Marcin Kowalik, Michał Kowalczyk, Jan M. Michalik, Marek Giebułtowski, Ryszard Zalecki, Janusz Niewolski, Waldemar Tokarz
This paper demonstrates the method of estimation of critical temperature Tc value of high-temperature superconductors from the dispersive part of AC susceptibility measurement using a pair of neural networks.
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We calculate the spin susceptibility of a superconductor without inversion symmetry, both in the clean and disordered cases. The susceptibility has a large residual value at zero temperature, which is further enhanced in the presence of scalar impurities.
We calculate the specific heat and susceptibility of rare-earth magnetic superconductors in the context of the Ginzburg-Landau theory. The specific heat and susceptibility are calculated both at the coexistence phase of antiferromagnetism and superconductivity and normal phase. Theoretical results are compared with experimental results, which agree excellently well.
Spin susceptibility of nonunitary spin-triplet superconductors
本文推导了非幺正自旋三重态超导体在单带模型中的自旋磁化率一般公式，并用于批判性评估相关实验声称。
ARPES measurements on HiTc superconductors such as BiSrCaCuO reveal a quasiparticle peak, a broad background and a dip. The background may originate from inelastic spin fluctuation emission. Calculations of the spectral weight are presented incorporating these inelastic processes. Superconducting correlations have been included in the magnetic susceptibility. The dip feature in the spectral weight is evidence for a spin gap in the superconducting state.
Finite-difference time-domain methods are increasingly being used to develop, model and analyze the response of materials, including engineered metamaterials that may contain superconductors. Though simple and useful expressions for the time-domain susceptibility exist for basic metals and dielectrics, the time-domain response for a superconductor has not been developed, mainly because the frequency-dependent expressions themselves are rather complex. In this paper we present a simple approximate expression for the time-domain susceptibility of a superconductor for the hbar/2Delta time scale (…
Recent experiments indicate that the Bechgaard salts (TMTSF)$_2$ ClO$_4$ and (TMTSF)$_2$ PF$_6$ may be unconventional triplet superconductors. The quasiparticle density of states and the uniform spin susceptibility tensor are computed at low temperatures for order parameter symmetries, as an attempt to narrow the number of possibilities based on experimental evidence.
Spin Susceptibility of a J=3/2 Superconductor
本文解析计算了立方超导体中J=3/2赝自旋五重态的自旋磁化率，发现其各向同性或各向异性及非对角元素取决于序参量的对称性选择。
Experiment and analytical calculations show that the demagnetizing field of a superconductor is a sensitive probe of quantities otherwise difficult to measure, such as the sample-probe distance in flux-density imaging experiments, and the field of first flux penetration Hp. In particular, the ratio of the maximum field measured above the superconductor edge and the applied field can be determined unambiguously so as to define a linear "geometric" susceptibility. The evolution of this susceptibility with field depends on the regime of flux penetration, and can be used as a means to determine Hp…
Experiment and theory indicate that UPt3 is a topological superconductor in an odd-parity state, based in part from temperature independence of the NMR Knight shift. However, quasiparticle spin-flip scattering near a surface, where the Knight shift is measured, might be responsible. We use polarized neutron scattering to measure the bulk susceptibility with H||c, finding consistency with the Knight shift but inconsistent with theory for this field orientation. We infer that neither spin susceptibility nor Knight shift are a reliable indication of odd-parity.
The nematic susceptibility of hole-doped Ba1-xKxFe2As2 and electron-doped Ba(Fe1-xCox)2As2 iron-based superconductors is obtained from measurements of the elastic shear modulus using a three-point bending setup in a capacitance dilatometer. Nematic fluctuations, although weakened by doping, extend over the whole superconducting dome in both systems, suggesting their close tie to superconductivity. Evidence for quantum critical behavior of the nematic susceptibility is, surprisingly, only found for Ba(Fe1-xCox)2As2, the system with the lower maximal Tc value.
