Página 1 dos resultados de 528 itens digitais encontrados em 0.027 segundos

Estudo das propriedades estruturais e ópticas em materiais nanoestruturados a base de silício.; Study of structural and optical properties in nanostructured silicon based films.

Ribeiro, Márcia
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/05/2009 PT
Relevância na Pesquisa
57.912583%
Esta tese de doutorado tem por objetivo aprofundar as pesquisas realizadas no mestrado, a saber, da caracterização e estudo das propriedades estruturais e ópticas de filmes de oxinitreto de silício (SiOxNy:H) ricos em silício depositados pela técnica de deposição química a vapor assistida por plasma a baixa temperatura (PECVD). Os resultados obtidos no mestrado indicaram que os filmes de SiOxNy:H ricos em silício apresentam emissão luminescente na faixa do visível cuja intensidade e freqüência de emissão estão em correlação com o excesso de silício. Os resultados sugeriram que o excesso de silício na matriz do SiOxNy:H estava disposto na forma de aglomerados de silício de dimensões nanométricas responsáveis por efeitos de tamanho quântico bem como a estados radiativos na interface dos aglomerados com a matriz isolante. Neste trabalho a fim de avaliar o efeito da separação de fases, do tamanho quântico, e da interface, foram produzidos sistemas nanoestruturados a base de silício com total e parcial separação de fases para caracterizar e analisar suas propriedades ópticas e estruturais e compará-las com as dos filmes ricos em silício. Assim foram produzidas multicamadas de a-Si:H de poucos nanômetros de espessura com materiais dielétricos. Em algumas destas multicamadas foi promovida a mistura parcial das camadas por meio de bombardeamento iônico. O estudo nas estruturas de multicamadas permitiu caracterizar e analisar as propriedades estruturais e ópticas de materiais nanoestruturados com total e parcial separação de fases para posteriormente contrastá-los com as características dos filmes de oxinitreto de silício ricos em silício. A fim de analisar a influência da interface nas propriedades ópticas destes sistemas as multicamadas foram fabricadas com dois dielétricos diferentes: o óxido de silício e o ni treto de silício. A espessura das camadas dielétricas foi mantida fixa entanto que a das camadas de silício foi variada para avaliar efeitos de confinamento no silício. A caracterização foi feita utilizando técnicas de absorção óptica no UV-Vis...

Properties of nanocones formed on a surface of semiconductors by laser radiation: quantum confinement effect of electrons, phonons, and excitons

Medvid, Artur; Onufrijevs, Pavels; Mychko, Alexander
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 07/11/2011 EN
Relevância na Pesquisa
67.54851%
On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in temperature-gradient field induced by laser radiation. The second stage is characterized by mechanical plastic deformation of the stained top layer leading to arising of nanocones, due to selective laser absorption of the top layer. The nanocones formed on the irradiated surface of semiconductors by Nd:YAG laser possessing the properties of 1D graded bandgap have been found for Si, Ge, and SiGe as well, however QD structure in CdTe was observed. The model is confirmed by "blue shift" of bands in photoluminescence spectrum, "red shift" of longitudinal optical line in Raman back scattering spectrum of Ge crystal, appearance of Ge phase in SiGe solid solution after irradiation by the laser at intensity 20 MW/cm2, and non-monotonous dependence of Si crystal micro-hardness as function of the laser intensity.

Nonlinear optical properties of free standing films of PbS quantum dots in the nonresonant femtosecond regime

