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52. Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

Author

Kevy, Simone M., Lund, Henriette E., Wollesen, Laura, Dalgaard, Kirstine J., Hsu, Yu Te, Wiedmann, Steffen, Bianchi, Marco, Holt, Ann Julie Utne, Curcio, Davide, Biswas, Deepnarayan, Jones, Alfred J.H., Volckaert, Klara, Cacho, Cephise, Dudin, Pavel, Hofmann, Philip, and Bremholm, Martin

Subjects
Condensed Matter::Superconductivity
Abstract

The crystal structure, electronic structure, and transport properties of crystals with the nominal composition Nb0.25Bi2Se3 are investigated. X-ray diffraction reveals that the as-grown crystals display phase segregation and contain major contributions of BiSe and the superconducting misfit layer compound (BiSe)1.1NbSe2. The inhomogeneous character of the samples is also reflected in the electronic structure and transport properties of different single crystals. Angle-resolved photoemission spectroscopy (ARPES) reveals an electronic structure that resembles poor-quality Bi2Se3 with an ill-defined topological surface state. High-quality topological surface states are instead observed when using a highly focused beam size, i.e., nanoARPES. While the superconducting transition temperature is found to vary between 2.5 and 3.5 K, the majority of the bulk single crystals does not exhibit a zero-resistance state suggesting filamentary superconductivity in the materials. Susceptibility measurements of the system together with the temperature dependence of the coherence length extracted from the upper critical field are consistent with conventional BCS superconductivity of a type II superconductor.

Published
2021
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53. Structural and electronic inhomogeneity of superconducting Nb-doped $Bi_{2}Se_{3}$

Author

Kevy, Simone M., Lund, Henriette E., Wollesen, Laura, Dalgaard, Kirstine J., Hsu, Yu-Te, Wiedmann, Steffen, Bianchi, Marco, Holt, Ann Julie Utne, Curcio, Davide, Biswas, Deepnarayan, Jones, Alfred J. H., Volckaert, Klara, Cacho, Cephise, Dudin, Pavel, Hofmann, Philip, and Bremholm, Martin

Subjects
Condensed Matter::Superconductivity, ddc:530
Abstract

Physical review / B 103(8), 085107 (1-9) (2021). doi:10.1103/PhysRevB.103.085107, The crystal structure, electronic structure, and transport properties of crystals with the nominal composition Nb$_{0.25}$Bi$_2$Se$_3$ are investigated. X-ray diffraction reveals that the as-grown crystals display phase segregation and contain major contributions of BiSe and the superconducting misfit layer compound (BiSe)$_{1.1}$NbSe$_2$. The inhomogeneous character of the samples is also reflected in the electronic structure and transport properties of different single crystals. Angle-resolved photoemission spectroscopy (ARPES) reveals an electronic structure that resembles poor-quality Bi$_2$Se$_3$ with an ill-defined topological surface state. High-quality topological surface states are instead observed when using a highly focused beam size, i.e., nanoARPES. While the superconducting transition temperature is found to vary between 2.5 and 3.5 K, the majority of the bulk single crystals does not exhibit a zero-resistance state suggesting filamentary superconductivity in the materials. Susceptibility measurements of the system together with the temperature dependence of the coherence length extracted from the upper critical field are consistent with conventional BCS superconductivity of a type II superconductor., Published by Inst., Woodbury, NY

Published
2021
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54. Inelastic Helium Atom Scattering from Sb2Te3(111): Phonon Dispersion, Focusing Effects and Surfing

Author

Física de materiales, Materialen fisika, Ruckhofer, Adrian, Halbritter, Simon, Lund, Henriette E., Holt, Ann Julie U., Bianchi, Marco, Bremholm, Martin, Benedek, Giorgio, Hofmann, Philip, Ernst, Wolfgang E., Tamtoegl, Anton, Física de materiales, Materialen fisika, Ruckhofer, Adrian, Halbritter, Simon, Lund, Henriette E., Holt, Ann Julie U., Bianchi, Marco, Bremholm, Martin, Benedek, Giorgio, Hofmann, Philip, Ernst, Wolfgang E., and Tamtoegl, Anton

