Article
Nanoscience & Nanotechnology
Alina Mrenca-Kolasinska, Szu-Chao Chen, Ming-Hao Liu
Summary: The presence of periodic modulation in graphene leads to the formation of minibands and a fractal energy spectrum called Hofstadter butterfly. The quantum transport modeling in a gate-induced superlattice in graphene reveals insights into the band structure and can be applied to other superlattice geometries. The technique of transverse magnetic focusing proves to be useful in investigating the minibands and their extent.
NPJ 2D MATERIALS AND APPLICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Nadia Benlakhouy, Ahmed Jellal, Hocine Bahlouli, Michael Vogl
Summary: The magnetic field induced Hofstadter butterfly in twisted bilayer graphene (TBG) is studied in different situations. It is found that the appearance of the butterfly is closely related to AA stacking type interlayer hoppings, which is different from AB/BA-type hoppings that are important for the appearance of flat bands. The role of AA-type hoppings in combination with lattice relaxation effects can make individual Landau levels slightly harder to resolve. The impact of circularly polarized light and longitudinal light on the fractal structure of the butterfly spectrum is also studied. Circularly polarized light introduces a gap term that breaks the chiral symmetries, while longitudinal light does not increase the asymmetry of the energy spectrum.
Article
Materials Science, Multidisciplinary
Yoshiyuki Matsuki, Kazuki Ikeda, Mikito Koshino
Summary: The study found that introducing a single defect site in a two-dimensional lattice of Bloch electrons in a uniform magnetic field creates a defect energy level in each energy gap of the Hofstadter butterfly. The wave functions of different defect levels have different localization lengths, but can be described by a single universal function after fractal scaling. Each defect state has its own characteristic orbital magnetic moment correlated to the energy level gradient in the Hofstadter diagram, providing insight into the fractal nature of the Hofstadter butterfly.
Article
Physics, Multidisciplinary
Yuxuan Zhang, Naren Manjunath, Gautam Nambiar, Maissam Barkeshli
Summary: In the presence of crystalline symmetries, this study investigates a particular invariant, the discrete shift 6', in the square lattice Hofstadter model. The results show that 6' is related to quantized contributions to fractional charge and angular momentum. The study also proposes an empirical formula for 6' and shows that bands with the same Chern number may have different values of 6'.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Multidisciplinary
Yu Saito, Jingyuan Ge, Louk Rademaker, Kenji Watanabe, Takashi Taniguchi, Dmitry A. Abanin, Andrea F. Young
Summary: A small twist between two layers of graphene can lead to flat band structures, which can form ferromagnetic Chern insulators when the moire superlattice interacts with a magnetic field. In twisted bilayer graphene, Coulomb interactions and magnetic field effects give rise to new quantum states.
Article
Chemistry, Physical
Sun-Woo Kim, Sunam Jeon, Moon Jip Park, Youngkuk Kim
Summary: The energy spectrum of twisted bilayer graphene (TBG) exhibits recursive higher-order topological properties known as higher-order topological insulator (HOTI) phases. These HOTI phases, characterized by localized corner states, are replicas of the original HOTIs and maintain the self-similarity of the Hofstadter spectrum. It is shown that TBG exhibits exact flux translational symmetry at all commensurate angles, and the original HOTI phase re-emerges at a half-flux periodicity, preserving the effective twofold rotation. Multiple replicas of the original HOTIs are also found for fluxes without protecting symmetries, featuring localized corner states and edge-localized real-space topological markers. These replica HOTIs result from different interaction scales in TBG, including intralayer and interlayer couplings. The topological aspect of the Hofstadter butterflies observed in this study highlights the symmetry-protected topology in quantum fractals.
NPJ COMPUTATIONAL MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Vincent Liu, Yi Yang, John D. Joannopoulos, Marin Soljacic
Summary: In this theoretical study, a three-dimensional Hofstadter model with linearly varying non-Abelian gauge potentials along all dimensions is introduced and analyzed. The model can be interpreted as spin-orbit coupling among a trio of Hofstadter butterfly pairs. It is found that under different choices of gauge fields, both weak and strong topological insulating phases can be identified in the model.
Article
Materials Science, Multidisciplinary
Gaia Forghieri, Paolo Bordone, Andrea Bertoni
Summary: Graphene nanoribbons serve as an ideal platform for electronic interferometry in the integer quantum Hall regime. By solving the time-dependent Schrodinger equation for single carriers in graphene, the study reveals the effects of carrier localization on their transport characteristics in pn junctions. Two types of Mach-Zender interferometers are simulated, showing expected and unexpected phenomena.