Kurian, Pushpa Ann; Vijayan, C.; Nag, Amit; Goswami, Debabrata
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 17/09/2007 EN
Relevância na Pesquisa
47.781597%
Devices based on optical technology for high speed communication networks require materials with large nonlinear optical response in the ultrafast regime. Nonlinear optical materials have also attracted wide attention as potential candidates for the protection of optical sensors and eyes while handling lasers. Optical limiters have a constant transmittance at low input influence and a decrease in transmittance at higher fluences and are based on a variety of mechanisms such as nonlinear refraction, nonlinear scattering, multiphoton absorption and free carrier absorption. As we go from bulk to nanosized materials especially in the strong quantum confinement regime where radius of the nanoparticle is less than the bulk exciton Bohr radius, the optical nonlinearity is enhanced due to quantum confinement effect. This paper is on the ultrafast nonresonant nonlinearity in free standing films of PbS quantum dots stabilized in a synthetic glue matrix by a simple chemical route which provides flexibility of processing in a variety of physical forms. Optical absorption spectrum shows significant blue shift from the bulk absorption onset indicating strong quantum confinement. PbS quantumdots of mean size 3.3nm are characterized by X-ray diffraction and transmission electron microscopy. The mechanism of nonlinear absorption giving rise to optical limiting is probed using open z-scan technique with laser pulses of 150 fs pulse duration at 780 nm and the results are presented in the nonresonant femtosecond regime. Irradiance dependence on nonlinear absorption are discussed.

Quantum confinement in hydrogen bond

Santos, Carlos da Silva dos; Drigo Filho, Elso; Ricotta, Regina Maria
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 765-770
ENG
Relevância na Pesquisa
77.894844%
In this work, the quantum confinement effect is proposed as the cause of the displacement of the vibrational spectrum of molecular groups that involve hydrogen bonds. In this approach, the hydrogen bond imposes a space barrier to hydrogen and constrains its oscillatory motion. We studied the vibrational transitions through the Morse potential, for the NH and OH molecular groups inside macromolecules in situation of confinement (when hydrogen bonding is formed) and nonconfinement (when there is no hydrogen bonding). The energies were obtained through the variational method with the trial wave functions obtained from supersymmetric quantum mechanics formalism. The results indicate that it is possible to distinguish the emission peaks related to the existence of the hydrogen bonds. These analytical results were satisfactorily compared with experimental results obtained from infrared spectroscopy. (c) 2015 Wiley Periodicals, Inc.

Strain relaxation and phonon confinement in self-assembled InAsSb/InP (001) quantum dashes: Effect of deposition thickness and composition

Lei, W.; Tan, H. H.; Jagadish, C.; Ren, Q. J.; Lu, J.; Chen, Z. H.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
67.81292%
This paper presents a study on the strain relaxation and phonon confinement effect in InAsSb/InP quantum dashes QDashes. The phonon mode with a frequency between that of InAs-like longitudinal optical mode and that of InP transverse optical mode is determined to be originated from InAsSb QDashes. Despite the small height of the QDashes, their phonon frequency is found to be mainly determined by the strain relaxation in the dashes. With increasing InAsSb deposition thickness and Sb composition in InAsSb dashes, the phonon mode shows an upward shift of its frequency due to the increased compressive strain.; Financial support from Australian Research Council DP0774366 is gratefully acknowledged.

Anisotropic Quantum Confinement Effect and Electric Control of Surface States in Dirac Semimetal Nanostructures

Xiao, Xianbo; Yang, Shengyuan A.; Liu, Zhengfang; Li, Huili; Zhou, Guanghui
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 20/01/2015 EN
Relevância na Pesquisa
57.824424%
The recent discovery of Dirac semimetals represents a new achievement in our fundamental understanding of topological states of matter. Due to their topological surface states, high mobility, and exotic properties associated with bulk Dirac points, these new materials have attracted significant attention and are believed to hold great promise for fabricating novel topological devices. For nanoscale device applications, effects from finite size usually play an important role. In this report, we theoretically investigate the electronic properties of Dirac semimetal nanostructures. Quantum confinement generally opens a bulk band gap at the Dirac points. We find that confinement along different directions shows strong anisotropic effects. In particular, the gap due to confinement along vertical c-axis shows a periodic modulation, which is absent for confinement along horizontal directions. We demonstrate that the topological surface states could be controlled by lateral electrostatic gating. It is possible to generate Rashba-like spin splitting for the surface states and to shift them relative to the confinement-induced bulk gap. These results will not only facilitate our fundamental understanding of Dirac semimetal nanostructures, but also provide useful guidance for designing all-electrical topological spintronics devices.

