Weak Superconducting Pairing and a Single Isotropic Energy Gap in Stoichiometric LiFeAs

The surface resistance of specimens of superconducting tin and of tin-indium alloys has been measured at a frequency of 140 kmc/s and at temperatures near to the superconducting transition. In both single crystal and polycrystalline alloy specimens, the onset of quantum absorption was well defined and corresponded to an isotropic energy gap with a value at absolute zero of about 3·6 kT c . With pure tin, however, the absorption edge was not well defined in specimens oriented away from the tetrad axis; but near to the tetrad axis, there seems to be a considerable region in which the gap varies com paratively slowly, taking a value of about 3·6 kT c . Assuming that the absence of a clearly defined absorption edge for other orientations is the result of gap anisotropy, it is shown that regions in which the gap takes values very different from 3·6 kT c must lie well away from the tetrad axis. The analysis also shows that such regions are comparatively unimportant, and that the 3·6 kT c gap predominates strongly.

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Minimal Zeeman field requirement for a topological transition in superconductors

SciPost Physics ◽

10.21468/scipostphys.10.5.108 ◽

2021 ◽

Vol 10 (5) ◽

Author(s):

Kim Pöyhönen ◽

Daniel Varjas ◽

Michael Wimmer ◽

Anton Akhmerov

Keyword(s):

Time Reversal ◽

Energy Gap ◽

Topological Phase ◽

Zeeman Energy ◽

S Wave ◽

Zeeman Field ◽

Topological Phase Transition ◽

Rigorous Bounds ◽

Superconducting Pairing ◽

The Relationship

Platforms for creating Majorana quasiparticles rely on superconductivity and breaking of time-reversal symmetry. By studying continuous deformations to known trivial states, we find that the relationship between superconducting pairing and time reversal breaking imposes rigorous bounds on the topology of the system. Applying these bounds to s-wave systems with a Zeeman field, we conclude that a topological phase transition requires that the Zeeman energy at least locally exceed the superconducting pairing by the energy gap of the full Hamiltonian. Our results are independent of the geometry and dimensionality of the system.

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TUNNELING MEASUREMENTS ON SUPERCONDUCTORS WITH ISOTROPIC ENERGY GAPS

Canadian Journal of Physics ◽

10.1139/p67-117 ◽

1967 ◽

Vol 45 (4) ◽

pp. 1541-1548 ◽

Cited By ~ 4

Author(s):

D. G. Walmsley ◽

C. K. Campbell

Keyword(s):

Thin Films ◽

Temperature Dependence ◽

Energy Gap ◽

Pure Metal ◽

Isotropic Energy ◽

Bulk Superconductors ◽

Energy Gaps ◽

Gap Anisotropy ◽

Gap Parameter

The energy-gap anisotropy found in bulk superconductors is considerably reduced in thin films whose thickness, d, is much less than the range of coherence, ξ0, of the pure metal from which they are fabricated. By preparing such thin films of tin, indium, and lead, we have been able to examine the temperature dependence of the energy gap in each above 1.2 °K, using the tunneling technique. Values of the energy-gap parameter 2Δ(0)/kTe are given as 3.67 ± 0.07 and 3.87 ± 0.08, for tin and indium respectively, while the energy gap for lead is estimated to be 2ΔPb(0) = 2.70 ± 0.02 meV.

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Formation of high temperature phase in flash-evaporated SnSe films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100176629 ◽

1990 ◽

Vol 48 (4) ◽

pp. 698-699

Author(s):

J.P.S. Hanjra

Keyword(s):

Thin Films ◽

Electrical Properties ◽

Energy Gap ◽

Dominant Role ◽

Fine Powder ◽

High Temperature Phase ◽

Temperature Phase ◽

Water Mixture ◽

Flash Evaporation ◽

Photovoltaic Applications

Tin mono selenide (SnSe) with an energy gap of about 1 eV is a potential material for photovoltaic applications. Various authors have studied the structure, electronic and photoelectronic properties of thin films of SnSe grown by various deposition techniques. However, for practical photovoltaic junctions the electrical properties of SnSe films need improvement. We have carried out investigations into the properties of flash evaporated SnSe films. In this paper we report our results on the structure, which plays a dominant role on the electrical properties of thin films by TEM, SEM, and electron diffraction (ED).Thin films of SnSe were deposited by flash evaporation of SnSe fine powder prepared from high purity Sn and Se, onto glass, mica and KCl substrates in a vacuum of 2Ø micro Torr. A 15% HF + 2Ø% HNO3 solution was used to detach SnSe film from the glass and mica substrates whereas the film deposited on KCl substrate was floated over an ethanol water mixture by dissolution of KCl. The floating films were picked up on the grids for their EM analysis.

