Publications

Quantitative local current-voltage analysis and calculation of performance parameters of single solar cells in modules

Bauer, J., F. Frühauf, O. Breitenstein

Solar Energy Materials and Solar Cells 159, pp 8-19 (2017)

Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field

Ben Dor, O., S. Yochelis, A. Radko, K. Vankayala, E. Capua, A. Capua, S. H. Yang, L. T. Baczewski, S. S. P. Parkin, R. Naaman, Y. Paltiel

Nature Communications 8, pp 14567/1-7 (2017)

Alternative luminescence image evaluation - comparison with lock-in thermography

Breitenstein, O., F. Frühauf

Solar Energy Materials and Solar Cells 173, pp 72-79 (2017)

abstract

It was shown recently that previous approaches for quantitative luminescence image evaluation based on the model of independent diodes inevitably lead to erroneous results for imaging saturation current densities. However, the pioneering work of Fuyuki on electroluminescence imaging of solar cells was not based on this model. There it was claimed that the calibration constant of the local luminescence signal should be proportional to the local effective diffusion length. With increasing diffusion length, however, the luminescence reaches a saturation value. Recently a simple formula for the calibration constant was proposed, which describes both the proportionality for small diffusion lengths and the saturation property for large ones. While this non-linear Fuyuki PL evaluation method was previously only applied to standard BSF cells, in this work it is applied to modern multicrystalline PERC cells processed from different high performance multicrystalline silicon materials. The results are compared to that of dark lock-in thermography (DLIT) and Laplacian PL investigations of these cells. It is found that saturation current density images obtained from the alternative luminescence evaluation methods are close to that based on DLIT in low lifetime regions, but show a much better spatial resolution. In high lifetime regions, however, this alternative PL evaluation is generally less reliable than DLIT. These alternative kinds of luminescence image evaluation may replace previous approaches of quantitative PL evaluation based on the model of independent diodes.

Advanced local characterization of silicon solar cells

Breitenstein, O., F. Frühauf, J. Bauer

Physica Status Solidi A 214 (12), pp 1700611/1-12 (2017)

Ensemble-averaged Rabi oscillations in a ferromagnetic CoFeB film

Capua, A., C. Rettner, S. H. Yang, T. Phung, S. S. P. Parkin

Nature Communications 8, pp 16004/1-7 (2017)

Phase-resolved detection of the spin Hall angle by optical ferromagnetic resonance in perpendicularly magnetized thin films

Capua, A., T. Y. Wang, S. H. Yang, C. Rettner, T. Phung, S. S. P. Parkin

Physical Review B 95 (6), pp 064401/1-6 (2017)

Electric-field control of oxygen vacancies and magnetic phase transition in a cobaltite/manganite bilayer

Cui, B., C. Song, F. Li, X. Y. Zhong, Z. C. Wang, P. Werner, Y. D. Gu, H. Q. Wu, M. S. Saleem, S. S. P. Parkin, F. Pan

Physical Review Applied 8 (4), pp 044007/1-9 (2017)

Coherent Fe-rich nano-scale perovskite oxide phase in epitaxial Sr₂FeMoO₆ films grown on cubic and scandate substrates

Deniz, H., D. Preziosi, M. Alexe, D. Hesse

Journal of Applied Physics 121 (2), pp 023906/1-8 (2017)

Heusler compounds with perpendicular magnetic anisotropy and large tunneling magnetoresistance

Faleev, S. V., Y. Ferrante, J. Jeong, M. G. Samant, B. Jones, S. S. P. Parkin

Physical Review Materials 1 (2), pp 024402/1-9 (2017)

Origin of the tetragonal ground state of Heusler compounds

Faleev, S. V., Y. Ferrante, J. Jeong, M. G. Samant, B. Jones, S. S. P. Parkin

Physical Review Applied 7 (3), pp 034022/1-12 (2017)

Unified explanation of chemical ordering, the Slater-Pauling rule, and half-metallicity in full Heusler compounds

Faleev, S. V., Y. Ferrante, J. Jeong, M. G. Samant, B. Jones, S. S. P. Parkin

Physical Review B 95 (4), pp 045140/1-10 (2017)

Atomic structure governed diversity of exchange-driven spin helices in Fe nanoislands: Experiment and theory

Fischer, J. A., L. M. Sandratskii, S.-H. Phark, D. Sander, S. S. P. Parkin

Physical Review B 96 (14), pp 140407(R)/1-5 (2017)

abstract

We combine spin-polarized scanning tunneling microscopy (SP-STM) and first-principles calculations to demonstrate the control of the wavelength of helical spin textures in Fe nanoislands by varying their atomic structure. We make use of the complexity of submonolayer growth of Fe on Cu(111) to prepare nanoislands characterized by different thickness and in-plane atomic structure. SP-STM results reveal that the magnetic states of different nanoislands are spin helices. The wavelength of the spin helices varies strongly. Calculations performed for Fe films with different thickness and in-plane atomic structure explain the strong variation of the wavelength by a subtle balance in the competition between ferromagnetic and antiferromagnetic exchange interactions. We identify the crucial role of the effectively enhanced weak antiferromagnetic exchange interactions between distant atoms.