Article
Engineering, Multidisciplinary
Jae Won Lee, Tolendra Kshetri, Kyoung Ryeol Park, Nam Hoon Kim, Ok-Kyung Park, Joong Hee Lee
Summary: The study synthesized boron nitride quantum dot (BNQD) covalently bonded reduced graphene oxide (rGO) hybrid materials as a novel electrode material for supercapacitors. The hybrid material showed improved charge carrier density, wettability of electrolyte, and durability, resulting in higher specific capacitance and cycling stability compared to rGO and raw BNQD/rGO. The fabricated A-BNQD/rGO exhibited great potential as electrode materials for high-performance supercapacitors.
COMPOSITES PART B-ENGINEERING
(2021)
Article
Physics, Applied
Takatoshi Yamada, Tomoaki Masuzawa, Yuki Okigawa
Summary: To enhance the carrier mobility and suppress the intrinsic carrier density of graphene on a silicon dioxide substrate, a potassium-doped nano graphene intermediate layer was introduced. Electrical properties of the fabricated graphene field-effect transistors were measured, and the results showed a shift in the Dirac point and increased carrier density and mobility. The ionized potassium atoms in the intermediate layer shielded the electric force from the negatively charged impurities, resulting in improved field-effect mobilities.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Multidisciplinary
Wei Feng, Dexi Shao, Guo-Qiang Zhang, Qi-Ping Su, Jun-Xiang Zhang, Chui-Ping Yang
Summary: Motivated by recent realizations of 2D superconducting-qubit lattices, this study proposes a protocol to simulate the Hofstadter butterfly with synthetic gauge fields in superconducting circuits. By constructing a generalized Hofstadter model on zigzag lattices, a fractal energy spectrum similar to the original Hofstadter butterfly is achieved. The resonant frequencies of qubits are periodically modulated to engineer a synthetic gauge field, and a spectroscopic method is used to demonstrate the butterfly spectrum. Numerical simulations with realistic parameters confirm the presence of the butterfly spectrum. This proposal provides a promising approach for realizing the Hofstadter butterfly on the latest 2D superconducting-qubit lattices and will stimulate quantum simulation of novel properties induced by magnetic fields in superconducting circuits.
FRONTIERS OF PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
Vasil Rokaj, Markus Penz, Michael A. Sentef, Michael Ruggenthaler, Angel Rubio
Summary: In this paper, a translationally invariant framework called quantum-electrodynamical Bloch (QED-Bloch) theory is introduced to describe the behavior of periodic materials in a homogeneous magnetic field and their strong coupling to the quantized photon field. The theory predicts the existence of fractal polaritonic spectra and reveals how a terahertz cavity can modify the standard Hofstadter butterfly. When the quantized photon field is absent, the QED-Bloch theory captures the well-known fractal spectrum of the Hofstadter butterfly and can be used to describe the behavior of two-dimensional materials in strong magnetic fields. The paper also explores the effect of cavity confinement on Landau levels and finds that the cavity alters the quantized Hall conductance and modifies the Hall plateaus.
Article
Chemistry, Multidisciplinary
Toktam Pedram-rad, Zarrin Es'haghi, Ali Ahmadpour, Malihe Samadi Kazemi, Ali Akbar Mohammadi
Summary: In this study, C-nanodots with low resistivity were combined with graphene-like boron nitride (g-BN) to form C-dots/g-BN catalyst. The catalyst showed superior performance in high-temperature oxidation reactions in fuel oil, with high catalytic activity and good controllability.
ARABIAN JOURNAL OF CHEMISTRY
(2022)
Article
Multidisciplinary Sciences
Y. Dong, L. Xiong, I. Y. Phinney, Z. Sun, R. Jing, A. S. McLeod, S. Zhang, S. Liu, F. L. Ruta, H. Gao, Z. Dong, R. Pan, J. H. Edgar, P. Jarillo-Herrero, L. S. Levitov, A. J. Millis, M. M. Fogler, D. A. Bandurin, D. N. Basov
Summary: The phenomenon of dragging light by moving media, predicted by Fresnel and verified by Fizeau, plays a key role in Einstein's special relativity theory. While experiments on dragging photons by an electron flow in solids have inconsistencies, the dragging of surface plasmon polaritons by an electron flow in graphene is a unique and complex phenomenon that challenges simple kinematics explanations.
