. Strong Nernst signals persist above the superconducting transition, suggesting that the Nernst effect is a sensitive probe to superconducting fluctuations. A magnetic field induced superconductor--insulator transition (SIT) is evident, which is surprising in that such a SIT usually takes place in disordered dirty superconductors, while our samples are highly crystalline and close to the clean limit. Hence, our results expand the scope of SIT into 2D crystal clean superconductors. [ABSTRACT FROM AUTHOR]

Theodore H. Geballe: Selected Research Papers (1950-2019) D. N. Lyon, T. H. Geballe, The temperature coefficient of resistance of tin oxide-coated electrically conducting glass between 1-degrees-K and 300-degrees-K, I Review of Scientific Instruments i B 21 b , 769-770 (1950). I. Bozovic, D. Kirillov, A. Kapitulnik, K. Char, M. R. Hahn, M. R. Beasley, T. H. Geballe, Y. H. Kim, A. J. Heeger, Optical measurements on oriented thin YBa SB 2 sb Cu SB 3 sb O SB 7- sb films - lack of evidence for excitonic superconductivity, I Physical Review Letters i B 59 b , 2219-2221 (1987). B. Oh, K. Char, A. D. Kent, M. Naito, M. R. Beasley, T. H. Geballe, R. H. Hammond, A. Kapitulnik, J. M. Graybeal, Upper critical-field, fluctuation conductivity, and dimensionality of YBa SB 2 sb Cu SB 3 sb O SB 7-x sb , I Physical Review B i B 37 b , 7861-7864 (1988). J. J. Yeh, I. Lindau, J. Z. Sun, K. Char, N. Missert, A. Kapitulnik, T. H. Geballe, M. R. Beasley, Variation of Cu-O charge-transfer energies in YBa SB 2 sb Cu SB 3 sb O SB 7- sb thin-films studied by photoemission spectroscopy, I Physical Review B i B 42 b , 8044-8048 (1990). [Extracted from the article]

• Highly c -oriented textured YBCO films obtained on [001] quartz. • T c =85 K, width 1 K, j c ≈ 104 A cm−2 at 77 K. • The obtained results are a step towards realization of YBCO thin films on amorphous silica fibers. We present an investigation of the superconducting properties of thin YBa 2 Cu 3 O 7-x (YBCO) films grown on [001] single-crystalline quartz substrates by pulsed laser deposition (PLD) technique. The growth of YBCO on quartz is challenging due to large crystal lattice mismatch between YBCO and quartz. We obtained highly c -oriented textured films with superconducting transition at about 85 K, transition width of 1 K, and critical current density j c ≈ 104 A cm−2 at 77 K. Analysis of the temperature dependences of the resistivity and current-voltage characteristics has shown the presence of the thermally-assisted flux flow at temperatures above 70 K. From the temperature and magnetic field dependences of critical current, vortex activation energy, U 0 (H), was estimated for both parallel and perpendicular orientation of magnetic field. Second critical field, H c2 (0), was estimated from extrapolation of the H c2 (T) dependences. The obtained results are an important step towards realization of YBCO thin films on amorphous silica fibers for the third generation (3 G) of the HTS long wire with low losses in alternative current applications. [ABSTRACT FROM AUTHOR]

The Dirac-Bogoliubov-de Gennes equation and Blonder-Tinkham-Klapwijk theory are used to calculate the tunneling conductance and shot noise in topological insulator-based ferromagnet/ d x 2 − y 2 + i d x y mixed wave superconductor (TI-based FM/ d x 2 − y 2 + i d x y SC) junctions. The Andreev reflection is investigated by analyzing the conductance and shot noise. Results show that the Andreev reflection process strongly depend on the magnetic gap m in FM, the gate potential U applied to the electrode on top of SC, and the magnitude of the ratio of Δ 1 / Δ 0 with Δ 0 (Δ 1) the absolute of pair potential of d x 2 − y 2 (d x y) component. The specular Andreev reflection can be enhanced by m as well as U. The conventional Andreev retro-reflection, however, can be enhanced by U but be suppressed by m. Which of the two reflections dominates the tunneling phenomenon exists a turning point at m = E F where both the tunneling conductance and differential shot noise become zero. This can be used as a criterion for distinguishing between the specular Andreev reflection and the Andreev retro-reflection in thin film TI-based FM/ d x 2 − y 2 + i d x y SC structures. In addition, the d x 2 − y 2 + i d x y pairing symmetry as well as the magnitude of magnetic gap can be determined by the experiment of scanning tunnel spectroscopy. • The Andreev reflection is investigated theoretically by analyzing the tunneling conductance and shot noise in a thin-film TI-based FM/ d x 2 − y 2 + i d x y mixed wave superconductor structures. • It is found that whether for d x 2 − y 2 or d x 2 − y 2 + i d x y pairing, the magnetic gap m as well as the gate potential U can enhance the specular Andreev reflection.The conventional Andreev retro-reflection can be enhanced by U but suppressed by m. • Which of the two reflections dominates the tunneling phenomenon exists a turning point at m = E F where both the tunneling conductance and differential shot noise become zero. • When m > E F , the influence of the magnetic gap on both the conductance and the shot noise for the case of d x 2 − y 2 -wave is greater than that for d x 2 − y 2 + i d x y -wave case. • These results could not only be used to understand more about the specular Andreev reflection but also to experimentally determine the d x 2 − y 2 + i d x y mixed wave pairing symmetry. [ABSTRACT FROM AUTHOR]