Correcting lateral photon scattering in an InSb infrared detector

Frühauf, F., J. Bauer, O. Breitenstein

Physica Status Solidi RRL 11 (1), pp 1600346/1-5 (2017)

abstract

Both luminescence and lock-in thermography imaging, which are also evaluated quantitatively, are valuable methods for characterizing solar cells. For luminescence imaging of silicon solar cells it was recently discovered that photon scattering in the detector of the used camera leads to a certain amount of blurring, which may be corrected by image deconvolution for enabling a correct quantitative image interpretation. In this work the same effect is investigated for an infrared camera employing a cooled InSb-based quantum detector. It is found that also here the photon scattering effect exists, though its influence is weaker than for luminescence imaging.

DLIT- versus ILIT-based efficiency imaging of solar cells

Frühauf, F., O. Breitenstein

Solar Energy Materials and Solar Cells 199, pp 195-202 (2017)

abstract

Efficiency imaging of solar cells means to know which region of an inhomogeneous cell contributes by which degree to the efficiency at maximum power point of the cell. This knowledge allows us to judge how strong certain defect regions influence the efficiency of the whole cell. Efficiency imaging can be performed based on dark lock-in thermography (DLIT) imaging within the model of independent diodes, or based on illuminated lock-in thermography (ILIT), which does not assume any cell model. Moreover, by 2-dimensional finite element simulation of the cell based on DLIT results, an efficiency image can be obtained, which takes into account the distributed nature of the series resistance. In this contribution these three methods are applied to one and the same multicrystalline cell containing ohmic shunts and the results are compared to each other. Conclusions to the accuracy of solely DLIT-based efficiency imaging are drawn.

Finite element simulation of inhomogeneous solar cells based on lock-in thermography and luminescence imaging

Frühauf, F., J. Wong, J. Bauer, O. Breitenstein

Solar Energy Materials and Solar Cells 162, pp 103-113 (2017)

Dramatic influence of curvature of nanowire on chiral domain wall velocity

Garg, C., S. Yang, T. Phung, A. Pushp, S. S. P. Parkin

Science Advances 3, pp 1602304/1-7 (2017)

Signature of type-II Weyl semimetal phase in MoTe₂

Jiang, J., Z. K. Liu, Y. Sun, H. F. Yang, C. R. Rajamathi, Y. P. Qi, L. X. Yang, C. Chen, H. Peng, C. C. Hwang, S. Z. Sun, S. K. Mo, I. Vobornik, J. Fujii, S. S. P. Parkin, C. Felser, B. H. Yan, Y. L. Chen

Nature Communications 8, pp 13973/1-6 (2017)

Influence of nanoscale order-disorder transitions on the magnetic properties of Heusler compounds for spintronics

Karel, J., J. E. Fischer, S. Fabricci, E. Pippel, P. Werner, M. V. Castergnaro, P. Adler, S. Ouardi, B. Balke, G. H. Fecher, J. Morais, F. Albertini, S. S. P. Parkin, C. Felser

Journal of Materials Chemistry 5, pp 4388-4392 (2017)

abstract

Modifications in nanoscale chemical order are used to tune the magnetic properties, namely T-C, of Co2FeSixAl1-x (0 < x < 1). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast reveals nanoscale regions of L2(1) order within a B2 matrix in the off-stoichiometry samples. Perhaps surprisingly, the latter, more chemically disordered structure, exhibits a higher T-C. Upon annealing, the off-stoichiometry samples become more homogeneous with the fraction of L2(1) order decreasing. The short-range order was also investigated using X-ray absorption fine structure (XAFS) measurements at the Co and Fe K edges. Since the local atomic environments of Co atoms in the L2(1) and B2 structures are identical, the features presented in the Co K edge XAFS data are the same in both cases. By contrast, the L2(1) and B2 structures exhibit different signatures at the Fe K edge owing to the different chemical environments. Fitting of these spectra confirms the nanoscale chemical disorder observed by HAADF-STEM and the expected role this disorder plays on T-C. Our results point to a methodology that might be extended to modify the magnetic and electronic properties of any Heusler compound; chemical disorder can be an engineering tool to realize highly tailored properties.

