DFF Sapere Aude Topforsker project

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In June 2014, Philip Hofmann was awarded a Sapere Aude Topforkser grant from the Danish Council for Independent Research (DFF). This page reports on the progress of the project.



The project


The experimental isolation of graphene, a single layer of carbon atoms, has shown that truly two-dimensional (2D) materials can exist, contrary to previous predictions. Meanwhile, it has been shown that small flakes of 2D MoS2 or TaS2 can also be isolated from their three-dimensional (3D) parent materials and that the materials' 2D and 3D versions behave very differently. In this project we will use an alternative approach to grow 2D materials directly on a surface in ultra-high vacuum. This will give rise to higher quality, larger areas and the freedom to design entirely new materials.  This type of synthesis will also allow studies by powerful and complementary techniques such as angle-resolved photoemission spectroscopy, scanning tunnelling microscopy and nano-scale transport. We will determine in what way and why the 2D solids are different from their 3D counterparts and how we can influence their properties.


Senior people associated with the project


Philip Hofmann

Jeppe Vang Lauritsen

Alexander Ako Khajetoorians


Publications


Unraveling the Spin Structure of Unoccupied States in Bi2Se3, Christian Datzer,  Anna Zumbülte, Jürgen Braun, Tobias Förster, Anke B. Schmidt, Jianli Mi, Bo Iversen, Philip Hofmann, Jan Minár, Hubert Ebert, Peter Krüger, Michael Rohlfing, and Markus Donath,

Phys. Rev. B 95, 115401 (2017).


Strong electron-phonon coupling in the sigma band of graphene, Federico Mazzola, Thomas Frederiksen, Thiagarajan Balasubramanian, Philip Hofmann, Bo Hellsing and Justin W. Wells, arxiv1607.00939

Phys. Rev. B 95, 075430 (2017).


Evidence for a two-fold symmetric superconducting gap in a monolayer of FeSe0.5Te0.5 on a topological insulator, Anand Kamlapure, Sujit Manna, Lasse Cornils, Torben Hänke, Martin Bremholm, Philip Hofmann, Jens Wiebe, Roland Wiesendanger, arxiv1608.03827

Phys. Rev. B, in press.


Spin and Valley Control of Free Carriers in Single-Layer WS2, Søren Ulstrup, Antonija Grubišić Čabo, Deepnarayan Biswas, Jonathon M. Riley, Maciej Dendzik, Charlotte E. Sanders, Marco Bianchi, Cephise Cacho, Dan Matselyukh, Richard T. Chapman, Emma Springate, Phil D. C. King, Jill A. Miwa, Philip Hofmann, arxiv1608.060230

Phys. Rev. B 95, 041405(R) 2017).


Reorientation of the bicollinear antiferromagnetic structure at the surface of Fe1+yTe bulk and thin films

Torben Hänke, Udai Raj Singh, Lasse Cornils, Sujit Manna, Anand Kamlapure, Martin Bremholm, Ellen Marie Jensen Hedegaard, Bo Brummerstedt Iversen, Philip Hofmann, Jin Hu, Jens Wiebe, Zhiqiang Mao, Roland Wiesendanger, arxiv1609.09192

Nature Communications 8, 13939 (2017).


Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator, S. Manna, A. Kamlapure, L. Cornils, T. Hänke, E. M. J. Hedegaard, M. Bremholm, B. B. Iversen, Ph. Hofmann, J. Wiebe, and R. Wiesendanger, arxiv1606.03249

Nature Communications 8, 14074 (2017)


Symmetry Driven Band Gap Engineering in Hydrogen Functionalized Graphene, Jakob Jørgensen, Antonija Čabo, Richard Balog, Line Kyhl, Michael Groves, Andrew Cassidy, Albert Bruix, Marco Bianchi, Maciej Dendzik, Mohammad Arman, Lutz Lammich, Jose Pascual, Jan Knudsen, Bjørk Hammer, Philip Hofmann and Liv Hornekaer,

ACS Nano 10, 10798 (2016).