• The differential shot noise and Fano factor in topological insulator-based ferromagnet/ p -wave superconductor (TI-based FM/ p -wave SC) junctions is theoretically investigated based on the Dirac-Bogoliubov-de Gennes equation. Three kinds of pairings p x , p y , and p x + ip y -waves for SC are chosen. • It is found that the shot noise spectrum strongly depends on the finite-quasi-particle lifetime, the magnetic gap m induced by an applied magnetization, the Fermi-energy mismatch between FM and SC as well as the type of the pair potential symmetry. • Shortening the quasi-particles lifetime leads to the dips in the shot noise smoothed out. Increasing the magnetic gap can suppress the shot noise and Fano factor when the conventional Andreev retro-reflection is the dominant process but the shot noise can be enhanced when the dominant process is the specular Andreev reflection. • Which type of reflection dominates the tunneling process with a turning point at the Fermi energy E F = m , where the values of shot noise in all energy ranges become zero. • The obtained results can be used not only to distinguish the specular Andreev reflection from the Andreev retro-reflection in thin film TI-based FM/ p- wave SC structures but also to determine the energy-mass gap induced by the applied magnetization. The differential shot noise and Fano factor in topological insulator-based ferromagnet/ p -wave superconductor (TI-based FM/ p -wave SC) junctions is theoretically investigated based on the Dirac-Bogoliubov-de Gennes equation. Three kinds of pairings p x , p y , and p x + ip y -waves for SC are chosen. It is found that the shot noise spectrum strongly depends on the finite-quasi-particle lifetime, the magnetic gap m induced by an applied magnetization, the Fermi-energy mismatch between FM and SC as well as the type of the pair potential symmetry. Shortening the quasi-particles lifetime leads to the dips in the shot noise smoothed out. Increasing the magnetic gap can suppress the shot noise and Fano factor when the conventional Andreev retro-reflection is the dominant process but the shot noise can be enhanced when the dominant process is the specular Andreev reflection. Which type of reflection dominates the tunneling process with a turning point at the Fermi energy E F = m , where the values of shot noise in all energy ranges become zero. This result can be used not only to distinguish the specular Andreev reflection from the Andreev retro-reflection in thin film TI-based FM/ p- wave SC structures but also to determine the energy-mass gap induced by the applied magnetization. [ABSTRACT FROM AUTHOR]

• Description of growth methodology to synthesize type-II TSMs XTe 2 thin films using DC co-sputtering technique. • The crystallites of the films are found to be highly textured along the (0 0 l) family of planes, indicating van der Waals layered growth. • The semi metallic characteristics and superconducting transition at low temperatures are observed. • The MC curves exhibited WAL behavior which fitted to estimated the coherency factor and the dephasing factor. The values of these parameters established the presence of 2D nontrivial states in the films. • The PT/CFB bilayer have a effective spin mixing conductance (212 - 24 n m - 2 ) and spin current density (0.5 - 2.5 M A m - 2). The topological phases such as Dirac/Weyl semimetals are recently observed in Layered transition metal dichalcogenides (TMDs). The family of materials XTe 2 (with X = Pd, Pt and Ni) possesses a type-II topological semimetal (TSM) phase. Here, we report the synthesis of the layered XTe 2 thin films using the industry-friendly sputtering technique. The structural and morphological qualities of the sputtered-grown XTe 2 thin films are analysed using X-ray diffraction and Raman measurements. The crystallites are highly oriented along the c-axis of the sapphire substrate, which suggests that growth is driven by van der Waals epitaxy. The magneto-transport measurements namely temperature-dependent resistivity and magnetoresistance measurement in out-of-plane field configuration are performed on PdTe 2 thin films. The semi-metallic trend and superconducting transition are observed in the temperature-dependent resistivity curve. The weak antilocalization behavior observed in the magnetoconductance curves at a low magnetic field signifies the possibility of a non-zero Berry phase, possibly arising from the Dirac fermionic nature of electronic states. The spin dynamics measurements are performed on the PdTe 2 /Co 60 Fe 20 B 20 bilayers. The effective spin mixing conductance and spin current density are found to be ∼ 2 × 10 20 m - 2 and 2.5 M A m - 2 , respectively in PdTe 2 /Co 60 Fe 20 B 20 bilayer which are quite larger than those observed in heavy metal-ferromagnets bilayers, and comparable to MBE-grown topological insulator-ferromagnets heterostructures. This work paves the way to synthesize Te-based layered TMDs using the industrially viable sputtering technique, and demonstrates the prospects for exploring the topological superconductive phase in PdTe 2 films and large spin-charge conversion efficiency in PdTe 2 /Co 60 Fe 20 B 20 heterostructures. [ABSTRACT FROM AUTHOR]