We calculate the wave-vector dependent electronic spin susceptibility $χ_{αβ}(\mathbf q, \mathbf H_0)$ of a d-wave superconductor in uniform magnetic field $\mathbf{H}_0$ with Pauli pair-breaking. We find that the transverse component of the susceptibility tensor can be greater than its normal state value; the longitudinal component also slightly increases but in a very limited range of $q$s. We identify several wave vectors $\{\mathbf q_\perp,\mathbf q_\parallel\}$, that correspond to the maxima of either $χ_\perp$ or $χ_\parallel$. We compare our results with available data on the high-field…
We show that in some trigonal and hexagonal crystals the Zeeman coupling of band electrons with an external magnetic field is strongly anisotropic and necessarily vanishes along the main symmetry axis. This leads to qualitative changes in the temperature dependence of the electron spin susceptibility in the superconducting state. In particular, the power-law exponents at low temperatures due to the contribution of the nodal quasiparticles are considerably modified compared to their textbook values.
The non-centrosymmetric superconductors Li2Pd3B and Li2Pt3B show different superconducting properties despite having the same crystal symmetry. Motivated by experimental results, we investigate the spin susceptibility of non-centrosymmetric superconductors accompanied by the topological transition of Fermi surfaces due to antisymmetric spin-orbit coupling, which is indicated by the first-principles band structure calculation for Li2Pt3B. We study three types of topological transition, namely, (A) the disappearance of the Fermi surface, (B) crossing the Dirac point, and (C) crossing the saddle …
The spin susceptibility of noncentrosymmetric superconductors is studied when the gap function has line nodes. As examples, d-wave states, where the gap function has an additional odd-parity phase factor, are examined. The curve of the spin susceptibility $χ(T)$ is upward convex when all line nodes are parallel to the magnetic field, while it is downward convex in the other d-wave states and an s-wave state. For polycrystalline powder samples, the temperature dependences of $χ(T)$ are predicted by assuming three explicit conditions of the powder particles. The results are compared with the exp…
A theoretical study is presented on the odd-frequency spin-singlet pairing that arises in nonuniform even-frequency superconductors as a consequence of broken translation symmetry. The effect of the odd-frequency pairing on the superfluid density and the spin susceptibility is analyzed by using the quasiclassical theory of superconductivity. It is shown that (1) the superfluid density is reduced by the formation of the odd-frequency singlet pairs and (2) the odd-frequency pairing increases the spin susceptibility even though its spin symmetry is singlet. The two unusual phenomena are related t…
We propose that the orbital angular momentum of the conduction electrons in the Iron-based superconductors is activated in their low energy physics. Using a five-band tight-binding model derived from fitting the LDA band structure, we find that the orbital magnetic susceptibility of the conduction electrons in such a multi-orbital system is several times larger than the Pauli spin susceptibility and is comparable in magnitude to the observed total magnetic susceptibility. The orbital magnetic susceptibility in the Fe-As plane($χ^{x}_{L}$) is found to be larger than that perpendicular to the Fe…
We demonstrate that a new tool, a model independent numerical Eliashberg inversion of the optical self-energy, based on maximum entropy considerations can be used to extract the magnetic excitation spectra of high-transition-temperature superconductors. In Bi-2212 we explicitly show that the magnetic mode that dominates the self-energy at low temperatures directly evolves out of a smooth transfer of spectral weight to the mode from the continuum just above it. This redistribution starts already at 200 K in optimally doped materials but is much weaker in overdoped samples. This provides evidenc…
Static spin susceptibility of superconductors with spin-orbit relaxation has been calculated in the seminal work of A.A. Abrikosov and L.P. Gor'kov [Sov. Phys. JETP, {\bf 15}, 752 (1962)]. Surprisingly the generalization of this result to finite frequencies has not been done despite being quite important for the modern topic of superconducting spintronics. The present paper fills this gap by deriving the analytical expression for spin susceptibility. The time-dependent spin response is shown to be captured by the quasiclassical Eilenberger equation with collision integrals corresponding to the…