Ferromagnetic properties of barium titanate ceramics doped with cobalt, iron, and nickel

Langhammer, H. T., T. Müller, T. Walther, R. Böttcher, D. Hesse, E. Pippel, S. G. Ebbinghaus

Journal of Materials Science 51, pp 10429-10441 (2017)

Manipulating charge ordering in Fe₃O₄ by field cooling

Ma, T. P., Y. Yang, Z. Ding, Z. H. Chen, H. B. Zhao, P. Werner, S. S. P. Parkin, Y. Z. Wu

Physical Review B 95 (1), pp 014103/1-8 (2017)

Magnetic antiskyrmions above room temperature in tetragonal Heusler materials

Nayak, A. K., V. Kumar, T. P. Ma, P. Werner, E. Pippel, R. Sahoo, F. Damay, U. Rößler, C. Felser, S. S. P. Parkin

Nature 548, pp 561 (2017)

Multiple Dirac cones at the surface of the topological metal LaBi

Nayak, J., S. Wu, N. Kumar, C. Shekhar, S. Singh, J. Fink, E. E. D. Rienks, G. H. Fecher, S. S. P. Parkin, B. Yan, C. Felser

Nature Communications 8, pp 13942/1-5 (2017)

Geometric and electronic structure of the Cs-doped Bi₂Se₃(0001) surface

Otrokov, M. M., A. Ernst, K. Mohseni, H. Fulara, S. Roy, G. R. Castro, J. Rubio-Zuazo, A. G. Ryabishchenkova, K. A. Kokh, O. E. Tereshchenko, Z. S. Aliev, M. B. Babanly, E. V. Chulkov, H. L. Meyerheim, S. S. P. Parkin

Physical Review B 95 (20), pp 205429/1-9 (2017)

abstract

Using surface x-ray diffraction and scanning tunneling microscopy in combination with first-principles calculations, we have studied the geometric and electronic structure of Cs-deposited Bi₂Se₃(0001) surface kept at room temperature. Two samples were investigated: a single Bi₂Se₃ crystal, whose surface was Ar sputtered and then annealed at ∼ 500 ^°C for several minutes prior to Cs deposition, and a 13-nm-thick epitaxial Bi₂Se₃ film that was not subject to sputtering and was annealed only at ∼ 350 ^°C. In the first case, a considerable fraction of Cs atoms occupy top layer Se atoms sites both on the terraces and along the upper step edges where they form one-dimensional-like structures parallel to the step. In the second case, Cs atoms occupy the f cc hollow site positions. First-principles calculations reveal that Cs atoms prefer to occupy Se positions on the Bi₂Se₃(0001) surface only if vacancies are present, which might be created during the crystal growth or during the surface preparation process. Otherwise, Cs atoms prefer to be located in f cc hollow sites in agreement with the experimental finding for the MBE-grown sample.

Evidence for ionic liquid gate-induced metallization of vanadium dioxide bars over micron length scales

Passarello, D., S. G. Altendorf, J. Jeong, C. Rettner, N. Arellano, T. Topuria, M. G. Samant, S. S. P. Parkin

Nano Letters 17, pp 2796-2801 (2017)

Instability of the topological surface state in Bi₂Se₃ upon deposition of gold

Polyakov, A., C. Tusche, M. Ellguth, E. D. Crozier, K. Mohseni, M. M. Otrokov, X. Zubizarreta Iriarte, M. G. Vergniory, M. Geilhufe, E. V. Chulkov, A. Ernst, H. L. Meyerheim, S. S. P. Parkin

Physical Review B 95 (18), pp 180202/1-5 (2017)

abstract

Momentum-resolved photoemission spectroscopy indicates the instability of the Dirac surface state upon deposition of gold on the (0001) surface of the topological insulator Bi₂Se₃. Based on the structure model derived from extended x-ray absorption fine structure experiments showing that gold atoms substitute bismuth atoms, first-principles calculations provide evidence that a gap appears due to hybridization of the surface state with gold d states near the Fermi level. Our findings provide insights into the mechanisms affecting the stability of the surface state.