Superconductor–insulator transition is one of the remarkable phenomena driven by quantum fluctuation in two-dimensional (2D) systems. Such a quantum phase transition (QPT) was investigated predominantly on highly disordered thin films with amorphous or granular structures using scaling law with constant exponents. Here, we provide a totally different view of QPT in highly crystalline 2D superconductors. According to the magneto-transport measurements in 2D superconducting ZrNCl and MoS2, we found that the quantum metallic state commonly observed at low magnetic fields is converted via the quantum Griffiths state to the weakly localized metal at high magnetic fields. The scaling behavior, characterized by the diverging dynamical critical exponent (Griffiths singularity), indicates that the quantum fluctuation manifests itself as superconducting puddles, in marked contrast to the thermal fluctuation. We suggest that an evolution from the quantum metallic to the quantum Griffiths state is generic nature in highly crystalline 2D superconductors with weak pinning potentials. [ABSTRACT FROM AUTHOR]

In superconducting transition-edge sensor X-ray detectors, we observe that as the thermal conductance (G) to the heat bath increases, the resistive transition broadens. Consequently, the sensitivity of films to deposited energy worsens. Using a two-fluid model for the superconducting-to-normal transition in a thin film, we show that this broadening can be attributed to the larger current (I0) necessary for biasing the film at a given point in the transition for higher-G devices, resulting in a higher Ic0/I0 ratio (Ic0 is the film's critical current at zero temperature). To recover a sharper transition, we fabricated rectangular films with varying numbers of internal normal-metal structures while keeping G constant, allowing the independent variation of both I0 and Ic0. We show that it is possible to manipulate the transition width and G independently, thus enabling fast thermal sensors with an excellent energy resolution. [ABSTRACT FROM AUTHOR]

• Superconducting paste using Nb 3 Al particles for superconducting connections were synthesized by a simple traditional method often used to prepare Ag paste. • The resistivity of the Nb 3 Al film after solidification became zero at 9 K. • NbTi-thin-film pad/Nb 3 Al/NbTi-thin-film pad connections were fabricated and two superconducting transitions were obtained as a result of temperature-dependent measurements of resistance. • Superconducting connections fabricated using the Nb 3 Al paste can function well at liquid helium temperatures (4.2 K), making it a useful candidate for connecting superconducting devices. We achieved a superconducting transition temperature of 9 K in a superconducting paste prepared using Nb 3 Al particles. The paste was synthesized by a simple traditional method often used to prepare Ag paste. Subsequently, the paste was screen printed on a solid substrate and thermally cured under optimum conditions to form a single-phase film with a thickness of 150 µm. The single-phase nature of the Nb 3 Al film was confirmed by X-ray diffraction, and the close contact of each Nb 3 Al particle with its neighboring particles was confirmed by cross-sectional scanning electron microscopy. The resistivity of this thick Nb 3 Al film is zero at temperatures lower than 9 K, indicating that this film is superconducting at cryogenic temperatures. Furthermore, NbTi-thin-film-pad/Nb 3 Al/NbTi-thin-film-pad connections were fabricated by vapor-phase growth and screen printing. The temperature dependence of the connection resistivity showed two superconducting transitions: a gradual decrease in resistivity from 13 K to 9 K, attributed to Nb 3 Al, and a sharp decrease at 6.2 K, attributed to the superconducting transition of the NbTi thin film. These results indicated that the Nb 3 Al superconducting paste is a candidate for achieving superconducting-thin-film-based device-to-device integration technology comprising three elements, namely superconducting wires, a superconducting crossover, and a superconducting contact. [ABSTRACT FROM AUTHOR]