Abstract

We present an experimental study of inelastic scattering processes on the (111) surface of the topological insulator Sb2Te3 using helium atom scattering. In contrast to other binary topological insulators such as Bi2Se3 and Bi2Te3, Sb2Te3 is much less studied and the as-grown Sb2Te3 sample turns out to be p-doped, with the Fermi-level located below the Dirac-point as confirmed by angle-resolved photoemission spectroscopy. We report the surface phonon dispersion along both high symmetry directions in the energy region below 11 meV, where the Rayleigh mode exhibits the strongest intensity. The experimental data is compared with a study based on density functional perturbation theory calculations, providing good agreement except for a set of additional peculiar inelastic events below the Rayleigh mode. In addition, an analysis of angular scans with respect to a number of additional inelastic events is presented, including resonance enhancement, kinematical focusing, focused inelastic resonance and surfing. In the latter case, phonon-assisted adsorption of the incident helium atom gives rise to a bound state where the helium atom rides the created Rayleigh wave.

Published
2021

57. Anomalous Shubnikov-de Haas quantum oscillations in rare-earth tritelluride NdTe3

Author

Dalgaard, Kirstine J., Lei, Shiming, Wiedmann, Steffen, Bremholm, Martin, Schoop, Leslie M., Dalgaard, Kirstine J., Lei, Shiming, Wiedmann, Steffen, Bremholm, Martin, and Schoop, Leslie M.

Abstract

Materials with the structural motif of a square net have in recent years attracted attention for their often unexpected electronic properties. Here, we present low-temperature magnetotransport experiments on high-quality NdTe3 single crystals with a carrier mobility of 6×104 cm2/V s at 2.25 K; an increase of 58% is observed below the Néel temperature. Shubnikov-de Haas oscillations up to 9 T exhibit anomalies in their amplitude which deviates from the conventional Lifshitz-Kosevich behavior below the magnetic ordering temperature and around 20 K. The latter, which has so far not been observed in any tritelluride, suggests a field- and temperature-induced electronic structure transition. We provide a thorough analysis of three different samples, highlighting the importance of sample quality for elucidating details in the transport behavior. Our results on NdTe3 suggest that rare-earth tritellurides may display so-far obscured exotic electronic properties in addition to the well-studied high-temperature charge density wave anomalies.

Published
2020

58. Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

Author

Kevy, Simone M., primary, Lund, Henriette E., additional, Wollesen, Laura, additional, Dalgaard, Kirstine J., additional, Hsu, Yu-Te, additional, Wiedmann, Steffen, additional, Bianchi, Marco, additional, Holt, Ann Julie Utne, additional, Curcio, Davide, additional, Biswas, Deepnarayan, additional, Jones, Alfred J. H., additional, Volckaert, Klara, additional, Cacho, Cephise, additional, Dudin, Pavel, additional, Hofmann, Philip, additional, and Bremholm, Martin, additional

Published
2021
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63. Tuning the Structural and Optoelectronic Properties of Cs 2 AgBiBr 6 Double‐Perovskite Single Crystals through Alkali‐Metal Substitution

Author

Keshavarz, Masoumeh, primary, Debroye, Elke, additional, Ottesen, Martin, additional, Martin, Cristina, additional, Zhang, Heng, additional, Fron, Eduard, additional, Küchler, Robert, additional, Steele, Julian A., additional, Bremholm, Martin, additional, Van de Vondel, Joris, additional, Wang, Hai I., additional, Bonn, Mischa, additional, Roeffaers, Maarten B. J., additional, Wiedmann, Steffen, additional, and Hofkens, Johan, additional

Published
2020
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65. Helium-Surface Interaction and Electronic Corrugation of Bi2Se3(111)

Author

Ruckhofer, Adrian, Tamtoegl, Anton, Pusterhofer, Michael, Bremholm, Martin, and Ernst, Wolfgang E.

