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Anthony T. Fiory

Publications and source records attributed to Anthony T. Fiory.

At least 19 recordsLinked to original sources
arXiv2025

Interfacial superconductivity in Cu/Cu$_{\rm{2}}$O and its effect on shielding ambient electric fields

A model is presented for two-dimensional superconductivity at semiconductor-on-metal interfaces mediated by Coulomb interactions between electronically-active interface charges in the semiconductor and screening charges in the metal. The junction considered is native Cu$_{\rm{2}}$O on Cu in which an interfacial double charge layer of areal density $n$, comprising superconducting holes in Cu$_{\rm{2}}$O and mediating electrons in Cu, is induced in proportion to a sub-monolayer of adsorbed $^{\rm{4}}\rm{He}$ atoms. Evidence for superconductivity on copper with prior air exposure is revealed in new analysis of previously published work function data. Based on a theory developed for layered superconductors, the intrinsic transition temperature $T_{\rm{C}}$ = $\beta$ $n$$^{\rm{1/2}}$/$\zeta$ is determined by $n$ and transverse distance $\zeta$ $\simeq$ 2.0 $\rm{\r{A}}$ between the charge layers; $\beta$ = 1.933(6) $e$$^{\rm{2}}$$\bar{\lambda}$$_{\rm{C}}$/k$_{\rm{B}}$ = 1247.4(3.7) K-$\rm{\r{A}}$$^{\rm{2}}$ is a universal constant involving the reduced Compton wavelength of the electron $\bar{\lambda}$$_{\rm{C}}$. This model is applied to understanding the shielding of copper work-function patch and gravitational compression electric fields reported in the Witteborn-Fairbank gravitational electron free fall experiment. Interfacial superconductivity with $n$ $\simeq$ 1.6 $\times$ 10$^{\rm{12}}$ $\rm{cm}^{\rm{-2}}\rm{,}$ $T_{\rm{C}}$ $\simeq$ 7.9 K and Berezinski\u{i}-Kosterlitz-Thouless temperature $T_{\rm{BKT}}$ $\simeq$ 4.4 K accounts for the shielding observed at temperature $T$ $\simeq$ 4.2 K. Helium desorption and concomitant decreases in $n$ and $T_{\rm{C}}$ replicate the temperature transition in ambient electric fields on falling electrons, as observed by Lockhart et al., and the vanishing of superconductivity above $T$ $\simeq$ 4.8 K.

cond-mat.supr-con↗
arXiv2023

Determining the upper critical magnetic field for N-doped lutetium hydride directly from the source data files in Dasenbrock-Gammon et al., Nature $\underline{615}$, 244 (2023)

The Ginzburg-Landau-based upper critical magnetic field $H_{\textrm{C2}}$ (0) $\approx$ 88 T for N-doped lutetium hydride, reported in Dasenbrock-Gammon et al., Nature $\textbf{615}$, 244 (2023), is obtained therein by modeling resistance behavior, defining transitions widths, and applying magnetic fields $H$ = 1 T and 3 T. A method is presented herein for determining the critical temperature $T_{\textrm{C}}$ ($H$) directly from the resistance drops in the source data, implying a temperature slope -d$H_{\textrm{C2}}$ /d$T$ of 0.46(6) ${-}$ 0.51(5) T/K and, by applying pure BCS theory, an $H_{\textrm{C2}}$ (0) of 71(10) ${-}$ 79(8) T.

cond-mat.supr-con↗
arXiv2022

Analysis of electrical resistance data from Snider et al., Nature $\underline{586}$, 373 (2020)

Digital data for the temperature dependence of electrical resistance, which were extracted and analyzed by Hamlin (arXiv:2210.10766v1) from the pdf file published for "Room temperature superconductivity in a carbonaceous sulfur hydride," show asymmetric serrations in data for 267 GPa in zero magnetic field that comprise smooth and digitized parts. Further analysis shows that the smooth part exhibits a step at the transition of ~16% in magnitude relative to the data. Notably, there is no evidence of asymmetric serrations in extracted data for lower pressures (184-258 GPa) or for 267 GPa in an applied magnetic field (1-9 T). Several questions are raised, the answers to which would help toward resolving these outstanding issues.

