Todas as Publicações do INCT-MI

@article{SOUZA2023108460,

title = {Benchmarking DFT functionals for photophysics of pyranoflavylium cations},

author = {Jhonathan R. Souza and Carles Curutchet and Yuri A. Aoto and Paula Homem-De-Mello},

url = {https://www.sciencedirect.com/science/article/pii/S109332632300058X},

doi = {https://doi.org/10.1016/j.jmgm.2023.108460},

issn = {1093-3263},

year  = {2023},

date = {2023-01-01},

journal = {Journal of Molecular Graphics and Modelling},

volume = {122},

pages = {108460},

abstract = {An intense absorption, phosphorescence, a long triplet excited state lifetime and singlet oxygen generation capabilities are characteristics of pyranoflavylium cations, analogues to pyranoanthocyanidins originated in the maturation process of red wine. Such properties make these compounds potential photosensitizers to be applied in photodynamic therapy. In this context, the photophysical processes underlying that treatment critically depend on the electronic structure of the pyranoflavylium molecules. When employing density functional theory to describe the electronic structure of molecules, the choice of the most suitable functional is not trivial, and benchmark studies are needed to orient practitioners in the field. In this work, a benchmark of seven of the most commonly used density functionals in addressing the photophysical properties of a set of eight pyranoflavylium cations is reported. Ground and excited state geometries, molecular orbitals, and absorption, fluorescence and phosphorescence transition energies were calculated using density functional theory approaches, and evaluated and compared to experimental data and monoreferential wave function-based methodologies. Statistical analysis of the results indicates that global-hybrid functionals allow an excellent description of absorption and emission energies, with errors around 0.05 eV, while range-separated variants led to somewhat larger errors in the range 0.1–0.2 eV. In contrast, range-separated functionals display excellent phosphorescence energies with errors close to 0.05 eV, in this case global-hybrids showing increased discrepancies around 0.5–0.1 eV.},

keywords = {Benchmark, Electronic structure, Excited-states, Photophysics, Photosensitizers, Time-dependent density functional theory (TD-DFT)},

pubstate = {published},

tppubtype = {article}

}

@article{VOVUSHA2023101543,

title = {Sensing of sulfur containing toxic gases with double transition metal carbide MXenes},

author = {H. Vovusha and Rodrigo G. Amorim and H. Bae and S. Lee and T. Hussain and H. Lee},

url = {https://www.sciencedirect.com/science/article/pii/S2468519423001702},

doi = {https://doi.org/10.1016/j.mtchem.2023.101543},

issn = {2468-5194},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {Materials Today Chemistry},

volume = {30},

pages = {101543},

abstract = {Sensing of sulfur containing gases, such as hydrogen sulfide (H2S) and sulfur dioxide (SO2), on double transition metal carbide MXenes has been studied by means of density functional theory calculations. It is found that both H2S and SO2 strongly physisorbed on M2TiC2Tx (M = Mo, Cr; Tx = O, S, OH) monolayers. The adsorption of H2S is stronger in the case of oxygen termination, (Mo2TiC2O2, Cr2TiC2O2), whereas SO2 has stronger adsorption on sulfur terminated (Mo2TiC2S2, Cr2TiC2S2) monolayers. Binding characteristics of H2S and SO2 are further confirmed with Bader charge transfer, density of states, and charge density differences. Using a statistical thermodynamic analysis, the sensing mechanism of H2S and SO2 is studied under varied pressures and temperature conditions. By means of non-equilibrium Green's function calculations, the sensitivities of H2S and SO2 on the Mo2TiC2S2 monolayer are found to be 16.3%, 10.3%, respectively, which showed promising sensing characteristics. Our results reveal that double transition metal carbide MXenes can be a potential candidate for the sensing of sulfur containing gases.},

keywords = {Adsorption, Double MXenes, Green's functions, Sulfur containing gases, Thermodynamic analysis},

pubstate = {published},

tppubtype = {article}

}

@article{WATANABE2023155070,

title = {Surface characterization using Friction Force Microscopy and the Jarzynski equality},