Exciton quantum confinement in nanocones formed on a surface of CdZnTe solid solution by laser radiation

Medvid', Artur; Litovchenko, Natalia; Mychko, Aleksandr; Naseka, Yuriy
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 20/09/2012 EN
Relevância na Pesquisa
57.54851%
The investigation of surface morphology using atomic force microscope has shown self-organizing of the nanocones on the surface of CdZnTe crystal after irradiation by strongly absorbed Nd:YAG laser irradiation at an intensity of 12.0 MW/cm2. The formation of nanocones is explained by the presence of a thermogradient effect in the semiconductor. The appearance of a new exciton band has been observed after irradiation by the laser which is explained by the exciton quantum confinement effect in nanocones.

Thickness-Induced Metal-Insulator Transition in Sb-doped SnO2 Ultrathin Films: The Role of Quantum Confinement

Ke, Chang; Zhu, Weiguang; Zhang, Zheng; Soon Tok, Eng; Ling, Bo; Pan, Jisheng
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 30/11/2015 EN
Relevância na Pesquisa
57.494697%
A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition. Both electrical and spectroscopic studies provide clear evidence of a critical thickness for the metallic conductivity in SnO2:Sb thin films and the oxidation state transition of the impurity element Sb. With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect. Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.

Interplay between Phonon Confinement and Fano Effect on Raman line shape for semiconductor nanostructures: Analytical study

Yogi, Priyanka; Saxena, Shailendra K.; Mishra, Suryakant; Mishra, Vikash; Rai, Hari M.; Late, Ravikiran; Kumar, Vivek; Joshi, Bipin; Sagdeo, Pankaj R.; Kumar, Rajesh
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/08/2015
Relevância na Pesquisa
47.920107%
Theoretical Raman line shape functions have been studied to take care of quantum confinement effect and Fano effect individually and jointly. The characteristics of various Raman line shapes have been studied in terms of the broadening and asymmetry of Raman line shapes. It is shown that the asymmetry in the Raman line-shape function caused by these two effects individually does not add linearly to give asymmetry of line-shape generated by considering the combined effect. This indicates existence of interplay between the two effects. The origin of interplay lies in the fact that Fano effect itself depends on quantum confinement effect and in turn provides an asymmetry. This can not be explained by considering the two effects contribution independent of each other.; Comment: 10 Pages

Effect of interdiffusion and quantum confinement on Raman spectra of the Ge/Si(100) heterostructures with quantum dots

Kucherenko, I. V.; Vinogradov, V. S.; Melnik, N. N.; Arapkina, L. V.; Chapnin, V. A.; Chizh, K. V.; Yuryev, V. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/08/2009
Relevância na Pesquisa
47.751045%
We used Raman scattering for study the phonon modes of self-organized Ge/Si quantum dots, grown by a molecular-beam epitaxy method. It is revealed, that Ge-Ge and Si-Ge vibrational modes considerably intensify at excitation of exciton between the {Lambda}3 valence and {Lanbda}1 conduction bands (transitions E1 and E1+{Delta}1), that allows to observe Raman scattering spectrum from extremely small volumes of Ge, even from one layer of quantum dots with the layer thickness of ~ 10 A. It is shown that Si diffuses into the Ge quantum dots from the Si spacer layers forming Ge_xSi_{1-x} solid solution, and Si concentration was estimated. It is revealed, that the frequency of Ge-Ge mode decreases in 10 1/cm at decreasing of the Ge layer thickness from 10 up to 6 A as a result of phonon size confinement effect.; Comment: Reported at the 16th Int. Symp. "Nanostructures: Physics and Technology", Vladivostok, Russia, July 14-18, 2008

The Fate of the Photon in Topological Matter: Superconductivity, Confinement and the Vortex Quantum Hall Effect

