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“Erratum: Spontaneous magnetization and electron momentum density in three-dimensional quantum dots [Phys. Rev. B 68, 165326 (2003)]”. Saniz R, Barbiellini B, Denison AB, Bansil A, Physical review : B : condensed matter and materials physics 84, 119907 (2011). http://doi.org/10.1103/PhysRevB.84.119907
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
DOI: 10.1103/PhysRevB.84.119907
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“Excitonic Aharonov-Bohm effect : unstrained versus strained type-I semiconductor nanorings”. Tadić, M, Čukarić, N, Arsoski V, Peeters FM, Physical review : B : condensed matter and materials physics 84, 125307 (2011). http://doi.org/10.1103/PhysRevB.84.125307
Abstract: We study how mechanical strain affects the magnetic field dependence of the exciton states in type-I semiconductor nanorings. Strain spatially separates the electron and hole in (In,Ga)As/GaAs nanorings which is beneficial for the occurrence of the excitonic Aharonov-Bohm (AB) effect. In narrow strained (In,Ga)As/GaAs nanorings the AB oscillations in the exciton ground-state energy are due to anticrossings with the first excited state. No such AB oscillations are found in unstrained GaAs/(Al,Ga)As nanorings irrespective of the ring width. Our results are obtained within an exact numerical diagonalization scheme and are shown to be accurately described by a two-level model with off-diagonal coupling t. The later transfer integral expresses the Coulomb coupling between states of electron-hole pairs. We also found that the oscillator strength for exciton recombination in (In,Ga)As/GaAs nanorings exhibits AB oscillations, which are superimposed on a linear increase with magnetic field. Our results agree qualitatively with recent experiments on the excitonic Aharonov-Bohm effect in type-I (In,Ga)As/GaAs nanorings.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 13
DOI: 10.1103/PhysRevB.84.125307
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“Fano resonances and electron spin transport through a two-dimensional spin-orbit-coupled quantum ring”. Nowak MP, Szafran B, Peeters FM, Physical review : B : condensed matter and materials physics 84, 235319 (2011). http://doi.org/10.1103/PhysRevB.84.235319
Abstract: Electron transport through a spin-orbit-coupled quantum ring is investigated within linear response theory. We show that the finite width of the ring results in the appearance of Fano resonances in the conductance. This turns out to be a consequence of the spin-orbit interaction that leads to a breaking of the parity of the states localized in the ring. The resonances appear when the system is close to maxima of Aharonov-Casher conductance oscillations where spin transfer is heavily modified. When the spin-orbit coupling strength is detuned from the Aharonov-Casher maxima the resonances are broadened resulting in a dependence of the spin transport on the electron Fermi energy in contrast to predictions from one-dimensional models.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 19
DOI: 10.1103/PhysRevB.84.235319
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“Fluctuations in superconducting rings with two order parameters”. Berger J, Milošević, MV, Physical review : B : condensed matter and materials physics 84, 214515 (2011). http://doi.org/10.1103/PhysRevB.84.214515
Abstract: Motivated by two-band superconductivity in, e.g., borides and pnictides, starting from the two-band Ginzburg-Landau energy functional, we discuss how the presence of two order parameters and the coupling between them influence a superconducting ring in the fluctuative regime. Our method is an extension of the von OppenRiedel formalism for rings; it is exact, but requires numerical implementation. We also study approximations for which analytic expressions can be obtained, and check their ranges of validity. We provide estimates for the temperature ranges where fluctuations are important, calculate the persistent current in MgB2 rings as a function of temperature and enclosed flux, and point out its additional dependence on the cross-section area of the wire from which the ring is made. We find temperature regions in which fluctuations enhance the persistent currents and regions where they inhibit the persistent current. The presence of two order parameters that can fluctuate independently always leads to larger averages of the order parameters at Tc, but yields larger persistent current only for appropriate parameters. In cases of very different material parameters for the two coupled condensates, the persistent current is inhibited.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 7
DOI: 10.1103/PhysRevB.84.214515
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“Geometry-driven vortex states in type-I superconducting Pb nanowires”. Engbarth MA, Bending SJ, Milošević, MV, Physical review : B : condensed matter and materials physics 83, 224504 (2011). http://doi.org/10.1103/PhysRevB.83.224504
