Interlayer Josephson Coupling Research Articles

Probing inhomogeneous cuprate superconductivity by terahertz Josephson echo spectroscopy

Inhomogeneities crucially influence the properties of quantum materials, yet methods that can measure them remain limited and can access only a fraction of relevant observables. For example, local probes such as scanning tunnelling microscopy have documented that the electronic properties of cuprate superconductors are inhomogeneous over nanometre length scales. However, complementary techniques that can resolve higher-order correlations are needed to elucidate the nature of these inhomogeneities. Furthermore, local tunnelling probes are often effective only far below the critical temperature. Here we develop a two-dimensional terahertz spectroscopy method to measure Josephson plasmon echoes from an interlayer superconducting tunnelling resonance in a near-optimally doped cuprate. The technique allows us to study the multidimensional optical response of the interlayer Josephson coupling in the material and disentangle intrinsic lifetime broadening from extrinsic inhomogeneous broadening for interlayer superconducting tunnelling. We find that inhomogeneous broadening persists up to a substantial fraction of the critical temperature, above which this is overcome by the thermally increased lifetime broadening.

Charge-4e superconductivity and chiral metal in 45°-twisted bilayer cuprates and related bilayers

The material realization of charge-4e/6e superconductivity (SC) is a big challenge. Here, we propose to realize charge-4e SC in maximally-twisted homobilayers, such as 45∘-twisted bilayer cuprates and 30∘-twisted bilayer graphene, referred to as twist-bilayer quasicrystals (TB-QC). When each monolayer hosts a pairing state with the largest pairing angular momentum, previous studies have found that the second-order interlayer Josephson coupling would drive chiral topological SC (TSC) in the TB-QC. Here we propose that, above the Tc of the chiral TSC, either charge-4e SC or chiral metal can arise as vestigial phases, depending on the ordering of the total- and relative-pairing-phase fields of the two layers. Based on a thorough symmetry analysis to get the low-energy effective Hamiltonian, we conduct a combined renormalization-group and Monte-Carlo study and obtain the phase diagram, which includes the charge-4e SC and chiral metal phases.

Generalized Fresnel-Floquet equations for driven quantum materials

Optical drives at terahertz and midinfrared frequencies in quantum materials are increasingly used to reveal the nonlinear dynamics of collective modes in correlated many-body systems and their interplay with electromagnetic waves. Recent experiments demonstrated several surprising optical properties of transient states induced by driving, including the appearance of photo-induced edges in the reflectivity in cuprate superconductors (SCs), observed both below and above the equilibrium transition temperature. Furthermore, in other driven materials, reflection coefficients larger than unity have been observed. In this paper we demonstrate that unusual optical properties of photoexcited systems can be understood from the perspective of a Floquet system, a system with periodically modulated parameters originating from pump-induced oscillations of a collective mode. These oscillations lead to an effective Floquet system with periodically modulated parameters. We present a general phenomenological model of reflectivity from Floquet materials, which takes into account parametric generation of excitation pairs. We find a universal phase diagram of drive-induced features in reflectivity which evidence a competition between driving and dissipation. To illustrate our general analysis, we apply our formalism to two concrete examples motivated by recent experiments: A single plasmon band, which describes Josephson plasmons (JPs) in layered SCs, and a phonon-polariton system, which describes upper and lower polaritons in materials such as insulating SiC. Finally, we demonstrate that our model can be used to provide an accurate fit to results of phonon-pump--terahertz-probe experiments in the high-temperature SC ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}$. Our model explains the appearance of a pump-induced edge, which is higher in energy than the equilibrium JP edge, even if the interlayer Josephson coupling is suppressed by the pump pulse.

Physical properties of superconducting Ca10(Pt4As8)((Fe0.92Pt0.08)2As2)5 crystal and comprehensive cognition on the transition temperature for Ca10-3(4)-8

Superconducting single crystal of Ca10(Pt4As8)((Fe0.92Pt0.08)2As2)5 has been prepared using flux method, and the physical properties of which are careful examined. Resistivity anisotropy between ab plane and c-axis is observed, T −0.5 term originated from the interlayer Josephson coupling is essential to be added to the formula used to describe the out-of-plane resistivity. The density of state (DOS) value at Fermi level derived from the fitting of specific heat data is consistent with the calculation results. Both direct and indirect platinum doping effect have influences on the superconducting transition temperature (Tc) of Ca 10-3(4)-8 system, the Tc of our sample falls well into the trend strip formed by the data reported previously.

