“Structural phase transition and spontaneous interface reconstruction in La2/3Ca1/3MnO3/BaTiO3 superlattices”. Turner S, Lebedev OI, Verbeeck J, Gehrke K, Moshnyaga V, Van Tendeloo G, Physical review : B : condensed matter and materials physics 87, 035418 (2013). http://doi.org/10.1103/PhysRevB.87.035418
Abstract: (La2/3Ca1/3MnO3)n/(BaTiO3)m (LCMOn/BTOm) superlattices on MgO and SrTiO3 substrates with different layer thicknesses (n = 10, 38, 40 and m = 5, 18, 20) have been grown by metal organic aerosol deposition (MAD) and have been fully characterized down to the atomic scale to study the interface characteristics. Scanning transmission electron microscopy combined with spatially resolved electron energy-loss spectroscopy provides clear evidence for the existence of atomically sharp interfaces in MAD grown films, which exhibit epitaxial growth conditions, a uniform normal strain, and a fully oxidized state. Below a critical layer thickness the LCMO structure is found to change from the bulk Pnma symmetry to a pseudocubic R3̅ c symmetry. An atomically flat interface reconstruction consisting of a single Ca-rich atomic layer is observed on the compressively strained BTO on LCMO interface, which is thought to partially neutralize the total charge from the alternating polar atomic layers in LCMO as well as relieving strain at the interface. No interface reconstruction is observed at the tensile strained LCMO on BTO interface.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 12
DOI: 10.1103/PhysRevB.87.035418
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“Homologous series of layered structures in binary and ternary Bi-Sb-Te-Se systems : ab initio study”. Govaerts K, Sluiter MHF, Partoens B, Lamoen D, Physical review : B : condensed matter and materials physics 89, 054106 (2014). http://doi.org/10.1103/PhysRevB.89.054106
Abstract: In order to account explicitly for the existence of long-periodic layered structures and the strong structural relaxations in the most common binary and ternary alloys of the Bi-Sb-Te-Se system, we have developed a one-dimensional cluster expansion (CE) based on first-principles electronic structure calculations, which accounts for the Bi and Sb bilayer formation. Excellent interlayer distances are obtained with a van der Waals density functional. It is shown that a CE solely based on pair interactions is sufficient to provide an accurate description of the ground-state energies of Bi-Sb-Te-Se binary and ternary systems without making the data set of ab initio calculated structures unreasonably large. For the binary alloys A1−xQx (A=Sb, Bi; Q=Te, Se), a ternary CE yields an almost continuous series of (meta)stable structures consisting of consecutive A bilayers next to consecutive A2Q3 for 0<x<0.6. For x>0.6, the binary alloy segregates into pure Q and A2Q3. The Bi-Sb system is described by a quaternary CE and is found to be an ideal solid solution stabilized by entropic effects at T≠0 K but with an ordered structure of alternating Bi and Sb layers for x=0.5 at T=0 K. A quintuple CE is used for the ternary Bi-Sb-Te system, where stable ternary layered compounds with an arbitrary stacking of Sb2Te3, Bi2Te3, and Te-Bi-Te-Sb-Te quintuple units are found, optionally separated by mixed Bi/Sb bilayers. Electronic properties of the stable compounds were studied taking spin-orbit coupling into account.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 5
DOI: 10.1103/PhysRevB.89.054106
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“Compositional changes of Pd-Au bimetallic nanoclusters upon hydrogenation”. di Vece M, Bals S, Lievens P, Van Tendeloo G, Physical review : B : solid state 80, 125420 (2009). http://doi.org/10.1103/PhysRevB.80.125420
Abstract: Changes in the size distribution and composition of bimetallic Pd-Au nanoclusters have been observed after hydrogen exposure. This effect is caused by hydrogen-induced Ostwald ripening whereby the hydrogen reduces the binding energy of the cluster atoms leading to their detachment from the cluster. The composition changes due to a difference in mobility of the detached palladium and gold atoms on the surface. Fast palladium atoms contribute to the formation of larger nanoclusters, while the slower gold atoms are confined to the smaller nanoclusters. These transformations in the Pd-Au nanocluster size and composition set a limit for chemical reactions in which such nanoclusters are involved together with hydrogen.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 28
DOI: 10.1103/PhysRevB.80.125420