Photochemical water splitting by bismuth chalcogenide topological insulators

Rajamathi, C., U. Gupta, P. Koushik, N. Kumar, H. Yang, Y. Sun, C. Shekhar, B. Yan, S. S. P. Parkin, U. V. Waghmare, C. Felser, C. N. R. Rao

ChemPhysChem 18 (17), pp 2322-2327 (2017)

Weyl semimetals as hydrogen evolution catalysts

Rajamathi, C. R., U. Gupta, N. Kumar, H. Yang, Y. Sun, V. Süß, C. Shekhar, M. Schmidt, H. Blumtritt, P. Werner, B. Yan, S. S. P. Parkin, C. Felser, C. N. R. Rao

Advanced Materials 29 (19), pp 1606202/1-6 (2017)

Growth of carbon and nitrogen containing precipitates in crystalline solar silicon and their influence on solar cells

Richter, S., J. Bauer, O. Breitenstein

Physica Status Solidi RRL 11 (2), pp 1600354/1-17 (2017)

Spin pumping and inverse spin Hall effect in ultrathin SrRuO₃ films around the percolation limit

Richter, T., M. Paleschke, M. Wahler, F. Heyroth, H. Deniz, D. Hesse, G. Schmidt

Physical Review B 96 (18), pp 184407/1-7 (2017)

Producing ZnFe₂O₄ thin films from ZnO/FeO multilayers

Salcedo Rodríguez, K. L., M. Hoffmann, F. Golmar, G. Pasquevich, P. Werner, W. Hergert, C. E. Rodríguez Torres

Applied Surface Science 393, pp 256-261 (2017)

Similar ultrafast dynamics of several dissimilar Dirac and Weyl semimetals

Weber, C. P., B. S. Berggren, M. G. Masten, T. C. Ogloza, S. Deckoff-Jones, J. Madéo, M. K. L. Man, K. M. Dani, L. Zhao, G. Chen, J. Liu, Z. Mao, L. M. Schoop, B. V. Lotsch, S. S. P. Parkin, M. N. Ali

Journal of Applied Physics 122 (22), pp 223102/1-7 (2017)

Organic crystal lattices in the axial filament of silica spicules of Demospongiae

Werner, P., H. Blumtritt, F. Natalio

Journal of Structural Biology 198, pp 186-195 (2017)

Investigation of non-reciprocal magnon propagation using lock-in thermography

Wid, O., J. Bauer, A. Müller, O. Breitenstein, S. S. P. Parkin, G. Schmidt

Journal of Physics D 50, pp 134001/1-7 (2017)

Heusler 4.0: Tunable materials

Wollmann, L., A. K. Nayak, S. S. P. Parkin, C. Felser

Annual Review of Materials Science 47, pp 247-270 (2017)

Reversible formation of 2D electron gas at the LaFeO₃/SrTiO₃ interface via control of oxygen vacancies

Xu, P., W. Han, P. M. Rice, J. Jeong, M. G. Samant, K. Mohseni, H. L. Meyerheim, S. Ostanin, I. V. Maznichenko, I. Mertig, E. K. U. Gross, A. Ernst, S. S. P. Parkin

Advanced Materials 29, pp 1604447/1-8 (2017)

abstract

A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO₃ layers >3 unit cells thick and the surface of SrTiO₃ single crystals. The 2DEG is exquisitely sensitive to cation intermixing and oxygen nonstoichiometry. It is shown that the latter thus allows the controllable formation of the 2DEG via ionic liquid gating, thereby forming a nonvolatile switch.

Topological Weyl semimetals in the chiralantiferromagnetic materials Mn₃Ge and Mn₃Sn

Yang, H., Y. Sun, Y. Zhang, W.-J. Shi, S. S. P. Parkin, B. Yan

New Journal of Physics 19 (1), pp 015008/1-7 (2017)

Prediction of triple point fermions in simple half-Heusler topological insulators

Yang, H., J. Yu, S. S. P. Parkin, C. Felser, C.-X. Liu, B. Yan

Physical Review Letters 119 (13), pp 136401-136406 (2017)

Bias dependence of spin transfer torque in Co₂MnSi Heusler alloy based magnetic tunnel junctions

Zhang, J., T. Phung, A. Pushp, Y. Ferrante, J. Jeong, C. Rettner, P. B Hughes, Y. See-Hun, Y. Jiang, S. S. P. Parkin

Applied Physics Letters 110 (17), pp 172403/1-5 (2017)

Strong anisotropic anomalous Hall effect and spin Hall effect in the chiral antiferromagnetic compounds Mn₃X (X=Ge, Sn, Ga, Ir, Rh, and Pt)

Zhang, Y., Y. Sun, H. Yang, J. Zelezny, S. S. P. Parkin, C. Felser, B. Yan

Physical Review B 95 (7), pp 075128/1-9 (2017)