Article
Chemistry, Multidisciplinary
Jianchen Dang, Mingwei Yang, Xin Xie, Zhen Yang, Danjie Dai, Zhanchun Zuo, Can Wang, Kuijuan Jin, Xiulai Xu
Summary: In the WS2/LaMnO3 thin film heterostructure, the valley polarization of monolayer WS2 can be greatly enhanced up to 80%, and this greatly enhanced valley polarization can be maintained to a temperature as high as 160K with a valley polarization of 53%.
Article
Nanoscience & Nanotechnology
Yang Chen, Shuhang Qian, Kai Wang, Xiangyuan Xing, Andrew Wee, Kian Ping Loh, Bing Wang, Dong Wu, Jiaru Chu, Andrea Alu, Peixiang Lu, Cheng-Wei Qiu
Summary: Valleytronics, a promising technology for energy-efficient signal transport on chip, faces challenges in achieving high-fidelity, high-directionality, and room-temperature valley transport. In this study, a nanophotonic circuit is demonstrated to unidirectionally route valley indices using the chirality of photons, with 98% valley fidelity and a circulation directionality of 0.44 +/- 0.04 at room temperature. This research opens up possibilities for large-scale valleytronic networks and hybrid spin-valley-photon ecosystems at the nanoscale.
NATURE NANOTECHNOLOGY
(2022)
Article
Chemistry, Multidisciplinary
Xu Li, Chengbiao Yang, Yuanzheng Xia, Xinlong Zeng, Peng Shen, Linglong Li, Feiya Xu, Duanjun Cai, Yaping Wu, Zhiming Wu, Shuping Li, Junyong Kang
Summary: This study demonstrates nonvolatile electrical tuning of valley excitons in monolayer and bilayer WS2 using a ferroelectric gating approach, which enhances the room-temperature valley polarization through control of interfacial charge trapping/detrapping and other effects. This work reveals effective electrical control over valley excitons in semiconductors, providing a promising strategy for the development of valleytronics devices.
Article
Chemistry, Physical
John C. Thomas, Antonio Rossi, Darian Smalley, Luca Francaviglia, Zhuohang Yu, Tianyi Zhang, Shalini Kumari, Joshua A. Robinson, Mauricio Terrones, Masahiro Ishigami, Eli Rotenberg, Edward S. Barnard, Archana Raja, Ed Wong, D. Frank Ogletree, Marcus M. Noack, Alexander Weber-Bargioni
Summary: This study investigates the impact of individual atomic defects on the macroscopic functionality of 2D materials using intelligent hyperspectral scanning tunneling spectroscopy (STS) mapping. By utilizing machine learning methods, the researchers autonomously collect and analyze spectroscopic data, and provide a customizable workflow for experimental decision-making. The results demonstrate the potential of artificial intelligence in hyperspectral STS mapping.
NPJ COMPUTATIONAL MATERIALS
(2022)
Article
Multidisciplinary Sciences
Cedric Robert, Sangjun Park, Fabian Cadiz, Laurent Lombez, Lei Ren, Hans Tornatzky, Alistair Rowe, Daniel Paget, Fausto Sirotti, Min Yang, Dinh Van Tuan, Takashi Taniguchi, Bernhard Urbaszek, Kenji Watanabe, Thierry Amand, Hanan Dery, Xavier Marie
Summary: The study demonstrates efficient spin/valley optical pumping of resident electrons in n-doped WSe2 and WS2 monolayers, achieving large dynamic polarization of resident electrons using circular light with continuous wave laser and appropriate doping and excitation densities.
NATURE COMMUNICATIONS
(2021)
Article
Chemistry, Physical
Maomiao Xiang, Jun Fu, Chenxi Huang, Yue Xing, Jiefu Zhang, Hualing Zeng, Xiang Shao
Summary: In this study, a simple chemical vapor deposition method was utilized to directly grow large-size monolayer WS2 on an atomically flat rutile TiO2(110) substrate. The as-grown WS2 exhibited highly single crystallinity and an atomically clean WS2/TiO2 interface. These structural characteristics resulted in a neutral excitonic photoluminescence of WS2 with minimal spectral broadening at cryogenic temperature. Additionally, the low defect concentration suppressed intervalley scattering and the efficient interfacial electron transfer reduced the Coulomb interaction between valleys of WS2, leading to enhanced valley polarization and coherence even at room temperature under ambient conditions. These findings highlight the potential of substrate tuning and interface control as promising strategies for practical valleytronics utilizing transition-metal dichalcogenides.