author = {Yasmin Watanabe and Rodrigo B. Capaz and Renata A. Simao},

url = {https://www.sciencedirect.com/science/article/pii/S0169433222025983},

doi = {https://doi.org/10.1016/j.apsusc.2022.155070},

issn = {0169-4332},

year  = {2023},

date = {2023-01-01},

journal = {Applied Surface Science},

volume = {607},

pages = {155070},

abstract = {The Jarzynski equality is a fundamental result from non-equilibrium statistical mechanics that provides the difference in free energy between two states from the work done on the system by processes that can be carried out far from equilibrium. We evaluate the applicability of Jarzynski equality to map the potential energy of a model graphene surface using data from simulated Friction Force Microscopy (FFM). We model the scanning process of the FFM using the Prandtl-Tomlinson model and Langevin dynamics. By varying the simulation parameters, we verify the “stick–slip” and thermolubricity friction regimes, as well as the crossover between them. We then calculate the surface potential energy using the Jarzynski equality for these regimes. A new method for properly evaluating the free energy of the cantilever is introduced. We observe that the applicability of Jarzynski's equality is linked to the friction regimes: For thermolubricity, a very accurate potential energy curve is obtained for relatively few repetitions, but for the “stick–slip” movement, it is only possible to use Jarzynski’s equation in a small fraction of the scanning distance. For the crossover regime, it is possible to obtain a relatively accurate potential energy curve for a sufficiently large number of sampling repetitions.},

keywords = {Friction Force Microscopy, Jarzynski equality, Prandtl-Tomlinson model, Stick-slip, Thermolubricity},

pubstate = {published},

tppubtype = {article}

}

@article{BENATTO2023108715,

title = {FRET–Calc: A free software and web server for Förster Resonance Energy Transfer Calculation},

author = {Leandro Benatto and Omar Mesquita and João L. B. Rosa and Lucimara S. Roman and Marlus Koehler and Rodrigo B. Capaz and Graziâni Candiotto},

url = {https://www.sciencedirect.com/science/article/pii/S0010465523000607},

doi = {https://doi.org/10.1016/j.cpc.2023.108715},

issn = {0010-4655},

year  = {2023},

date = {2023-01-01},

journal = {Computer Physics Communications},

volume = {287},

pages = {108715},

abstract = {Förster Resonance Energy Transfer Calculator (FRET−Calc) is a program and web server that analyzes molar extinction coefficient of the acceptor, emission spectrum of the donor, and the refractive index spectrum of the donor/acceptor blend. Its main function is to obtain important parameters of the FRET process from experimental data, such as: (i) effective refractive index, (ii) overlap integral, (iii) Förster radius, (iii) FRET efficiency and (iv) FRET rate. FRET−Calc is license free software that can be run via dedicated web server (nanocalc.org) or downloading the program executables (for Unix, Windows, and macOS) from the FRET−Calc repository on GitHub. The program features a user−friendly interface, making it suitable for materials research and teaching purposes. In addition, the program is optimized to run on normal computers and is lightweight. An example will be given with the step by step of its use and results obtained.},

keywords = {Energy transfer, Fluorescence, Förster radius, FRET, Organic semiconductor, Software},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1021/acsami.3c04509,

title = {Improved Performance of Organic Light-Emitting Transistors Enabled by Polyurethane Gate Dielectric},

author = {Arthur R. J. Barreto and Graziâni Candiotto and Harold J. C. Avila and Rafael S. Carvalho and Aline Magalhães Santos and Mario Prosa and Emilia Benvenuti and Salvatore Moschetto and Stefano Toffanin and Rodrigo B. Capaz and Michele Muccini and Marco Cremona},

url = {https://doi.org/10.1021/acsami.3c04509},

doi = {10.1021/acsami.3c04509},

year  = {2023},

date = {2023-01-01},

journal = {ACS Applied Materials & Interfaces},

volume = {15},

number = {28},

pages = {33809-33818},

abstract = {Organic light-emitting transistors (OLETs) are multifunctional optoelectronic devices that combine in a single structure the advantages of organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs). However, low charge mobility and high threshold voltage are critical hurdles to practical OLET implementation. This work reports on the improvements obtained by using polyurethane films as a dielectric layer material in place of the standard poly(methyl methacrylate) (PMMA) in OLET devices. It was found that polyurethane drastically reduces the number of traps in the device, thereby improving electrical and optoelectronic device parameters. In addition, a model was developed to rationalize an anomalous behavior at the pinch-off voltage. Our findings represent a step forward to overcome the limiting factors of OLETs that prevent their use in commercial electronics by providing a simple route for low-bias device operation.},

