References of "PHYSICAL REVIEW B"
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See detailTransport through a quantum spin Hall antidot as a spectroscopic probe of spin textures
Rod, Alexia UL; Dolcetto, Giacomo UL; Rachel, Stephan et al

in Physical Review B (2016), 94

We investigate electron transport through an antidot embedded in a narrow strip of two-dimensional topological insulator. We focus on the most generic and experimentally relevant case with broken axial ... [more ▼]

We investigate electron transport through an antidot embedded in a narrow strip of two-dimensional topological insulator. We focus on the most generic and experimentally relevant case with broken axial spin symmetry. Spin-non-conservation allows additional scattering processes which change the transport properties profoundly. We start from an analytical model for noninteracting transport, which we also compare with a numerical tight-binding simulation. We then extend this model by including Coulomb repulsion on the antidot, and we study the transport in the Coulomb-blockade limit. We investigate sequential tunneling and cotunneling regimes, and we find that the current-voltage characteristic allows a spectroscopic measurement of the edge-state spin textures. [less ▲]

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See detailModeling charge relaxation in graphene quantum dots induced by electron-phonon interaction
Reichardt, Sven UL; Stampfer, Christoph

in Physical Review B (2016), 93(24), 245423

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See detailSpin-thermoelectric transport induced by interactions and spin-flip processes in two dimensional topological insulators
Ronetti; Vannucci, Luca; Dolcetto, Giacomo UL et al

in Physical Review B (2016), 93(16), 165414

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See detailDensity-functional theory with screened van der Waals interactions applied to atomic and molecular adsorbates on close-packed and non-close-packed surfaces
Ruiz, Victor G.; Liu, Wei; Tkatchenko, Alexandre UL

in PHYSICAL REVIEW B (2016), 93(3),

Modeling the adsorption of atoms and molecules on surfaces requires efficient electronic-structure methods that are able to capture both covalent and noncovalent interactions in a reliable manner. In ... [more ▼]

Modeling the adsorption of atoms and molecules on surfaces requires efficient electronic-structure methods that are able to capture both covalent and noncovalent interactions in a reliable manner. In order to tackle this problem, we have developed a method within density-functional theory (DFT) to model screened van der Waals interactions (vdW) for atoms and molecules on surfaces (the so-called DFT+vdW(surf) method). The relatively high accuracy of the DFT+vdW(surf) method in the calculation of both adsorption distances and energies, as well as the high degree of its reliability across a wide range of adsorbates, indicates the importance of the collective electronic effects within the extended substrate for the calculation of the vdW energy tail. We examine in detail the theoretical background of the method and assess its performance for adsorption phenomena including the physisorption of Xe on selected close-packed transition metal surfaces and 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on Au(111). We also address the performance of DFT+vdW(surf) in the case of non-close-packed surfaces by studying the adsorption of Xe on Cu(110) and the interfaces formed by the adsorption of a PTCDA monolayer on the Ag(111), Ag(100), and Ag(110) surfaces. We conclude by discussing outstanding challenges in the modeling of vdW interactions for studying atomic and molecular adsorbates on inorganic substrates. [less ▲]

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See detailRaman spectroscopy of rare-earth orthoferrites RFeO3 (R=La, Sm, Eu, Gd Tb, Dy)
Weber, Mads Christof; Guennou, Mael UL; Zhao, Hong Jian et al

in PHYSICAL REVIEW B (2016), 94(21),

We report a Raman scattering study of six rare-earth orthoferrites La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment ... [more ▼]

We report a Raman scattering study of six rare-earth orthoferrites La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment of the observed phonon modes to vibrational symmetries and atomic displacements. The assignment of the spectra and their comparison throughout the whole series allow correlating the phonon modes with the orthorhombic structural distortions of RFeO3 perovskites. In particular the positions of two specific A(g) modes scale linearly with the two FeO6 octahedra tilt angles, allowing the distortion to be tracked throughout the series. At variance with literature, we find that the two octahedra tilt angles scale differently with the vibration frequencies of their respective A(g) modes. This behavior, as well as the general relations between the tilt angles, the frequencies of the associated modes, and the ionic radii are rationalized in a simple Landau model. The reported Raman spectra and associated phonon-mode assignment provide reference data for structural investigations of the whole series of orthoferrites. [less ▲]