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Effect of the structural changes on the mechanical properties of the sintered films

JOURNAL OF ADVANCES IN PHYSICS ◽

10.24297/jap.v12i1.168 ◽

2016 ◽

Vol 12 (1) ◽

pp. 4141-4144

Author(s):

Garima Jain

Keyword(s):

Crystallite Size ◽

Lattice Constant ◽

Structural Changes ◽

Structural Investigation ◽

Energy Gap ◽

Lattice Parameter ◽

Metal Chalcogenides ◽

Optical Energy Gap ◽

Tin Telluride ◽

Physical Quantities

Polycrystalline films of tin telluride were prepared by sintering technique. The structural investigation of the films with different thicknesses enables to determine lattice parameter, crystallite size and strain existing in the films. The XRD traces showed that strain was tensile in nature. The crystallite size increases with thickness while strain decreases. Higher the value of tensile strain, larger is the lattice constant. The optical energy gap shows a descending nature with increasing strain and so with the lattice constant. Such an attempt made to delve into interdependence of basic physical quantities helps to explore the properties of SnTe and utilize it as an alternative to heavy metal chalcogenides in various technological applications. Â

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Structure, Stability and Water Adsorption on Ultra-Thin TiO2 Supported on TiN

10.26434/chemrxiv.8425367.v1 ◽

2019 ◽

Author(s):

Jose Julio Gutierrez Moreno ◽

Marco Fronzi ◽

Pierre Lovera ◽

alan O'Riordan ◽

Mike J Ford ◽

...

Keyword(s):

Density Functional ◽

Water Adsorption ◽

Chemical Potential ◽

Energy Gap ◽

Molecular Water ◽

Structure Stability ◽

Ambient Conditions ◽

Rutile Structure ◽

The Stability ◽

The One

Interfacial metal-oxide systems with ultrathin oxide layers are of high interest for their use in catalysis. In this study, we present a density functional theory (DFT) investigation of the structure of ultrathin rutile layers (one and two TiO2 layers) supported on TiN and the stability of water on these interfacial structures. The rutile layers are stabilized on the TiN surface through the formation of interfacial Ti–O bonds. Charge transfer from the TiN substrate leads to the formation of reduced Ti3+ cations in TiO2. The structure of the one-layer oxide slab is strongly distorted at the interface, while the thicker TiO2 layer preserves the rutile structure. The energy cost for the formation of a single O vacancy in the one-layer oxide slab is only 0.5 eV with respect to the ideal interface. For the two-layer oxide slab, the introduction of several vacancies in an already non-stoichiometric system becomes progressively more favourable, which indicates the stability of the highly non-stoichiometric interfaces. Isolated water molecules dissociate when adsorbed at the TiO2 layers. At higher coverages the preference is for molecular water adsorption. Our ab initio thermodynamics calculations show the fully water covered stoichiometric models as the most stable structure at typical ambient conditions. Interfacial models with multiple vacancies are most stable at low (reducing) oxygen chemical potential values. A water monolayer adsorbs dissociatively on the highly distorted 2-layer TiO1.75-TiN interface, where the Ti3+ states lying above the top of the valence band contribute to a significant reduction of the energy gap compared to the stoichiometric TiO2-TiN model. Our results provide a guide for the design of novel interfacial systems containing ultrathin TiO2 with potential application as photocatalytic water splitting devices.

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Molecular Investigations of the Newly Synthesized Azomethines as Antioxidants: Theoretical and Experimental Studies

Current Molecular Medicine ◽

10.2174/1566524019666190509102620 ◽

2019 ◽

Vol 19 (6) ◽

pp. 419-433 ◽

Cited By ~ 1

Author(s):

Siyamak Shahab ◽

Masoome Sheikhi ◽

Liudmila Filippovich ◽

Evgenij Dikusar ◽

Anhelina Pazniak ◽

...

Keyword(s):

Density Functional ◽

Energy Gap ◽

Experimental Studies ◽

Antioxidant Property ◽

Nbo Analysis ◽

Antioxidant Potential ◽

Functional Theory ◽

Homo And Lumo ◽

Intramolecular Hydrogen ◽

Activity Mechanism

: In this study, the antioxidant property of new synthesized azomethins has been investigated as theoretical and experimental. Methods and Results: Density functional theory (DFT) was employed to investigate the Bond Dissociation Enthalpy (BDE), Mulliken Charges, NBO analysis, Ionization Potential (IP), Electron Affinities (EA), HOMO and LUMO energies, Hardness (η), Softness (S), Electronegativity (µ), Electrophilic Index (ω), Electron Donating Power (ω-), Electron Accepting Power (ω+) and Energy Gap (Eg) in order to deduce scavenging action of the two new synthesized azomethines (FD-1 and FD-2). Spin density calculations and NBO analysis were also carried out to understand the antioxidant activity mechanism. Comparison of BDE of FD-1 and FD-2 indicate the weal antioxidant potential of these structures. Conclusion: FD-1 and FD-2 have very high antioxidant potential due to the planarity and formation of intramolecular hydrogen bonds.