Abstract: Hall probe magnetometry has been used to investigate the magnetization of individual cylindrically shaped Pb nanowires grown by electrocrystallization on a highly oriented pyrolytic graphite electrode. These measurements have been interpreted by comparison with three-dimensional Ginzburg-Landau (GL) calculations for nanowires with our sample parameters. We find that the measured superheating field and the critical field for surface superconductivity are strongly influenced by the temperature-dependent coherence length, ξ(T) and penetration depth λ(T) and their relationship to the nanowire diameter. As the temperature is increased toward Tc this drives a change in the superconductor-normal transition from first order irreversible to first order reversible and finally second order reversible. We find that the geometrical flux confinement in our type-I nanowires leads to the formation of a one-dimensional row of single-quantum vortices. While GL calculations show a quite uniform distribution of vortices in thin nanowires, clear vortex bunching is found as the diameter increases, suggesting a transition to a more classical type-I behavior. Subtle changes in minor magnetization loops also indicate that slightly different flux configurations can form with the same vorticity, which depend on the sample history.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 19
DOI: 10.1103/PhysRevB.83.224504
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“Ginzburg-Landau theory of the zigzag transition in quasi-one-dimensional classical Wigner crystals”. Galván Moya JE, Peeters FM, Physical review : B : condensed matter and materials physics 84, 134106 (2011). http://doi.org/10.1103/PhysRevB.84.134106
Abstract: We present a mean-field description of the zigzag phase transition of a quasi-one-dimensional system of strongly interacting particles, with interaction potential r−ne−r/λ, that are confined by a power-law potential (yα). The parameters of the resulting one-dimensional Ginzburg-Landau theory are determined analytically for different values of α and n. Close to the transition point for the zigzag phase transition, the scaling behavior of the order parameter is determined. For α=2, the zigzag transition from a single to a double chain is of second order, while for α>2, the one-chain configuration is always unstable and, for α<2, the one-chain ordered state becomes unstable at a certain critical density, resulting in jumps of single particles out of the chain.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 16
DOI: 10.1103/PhysRevB.84.134106
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“Heating of quasiparticles driven by oscillations of the order parameter in short superconducting microbridges”. Vodolazov DY, Peeters FM, Physical review : B : condensed matter and materials physics 83, 224523 (2011). http://doi.org/10.1103/PhysRevB.83.224523
Abstract: We predict heating of quasiparticles driven by order parameter oscillations in the resistive state of short superconducting microbridges. The finite relaxation time of the magnitude of the order parameter |Δ| and the dependence of the spectral functions both on |Δ| and the supervelocity Q are the origin of this effect. Our results are opposite to those of Aslamazov and Larkin [ Zh. Eks. Teor. Fiz. 70 1340 (1976)] and Schmid et al. [ Phys. Rev. B 21 5076 (1980)] where cooling of quasiparticles was found.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 4
DOI: 10.1103/PhysRevB.83.224523
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“High-temperature conductance of a two-dimensional superlattice controlled by spin-orbit interaction”. Földi P, Szaszkó-Bogár V, Peeters FM, Physical review : B : condensed matter and materials physics 83, 115313 (2011). http://doi.org/10.1103/PhysRevB.83.115313
Abstract: Rashba-type spin-orbit interaction (SOI) controlled band structure of a two-dimensional superlattice allows for the modulation of the conductance of finite size devices by changing the strength of the SOI. We consider rectangular arrays and find that the temperature dependence of the conductance disappears for high temperatures, but the strength of the SOI still affects the conductance at these temperatures. The modulation effect can be seen even in the presence of strong dephasing, which can be important for practical applications.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 8
DOI: 10.1103/PhysRevB.83.115313
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“Impact of spin-orbit coupling on the Holstein polaron”. Li Z, Covaci L, Berciu M, Baillie D, Marsiglio F, Physical review : B : condensed matter and materials physics 83, 195104 (2011). http://doi.org/10.1103/PhysRevB.83.195104