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See detailMultiple strain-induced phase transitions in LaNiO3 thin films
Weber, M. C.; Guennou, Mael UL; Dix, N. et al

in PHYSICAL REVIEW B (2016), 94(1),

Strain effects on epitaxial thin films of LaNiO3 grown on different single crystalline substrates are studied by Raman scattering and first-principles simulation. New Raman modes, not present in bulk or ... [more ▼]

Strain effects on epitaxial thin films of LaNiO3 grown on different single crystalline substrates are studied by Raman scattering and first-principles simulation. New Raman modes, not present in bulk or fully relaxed films, appear under both compressive and tensile strains indicating symmetry reductions. Interestingly, the Raman spectra and the underlying crystal symmetry for tensile and compressively strained films are different. Extensive mapping of LaNiO3 phase stability is addressed by simulations, showing that a variety of crystalline phases are indeed stabilized under strain. The calculated Raman frequencies reproduce the principal features of the experimental spectra, supporting the validity of the multiple strain-driven structural transitions predicted by the simulations. [less ▲]

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See detailNon local quantum state engineering with the Cooper pair splitter beyond the Coulomb blockade regime
Amitai, Ehud; Tiwari, Rakesh; Walter, Stefan et al

in Physical Review B (2015), 93

A Cooper pair splitter consists of two quantum dots side-coupled to a conventional superconductor. Usually, the quantum dots are assumed to have a large charging energy compared to the superconducting gap ... [more ▼]

A Cooper pair splitter consists of two quantum dots side-coupled to a conventional superconductor. Usually, the quantum dots are assumed to have a large charging energy compared to the superconducting gap, in order to suppress processes other than the coherent splitting of Cooper pairs. In this work, in contrast, we investigate the limit in which the charging energy is smaller than the superconducting gap. This allows us, in particular, to study the effect of a Zeeman field comparable to the charging energy. We find analytically that in this parameter regime the superconductor mediates an inter-dot tunneling term with a spin symmetry determined by the Zeeman field. Together with electrostatically tunable quantum dots, we show that this makes it possible to engineer a spin triplet state shared between the quantum dots. Compared to previous works, we thus extend the capabilities of the Cooper pair splitter to create entangled non local electron pairs. [less ▲]

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See detailTime-resolved pure spin fractionalization and spin-charge separation in helical Luttinger liquid based devices
Calzona, Alessio; Carrega, Matteo; Dolcetto, Giacomo UL et al

in Physical Review B (2015)

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See detailSpin texture of generic helical edge states
Rod, Alexia UL; Schmidt, Thomas UL; Rachel, Stephan

in Physical Review B (2015), 91

We study the spin texture of a generic helical liquid, the edge modes of a two-dimensional topological insulator with broken axial spin symmetry. By considering honeycomb and square-lattice realizations ... [more ▼]

We study the spin texture of a generic helical liquid, the edge modes of a two-dimensional topological insulator with broken axial spin symmetry. By considering honeycomb and square-lattice realizations of topological insulators, we show that in all cases the generic behavior of a momentum-dependent rotation of the spin quantization axis is realized. Here we establish this mechanism also for disk geometries with continuous rotational symmetry. Finally, we demonstrate that the rotation of spin-quantization axis remains intact for arbitrary geometries, i.e., in the absence of any continuous symmetry. We also calculate the dependence of this rotation on the model and material parameters. Finally, we propose a spectroscopy measurement which should directly reveal the rotation of the spin-quantization axis of the helical edge states. [less ▲]

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See detailTunneling between helical Majorana modes and helical Luttinger liquids
Chao, Sung-Po; Schmidt, Thomas UL; Chung, Chung-Hou

in Physical Review B (2015), 91

We propose and study the charge transport through single and double quantum point contacts setup between helical Majorana modes and an interacting helical Luttinger liquid. We show that the differential ... [more ▼]

We propose and study the charge transport through single and double quantum point contacts setup between helical Majorana modes and an interacting helical Luttinger liquid. We show that the differential conductance decreases for stronger repulsive interactions and that the point contacts become insulating above a critical interaction strength. For a single-point contact, the differential conductance as a function of bias voltage shows a series of peaks due to Andreev reflection of electrons in the Majorana modes. In the case of two point contacts, interference phenomena make the structure of the individual resonance peaks less universal and show modulations with different separation distance between the contacts. For small separation distance, the overall features remain similar to the case of a single-point contact. [less ▲]

