Ginzburg-Landau Parameter Research Articles

Investigation of Upper Critical Magnetic Field in 1111‐Type High‐Temperature Iron‐Based Superconductor SmFeAsO1−xFx

ABSTRACTIn this research work, we used a two‐band model to study the theoretical analysis of the upper critical magnetic field of a high‐temperature iron‐based superconductor . The graphs of the high‐temperature iron‐based superconductor's upper critical magnetic field (((T) and ) and angular dependence of the field () versus temperature were effectively plotted. The phase diagrams of the temperature‐dependent upper critical magnetic fields versus temperature were suppressed at the transitional temperature and decreased with rising temperature for both directions of the symmetry axis. Additionally, we plotted the phase diagrams and derived the Ginzburg–Landau (GL) parameters (( and ). At the superconducting critical temperature of the superconducting material, these GL parameters diverge at the transitional temperature. Furthermore, a phase diagram of GL characteristic parameter temperature dependence was plotted. By doping fluorine atoms into the parent compound Sm‐1111, the transitional temperature of this superconductor material increased, reaching a value of 54 K and above. Finally, our theoretical conclusion is consistent with the previous experimental results.

Tc and the elastocaloric effect of Sr2RuO4 under 〈110〉 uniaxial stress: No indications of transition splitting

There is considerable evidence that the superconductivity of Sr2RuO4 has two components. Among this evidence is a jump in the shear elastic modulus c66 at the critical temperature Tc, observed in ultrasound measurements. Such a jump is forbidden for homogeneous single-component order parameters, and it implies that Tc should develop as a cusp under the application of shear strain with 〈110〉 principal axes. This shear strain should split the onset temperatures of the two components, if they coexist, or select one component if they do not. Here, we report measurements of Tc and the elastocaloric effect of Sr2RuO4 under uniaxial stress applied along the [110] lattice direction. Within experimental resolution, we resolve neither a cusp in the stress dependence of Tc, nor any second transition in the elastocaloric effect data. We show that reconciling these null results with the observed jumps in c66 requires extraordinarily fine tuning to a triple point of the Ginzburg-Landau parameter space. In addition, our results are inconsistent with homogeneous time-reversal symmetry breaking at a temperature T2≤Tc as identified in muon spin relaxation experiments. Published by the American Physical Society 2024

Structural and superconducting properties in hard Mo2BC

The utilization of high-hardness superconducting materials enhances and broadens the applications of superconductors. In this study, a high-hardness Mo2BC superconductor is synthesized using the high-pressure and high-temperature (HPHT) method. Our results demonstrate that it exhibits zero-resistance and Meissner effect below a superconducting critical temperature (Tc) of 7.0 K. The upper critical magnetic field of 4.3 T and the lower critical magnetic field of 226 Oe were obtained by data fitting, respectively. Type-II superconducting properties were confirmed by critical states analysis and Ginzburg-Landau (GL) parameters. Specific thermal properties revealed a Debye temperature as 565.1 K, while an electron-phonon coupling (EPC) parameter λ of 0.588 indicated properly coupled BCS conventional superconductivity. Mo2BC exhibits a Vickers hardness of up to 18.2 GPa, significantly surpassing that of traditional superconducting ceramics. It can be attributed to the robust covalent boron-zigzag-chains coupled with appropriate covalent [Mo6C] octahedrons within a non-centrosymmetric structure. The coexistence of both superconductivity and high hardness enables the versatility of Mo2BC, thereby laying the way for the development of high-hardness superconductors.

On the existence of nematic-superconducting states in the Ginzburg–Landau regime

In this article, we investigate the existence of nematic-superconducting states in the Ginzburg–Landau regime, both analytically and numerically. From the configurations considered, a slab and a cylinder with a circular cross-section, we demonstrate the existence of geometrical thresholds for the obtention of non-zero nematic order parameters. Within the frame of this constraint, the numerical calculations on the slab reveal that the competition or collaboration between nematicity and superconductivity is a complex energy minimization problem, requiring the accommodation of the Ginzburg–Landau parameters of the decoupled individual systems, the sign of the bi-quadratic potential energy relating both order parameters and the magnitude of the applied magnetic field. Specifically, the numerical results show the existence of a parameter regime for which it is possible to find mixed nematic-superconducting states. These regimes depend strongly on both the applied magnetic field and the potential coupling parameter. Since the proposed model corresponds to the weak coupling regime, and since it is a condition on these parameters, we design a test to decide whether this condition is fulfilled.