Electroinduced Intercalation of Tetraalkylammonium Ions at the Interface of Graphene Grown on Copper, Platinum, and Iridium, Zakaria Salmi, Line Koefoed, Bjarke B. E. Jensen, Antonija Grubisic Cabo, Philip Hofmann, Steen U. Pedersen, and Kim Daasbjerg,

ChemElectroChem 3, 1 (2016).


Reconstruction-induced trefoil knot Fermi contour of Au(111), Maciej Dendzik, Marco Bianchi, Matteo Michiardi, Charlotte E. Sanders and Philip Hofmann, arxiv1610.01736

Phys. Rev. B 94, 201401(R) (2016).


Crystalline and electronic structure of single-layer TaS2 Charlotte E. Sanders, Maciej Dendzik, Arlette S. Ngankeu, Andreas Eich, Albert Bruix, Marco Bianchi, Jill A. Miwa, Bjørk Hammer, Alexander A. Khajetoorians, Philip Hofmann, arxiv1606.05856

Phys. Rev. B 94, 081404(R) (2016).


Absence of superconductivity in ultra-thin layers of FeSe synthesized on a topological insulator, Andreas Eich, Nils Rollfing, Fabian Arnold, Charlotte Sanders, Pascal R. Ewen, Marco Bianchi, Maciej Dendzik, Matteo Michiardi, Jian-Li Mi, Martin Bremholm, Daniel Wegner, Philip Hofmann, Alexander A. Khajetoorians, arxiv1606.05738

Phys. Rev. B 94, 125437 (2016).


Ultrafast Band Structure Control of a Two-Dimensional Heterostructure, Søren Ulstrup, Antonija Grubišić Čabo, Jill A. Miwa, Jonathon M. Riley, Signe S. Grønborg, Jens C. Johannsen, Cephise Cacho, Oliver Alexander, Richard T. Chapman, Emma Springate, Marco Bianchi, Maciej Dendzik, Jeppe V. Lauritsen, Phil D. C. King, and Philip Hofmann, arxiv1606.03555

ACS Nano 10, 6315 (2016). 


Manifestation of nonlocal electron-electron interaction in graphene, Søren Ulstrup, Malte Schüler, Marco Bianchi, Felix Fromm, Christian Raidel, Thomas Seyller, Tim Wehling and Philip Hofmann, arxiv1604.00496

Phys. Rev. B 94, 081403(R) (2016).


Nickel: The time-reversal symmetry conserving partner of iron on a chalcogenide topological insulator, M. Vondráček, L. Cornils, J. Minár, J. Warmuth, M. Michiardi, C. Piamonteze, L. Barreto, J. A. Miwa, M. Bianchi, Ph. Hofmann, L. Zhou, A. Kamlapure, A. A. Khajetoorians, R. Wiesendanger, J.-L. Mi, B.-B. Iversen, S. Mankovsky, St. Borek, H. Ebert, M. Schüler, T. Wehling, J. Wiebe, and J. Honolka, arxiv1603.09689

Phys. Rev. B 94, 161114 (2016).


Band gap engineering by Bi intercalation of graphene on Ir(111), Jonas Warmuth, Albert Bruix, Matteo Michiardi, Torben Hänke, Marco Bianchi, Jens Wiebe, Roland Wiesendanger, Bjørk Hammer, Philip Hofmann, Alexander A. Khajetoorians, arxiv1603.08724

Physical Review B, 93, 165437 (2016).


Topological insulator homojunctions including magnetic layers: the example of n-p type (n-QLs Bi2Se3/Mn-Bi2Se3) heterostructures, M. Valiska, J. Warmuth, M. Michiardi, M. Vondracek, A. S. Ngankeu, V. Holy, V. Sechovsky, G. Springholz, M. Bianchi, J. Wiebe, P. Hofmann, and J. Honolka, arxiv1602.03450,

Applied Physics Lett.,108, 262402 (2016).