Contribution of vanadium particles to thermal movement of correlated two-dimensional pancake Abrikosov vortices in Bi-2223 superconducting system

This article breaks new ground in understanding of variation in the magnetic strength performance, flux pinning and energy dissipation mechanism of polycrystalline bulk Bi1.8Sr2.0Ca2.2Cu3.0Oy (Bi-2223) superconducting materials added with the different vanadium concentration level (0.0≤x≤0.30) under the magnetic field strengths applied up to 5T for the first time. We provide the sophisticated and phenomenological discussions on the magnetoresistivity measurement results in three main sections along the paper. All the findings show that the increase of both the vanadium concentration in the crystal structure and external magnetic field strength damages significantly the magnetic strength performance, vortex dynamics, flux pinning ability and vortex lattice elasticity of bulk Bi-2223 superconducting ceramics. The vanadium addition promotes thermally the movement of correlated two-dimensional (2D) pancake Abrikosov vortices between the in-plane Cu–O2 layers in the valance band, vortex lattice elasticity, vortex dynamics, distance for interlayer Josephson couplings and flux pinning centers and the theoretical computations confirm the remarkable degradation in the formation of super-electrons in the Bi-2223 crystal system. Thus, the vanadium addition is anticipated to be one of the best selectable materials to examine the differentiation in the thermal movement of correlated 2D Pancake Abrikosov vortices in the bulk Bi-2223 superconducting system.

Discovery of Dome-Shaped Superconducting Phase and Anisotropic Transport in a van der Waals Layered Candidate NbIrTe4 under Pressure.

The unique electronic structure and crystal structure driven by external pressure in transition metal tellurides (TMTs) can host unconventional quantum states. Here, the discovery of pressure‐induced phase transition at ≈2 GPa, and dome‐shaped superconducting phase emerged in van der Waals layered NbIrTe4 is reported. The highest critical temperature (T c) is ≈5.8 K at pressure of ≈16 GPa, where the interlayered Te–Te covalent bonds form simultaneously derived from the synchrotron diffraction data, indicating the hosting structure of superconducting evolved from low‐pressure two‐dimensional (2D) phase to three‐dimensional (3D) structure with pressure higher than 30 GPa. Strikingly, the authors have found an anisotropic transport in the vicinity of the superconducting state, suggesting the emergence of a “stripe”‐like phase. The dome‐shaped superconducting phase and anisotropic transport are possibly due to the spatial modulation of interlayer Josephson coupling .

Interlayer Transport and Josephson Coupling in a 1212-type Cuprate Superconductor with a (Pb,Cu)–O Barrier Layer

A quasi-two-dimensional electron system resulting from a layered crystal structure is a common feature of high-temperature superconductors. In such a system, an interlayer Josephson coupling is res...

Fluctuation Conductivity in MOD-Derived YBCO Thin Films

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.

Experimental evidence that zinc impurities pin pair-density-wave order in La2−xBaxCuO4

Both Zn doping and $c$-axis magnetic fields have been observed to increase the spin stripe order in ${\mathrm{La}}_{2\text{\ensuremath{-}}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4}$ with $x$ close to 1/8. For $x=0.095$, the applied magnetic field also causes superconducting layers to decouple, presumably by favoring pair-density-wave order that consequently frustrates interlayer Josephson coupling. Here we show that introducing 1% Zn also leads to an initial onset of two-dimensional (2D) superconductivity, followed by 3D superconductivity at lower temperatures, even in zero field. We infer that the Zn pins pair-density-wave order locally, establishing the generality of such behavior.

Effect of Cr Substitution on the Formation and Fuctuation-Induced Conductivity Analysis of (Tl<sub>1-x</sub>Cr<sub>x</sub>)Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>7</sub> Superconductor

The (Tl1-xCrx)Sr2CaCu2O7 (Tl-1212) sample with nominal starting composition for x = 0.0, 0.2 and 0.3 were prepared by the solid-state reaction method. The samples were studied by powder x-ray diffraction method and electrical resistance versus temperature measurement. Excess conductivity analysis was carried out using the Aslamazov–Larkin (AL) theory, and the dimension of fluctuation-induced conductivity (λ) was determined. The Lawrence–Donaich (LD) theory was used to calculate the coherence length (ξc(0)), Josephson coupling (J), and γ = (ξab(0)/ξc(0)) of the superconductive samples. Excess conductivity analysis showed that Cr substitution induced 2D-to-3D conductivity transition at the highest transition temperature (T2D-3D) observed at x = 0.3. The calculations based on the Lawrence–Doniach model revealed that the shortest coherence length and weakest inter-plane coupling (J) occurred when x = 0.2. The sample with x = 0.2 and 0.3 showed the Tl-1212 as the major phase. The highest onset temperature of 110 K was observed in the x = 0.2 sample. Our result showed that the formal value of 2.3+ is more important than the Josephson interlayer coupling J in optimizing the transition temperature.