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“Influence of finite size effects on exchange anisotropy in oxidized Co nanocluster assembled films”. Dobrynin AN, Ievlev DN, Hendrich C, Temst K, Lievens P, Hörmann U, Verbeeck J, Van Tendeloo G, Vantomme A, Physical review : B : condensed matter and materials physics 73, 245416 (2006). http://doi.org/10.1103/PhysRevB.73.245416
Abstract: We compare the magnetic properties of Co cluster assembled films with different degrees of oxidation. Clusters with grain size (2.3 +/- 0.7) nm are produced in a laser vaporization cluster source and soft-landed in ultrahigh vacuum conditions, forming highly porous nanogranular films. After exposure to air for different periods of time, the Co clusters oxidize and the sample may be considered as a thin antiferromagnetic Co oxide matrix containing ferromagnetic Co clusters. Magnetization measurements were performed in a temperature range from 300 down to 5 K, at applied magnetic fields up to 30 kOe. The exchange bias value at 5 K for the strongly oxidized sample is 4.8 kOe against the value of 0.75 kOe for the less oxidized sample. The mean values of the thicknesses of the Co oxide layers are estimated to be 0.6 and 0.3 nm for the more and less oxidized sample, respectively. We propose a method of measuring the exchange bias inducing temperature, i.e., the temperature at which exchange anisotropy is established. We determined the mean inducing temperatures for both samples, which are 55 and 25 K, respectively, for the more and less oxidized samples. Both temperatures are well below the bulk CoO Neel temperature of 292 K. A low value of the inducing temperature of the Co oxide layer is a consequence of its subnanometer thickness, while a large exchange bias value is a consequence of different dimensionality of Co clusters and Co oxide matrix.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 17
DOI: 10.1103/PhysRevB.73.245416
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“Microstructure and interface studies of LaVO3/SrVO3 superlattices”. Boullay P, David A, Sheets WC, Lüders U, Prellier W, Tan H, Verbeeck J, Van Tendeloo G, Gatel C, Vincze G, Radi Z, Physical review : B : condensed matter and materials physics 83, 125403 (2011). http://doi.org/10.1103/PhysRevB.83.125403
Abstract: The structure and interface characteristics of (LaVO3)6m(SrVO3)m superlattices deposited on a (100)-SrTiO3 substrate were studied using transmission electron microscopy (TEM). Cross-section TEM studies revealed that both LaVO3 (LVO) and SrVO3 (SVO) layers are good single-crystal quality and epitaxially grown with respect to the substrate. It is evidenced that LVO layers are made of two orientational variants of a distorted perovskite compatible with bulk LaVO3, while SVO layers suffers from a tetragonal distortion due to the substrate-induced stain. Electron energy loss spectroscopy investigations indicate changes in the fine structure of the V L23 edge, related to a valence change between the LaVO3 and the SrVO3 layers.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 26
DOI: 10.1103/PhysRevB.83.125403
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“Multiple scattering calculations of relativistic electron energy loss spectra”. Jorissen K, Rehr JJ, Verbeeck J, Physical review : B : condensed matter and materials physics 81, 155108 (2010). http://doi.org/10.1103/PhysRevB.81.155108
Abstract: A generalization of the real-space Greens-function approach is presented for ab initio calculations of relativistic electron energy loss spectra (EELS) which are particularly important in anisotropic materials. The approach incorporates relativistic effects in terms of the transition tensor within the dipole-selection rule. In particular, the method accounts for relativistic corrections to the magic angle in orientation resolved EELS experiments. The approach is validated by a study of the graphite C K edge, for which we present an accurate magic angle measurement consistent with the predicted value.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 24
DOI: 10.1103/PhysRevB.81.155108
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“Interfacial spin glass state and exchange bias in manganite bilayers with competing magnetic orders”. Ding JF, Lebedev OI, Turner S, Tian YF, Hu WJ, Seo JW, Panagopoulos C, Prellier W, Van Tendeloo G, Wu T, Physical review : B : condensed matter and materials physics 87, 054428 (2013). http://doi.org/10.1103/PhysRevB.87.054428