Abstract: We utilize an exact variational numerical procedure to calculate the ground state properties of a polaron in the presence of a Rashba-like spin-orbit interaction. Our results corroborate previous work performed with the momentum average approximation and with weak-coupling perturbation theory. We find that spin-orbit coupling increases the effective mass in the regime with weak electron-phonon coupling, and decreases the effective mass in the regimes of intermediate and strong electron-phonon coupling. Analytical strong-coupling perturbation theory results confirm our numerical results in the small-polaron regime. A large amount of spin-orbit coupling can lead to a significant lowering of the polaron effective mass.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 9
DOI: 10.1103/PhysRevB.83.195104
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“Influence of electron-electron interaction on the cyclotron resonance spectrum of magnetic quantum dots containing few electrons”. Nga TTN, Peeters FM, Physical review : B : condensed matter and materials physics 83, 075419 (2011). http://doi.org/10.1103/PhysRevB.83.075419
Abstract: The configuration interaction method is used to obtain the magneto-optical absorption spectrum of a few-electron (Ne=1,2,,5) quantum dot containing a single magnetic ion. We find that the IR spectrum (the position, the number, and the oscillator strength of the cyclotron resonance peaks) depends on the strength of the Coulomb interaction, the number of electrons, and the position of the magnetic ion. We find that the Kohn theorem is no longer valid as a consequence of the electron-spin-magnetic-ion-spin-exchange interaction.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 8
DOI: 10.1103/PhysRevB.83.075419
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“Influence of impurities and surface defects on the flux-induced current in mesoscopic d-wave superconducting loops”. Zha G-Q, Milošević, MV, Zhou S-P, Peeters FM, Physical review : B : condensed matter and materials physics 84, 132501 (2011). http://doi.org/10.1103/PhysRevB.84.132501
Abstract: We investigated the magnetic flux dependence of the supercurrent in mesoscopic d-wave superconducting loops, containing impurities and surface defects, by numerically solving the Bogoliubovde Gennes equations self-consistently. In the presence of impurities, bound states arise close to the Fermi energy. In the case of a single impurity, the flux-induced current is found to be suppressed. This can be different when more impurities are introduced in the sample due to the quantum interference effect, which depends sensitively on the relative position between the impurities. We further analyze the effect of small surface defects at the inner or outer edge of the loop, and show that indentation and bulge defects have pronounced and different effects on the supercurrent.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 13
DOI: 10.1103/PhysRevB.84.132501
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“Landau levels in asymmetric graphene trilayer”. Sena SHR, Pereira JM, Peeters FM, Farias GA, Physical review : B : condensed matter and materials physics 84, 205448 (2011). http://doi.org/10.1103/PhysRevB.84.205448
Abstract: The electronic spectrum of three coupled graphene layers (graphene trilayers) is investigated in the presence of an external magnetic field. We obtain analytical expressions for the Landau level spectrum for both the ABA and ABC type of stacking, which exhibit very different dependence on the magnetic field. We show that layer asymmetry and an external gate voltage can strongly influence the properties of the system.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 30
DOI: 10.1103/PhysRevB.84.205448
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“Lattice thermal properties of graphane : thermal contraction, roughness, and heat capacity”. Neek-Amal M, Peeters FM, Physical review : B : condensed matter and materials physics 83, 235437 (2011). http://doi.org/10.1103/PhysRevB.83.235437
Abstract: Using atomistic simulations, we determine the roughness and the thermal properties of a suspended graphane sheet. As compared to graphene, we found that (i) hydrogenated graphene has a larger thermal contraction, (ii) the roughness exponent at room temperature is smaller, i.e., ≃ 1.0 versus ≃ 1.2 for graphene, (iii) the wavelengths of the induced ripples in graphane cover a wide range corresponding to length scales in the range 30125 Å at room temperature, and (iv) the heat capacity of graphane is estimated to be 29.32±0.23 J/mol K, which is 14.8% larger than that for graphene, i.e., 24.98±0.14 J/mol K. Above 1500 K, we found that graphane buckles when its edges are supported in the x-y plane.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 42
DOI: 10.1103/PhysRevB.83.235437
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“Measuring the corrugation amplitude of suspended and supported graphene”. Kirilenko DA, Dideykin AT, Van Tendeloo G, Physical review : B : condensed matter and materials physics 84, 235417 (2011). http://doi.org/10.1103/PhysRevB.84.235417