Spin susceptibility in quasicrystal superconductor with spin-orbit interactions
研究准晶体超导体中自旋轨道相互作用对自旋磁化率的影响，揭示不同相互作用类型对磁化率的增强机制及温度依赖性变化。
Magnetic Field Dependence of the Spin Susceptibility on Conventional s-wave Superconductor LaRu$_4$P$_{12}$ Revealed by $^{31}$P-NMR and $^{139}$La-NMR
通过$^{31}$P和$^{139}$La核磁共振研究，证实常规s波超导体LaRu$_4$P$_{12}$中超导态自旋磁化率与磁场成正比，并平滑连接正常态，体现轨道对破缺效应。
We review our recent experimental results on the electronic nematic phase in electron- and hole-doped BaFe$_2$As$_2$ and FeSe. The nematic susceptibility is extracted from shear-modulus data (obtained using a three-point-bending method in a capacitance dilatometer) using Landau theory and is compared to the nematic susceptibility obtained from elastoresistivity and Raman data. FeSe is particularly interesting in this context, because of a large nematic, i.e., a structurally distorted but paramagnetic, region in its phase diagram. Scaling of the nematic susceptibility with the spin lattice rela…
Linear magnetic susceptibility of anisotropic superconductors of cuboidal shape
本文提出立方体形超导样品迈斯纳-伦敦无涡旋态下各向异性磁化率的简化模型，通过测量三个垂直方向磁响应提取伦敦穿透深度分量，可评估超导能隙结构分析所需的超流密度张量。
We here examine the relation between odd-frequency spin-triple even-parity (OTE) Cooper pairs and anomalous surface magnetic response in time-reversal invariant (TRI) spin-triplet superfluids and superconductors. The spin susceptibility generally consists of two contributions: Even-frequency odd-parity pair amplitudes and odd-frequency even-parity pair amplitudes. The OTE pair amplitudes are absent in the bulk region, but ubiquitously exist in the surface and interface region as Andreev bound states. We here clarify that additional discrete symmetries, originating from the internal symmetry an…
We have studied the interplay of magnetism and superconductivity in LaFeAsO$_{1-x}$F$_x$ and Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$. While antiferromagnetic spin density wave formation is suppressed and superconductivity evolves, all samples show a doping independent strong increase of the normal state susceptibility upon heating which appears a general feature of iron pnictides. The data provide evidence for robust local antiferromagnetic correlations persisting even in the superconducting regime of the phase diagram.
A phenomenological theory to describe the electromagnetic properties of granular superconductors, based on known bulk superconductors expressions and conventional Josephson's junctions tunneling currents, is presented and succesfully used to fit distinct experimental results for the magnetic susceptibility as a function of the temperature and the applied magnetic field of rather different samples.
The magnetic ac susceptibility of high-temperature superconductors is shown to obey some scaling relations.We try to ananlyse this behavior within the framework of a common nonlinear response function of mixed state.The derived equations for critical current and ac susceptibility (x(T)) agree with the scaling relations of experimental data.
We propose a microscopic explanation of the pseudogap features discovered in the normal state specific heat and magnetic susceptibility of cuprates. In the framework of the bipolaron theory of high-Tc superconductors we explain the magnitude of the carrier specific heat and susceptibility as well as their universal scaling with temperature over a wide range of doping.
The AC susceptibility at zero DC magnetic field of a polycrystalline sample of LaFeAsO_{0.94}F_{0.06} (T_c = 24 K) has been investigated as a function of the temperature, the amplitude of the AC magnetic field (in the range Hac = 0.003 - 4 Oe) and the frequency (in the range f = 10 kHz - 100 kHz). The temperature dependence of the AC susceptibility exhibits the typical two-step transition arising from the combined response of superconduncting grains and intergranular weak-coupled medium. The intergranular part of the susceptibility strongly depends on both the amplitude and the frequency of th…
We calculate the diamagnetic susceptibility in zero external magnetic field above the phase transition from ferromagnetic phase to phase of coexistence of ferromagnetic order and unconventional superconductivity. For this aim we use generalized Ginzburg-Landau free energy of unconventional ferromagnetic superconductor with spin-triplet electron pairing. A possible application of the result to some intermetallic compounds is briefly discussed.
