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- ItemCoulomb exchange as source of Kitaev and off-diagonal symmetric anisotropic couplings(London : Springer Nature, 2024) Bhattacharyya, Pritam; Petersen, Thorben; Bogdanov, Nikolay A.; Hozoi, LiviuExchange underpins the magnetic properties of quantum matter. In its most basic form, it occurs through the interplay of Pauli’s exclusion principle and Coulomb repulsion, being referred to as Coulomb or direct exchange. Pauli’s exclusion principle combined with inter-atomic electron hopping additionally leads to kinetic exchange and superexchange. Here we disentangle the different exchange channels in anisotropic Kitaev–Heisenberg context. By quantum chemical computations, we show that anisotropic Coulomb exchange, completely neglected so far in the field, may be as large as (or even larger than) other contributions — kinetic exchange and superexchange. This opens new perspectives onto anisotropic exchange mechanisms and sets the proper conceptual framework for further research on tuning Kitaev–Heisenberg magnetism.
- ItemImpacts of meeting minimum access on critical earth systems amidst the Great Inequality(London : Springer Nature, 2022) Rammelt, Crelis F.; Gupta, Joyeeta; Liverman, Diana; Scholtens, Joeri; Ciobanu, Daniel; Abrams, Jesse F.; Bai, Xuemei; Gifford, Lauren; Gordon, Christopher; Hurlbert, Margot; Inoue, Cristina Y. A.; Jacobson, Lisa; Lade, Steven J.; Lenton, Timothy M.; McKay, David I. Armstrong; Nakicenovic, Nebojsa; Okereke, Chukwumerije; Otto, Ilona M.; Pereira, Laura M.; Prodani, Klaudia; Rockström, Johan; Stewart-Koster, Ben; Verburg, Peter H.; Zimm, CarolineThe Sustainable Development Goals aim to improve access to resources and services, reduce environmental degradation, eradicate poverty and reduce inequality. However, the magnitude of the environmental burden that would arise from meeting the needs of the poorest is under debate—especially when compared to much larger burdens from the rich. We show that the ‘Great Acceleration’ of human impacts was characterized by a ‘Great Inequality’ in using and damaging the environment. We then operationalize ‘just access’ to minimum energy, water, food and infrastructure. We show that achieving just access in 2018, with existing inequalities, technologies and behaviours, would have produced 2–26% additional impacts on the Earth’s natural systems of climate, water, land and nutrients—thus further crossing planetary boundaries. These hypothetical impacts, caused by about a third of humanity, equalled those caused by the wealthiest 1–4%. Technological and behavioural changes thus far, while important, did not deliver just access within a stable Earth system. Achieving these goals therefore calls for a radical redistribution of resources.
- ItemCoupled mechanical oscillator enables precise detection of nanowire flexural vibrations(London : Springer Nature, 2023) Sharma, Maneesha; Sathyadharma Prasad, Aniruddha; Freitag, Norbert H.; Büchner, Bernd; Mühl, ThomasThe field of nanowire (NW) technology represents an exciting and steadily growing research area with applications in ultra-sensitive mass and force sensing. Existing detection methods for NW deflection and oscillation include optical and field emission approaches. However, they are challenging for detecting small diameter NWs because of the heating produced by the laser beam and the impact of the high electric field. Alternatively, the deflection of a NW can be detected indirectly by co-resonantly coupling the NW to a cantilever and measuring it using a scanning probe microscope. Here, we prove experimentally that co-resonantly coupled devices are sensitive to small force derivatives similar to standalone NWs. We detect force derivatives as small as 10−9 N/m with a bandwidth of 1 Hz at room temperature. Furthermore, the measured hybrid vibration modes show clear signatures of avoided crossing. The detection technique presented in this work verifies a major step in boosting NW-based force and mass sensing.