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See detailEfficiency fluctuations in quantum thermoelectric devices
Esposito, Massimiliano UL; Ochoa, M. A.; Galperin, M.

in Physical Review B (2015), 91(11),

We present a method, based on characterizing efficiency fluctuations, to assess the performance of nanoscale thermoelectric junctions. This method accounts for effects typically arising in small junctions ... [more ▼]

We present a method, based on characterizing efficiency fluctuations, to assess the performance of nanoscale thermoelectric junctions. This method accounts for effects typically arising in small junctions, namely, stochasticity in the junction's performance, quantum effects, and nonequilibrium features preventing a linear response analysis. It is based on a nonequilibrium Green's function (NEGF) approach, which we use to derive the full counting statistics (FCS) for heat and work, and which in turn allows us to calculate the statistical properties of efficiency fluctuations. We simulate the latter for a variety of simple models where our method is exact. By analyzing the discrepancies with the semiclassical prediction of a quantum master equation (QME) approach, we emphasize the quantum nature of efficiency fluctuations for realistic junction parameters. We finally propose an approximate Gaussian method to express efficiency fluctuations in terms of nonequilibrium currents and noises which are experimentally measurable in molecular junctions. [less ▲]

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See detailOrder-parameter symmetries of domain walls in ferroelectrics and ferroelastics
Toledano, Pierre; Guennou, Mael; Kreisel, Jens UL

in Physical Review B (2014), 89(13),

The symmetry of boundaries between ferroelectric, ferroelastic, and antiphase domains is a key element for a theoretical understanding of their properties. Here, we derive this symmetry from their organic ... [more ▼]

The symmetry of boundaries between ferroelectric, ferroelastic, and antiphase domains is a key element for a theoretical understanding of their properties. Here, we derive this symmetry from their organic relation to the symmetry of the primary transition order parameters. The domain wall symmetries are shown to coincide with directions of the order-parameter n-dimensional vector space, corresponding to sum of the vectors associated with adjacent domain states. This property is illustrated by the determination of the maximal symmetries of domain walls in BaTiO3, LaAlO3, SrTiO3, and Gd2(MoO4)3. Besides, the domain pattern in YMnO3 is interpreted as resulting from an annihilation-creation process, the annihilation of the antiphase domain walls creating six ferroelectric domain walls merging at a single point. [less ▲]

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See detailDynamic and structural properties of orthorhombic rare-earth manganites under high pressure
Mota, D. A.; Almeida, A.; Rodrigues, V. H. et al

in Physical Review B (2014), 90(5),

We report a high-pressure study of orthorhombic rare-earth manganites AMnO3 using Raman scattering (for A = Pr, Nd, Sm, Eu, Tb, and Dy) and synchrotron x-ray diffraction (XRD), for A = Pr, Sm, Eu, and Dy ... [more ▼]

We report a high-pressure study of orthorhombic rare-earth manganites AMnO3 using Raman scattering (for A = Pr, Nd, Sm, Eu, Tb, and Dy) and synchrotron x-ray diffraction (XRD), for A = Pr, Sm, Eu, and Dy. In all cases, a phase transition was evidenced by the disappearance of the Raman signal at a critical pressure that depends on the A cation. For the compounds with A = Pr, Sm, and Dy, XRD confirms the presence of a corresponding structural transition to a noncubic phase, so that the disappearance of the Raman spectrum can be interpreted as an insulator-to-metal transition. We analyze the compression mechanisms at work in the different manganites via the pressure dependence of the lattice parameters, the shear strain in the ac plane, and the Raman bands associated with out-of-phase MnO6 rotations and in-plane O2 symmetric stretching modes. Our data show a crossover across the rare-earth series between two different kinds of behavior. For the smaller A cations considered in this study (Dy and Tb), the compression is nearly isotropic in the ac plane, with only small evolutions of the tilt angles and cooperative Jahn-Teller distortion. As the radius of the A cation increases, the pressure-induced reduction of Jahn-Teller distortion becomes more pronounced and increasingly significant as a compression mechanism, while the pressure-induced tilting of octahedra chains becomes conversely less pronounced. We finally discuss our results in light of the notion of chemical pressure and show that the analogy with hydrostatic pressure works quite well for manganites with the smaller A cations considered in this paper but can be misleading with large A cations. [less ▲]