Abstract: Nanoscale corrugation is a fundamental property of graphene arising from its low-dimensional nature. It places a fundamental limit to the conductivity of graphene and influences its properties. However the degree of the influence of the corrugation has not been well established because of the little knowledge about its spectrum in suspended graphene. We present a transmission electron microscopy technique that enables us to measure the average corrugation height and length. We applied the technique also to measure the temperature dependence of the corrugation. The difference in corrugation between suspended and supported graphene has been illustrated.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 31
DOI: 10.1103/PhysRevB.84.235417
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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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“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 Dirac particles in AA-stacked graphite and multilayers of graphene”. Lobato I, Partoens B, Physical review : B : condensed matter and materials physics 83, 165429 (2011). http://doi.org/10.1103/PhysRevB.83.165429
Abstract: Using the tight-binding formalism we show that in the recently experimentally realized AA-stacked graphite in essence two types of massless relativistic Dirac particles are present with a different effective speed of light. We also investigate how the electronic structure evolves from a single graphene sheet into AA-stacked graphite. It is shown that in contrast to AB-stacked graphene layers, the spectrum of AA-stacked graphene layers can be considered as a superposition of single-layer spectra and only particles with a linear spectrum at the Fermi energy around the K point are present. From the evolution of the band overlap we show that 6 multilayers of AA-stacked graphene already behave as AA-stacked graphite. The evolution of the effective speeds of light of the Dirac particles to their bulk values shows exactly the same behavior. The tight-binding parameters we use to describe AA-stacked graphite and multilayers of graphene are obtained by ab initio calculations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 68
DOI: 10.1103/PhysRevB.83.165429
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“Orientational properties of C70 and C80 fullerenes in carbon nanotubes”. Verberck B, Physical review : B : condensed matter and materials physics 83, 045405 (2011). http://doi.org/10.1103/PhysRevB.83.045405
Abstract: We present energy calculations of a C80 molecule with D5d symmetry encapsulated in a carbon nanotube. The approximation of a continuous tube rather than a rolled-up graphene sheet, justified by comparison with atomistic calculations, allows an expansion of the energy field into symmetry-adapted rotator functions. For a given tube radius R, we observe a strong dependence of the interaction energy on the molecular tilt angle and on the molecules lateral position in the tube. We observe a transition from on-axis lying orientations to tilted orientations at R1≈6.95 Å and a subsequent transition to standing orientations at R2≈7.6 Å. For tube radii larger than R3≈8.0 Å, the molecule starts to occupy off-axis positions and assumes a lying orientation. Results are compared to the case of C70 molecules, with D5h symmetry. Our findings are consistent with recent high-resolution transmission electron microscopy measurements and are relevant for the design of new materials with tunable electronic properties.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 6
DOI: 10.1103/PhysRevB.83.045405
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“Origin of the hysteresis of the current voltage characteristics of superconducting microbridges near the critical temperature”. Vodolazov DY, Peeters FM, Physical review : B : condensed matter and materials physics 84, 094511 (2011). http://doi.org/10.1103/PhysRevB.84.094511
Abstract: The current voltage (IV) characteristics of short [with length L less than or similar to xi(T)] and long [L >> xi(T)] microbridges are theoretically investigated near the critical temperature of the superconductor. Calculations are made in the nonlocal (local) limit when the inelastic relaxation length due to electron-phonon interactions L(in) = (D tau(in))(1/2) is larger (smaller) than the temperature-dependent coherence length xi(T) (D is the diffusion coefficient, tau(in) is the inelastic relaxation time of the quasiparticle distribution function). We find that, in both limits, the origin of the hysteresis in the IV characteristics is mainly connected with the large time scale over which the magnitude of the order parameter varies in comparison with the time-scale variation of the superconducting phase difference across the microbridge in the resistive state. In the nonlocal limit, the time-averaged heating and cooling of quasiparticles are found in different areas of the microbridge, which are driven, respectively, by oscillations of the order parameter and the electric field. We show that, by introducing an additional term in the time-dependent Ginzburg-Landau equation, it is possible to take into account the cooling effect in the local limit too.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 7