- ItemQuantum critical fluctuations in an Fe-based superconductor(London : Springer Nature, 2022) Jost, Daniel; Peis, Leander; He, Ge; Baum, Andreas; Geprägs, Stephan; Palmstrom, Johanna C.; Ikeda, Matthias S.; Fisher, Ian R.; Wolf, Thomas; Lederer, Samuel; Kivelson, Steven A.; Hackl, RudiQuantum critical fluctuations may prove to play an instrumental role in the formation of unconventional superconductivity. Here, we show that the characteristic scaling of a marginal Fermi liquid is present in inelastic light scattering data of an Fe-based superconductor tuned through a quantum critical point (QCP) by chemical substitution or doping. From the doping dependence of the imaginary time dynamics we are able to distinguish regions dominated by quantum critical behavior from those having classical critical responses. This dichotomy reveals a connection between the marginal Fermi liquid behavior and quantum criticality. In particular, the overlap between regions of high superconducting transition temperatures and quantum critical scaling suggests a contribution from quantum fluctuations to the formation of superconductivity.
- ItemAll-optical supercontinuum switching(London : Springer Nature, 2020) Melchert, Oliver; Brée, Carsten; Tajalli, Ayhan; Pape, Alexander; Arkhipov, Rostislav; Willms, Stephanie; Babushkin, Ihar; Skryabin, Dmitry; Steinmeyer, Günter; Morgner, Uwe; Demircan, AyhanEfficient all-optical switching is a challenging task as photons are bosons and cannot immediately interact with each other. Consequently, one has to resort to nonlinear optical interactions, with the Kerr gate being the classical example. However, the latter requires strong pulses to switch weaker ones. Numerous approaches have been investigated to overcome the resulting lack of fan-out capability of all-optical switches, most of which relied on types of resonant enhancement of light-matter interaction. Here we experimentally demonstrate a novel approach that utilizes switching between different portions of soliton fission induced supercontinua, exploiting an optical event horizon. This concept enables a high switching efficiency and contrast in a dissipation free setting. Our approach enables fan-out, does not require critical biasing, and is at least partially cascadable. Controlling complex soliton dynamics paves the way towards building all-optical logic gates with advanced functionalities. © 2020, The Author(s).
- ItemNucleation of jet engine oil vapours is a large source of aviation-related ultrafine particles(London : Springer Nature, 2022) Ungeheuer, Florian; Caudillo, Lucía; Ditas, Florian; Simon, Mario; van Pinxteren, Dominik; Kılıç, Doğuşhan; Rose, Diana; Jacobi, Stefan; Kürten, Andreas; Curtius, Joachim; Vogel, Alexander L.Large airports are a major source of ultrafine particles, which spread across densely populated residential areas, affecting air quality and human health. Jet engine lubrication oils are detectable in aviation-related ultrafine particles, however, their role in particle formation and growth remains unclear. Here we show the volatility and new-particle-formation ability of a common synthetic jet oil, and the quantified oil fraction in ambient ultrafine particles downwind of Frankfurt International Airport, Germany. We find that the oil mass fraction is largest in the smallest particles (10-18 nm) with 21% on average. Combining ambient particle-phase concentration and volatility of the jet oil compounds, we determine a lower-limit saturation ratio larger than 1 × 105 for ultra-low volatility organic compounds. This indicates that the oil is an efficient nucleation agent. Our results demonstrate that jet oil nucleation is an important mechanism that can explain the abundant observations of high number concentrations of non-refractory ultrafine particles near airports.
- ItemGlobal perturbation of stratospheric water and aerosol burden by Hunga eruption(London : Springer Nature, 2022) Khaykin, Sergey; Podglajen, Aurelien; Ploeger, Felix; Grooß, Jens-Uwe; Tence, Florent; Bekki, Slimane; Khlopenkov, Konstantin; Bedka, Kristopher; Rieger, Landon; Baron, Alexandre; Godin-Beekmann, Sophie; Legras, Bernard; Sellitto, Pasquale; Sakai, Tetsu; Barnes, John; Uchino, Osamu; Morino, Isamu; Nagai, Tomohiro; Wing, Robin; Baumgarten, Gerd; Gerding, Michael; Duflot, Valentin; Payen, Guillaume; Jumelet, Julien; Querel, Richard; Liley, Ben; Bourassa, Adam; Clouser, Benjamin; Feofilov, Artem; Hauchecorne, Alain; Ravetta, FrançoisThe eruption of the submarine Hunga volcano in January 2022 was associated with a powerful blast that injected volcanic material to altitudes up to 58 km. From a combination of various types of satellite and ground-based observations supported by transport modeling, we show evidence for an unprecedented increase in the global stratospheric water mass by 13% relative to climatological levels, and a 5-fold increase of stratospheric aerosol load, the highest in the last three decades. Owing to the extreme injection altitude, the volcanic plume circumnavigated the Earth in only 1 week and dispersed nearly pole-to-pole in three months. The unique nature and magnitude of the global stratospheric perturbation by the Hunga eruption ranks it among the most remarkable climatic events in the modern observation era, with a range of potential long-lasting repercussions for stratospheric composition and climate.