Diamantini, M. C.; Trugenberger, C. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
48.08348%
Topological matter is characterized by the presence of a topological BF term in its long-distance effective action. Topological defects due to the compactness of the U(1) gauge fields induce quantum phase transitions between topological insulators, topological superconductors and topological confinement. In conventional superconductivity, due to spontaneous symmetry breaking, the photon acquires a mass due to the Anderson-Higgs mechanism. In this paper we derive the corresponding effective actions for the electromagnetic field in topological superconductors and topological confinement phases. In topological superconductors magnetic flux is confined and the photon acquires a topological mass through the BF mechanism: no symmetry breaking is involved, the ground state has topological order and the transition is induced by quantum fluctuations. In topological confinement, instead, electric charge is linearly confined and the photon becomes a massive antisymmetric tensor via the St\"uckelberg mechanism. Oblique confinement phases arise when the string condensate carries both magnetic and electric flux (dyonic strings). Such phases are characterized by a vortex quantum Hall effect potentially relevant for the dissipationless transport of information stored on vortices.; Comment: 5 pages...

Efimov trimers under strong confinement

Levinsen, Jesper; Massignan, Pietro; Parish, Meera M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.86868%
The dimensionality of a system can fundamentally impact the behaviour of interacting quantum particles. Classic examples range from the fractional quantum Hall effect to high temperature superconductivity. As a general rule, one expects confinement to favour the binding of particles. However, attractively interacting bosons apparently defy this expectation: while three identical bosons in three dimensions can support an infinite tower of Efimov trimers, only two universal trimers exist in the two dimensional case. We reveal how these two limits are connected by investigating the problem of three identical bosons confined by a harmonic potential along one direction. We show that the confinement breaks the discrete Efimov scaling symmetry and destroys the weakest bound trimers. However, the deepest bound Efimov trimer persists under strong confinement and hybridizes with the quasi-two-dimensional trimers, yielding a superposition of trimer configurations that effectively involves tunnelling through a short-range repulsive barrier. Our results suggest a way to use strong confinement to engineer more stable Efimov-like trimers, which have so far proved elusive.; Comment: 8 pages, 4 figures. Typos corrected, published version

Quantum Confinement in Hydrogen Bond

Santos, Carlos da Silva dos; Filho, Elso Drigo; Ricotta, Regina Maria
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/02/2015
Relevância na Pesquisa
67.894844%
In this work, the quantum confinement effect is proposed as the cause of the displacement of the vibrational spectrum of molecular groups that involve hydrogen bonds. In this approach the hydrogen bond imposes a space barrier to hydrogen and constrains its oscillatory motion. We studied the vibrational transitions through the Morse potential, for the NH and OH molecular groups inside macromolecules in situation of confinement (when hydrogen bonding is formed) and non-confinement (when there is no hydrogen bonding). The energies were obtained through the variational method with the trial wave functions obtained from Supersymmetric Quantum Mechanics (SQM) formalism. The results indicate that it is possible to distinguish the emission peaks related to the existence of the hydrogen bonds. These analytical results were satisfactorily compared with experimental results obtained from infrared spectroscopy.; Comment: 20 pages, 2 figures. To appear in Int.J.Quantum Chem

Suppressing the loss of ultracold molecules via the continuous quantum Zeno effect

Zhu, Bihui; Gadway, Bryce; Foss-Feig, Michael; Schachenmayer, Johannes; Wall, Michael; Hazzard, Kaden R. A.; Yan, Bo; Moses, Steven A.; Covey, Jacob P.; Jin, Deborah S.; Ye, Jun; Holland, Murray; Rey, Ana Maria
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
57.358184%
We investigate theoretically the suppression of two-body losses when the on-site loss rate is larger than all other energy scales in a lattice. This work quantitatively explains the recently observed suppression of chemical reactions between two rotational states of fermionic KRb molecules confined in one-dimensional tubes with a weak lattice along the tubes [Yan et al., Nature 501, 521-525 (2013)]. New loss rate measurements performed for different lattice parameters but under controlled initial conditions allow us to show that the loss suppression is a consequence of the combined effects of lattice confinement and the continuous quantum Zeno effect. A key finding, relevant for generic strongly reactive systems, is that while a single-band theory can qualitatively describe the data, a quantitative analysis must include multiband effects. Accounting for these effects reduces the inferred molecule filling fraction by a factor of five. A rate equation can describe much of the data, but to properly reproduce the loss dynamics with a fixed filling fraction for all lattice parameters we develop a mean-field model and benchmark it with numerically exact time-dependent density matrix renormalization group calculations.; Comment: 4+ pages main text...