Subjects
HE ATOMS, TOPOLOGICAL-INSULATOR, LIF, SINGLE DIRAC CONE, DIFFRACTION, SB2TE3, INELASTIC-SCATTERING, QUANTUM, SELECTIVE-ADSORPTION RESONANCES
Abstract

We present a study of the atom surface interaction potential for the He Bi2Se3(111) system. Using selective adsorption resonances, we are able to obtain the complete experimental band structure of atoms in the corrugated surface potential of the topological insulator Bi2Se3. He atom scattering spectra show several selective adsorption resonance features that are analyzed, starting with the free-atom approximation and a laterally averaged atom surface interaction potential. Based on quantum mechanical calculations of the He surface scattering intensities and resonance processes, we are then considering the three-dimensional atom surface interaction potential, which is further refined to reproduce the experimental data. Following this analysis, the He Bi2Se3(111) interaction potential is best represented by a corrugated Morse potential with a well depth of D = (6.54 +/- 0.05) meV, a stiffness of kappa = (0.58 +/- 0.02) A(-1), and a surface electronic corrugation of (5.8 +/- 0.2)% of the lattice constant. The experimental data may also be used as a challenging benchmark system to analyze the suitability of several van der Waals approaches: the He-Bi2Se3(111) interaction captures the fundamentals of weak adsorption systems where the binding is governed by long-range electronic correlations.

Published
2019
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66. Perovskite Photovoltaics

Author

Ottesen, Martin, Bremholm, Martin, Keshavarz, Masoumeh, and Wiedmann, Steffen

Published
2019

69. Computational search for Dirac and Weyl nodes in f-electron antiperovskites

Author

Pertsova, Anna, Geilhufe, Matthias, Bremholm, Martin, Balatsky, Alexander V., Pertsova, Anna, Geilhufe, Matthias, Bremholm, Martin, and Balatsky, Alexander V.

Abstract

We present the result of an ab initio search for new Dirac materials among inverse perovskites. Our investigation is focused on the less studied class of lanthanide antiperovskites containing heavy f-electron elements in the cation position. Some of the studied compounds have not yet been synthesized experimentally. Our computational approach is based on density functional theory calculations which account for spin-orbit interaction and strong correlations of the f-electron atoms. We find several promising candidates among lanthanide antiperovskites which host bulk Dirac states close to the Fermi level. Specifically, our calculations reveal massive three-dimensional Dirac states in materials of the class A(3)BO, where A=Sm, Eu, Gd, Yb, and B=Sn, Pb. In materials with finite magnetic moment, such as Eu3BO (B=Sn, Pb), the degeneracy of the Dirac nodes is lifted, leading to appearance of Weyl nodes., QC 20200325

Published
2019
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70. Bulk band structure of Sb2Te3 determined by angle-resolved photoemission spectroscopy.

Author

Lund, Henriette E., Volckaert, Klara, Majchrzak, Paulina, Jones, Alfred J. H., Bianchi, Marco, Bremholm, Martin, and Hofmann, Philip

Abstract

The bulk band structure of the topological insulator Sb2Te3 is investigated by angle-resolved photoemission spectroscopy. Of particular interest is the dispersion of the uppermost valence band with respect to the topological surface state Dirac point. The valence band maximum has been calculated to be either near the Brillouin zone centre or in a low-symmetry position in the –M¯ azimuthal direction. In order to observe the full energy range of the valence band, the strongly p-doped crystals are counter-doped by surface alkali adsorption. The data show that the absolute valence band maximum is likely to be found at the bulk Γ point and predictions of a low-symmetry position with an energy higher than the surface Dirac point can be ruled out. [ABSTRACT FROM AUTHOR]

Published
2021
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71. Structural and Magnetic Properties of RMO3 (R = Pr, Nd and M = Fe, Co) Perovskites.