cond-mat.supr-con↗
arXiv2022

Superconducting $I$$\overline{4}$3$m$ CSH$_7$ model applied to resistive transition temperature data for compressed C-S-H at high pressure

This article updates version 1 by restricting consideration to only the resistive data and excluding the questioned 287.7-K datum reported for carbonaceous sulfur hydride in Snider et al., Nature $\textbf{585}$, 373 (2020). The superconducting transitions are considered in terms of the theoretically-discovered compressed $I$$\overline{\textrm{4}}$3$m$ CSH$_7$ structure of Sun et al., Phys. Rev. B $\textbf{101}$, 174102 (2020), which comprises a sublattice similar to $Im$$\overline{\textrm{3}}$$m$ H$_3$S with CH$_4$ intercalates. Positing an electronic genesis of the superconductivity, a model is presented in analogy with earlier work on superconductivity in $Im$$\overline{\textrm{3}}$$m$ H$_3$S, in which pairing is induced via purely electronic Coulomb interactions across the mean distance $\zeta$ between the S and H$_4$ tetrahedra enclosing C. Theoretical superconducting transition temperatures for $I$$\overline{\textrm{4}}$3$m$ CSH$_7$ are derived as $T$$_{\textrm{C0}}$ = (2/3)$^{1/2}$ $\sigma^{1/2}$ $\beta$/$a$$\zeta$, where $\beta$ = 1247.4 $\mathring{\mathrm{A}}$$^2$K is a universal constant, $\sigma$ is the participating charge fraction, and $a$ is the lattice parameter. Analysis suggests persistent bulk superconductivity with a pressure-dependent $\sigma$, increasing from $\sigma$ = 3.5, determined previously for $Im$$\overline{3}$$m$ H$_3$S, to $\sigma$ = 7.5 at high pressure owing to additionally participating C-H bond electrons. With $a$ and $\zeta$ determined by theoretical structure, calculations of $T$$_{\textrm{C0}}$ at the highest pressures, 258 and 271 GPa, are in agreement with resistive transitions to within an overall uncertainty of $\pm$ 3.5 K.

cond-mat.supr-con↗
arXiv2021

Optical polarizability of erbium-oxygen complexes in sol-gel-based silica films

For erbium-doped amorphous oxides, such as those that are used in compact lightwave devices interfaced with silicon, values of the refractive indices are commonly obtained empirically. This work, combining experimental and theoretical studies, examines silica as the exemplary host and the influence of erbium doping on the refractive index. Analysis of data is presented for the spectral refractive index in the ultraviolet to near infrared wavelength range of heavily erbium-doped silica thin films prepared by spin coating a sol-gel precursor on silicon and subsequent vacuum annealing. Effective medium Lorentz-Lorenz data analysis determines that the dopant component has a refractive index of 1.76(0.24) with wavelength dispersion constrained to within 2 percent. Considering the dopant as a localized ErO6 impurity complex, a corresponding theoretical refractive index of 1.662 is derived by calculating the optical polarizability and volume of the impurity. Data presented for room-temperature (293 K) photoluminescence in the vicinity of 1.54 micron are shown to be consistent with random variability in impurity sites. Inherent advantages of studying colloid-based materials are discussed. To the best of the authors knowledge, such a detailed study of the refractive index associated with erbium impurities in silica is being reported for the first time in the literature.

physics.optics↗
arXiv2020

High-$T$$_\textrm{C}$ Superconductivity in Hydrogen Clathrates Mediated by Coulomb Interactions between Hydrogen and Central-Atom Electrons