DOI: 10.1103/PhysRevB.84.094511
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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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“Phase separation and frustrated square lattice magnetism of Na1.5VOPO4F0.5”. Tsirlin AA, Nath R, Abakumov AM, Furukawa Y, Johnston DC, Hemmida M, Krug von Nidda H-A, Loidl A, Geibel C, Rosner H, Physical review : B : condensed matter and materials physics 84, 014429 (2011). http://doi.org/10.1103/PhysRevB.84.014429
Abstract: Crystal structure, electronic structure, and magnetic behavior of the spin-1/2 quantum magnet Na1.5VOPO4F0.5 are reported. The disorder of Na atoms leads to a sequence of structural phase transitions revealed by synchrotron x-ray powder diffraction and electron diffraction. The high-temperature second-order α↔β transition at 500 K is of the order-disorder type, whereas the low-temperature β↔γ+γ′ transition around 250 K is of the first order and leads to a phase separation toward the polymorphs with long-range (γ) and short-range (γ′) order of Na. Despite the complex structural changes, the magnetic behavior of Na1.5VOPO4F0.5 probed by magnetic susceptibility, heat capacity, and electron spin resonance measurements is well described by the regular frustrated square lattice model of the high-temperature α-polymorph. The averaged nearest-neighbor and next-nearest-neighbor couplings are J̅ 1≃−3.7 K and J̅ 2≃6.6 K, respectively. Nuclear magnetic resonance further reveals the long-range ordering at TN=2.6 K in low magnetic fields. Although the experimental data are consistent with the simplified square-lattice description, band structure calculations suggest that the ordering of Na atoms introduces a large number of inequivalent exchange couplings that split the square lattice into plaquettes. Additionally, the direct connection between the vanadium polyhedra induces an unusually strong interlayer coupling having effect on the transition entropy and the transition anomaly in the specific heat. Peculiar features of the low-temperature crystal structure and the relation to isostructural materials suggest Na1.5VOPO4F0.5 as a parent compound for the experimental study of tetramerized square lattices as well as frustrated square lattices with different values of spin.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 47
DOI: 10.1103/PhysRevB.84.014429
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“Phonon dispersions and piezoelectricity in bulk and multilayers of hexagonal boron nitride”. Michel KH, Verberck B, Physical review : B : condensed matter and materials physics 83, 115328 (2011). http://doi.org/10.1103/PhysRevB.83.115328
Abstract: A unified theory of phonon dispersions and piezoelectricity in bulk and multilayers of hexagonal boron nitride (h-BN) is derived. The dynamical matrix is calculated on the basis of an empirical force constant model of intralayer valence and interlayer van der Waals interactions. Coulomb interactions are calculated by Ewalds method, adapted for the three-dimensional (3D) and the multilayer case. The deformation of the ionic charge distribution with long-wave lattice displacements is taken into account. Special attention is devoted to the nonanalytic long-range Coulomb contribution to the dynamical matrix which is different for the 3D crystal and the multilayer case. Consequently there is a splitting of the transverse optical (TO) and longitudinal optical (LO) phonon branches of E1u symmetry and a discontinuity of the A2u branch at the Γ point in 3D h-BN. No such splitting and discontinuity at Γ are present in multilayer crystals with a finite number N of layers. There a diverging bundle of N overbending optical phonon branches emerges from Γ. Borns long-wave theory is applied and extended for the study of piezoelectricity in layered crystals. While 3D h-BN and h-BN multilayers with an even number of layers (symmetry D6h) are not piezoelectric, multilayers with an uneven number of Nu layers (symmetry D3h) are piezoelectric; the piezoelectric coefficient e1,11 is inversely proportional to Nu.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 82
DOI: 10.1103/PhysRevB.83.115328
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“Real-space multiple scattering method for angle-resolved photoemission and valence-band photoelectron diffraction and its application to Cu(111)”. Krüger P, da Pieve F, Osterwalder J, Physical review : B : condensed matter and materials physics 83, 115437 (2011). http://doi.org/10.1103/PhysRevB.83.115437