• NbTiN thin films were grown by reactive sputtering on polyamide and silicon substrates at room temperature. • NbTiN thin films on flexible polyamide display superconductivity with properties close to those observed in silicon. • NbTiN thin films on flexible polyamide tolerate mechanical deformation. We compare the superconducting properties of 100 nm thick NbTiN films grown by reactive sputtering on silicon and flexible commercial polyimide. The samples are fabricated by co-sputtering using Nb and Ti targets at room temperature with a reactive atmosphere of N 2 and Ar. The films display a polycrystalline structure and superconducting critical temperatures of 13.2 K on polyimide and 13.4 K on silicon. The analysis of the upper critical field reveals huge values, with extrapolation to zero close to 29 T for films on silicon and 23 T for those on polyimide. A comparison of the superconducting transition applying mechanical deformation is shown. Presenting a higher superconducting gap and upper critical fields above than the commonly used elemental Nb, the development of NbTiN thin films on flexible polyimide appears as a potential material for application in superconducting electronics. [ABSTRACT FROM AUTHOR]

We investigated transport properties under magnetic fields up to 8 T for FeSe 1 − x Te x thin films on CaF 2 . For x = 0.2 -- 0.4 , where T c ’s are the highest, resistive broadening was observed, while the width of superconducting transition was almost the same with increasing magnetic fields in x = 0 -- 0.1 , indicating differences in the nature of superconductivity between these two groups. [ABSTRACT FROM AUTHOR]

The temperature-dependent electronic transport on the superconducting and insulating sides of the superconductor-insulator transition in disordered quasi-two-dimensional textured FeSe thin films is reported. The transition is driven by a perpendicular magnetic field applied to a film with its thickness close to the critical thickness of the thickness-, i.e., disorder-induced transition. The resistance in the superconducting phase might be dominated by thermally assisted flux flow, and in the phase diagram a metallic phase might intervene between the superconducting and insulating state at very low temperatures. In the insulating phase, weak insulating behavior is observed that can be described by weak localization theory of bosons, thus supporting the bosonic description of the superconductor-insulator transition in FeSe thin films. [ABSTRACT FROM AUTHOR]

We explore the implications of Berezinskii-Kosterlitz-Thouless (BKT) critical behavior and variable-range hopping on the two-dimensional (2D) quantum superconductor-insulator (QSI) transition driven by tuning the gate voltage. To illustrate the potential and the implications of this scenario we analyze sheet resistance data of Parendo et al. taken on a gate voltage tuned ultrathin amorphous bismuth film. The finite size scaling analysis of the BKT-transition uncovers a limiting length L preventing the correlation length to diverge and to enter the critical regime deeply. Nevertheless the attained BKT critical regime reveals consistency with two parameter quantum scaling and an explicit quantum scaling function determined by the BKT correlation length. The two parameter scaling yields for the zero temperature critical exponents of the QSI-transition the estimates $z\overline{\nu }\simeq 3/2$, z≃3 and $\overline{\nu} \simeq 1/2$, revealing that hyperscaling is violated and in contrast to finite temperature disorder is relevant at zero temperature. Furthermore, $z\overline{\nu }\simeq 3/2$ is also consistent with the two variable quantum scaling form associated with a variable-range hopping controlled insulating ground state. [ABSTRACT FROM AUTHOR]

The Berezinskii-Kosterlitz-Thouless (BKT) transition is a generic transition describing the loss of coherence in two-dimensional systems and has been invoked, for example, to describe the superconductor-insulator transition in thin films. However, recent experiments have shown that the BKT transition, driven by phase fluctuations, is not sufficient to describe the loss of superconducting order, and amplitude fluctuations must also be taken into account. The standard models that are extensively used to model two-dimensional superconductors are the Hubbard and XY models. Whereas the XY model allows only phase fluctuations, the Hubbard model has an extra degree of freedom: amplitude fluctuations. In this paper we compare two Hubbard models with the same critical temperature but with different interactions and deduce the role of the amplitude fluctuations in the superconducting transition. For this purpose, a novel approximation is presented and used. We derive an effective phase-only (XY) Hamiltonian, incorporating amplitude fluctuations in an explicit temperature dependence of the phase rigidity. We study the relation between amplitude fluctuations and coupling strength. Our results support existing claims about the suppression of phase rigidity due to amplitude fluctuations not present in the XV model. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the near-field radiative heat transfer between high- T c superconducting thin films. We focus on ceramic materials like optimally doped YBa 2 Cu 3 O 7 − δ , with a critical temperature T c = 93 K. We show that thin films significantly enhance the radiative heat transfer by efficiently coupling each interface's optical modes. The heat transfer between thin films turns out to be up to one order of magnitude higher than that for bulk plates both in the normal and superconducting states. On the other hand, the drastic change of the optical response above and below T c also plays an important role, since the superconducting phase transition leads to an abrupt suppression of the total heat flux. Our findings are relevant for the rational design of proficient thermal devices involving thin layers of this kind of materials. The strong temperature-dependent modulation of the heat flux across the phase transition is promising for thermal switches and thermal emitters' control. [ABSTRACT FROM AUTHOR]