- ItemMagnetization-driven Lifshitz transition and charge-spin coupling in the kagome metal YMn6Sn6(London : Springer Nature, 2022) Siegfried, Peter E.; Bhandari, Hari; Jones, David C.; Ghimire, Madhav P.; Dally, Rebecca L.; Poudel, Lekh; Bleuel, Markus; Lynn, Jeffrey W.; Mazin, Igor I.; Ghimire, Nirmal J.The Fermi surface (FS) is essential for understanding the properties of metals. It can change under both conventional symmetry-breaking phase transitions and Lifshitz transitions (LTs), where the FS, but not the crystal symmetry, changes abruptly. Magnetic phase transitions involving uniformly rotating spin textures are conventional in nature, requiring strong spin-orbit coupling (SOC) to influence the FS topology and generate measurable properties. LTs driven by a continuously varying magnetization are rarely discussed. Here we present two such manifestations in the magnetotransport of the kagome magnet YMn6Sn6: one caused by changes in the magnetic structure and another by a magnetization-driven LT. The former yields a 10% magnetoresistance enhancement without a strong SOC, while the latter a 45% reduction in the resistivity. These phenomena offer a unique view into the interplay of magnetism and electronic topology, and for understanding the rare-earth counterparts, such as TbMn6Sn6, recently shown to harbor correlated topological physics.
- ItemStabilization mechanism of molecular orbital crystals in IrTe2(London : Springer Nature, 2022) Ritschel, Tobias; Stahl, Quirin; Kusch, Maximilian; Trinckauf, Jan; Garbarino, Gaston; Svitlyk, Volodymyr; Mezouar, Mohamed; Yang, Junjie; Cheong, Sang-Wook; Geck, JochenDoped IrTe2 is considered a platform for topological superconductivity and therefore receives currently a lot of interest. In addition, the superconductivity in these materials exists in close vicinity to electronic order and the formation of molecular orbital crystals, which we explore here by means of high-pressure single crystal x-ray diffraction in combination with density functional theory. Our crystallographic refinements provide detailed information about the structural evolution as a function of applied pressure up to 42 GPa. Using this structural information for density functional theory calculations, we show that the local multicenter bonding in IrTe2 is driven by changes in the Ir-Te-Ir bond angle. When the electronic order sets in, this bond angle decreases drastically, leading to a stabilization of a multicenter molecular orbital bond. This unusual local mechanism of bond formation in an itinerant material provides a natural explanation for the different electronic orders in IrTe2. It further illustrates the strong coupling of the electrons with the lattice and is most likely relevant for the superconductivity in this material.
- ItemExperimental realization of a 12,000-finesse laser cavity based on a low-noise microstructured mirror(London : Springer Nature, 2023) Dickmann, Johannes; Sauer, Steffen; Meyer, Jan; Gaedtke, Mika; Siefke, Thomas; Brückner, Uwe; Plentz, Jonathan; Kroker, StefanieThe most precise measurement tools of humankind are equipped with ultra-stable lasers. State-of-the-art laser stabilization techniques are based on external cavities, that are limited by noise originated in the coatings of the cavity mirrors. Microstructured mirror coatings (so-called meta-mirrors) are a promising technology to overcome the limitations of coating noise and therewith pave the way towards next-generation ultra-stable lasers. We present experimental realization of a 12,000-finesse optical cavity based on one low-noise meta-mirror. The use of the mirrors studied here in cryogenic silicon cavities represents an order of magnitude reduction in the current limiting mirror noise, such that the stability limit due to fundamental noise can be reduced to 5 × 10−18.
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