Abstract: The magnetic properties of manganite bilayers composed of G-type antiferromagnetic (AFM) SrMnO3 and double-exchange ferromagnetic (FM) La0.7Sr0.3MnO3 are studied. A spin-glass state is observed as a result of competing magnetic orders and spin frustration at the La0.7Sr0.3MnO3/SrMnO3 interface. The dependence of the irreversible temperature on the cooling magnetic field follows the Almeida-Thouless line. Although an ideal G-type AFM SrMnO3 is featured with a compensated spin configuration, the bilayers exhibit exchange bias below the spin glass freezing temperature, which is much lower than the Néel temperature of SMO, indicating that the exchange bias is strongly correlated with the spin glass state. The results indicate that the spin frustration that originates from the competition between the AFM super-exchange and the FM double-exchange interactions can induce a strong magnetic anisotropy at the La0.7Sr0.3MnO3/SrMnO3 interface.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 98
DOI: 10.1103/PhysRevB.87.054428
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“Using electron vortex beams to determine chirality of crystals in transmission electron microscopy”. Juchtmans R, Béché, A, Abakumov A, Batuk M, Verbeeck J, Physical review : B : condensed matter and materials physics 91, 094112 (2015). http://doi.org/10.1103/PhysRevB.91.094112
Abstract: We investigate electron vortex beams elastically scattered on chiral crystals. After deriving a general expression for the scattering amplitude of a vortex electron, we study its diffraction on point scatterers arranged on a helix. We derive a relation between the handedness of the helix and the topological charge of the electron vortex on one hand and the symmetry of the higher-order Laue zones in the diffraction pattern on the other for kinematically and dynamically scattered electrons. We then extend this to atoms arranged on a helix as found in crystals which belong to chiral space groups and propose a method to determine the handedness of such crystals by looking at the symmetry of the diffraction pattern. In contrast to alternative methods, our technique does not require multiple scattering, which makes it possible to also investigate extremely thin samples in which multiple scattering is suppressed. In order to verify the model, elastic scattering simulations are performed, and an experimental demonstration on Mn2Sb2O7 is given in which we find the sample to belong to the right-handed variant of its enantiomorphic pair. This demonstrates the usefulness of electron vortex beams to reveal the chirality of crystals in a transmission electron microscope and provides the required theoretical basis for further developments in this field.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 54
DOI: 10.1103/PhysRevB.91.094112
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“Procedure to count atoms with trustworthy single-atom sensitivity”. Van Aert S, de Backer A, Martinez GT, Goris B, Bals S, Van Tendeloo G, Rosenauer A, Physical review : B : condensed matter and materials physics 87, 064107 (2013). http://doi.org/10.1103/PhysRevB.87.064107
Abstract: We report a method to reliably count the number of atoms from high-angle annular dark field scanning transmission electron microscopy images. A model-based analysis of the experimental images is used to measure scattering cross sections at the atomic level. The high sensitivity of these measurements in combination with a thorough statistical analysis enables us to count atoms with single-atom sensitivity. The validity of the results is confirmed by means of detailed image simulations. We will show that the method can be applied to nanocrystals of arbitrary shape, size, and atom type without the need for a priori knowledge about the atomic structure.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 106
DOI: 10.1103/PhysRevB.87.064107
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“Dependence of superconducting properties on the size and shape of a nanoscale superconductor: from nanowire to film”. Croitoru MD, Shanenko AA, Peeters FM, Physical review : B : condensed matter and materials physics 76, 024511 (2007). http://doi.org/10.1103/PhysRevB.76.024511
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 54
DOI: 10.1103/PhysRevB.76.024511
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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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“Observation of cyclotron resonance in an InAs/GaAs wetting layer with shallowly formed quantum dots”. Janssen G, Goovaerts E, Bouwen A, Partoens B, van Daele B, Zurauskiene N, Koenraad PM, Wolter JH, Physical review : B : condensed matter and materials physics 68, 045329 (2003). http://doi.org/10.1103/PhysRevB.68.045329
Keywords: A1 Journal article; Nanostructured and organic optical and electronic materials (NANOrOPT); Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 10
DOI: 10.1103/PhysRevB.68.045329