On the Character of Superconductivity and Topological Properties of SnAs

The paper describes results of the band structure measurements of SnAs single crystals by the ARPES technique. We performed detailed analysis of isoenergetic surfaces in the vicinity and below the Fermi energy. The ARPES experimental data are consistent with theoretically predicted shape of the SnAs Fermi surface. The determined type of the Fermi surface provides the basis for estimating the Ginzburg–Landau parameter, from which it follows that SnAs is a type-I superconductor. In addition, our results of ARPES measurements confirm the presence of band splitting in the energy spectrum at theΓ¯point at electron binding energies in the range of 0.6–1.2 eV associated with spin–orbit interaction.

Extended Ginzburg-Landau theory of superconductivity from generalized momentum operator and position-dependent mass

The concept of generalized momentum operator which is motivated from the generalized uncertainty principle has been extensively investigated in quantum mechanics and various aspects of theoretical and applied physics. In this study, we have applied this formalism to Ginzburg-Landau theory of superconductvity and Abrikosov vortex lattice in type II-superconductors. After deriving the extended Ginzburg-Landau equations, we have discussed several independent structures of the auxiliary function of position operator in the generalized momentum operator and we have analyzed their features in both Ginzburg-Landau and London theories. Comparable properties to the basic formalism have been obtained even without the presence of the cubic nonlinear term in Ginzburg-Landau equations. However, not all structures of the auxiliary function of position operator result on the exclusion of the magnetic field from a superconductor when it's below its critical temperature. But, only specific forms may succeed to eliminate the magnetic field. This approach has been generalized by considered a position-dependent mass of the electric charge. Amazingly, for a position-dependent mass of hyperbolic soliton-like structure, the extended Ginzburg-Landau wave function is identical to the result obtained in the conventional formalism and besides, for specific correlations between the auxiliary function of the position operator and position-dependent mass, the exclusion of the magnetic field is conceivable. We have also discussed the Abrikosov vortex lattice solution based on the extended Ginzburg-Landau formalism with position-dependent mass of the electric charge. It was observed that, for a specific structure of the position-dependent mass and for a quantum number n=0, a transition between a type-II and type-I superconductor takes place if the Ginzburg-Landau parameter is κ=121+257≈2.0634. For large n, the problem depends on the asymptotic form of the Hermite polynomial and periodicity occurs if the electric charge is quantized. Further details are obtained and analyzed.

Superconducting properties and vortex pinning in intermetallic BaBi3 single crystals: A magnetization study

Hysteresis and magnetic relaxation measurements were performed on single crystals of BaBi3, which is an intermetallic compound exhibiting superconductivity with a critical temperature (Tc) of 5.9 K. The London penetration depth (λ) was determined to be 130 nm, and the coherence length (ξ) was estimated to be 13 nm. The critical current density (Jc) was found remarkably low, measuring 20,000 A/cm2 under self-field conditions at 1.8 K. Analysis of the pinning forces suggests vortex pinning by crystalline defects associated with volume Δk (variations in the Ginzburg-Landau parameter). The relaxation rate follows the Anderson-Kim model, and the pinning energies range from 1600 K at 0.02 T to 500 K at 0.5 T. Our study aims to advance our understanding of the connection between intrinsic superconducting properties and vortex behavior in intermetallic materials characterized by low thermal fluctuations.