Article
Physics, Multidisciplinary
Nadia Benlakhouy, Ahmed Jellal, Hocine Bahlouli
Summary: The magnetic field generated Hofstadter butterfly in single-twist trilayer graphene is investigated using circularly polarized light and longitudinal light from a waveguide. It is found that single-twist trilayer graphene has two distinct chiral limits and the central branch of the butterfly splits into two precisely degenerate components. The effect of circularly polarized light on the butterfly energy spectrum and the asymmetry corresponding to energy E = 0 is studied. The impact of longitudinally polarized light from a waveguide on the chiral symmetries of the butterfly energy spectrum is also explored.
Article
Chemistry, Multidisciplinary
Janine Schwestka, Heena Inani, Mukesh Tripathi, Anna Niggas, Niall McEvoy, Florian Libisch, Friedrich Aumayr, Jani Kotakoski, Richard A. Wilhelm
Article
Materials Science, Multidisciplinary
Raphael Hoeller, Florian Libisch, Christian Hellmich
Summary: This study computes large deflections of suspended circular graphene sheets with simply supported boundaries under various types of vertical axisymmetric forces based on the principle of virtual power. The deflections are approximated using a Fourier series, resulting in a nonlinear algebraic system of equations solved by an iterative Newton-Raphson procedure. The method is validated using experimental nanoindentation measurements.
MECHANICS OF ADVANCED MATERIALS AND STRUCTURES
(2022)
Article
Chemistry, Multidisciplinary
Valerie Smejkal, Florian Libisch, Alejandro Molina-Sanchez, Chiara Trovatello, Ludger Wirtz, Andrea Marini
Summary: The study investigates the time evolution of the transient reflection signal in an MoS2 monolayer on a SiO2/Si substrate using first-principles out-of-equilibrium real-time methods, finding that the delayed buildup of the signal is caused by coordinated carrier dynamics and its influence on screening.
Article
Chemistry, Physical
Tobias Schafer, Florian Libisch, Georg Kresse, Andreas Gruneis
Summary: An embedding approach is presented to efficiently handle local electron correlation effects in periodic environments by integrating high-level correlation calculations into low-level ones. The method demonstrates accelerated convergence with respect to the local fragment size and has shown capabilities in accurately calculating adsorption energies of molecules and lattice impurities in solids.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Correction
Chemistry, Physical
Jiamin Quan, Lukas Linhart, Miao-Ling Lin, Daehun Lee, Jihang Zhu, Chun-Yuan Wang, Wei-Ting Hsu, Junho Choi, Jacob Embley, Carter Young, Takashi Taniguchi, Kenji Watanabe, Chih-Kang Shih, Keji Lai, Allan H. MacDonald, Ping-Heng Tan, Florian Libisch, Xiaoqin Li
Article
Chemistry, Physical
Jiamin Quan, Lukas Linhart, Miao-Ling Lin, Daehun Lee, Jihang Zhu, Chun-Yuan Wang, Wei-Ting Hsu, Junho Choi, Jacob Embley, Carter Young, Takashi Taniguchi, Kenji Watanabe, Chih-Kang Shih, Keji Lai, Allan H. MacDonald, Ping-Heng Tan, Florian Libisch, Xiaoqin Li
Summary: The phonon spectra in MoS2 twisted bilayers are renormalized due to ultra-strong coupling between different phonon modes and atomic reconstructions of the moire pattern, providing new insights into moire physics. A low-energy continuum model for phonons has been developed to successfully capture experimental observations and reveal the rapid evolution of phonon spectra over a range of small twist angles. Remarkably, simple optical spectroscopy experiments can offer information on strain and lattice distortions in nanometre-size moire crystals.
Article
Optics
Marcel Neuhaus, Johannes Schoetz, Mario Aulich, Anchit Srivastava, Dziugas Kimbaras, Valerie Smejkal, Vladimir Pervak, Meshaal Alharbi, Abdallah M. Azzeer, Florian Libisch, Christoph Lemell, Joachim Burgdoerfer, Zilong Wang, Matthias F. Kling
Summary: Transient field-resolved spectroscopy enables the study of ultrafast dynamics with sub-cycle resolution. Previous work focused on frequencies below 50 THz, but this study implemented transient field-resolved reflectometry at 50-100 THz. The technique was demonstrated in studies of ultrafast photorefractive changes in Ge and GaAs semiconductors, exploring the resonance-free Drude response. The extended frequency range in transient field-resolved spectroscopy allows for previously inaccessible transitions to be studied in a wide range of systems.