We perform calculations relating the order parameter symmetry of organic quasi-one-dimensional superconductors to the bulk quasiparticle density of states and the bulk uniform spin susceptibility tensor at finite temperatures. Current experimental results suggest that some organic quasi-one-dimensional superconductors may exhibit triplet pairing symmetry. The purpose of our analysis is to attempt to narrow down the number of possibilities for the symmetry of the order parameter based on the experimental evidence.
In materials without spatial inversion symmetry the spin degeneracy of the conduction electrons can be lifted by an antisymmetric spin-orbit coupling. We discuss the influence of this spin-orbit coupling on the spin susceptibility of such superconductors, with a particular emphasis on the recently discovered heavy Fermion superconductor CePt3Si. We find that, for this compound (with tetragonal crystal symmetry,) irrespective of the pairing symmetry, the stable superconducting phases would give a very weak change of the spin susceptibility for fields along the c-axis and an intermediate reducti…
Nuclear magnetic resonance (NMR) and Knight shift measurements are critical tools in the identification of spin-triplet superconductors. We discuss the effects of spin orbit coupling on the Knight shift and susceptibilities for a variety of spin triplet multi-orbital gap functions with orbital-singlet character and compare their responses to "traditional" single band spin-triplet ($p_x+ip_y$) superconductors. We observe a non-negligible residual spin-susceptibility at low temperature.
We study the spin susceptibility of the orbital-singlet pairings, including the spin-triplet/orbital-singlet/$s$-wave $E_g$ representation proposed by Suh \textit{et al}., [H.\ G.\ Suh \textit{et al}., Phys.\ Rev.\ Research \textbf{2}, 032023 (2020)], for a three-orbital model of superconducting Sr$_2$RuO$_4$ in three dimensions. For the pseudospin-singlet states represented in the band basis, the spin susceptibility decreases when reducing the temperature, irrespective of the direction of the applied magnetic fields, even if they are spin-triplet/orbital-singlet pairings in the spin-orbital s…
Determination of gap structure of triplet superconductors from field-dependent Knight shift measurements
通过磁场依赖的Knight位移测量研究三重态超导体的间隙结构，揭示了自旋磁化率与序参量自旋配置的关系。
We have investigated the pressure dependence of ac and dc susceptibilities of the heavy-fermion superconductor CePt3Si (Tc= 0.75 K) that coexists with antiferromagnetism (TN = 2.2 K). As hydrostatic pressure is increased, Tc first decreases rapidly, then rather slowly near the critical pressure Pc = 0.6 GPa and shows a stronger decrease again at higher pressures, where Pc is the pressure at which TN becomes zero. A transition width and a difference in the two transition temperatures defined in the form of structures in the out-of-phase component of ac susceptibilities also become small near Pc…
Within the Landau paradigm of continuous phase transitions, ordered states of matter are characterized by a broken symmetry. Although the broken symmetry is usually evident, determining the driving force behind the phase transition is often a more subtle matter due to coupling between otherwise distinct order parameters. In this paper we show how measurement of the divergent nematic susceptibility of an iron pnictide superconductor unambiguously distinguishes an electronic nematic phase transition from a simple ferroelastic distortion. These measurements also reveal an electronic nematic quant…
