11 results
Search Results
Now showing 1 - 10 of 11
- ItemAuthor Correction: Ultrafast X-ray imaging of the light-induced phase transition in VO2 (Nature Physics, (2022), 10.1038/s41567-022-01848-w)(Basingstoke : Nature Publishing Group, 2023) Johnson, Allan S.; Perez-Salinas, Daniel; Siddiqui, Khalid M.; Kim, Sungwon; Choi, Sungwook; Volckaert, Klara; Majchrzak, Paulina E.; Ulstrup, Søren; Agarwal, Naman; Hallman, Kent; Haglund, Richard F.; Günther, Christian M.; Pfau, Bastian; Eisebitt, Stefan; Backes, Dirk; Maccherozzi, Francesco; Fitzpatrick, Ann; Dhesi, Sarnjeet S.; Gargiani, Pierluigi; Valvidares, Manuel; Artrith, Nongnuch; de Groot, Frank; Choi, Hyeongi; Jang, Dogeun; Katoch, Abhishek; Kwon, Soonnam; Park, Sang Han; Kim, Hyunjung; Wall, Simon E.In the version of this article initially published, the Acknowledgements was missing thanks from Soonnam Kwon for support from the National Research Foundation of Korea (NRF-2020R1A2C1007416). The error has been corrected in the HTML and PDF versions of the article.
- ItemUnconventional charge order in a co-doped high-Tc superconductor(London : Nature Publishing Group, 2016) Pelc, D.; Vucˇkovic, M.; Grafe, H.-J.; Baek, S.-H.; Požek, M.Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8xEu0.2SrxCuO4. We use three complementary experiments—nuclear quadrupole resonance, nonlinear conductivity and specific heat—to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order.
- ItemDirect evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor(London : Nature Publishing Group, 2015) Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P.K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; Morenzoni, E.; Fernandes, Rafael M.; Khasanov, R.The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.
- ItemIn situ correlation between metastable phase-transformation mechanism and kinetics in a metallic glass([London] : Nature Publishing Group, 2021) Orava, Jiri; Balachandran, Shanoob; Han, Xiaoliang; Shuleshova, Olga; Nurouzi, Ebrahim; Soldatov, Ivan; Oswald, Steffen; Gutowski, Olof; Ivashko, Oleh; Dippel, Ann-Christin; v. Zimmermann, Martin; Ivanov, Yurii P.; Greer, A. Lindsay; Raabe, Dierk; Herbig, Michael; Kaban, IvanA combination of complementary high-energy X-ray diffraction, containerless solidification during electromagnetic levitation and transmission electron microscopy is used to map in situ the phase evolution in a prototype Cu-Zr-Al glass during flash-annealing imposed at a rate ranging from 102 to 103 K s−1 and during cooling from the liquid state. Such a combination of experimental techniques provides hitherto inaccessible insight into the phase-transformation mechanism and its kinetics with high temporal resolution over the entire temperature range of the existence of the supercooled liquid. On flash-annealing, most of the formed phases represent transient (metastable) states – they crystallographically conform to their equilibrium phases but the compositions, revealed by atom probe tomography, are different. It is only the B2 CuZr phase which is represented by its equilibrium composition, and its growth is facilitated by a kinetic mechanism of Al partitioning; Al-rich precipitates of less than 10 nm in a diameter are revealed. In this work, the kinetic and chemical conditions of the high propensity of the glass for the B2 phase formation are formulated, and the multi-technique approach can be applied to map phase transformations in other metallic-glass-forming systems.
- ItemStrain derivative of thermoelectric properties as a sensitive probe for nematicity([London] : Nature Publishing Group, 2021) Caglieris, F.; Wuttke, C.; Hong, C.; Sykora, S.; Kappenberger, R.; Aswartham, S.; Wurmehl, S.; Büchner, B.; Hess, C.The nematic instability is an undebatable ingredient of the physics of iron-based superconductors. Yet, its origin remains enigmatic as it involves a fermiology with an intricate interplay of lattice-, orbital-, and spin degrees of freedom. It is well known that thermoelectric transport is an excellent probe for revealing even subtle signatures of instabilities and pertinent fluctuations. In this paper, we report a strong response of the thermoelectric transport properties of two underdoped 1111 iron-based superconductors to a vanishingly small strain. By introducing the strain derivative of the Seebeck and the Nernst coefficients, we provide a description of the nematic order parameter, proving the existence of an anisotropic Peltier-tensor beside an anisotropic conductivity tensor. Our measurements reveal that the transport nematic phenomenology is the result of the combined effect of both an anisotropic scattering time and Fermi surface distortions, pointing out that in a realistic description, abreast of the spin fluctuations also the orbital character is a fundamental ingredient. In addition, we show that nematic fluctuations universally relax in a Curie–Weiss fashion above TS in all the elasto-transport measurements and we provide evidences that nematicity must be band selective.
