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“Giant drop in the Bardeen-Cooper-Schrieffer coherence length induced by quantum size effects in superconducting nanowires”. Shanenko AA, Croitoru MD, Vagov A, Peeters FM, Physical review : B : condensed matter and materials physics 82, 104524 (2010). http://doi.org/10.1103/PhysRevB.82.104524
Abstract: The BCS coherence length in low-dimensional superconductors is dramatically modified by quantum-size effects. In particular, for nanowires made of conventional superconducting materials, we show that the longitudinal zero-temperature coherence length exhibits width-dependent drops by 23 orders of magnitude each time when the bottom of one of single-electron subbands formed due to the transverse quantization of electron motion is situated in a close vicinity to the Fermi level. This phenomenon has strong similarities to the well-known BCS-BEC (Bose-Einstein condensation) crossover in ultracold fermionic condensates but with an important exception: it is driven by the transverse quantization of the electron motion rather than by the externally controlled strength of the fermion-fermion interaction.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 29
DOI: 10.1103/PhysRevB.82.104524
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“Magnetic-field induced quantum-size cascades in superconducting nanowires”. Shanenko AA, Croitoru MD, Peeters FM, Physical review : B : condensed matter and materials physics 78, 024505 (2008). http://doi.org/10.1103/PhysRevB.78.024505
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 42
DOI: 10.1103/PhysRevB.78.024505
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“Metallic nanograins : spatially nonuniform pairing induced by quantum confinement”. Croitoru MD, Shanenko AA, Kaun CC, Peeters FM, Physical review : B : condensed matter and materials physics 83, 214509 (2011). http://doi.org/10.1103/PhysRevB.83.214509
Abstract: 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. We find that, 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 illustrative purposes, we consider spherical metallic nanograins and also rectangular shapes. 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 δ is approaching the scale of the bulk gap ΔB, i.e., δ>0.10.2 ΔB.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 23
DOI: 10.1103/PhysRevB.83.214509
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“Oscillations of the superconducting temperature induced by quantum well states in thin metallic films: numerical solution of the Bogoliubov-de Gennes equations”. Shanenko AA, Croitoru MD, Peeters FM, Physical review : B : condensed matter and materials physics 75, 014519 (2007). http://doi.org/10.1103/PhysRevB.75.014519
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 85
DOI: 10.1103/PhysRevB.75.014519
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“Parity-fluctuation induced enlargement of the ratio \DeltaE/kBTc in metallic grains”. Croitoru MD, Shanenko AA, Peeters FM, Axt VM, Physical review : B : condensed matter and materials physics 84, 214518 (2011). http://doi.org/10.1103/PhysRevB.84.214518
Abstract: We investigate how the interplay of quantum confinement and particle number-parity fluctuations affects superconducting correlations in ultra-small metallic grains. Using the number-parity projected BCS formalism we calculate the critical temperature and the excitation gap as a function of the grain size for grains with even and odd number of confined carriers. We show that the experimentally observed anomalous increase of the coupling ratio ΔE/kBTc with decreasing superconducting grain size can be attributed to an enhancement of the number-parity fluctuations in ultra-small grains.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 14
DOI: 10.1103/PhysRevB.84.214518
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“Peculiarities of the orbital effect in the Fulde-Ferrell-Larkin-Ovchinnikov state in quasi-one-dimensional superconductors”. Croitoru MD, Buzdin AI, Physical review : B : condensed matter and materials physics 89, 224506 (2014). http://doi.org/10.1103/PhysRevB.89.224506
Abstract: Using the quasiclassical formalism, we determine the low-temperature phase diagram of a quasi-one-dimensional superconductor, taking into account the interchain Josephson coupling and the paramagnetic spin splitting. We show that the anisotropy of the onset of superconductivity changes in the FFLO state as compared with the conventional superconducting phase. It can result in anomalous peaks in the field-direction dependence of the upper critical field when the magnetic field length equals to the FFLO period. This regime is characterized by the lock-in effect of the FFLO modulation wave vector, which is governed by the magnetic length. Furthermore, in the FFLO phase, the anisotropy of the upper critical field is inverted at T-1(**) = 0.5T(c0), where the orbital anisotropy disappears. We suggest that an experimental study of the anisotropy of the upper critical field can provide very reach information about the parameters of the FFLO phase in quasi-1D samples.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
DOI: 10.1103/PhysRevB.89.224506
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“Resonant tunneling and localized states in a graphene monolayer with a mass gap”. Zalipaev V, Linton CM, Croitoru MD, Vagov A, Physical review : B : condensed matter and materials physics 91, 085405 (2015). http://doi.org/10.1103/PhysRevB.91.085405