Local magnetic properties around a nonmagnetic impurity are investigated in high-Tc cuprate superconductors. We consider a model two-dimensional d-wave superconductor with strong antiferromagnetic (AF) spin fluctuations and calculate the spin susceptibility around the impurity. We show that the uniform susceptibility, which is usually suppressed in spin-singlet superconductivity, is enhanced at low temperatures around the impurity when the impurity scattering is in the unitarity limit. This anomalous behavior is more remarkable when the impurity potential is extended spatially and the AF spin …
In an attempt to clarify conflicting published data, we report new measurements of specific heat, resistivity, magnetic susceptibility, and thermal expansivity up to room temperature for the 6 K superconductor ZrB12, using well-characterized single crystals with a residual resistivity ratio >9. The specific heat gives the bulk result 2*delta(0)/(k_B*Tc)=3.7 for the superconducting gap ratio, and excludes multiple gaps and d-wave symmetry for the Cooper pairs. The Sommerfeld constant gamma_n = 0.34 mJ K-2 gat-1 and the magnetic susceptibility xsi = -2.1 x 10^-5 indicate a low density of states …
We report 29Si-NMR study on a single crystal of the heavy-fermion superconductor CeIrSi3 without an inversion symmetry along the c-axis. The 29Si-Knight shift measurements under pressure have revealed that the spin susceptibility for the ab-plane decreases slightly below Tc, whereas along the c-axis it does not change at all. The result can be accounted for by the spin susceptibility in the superconducting state being dominated by the strong antisymmetric (Rashba-type) spin-orbit interaction that originates from the absence of an inversion center along the c-axis and it being much larger than …
For assemblies of superconductor nanograins, the magnetic response is analyzed as a function of both temperature and magnetic field. In order to describe the interaction energy of electron pairs for a huge number of many-particle states, involved in calculations, we develop a simple approximation, based on the Richardson solution for the reduced BCS Hamiltonian and applicable over a wide range of the grain sizes and interaction strengths at arbitrary distributions of single-electron energy levels in a grain. Our study is focused upon ultra-small grains, where both the mean value of the nearest…
Faulty evidence for superconductivity in ac magnetic susceptibility of sulfur hydride under pressure
本文质疑高压下硫氢化物超导性的现有证据，通过分析已发表实验数据，指出其不足以支持超导结论。
A theoretical study is performed on the entropy $S_{\rm s}$ and the spin susceptibility $χ_{\rm s}$ near the upper critical field $H_{c2}$ of s-wave type-II superconductors with arbitrary impurity concentrations. The changes of these quantities through $H_{c2}$ may be expressed as $[S_{\rm s}(T,B)-S_{\rm s}(T,0)]/[S_{\rm n}(T)-S_{\rm s}(T,0)]=1-α_{S}(1-B/H_{c2})\approx (B/H_{c2})^{α_{S}}$, for example, where $B$ is the average flux density and $S_{\rm n}$ denotes entropy in the normal state. It is found that the slopes $α_{S}$ and $α_χ$ at T=0 are identical, connected directly with the zero-en…
We study the order parameter phase fluctuation effects in cuprate superconductors near T=0, using a quasi-two-dimensional d-wave BCS model. An effective phason theory is obtained which is used to estimate the strength of the fluctuations, the fluctuation correction to the in-plane penetration depth, and the pair-field susceptibility. We find that while the phase fluctuation effects are difficult to observe in the renormalization of the superfluid phase stiffness, they may be observed in a pair tunneling experiment which measures the pair-field susceptibility.