Abstract: A computational method is presented for angle-resolved photoemission spectra (ARPES) and photoelectron diffraction (PED) in the ultraviolet regime. The one-step model is employed and both initial valence and final continuum states are calculated using the finite-cluster, real-space multiple scattering method. Thereby the approach is versatile and provides a natural link to core-level PED. The method is applied to the Cu(111) valence band and good agreement with experiment is found for both ARPES spectra and PED patterns. When the PED patterns are integrated over a filled band of a single-orbital symmetry, such as Cu-3d, we show, both numerically and analytically, that the exact theory with delocalized initial states can be replaced by the much simpler, core-level-type theory where the initial states are taken as localized.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 17
DOI: 10.1103/PhysRevB.83.115437
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“Rectification of vortex motion in a circular ratchet channel”. Lin NS, Heitmann TW, Yu K, Plourde BLT, Misko VR, Physical review : B : condensed matter and materials physics 84, 144511 (2011). http://doi.org/10.1103/PhysRevB.84.144511
Abstract: We study the dynamics of vortices in an asymmetric (i.e., consisting of triangular cells) ring channel driven by an external ac current I in a Corbino setup. The asymmetric potential rectifies the motion of vortices and induces a net vortex flow without any unbiased external drive, i.e., the ratchet effect. We show that the net flow of vortices strongly depends on vortex density and frequency of the driving current. Depending on the density, we distinguish a single-vortex rectification regime (for low density, when each vortex is rectified individually) determined by the potential-energy landscape inside each cell of the channel (i.e., hard and easy directions) and multi-vortex, or collective, rectification (high-density case) when the inter-vortex interaction becomes important. We analyze the average angular velocity ω of vortices as a function of I and study commensurability effects between the numbers of vortices and cells in the channel and the role of frequency of the applied ac current. We have shown that the commensurability effect results in a stepwise ω-I curve. Besides the integer steps, i.e., the large steps found in the single-vortex case, we also found fractional steps corresponding to fractional ratios between the numbers of vortices and triangular cells. We have performed preliminary measurements on a device containing a single weak-pinning circular ratchet channel in a Corbino geometry and observed a substantial asymmetric vortex response.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 27
DOI: 10.1103/PhysRevB.84.144511
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“Role of carbon and nitrogen in Fe2C and Fe2N from first-principles calculations”. Fang CM, van Huis MA, Jansen J, Zandbergen HW, Physical review : B : condensed matter and materials physics 84, 094102 (2011). http://doi.org/10.1103/PhysRevB.84.094102
Abstract: Although Fe2C and Fe2N are technologically important materials, the exact nature of the chemical bonding of C and N atoms and the related impact on the electronic properties are at present unclear. Here, results of first-principles electronic structure calculations for Fe2X (X = C, N) phases are presented. The electronic structure calculations show that the roles of N and C in iron nitrides and carbides are comparable, and that the X-X interactions have significant impact on electronic properties. Accurate analysis of the spatially resolved differences in electron densities reveals a subtle distinction between the chemical bonding and charge transfer of N and C ions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 24
DOI: 10.1103/PhysRevB.84.094102
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“Scattering of Dirac electrons by circular mass barriers : valley filter and resonant scattering”. Masir MR, Matulis A, Peeters FM, Physical review : B : condensed matter and materials physics 84, 245413 (2011). http://doi.org/10.1103/PhysRevB.84.245413
Abstract: The scattering of two-dimensional (2D) massless Dirac electrons is investigated in the presence of a random array of circular mass barriers. The inverse momentum relaxation time and the Hall factor are calculated and used to obtain parallel and perpendicular resistivity components within linear transport theory. We found a nonzero perpendicular resistivity component which has opposite sign for electrons in the different K and K′ valleys. This property can be used for valley filter purposes. The total cross section for scattering on penetrable barriers exhibits resonances due to the presence of quasibound states in the barriers that show up as sharp gaps in the cross section while for Schrödinger electrons they appear as peaks.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 32
DOI: 10.1103/PhysRevB.84.245413
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“Spin-current generation from Coulomb-Rashba interaction in semiconductor bilayers”. Glazov MM, Semina MA, Badalyan SM, Vignale G, Physical review : B : condensed matter and materials physics 84, 033305 (2011). http://doi.org/10.1103/PhysRevB.84.033305