JOURNAL OF PHYSICAL CHEMISTRY C
(2023)
Article
Physics, Multidisciplinary
Elena Blundo, Paulo E. Faria, Alessandro Surrente, Giorgio Pettinari, Mikhail A. Prosnikov, Katarzyna Olkowska-Pucko, Klaus Zollner, Tomasz Wozniak, Andrey Chaves, Tomasz Kazimierczuk, Marco Felici, Adam Babinski, Maciej R. Molas, Peter C. M. Christianen, Jaroslav Fabian, Antonio Polimeni
Summary: This study demonstrates that strain has a significant impact on the exciton magnetic moment in WS2 monolayers. The findings suggest that strain can influence the valley number of excitons, which is crucial for processing binary information in two-dimensional crystals.
PHYSICAL REVIEW LETTERS
(2022)
Article
Materials Science, Multidisciplinary
Xinlong Zeng, Wenyu Kang, Xiaowen Zhou, Linglong Li, Yuanzheng Xia, Haiyang Liu, Chengbiao Yang, Yaping Wu, Zhiming Wu, Xu Li, Junyong Kang
Summary: This study demonstrates highly tunable exciton and valley characteristics in monolayer and bilayer WS2 through coupling to AlGaN with different doping levels. The exciton energy can be redshifted by interfacing WS2 with n-type AlGaN, and an interlayer exciton peak can emerge in bilayer WS2 due to type-II band alignment. The valley polarization can be achieved in monolayer WS2 by coupling with n-type AlGaN, and the polarization of interlayer exciton is higher than that of intralayer exciton.
SCIENCE CHINA-MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Ioanna Demeridou, Emmanouil G. Mavrotsoupakis, Leonidas Mouchliadis, Pavlos G. Savvidis, Emmanuel Stratakis, George Kioseoglou
Summary: This study investigates the room temperature valley polarization of monolayer WS2 on different substrates. It is found that a degree of polarization of photoluminescence (PL) in excess of 27% can be achieved on graphite substrate through resonant excitation. By chemical doping, the polarization of the neutral exciton emission can be modulated from 27% to 38% for 1L-WS2/graphite. The results indicate that the valley polarization strongly depends on the interplay between doping and the choice of the supporting layer of TMDs. Time-resolved PL measurements and a rate equation model support these findings, suggesting a pathway towards engineering valley polarization and exciton lifetimes in TMDs.
Article
Chemistry, Multidisciplinary
Gyeongbae Park, Anupam Giri, Manish Kumar, Sungmin Moon, Monalisa Pal, Dong Wook Kim, Unyong Jeong
Summary: This study presents a novel chemical process termed pseudoequilibrium of etching and selective grain growth, using a quaternary ammonium halide to convert randomly oriented multigrain gold ultrathin films into (111)-oriented gold ultrathin films. The reaction variables for the chemical conversion process are systematically investigated, and the inplane rotational degeneracy in the Au(111) thin film epitaxially grown on a Si(111) substrate is revealed. This chemical process can be applied to a broad range of thicknesses from 9 to 100 nm.
Article
Nanoscience & Nanotechnology
Gaohong Liu, Xuanli Zheng, Haiyang Liu, Jun Yin, Congming Ke, Weihuang Yang, Yaping Wu, Zhiming Wu, Xu Li, Chunmiao Zhang, Junyong Kang
Summary: Transition-metal dichalcogenides with intrinsic spin-valley degree of freedom show great potential for valleytronic and optoelectronic applications. By designing metallic arrays and resonantly coupling with transition-metal dichalcogenides, valley polarization enhancement and significant emission gains have been achieved. The enhancement of valley polarization is quantitatively predicted and realized through increased electromagnetic field intensity and radiation efficiency. Tunable valley polarization up to 30.0% is achieved in bilayer WS2 under nonresonant excitation at room temperature, providing a promising route for the development of room-temperature valley-dependent optoelectronic devices.