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See detailFirst-principles study of PbTiO3 under uniaxial strains and stresses
Sharma, Henu; Kreisel, Jens UL; Ghosez, Philippe

in Physical Review B (2014), 90(21),

The behavior of PbTiO3 under uniaxial strains and stresses is investigated from first-principles calculations within density functional theory. We show that irrespective of the uniaxial mechanical ... [more ▼]

The behavior of PbTiO3 under uniaxial strains and stresses is investigated from first-principles calculations within density functional theory. We show that irrespective of the uniaxial mechanical constraint applied, the system keeps a purely ferroelectric ground state, with the polarization aligned either along the constraint direction (FEz phase) or along one of the pseudocubic axes perpendicular to it (FEx phase). This contrasts with the cases of isotropic and biaxialmechanical constraints for which novel phases combining ferroelectric and antiferrodistortive motions have been previously reported. Under uniaxial strain, PbTiO3 switched from an FEx ground state under compressive strain to an FEz ground state under tensile strain beyond a critical strain ηc zz ≈ +1%. Under uniaxial stress, PbTiO3 exhibits either an FEx ground state under compression (σzz < 0) or an FEz ground state under tension (σzz > 0). Here, however, an abrupt jump of the structural parameters is also predicted under both compressive and tensile stresses at critical values σzz ≈ +2 and −8 GPa. This behavior appears to be similar to that predicted under negative isotropic pressure and might turn out to be practically useful for enhancing the piezoelectric response in nanodevices. [less ▲]

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See detailPrediction of giant elastocaloric strength and stress-mediated electrocaloric effect in BaTiO3 single crystals
Liu, Yang; Wei, Jie; Janolin, Pierre-Eymeric et al

in Physical Review B (2014), 90(10),

An applied stress field σ3 can reversibly change the temperature of an elastocaloric material under adiabatic conditions, and the temperature change Tσ3 is usually maximized near phase transitions.Using a ... [more ▼]

An applied stress field σ3 can reversibly change the temperature of an elastocaloric material under adiabatic conditions, and the temperature change Tσ3 is usually maximized near phase transitions.Using a thermodynamic approach, we demonstrate that an elastocaloric strength α = | Tσ3 |/|σ3| of 0.016 K/MPa can be achieved benefiting from the full first-order phase transition in BaTiO3 single crystals, which is comparable with typical elastocaloric materials reported in the literature. The elastocaloric temperature change is found to be giant (3.2 K) under a stress of 200 MPa with a temperature span of over 50 K, which can be significantly larger than its electrocaloric counterpart (∼1 K). Moreover, it is found that the elastocaloric strength can be remarkably enhanced (2.32 K/MPa) as long as the phase transition is triggered even by a modest stress near the sharp first-order phase transition, which is two orders of magnitude larger than those accomplished by full transition. Therefore, even a low stress (<30 MPa) can induce a modest elastocaloric effect (1.3 K) comparable with the electrocaloric counterpart, which is accompanied by a reduction of the working temperature span. In addition, it is found that the electrocaloric peak under tensile stresses moves towards higher temperatures with its magnitude slightly enhanced. Hopefully, our study will stimulate further investigations on elastocaloric and stress-mediated electrocaloric effects in ferroelectrics. [less ▲]

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See detailSingle-crystalline BiMnO3 studied by temperature-dependent x-ray diffraction and Raman spectroscopy
Toulemonde, P.; Bordet, P.; Bouvier, P. et al

in Physical Review B (2014), 89(22),

We report on the temperature dependence of the phonons and crystallographic parameters in BiMnO3 single crystals grown under high pressure and high temperature. The crystallographic structure of the ... [more ▼]

We report on the temperature dependence of the phonons and crystallographic parameters in BiMnO3 single crystals grown under high pressure and high temperature. The crystallographic structure of the sample was refined from room temperature to liquid helium temperature in the centrosymmetric C2/c space group, i.e., a group which does not allow ferroelectricity. In addition, the lattice dynamics was probed by Raman spectroscopy down to liquid nitrogen temperature, i.e., below the ferromagnetic transition at TC = 100 ± 2 K. Both crystallographic and Raman data indicate the absence of a structural phase transition at the ferromagnetic ordering or any other temperature. The Raman signature around TC shows a significant spin-phonon coupling for the high-frequency bands. [less ▲]