Author

Nakhaei, Mehrnoush, Bremholm, Martin, and Khoshnoud, Davoud Sanavi

Subjects
*MAGNETIC properties, *SPACE groups, *NUCLEAR spin, *CURIE-Weiss law, *PEROVSKITE, *SCANNING electron microscopy
Abstract

In this work, the RMO3 (R = Pr, Nd and M = Fe, Co) perovskites had been synthesized by hydrothermal method. The structural properties of RMO3 prepared samples were investigated by using X-ray diffraction (XRD) analysis. These prepared perovskites showed the orthorhombic structure with the Pbnm space group. The Williamson-Hall method was used for determining the size of crystallites (DW–H) and lattice strains (ε) of the samples. In addition, scanning electron microscopy (SEM) was used for investigating the morphology and for determining the sizes of RMO3 particles. For magnetic characterizations of the samples, vibrating sample magnetometer (VSM) and FC and ZFC measurements had been used. The Neel temperatures (TN) of R ions were determined at TN = 29, 8 and 9 K for PrFeO3, PrCoO3, and NdCoO3 perovskites, respectively. The spin reorientation temperature (TSR) of NdFeO3 had been displayed at T = 163 K during FC and ZFC protocols. Thereafter, the Curie–Weiss law had been used for calculating the CW temperatures (θCW) and Curie constants (C) of the all samples based on FC measurements data. [ABSTRACT FROM AUTHOR]

Published
2021
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73. Struktur-egenskab undersøgelse af superledning i Nb-dopet Bi2Se3

Author

Munkholm Kevy, Simone, Bremholm, Martin, Wollesen, Laura, Lund, Henriette Elisabeth, and Hofmann, Philip

Subjects
Condensed Matter::Superconductivity
Abstract

Topological insulators (TI) have over the past decade been studied extensively due to their interesting electronic properties that make them excellent candidates for applications in quantum computing [1]. Bi2Se3 is a highly studied TI and a large number of studies have investigated the effects of doping. Of particular interest, doping of Bi2Se3 with Cu, Sr or Nb, the topological surface states are maintained, but it becomes superconducting in the bulk, the surfaces can now harbor Majorana fermions [2-4]. NbxBi2Se3 is a rare instance of such a system, referred to as a topological superconductor. Despite the high interest in this system, no complete structural determination has been reported.In this study, high quality crystals are being grown by a melt growth quench technique for investigations of the structure-property relations of MxBi2Se3. Studies of the temperature dependence of the intercalation is mapped to determine optimal growth conditions while crystallographic studies are used to provide solid structural evidence for the proposed structures.

Published
2018

77. Tracking Structural Phase Transitions in Lead‐Halide Perovskites by Means of Thermal Expansion

Author

Keshavarz, Masoumeh, primary, Ottesen, Martin, additional, Wiedmann, Steffen, additional, Wharmby, Michael, additional, Küchler, Robert, additional, Yuan, Haifeng, additional, Debroye, Elke, additional, Steele, Julian A., additional, Martens, Johan, additional, Hussey, Nigel E., additional, Bremholm, Martin, additional, Roeffaers, Maarten B. J., additional, and Hofkens, Johan, additional

Published
2019
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79. Inelastic helium atom scattering from Sb2Te3(111): phonon dispersion, focusing effects and surfing.