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“Incorporation and localization of substitutional Mn2+ ions in cubic ZnS quantum dots”. Nistor SV, Stefan M, Nistor LC, Goovaerts E, Van Tendeloo G, Physical review : B : condensed matter and materials physics 81, 035336 (2010). http://doi.org/10.1103/PhysRevB.81.035336
Abstract: Multifrequency electron paramagnetic resonance (EPR) and high resolution transmission electron microscopy (HRTEM) investigations were performed on small (2 nm) cubic ZnS nanocrystals (quantum dotsQDs) doped with 0.2% mol Mn2+, self-assembled into a mesoporous structure. The EPR data analysis shows that the substitutional Mn2+ ions are localized at Zn2+ sites subjected to a local axial lattice distortion, resulting in the observed zero-field-splitting parameter |D|=41×10−4 cm−1. The local distortion is attributed to the presence in the second shell of ligands of a stacking fault or twin, which alters the normal stacking sequence of the cubic structure. The HRTEM results confirm the presence of such extended planar defects in a large percentage of the investigated QDs, which makes possible the proposed substitutional Mn2+ impurity ions localization model. Based on these results it is suggested that the high doping levels of Mn2+ ions observed in cubic ZnS and possible in other II-VI semiconductor QDs prepared at low temperatures can be explained by the assistance of the extended lattice defects in the impurities incorporation.
Keywords: A1 Journal article; Nanostructured and organic optical and electronic materials (NANOrOPT); Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 55
DOI: 10.1103/PhysRevB.81.035336
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“Ultralow blocking temperature and breakdown of the giant spin model in Er3+-doped nanoparticles”. van den Heuvel W, Tikhomirov VK, Kirilenko D, Schildermans N, Chibotaru LF, Vanacken J, Gredin P, Mortier M, Van Tendeloo G, Moshchalkov VV, Physical review : B : condensed matter and materials physics 82, 094421 (2010). http://doi.org/10.1103/PhysRevB.82.094421
Abstract: The magnetization of luminescent Er3+-doped PbF2 nanoparticles (formula Er0.3Pb0.7F2.3) has been studied. Despite the high concentration of the doping Er3+ ions and relatively large size (8 nm) of these nanoparticles we have found no deviation between field-cooled and zero-field-cooled magnetization curves down to T=0.35 K, which points out an ultralow blocking temperature for the reversal of magnetization. We also have found strongly deviating magnetization curves M(H/T) for different temperatures T. These results altogether show that the investigated nanoparticles are not superparamagnetic, but rather each Er3+ ion in these nanoparticles is found in a paramagnetic state down to very low temperatures, which implies the breakdown of the Néel-Brown giant spin model in the case of these nanoparticles. Calculations of magnetization within a paramagnetic model of noninteracting Er3+ ions completely support this conclusion. Due to the ultralow blocking temperature, these nanoparticles have a potential for magnetic field-induced nanoscale refrigeration with an option of their optical localization and temperature control.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 11
DOI: 10.1103/PhysRevB.82.094421
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“Distinctive magnetic properties of CrI3 and CrBr3 monolayers caused by spin-orbit coupling”. Bacaksiz C, Šabani D, Menezes RM, Milošević, MV, Physical Review B 103, 125418 (2021). http://doi.org/10.1103/PhysRevB.103.125418
Abstract: After the discovery of magnetism in monolayer CrI3, the magnetic properties of different 2D materials from the chromium-trihalide family are intuitively assumed to be similar, yielding magnetic anisotropy from the spin-orbit coupling on halide ligands. Here we reveal significant differences between the CrI3 and CrBr3 magnetic monolayers in their magnetic anisotropy, resulting Curie temperature, hysteresis in external magnetic field, and evolution of magnetism with strain, all predominantly attributed to distinctly different interplay of atomic contributions to spin-orbit coupling in two materials.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 18
DOI: 10.1103/PhysRevB.103.125418
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“Anisotropic type-I superconductivity and anomalous superfluid density in OsB2”. Bekaert J, Vercauteren S, Aperis A, Komendová, L, Prozorov R, Partoens B, Milošević, MV, Physical review B 94, 144506 (2016). http://doi.org/10.1103/PhysRevB.94.144506
Abstract: We present a microscopic study of superconductivity in OsB2 , and discuss the origin and characteristic length