Formation of artificial flux pinning centers in Bi-2223 cuprate superconductor with Ni impurities and enhanced resistant to thermal fluxon motions of correlated 2D pancake vortices in new matrix

This comprehensive study attempts to find out the evaluation of magnetoresistivity performance and flux pinning centers in the Bi-2223 superconductor with nickel impurities and diffusion annealing temperature interval 650 °C–850 °C by means of magnetotransport measurements (0–5T). It is found that the cooper-pair probabilities as well as pinning of thermal fluxon motions of two-dimensional (2D) pancake vortices and interlayer Josephson coupling between the isolated grains considerably improve with the annealing temperature up to 700 °C as a result of enhancement in the effective flux pinning regions. However, from 700 °C onwards the potential energy barriers decrease significantly due to the increment of permanent structural problems in the crystal system. Namely, the presence of excess Ni impurities develops the recoupling linelike/discrete pancakelike nature. In this respect, the bulk sample exposed to the diffusion annealing temperature of 850 °C exhibits the worst magnetic performance characteristics. The flux lines in the material more easily jump to neighboring states due to the cooper pair-breaking mechanism, and thus the thermal fluxon motions of 2D pancake vortices lead to the energy dissipation. We also discuss the differentiation of vortex lattice elasticity for the materials with the aid of the theoretically calculated quantities such as the thermodynamic critical field (μ0Hc), irreversibility field (μ0Hirr), lower critical field (μ0Hc1), upper critical field (μ0Hc2), penetration depth (λ), coherence length (ξ) and Ginzburg Landau parameter (κ). According to the computational values, the optimum annealing temperature of 700 °C strengthens the pinning of 2D pancake vortices, vortex lattice period and elasticity as a result of the decrease in the inter-plane interaction energy. To sum up, 700 °C favors the applications of bulk Ni surface-layered Bi-2223 compounds in rather higher magnetic fields for a major innovation.

Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa2Cu3O6.48.

Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. The empty chain Cu dy2-z2 orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.

Significant development on pinning of vortices in Y-123 superconductor with homovalent Ba/Nd substitution

In this study, the magnetotransport measurements are performed in the field range of 0–7 T to determine the effect of Nd nanoparticles inserted in the Y-123 crystal structure on the superconducting characteristics and flux pinning mechanism of the YBa2−yNdyCu3O7 materials (0.000 ≤ y ≤ 0.500). Moreover, the experimental measurement results enable us to evaluate the crucial parameters as regards critical transition temperatures (\(T_{c}^{onset}\) and \(T_{c}^{offset}\)), room temperature resistivities (ρ300), residual resistivity ratios (RRR), thermodynamic critical fields (μ0Hc), lower critical fields (μ0Hc1), upper critical fields (μ0Hc2), critical fields (μ0Hc3), irreversibility fields (μ0Hirr), coherence lengths (ξ), penetration depths (λ) and Ginzburg–Landau (\(\kappa\)) parameters. All the values obtained show the considerable improvement with the increment of the Nd nanoparticles in the Y-123 crystal system up to the critical value of y = 0.250 beyond which the prompt degradation begins in the crystal structure due to new induced artificial dislocations and permanent disorders in the Cu–O2 consecutively stacked layers. Hence, the excess Nd inclusions lead to the thermal motion of the vortices easily. This fact is completely confirmed by the magnetotransport measurements performed in the external magnetic fields. Namely, the optimum level of Nd dopant seriously increases the coupled regions as a result of the degradation of pancake positional fluctuations, and pinning of two-dimensional pancake vortices enhances with the recoupling of the adjacent layers. However in case of the maximum Nd inclusions, the flattened pancakes with more interplane interaction energy never travel from layer to layer due to the alteration of the coupled vortices into the discrete pancakelike (recoupling linelike) nature. In other words, the excess Nd nanoparticles inserted in the Y-123 crystal system reduce significantly the interlayer Josephson coupling length, elastic moduli of the vortex lattice and magnetic field carrying capacity. Furthermore, the flux pinning energy (U0) is calculated from thermally activated flux flow model. The activation energy computed increases regularly with the increment of Nd decorations until y = 0.250 after which the value significantly decreases towards to the global minimum point. However, the pinning energy values always decrease with the increase of the external magnetic field strength. In case of external magnetic fields of 7 T the maximum activation energy is found to be about 477 K. As for the Y-123 material doped with maximum Nd additives of y = 0.500, the flux pinning energy values are not calculated at any applied magnetic field which is >0.1 T due to the cooper pair-breaking in Ba-site Nd substituted Y-123 systems. At the same time, the evaluated parameters follow the same trend: firstly enhancement up to the critical Nd dopant value of y = 0.250 and then the rapid regression towards the global minimum point. Finally, the optimum Nd impurity level is found to be y = 0.250 in the Y-123 system at even higher applied magnetic field strengths.