ACS APPLIED MATERIALS & INTERFACES
(2021)
Article
Chemistry, Multidisciplinary
Paolo D'Agosta, Francesco Tumino, Valeria Russo, Andrea Li Bassi, Carlo S. Casari
Summary: In this work, the growth of WS2/MoS2 and MoS2/WS2 heterobilayers by pulsed laser deposition (PLD) under ultra-high vacuum conditions was studied. The heterobilayer morphology and structure at the nanoscale were investigated using in situ scanning tunneling microscopy. The experiments showed that the growth of the heterostructure can be controlled by tuning the number of laser pulses, achieving high coverage and thickness sensitivity. Raman spectroscopy revealed the effect of the interaction with the metallic substrate on the TMD vibrational properties and a strong interlayer coupling between the MoS2 and WS2 layers. The transfer of the heterobilayers onto a silica substrate confirmed that the interlayer coupling is not substrate-dependent. This work highlights the potential of PLD technique in growing TMD heterostructures and opens new perspectives in the synthesis of complex 2D layered materials.
Article
Biochemistry & Molecular Biology
Pawel Krukowski, Takuma Hattori, Megumi Akai-Kasaya, Akira Saito, Hideji Osuga, Yuji Kuwahara
Summary: The light emission properties of helicene molecules on Au(111) surfaces were investigated using tunneling-current-induced light-emission technique. Plasmon-originated light emission was observed on the helicene/Au(111) surface, but suppressed at the edges of the Au(111) terraces where the molecules were adsorbed. To overcome this, C-60 layers were used as decoupling buffer layers. The multilayers of helicene molecules on C-60 showed strong luminescence modulated by the molecular electronic states.
INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES
(2022)
Article
Chemistry, Physical
Samrat Ghosh, Yusuke Tsutsui, Takahiro Kawaguchi, Wakana Matsuda, Shusaku Nagano, Katsuaki Suzuki, Hironori Kaji, Shu Seki
Summary: This study developed crystalline pi-conjugated covalent organic frameworks (COFs) and demonstrated their potential in terms of conductivity and photoresponsivity, providing new active materials for multifunctional organic electronics.
CHEMISTRY OF MATERIALS
(2022)
Article
Chemistry, Multidisciplinary
Pei-Gang Chen, Zhiyong Li, Yun Qi, Tsz Wing Lo, Shubo Wang, Wei Jin, Kwok-Yin Wong, Shanhui Fan, Anatoly Zayats, Dangyuan Lei
Summary: The research demonstrates a valleytronic system based on high-quantum-yield trion emission in monolayer WS2, chirally coupled to a low-loss microfiber, achieving long-range directional routing of valley excitations and selective address of valley-dependent emission from different spatial locations. This valleytronic interface can be integrated with fiber communication devices, providing a new mechanism for optical information transport and manipulation in classical and quantum regimes.
Article
Physics, Condensed Matter
Hermann Erk, Klaas Opitz, Petra Hein, Stephan Jauernik, Michael Bauer
Summary: Cone-type bands near the center of the surface Brillouin zone were observed in the low-energy angle-resolved photoemission spectra of tin phthalocyanine adsorbed on graphite. The simulation results showed that these spectral features are replicas of the electronic structure of graphite near (K) over bar resulting from high-order momentum transfer processes up to the fourth order due to the interaction of substrate electrons with the long-range structural order of the adsorbate overlayer. The analysis of time-resolved photoemission data from one of the replicas yielded quantitative and very good agreement with previous studies on the excited carrier dynamics in the Dirac cones of graphite and graphene.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2023)
Article
Chemistry, Multidisciplinary
Chao Li, Roberto Robles, Nicolas Lorente, Sanjoy Kr Mahatha, Sebastian Rohlf, Kai Rossnagel, Alessandro Barla, Boris V. Sorokin, Stefano Rusponi, Philippe Ohresser, Sara Realista, Paulo N. Martinho, Torben Jasper-Toennies, Alexander Weismann, Richard Berndt, Manuel Gruber
Summary: The magnetic properties of transition-metal ions are usually described by atomic spins and exchange coupling, with the orbital moment seen as a perturbation. However, our study on a Co-(II) complex with antiferromagnetically coupled 1/2 spins on Au(111) reveals that each Co ion has a comparable orbital moment to the spin, leading to magnetic anisotropy. This finding emphasizes the importance of considering orbital moments, even in systems with strong ligand fields, and has important consequences for quantum operations.