Abstract: We study tunneling of quasiparticles through potential barriers in a graphene monolayer with the mass gap using a semiclassical (WKB) approach. The main equations are derived in away similar to the WKB theory for the Schrodinger equation, which allows for explicit solutions at all orders. The analog of the classical action is used to distinguish types of possible stationary states in the system. The analysis focuses on the resonant scattering and the hole states localized in the vicinity of a barrier that are often overlooked. The scattering coefficients for the physically interesting limits are obtained by matching the WKB approximation with the known solutions at turning points. The localized states demonstrate unconventional properties and lead to alterations of the single particle density of states.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 3
DOI: 10.1103/PhysRevB.91.085405
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“Shape resonances in the superconducting order parameter of ultrathin nanowires”. Shanenko AA, Croitoru MD, Physical review : B : condensed matter and materials physics 73, 012510 (2006). http://doi.org/10.1103/PhysRevB.73.012510
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 41
DOI: 10.1103/PhysRevB.73.012510
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“Size-dependent enhancement of superconductivity in Al and Sn nanowires: shape-resonance effect”. Shanenko AA, Croitoru MD, Zgirski M, Peeters FM, Arutyunov K, Physical review : B : condensed matter and materials physics 74, 052502 (2006). http://doi.org/10.1103/PhysRevB.74.052502
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 95
DOI: 10.1103/PhysRevB.74.052502
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“Superconducting nanofilms: Andreev-type states induced by quantum confinement”. Shanenko AA, Croitoru MD, Peeters FM, Physical review : B : solid state 78, 054505 (2008). http://doi.org/10.1103/PhysRevB.78.054505
Abstract: Quantum confinement of the transverse electron motion is the major effect governing the superconducting properties of high-quality metallic nanofilms, leading to a nonuniform transverse distribution of the superconducting condensate. In this case the order parameter can exhibit significant local enhancements due to these quantum-size effects and, consequently, quasiparticles have lower energies when they avoid the local enhancements of the pair condensate. Such excitations can be considered as new Andreev-type quasiparticles but now induced by quantum confinement. By numerically solving the Bogoliubovde Gennes equations and using Anderson's approximate solution to these equations, we: (a) formulate a criterion for such new Andreev-type states (NATS) and (b) study their effect on the superconducting characteristics in metallic nanofilms. We also argue that nanofilms made of low-carrier-density materials, e.g., of superconducting semiconductors, can be a more optimal choice for the observations of NATS and other quantum-size superconducting effects.
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 14
DOI: 10.1103/PhysRevB.78.054505
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“Superconducting nanowires: interplay of discrete transverse modes with supercurrent”. Croitoru MD, Shanenko AA, Kaun CC, Peeters FM, Physical review : B : solid state 80, 024513 (2009). http://doi.org/10.1103/PhysRevB.80.024513
Abstract: From a numerical solution of the Bogoliubov-de Gennes equations, we investigate an interplay of the transverse discrete modes with a longitudinal supercurrent in a metallic cylindrical superconducting nanowire. The superconductor-to-normal transition induced by a longitudinal superflow of electrons is found to occur as a cascade of jumps in the order parameter (supercurrent and superfluid density) as a function of the superfluid velocity for diameters d<1015 nm (for Al parameters) and sufficiently low temperatures T<0.30.4Tc, with Tc the critical temperature. When approaching Tc, the jumps are smoothed into steplike but continuous drops. A similar picture occurs for d>1520 nm. Only when the diameter exceeds 5070 nm the quantum-size cascades are fully washed out, and we arrive at the mesoscopic regime. Below this regime the critical current density jc exhibits the quantum-size oscillations with pronounced resonant enhancements: the smaller the diameter, the more significant is the enhancement. Thickness fluctuations of real samples will smooth out such oscillations into an overall growth of jc with decreasing nanowire diameter.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 21
DOI: 10.1103/PhysRevB.80.024513
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“Electroluminescence spectra of an STM-tip-induced quantum dot”. Croitoru MD, Gladilin VN, Fomin VM, Devreese JT, Kemerink M, Koenraad PM, Sauthoff K, Wolter JH, Physica. E: Low-dimensional systems and nanostructures 21, 270 (2004). http://doi.org/10.1016/j.physe.2003.11.028
Keywords: A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 2.221
Times cited: 1
DOI: 10.1016/j.physe.2003.11.028
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“Influence of the characteristics of the STM-tip on the electroluminescence spectra”. Croitoru MD, Gladilin VN, Fomin VM, Devreese JT, Kemerink M, Koenraad PM, Sauthoff K, Wolter JH, Physica. E: Low-dimensional systems and nanostructures 27, 13 (2005). http://doi.org/10.1016/j.physe.2004.10.002
Keywords: A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 2.221
DOI: 10.1016/j.physe.2004.10.002
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“Influence of disorder on superconducting correlations in nanoparticles”. Croitoru MD, Shanenko AA, Vagov A, Vasenko AS, Milošević, MV, Axt VM, Peeters FM, Journal of superconductivity and novel magnetism 29, 605 (2016). http://doi.org/10.1007/s10948-015-3319-8