note = {PMID: 37403922},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{MOURA2023118123,

title = {Resonance Raman spectroscopy characterization of linear carbon chains encapsulated by multi-walled carbon nanotubes},

author = {Thiago A. Moura and Wellington Q. Neves and Rafael S. Alencar and Y. A. Kim and M. Endo and Thiago L. Vasconcelos and Deyse G. Costa and Graziâni Candiotto and Rodrigo B. Capaz and Paulo T. Araujo and Antonio G. Souza Filho and Alexandre R. Paschoal},

url = {https://www.sciencedirect.com/science/article/pii/S0008622323003688},

doi = {https://doi.org/10.1016/j.carbon.2023.118123},

issn = {0008-6223},

year  = {2023},

date = {2023-01-01},

journal = {Carbon},

volume = {212},

pages = {118123},

abstract = {The unique electronic and vibrational properties of linear carbon chains (LCCs) have attracted close attention from the scientific community in recent years. Raman spectroscopy addressing the LCC spectral signature around 1850 cm−1 has been widely used to identify the LCC and probe electronic and vibrational properties as a function of carbon length. Despite the number of works available in literature, some aspects of the LCC's aforementioned properties remain unclear. Using a combination of confocal and Tip-enhanced Raman Spectroscopy (TERS), along with different laser lines, this work addresses important aspects of the optical resonance window of LCCs encapsulated by multi-walled carbon nanotubes (MWCNTs) (i.e. LCC@MWCNT) as well as an elusive Raman signature around 1637 cm−1, which is assigned to the LCC's longitudinal acoustic (LA) phonon mode at the X point (zone edge), which becomes Raman active likely due to disorder effects. First-principles calculations endorse our conclusions.},

keywords = {Carbon nanotubes, Linear carbon chains, Raman spectroscopy, TERS},

pubstate = {published},

tppubtype = {article}

}

@article{D2CP03666E,

title = {Combined computational and experimental study about the incorporation of phosphorus into the structure of graphene oxide},

author = {Tainara L. G. Costa and Mariana A. Vieira and Gustavo R. Gonçalves and Daniel F. Cipriano and Valdemar Lacerda and Arlan S. Gonçalves and Wanderlã L. Scopel and Abner Siervo and Jair C. C. Freitas},

url = {http://dx.doi.org/10.1039/D2CP03666E},

doi = {10.1039/D2CP03666E},

year  = {2023},

date = {2023-01-01},

journal = {Phys. Chem. Chem. Phys.},

volume = {25},

issue = {9},

pages = {6927-6943},

publisher = {The Royal Society of Chemistry},

abstract = {Phosphorus-containing graphene-based hybrids are materials with outstanding properties for diverse applications. In this work, an easy route to produce phosphorus-graphene oxide hybrid materials is described, involving the use of variable amounts of H3PO4 and H2SO4 during the reaction of oxidation of a graphitic precursor. The physical and chemical features of the hybrids change significantly with the variation in the acid amounts used in the syntheses. XPS and solid-state 13C and 31P NMR results show that the hybrids contain large amounts of oxygen functional groups, with the phosphorus incorporation proceeding mostly through the formation of phosphate-like linkages and other functions with C–O–P bonds. The experimental findings are supported by DFT calculations, which allow the assessment of the energetics and the geometry of the interaction between phosphate groups and graphene-based models; these calculations are also used to predict the chemical shifts in the 31P and 13C NMR spectra of the models, which show good agreement with the experimentally observed solid-state NMR spectra.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{SILVEIRA2023122570,

title = {A comprehensive study of the reduction of nitrate on natural FeTiO3: Photocatalysis and DFT calculations},

author = {Jefferson E. Silveira and Aramille S. Souza and Fernando N. N. Pansini and Alyson R. Ribeiro and Wanderlã L. Scopel and Juan A. Zazo and Jose A. Casas and Wendel S. Paz},