Study of the Vortex Dynamics of the Single Crystal Tl0.4 K 0.41Fe1.71Se2

We have studied the vortex dynamics of the Tl0.4 K 0.41Fe2−y Se2 single crystal through the measurements of temperature and magnetic field dependencies of electrical resistivity. Due to the existence of intra-layer Fe-site vacancy and inter-layer Josephson coupling, it is found that the pinning of vortices is very strong, which hinders the flux flow. A very high upper critical field H c2 value and a moderate anisotropy parameter γ are obtained, similar to those found in YBa2Cu3O7−δ superconductor. These results suggest that the Tl0.4 K 0.41Fe2−y Se2 superconductor has a good sustainability under high magnetic field, indicating a good potential for application.

Important defeats on pinning of 2D pancake vortices in highly anisotropic Bi-2212 superconducting matrix with homovalent Bi/La substitution

This comprehensive study aims to investigate the change of the flux pinning mechanism, electrical and superconducting properties of the inorganic solid Bi-2212 materials with the La inclusions inserted in the crystal structure by means of magnetotransport measurements exerted in the applied magnetic field range of 0—7T. Crucial characteristics as regards critical transition temperatures (Tconset and Tcoffset), room temperature resistivities (ρ300K), residual resistivities (ρ0), residual resistivity ratios (RRR), irreversibility fields (μ0Hirr), upper critical fields (μ0Hc2), thermodynamic critical fields (μ0Hc), activation energies (U0), penetration depths (λ) and coherence lengths (ξ) are evaluated from the experimental magnetoresistivity curves and available theoretical approaches. All the properties obtained above confirm the considerable degradation in the pinning of 2D pancake vortices with the increment of the La individuals randomly distributed in the Bi-2212 superconducting system. Thus, the improved recoupling linelike nature among the consecutively stacked layers leads to decoupling of the adjacent layers and suppression of the interlayer Josephson coupling length as a result of the enhancement in the thermal fluctuations of flattened pancake vortices. The long and short of it is that the La impurities undermine the elasticity of the vortex lattice. For example, the Tcoffset and Tconset values are found to be about 84.5K and 85.7K for the best (pure) sample while the material exposed to the La content level of x=0.2 obtains the values of 82.2K and 15.1K, respectively at zero applied magnetic field. In the case of the applied magnetic field of 7T, the Tcoffset value reduces considerably towards the lower temperature values of 72.6K for the former compound. However, the values belonging to the worst sample (La4) cannot be determined at higher external magnetic field value such as 1T due to the hybridization of La-3/states with the Cu3d–O2p states in the Cu–O2 layers (dissipation). This is attributed to the existence of the pair-breaking mechanism in Bi-site La substituted Bi-2212 systems. Moreover, the flux pinning energy values calculated from thermally activated flux flow (TAFF) model decrease dramatically with the enhancement of both the La content level and external magnetic fields. Numerically, the activation energy value is calculated to be about 5173K (1077K) for the pure sample at the field value of 0T (7T) whereas the values pertaining to the compound substituted by the La concentration level of x=0.15 are found to be in a range of 1196–281K. The lack of the experimental evidences does not enable us to find the energy values belonging to the La4 sample at higher applied field. As for the critical field parameters (μ0Hc1, μ0Hc, μ0Hirr, μ0Hc2 and μ0Hc3) and the extracted values (λ, ξ and κ), the changes in the parameters given also verify the degradation of the flux pinning ability (random distribution of the artificial pinning centers) with the La concentration as a result of the Cooper pair-breaking mechanism. To sum up, the La impurities are unfavorable for the potential applications of these materials in the commercial sector at high temperatures and magnetic fields.