Article
Chemistry, Multidisciplinary
Klara Volckaert, Paulina Majchrzak, Deepnarayan Biswas, Alfred J. H. Jones, Marco Bianchi, Zhihao Jiang, Raphael Dubourg, Rasmus Ornekoll Stenshoj, Mads Lykke Jensen, Nykola C. Jones, Soren V. Hoffmann, Jian-Li Mi, Martin Bremholm, Xing-Chen Pan, Yong P. Chen, Philip Hofmann, Jill A. Miwa, Soren Ulstrup
Summary: Modification of the electronic structure of MnBi2Te4 based magnetic topological insulators by ad atom deposition was studied using micro-focused angle-resolved photoemission spectroscopy. The deposition of rubidium atoms resulted in complex changes in the band structure, including coverage-dependent ambipolar doping effects, removal of surface state hybridization, and collapse of a surface state band gap. Doping-dependent band bending also gave rise to tunable quantum well states. These findings provide new ways to exploit the topological states and rich surface electronic structures of manganese bismuth tellurides.
ADVANCED MATERIALS
(2023)
Article
Physics, Multidisciplinary
Masoud Taleb, Mario Hentschel, Kai Rossnagel, Harald Giessen, Nahid Talebi
Summary: Ultrafast photon-electron spectroscopy in electron microscopes commonly requires ultrafast laser setups. Now, an inverse approach based on cathodoluminescence spectroscopy has allowed a compact solution to spectral interferometry inside an electron microscope, without a laser.
Article
Multidisciplinary Sciences
Shuvam Sarkar, Joydipto Bhattacharya, Pampa Sadhukhan, Davide Curcio, Rajeev Dutt, Vipin Kumar Singh, Marco Bianchi, Arnab Pariari, Shubhankar Roy, Prabhat Mandal, Tanmoy Das, Philip Hofmann, Aparna Chakrabarti, Sudipta Roy Barman
Summary: LaTe3 is a non-centrosymmetric material with time reversal symmetry, hosting a Kramers nodal line connecting time reversal-invariant momenta. The nodal line imposes gapless crossings between the bilayer-split charge density wave-induced shadow bands and the main bands. The presence of the Kramers nodal line and its crossings traversing the Fermi level are confirmed by spectroscopic data and calculations.
NATURE COMMUNICATIONS
(2023)
Article
Physics, Multidisciplinary
Marco Bianchi, Philip Hofmann, Soren V. Hoffmann, Nykola C. Jones, Zheshen Li, Jill A. Miwa, Soren P. Moller, Jorgen S. Nielsen, Heine D. Thomsen, Soren Ulstrup, Torben Worm
Summary: ASTRID2 is a third-generation UV to soft X-ray light source at Aarhus University in Denmark, providing a user beam in top-up mode 24/7 for about 40 weeks per year to both local university research groups and external visitors. This article presents the facility, beam line suite, scientific examples, and discusses recent upgrades and future plans.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Physics, Multidisciplinary
Tobias Heinrich, Hung-Tzu Chang, Sergey Zayko, Kai Rossnagel, Murat Sivis, Claus Ropers
Summary: Femtosecond core-level transient absorption spectroscopy was used to investigate the photoinduced dynamics of the charge density wave in 1T-TiSe2. Redshifts in core-level excitations were primarily induced by photoexcited carriers and phonons, with carrier relaxation time and phonon heating time of approximately 360 fs and 1.0 ps, respectively. Oscillations in the absorption spectra were assigned to coherent excitations of the optical A1g phonon and the A?1g charge density wave amplitude mode, and their momentary atomic displacements and amplitudes were determined through simulations.
