Landau Parameters Research Articles

Fermi surface renormalization group

The low energy manifold for fermions at finite density is the Fermi surface. I describe renormalization group (RG) in which modes encountered on approaching the Fermi surface are systematically integrated out. The fixed point is described by strictly marginal coupling functions identified as the Landau parameters and marginally relevant coupling functions describing the BCS instability in various angular momentum channels.

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.

Al1−xScxSbyN1−y: An opportunity for ferroelectric semiconductor field effect transistor

For the in-memory computation architecture, a ferroelectric semiconductor field-effect transistor (FeSFET) incorporates ferroelectric material into the FET channel to realize logic and memory in a single device. The emerging group III nitride material Al1−xScxN provides an excellent platform to explore FeSFET, as this material has significant electric polarization, ferroelectric switching, and high carrier mobility. However, steps need to be taken to reduce the large band gap of ∼5 eV of Al1−xScxN to improve its transport property for in-memory logic applications. By state-of-the-art first principles analysis, here we predict that alloying a relatively small amount (less than ∼5%) of Sb impurities into Al1−xScxN very effectively reduces the band gap while maintaining excellent ferroelectricity. We show that the co-doped Sb and Sc act cooperatively to give a significant band bowing leading to a small band gap of ∼1.76 eV and a large polarization parameter ∼0.87 C/m2, in the quaternary Al1−xScxSbyN1−y compounds. The Sb impurity states become more continuous as a result of interactions with Sc and can be used for impurity-mediated transport. Based on the Landau-Khalatnikov model, the Landau parameters and the corresponding ferroelectric hysteresis loops are obtained for the quaternary compounds. These findings indicate that Al1−xScxSbyN1−y is an excellent candidate as the channel material of FeSFET.

Localized Superconductivity in LaB6 Hexaboride with Dynamic Charge Stripes

Type II superconductivity with Tc ∼ 6 K is discovered in LaB6. The critical fields are determined and the estimates for the coherence length ξ(0) ∼ 240 Å, the Ginzburg−Landau parameter κGL ∼ 2, and the electron–phonon coupling constant λe−ph ≈ 0.75 are obtained. Precision X-ray diffraction studies at T = 30 K reveal three-dimensional charge-stripe structures in LaB6. The scenario of superconductivity localized near filamentary channels with a fluctuating electron density arising in the lanthanum hexaboride matrix is discussed.

Unveiling the reliability of negative capacitance FinFET with confrontation of different HfO2-ferroelectric dopants

The CMOS compatibility of Negative Capacitance (NC) FETs has been enhanced tremendously after introducing a thin film-doped HfO2 as a ferroelectric (FE) layer. For a given FE layer, the NC property is governed by specific HfO2 dopants (e.g., La, Zr, Al, Sr, Gd, Y, and Si). Thus, the TCAD simulation considerably depends on the dopant-specific Landau parameters (αx,βx,γx,ρx,gx), and its solidity needs proper attention. Further, the reliability of the NC devices is severely affected by process variations, i.e., interface trap charges, work function variation, random dopant fluctuation, and ambient temperature (external), which modulates the device threshold voltage (Vth); in turn, the device aging. In this paper, using well-calibrated TCAD models, we investigated reliability for the different dopant-specific NC-FinFET, in terms of Vth, ON current (ION), and OFF current (IOFF) modulation induced by: (i) the interface trap variability (ITV) considering the different trap concentration and energy location; (ii) the work function variability (WFV) considering different metal grain sizes (Gr); (iii) the random dopant fluctuations (RDF); and (iv) the ambient temperature. In this way, the device aging is calculated by inspecting Vth shift by ±50mV. These investigations pave the path for realizing a reliable NC-FinFET design.

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.

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.

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.

Landau theory-based relaxational modeling of first-order magnetic transition dynamics in magnetocaloric materials

The magnetocaloric effect is often largest within the neighborhood of a first-order phase transition. This effect can be utilized in magnetocaloric refrigeration, which completely eliminates the need for the greenhouse gases utilized in conventional refrigeration. However, such transitions present unique dynamical effects and are accompanied by hysteresis, which can be detrimental for such refrigeration applications. In this work, a Landau theory-based relaxational model is used to study the magnetic hysteresis and dynamics of the first-order magnetic transition of LaFe13−x Si x . Fitting the experimental magnetization data as a function of applied magnetic field under different field sweep rates with this model provided the Landau parameters (A, B, and C) and the kinetic coefficient of the studied material. We demonstrate the tendency of the magnetic hysteresis to increase with the magnetic field sweep rate, underlining the importance of studying and minimizing the magnetic hysteresis in magnetic refrigerants at practical field sweep rates. While evaluating the temperature dependence of the time required for a complete transition to occur, a nonmonotonic behavior and a sharp peak were found for temperatures near the transition temperature. Such peaks occur at the same temperature as the peak of the magnetic entropy change for low fields, whereas for higher fields the two peaks decouple. This information is critical for technological applications (such as refrigerators/heat pumps) as it provides guidelines for the optimization of the magnetic field amplitude in order to reduce the transition timescale and consequently maximize the machine operational frequency and amount of heat that is pumped in/out per second.