scales of the superconducting state. From first-principles we show that OsB2 is characterized by three different
Fermi sheets, and we prove that this fermiology complies with recent quantum-oscillation experiments. Using the
found microscopic properties, and experimental data from the literature, we employ Ginzburg-Landau relations
to reveal that OsB2 is a distinctly type-I superconductor with a very low Ginzburg-Landau parameter κ—a rare
property among compound materials. We show that the found coherence length and penetration depth corroborate
the measured thermodynamic critical field. Moreover, our calculation of the superconducting gap structure using
anisotropic Eliashberg theory and ab initio calculated electron-phonon interaction as input reveals a single but
anisotropic gap. The calculated gap spectrum is shown to give an excellent account for the unconventional
behavior of the superfluid density of OsB2 measured in experiments as a function of temperature. This reveals
that gap anisotropy can explain such behavior, observed in several compounds, which was previously attributed
solely to a two-gap nature of superconductivity.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 19
DOI: 10.1103/PhysRevB.94.144506
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“Effects of spatially engineered Dzyaloshinskii-Moriya interaction in ferromagnetic films”. Mulkers J, Van Waeyenberge B, Milošević, MV, Physical review B 95, 144401 (2017). http://doi.org/10.1103/PhysRevB.95.144401
Abstract: The Dzyaloshinskii-Moriya interaction (DMI) is a chiral interaction that favors formation of domain walls. Recent experiments and ab initio calculations show that there are multiple ways to modify the strength of the interfacially induced DMI in thin ferromagnetic films with perpendicular magnetic anisotropy. In this paper we reveal theoretically the effects of spatially varied DMI on the magnetic state in thin films. In such heterochiral 2D structures we report several emergent phenomena, ranging from the equilibrium spin canting at the interface between regions with different DMI, over particularly strong confinement of domain walls and skyrmions within high-DMI tracks, to advanced applications such as domain tailoring nearly at will, design of magnonic waveguides, and much improved skyrmion racetrack memory.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 60
DOI: 10.1103/PhysRevB.95.144401
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“Application of the weighted-density approximation to the accurate description of electron-positron correlation effects in materials”. Callewaert V, Saniz R, Barbiellini B, Bansil A, Partoens B, Physical review B 96, 085135 (2017). http://doi.org/10.1103/PhysRevB.96.085135
Abstract: We discuss positron-annihilation lifetimes for a set of illustrative bulk materials within the framework of the weighted-density approximation (WDA). The WDA can correctly describe electron-positron correlations in strongly inhomogeneous systems, such as surfaces, where the applicability of (semi-)local approximations is limited. We analyze the WDA in detail and show that the electrons which cannot screen external charges efficiently, such as the core electrons, cannot be treated accurately via the pair correlation of the homogeneous electron gas. We discuss how this problem can be addressed by reducing the screening in the homogeneous electron gas by adding terms depending on the gradient of the electron density. Further improvements are obtained when core electrons are treated within the LDA and the valence electron using the WDA. Finally, we discuss a semiempirical WDA-based approach in which a sum rule is imposed to reproduce the experimental lifetimes.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 6
DOI: 10.1103/PhysRevB.96.085135
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“Crosshatching on La0.5Ca0.5MnO3 ultrathin films epitaxially grown on SrTiO3(100)”. Wang Z-H, Lebedev OI, Van Tendeloo G, Cristiani G, Habermeier H-U, Physical review : B : condensed matter and materials physics 77, 1 (2008). http://doi.org/10.1103/PhysRevB.77.115330
Abstract: The morphological evolution in La(0.5)Ca(0.5)MnO(3)/SrTiO(3)(100) ultrathin films has been revealed by atomic force microscopy. It was found that ordered linear defects, which are in 1-2 unit cells high and oriented along the cubic [110] and [100] directions, first appear on the smooth surface of films with a thickness of 10 nm. As the epitaxial growth proceeds, these lines on surface develop into a crosshatch pattern for films with a thickness of 25 nm. Using the results of transmission electron microscopy and electrical measurements, we discuss the interplay between the surface pattern formation, the internal dislocation structure, and the variations in the electrical properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 8