The uniquely characteristic macrostructures of binary hydrogen-clathrate compounds $M$H$_\textrm{n}$ formed at high pressure, a cage of hydrogens surrounding a central-atom host, is theoretically predicted in various studies to include structurally stable phonon-mediated superconductors. High superconductive transition temperatures $T$$_\textrm{C}$ have thus far been measured for syntheses with $M$ = La, Y, and Th. In compressed LaH$_\textrm{10}$, independent studies report $T$$_\textrm{C}$ of 250 K and over 260 K, a maximum in $T$$_\textrm{C}$ with pressure $P$, and normal-state resistance scaling with temperature (suggesting unconventional pairing). According to reported band structure calculations of $Fm$$\bar{3}$$m$-phase LaH$_\textrm{10}$, the La is anionic, with the chemical valence electrons appearing evenly split between La and H$_\textrm{10}$. Thus, compressed LaH$_\textrm{10}$ contains the combination of structure, charge separation, and optimal balanced allocation of valence electrons for supporting unconventional high-$T$$_\textrm{C}$ superconductivity mediated by Coulomb interactions between electronic charges associated with La and H$_\textrm{10}$. A general expression for the optimal superconducting transition temperature for $M$H$_\textrm{n}$ clathrates is derived as $T$$_\textrm{C0}$ = $k$$_\textrm{B}$$^{-1}$$\Lambda$[(n + $v$)/2$A$]$^{1/2}$$e$$^{2}$/$\zeta$, where $\Lambda$ is a universal constant, (n + $v$) is the chemical valence sum per formula unit, taking unity for H and $v$ for atom $M$, $A$ is the surface area of the H-polyhedron cage, and $\zeta$ is the mean distance between the $M$ site and the centroids of the polyhedron faces. Applied to $Fm$$\bar{3}$$m$ LaH$_\textrm{10}$, $T$$_\textrm{C0}$ values of 249.8(1.3) K and 260.7(2.0) K are found for the two experiments. Associated attributes of charge allocation, structure, effective Coulomb potential, . . .

cond-mat.supr-con↗
arXiv2019

High-$T_\textrm{C}$ Superconductivity Originating from Interlayer Coulomb Coupling in Gate-Charged Twisted Bilayer Graphene Moir$\'{e}$ Superlattices

Unconventional superconductivity in bilayer graphene has been reported for twist angles $\theta$ near the first magic angle and charged electrostatically with holes near half filling of the lower flat bands. A maximum superconducting transition temperature $T_\textrm{C}$ $\approx$ 1.7 K was reported for a device with $\theta$ = 1.05$\deg$ at ambient pressure and a maximum $T_\textrm{C}$ $\approx$ 3.1 K for a device with $\theta$ = 1.27$\deg$ under 1.33 GPa hydrostatic pressure. A high-$T_\textrm{C}$ model for the superconductivity is proposed herein, where pairing is mediated by Coulomb coupling between charges in the two graphene sheets. The expression derived for the optimal transition temperature, $T_\textrm{C0}$ = $k_\textrm{B}^{-1}$$\Lambda$(|$n_\textrm{opt}$ - $n_\textrm{0}$|/2)$^{1/2}$$e^2$/$\zeta$, is a function of mean bilayer separation distance $\zeta$, measured gated charge areal densities $n_\textrm{opt}$ and $n_\textrm{0}$ corresponding to maximum $T_\textrm{C}$ and superconductivity onset, respectively, and the length constant $\Lambda$ = 0.00747(2) $\mathring{\textrm{A}}$. Based on existing experimental carrier densities and theoretical estimates for $\zeta$, $T_\textrm{C0}$ = 1.94(4) K is calculated for the $\theta$ = 1.05$\deg$ ambient-pressure device and $T_\textrm{C0}$ = 3.02(3) K for the $\theta$ = 1.27$\deg$ pressurized device. Experimental mean-field transition temperatures $T_\textrm{C}^\textrm{mf}$ = 1.83(5) K and $T_\textrm{C}^\textrm{mf}$ = 2.86(5) K are determined by fitting superconducting fluctuation theory to resistance transition data for the ambient-pressure and pressurized devices, respectively; the theoretical results for $T_\textrm{C0}$ are in remarkable agreement with these experimental values. Corresponding Berezinskii-Kosterlitz-Thouless temperatures $T_\textrm{BKT}$ of 0.96(3) K and 2.2(2) K are also determined and interpreted.

cond-mat.supr-con↗
arXiv2017

Compressed H$_3$S: inter-sublattice Coulomb coupling in a high-$\textit{T}$$_C$ superconductor