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.

A Theoretical Study of Negative Capacitance Field‐Effect Transistors Using Ferroelectrics Having First‐ and Second‐Order Phase Transitions

Herein, a theoretical study of negative capacitance field‐effect transistors (NCFETs) using ferroelectrics (FEs), having first‐ and second‐order phase transitions (FPT and SPT, respectively), applying the Landau–Devonshire (LD) theory, is presented. The expressions for the Landau parameters for FPT FEs are derived from the basic relations, and subsequently, these are used in the numerical models for the surface potential, gate charge, and drain current for NCFETs with FPT FEs, developed in this work. The results show an excellent match with those obtained from technology computer‐aided design (TCAD) simulations. Next, the Landau parameters and the numerical models for the charge and drain current for NCFETs with SPT FEs are developed, following a similar procedure, and then the results of these two structures are compared, along with those obtained from TCAD simulations, which shows an excellent match. The results bring out some interesting observations—notable among them is a higher Ion/Ioff ratio for FPT structures, as compared to that for SPT ones, caused by a reduction in the subthreshold current, with a marginal increase in the strong inversion current in the former. This feature, by itself, may make NCFETs with FPT FEs more suitable than those with SPT FEs for low‐power applications.

The effect of the spin–orbit coupling on the physical properties of ScGa[formula omitted] and LuGa[formula omitted] superconductors

In this work, we have aimed to reveal the impacts of spin–orbit coupling (SOC) on the elastic, mechanical, electronic, phonon, and electron–phonon interaction properties of ScGa3 and LuGa3 by executing both scalar and full-relativistic ab initio pseudopotential calculations based on the density functional theory with its local density approximation. The effect of this coupling on the physical properties of LuGa3 is slightly more pronounced than those of ScGa3. This finding has a physical explanation because spin–orbit interaction in an atom is due to the interaction of electronic spin moment with the magnetic field formed by the traveling electron in the electric field of the nucleus. Since the nuclear charge enhances with the rise in atomic number of the elements, heavier atoms are characterized by larger SOC strength and the mass of Lu atom is considerably heavier than that of Sc atom. In particular, the inclusion of SOC changes the value of the electron–phonon coupling parameter for LuGa3 from 0.593 to 0.583 by less 2%, while the corresponding parameter of ScGa3 remains almost unchanged (from 0.536 to 0.537). The superconducting transition temperature is estimated to be 2.09 K for ScGa3, and 2.15 K for LuGa3 are almost equal to their experimental values of 2.1 and 2.2 K, respectively. Finally, we have estimated three superconducting parameters: the Ginzburg–Landau parameter (κ(0)), the London penetration depth (λL(0)) and the coherence length (ξ(0)). Their calculated values confirm the existence of type-I superconductivity in both superconductors.

Bounded vorticity for the 3D Ginzburg–Landau model and an isoflux problem

AbstractWe consider the full three‐dimensional Ginzburg–Landau model of superconductivity with applied magnetic field, in the regime where the intensity of the applied field is close to the ‘first critical field’ at which vortex filaments appear, and in the asymptotics of a small inverse Ginzburg–Landau parameter . This onset of vorticity is directly related to an ‘isoflux problem’ on curves (finding a curve that maximizes the ratio of a magnetic flux by its length), whose study was initiated in [22] and which we continue here. By assuming a nondegeneracy condition for this isoflux problem, which we show holds at least for instance in the case of a ball, we prove that if the intensity of the applied field remains below , the total vorticity remains bounded independently of , with vortex lines concentrating near the maximizer of the isoflux problem, thus extending to the three‐dimensional setting a two‐dimensional result of [28]. We finish by showing an improved estimate on the value of in some specific simple geometries.

Acoustic plasmons and isotropic short-range interaction in two-component electron liquids

Dispersion of acoustic plasmons and isotropic Landau parameters are calculated in three- and two-dimensional two-component electron-electron and electron-hole liquids at various concentration and mass ratios using Landau-Silin kinetic equation and the random phase approximation for the self-energy. It is shown that the mode propagation and the strength of quasiparticle interaction are determined by the intercomponent screening and are asymmetric with respect to charge composition of two-component liquid. The well-defined acoustic plasmon-zero sound mode arises at strong difference in concentrations between components and its renormalization by the short-range exchange-correlation interaction is negligible. The acoustic plasmon mediated interparticle effective interaction in the fast component is weak in both the three- and two-dimensional electron liquids with parabolic dispersion, so the associated plasmonic superconductivity and the formation of acoustic plasmarons are unfavorable.