- ItemModulations in martensitic Heusler alloys originate from nanotwin ordering(London : Nature Publishing Group, 2018) Gruner, M.E.; Niemann, R.; Entel, P.; Pentcheva, R.; Rößler, U.K.; Nielsch, K.; Fähler, S.Heusler alloys exhibiting magnetic and martensitic transitions enable applications like magnetocaloric refrigeration and actuation based on the magnetic shape memory effect. Their outstanding functional properties depend on low hysteresis losses and low actuation fields. These are only achieved if the atomic positions deviate from a tetragonal lattice by periodic displacements. The origin of the so-called modulated structures is the subject of much controversy: They are either explained by phonon softening or adaptive nanotwinning. Here we used large-scale density functional theory calculations on the Ni2MnGa prototype system to demonstrate interaction energy between twin boundaries. Minimizing the interaction energy resulted in the experimentally observed ordered modulations at the atomic scale, it explained that a/b twin boundaries are stacking faults at the mesoscale, and contributed to the macroscopic hysteresis losses. Furthermore, we found that phonon softening paves the transformation path towards the nanotwinned martensite state. This unified both opposing concepts to explain modulated martensite.
- ItemOrdered states in the Kitaev-Heisenberg model: From 1D chains to 2D honeycomb(London : Nature Publishing Group, 2018) Agrapidis, Cliò Efthimia; van den Brink, Jeroen; Nishimoto, SatoshiWe study the ground state of the 1D Kitaev-Heisenberg (KH) model using the density-matrix renormalization group and Lanczos exact diagonalization methods. We obtain a rich ground-state phase diagram as a function of the ratio between Heisenberg (J = cosϕ) and Kitaev (K = sinϕ) interactions. Depending on the ratio, the system exhibits four long-range ordered states: ferromagnetic-z, ferromagnetic-xy, staggered-xy, Néel-z, and two liquid states: Tomonaga-Luttinger liquid and spiral-xy. The two Kitaev points ϕ=π2 and φ=3π2 are singular. The ϕ-dependent phase diagram is similar to that for the 2D honeycomb-lattice KH model. Remarkably, all the ordered states of the honeycomb-lattice KH model can be interpreted in terms of the coupled KH chains. We also discuss the magnetic structure of the K-intercalated RuCl3, a potential Kitaev material, in the framework of the 1D KH model. Furthermore, we demonstrate that the low-lying excitations of the 1D KH Hamiltonian can be explained within the combination of the known six-vertex model and spin-wave theory.
- ItemSelective mass enhancement close to the quantum critical point in BaFe2(As1−x P x )2(London : Nature Publishing Group, 2017) Grinenko, V.; Iida, K.; Kurth, F.; Efremov, D.V.; Drechsler, S.-L.; Cherniavskii, I.; Morozov, I.; Hänisch, J.; Förster, T.; Tarantini, C.; Jaroszynski, J.; Maiorov, B.; Jaime, M.; Yamamoto, A.; Nakamura, I.; Fujimoto, R.; Hatano, T.; Ikuta, H.; Hühne, R.A quantum critical point (QCP) is currently being conjectured for the BaFe2(As1−x P x )2 system at the critical value x c ≈ 0.3. In the proximity of a QCP, all thermodynamic and transport properties are expected to scale with a single characteristic energy, given by the quantum fluctuations. Such a universal behavior has not, however, been found in the superconducting upper critical field Hc2. Here we report Hc2 data for epitaxial thin films extracted from the electrical resistance measured in very high magnetic fields up to 67 Tesla. Using a multi-band analysis we find that Hc2 is sensitive to the QCP, implying a significant charge carrier effective mass enhancement at the doping-induced QCP that is essentially band-dependent. Our results point to two qualitatively different groups of electrons in BaFe2(As1−x P x )2. The first one (possibly associated to hot spots or whole Fermi sheets) has a strong mass enhancement at the QCP, and the second one is insensitive to the QCP. The observed duality could also be present in many other quantum critical systems.
- ItemInteraction-induced singular Fermi surface in a high-temperature oxypnictide superconductor(London : Nature Publishing Group, 2015) Charnukha, A.; Thirupathaiah, S.; Zabolotnyy, V.B.; Büchner, B.; Zhigadlo, N.D.; Batlogg, B.; Yaresko, A.N.; Borisenko, S.V.In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe0.92Co0.08AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.
- ItemHeavy fermion properties of the Kondo Lattice model(London : Nature Publishing Group, 2013) Sykora, Steffen; Becker, Klaus W.We study the S = 1/2 Kondo lattice model which is widely used to describe heavy fermion behavior. In conventional treatments of the model the Kondo interaction is decoupled in favour of a hybridization of conduction and localized f electrons. However, such an approximation breaks the local gauge symmetry and implicates that the local f-occupation is no longer conserved. To avoid these problems, we use in this work an alternative approach to the model based on the Projective Renormalization Method (PRM). Thereby, within the conduction electron spectral function we identify the lattice Kondo resonance as an almost flat excitation near the Fermi surface which is composed of conduction electron creation operators combined with localized spin fluctuations. This leads to an alternative description of the Kondo resonance without having to resort to an artificial symmetry breaking.