Upon thermal annealing at or above room temperature (RT) and high pressure $\it P$ $\sim$ 155 GPa, H$_3$S exhibits superconductivity at $\it T_C$ $\sim$ 200 K. Various theoretical frameworks with strong electron-phonon coupling and Coulomb repulsion have reproduced this record-level $\it T_C$. Of particular relevance is that observed H-D isotopic correlations among $\it T_C$, $\it P$, and annealed order indicate limitations on the H-D isotope effect, leaving open for consideration unconventional high-$\it T_C$ superconductivity with electronic-based enhancements. The present work examines Coulombic pairing arising from interactions between neighboring S and H species on separate interlaced sublattices constituting H$_3$S in the Im$\overline{3}$m structure. The optimal transition temperature is calculated from $\it{T}$$_{C0}$ = $\it{k}$$_B$$^{-1}$$\Lambda$$\it{e}$$^2$/$\ell$$\zeta$, with $\Lambda$ = 0.007465 $\AA$, inter-sublattice S-H separation spacing $\zeta$ = $\it{a}$$_0$/$\sqrt{2}$, interaction charge linear spacing $\ell$ = $\it{a}$$_0$(3/$\sigma$)$^{1/2}$, average participating charge fraction $\sigma$ = 3.43 $\pm$ 0.10 estimated from theory, and lattice parameter $\it{a}$$_0$ = 3.0823 \AA. The result $\it{T}$$_{C0}$ = 198.5 $\pm$ 3.0 K is in excellent agreement with transition temperatures determined from resistivity and susceptibility data. Analysis of mid-infrared reflectivity confirms correlation between boson energy and $\zeta$$^{-1}$. Suppression of $\it T_C$ with increasing residual resistance for $<$ RT annealing is treated by scattering-induced pair breaking. Correspondence with layered high-$\it T_C$ superconductor structures are discussed. A model considering Compton scattering of virtual photons of energies $\leq$ $\it e$$^2$/$\zeta$ by inter-sublattice electrons is introduced, illustrating $\Lambda$ is proportional to the reduced electron Compton wavelength.

cond-mat.supr-con↗
arXiv2017

On the isotope effect in compressed superconducting H$_\textrm{3}$S and D$_\textrm{3}$S

A maximum superconductive transition temperature $T_\textrm{C}$ = 203.5 K has recently been reported for a sample of the binary compound tri-hydrogen sulfide (H$_\textrm{3}$S) prepared at high pressure and with room temperature annealing. Measurements of $T_\textrm{C}$ for H$_\textrm{3}$S and its deuterium counterpart D$_\textrm{3}$S have suggested a mass isotope effect exponent ${\alpha}$ with anomalous enhancements for reduced applied pressures. While widely cited for evidence of phonon-based superconductivity, the measured $T_\textrm{C}$ is shown to exhibit important dependences on the quality and character of the H$_\textrm{3}$S and D$_\textrm{3}$S materials under study; examination of resistance versus temperature data shows that variations in $T_\textrm{C}$ and apparent ${\alpha}$ are strongly correlated with residual resistance ratio, indicative of sensitivity to metallic order. Correlations also extend to the fractional widths of the superconducting transitions. Using resistance data to quantify and compensate for the evident materials differences between H$_\textrm{3}$S and D$_\textrm{3}$S samples, a value of ${\alpha}$ = 0.043 $\pm$ 0.140 is obtained. Thus, when corrected for the varying levels of disorder, the experimental upper limit ($\leq$0.183) lies well below ${\alpha}$ derived in phonon-based theories.

cond-mat.supr-con↗
arXiv2017

High-$T_\textrm {C}$ superconductivity in Cs$_3$C$_{60}$ compounds governed by local Cs-C$_{60}$ Coulomb interactions