Binary Iron selenide (FeSe) thin films have been widely studied for years to unveil the high temperature superconductivity in iron-based superconductors. However, the origin of superconducting transition in this unconventional system is still under debate and worth deep investigations. In the present work, the transition from insulator to superconductor was achieved in non-superconducting FeSe ultrathin films (~8 nm) grown on calcium fluoride substrates via a simple in-situ Mg-coating by a pulsed laser deposition technique. The Mg-coated FeSe film with an optimized amount of Mg exhibited a superconducting critical temperature as 9.7 K and an upper critical field as 30.9 T. Through systematic characterizations on phase identification, carrier transport behavior and high-resolution microstructural features, the revival of superconductivity in FeSe ultrathin films is mostly attributed to the highly crystallized FeSe and extra electron doping received from external Mg-coating process. Although the top few FeSe layers are incorporated with Mg, most FeSe layers are intact and protected by a stable magnesium oxide layer. This work provides a new strategy to induce superconductivity in FeSe films with non-superconducting behavior, which might contribute to a more comprehensive understanding of iron-based superconductivity and the benefit to downstream applications such as magnetic resonance imaging, high-field magnets and electrical cables. [ABSTRACT FROM AUTHOR]

• Re x Zr (x ≈6) thin films grown by pulsed laser deposition was found to be amorphous superconductors. • T c , H C2 , coherence length, penetration depth and energy gap change marginally with decreasing film thickness down to 8 nm. • The films showed superconductor-insulator transition below a thickness of 3 nm. • The films behaved like strong coupling Type II superconductor. • Temperature variation of penetration depth and energy gap of all the films are consistent with the BCS theory. We report the growth, characterization and superconducting properties of thin films of a new amorphous superconductor, Re x Zr (x≈6). Films were grown by pulsed laser deposition with the substrate kept at room temperature. Films with thicknesses larger than 40 nm showed a superconducting transition temperature (T c) of 5.9 K. Superconducting properties were measured for films with varying thickness from 120 to 3 nm. The normal state resistance scaled linearly with the inverse of thickness. The transition temperature, critical field, coherence length, penetration depth and superconducting energy gap changed marginally with decreasing film thickness down to 8 nm. Scanning tunneling spectroscopy and penetration depth measurements provide evidence for a single gap strong coupling s-wave superconductor. [ABSTRACT FROM AUTHOR]

• Nb 3 Sn superconducting films were fabricated by magnetron sputtering from a single target. • Effects of annealed pressure on the thin films' superconductivity and microstructural properties is examined. • argon atmosphere protection can significantly alleviate the tin loss problem. • the tc of the film on the sapphire substrate was 17 K, generally about 3.5 K higher than that on the copper substrate. Nb 3 Sn is an alternative material for future superconducting accelerators. With its higher critical temperature and superheating field than that of niobium, its application in the field of SRF is a great advantage. In this paper, the magnetron sputtering method is applied to prepare the Nb 3 Sn thin film on the oxygen-free copper substrate by the stoichiometric target—the ratio of 3:1 of niobium to tin, so as to explore the effect of different annealing air pressures on the properties of the film in detail. The film crystal structure, morphology, composition, and superconducting critical temperature were characterized by XRD, SEM, EDS, and MPMS. After in-situ annealing, XRD and MPMS reveal the existence of Nb 3 Sn crystal. The compact film with good surface properties is free of cracks and tin islands. The superconducting critical temperature reaches 13.6 K. The results show that if annealing was conducted in Ar atmosphere at 1 Pa, the obtained film exhibits better performance with a sharp transition from the superconducting state to the normal state. [ABSTRACT FROM AUTHOR]