Quantum confinement in Si and Ge nanostructures: Effect of crystallinity

Barbagiovanni, Eric G.; Lockwood, David J.; Filho, Raimundo N. Costa; Goncharova, Lyudmila V.; Simpson, Peter J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/12/2013
Relevância na Pesquisa
47.94544%
We look at the relationship between the preparation method of Si and Ge nanostructures (NSs) and the structural, electronic, and optical properties in terms of quantum confinement (QC). QC in NSs causes a blue shift of the gap energy with decreasing NS dimension. Directly measuring the effect of QC is complicated by additional parameters, such as stress, interface and defect states. In addition, differences in NS preparation lead to differences in the relevant parameter set. A relatively simple model of QC, using a `particle-in-a-box'-type perturbation to the effective mass theory, was applied to Si and Ge quantum wells, wires and dots across a variety of preparation methods. The choice of the model was made in order to distinguish contributions that are solely due to the effects of QC, where the only varied experimental parameter was the crystallinity. It was found that the hole becomes de-localized in the case of amorphous materials, which leads to stronger confinement effects. The origin of this result was partly attributed to differences in the effective mass between the amorphous and crystalline NS as well as between the electron and hole. Corrections to our QC model take into account a position dependent effective mass. This term includes an inverse length scale dependent on the displacement from the origin. Thus...

Engineering electronic structure of a 2D topological insulator Bi(111) bilayer on Sb nanofilms by quantum confinement effect

Bian, Guang; Wang, Z. F.; Wang, Xiaoxiong; Xu, Caizhi; Xu, Su-Yang; Miller, T.; Hasan, M. Zahid; Liu, Feng; Chiang, T. -C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/11/2015
Relevância na Pesquisa
67.64817%
We report on fabrication of a two-dimensional topological insulator-Bi(111) bilayer on Sb nanofilms via a sequential molecular beam epitaxy (MBE) growth technique. Our angle-resolved photoemission measurements demonstrate the evolution of the electronic band structure of the heterostructure as a function of the film thickness and reveal the existence of a two-dimensional spinful massless electron gas within the top Bi bilayer. Interestingly, Our first-principles calculation extrapolating the observed band structure shows that, by tuning down the thickness of the supporting Sb films into the quantum dimension regime, a pair of isolated topological edge states emerges in a partial energy gap at 0.32 eV above the Fermi level as a consequence of quantum confinement effect. Our results and methodology of fabricating nanoscale heterostructures establish the Bi bilayer/Sb heterostructure as a platform of great potential for both ultralow-energy-cost electronics and surface-based spintronics.

Metallic nanograins: spatially nonuniform pairing induced by quantum confinement

Croitoru, M. D.; Shanenko, A. A.; Kaun, C. C.; Peeters, F. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/11/2010
Relevância na Pesquisa
48.00677%
It is well-known that the formation of discrete electron levels strongly influences the pairing in metallic nanograins. Here we focus on another effect of quantum confinement in superconducting grains that was not studied previously, i.e., spatially nonuniform pairing. This effect is very significant when single-electron levels form bunches and/or a kind of shell structure: in highly symmetric grains the order parameter can exhibit variations with position by an order of magnitude. Nonuniform pairing is closely related to a quantum-confinement induced modification of the pairing-interaction matrix elements and size-dependent pinning of the chemical potential to groups of degenerate or nearly degenerate levels. For illustration we consider spherical metallic nanograins. We show that the relevant matrix elements are as a rule enhanced in the presence of quantum confinement, which favors spatial variations of the order parameter, compensating the corresponding energy cost. The size-dependent pinning of the chemical potential further increases the spatial variation of the pair condensate. The role of nonuniform pairing is smaller in less symmetric confining geometries and/or in the presence of disorder. However, it always remains of importance when the energy spacing between discrete electron levels $\delta$ is approaching the scale of the bulk gap $\Delta_B$...