url = {https://www.sciencedirect.com/science/article/pii/S1383586622021268},

doi = {https://doi.org/10.1016/j.seppur.2022.122570},

issn = {1383-5866},

year  = {2023},

date = {2023-01-01},

journal = {Separation and Purification Technology},

volume = {306},

pages = {122570},

abstract = {Experimental and theoretical investigation of the capacity of the natural ilmenite (FeTiO3) to reduce nitrate (NO3−) from ultra-pure and mineral water is presented. A comprehensive mechanism of NO3− photocatalytic transformation is proposed regarding the density functional theory (DFT) calculations and the photocatalytic reduction of nitrate. When ultra-pure water is employed, the nitrate is totally converted to NOX (2%) and N2 (98%) after 210 min. Additionally, using the stoichiometric dose of oxalate, the nitrate also vanishes from the mineral water, forming NO2−, NOX, and N2 as products. Thus, the findings reveal that natural ilmenite can be a great candidate for reducing NO3− in contaminated water.},

keywords = {DFT, Ilmenite, Nitrate, Photoreduction},

pubstate = {published},

tppubtype = {article}

}

@article{AMBROZIO2023100091,

title = {Combined experimental and computational 1H NMR study of water adsorption onto graphenic materials},

author = {Alan R. Ambrozio and Thierry R. Lopes and Daniel F. Cipriano and Fábio A. L. Souza and Wanderlã L. Scopel and Jair C. C. Freitas},

url = {https://www.sciencedirect.com/science/article/pii/S2666441022000619},

doi = {https://doi.org/10.1016/j.jmro.2022.100091},

issn = {2666-4410},

year  = {2023},

date = {2023-01-01},

journal = {Journal of Magnetic Resonance Open},

volume = {14-15},

pages = {100091},

abstract = {The effects caused by the interaction with graphene-like layers on the 1H NMR spectra of water molecules adsorbed onto porous carbon materials were investigated by a combination of shielding calculations using density functional theory (DFT) and 1H NMR experiments. Experimental 1H NMR spectra were recorded for different water-containing carbon materials (activated carbons and milled graphite samples); the 1H NMR signals due to adsorbed water in these materials showed a strong shielding effect caused by the electron currents present in the graphene-like layers. This effect was enhanced for activated carbons prepared at high heat treatment temperatures and for milled graphite samples with short milling times, evidencing that the structural organization of the graphene-like layers was the key feature defining the magnitude of the shielding on the 1H nuclei in the water molecules adsorbed by the analyzed materials. The DFT calculations of the shielding sensed by these 1H nuclei showed an increased interaction with the graphitic layers as the distance between these layers (representing the pore size) was reduced. A continuous decrease of the 1H NMR chemical shift was then predicted for pores of smaller sizes, in good agreement with the experimental findings. These calculations also showed a large dispersion of chemical shifts for the several 1H nuclei in the water clusters, attributed to intermolecular interactions and to shielding variations within the pores. This dispersion, combined with the effects due to the locally anisotropic diamagnetic susceptibility of graphite-like crystallites, are the main contributions to the broadening of the 1H NMR signals associated with water adsorbed onto porous carbon materials.},

keywords = {DFT, Graphenic materials, H NMR, Water adsorption},

pubstate = {published},

tppubtype = {article}

}

@article{YADAV20232711,

title = {First-principles investigations of 2D materials: Challenges and best practices},

author = {Asha Yadav and Carlos Mera Acosta and Gustavo M. Dalpian and Oleksandr I. Malyi},

url = {https://www.sciencedirect.com/science/article/pii/S2590238523002370},

doi = {https://doi.org/10.1016/j.matt.2023.05.019},

issn = {2590-2385},

year  = {2023},

date = {2023-01-01},

journal = {Matter},

volume = {6},

number = {9},

pages = {2711-2734},

abstract = {Summary 

The successful exfoliation of graphene from graphite has brought significant attention to predicting new two-dimensional (2D) materials that can be realized experimentally. As a consequence, first-principles studies of novel 2D materials become routine, with thousands of papers published every year. What makes these studies interesting is that they predict new materials that have not been realized yet but should be a panacea for topological insulators, next-generation battery electrodes, novel solar cell absorbers, etc. There is no doubt that some of the proposed materials can provide a specific solution, and their properties/performance can be confirmed experimentally. At the same time, there are many false predictions because of the computational errors or the Legoland approach used to study 2D materials. To reduce the gap between theoretical and experimental works, we performed a systematic review of computational and Legoland factors that should be minimized in future theoretical works.},