Superheating field in superconductors with nanostructured surfaces

We report calculations of a DC superheating field Hsh in superconductors with nanostructured surfaces. Numerical simulations of the Ginzburg–Landau (GL) equations were performed for a superconductor with an inhomogeneous impurity concentration, a thin superconducting layer on top of another superconductor, and superconductor–insulator–superconductor (S-I-S) multilayers. The superheating field was calculated taking into account the instability of the Meissner state with a non-zero wavelength along the surface, which is essential for the realistic values of the GL parameter κ. Simulations were performed for the material parameters of Nb and Nb3Sn at different values of κ and the mean free paths. We show that the impurity concentration profile at the surface and thicknesses of S-I-S multilayers can be optimized to enhance Hsh above the bulk superheating fields of both Nb and Nb3Sn. For example, an S-I-S structure with a 90-nm-thick Nb3Sn layer on Nb can boost the superheating field up to ≈500 mT, while protecting the superconducting radio-frequency (SRF) cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices.

Charge density wave and superconductivity in 6R-TaS[formula omitted

The layered transition metal dichalcogenide compounds 1T-TaS2 and 4H-TaS2 are well known for their exotic properties, which include charge density wave, superconductivity, Mott transition, etc., and lately quantum spin liquid. Here, we report the magnetic, transport and transmission electron microscopy study of the charge density wave and superconductivity in 6R-TaS2 which is a relatively less studied polymorph of this dichalcogenide TaS2. Our high temperature electron microscopy reveals multiple charge density wave transitions between room temperature and 660K. Magnetization, and the electrical resistivity measurements in the temperature range of 2-400 K reveal that 6R-TaS2 undergoes a charge density wave transition around 305 K and is followed by a transition to a superconducting state around 3.5 K. The low temperature specific heat measurement exhibits anomaly associated with the superconducting transition around 2.4 K. The estimated Ginzburg Landau parameter suggests that this compound lies at the extreme limit of type-II superconductivity.

The Ginzburg–Landau energy with a pinning term oscillating faster than the coherence length

The aim of this article is to study the magnetic Ginzburg–Landau functional with an oscillating pinning term. We consider here oscillations of the pinning term that are much faster than the coherence length \varepsilon>0 , which is also the inverse of the Ginzburg–Landau parameter. We study both the case of a periodic potential and of a random stationary ergodic one. We prove that we can reduce the study of the problem to the case where the pinning term is replaced by its average in the periodic case and by its expectation with respect to the random parameter in the random case. In order to do that, we use a decoupling of the energy (detailed in Lassoued and Mironescu’s 1999 paper) that leads us to the study of the convergence of a scalar positive minimizer of the Ginzburg–Landau energy with pinning term and with homogeneous Neumann boundary conditions. We prove uniform convergence of this minimizer towards the mean value of the pinning term by using a blowup argument and a Liouville-type result for non-vanishing entire solutions of the real Ginzburg–Landau/ Allen–Cahn equation, due to the results of Farina (2003).

DFT approach into the physical properties of MTe3 (M = Hf, Zr) superconductors: A comprehensive study

In this article, we investigated the structural, electronic, mechanical, optical, and superconducting state properties of the trichalcogenides, MTe3(M = Hf, Zr) compounds using the density functional theory. Electronic energy dispersion curves demonstrate that the title compounds are metallic in nature, with a significant contribution from the Te atom. The technologically important mechanical properties (stiffness constant, elastic moduli, brittle/ductile behavior, Poisson’s ratio, elastic anisotropy, machinability index, and hardness) are thoroughly examined and addressed. The value of Pugh’s ratio indicates the ductility (brittleness) of ZrTe3 (HfTe3). The Vickers hardness value is 0.86 and 0.54 GPa for MTe3 (M = Hf, Zr), respectively, which confirms their softness. The value of lattice thermal conductivity (in W m−1 K−1) for HfTe3 (3.64) and ZrTe3 (2.36) is low due to significant phonon scattering as confirmed by the Grüneisen parameter study. The optical constants were computed, which confirmed the strong optical anisotropy of MTe3 (M = Hf, Zr). For ZrTe3, with the electric field polarization along the [100] direction, the highest reflectivity (51.36%) is obtained compared to HfTe3 (45.21%). This shows promise for application as a radiative heat reflector of these two compounds. The superconducting state properties, such as London penetration depth, coherence length, Ginzburg–Landau parameter, and electron–phonon coupling parameters are estimated and discussed. The value of electron–phonon coupling parameters suggests that both compounds are moderately coupled superconductors.