Abstract: Electrons in double-layer semiconductor heterostructures experience a special type of spin-orbit interaction that arises in each layer from the perpendicular component of the Coulomb electric field created by electron-density fluctuations in the other layer. We show that this interaction, acting in combination with the usual spin-orbit interaction, can generate a spin current in one layer when a charge current is driven in the other. This effect is distinct symmetrywise from the spin-Hall drag. The spin current is not, in general, perpendicular to the drive current.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 5
DOI: 10.1103/PhysRevB.84.033305
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“Spiral ground state against ferroelectricity in the frustrated magnet BiMnFe2O6”. Abakumov AM, Tsirlin AA, Perez-Mato JM, Petřiček V, Rosner H, Yang T, Greenblatt M, Physical review : B : condensed matter and materials physics 83, 214402 (2011). http://doi.org/10.1103/PhysRevB.83.214402
Abstract: The spiral magnetic structure and underlying spin lattice of BiMnFe2O6 are investigated by low-temperature neutron powder diffraction and density functional theory band structure calculations. In spite of the random distribution of the Mn3+ and Fe3+ cations, this centrosymmetric compound undergoes a transition into an incommensurate antiferromagnetically ordered state below TN≃220 K. The magnetic structure is characterized by the propagation vector k=[0,β,0] with β≃0.14 and the P221211′(0β0)0s0s magnetic superspace symmetry. It comprises antiferromagnetic helixes propagating along the b axis. The magnetic moments lie in the ac plane and rotate about π(1+β)≃204.8-deg angle between the adjacent magnetic atoms along b. The spiral magnetic structure arises from the peculiar frustrated arrangement of exchange couplings in the ab plane. The antiferromagnetic coupling along the c axis cancels the possible electric polarization and prevents ferroelectricity in BiMnFe2O6.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 12
DOI: 10.1103/PhysRevB.83.214402
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“Study on the giant positive magnetoresistance and Hall effect in ultrathin graphite flakes”. Vansweevelt R, Mortet V, D' Haen J, Ruttens bart, van Haesendonck C, Partoens B, Peeters FM, Wagner P, Physica status solidi : A : applications and materials science 208, 1252 (2011). http://doi.org/10.1002/pssa.201001206
Abstract: In this paper, we report on the electronic transport properties of mesoscopic, ultrathin graphite flakes with a thickness corresponding to a stack of 150 graphene layers. The graphite flakes show an unexpectedly strong positive magnetoresistance (PMR) already at room temperature, which scales in good approximation with the square of the magnetic field. Furthermore, we show that the resistivity is unaffected by magnetic fields oriented in plane with the graphene layers. Hall effect measurements indicate that the charge carriers are p-type and their concentration increases with increasing temperature while the mobility is decreasing. The Hall voltage is non-linear in higher magnetic fields. Possible origins of the observed effects are discussed. Ball and stick model of the two topmost carbon layers of the hexagonal graphite structure.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.775
Times cited: 8
DOI: 10.1002/pssa.201001206
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“Superconducting proximity effect in graphene under inhomogeneous strain”. Covaci L, Peeters FM, Physical review : B : condensed matter and materials physics 84, 241401 (2011). http://doi.org/10.1103/PhysRevB.84.241401
Abstract: The interplay between quantum Hall states and Cooper pairs is usually hindered by the suppression of the superconducting state due to the strong magnetic fields needed to observe the quantum Hall effect. From this point of view, graphene is special since it allows the creation of strong pseudomagnetic fields due to strain. We show that in a Josephson junction made of strained graphene, Cooper pairs will diffuse into the strained region. The pair correlation function will be sublattice polarized due to the polarization of the local density of states in the zero pseudo-Landau level. We uncover two regimes: (1) one in which the cyclotron radius is larger than the junction length, in which case the supercurrent will be enhanced, and (2) the long junction regime where the supercurrent is strongly suppressed because the junction becomes an insulator. In the latter case quantized Hall states form and Andreev scattering at the normal/superconducting interface will induce edge states. Our numerical calculation has become possible due to an extension of the Chebyshev-Bogoliubovde Gennes method to computations on video cards (GPUs).
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 27
DOI: 10.1103/PhysRevB.84.241401
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