Unique among alkali-doped $\textit {A}$$_3$C$_{60}$ fullerene compounds, the A15 and fcc forms of Cs$_3$C$_{60}$ exhibit superconducting states varying under hydrostatic pressure with highest transition temperatures at $T_\textrm {C}$$^\textrm {meas}$ = 38.3 and 35.2 K, respectively. Herein it is argued that these two compounds under pressure represent the optimal materials of the $\textit {A}$$_3$C$_{60}$ family, and that the C$_{60}$-associated superconductivity is mediated through Coulombic interactions with charges on the alkalis. A derivation of the interlayer Coulombic pairing model of high-$T_\textrm {C}$ superconductivity employing non-planar geometry is introduced, generalizing the picture of two interacting layers to an interaction between charge reservoirs located on the C$_{60}$ and alkali ions. The optimal transition temperature follows the algebraic expression, $T_\textrm {C0}$ = (12.474 nm$^2$ K)/$\ell$${\zeta}$, where $\ell$ relates to the mean spacing between interacting surface charges on the C$_{60}$ and ${\zeta}$ is the average radial distance between the C$_{60}$ surface and the neighboring Cs ions. Values of $T_\textrm {C0}$ for the measured cation stoichiometries of Cs$_{3-\textrm{x}}$C$_{60}$ with x $\approx$ 0 are found to be 38.19 and 36.88 K for the A15 and fcc forms, respectively, with the dichotomy in transition temperature reflecting the larger ${\zeta}$ and structural disorder in the fcc form. In the A15 form, modeled interacting charges and Coulomb potential e$^2$/${\zeta}$ are shown to agree quantitatively with findings from nuclear-spin relaxation and mid-infrared optical conductivity. In the fcc form, suppression of $T_\textrm {C}$$^\textrm {meas}$ below $T_\textrm {C0}$ is ascribed to native structural disorder. Phononic effects in conjunction with Coulombic pairing are discussed.

cond-mat.supr-con↗
arXiv2015

Modeling Intercalated Group-4-Metal Nitride Halide Superconductivity with Interlayer Coulomb Coupling

Behavior consistent with Coulomb-mediated high-T$_C$ superconductivity is shown to be present in the intercalated group-4-metal nitride halides A$_x$(S)$_y$MNX, where the MNX host (M = Ti, Zr, Hf; X = Cl, Br) is partially intercalated with cations A$_x$ and optionally molecular species (S)$_y$ in the van der Waals gap between the halide X layers, expanding the basal-plane spacing d. The optimal transition temperature is modeled by T$_{C0}$ ${\propto}$ {\zeta}$^{-1}$({\sigma}/$A$)$^{1/2}$, where the participating fractional charge per area per formula unit {\sigma}/$A$ and the distance {\zeta}, given by the transverse A$_x$-X separation ({\zeta} < d), govern the interlayer Coulomb coupling. From experiment results for {\beta}-form compounds based on Zr and Hf, in which concentrations x of A$_x$ are varied, it is shown that {\sigma} = {\gamma}[v(x$_{opt}$ $-$ x$_0$)], where x$_{opt}$ is the optimal doping, x$_0$ is the onset of superconducting behavior, v is the A$_x$ charge state, and {\gamma} = 1/8 is a factor determined by the model. Observations of T$_C$ < T$_{C0}$ in the comparatively more disordered {\alpha}-A$_x$(S)$_y$TiNX compounds are modeled as pair-breaking by remote Coulomb scattering from the A$_x$ cations, which attenuates exponentially with increasing {\zeta}. The T$_{C0}$ values calculated for nine A$_x$(S)$_y$MNCl compounds, shown to be optimal, agree with the measured T$_C$ to within experimental error. The model for T$_{C0}$ is also found to be consistent with the absence of high-T$_C$ characteristics for A$_x$MNX compounds in which a spatially separated intercalation layer is not formed.

cond-mat.supr-con↗
arXiv2015

Superconducting interaction charge in thallium-based high-Tc cuprates: Roles of cation oxidation state and electronegativity