Ac susceptibility and static magnetization measurements were performed in the nearly-optimally doped LaFeAsO$_{0.9}$F$_{0.1}$ and CeFeAsO$_{0.92}$F$_{0.08}$ superconductors, complementing earlier results on SmFeAsO$_{0.8}$F$_{0.2}$ [Phys. Rev. {\bf B 83}, 174514 (2011)]. The magnetic field -- temperature phase diagram of the mixed superconducting state is drawn for the three materials, displaying a sizeable reduction of the liquid phase upon increasing $T_{c}$ in the range of applied fields ($H \leq 5$ T). This result indicates that SmFeAsO$_{0.8}$F$_{0.2}$ is the most interesting compound amo…
The study of non-s-wave unconventional superconductivities in strongly correlated-electron systems has been a central issue in condensed matter physics for more than 30 years. In such unconventional superconductivities, d-wave Cooper pairing with antiparallel spins has been often observed in various quasi-two-dimensional (quasi-2D) bulk systems. Interestingly, many theories predicted that the triangular lattice causes the d-wave pairing to be unstable and may lead to more exotic pairing such as parallel spin (spin-triplet) pairing. Here we focus on a bulk organic triangular-lattice system in w…
The specific heat C of a sintered polycrystalline sample of MgB2 with a bulk superconducting transition temperature Tc=36.7 K is measured as a function of the temperature (2-300 K) and magnetic field (0-16 T), together with magnetic properties (normal-state susceptibility, superconducting state magnetization, etc.). The Sommerfeld constant gamma=0.89+-0.05 mJ/K^2/gat (2.7 mJ/K^2/mol) is determined in the normal state above Hc2. The normal- and superconducting state entropies are equal at Tc. Several moments of the phonon density of states are obtained from the lattice specific heat. We report …
We calculate the change in susceptibility resulting from a thin sheet with reduced penetration depth embedded perpendicular to the surface of an isotropic superconductor, in a geometry applicable to scanning Superconducting QUantum Interference Device (SQUID) microscopy, by numerically solving Maxwell's and London's equations using the finite element method. The predicted stripes in susceptibility agree well in shape with the observations of Kalisky et al. of enhanced susceptibility above twin planes in the underdoped pnictide superconductor Ba(Fe1-xCox)2As2 (Ba-122). By comparing the predicte…
We calcuate electronic spin susceptibility and spin-lattice relaxation rate in singlet superconductor near a pairbreaking surface, or in a domain wall of the order parameter. We directly link presence of high-density Andreev bound states in the inhomogeneous region, combined with coherence factors, to enhancement of the susceptibility above the normal state's value for certain $\bf q$ vectors. Beside the dominant peak at ferromagnetic vector $q=0$, we find significant enhancement of antiferromagnetic correlations at vectors $q\lesssim 2 k_f$, with $\bf q$ $along$ the domain wall in $S$-wave su…
We report ac susceptibility measurements of polycrystalline CePt_3Si down to 60 mK and in applied fields up to 9 T. In zero field, a full Meissner state emerges at temperatures T/Tc < 0.3, where Tc=0.65 K is the onset transition temperature. Though transport measurements show a relatively high upper critical field Bc2 ~ 4-5 T, the low temperature susceptibility, χ', is quite fragile to applied field, with χ' diminishing rapidly in fields of a few kG. Interestingly, the field dependence of χ' is well described by the power law, 4πχ'=(B/B_c)^{1/2}, where Bc is the field at which the onset of res…
Anisotropic paramagnetic response of topological Majorana surface states in the superconductor $\text{UTe}_2$
本文通过递归格林函数方法计算 UTe2 的表面自旋磁化率，发现拓扑 Majorana 表面态导致 Ising 型各向异性和反常增强，为磁性测量探测拓扑超导提供了可能途径。
Two-particle (2-p) excitations such as spin and charge excitations play a key role in high-Tc cuprate superconductors (HTSC). On the basis of a parameter-free theory, which extends the Variational Cluster Approach (a recently developed embedded cluster method) to 2-p excitations, the magnetic excitations of HTSC are shown to be reproduced for a Hubbard model within the relevant strong-coupling regime. In particular, the resonance mode in the underdoped regime, its intensity and "hour-glass" dispersion are in good overall agreement with experiments.