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See detailElectrodynamic response and stability of molecular crystals
Schatschneider, Bohdan; Liang, Jian-Jie; Reilly, Anthony M. et al

in PHYSICAL REVIEW B (2013), 87(6),

We show that electrodynamic dipolar interactions, responsible for long-range fluctuations in matter, play a significant role in the stability of molecular crystals. Density functional theory calculations ... [more ▼]

We show that electrodynamic dipolar interactions, responsible for long-range fluctuations in matter, play a significant role in the stability of molecular crystals. Density functional theory calculations with van der Waals interactions determined from a semilocal ``atom-in-a-molecule'' model result in a large overestimation of the dielectric constants and sublimation enthalpies for polyacene crystals from naphthalene to pentacene, whereas an accurate treatment of nonlocal electrodynamic response leads to an agreement with the measured values for both quantities. Our findings suggest that collective response effects play a substantial role not only for optical excitations, but also for cohesive properties of noncovalently bound molecular crystals. DOI: 10.1103/PhysRevB.87.060104 [less ▲]

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See detailExploring the bonding of large hydrocarbons on noble metals: Diindoperylene on Cu(111), Ag(111), and Au(111)
Buerker, C.; Ferri, N.; Tkatchenko, Alexandre UL et al

in PHYSICAL REVIEW B (2013), 87(16),

We present a benchmark study for the adsorption of a large pi-conjugated organic molecule on different noble metal surfaces, which is based on x-ray standing wave (XSW) measurements and density functional ... [more ▼]

We present a benchmark study for the adsorption of a large pi-conjugated organic molecule on different noble metal surfaces, which is based on x-ray standing wave (XSW) measurements and density functional theory calculations with van der Waals (vdW) interactions. The bonding distances of diindenoperylene on Cu(111), Ag(111), and Au(111) surfaces (2.51, 3.01, and 3.10 angstrom, respectively) determined with the normal-incidence XSW technique are compared with calculations. Excellent agreement with the experimental data, i.e., deviations less than 0.1 angstrom, is achieved using the Perdew-Burke-Ernzerhof (PBE) functional with vdW interactions that include the collective response of substrate electrons (the PBE + vdW(surf) method). It is noteworthy that the calculations show that the vdW contribution to the adsorption energy increases in the order Au(111) < Ag(111) < Cu(111). [less ▲]

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See detailPhonon Raman scattering of RCrO3 perovskites (R = Y, La, Pr, Sm, Gd, Dy Ho, Yb, Lu)
Weber, M. C.; Kreisel, Jens UL; Thomas, P. A. et al

in PHYSICAL REVIEW B (2012), 85(5),

We report a systematic investigation of orthorhombic perovskite-type RCrO3 powder samples by Raman scattering for nine different rare earth Y, La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu). The room-temperature ... [more ▼]

We report a systematic investigation of orthorhombic perovskite-type RCrO3 powder samples by Raman scattering for nine different rare earth Y, La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu). The room-temperature Raman spectra and the associated phonon mode assignment provide reference data for structural investigation of the whole series of RCrO3 orthochromites and phonon ab-initio calculations. The assignment of the chromite spectra and comparison with Raman data on other orthorhombic perovskites allows correlating the phonon modes with the structural distortions in the RCrO3 series. In particular, two A(g) modes are identified as octahedra rotation soft modes, as their positions scale linearly with the octahedra tilt angle of the CrO6 octahedra. [less ▲]

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See detailBenzene adsorbed on Si(001): The role of electron correlation and finite temperature
Kim, Hyun-Jung; Tkatchenko, Alexandre UL; Cho, Jun-Hyung et al

in PHYSICAL REVIEW B (2012), 85(4),

van der Waals energy-corrected density functional theory (DFT + vdW) as well as the exact exchange with electron correlation in the random-phase approximation are used to study the adsorption of benzene ... [more ▼]

van der Waals energy-corrected density functional theory (DFT + vdW) as well as the exact exchange with electron correlation in the random-phase approximation are used to study the adsorption of benzene on the Si(001) surface with respect to two controversial adsorption structures (termed ``butterfly'' and ``tight bridge''). Our finding that the tight-bridge structure is energetically favored over the butterfly structure agrees with standard DFT but conflicts with previous vdW-inclusive calculations. However, the inclusion of zero-point energy and thermal vibrations reverses the stability of the two structures with increasing temperature. Our results provide an explanation for the recent experimental observation that both structures coexist at room temperature. [less ▲]

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