Article
Nanoscience & Nanotechnology
Finn Zahari, Richard Marquardt, Matthias Kallaene, Ole Gronenberg, Christoph Schlueter, Yury Matveyev, Georg Haberfehlner, Florian Diekmann, Alena Nierhauve, Jens Buck, Arndt Hanff, Gitanjali Kolhatkar, Gerald Kothleitner, Lorenz Kienle, Martin Ziegler, Juergen Carstensen, Kai Rossnagel, Hermann Kohlstedt
Summary: Memristive devices are being developed as non-volatile memory elements to enhance computing capabilities. Interface-based memristive devices are promising for emulating synaptic functionalities in neuromorphic circuits. A device composed of Nb/NbOx/Al2O3/HfO2/Au demonstrates analog switching, no electro-forming, and high current-voltage non-linearity. Spectroscopic evidence and device modeling support the concept of memristive switching based on charge traps within HfO2.
ADVANCED ELECTRONIC MATERIALS
(2023)
Article
Instruments & Instrumentation
Loic Le Guyader, Andrea Eschenlohr, Martin Beye, William Schlotter, Florian Doering, Cammille Carinan, David Hickin, Naman Agarwal, Christine Boeglin, Uwe Bovensiepen, Jens Buck, Robert Carley, Andrea Castoldi, Alessandro D'Elia, Jan-Torben Delitz, Wajid Ehsan, Robin Engel, Florian Erdinger, Hans Fangohr, Peter Fischer, Carlo Fiorini, Alexander Foehlisch, Luca Gelisio, Michael Gensch, Natalia Gerasimova, Rafael Gort, Karsten Hansen, Steffen Hauf, Manuel Izquierdo, Emmanuelle Jal, Ebad Kamil, Suren Karabekyan, Thomas Kluyver, Tim Laarmann, Tobias Lojewski, David Lomidze, Stefano Maffessanti, Talgat Mamyrbayev, Augusto Marcelli, Laurent Mercadier, Giuseppe Mercurio, Piter S. Miedema, Katharina Ollefs, Kai Rossnagel, Benedikt Roesner, Nico Rothenbach, Andrey Samartsev, Justine Schlappa, Kiana Setoodehnia, Gheorghe Sorin Chiuzbaian, Lea Spieker, Christian Stamm, Francesco Stellato, Simone Techert, Martin Teichmann, Monica Turcato, Benjamin Van Kuiken, Heiko Wende, Alexander Yaroslavtsev, Jun Zhu, Serguei Molodtsov, Christian David, Matteo Porro, Andreas Scherz
Summary: Femtosecond transient soft X-ray absorption spectroscopy (XAS) is a promising technique for studying out-of-equilibrium dynamics in material and energy research. This study presents a dedicated setup for soft X-rays at the European XFEL, which uses a beam-splitting zone plate to create three copies of the incoming beam for transmission measurement. Shot-by-shot analysis of transmission is enabled by simultaneously detecting the transmitted intensity through the excited and unexcited sample, as well as monitoring the incoming intensity. An imaging detector with high frame rate and sensitivity is employed for photon detection.
JOURNAL OF SYNCHROTRON RADIATION
(2023)
Article
Computer Science, Information Systems
Kasper Overgaard Mortensen, Fatemeh Zardbani, Mohammad Ahsanul Haque, Steinn Ymir Agustsson, Davide Mottin, Philip Hofmann, Panagiotis Karras
Summary: This paper proposes Marigold, a scalable algorithm for k-means clustering in high dimensions, which reduces the need for repeatedly computing Euclidean distances by using a tight distance-bounding scheme, a stepwise calculation over a multiresolution transform, and exploiting the triangle inequality. Experimental results show that Marigold achieves a significant improvement in clustering high-dimensional data.