keywords = {2D materials, materials design, materials realization, optical properties},

pubstate = {published},

tppubtype = {article}

}

@article{FREGOLENTE2023166835,

title = {Effects of chemical aging on carbonaceous materials: Stability of water-dispersible colloids and their influence on the aggregation of natural-soil colloid},

author = {Laís G. Fregolente and Maria T. Rodrigues and Naiara C. Oliveira and Bruno Sousa Araújo and Ícaro V. Nascimento and Antonio G. Souza Filho and Amauri J. Paula and Mirian C. G. Costa and Jaedson C. A. Mota and Odair P. Ferreira},

url = {https://www.sciencedirect.com/science/article/pii/S0048969723054608},

doi = {https://doi.org/10.1016/j.scitotenv.2023.166835},

issn = {0048-9697},

year  = {2023},

date = {2023-01-01},

journal = {Science of The Total Environment},

volume = {903},

pages = {166835},

abstract = {Although hydrochar and biochar have been used as soil conditioners, there is not a clear understanding of how their properties changes due to aging impacts their colloidal particles behavior on the soil system. From this premise, we produced hydrochar and biochar from the same feedstock (cashew bagasse) and aged with different chemical methods: (i) using hydrogen peroxide, (ii) a mixture of nitric and sulfuric acids, and (iii) hot water. It was analyzed the effects of aging on the stability of the carbonaceous materials (CMs) colloids in aqueous medium with different ionic strength (single systems), as well as the stability of the natural-soil colloid when interacting with biochar and hydrochar colloids (binary systems). A chemical composition (C, H, N, and O content) change in CMs due to the chemically induced aging was observed along with minor structural modifications. Chemical aging could increase the amount of oxygen functional groups for both biochar and hydrochar, though in a different level depending on the methodology applied. In this sense, hydrochar was more susceptive to chemical oxidation than biochar. The effectiveness of chemical aging treatments for biochar increased in the order of water < acid < hydrogen peroxide, whereas for hydrochar the order was water < hydrogen peroxide < acid. While the increase in surface oxidation improved the biochar colloidal stability in water medium at different ionic strengths (single systems), the stability and critical coagulation concentration (CCC) slightly changed for hydrochar. Natural-soil clay (NSC) interactions with oxidized carbonaceous material colloids (binary systems) enhanced NSC stability, which is less likely to aggregate. Therefore, the aging of carbonaceous materials modifies the interaction and dynamics of soil small particles, requiring far more attention to the environmental risks due to their application over time.},

keywords = {Aggregation, Biochar, Hydrochar, Hydrothermal carbonization, Oxidation, Pyrolysis},

pubstate = {published},

tppubtype = {article}

}

@article{Ussui2022,

title = {Room temperature plasticity of zirconia-yttria-titania ceramics: Experimental indications and structural modelling},

author = {Valter Ussui and Dolores Ribeiro Lazar and Nelson de Lima and Anelyse Arata and Fabio Ribeiro and Gustavo M. Dalpian and Juliana Marchi and José Octavio Paschoal},

doi = {10.2298/pac2204367u},

issn = {2406-1034},

year  = {2023},

date = {2023-00-00},

urldate = {2023-00-00},

journal = {PAC},

volume = {16},

number = {4},

pages = {367--373},

publisher = {National Library of Serbia},

abstract = {Yttria-stabilized tetragonal zirconia (Y-TZP) ceramics have excellent