Abstract: We investigate how the interplay of quantum confinement and level broadening caused by disorder affects superconducting correlations in ultra-small metallic grains. We use the electron-phonon interaction-induced electron mass renormalization and the reduced static-path approximation of the BCS formalism to calculate the critical temperature as a function of the grain size. We show how the strong electron-impurity scattering additionally smears the peak structure in the electronic density of states of a metallic grain and imposes additional limits on the critical temperature under strong quantum confinement.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.18
Times cited: 7
DOI: 10.1007/s10948-015-3319-8
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“FFLO-wave-vector lock-in effect in quasi-1D superconductors”. Croitoru MD, Buzdin AI, Journal of superconductivity and novel magnetism 28, 1305 (2015). http://doi.org/10.1007/s10948-014-2910-8
Abstract: We study the phase transition into the Fulde-Ferrell-Larkin-Ovchinnikov state in high magnetic field in quasi-one dimensional superconductors within the quasi-classical formalism, taking into account the interchain Josephson coupling and the paramagnetic spin splitting. We show that anomalies in the field-direction dependence of the upper critical field when the magnetic field length equals to the FFLO period, previously described in [29], are characterized by the lock-in effect of the FFLO modulation wave vector, which is governed by the magnetic length.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.18
Times cited: 4
DOI: 10.1007/s10948-014-2910-8
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“Tuning the superconducting properties of nanomaterials”. Croitoru MD, Shanenko AA, Peeters FM Springer, Dordrecht, page 1 (2009).
Abstract: Electron continement and its effect on the superconducting-to-normal phase transition driven by a magentic field and/or a current is studied in nanowires. Our investigation is based on a self-consistent numerical solution of the Bogoliubov-de Gennes equations. We find that in a parallel magneitc field and/or in the presence of a supercurrent the transition from the superconducting to the normal phase occurs as a cascade of discontinuous jumps in the superconducting order parameter for diameters D < 10 divided by 15 nm at T = 0. The critical magentic field exhibits quantum-size oscillations with pronounced resonant enhancements as a function of the wire radius.
Keywords: H1 Book chapter; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
DOI: 10.1007/978-90-481-3120-4_1
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“Superconducting nanowires : new type of BCS-BEC crossover driven by quantum-size effects”. Shanenko AA, Croitoru MD, Vagov A, Peeters FM, , 119 (2011). http://doi.org/10.1007/978-94-007-0044-4_9
Abstract: We show that a superconducting quantum nanowire undergoes a new type of BCS-BEC crossover each time when an electron subband approaches the Fermi surface. In this case the longitudinal Cooper-pair size drops by two-three orders of magnitude down to a few nanometers. This unconventional BCS-BEC crossover is driven by quantum-size effects rather than by tuning the fermion-fermion interaction.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT)
DOI: 10.1007/978-94-007-0044-4_9
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“Phonon limited superconducting correlations in metallic nanograins”. Croitoru MD, Shanenko AA, Vagov A, Milošević, MV, Axt VM, Peeters FM, Scientific reports 5, 16515 (2015). http://doi.org/10.1038/srep16515
Abstract: Conventional superconductivity is inevitably suppressed in ultra-small metallic grains for characteristic sizes smaller than the Anderson limit. Experiments have shown that above the Anderson limit the critical temperature may be either enhanced or reduced when decreasing the particle size, depending on the superconducting material. In addition, there is experimental evidence that whether an enhancement or a reduction is found depends on the strength of the electronphonon interaction in the bulk. We reveal how the strength of the e-ph interaction interplays with the quantum-size effect and theoretically obtain the critical temperature of the superconducting nanograins in excellent agreement with experimental data. We demonstrate that strong e-ph scattering smears the peak structure in the electronic density-of-states of a metallic grain and enhances the electron mass, and thereby limits the highest T-c achievable by quantum confinement.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.259
Times cited: 9
DOI: 10.1038/srep16515
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“Superconductivity in the quantum-size regime”. Shanenko AA, Croitoru MD, Peeters FM, , 79 (2008)
Abstract: Recent technological advances resulted in high-quality superconducting metallic nanofilms and nanowires. The physical properties of such nanostructures are governed by the size-quantization of the transverse electron spectrum. This has a substantial impact on the basic superconducting characteristics, e.g., the order parameter, the critical temperature and the critical magnetic field. In the present paper we give an overview of our theoretical results on this subject. Based on a numerical self-consistent solution of the Bogoliubov-de Gennes equations, we investigate how the superconducting properties are modified in the quantum-size regime.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
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