First principles study of mechanical, thermal, electronic, optical and superconducting properties of C40-type germanide-based MGe2 (M = V, Nb and Ta)

Non-centrosymmetric germanide-based superconductors have recently attracted particular attention because of their unconventional physical properties. In the present study, we comprehensively investigated the structural and hitherto unexplored electronic, optical, mechanical, thermal, and superconducting state properties of germanide-based superconductors, MGe2 (M = V, Nb, and Ta), using the density functional theory. The obtained lattice parameters and accordingly the volume of the unit cells agree very well with the earlier reported values, indicating the high reliability of the physical properties studied. All the compounds studied herein are dynamically and mechanically stable. The compounds are brittle (ranked: NbGe2 < VGe2 < TaGe2) and elastically anisotropic in nature.The estimated hardness values of MGe2 (M = V, Nb and Ta) are found to be 16.95, 14.96 and 19.6 GPa, respectively. Different optical functions (dielectric functions, reflectivity, absorption coefficient, photoconductivity, refractive index and loss function) and thermal properties (thermal conductivity, thermal expansion coefficient, Debye temperature, specific heat and melting point) are investigated.The reflectance spectra in the visible and near UV region were found to be >50% for all these compounds, demonstrating their potential for application as coating material to reduce heating from incident electromagnetic radiation. Based on the results obtained for thermal properties and comparison with benchmark system, Y4Al12O9 and some other predicted compounds, the titled compounds could also be used as thermal barrier coating materials. Some important parameters for the understanding of the superconducting behavior, such as the Coulomb pseudopotential, London penetration depth, coherence depth, Debye temperature, electron-phonon coupling constant, and Ginzburg-Landau parameter, are also estimated, and the results obtained support that the NbGe2and TaGe2 compounds should be categorized as a type-2 superconductors.

Effect of Column Defects on the Vortex Dynamics of Superconducting Thin Film with Ginzburg–Landau Parameters

Effect of Column Defects on the Vortex Dynamics of Superconducting Thin Film with Ginzburg–Landau Parameters

Significant improvement of the lower critical field in Y doped Nb: potential replacement of basic material for the radio-frequency superconducting cavity

The research of high energy and nuclear physics requires high power accelerators, and the superconducting radio-frequency (SRF) cavity is regarded as their engine. Up to now, the widely used practical and effective material for making the SRF cavity is pure Nb. The key parameter that governs the efficiency and the accelerating field (E acc) of a SRF cavity is the lower critical field H c1. Here, we report a significant improvement of H c1 for a new type of alloy, Nb1−x Y x fabricated by the arc melting technique. Experimental investigations with multiple tools including x-ray diffraction, scanning electron microscopy, resistivity and magnetization are carried out, showing that the samples have good quality and a 30%–60% enhancement of H c1. First principle calculations indicate that this improvement is induced by the delicate tuning of a Lifshitz transition of a Nb derivative band near the Fermi energy, which increases the Ginzburg–Landau parameter and H c1. Our results may trigger a replacement of the basic material and thus a potential revolution for manufacturing the SRF cavity.

Bulk superconductivity in transition metal oxide TaO

The discovery of coexistence of bulk superconductivity and nontrivial topological bands in the compounds, such as LaO and NbC, with a rocksalt structure, motivates us to study the physical properties of TaO with the same structure. Based on preparing successfully TaO polycrystalline sample, we measured its resistivity, magnetization, and specific heat. It was first found that TaO is a type-II superconductor with the critical temperature Tc = 6.20 K and the Ginzburg–Landau parameter κGL(0) = 16.2. The estimated electron–phonon coupling constant λep (0.62) and the specific heat jump ΔCel/γnTc (0.56) demonstrate that TaO is a weak-coupling phonon-mediated superconductor. The lack of single crystal sample impedes us to study experimentally its properties related to the electronic band topology, which is the subject of endeavor in the future.