Single-layer MoS2 on Au(111): band gap renormalization and substrate interaction, Albert Bruix, Jill A. Miwa, Nadine Hauptmann, Daniel Wegner, Søren Ulstrup, Signe S. Grønborg, Charlotte E. Sanders, Maciej Dendzik, Antonija Grubivic Cabo, Marco Bianchi, Jeppe V. Lauritsen, Alexander A. Khajetoorians, Bjørk Hammer and Philip Hofmann, arxiv1601.00095.

Physical Review B  93, 165422 (2016).


Sputtering induced re-emergence of the topological surface state in Bi2Se3, Raquel Queiroz, Gabriel Landolt, Stefan Muff, Bartosz Slomski, Thorsten Schmitt, Vladimir N. Strocov, Jianli Mi, Bo Brummerstedt Iversen, Philip Hofmann, Jürg Osterwalder, Andreas P. Schnyder, J. Hugo Dil, arxiv1512.06068

Physical Review B 93,165409 (2016).


Growth and electronic structure of epitaxial single-layer WS2 on Au(111), Maciej Dendzik, Matteo Michiardi, Charlotte Sanders, Marco Bianchi, Jill A. Miwa, Signe Grønborg, Jeppe Vang Lauritsen and Philip Hofmann, arxiv1509.05133

Physical Review B 92, 245442 (2015).


Observation of Ultrafast Free Carrier Dynamics in Single Layer MoS2, Antonija Grubisic Cabo, Jill Miwa, Signe Grønborg, Jonathon Riley, Jens Johannsen,  Cephise Cacho, Oliver Alexander, Richard Chapmann, Emma Springate, Marco Grioni, Jeppe Lauritsen, Philip King, Philip Hofmann, and Søren Ulstrup,

Nano Letters 15, 5883 (2015).


159. Synthesis of Epitaxial Single-Layer MoS2 on Au(111), Signe Grønborg, Søren Ulstrup, Marco Bianchi, Maciej Dendzik, Charlotte Sanders, Jeppe Lauritsen, Philip Hofmann, and Jill Miwa, Langmuir 35 9700 (2015).


Tunable Hot Carrier Multiplication and Cooling in Graphene, Jens Christian Johannsen, Søren Ulstrup, Alberto Crepaldi, Federico Cilento, Michele Zacchigna, Jill Miwa, Cephise Cacho, Richard Chapman, Emma Springate, Felix Fromm, Christian Raidel, Thomas Seyller, Philip King, Fulvio Parmigiani, Marco Grioni and Philip Hofmann,

Nano Letters 15, 326 (2015).


Electronic Structure of Epitaxial Single-Layer MoS2, Jill A. Miwa, Søren Ulstrup, Signe G. Sørensen, Maciej Dendzik, Antonija Grubišić Čabo, Marco Bianchi, Jeppe Vang Lauritsen, Philip Hofmann, arxiv1410.0615,

Physical Review Letters, 114, 046802 (2015).


Scientific Highlights


Electronic structure of single-layer MoS2


As in the case of graphene, many layered materials change their properties in subtle but important ways when thinned down to a single unit layer. Important examples of this are the transition metal dichalcogenites such as MoS2. While bulk MoS2 is a semiconductor with an indirect band gap, a single layer has a direct band gap. Moreover, the top of the valence band has been predicted to be split by the spin-orbit interaction. By growing high-quality epitaxial MoS2 layers on the (111) surface of gold and then inspecting these with angle-resolved photoemission spectroscopy on ASTRID2, we have been able to directly measure the band structure of single-layer MoS2 in unprecedented detail. In fact, the sample quality and resolution is so good that even the predicted spin-orbit splitting can be observed.
















Jill A. Miwa, Søren Ulstrup, Signe G. Sørensen, Maciej Dendzik, Antonija Grubišić Čabo, Marco Bianchi, Jeppe Vang Lauritsen, Philip Hofmann, arxiv1410.0615,  Physical Review Letters 114, 046802 (2015).