DOI: 10.1103/PhysRevB.77.115330
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“Electronic reconstruction at n-type SrTiO3/LaAlO3 interfaces”. Verbeeck J, Bals S, Lamoen D, Luysberg M, Huijben M, Rijnders G, Brinkman A, Hilgenkamp H, Blank DHA, Van Tendeloo G, Physical review : B : condensed matter and materials physics 81, 085113 (2010). http://doi.org/10.1103/PhysRevB.81.085113
Abstract: Electron-energy-loss spectroscopy (EELS) is used to investigate single layers of LaAlO3 grown on SrTiO3 having an n-type interface as well as multilayers of LaAlO3 and SrTiO3 in which both n- and p-type interfaces occur. Only minor changes in Ti valence at the n-type interface are observed. This finding seems to contradict earlier experiments for other SrTiO3/LaAlO3 systems where large deviations in Ti valency were assumed to be responsible for the conductivity of these interfaces. Ab initio calculations have been carried out in order to interpret our EELS results. Using the concept of Bader charges, it is demonstrated that the so-called polar discontinuity is mainly resolved by lattice distortions and to a far lesser extent by changes in valency for both single layer and multilayer geometries.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 25
DOI: 10.1103/PhysRevB.81.085113
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“Transport, magnetic, and structural properties of La0.7Ce0.3MnO3 thin films: evidence for hole-doping”. Werner R, Raisch C, Leca V, Ion V, Bals S, Van Tendeloo G, Chasse T, Kleiner R, Koelle D, Physical review : B : solid state 79, 054416 (2009). http://doi.org/10.1103/PhysRevB.79.054416
Abstract: Cerium-doped manganite thin films were grown epitaxially by pulsed laser deposition at 720 °C and oxygen pressure pO2=125 Pa and were subjected to different annealing steps. According to x-ray diffraction (XRD) data, the formation of CeO2 as a secondary phase could be avoided for pO28 Pa. However, transmission electron microscopy shows the presence of CeO2 nanoclusters even in those films which appear to be single phase in XRD. With O2 annealing, the metal-to-insulator transition temperature increases, while the saturation magnetization decreases and stays well below the theoretical value for electron-doped La0.7Ce0.3MnO3 with mixed Mn3+/Mn2+ valences. The same trend is observed with decreasing film thickness from 100 to 20 nm, indicating a higher oxygen content for thinner films. Hall measurements on a film which shows a metal-to-insulator transition clearly reveal holes as dominating charge carriers. Combining data from x-ray photoemission spectroscopy, for determination of the oxygen content, and x-ray absorption spectroscopy (XAS), for determination of the hole concentration and cation valences, we find that with increasing oxygen content the hole concentration increases and Mn valences are shifted from 2+ to 4+. The dominating Mn valences in the films are Mn3+ and Mn4+, and only a small amount of Mn2+ ions can be observed by XAS. Mn2+ and Ce4+ XAS signals obtained in surface-sensitive total electron yield mode are strongly reduced in the bulk-sensitive fluorescence mode, which indicates hole-doping in the bulk for those films which do show a metal-to-insulator transition.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 25
DOI: 10.1103/PhysRevB.79.054416
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“Crystal fields, disorder, and antiferromagnetic short-range order in Yb0.24Sn0.76Ru”. Klimczuk T, Wang CH, Lawrence JM, Xu Q, Durakiewicz T, Ronning F, Llobet A, Trouw F, Kurita N, Tokiwa Y, Lee Ho, Booth CH, Gardner JS, Bauer ED, Joyce JJ, Zandbergen HW, Movshovich R, Cava RJ, Thompson JD;, Physical review : B : condensed matter and materials physics 84, 075152 (2011). http://doi.org/10.1103/PhysRevB.84.075152
Abstract: We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a Γ7-doublet ground state and a Γ8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a Γ6-excited state resides at 32 meV; however, the Γ8/Γ6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the Γ7-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 8
DOI: 10.1103/PhysRevB.84.075152
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“Electrical nonlinearity in colossal magnetoresistance manganite films: relevance of correlated polarons”. Moshnyaga V, Gehrke K, Sudheendra L, Belenchuk A, Raabe S, Shapoval O, Verbeeck J, Van Tendeloo G, Samwer K, Physical review : B : solid state 79, 134413 (2009). http://doi.org/10.1103/PhysRevB.79.134413