Nonreciprocal supercurrent in thin film of type II superconducting Sn

The nonreciprocal supercurrent, namely the superconducting diode effect, can be realized with various mechanisms. The recent study has demonstrated the superconducting diode effect on thin films under the out-of-plane magnetic field, owing to the asymmetric Bean–Livingston barrier on the edge. In this study, we investigated the nonreciprocal supercurrent in a thin film of Sn deposited on a diamond substrate. The Ginzburg-Landau parameter κ in the thin film was estimated to be 0.711 which is slightly higher than (0.707). We observed the nonreciprocal supercurrent owing to the asymmetric energy barrier for flux penetration on the edge.

Superconducting properties and gap structure of the topological superconductor candidate Ti3Sb

We present a study of the superconducting properties of the candidate topological superconductor Ti_(3)Sb. Electrical transport measurements show zero resistance with a T_(c,onset) of ~ 5.9 K with a transition width {\Delta}T_c~ 0.6 K. The superconducting phase boundaries as derived from magneto-transport and magnetic susceptibility measurements agree well. We estimate an upper critical field Bc2(0)~4.5 T. A Ginzburg-Landau (GL) analysis yields values of the coherence length and penetration depth of {\zeta} = 6.2 nm and {\lambda} = 340 nm, respectively, and a GL parameter ~ 55, indicating extreme type-II behavior. Furthermore, we observed a step height in the specific heat ({\Delta}C_e)/({\gamma}T_c )~1.61, a value larger than the Bardeen-Cooper-Schrieffer (BCS) value of 1.43, suggesting modest coupling. Measurements of the temperature dependence of the London penetration depth via the tunnel-diode oscillator (TDO) technique down to ~ 450 mK show a full superconducting gap, consistent with a conventional s-wave gap structure.

Superconducting NbN for Strong Magnetic Field Applications: Impact of the Thin Films Intrinsic Disorder

The research on superconducting circuits for quantum information technologies progressively extends from the academic world towards the industry. Material sciences therefore become an essential lever for the development of technologies based on such circuits as they allow finding industry-compatible routes of improvements. In this context, we propose a study on the behavior of the niobium nitride (NbN), one of the most commonly used material for these devices, when exposed to strong magnetic fields. To this aim, the properties of NbN layers with the same composition but different microstructures, tuned by changing the deposition method, are compared. This study aims to establish interdependencies between the microstructure of the material and its behavior once exposed to a magnetic field. X-ray diffraction and Hall-effect characterizations are used to assess that the microstructure is significantly modified by the choice of the deposition technique. Pushing further these investigations also allowed to quantify and compare the level of disorder in both cases by extracting the Ioffe-regel and the Ginzburg-Landau parameters from characterizations of the superconducting transition temperature for several magnetic field amplitudes. This was used to conclude that in highly disordered NbN layers, the microstructure heterogeneities are responsible for a strong electron localization allowing to significantly enhance the resilience of their superconducting state under strong magnetic fields.

Vortex state in a two-condensate superconducting film considering a topological coupling

In this work, we studied the magnetization and the Cooper pairs density in a conventional superconducting thin square film in the presence of an external magnetic field H. Our investigation was carried out to solve the [Formula: see text]-wave-two-band Ginzburg–Landau equations (TB-TDGL) considering a topological-type coupling between the bands. We vary the size of the sample [Formula: see text], the weighty of the coupling [Formula: see text] and the effective Ginzburg–Landau parameter [Formula: see text], as a magnetic field function. We found an interesting vortex configuration and the respective generation of vortex clusters due to the coupling used between condensates. A high (weak) dependence of the first (second) critical field on the weight of the coupling is found. We revealed interesting magnetization curves, their dependence with the size of the sample, the relationship with the coherence length and penetration length and finally with the weight of the coupling between the bands ([Formula: see text]).

On the Stability of Axisymmetric States in the Ginzburg–Landau Theory

The stability of superconducting states with a trapped magnetic flux in a spherical sample is investigated. Superconductors with a finite value of the Ginzburg–Landau parameter are considered (in particular, type I superconductors for which the magnetic field distortion near the sample plays an important role). It is assumed that the sample size is not too large as compared to correlation length ξ(T), and the superconducting state is axially symmetric. The possibility of the existence of states with a trapped flux in zero external field is considered. The results are compared to those for a cylindrical sample.