Author

Ruckhofer, Adrian, Halbritter, Simon, Lund, Henriette E., Holt, Ann Julie U., Bianchi, Marco, Bremholm, Martin, Benedek, Giorgio, Hofmann, Philip, Ernst, Wolfgang E., and Tamtögl, Anton

Abstract

We present an experimental study of inelastic scattering processes on the (111) surface of the topological insulator Sb2Te3 using helium atom scattering. In contrast to other binary topological insulators such as Bi2Se3 and Bi2Te3, Sb2Te3 is much less studied and the as-grown Sb2Te3 sample turns out to be p-doped, with the Fermi-level located below the Dirac-point as confirmed by angle-resolved photoemission spectroscopy. We report the surface phonon dispersion along both high symmetry directions in the energy region below 11 meV, where the Rayleigh mode exhibits the strongest intensity. The experimental data is compared with a study based on density functional perturbation theory calculations, providing good agreement except for a set of additional peculiar inelastic events below the Rayleigh mode. In addition, an analysis of angular scans with respect to a number of additional inelastic events is presented, including resonance enhancement, kinematical focusing, focused inelastic resonance and surfing. In the latter case, phonon-assisted adsorption of the incident helium atom gives rise to a bound state where the helium atom rides the created Rayleigh wave. [ABSTRACT FROM AUTHOR]

Published
2021
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87. Novel single-layer vanadium sulphide phases

Author

Arnold, Fabian, primary, Stan, Raluca-Maria, additional, Mahatha, Sanjoy K, additional, Lund, H E, additional, Curcio, Davide, additional, Dendzik, Maciej, additional, Bana, Harsh, additional, Travaglia, Elisabetta, additional, Bignardi, Luca, additional, Lacovig, Paolo, additional, Lizzit, Daniel, additional, Li, Zheshen, additional, Bianchi, Marco, additional, Miwa, Jill A, additional, Bremholm, Martin, additional, Lizzit, Silvano, additional, Hofmann, Philip, additional, and Sanders, C E, additional

Published
2018
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89. Selective CO2 Reduction to CO in Water using Earth-Abundant Metal and Nitrogen-Doped Carbon Electrocatalysts

Author

Hu, Xin-Ming, primary, Hval, Halvor Høen, additional, Bjerglund, Emil Tveden, additional, Dalgaard, Kirstine Junker, additional, Madsen, Monica Rohde, additional, Pohl, Marga-Martina, additional, Welter, Edmund, additional, Lamagni, Paolo, additional, Buhl, Kristian Birk, additional, Bremholm, Martin, additional, Beller, Matthias, additional, Pedersen, Steen Uttrup, additional, Skrydstrup, Troels, additional, and Daasbjerg, Kim, additional

Published
2018
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91. Electronic structure of Fe1.08Te bulk crystals and epitaxial FeTe thin films on Bi2Te3

Author

Arnold, Fabian, primary, Warmuth, Jonas, additional, Michiardi, Matteo, additional, Fikáček, Jan, additional, Bianchi, Marco, additional, Hu, Jin, additional, Mao, Zhiqiang, additional, Miwa, Jill, additional, Raj Singh, Udai, additional, Bremholm, Martin, additional, Wiesendanger, Roland, additional, Honolka, Jan, additional, Wehling, Tim, additional, Wiebe, Jens, additional, and Hofmann, Philip, additional

Published
2018
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92. Nanoscale surface dynamics of Bi2Te3(111): observation of a prominent surface acoustic wave and the role of van der Waals interactions

Author

Tamtögl, Anton, primary, Campi, Davide, additional, Bremholm, Martin, additional, Hedegaard, Ellen M. J., additional, Iversen, Bo B., additional, Bianchi, Marco, additional, Hofmann, Philip, additional, Marzari, Nicola, additional, Benedek, Giorgio, additional, Ellis, John, additional, and Allison, William, additional

Published
2018
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100. Electron-phonon coupling and surface Debye temperature of Bi2Te3 (111) from helium atom scattering

Author

Tamtögl, Anton, primary, Kraus, Patrick, additional, Avidor, Nadav, additional, Bremholm, Martin, additional, Hedegaard, Ellen M. J., additional, Iversen, Bo B., additional, Bianchi, Marco, additional, Hofmann, Philip, additional, Ellis, John, additional, Allison, William, additional, Benedek, Giorgio, additional, and Ernst, Wolfgang E., additional

Published
2017
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