PROCEEDINGS OF THE VLDB ENDOWMENT
(2023)
Article
Chemistry, Physical
Till Domroese, Thomas Danz, Sophie F. Schaible, Kai Rossnagel, Sergey V. Yalunin, Claus Ropers
Summary: The authors discovered a transient hexatic state during the laser-induced transformation between two charge-density wave (CDW) phases in the CDW material 1T-TaS2. The ability to control material properties using light holds great potential for future applications in energy conversion and information technology. Strongly correlated materials such as transition metal dichalcogenides allow for optical control of electronic phases, charge ordering, and interlayer correlations through photodoping.
Article
Microscopy
O. Tkach, T. -P. Vo, O. Fedchenko, K. Medjanik, Y. Lytvynenko, S. Babenkov, D. Vasilyev, Q. L. Nguyen, T. R. F. Peixoto, A. Gloskowskii, C. Schlueter, S. Chernov, M. Hoesch, D. Kutnyakhov, M. Scholz, L. Wenthaus, N. Wind, S. Marotzke, A. Winkelmann, K. Rossnagel, J. Minar, H. -J. Elmers, G. Schonhense
Summary: X-ray photoelectron diffraction (XPD) is a powerful technique that provides detailed structural information of solids and thin films, complementing electronic structure measurements. XPD patterns exhibit pronounced circular dichroism in the angular distribution (CDAD) with asymmetries up to 80%, alongside rapid variations on a small kll-scale. Measurements with circularly-polarized hard X-rays confirm that core-level CDAD is a general phenomenon independent of atomic number.
Article
Materials Science, Multidisciplinary
Marco Bianchi, Swagata Acharya, Florian Dirnberger, Julian Klein, Dimitar Pashov, Kseniia Mosina, Zdenek Sofer, Alexander N. Rudenko, Mikhail I. Katsnelson, Mark van Schilfgaarde, Malte Roesner, Philip Hofmann
Summary: We investigate the electronic structure of paramagnetic CrSBr through first-principles calculations and angle-resolved photoemission spectroscopy. By using a supercell approximation and quasiparticle self-consistent GW theory with excitonic vertex corrections, we calculate the paramagnetic phase with broken long-range order. Comparing the calculated quasiparticle band structure with experimental photoemission data at 200 K shows excellent agreement, allowing us to explain the broadening of some bands due to broken magnetic order and/or electronic dispersion perpendicular to the quasi-two-dimensional layers. The experimental band gap at 200 K is found to be at least 1.51 eV, while calculations suggest a larger gap of approximately 2.1 eV at lower temperature.
Article
Materials Science, Multidisciplinary
H. Beyer, P. Hein, K. Rossnagel, M. Bauer
Summary: Time- and angle-resolved photoelectron spectroscopy was used to investigate the thermalization process of nonequilibrium carrier distribution in the Dirac cone of graphite after absorbing linearly polarized near-infrared laser pulses. The results showed a decay time constant of (20 +/- 3) fs for the photoinduced momentum anisotropy in the initial carrier population. The spectral peak of the initial carriers also exhibited an energy downshift of -100 meV within the first 30 fs, which was attributed to the emission of strongly coupled A'1 optical phonons at K. A fully thermalized distribution was established on a characteristic timescale of (40 +/- 10) fs. These findings highlight the complexity of carrier thermalization on ultrafast timescales, which result from the interplay between carrier-carrier and carrier-phonon interactions.
Article
Materials Science, Multidisciplinary
Alla Chikina, Henriette Lund, Marco Bianchi, Davide Curcio, Kirstine J. Dalgaard, Martin Bremholm, Shiming Lei, Ratnadwip Singha, Leslie M. Schoop, Philip Hofmann
Summary: The electronic structure of NdTe3 in the charge density wave phase is examined using angle-resolved photoemission spectroscopy. The study uncovers previously unseen details in the Fermi surface topology and offers an explanation for the complex quantum oscillations observed in rare earth tritellurides. It is found that the charge density wave not only removes Fermi surface elements but also creates new ones that can be observed in transport experiments.