Superconductivity in the Tl-based cuprates encompasses a notably broad range of measured optimal transition temperatures Tc0, ranging from lowest in the charge-depleted Tl-1201 compounds (Tl$_{1-x}$(Ba/Sr)$_{1+y}$La$_{1-y}$CuO$_{5-{\delta}}$), such as Tl$_{0.7}$LaSrCuO$_5$ (37 K) and TlBa$_{1.2}$La$_{0.8}$CuO$_5$ (45.4 K), to highest in the Tl-1223 compound TlBa$_2$Ca$_2$Cu$_3$O$_{9{\pm}{\delta}}$ (133.5 K). Seven Tl-based cuprates are considered and compared using the model of superconductive pairing via electronic interactions between two physically separated charge reservoirs, where Tc0 $\propto$ ({\sigma}{\eta}/A)$^{1/2}${\zeta}$^{-1}$ is determined by the superconducting interaction charge fraction {\sigma} the number {\eta} of CuO$_2$ layers, and the basal-plane area A, each per formula unit, and the transverse distance {\zeta} between interacting layers. Herein it is demonstrated that {\sigma} follows from the elemental electronegativity and the oxidation state of Tl, and other structurally analogous cations. The comparatively lower elemental electronegativity of Tl, in conjunction with its oxidation state, explains the higher {\sigma} and Tc0 values in the Tl-based compounds relative to their Bi-based cuprate homologues. A derivation of {\sigma} is introduced for the optimal Tl$_2$Ba$_2$Ca$_{{\eta}-1}$Cu$_{\eta}$O$_{2{\eta}+4}$ (for {\eta} = 1, 2, 3) compounds, which exhibit a Tl oxidation state at or near +3, obtaining the fundamental value {\sigma}$_0$ = 0.228 previously established for YBa$_2$Cu$_3$O$_{6.92}$. Also reported is the marked enhancement in {\sigma} associated with Tl$^{+1}$ and analogous inner-layer cations relative to higher-valence cations. For a model proposition of {\sigma} = {\sigma}$_0$, the fractional Tl$^{+1}$ content of the mixed-valence compound, TlBa$_2$Ca$_2$Cu$_3$O$_{9{\pm}{\delta}}$, is predicted to be 1/3 at optimization, in agreement ...

cond-mat.supr-con↗
arXiv2014

Comment on "Superconductivity in electron-doped layered TiNCl with variable interlayer coupling"

In their article, Zhang et al. [Phys. Rev. B 86, 024516 (2012)] present a remarkable result for A$_x$(S)$_y$TiNCl compounds ($\alpha$-phase TiNCl partially intercalated with alkali A and optionally co-intercalated molecular species S), finding the superconducting transition temperature T$_C$ scales with $d$$^{-1}$, where the spacing $d$ between TiNCl layered structures depends on intercalant thickness. Recognizing that this behavior indicates interlayer coupling, Zhang et al. cite, among other papers, the interlayer Coulombic pairing mechanism picture [Harshman et al., J. Phys.: Condens. Matter 23, 295701 (2011)]. This Comment shows that superconductivity occurs by interactions between the chlorine layers of the TiNCl structure and the layers containing A$_x$, wherein the transverse A$_x$-Cl separation distance {\zeta} is smaller than $d$. In the absence of pair-breaking interactions, the optimal transition temperature is modeled by T$_{C0}$ $\propto$ ({\sigma}/$A$)$^{1/2}$$\zeta$$^{-1}$, where {\sigma}/$A$ is the fractional charge per area per formula unit. Particularly noteworthy are the rather marginally-metallic trends in resistivities of A$_x$(S)$_y$TiNCl, indicating high scattering rates, which are expected to partially originate from remote Coulomb scattering (RCS) from the A$_x$ ions. By modeling a small fraction of the RCS as inducing pair-breaking, taken to cut off exponentially with {\zeta}, observations of T$_C$ < T$_{C0}$ are quantitatively described for compounds with {\zeta} < 4 {\AA}, and T$_C$ $\approx$ T$_{C0}$ for Na$_{0.16}$(S)$_y$TiNCl with propylene carbonate and butylene carbonate co-intercalants for which {\zeta} > 7 {\AA}. Since a spatially separated alkali-ion layer is not formed in Li$_{0.13}$TiNCl, the observed T$_C$ of 5.9 K is attributed to an intergrowth phase related to TiN (T$_C$ = 5.6 K).

cond-mat.supr-con↗
arXiv2012

Charge compensation and optimal stoichiometry in superconducting (Ca$_x$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_3$O$_y$