Abstract: The metal-insulator (MI) transition in epitaxial thin films of La0.75Ca0.25MnO3 (LCMO) is accompanied by the appearance of an intrinsic electrical nonlinearity. The latter, probed by electrical third harmonic voltage, U3, or resistance, R3=dU3/dJ, is drastically enhanced in the vicinity of the MI transition, TMI=267 K. Applied magnetic field, B=5 T, suppresses the nonlinearity, resulting in a huge nonlinear CMR3(TMI)~105%. R3 shows a peculiar low-frequency (1 kHz) dependence, R3~(-0)n, with exponent, n, changing across the MI transition from n~1,52 for TTMI to n=1 (T<TMI). The observed electrical nonlinearity in LCMO reflects the behavior of correlated polarons, the number of which dramatically enhances in the vicinity of TMI. We argued that correlated polarons, considered as electric-elastic quadrupoles, provide a nonlinear (quadratic) coupling to the electric field, yielding a third harmonic electric nonlinearity in LCMO. The reference film of La0.7Sr0.3MnO3 (LSMO), a prototypic double exchange system with second-order phase transition, is characterized as a linear metallic material in the whole range of temperatures (T=10400 K), magnetic fields (B=05 T), and frequencies (=11000 Hz).
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 28
DOI: 10.1103/PhysRevB.79.134413
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“Model-based determination of dielectric function by STEM low-loss EELS”. Zhang L, Turner S, Brosens F, Verbeeck J, Physical review : B : condensed matter and materials physics 81, 035102 (2010). http://doi.org/10.1103/PhysRevB.81.035102
Abstract: Dielectric properties of materials are crucial in describing the electromagnetic response of materials. As devices are becoming considerably smaller than the optical wavelength, the conventional measuring methods based on optical response are limited by their spatial resolution. Electron energy loss spectroscopy performed in a scanning transmission electron microscope is a good alternative to obtain the dielectric properties with excellent spatial resolution. Due to the overlap of diffraction discs in scanning transmission electron microscopy, it is difficult to apply conventional experimental settings to suppress retardation losses. In this contribution, a relativistic dielectric model for the loss function is presented which is used in a model based optimization scheme to estimate the complex dielectric function of a material. The method is applied to experiments on bulk diamond and SrTiO3 and shows a good agreement with optical reference data when retardation effects are included. Application of this technique to nanoparticles is possible but several theoretical assumptions made in the model of the loss function are violated and interpretation becomes problematic.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Theory of quantum systems and complex systems
Impact Factor: 3.836
Times cited: 9
DOI: 10.1103/PhysRevB.81.035102
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“Electrostatics of electron-hole interactions in van der Waals heterostructures”. Cavalcante LSR, Chaves A, Van Duppen B, Peeters FM, Reichman DR, Physical review B 97, 125427 (2018). http://doi.org/10.1103/PhysRevB.97.125427
Abstract: The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poisson's equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 22
DOI: 10.1103/PhysRevB.97.125427
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“Superconductivity between standard types: Multiband versus single-band materials”. Vagov A, Shanenko AA, Milošević, MV, Axt VM, Vinokur VM, Aguiar JA, Peeters FM, Physical review B 93, 174503 (2016). http://doi.org/10.1103/PhysRevB.93.174503
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 37
DOI: 10.1103/PhysRevB.93.174503
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“In situ HREM irradiation study of point-defect clustering in MBE-grown strained Si1-xGex/(001)Si structures”. Fedina L, Lebedev OI, Van Tendeloo G, van Landuyt J, Mironov OA, Parker EHC, Physical review : B : condensed matter and materials physics 61, 10336 (2000). http://doi.org/10.1103/PhysRevB.61.10336