The temperature dependence of the 1st and 3rd harmonics of the AC magnetic susceptibility has been measured on melt grown YBCO samples for different frequencies and amplitudes of the AC magnetic field and intensity of a contemporaneously applied DC field. With the help of critical state models and of numerical simulations, we have devised a novel method, based on the combined analysis of the 1st and the 3rd harmonics that allows to distinguish different temperature ranges dominated by the different dissipative magnetic flux regimes. In particular, we identified three principal zones in the tem…
In order to determine the superconducting paring state in the ferromagnetic superconductor UCoGe, ^{59}Co NMR Knight shift, which is directly related to the microscopic spin susceptibility, was measured in the superconducting state under magnetic fields perpendicular to spontaneous magnetization axis: ^{59}K^{a, b}. ^{59}K^{a, b} shows to be constant, but does not decrease below a superconducting transition. These behaviors as well as the invariance of the internal field at the Co site in the superconducting state exclude the spin-singlet pairing, and can be interpreted with the equal-spin pai…
We report a systematic investigation of Ba[Fe(1-x)Co(x)]2As2 based on transport and 75-As NMR measurements, and establish the electronic phase diagram. We demonstrate that doping progressively suppresses the uniform spin susceptibility and low frequency spin fluctuations. The optimum superconducting phase emerges at x_c~0.08 when the tendency toward spin ordering completely diminishes. Our findings point toward the presence of a quantum critical point near x_c between the SDW (spin density wave) and superconducting phases.
In this study, we investigate the spin susceptibility in the superconducting state of a multilayer system with a layer-dependent Rashba spin-orbit coupling, representing a locally non-centrosymmetric superconductor. We show that the charge imbalance between different layers yields a strong layer dependence on the susceptibility, most significantly for a weak spin-orbit coupling, which is in contrast to a situation with an equally distributed charge. These results can be relevant for experimental test in multilayer high-Tc cuprates as well as in superconducting CeCoIn5/YbCoIn5 superlattices wit…
By using Nuclear Magnetic Resonance and ac-susceptibility, the characteristic correlation times for the vortex dynamics, in an iron-based superconductor, have been derived. Upon cooling, the vortex dynamics displays a crossover consistent with a vortex glass transition. The correlation times, in the fast motions regime, merge onto a universal curve which is fit by the Vogel-Fulcher law, rather than by an Arrhenius law. Moreover, the pinning barrier shows a weak dependence on the magnetic field which can be heuristically justified within a fragile glass scenario. In addition, the glass freezing…
In Nature 586, 373 (2020), Snider et al announced the experimental discovery of room temperature superconductivity in a carbonaceous sulfur hydride under high pressure, hereafter called CSH. The paper reported sharp drops in the measured magnetic susceptibility as a function of temperature for five different pressures, that were claimed to be a superior test signaling a superconducting transition. Here I present several arguments indicating that the susceptibility data published in that paper were probably fraudulent. This calls into question the validity of the entire paper and its claim of d…
Using a fermiology approach to the computation of the magnetic susceptibility measured by neutron scattering in hole-doped high-Tc superconductors, we estimate the effects on the incommensurate peaks caused by higher d-wave harmonics of the superconducting order parameter induced by underdoping. The input parameters for the Fermi surface and d-wave gap are taken directly from angle resolved photoemission (ARPES) experiments on Bi{2}Sr{2}CaCu{2}O{8+x} (Bi2212). We find that higher d-wave harmonics lower the momentum dependent spin gap at the incommensurate peaks as measured by the lowest spectr…
Rietveld analysis of the powder X-ray diffraction of a new layered oxyarsenide, LaNiOAs, which was synthesized by solid-state reactions, revealed that LaNiOAs belongs to the tetragonal ZrCuSiAs-type structure (P4/nmm) and is composed of alternating stacks of La-O and Ni-As layers. The electrical and magnetic measurements demonstrated that LaNiOAs exhibits a superconducting transition at 2.4 K, and above this, LaNiOAs shows metallic conduction and Pauli paramagnetism. The diamagnetic susceptibility measured at 1.8 K corresponded to ~20% of perfect diamagnetic susceptibility, substantiating that…
We report the effect of silver addition on superconducting performance of bulk YBCO (YBa2Cu3O7) superconductor. All the studied samples are prepared by conventional solid-state reaction method. Rietveld fitted X-ray diffraction data confirmed the single phase formation for all the studied samples. Detailed AC susceptibility measurements as a function of driven AC amplitude (1Oe-17Oe) of these samples revealed the enhancement of grains coupling with increasing Ag content in YBCO+Agx composite system. 10wt% Ag added YBCO superconductors exhibited the optimum inter granular coupling. The Scanning…
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