The superconductive and magnetic properties of charge$-$compensated (Ca$_x$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_3$O$_y$ (normally denoted as CLBLCO) are considered through quantitative examination of data for electrical resistivity, magnetic susceptibility, transition width, muon$-$spin rotation, x$-$ray absorption, and crystal structure. A derivative of LaBa$_2$Cu$_3$O$_y$, cation doping of this unique tetragonal cuprate is constrained by compensating La substitution for Ba with Ca substitution for La, where for 0 {\le} x {\le} 0.5 local maxima in T$_C$ occur for y near 7.15. It is shown that optimum superconductivity occurs for 0.4 {\le} x {\le} 0.5, that the superconductivity and magnetism observed are nonsymbiotic phenomena, and that charge$-$compensated doping leaves the carrier density in the cuprate planes nearly invariant with x, implying that only a small fraction of superconducting condensate resides therein. Applying a model of electronic interactions between physically separated charges in adjacent layers, the mean in-plane spacing between interacting charges, {\ell} = 7.1206 {\AA}, and the distance between interacting layers, {\zeta} = 2.1297 {\AA}, are determined for x = 0.45. The theoretical optimal T$_{C0}$ {\propto} {\ell}$^{-1}${\zeta}$^{-1}$ of 82.3 K is in excellent agreement with experiment ({\approx} 80.5 K), bringing the number of compounds for which T$_{C0}$ is accurately predicted to 37 from six different superconductor families (overall accuracy of {\pm}1.35 K).

cond-mat.supr-con↗
arXiv2012

Coexisting Holes and Electrons in High-Tc Materials: Implications from Normal State Transport

Normal state resistivity and Hall effect are shown to be successfully modeled by a two-band model of holes and electrons that is applied self-consistently to (i) DC transport data reported for eight bulk-crystal and six oriented-film specimens of YBa2Cu3O7-{\delta}, and (ii) far-infrared Hall angle data reported for YBa2Cu3O7-{\delta} and Bi2Sr2CaCu2O8+{\delta}. The electron band exhibits extremely strong scattering; the extrapolated DC residual resistivity of the electronic component is shown to be consistent with the previously observed excess thermal conductivity and excess electrodynamic conductivity at low temperature. Two-band hole-electron analysis of Hall angle data suggest that the electrons possess the greater effective mass.

cond-mat.supr-con↗
arXiv2012

Reply to "Comment on 'Isotope effect in high-Tc superconductors' "

Our paper on the isotope effect in high-temperature superconductors with cation substitutions presents a comprehensive analysis rooted completely in the experimental evidence. In this Reply we show that pair-breaking disorder, isotope effects, doping-induced variations in Tc and in the magnetic penetration depth, Coulomb's law, and Anderson's theorem are treated with correct physical and mathematical fundamentals. In contrast, the theory fostered in the Comment by Alexandrov and Zhao contradicts several specific experimental facts, eight of which are briefly discussed. Their Comment also uncritically repeats a previously discredited assertion of an isotope effect in the superconducting carrier mass, incorrectly assumes that cation doping continuously varies intrinsic superconducting parameters, unjustifiably assigns importance to data from samples with serious quality problems, and renders a false estimate of the pair-breaking strength.

cond-mat.supr-con↗
arXiv2012

The Superconducting Transition Temperatures of Fe1+xSe1--y, Fe1+xSe1--yTey and (K/Rb/Cs)zFe2--xSe2

In a recent contribution to this journal, it was shown that the transition temperatures of optimal high-Tc compounds obey the algebraic relation, Tc0 = kB-1{\beta}/\ell{\zeta}, where \ell is related to the mean spacing between interacting charges in the layers, {\zeta} is the distance between interacting electronic layers, {\beta} is a universal constant and kB is Boltzmann's constant. The equation was derived assuming pairing based on interlayer Coulomb interactions between physically separated charges. This theory was initially validated for 31 compounds from five different high-Tc families (within an accuracy of \pm1.37 K). Herein we report the addition of Fe1+xSe1-y and Fe1+xSe1-yTey (both optimized under pressure) and AzFe2-xSe2 (for A = K, Rb, or Cs) to the growing list of Coulomb-mediated superconducting compounds in which Tc0 is determined by the above equation. Doping in these materials is accomplished through the introduction of excess Fe and/or Se deficiency, or a combination of alkali metal and Fe vacancies. Consequently, a very small number of vacancies or interstitials can induce a superconducting state with a substantial transition temperature. The confirmation of the above equation for these Se-based Fe chalcogenides increases to six the number of superconducting families for which the transition temperature can be accurately predicted.

cond-mat.supr-con↗