   mechanical properties. However, such materials cannot undergo plastic

   deformation at room temperature due to their high hardness and brittleness

   values, hindering machinability. To overcome these limitations, we propose a

   zirconia-yttria-titania ceramics, based on zirconia containing 3mol% yttria

   and up to 15mol% titania. The zirconia-yttria-titania powders were

   synthesized by co-precipitation method, uniaxially pressed and sintered at

   1400?C/5 h. Sample characterizations were carried out by X-ray diffraction,

   scanning electron microscopy and mechanical properties through Vickers

   hardness and toughness measurements. Compared to the Y-TZP ceramics, the

   yttria stabilised tetragonal zirconia ceramics co-doped with 10mol%Ti showed

   noticeable increase of tetragonality parameter, higher toughness and lower

   hardness values, indicating plasticity at room temperature. Furthermore, the

   atomistic simulation by Density Functional Theory methodology suggests the

   occurrence of spatial arrangement of the atoms, explaining the proposed

   plasticity.},

keywords = {Ceramics and Composites},

pubstate = {published},

tppubtype = {article}

}

@article{Carozo2023,

title = {Raman spectroscopy of a few layers of bismuth telluride nanoplatelets},

author = {Victor Carozo and Bruno R. Carvalho and Syed Hamza Safeer and Leandro Seixas and Pedro Venezuela and Mauricio Terrones},

doi = {10.1039/d3na00585b},

issn = {2516-0230},

year  = {2023},

date = {2023-00-00},

journal = {Nanoscale Adv.},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Exploring the art of tailoring electronic and phonon properties in a few layers of Bi2Te3 crystals through layer variation with Raman spectroscopy.},

keywords = {and Optics, Atomic and Molecular Physics, Bioengineering, General Chemistry, General Engineering, General Materials Science},

pubstate = {published},

tppubtype = {article}

}

@article{Leong2021,

title = {Can Empirical Biplots Predict High Entropy Oxide Phases?},

author = {Zhaoyuan Leong and Pratik Desai and Nicola Morley},

doi = {10.3390/jcs5120311},

issn = {2504-477X},

year  = {2021},

date = {2021-12-00},

journal = {J. Compos. Sci.},

volume = {5},

number = {12},

publisher = {MDPI AG},

abstract = {High entropy oxides are entropy-stabilised oxides that adopt specific disordered structures due to entropy stabilisation. They are a new class of materials that utilises the high-entropy concept first discovered in metallic alloys. They can have interesting properties due to the interactions at the electronic level and can be combined with other materials to make composite structures. The design of new meta-materials that utilise this concept to solve real-world problems may be a possibility but further understanding of how their phase stabilisation is required. In this work, biplots of the composition’s mean electronegativity are plotted against the electron-per-atom ratio of the compounds. The test dataset accuracy in the resulting biplots improves from 78% to 100% when using atomic-number-per-atom Z/a ratios as a biplot parameter. Phase stability maps were constructed using a Voronoi tessellation. This can be of use in determining stability at composite material interfaces.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rocha2018,

title = {Finite-size correction scheme for supercell calculations in Dirac-point two-dimensional materials},

author = {C. G. Rocha and A. R. Rocha and P. Venezuela and J. H. Garcia and M. S. Ferreira},

doi = {10.1038/s41598-018-27632-6},

issn = {2045-2322},

year  = {2018},

date = {2018-12-00},

journal = {Sci Rep},

volume = {8},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {AbstractModern electronic structure calculations are predominantly implemented within the super cell representation in which unit cells are periodically arranged in space. Even in the case of non-crystalline materials, defect-embedded unit cells are commonly used to describe doped structures. However, this type of computation becomes prohibitively demanding when convergence rates are sufficiently slow and may require calculations with very large unit cells. Here we show that a hitherto unexplored feature displayed by several 2D materials may be used to achieve convergence in formation- and adsorption-energy calculations with relatively small unit-cell sizes. The generality of our method is illustrated with Density Functional Theory calculations for different 2D hosts doped with different impurities, all of which providing accuracy levels that would otherwise require enormously large unit cells. This approach provides an efficient route to calculating the physical properties of 2D systems in general but is particularly suitable for Dirac-point materials doped with impurities that break their sublattice symmetry.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Curran2015,

title = {Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales},

author = {P. J. Curran and W. M. Desoky and M. V. Milos̆ević and A. Chaves and J.-B. Laloë and J. S. Moodera and S. J. Bending},

doi = {10.1038/srep15569},

issn = {2045-2322},

year  = {2015},

date = {2015-12-07},

urldate = {2015-12-07},

journal = {Sci Rep},

volume = {5},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {AbstractScanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}