Abstract: We present a detailed analysis of the point-defect clustering in strained Si/Si(1-x)Ge(x)/(001)Si structures, including the interaction of the point defects with the strained interfaces and the sample surface during 400 kV electron irradiation at room temperature. Point-defect cluster formation is very sensitive to the type and magnitude of the strain in the Si and Si(1-x)Ge(x) layers. A small compressive strain (-0.3%) in the SiGe alloy causes an aggregation of vacancies in the form of metastable [110]-oriented chains. They are located on {113} planes and further recombine with interstitials. Tensile strain in the Si layer causes an aggregation of interstitial atoms in the forms of additional [110] rows which are inserted on {113} planes with [001]-split configurations. The chainlike configurations are characterized by a large outward lattice relaxation for interstitial rows (0.13 +/-0.01 nm) and a very small inward relaxation for vacancy chains (0.02+/-0.01 nm). A compressive strain higher than -0.5% strongly decreases point-defect generation inside the strained SiGe alloy due to the large positive value of the formation volume of a Frenkel pair. This leads to the suppression of point-defect clustering in a strained SiGe alloy so that SiGe relaxes via a diffusion of vacancies from the Si layer, giving rise to an intermixing at the Si/SiGe interface. In material with a 0.9% misfit a strongly increased flow of vacancies from the Si layer to the SiGe layer and an increased biaxial strain in SiGe bath promote the preferential aggregation of vacancies in the (001) plane, which relaxes to form intrinsic 60 degrees dislocation loops.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 27
DOI: 10.1103/PhysRevB.61.10336
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“Onset, evolution, and magnetic braking of vortex lattice instabilities in nanostructured superconducting films”. Adami O-A, Jelić, ŽL, Xue C, Abdel-Hafiez M, Hackens B, Moshchalkov VV, Milošević, MV, Van de Vondel J, Silhanek AV, Physical review: B: condensed matter and materials physics 92, 134506 (2015). http://doi.org/10.1103/PhysRevB.92.134506
Abstract: In 1976, Larkin and Ovchinnikov [Zh. Eksp. Teor. Fiz. 68, 1915 (1975) [Sov. Phys.–JETP 41, 960 (1976)]] predicted that vortex matter in superconductors driven by an electrical current can undergo an abrupt dynamic transition from a flux-flow regime to a more dissipative state at sufficiently high vortex velocities. Typically, this transition manifests itself as a large voltage jump at a particular current density, so-called instability current density J∗, which is smaller than the depairing current. By tuning the effective pinning strength in Al films, using an artificial periodic pinning array of triangular holes, we show that a unique and well-defined instability current density exists if the pinning is strong, whereas a series of multiple voltage transitions appear in the relatively weaker pinning regime. This behavior is consistent with time-dependent Ginzburg-Landau simulations, where the multiple-step transition can be unambiguously attributed to the progressive development of vortex chains and subsequently phase-slip lines. In addition, we explore experimentally the magnetic braking effects, caused by a thick Cu layer deposited on top of the superconductor, on the instabilities and the vortex ratchet effect.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 21
DOI: 10.1103/PhysRevB.92.134506
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“Biexciton binding energy in fractional dimensional semiconductors”. Rønnow TF, Pedersen TG, Partoens B, Physical review : B : condensed matter and materials physics 85, 045412 (2012). http://doi.org/10.1103/PhysRevB.85.045412
Abstract: Biexcitons in fractional dimensional spaces are studied using variational quantum Monte Carlo. We investigate the biexciton binding energy as a function of the electron-hole mass fraction sigma as well as study the dimensional dependence of biexcitons for sigma = 0 and sigma = 1. As our first application of this model we treat the H(2) molecule in two and three dimensions. Next we investigate biexcitons in carbon nanotubes within the fractional dimensional model. To this end we find a relation between the nanotube radius and the effective dimension. The results of both applications are compared with results obtained using different models and we find a reasonable agreement. Within the fractional dimensional model we find that the biexciton binding energy in carbon nanotubes accurately scales as E(B)(r,epsilon) = 1280 meV angstrom/(r epsilon), as a function of radius r and the dielectric screening epsilon.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 21
DOI: 10.1103/PhysRevB.85.045412
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“Erratum : First-principles study of possible shallow donors in ZnAl2O4 spinel [Phys. Rev. B 87, 174101 (2013)]”. Dixit H, Tandon N, Cottenier S, Saniz R, Lamoen D, Partoens B, Physical review : B : condensed matter and materials physics 88, 059905 (2013). http://doi.org/10.1103/PhysRevB.88.059905
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 1
DOI: 10.1103/PhysRevB.88.059905
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