Exploring intertwined orders in cuprate superconductors

The concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La2−xBaxCuO4 with x=0.125 provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling has motivated the concept of the pair-density-wave superconductor, a state that theoretical calculations show to be energetically competitive with the uniform d-wave superconductor. Even at x=0.095, where there is robust superconductivity below 32K in zero field, the coexistence of strong, low-energy, incommensurate spin excitations implies a spatially modulated and intertwined pair wave function. Recent observations of CDW order in YBa2Cu3O6+x and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. While there are differences in the doping dependence of the modulation wave vectors in YBa2Cu3O6+x and La2−xBaxCuO4, the maximum ordering strength is peaked at the hole concentration of 1/8 in both cases. There are also possible connections with the quantum oscillations that have been detected about the same hole concentration but at high magnetic fields. Resolving these relationships remains a research challenge.

Enhanced charge stripe order of superconducting La2−xBaxCuO4in a magnetic field

The effect of a magnetic field on the charge stripe order in ${\mathrm{La}}_{2\ensuremath{-}\mathit{x}}{\mathrm{Ba}}_{\mathit{x}}{\mathrm{CuO}}_{4}$ has been studied by means of high-energy (100 keV) x-ray diffraction for charge carrier concentrations ranging from strongly underdoped to optimally doped. We find that charge stripe order can be significantly enhanced by a magnetic field applied along the $c$ axis, but only at temperatures and dopings where it coexists with bulk superconductivity at zero field. The field also increases stripe correlations between the planes, which can result in an enhanced frustration of the interlayer Josephson coupling. Close to the famous $x=\frac{1}{8}$ compound, where zero field stripe order is pronounced and bulk superconductivity is suppressed, charge stripe order is independent of a magnetic field. The results for ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4}$ resemble recent observations in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+\ensuremath{\delta}}$ and, independent of potential differences in the microscopic origin of charge order in these two compounds, imply a very similar competition with three-dimensionally coherent superconductivity.

Effects of randomness on the critical temperature in quasi-two-dimensional organic superconductors

The effects of nonmagnetic disorder on the critical temperature ${T}_{c}$ of organic weak-linked layered superconductors with singlet in-plane pairing are considered. A randomness in the interlayer Josephson coupling is shown to destroy phase coherence between the layers, and ${T}_{c}$ suppresses smoothly in a large extent of the disorder strength. Nevertheless, the disorder of arbitrarily high strength cannot destroy completely the superconducting phase. The obtained quasilinear decrease of the critical temperature with increasing disorder strength is in good agreement with experimental measurements.

Extended Lawrence-Doniach model: The temperature evolution of the in-plane magnetic field anisotropy

Using the quasi-classical formalism we provide the description of the temperature and field-direction dependence of the in-plane upper critical field in layered superconductors, taking into account the interlayer Josephson coupling and the paramagnetic spin splitting. We generalize the Lawrence-Doniach model for the case of high magnetic fields and show that the re-entrant superconductivity is naturally described by our formalism when neglecting the Pauli pair breaking effect. We demonstrate that in layered superconductors the in-plane anisotropy of the onset of superconductivity exhibits four different\ temperature regimes: from the Ginzburg-Landau type in the vicinity of the critical temperature $T_{c0}$ with anisotropies of coherence lengths, up to the FFLO type induced by the strong interference between the modulation vector and the orbital effect. Our results are in agreement with the experimental measurements of the field-angle dependence of the superconducting onset temperature of the organic compound (TMTSF)$_{2} $ClO$_{4}$.

Anisotropic Ginzburg-Landau and Lawrence-Doniach models for layered ultracold Fermi gases

We derive and study the anisotropic Ginzburg-Landau and Lawrence-Doniach models describing a layered superfluid ultracold Fermi gas in optical lattices. We compute from the microscopic model the Josephson couplings entering the Lawrence-Doniach model across the crossover BCS-BEC passing from the 3D isotropic case to the quasi-2D one, showing that a model with only nearest-neighbor Josephson couplings is not adequate at the unitary limit (since the pairs have a diameter larger than the interlayer distance). We also show that the effective anisotropy of the system is strongly reduced at the unitary limit. Finally, we obtain a relation between the interlayer Josephson couplings and the Ginzburg-Landau masses: we find that using only couplings between adjacent planes is correct in the BEC side, while at the unitary limit one has to use also next-nearest-neighboring couplings.