Effect of Quantum Confinement on Electron Tunneling through a Quantum Dot

Kang, Kicheon; Min, B. I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/03/1997
Relevância na Pesquisa
47.781597%
Employing the Anderson impurity model, we study tunneling properties through an ideal quantum dot near the conductance minima. Considering the Coulomb blockade and the quantum confinement on an equal footing, we have obtained current contributions from various types of tunneling processes; inelastic cotunneling, elastic cotunneling, and resonant tunneling of thermally activated electrons. We have found that the inelastic cotunneling is suppressed in the quantum confinement limit, and thus the conductance near its minima is determined by the elastic cotunneling at low temperature ($k_BT \ll \Gamma$, $\Gamma$: dot-reservoir coupling constant), or by the resonant tunneling of single electrons at high temperature ($k_BT \gg \Gamma$).; Comment: 11 pages Revtex, 2 Postscript figures, To appear in Phys.Rev.B

Anisotropic Quantum Confinement Effect and Electric Control of Surface States in Dirac Semimetal Nanostructures

Xiao, Xianbo; Yang, Shengyuan A.; Liu, Zhengfang; Li, Huili; Zhou, Guanghui
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
57.824424%
The recent discovery of Dirac semimetals represents a new achievement in our fundamental understanding of topological states of matter. Due to their topological surface states, high mobility, and exotic properties associated with bulk Dirac points, these new materials have attracted significant attention and are believed to hold great promise for fabricating novel topological devices. For nanoscale device applications, effects from finite size usually play an important role. In this report, we theoretically investigate the electronic properties of Dirac semimetal nanostructures. Quantum confinement generally opens a bulk band gap at the Dirac points. We find that confinement along different directions shows strong anisotropiceffects. In particular, the gap due to confinement along vertical c-axis shows a periodic modulation, which is absent for confinement along horizontal directions. We demonstrate that the topological surface states could be controlled by lateral electrostatic gating. It is possible to generate Rashba-like spin splitting for the surface states and to shift them relative to the confinement-induced bulk gap. These results will not only facilitate our fundamental understanding of Dirac semimetal nanostructures, but also provide useful guidance for designing all-electrical topological spintronics devices.; Comment: 23 pages...

Vortex states in nanoscale superconducting squares: the influence of quantum confinement

Zhang, L. -F.; Covaci, L.; Milošević, M. V.; Berdiyorov, G. R.; Peeters, F. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.853296%
Bogoliubov-de Gennes theory is used to investigate the effect of the size of a superconducting square on the vortex states in the quantum confinement regime. When the superconducting coherence length is comparable to the Fermi wavelength, the shape resonances of the superconducting order parameter have strong influence on the vortex configuration. Several unconventional vortex states, including asymmetric ones, giant multi-vortex combinations, and states comprising giant antivortex, were found as ground states and their stability was found to be very sensitive on the value of $k_F\xi_0$, the size of the sample $W$, and the magnetic flux $\Phi$. By increasing the temperature and/or enlarging the size of the sample, quantum confinement is suppressed and the conventional mesoscopic vortex states as predicted by the Ginzburg-Laudau (GL) theory are recovered. However, contrary to the GL results we found that the states containing symmetry-induced vortex-antivortex pairs are stable over the whole temperature range. It turns out that the inhomogeneous order parameter induced by quantum confinement favors vortex-antivortex molecules, as well as giant vortices with a rich structure in the vortex core - unattainable in the GL domain.