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Investigation of Adsorption Effect of Carbon Monoxide on Coniine: A DFT Study

Letters in Organic Chemistry ◽

10.2174/1570178617666210108114822 ◽

2021 ◽

Vol 17 ◽

Author(s):

Siyamak Shahab ◽

Masoome Sheikhi ◽

Mehrnoosh Khaleghian ◽

Marina Murashko ◽

Mahin Ahmadianarog ◽

...

Keyword(s):

Carbon Monoxide ◽

Gas Phase ◽

Density Functional ◽

Energy Gap ◽

Adsorption Effect ◽

Chemical Shift Tensors ◽

Solvent Water ◽

Donor And Acceptor ◽

Before And After ◽

Electron Donor And Acceptor

: For the first time in the present study, the non-bonded interaction of the Coniine (C8H17N) with carbon monoxide (CO) was investigated by density functional theory (DFT/M062X/6-311+G*) in the gas phase and solvent water. The adsorption of the CO over C8H17N was affected on the electronic properties such as EHOMO, ELUMO, the energy gap between LUMO and HOMO, global hardness. Furthermore, chemical shift tensors and natural charge of the C8H17N and complex C8H17N/CO were determined and discussed. According to the natural bond orbital (NBO) results, the molecule C8H17N and CO play as both electron donor and acceptor at the complex C8H17N/CO in the gas phase and solvent water. On the other hand, the charge transfer is occurred between the bonding, antibonding or nonbonding orbitals in two molecules C8H17N and CO. We have also investigated the charge distribution for the complex C8H17N/CO by molecular electrostatic potential (MEP) calculations using the M062X/6-311+G* level of theory. The electronic spectra of the C8H17N and complex C8H17N/CO were calculated by time dependent DFT (TD-DFT) for investigation of the maximum wavelength value of the C8H17N before and after the non-bonded interaction with the CO in the gas phase and solvent water. Therefore, C8H17N can be used as strong absorbers for air purification and reduce environmental pollution.

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Spectroscopic investigations and DFT studies of synthesized 4-acetamidophenyl 3,4,5-trimethoxybenzoate and 4-acetyl phenyl 3,4,5-trimethoxybenzoate a novel conjugate of gallic acid

Letters in Organic Chemistry ◽

10.2174/1570178617999200818205347 ◽

2020 ◽

Vol 17 ◽

Author(s):

Sangeeta Srivastava ◽

Nadeem Ahmad Ansari ◽

Sadaf Aleem

Keyword(s):

Gallic Acid ◽

Density Functional ◽

Energy Gap ◽

Basis Set ◽

Major Constituent ◽

Orbital Energy ◽

Reactivity Descriptors ◽

Homo And Lumo ◽

Electrophilic Reactivity ◽

Global And Local

: Gallic acid is abundantly found in amla (Phyllanthus emblica), a deciduous of the family phyllanthaceae. Gallic acid, the major constituent of the plant was methylated to 3,4,5 trimethoxy gallic acid, which then underwent steglich esterification first with paracetamol and then with 4-hydroxy acetophenone to yield 4-acetamidophenyl 3,4,5-trimethoxybenzoate and 4-acetyl phenyl 3,4,5-trimethoxybenzoate “respectively”. 1H NMR, 13C NMR, UV, FT-IR and mass spectroscopy were used to characterize the synthesized compounds. Density functional theory (B3YLP) using 6-31G (d,p) basis set have been used for quantum chemical calculations. AIM (Atom in molecule) approach depicted weak molecular interactions within the molecules whereas the reactive site and reactivity within the molecule were examined by global and local reactivity descriptors. The HOMO and LUMO energies and frontier orbital energy gap were calculated by time dependant DFT approach using IEFPCM model. Small value for HOMO–LUMO energy gap indicated that easier charge transfer occurs within compound 4. The nucleophilic and electrophilic reactivity were determined by MEP (molecular electrostatic potential) experiment. Polarizability, dipole moment, and first hyperpolarizability values were calculated to depict the NLO (nonlinear optical) property of both the synthesized compounds. The antimicrobial activity was also carried out and broad spectrum antibacterial activity against several strains of bacteria and certain unicellular fungi were exhibited by synthesized compound 3.

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