Article
Multidisciplinary Sciences
M. Ossiander, K. Golyari, K. Scharl, L. Lehnert, F. Siegrist, J. P. Buerger, D. Zimin, J. A. Gessner, M. Weidman, I Floss, V Smejkal, S. Donsa, C. Lemell, F. Libisch, N. Karpowicz, J. Burgdoerfer, F. Krausz, M. Schultze
Summary: By utilizing light-field driven charge motion, semiconductor technology can be linked to electric fields with attosecond temporal control. The authors demonstrate the ability to sample optical fields and track charge motion driven by optical signals, by single-photon-populating the conduction band of a wide-gap dielectric and controlling the subsequent electron motion with the electric field of visible light.
NATURE COMMUNICATIONS
(2022)
Article
Chemistry, Physical
Christoph Schattauer, Milica Todorovic, Kunal Ghosh, Patrick Rinke, Florian Libisch
Summary: We apply machine learning to derive tight-binding parametrizations for the electronic structure of defects, and demonstrate the accuracy of our approach in predicting electronic structure properties in single layer graphene.
NPJ COMPUTATIONAL MATERIALS
(2022)
Article
Optics
Valerie Smejkal, Chiara Trovatello, Qiuyang Li, Stefano Dal Conte, Andrea Marini, Xiaoyang Zhu, Giulio Cerullo, Florian Libisch
Summary: Transient absorption spectroscopy is used to monitor the optical response of photoexcited semiconductors. In this study, the effect of different substrates on the transient optical response of monolayer MoS2 is investigated. It is found that interference effects caused by the substrates explain the differences observed in the transient spectra. The results highlight the significant role of the substrate in the transient response.
Article
Materials Science, Multidisciplinary
T. Johnsen, C. Schattauer, S. Samaddar, A. Weston, M. J. Hamer, K. Watanabe, T. Taniguchi, R. Gorbachev, F. Libisch, M. Morgenstern
Summary: Researchers used scanning tunneling microscopy to investigate the quantum Hall edge states of monolayer graphene and compared the results with theoretical calculations. They found that a proper choice of gate voltage allowed for accurate mapping of the edge state pattern, and observed extended compressible regions, the antinodal structure of edge states, and their meandering along the lateral interface.
Article
Materials Science, Multidisciplinary
T. Fabian, M. Kausel, L. Linhart, J. Burgdorfer, F. Libisch
Summary: The moire potential of graphene on hexagonal boron nitride creates a supercell large enough to contain a full magnetic flux quantum at experimentally accessible field strengths. By using numerical simulations, a novel approach was developed to analyze the Landau spectra of Dirac particles on graphene/hBN systems.
Article
Materials Science, Multidisciplinary
Thomas Fabian, Lukas Walzek, Joachim Burgdoerfer, Florian Libisch, George Datseris
Summary: This study identifies quasiclassical scattering states associated with well-defined quantum numbers of the valley degree of freedom specific to graphene, allowing for noiseless electron transport. Trigonal warping in the band structure of graphene due to its hexagonal lattice structure results in preferred propagation directions and scattering time delays.
Review
Chemistry, Multidisciplinary
Bipasa Samanta, Angel Morales-Garcia, Francesc Illas, Nicolae Goga, Juan Antonio Anta, Sofia Calero, Anja Bieberle-Hutter, Florian Libisch, Ana B. Munoz-Garcia, Michele Pavone, Maytal Caspary Toroker
Summary: Understanding the water splitting mechanism in photocatalysis is crucial for producing clean fuel in the future. Different theoretical methods at various scales have strengths and drawbacks, and a combination of methods is needed to model complex nano-photocatalysts accurately.
CHEMICAL SOCIETY REVIEWS
(2022)
Article
Materials Science, Multidisciplinary
Chao Lei, Lukas Linhart, Wei Qin, Florian Libisch, Allan H. MacDonald
Summary: Researchers constructed a continuum model to study twisted trilayer graphene and found that mirror symmetry plays a key role in electronic properties. They calculated characteristics such as the Drude weight and weak-field Hall conductivity, and evaluated the influence of accidental lateral stacking shifts on electronic properties in experimental devices. They also discussed the possible importance of these shifts for superconductivity in twisted trilayers.
