Tailoring Materials for Mottronics: Excess Oxygen Doping of a Prototypical Mott Insulator

The Mott transistor is a paradigm for a new class of electronic devices—often referred to by the term Mottronics—which are based on charge correlations between the electrons. Since correlation‐induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal–insulator transition to be switched by electric gating. Here, it is demonstrated that thin films of the prototypical Mott insulator LaTiO₃ grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band‐filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO_3+x thin films making it a promising channel material in future Mottronic devices.     

Pain therapy after thoracotomies--systemic patient-controlled analgesia (PCA) with opioid versus intercostal block and interpleural analgesia

Both regional analgesia and systemic opioid therapy (e.g. PCA) are commonly used for pain relief following thoracic surgery. Many anaesthesiologists are reluctant to use thoracic epidural analgesia on general surgical wards. Therefore, we investigated in a prospective randomised study the efficacy of intercostal blocks (ICB) or interpleural analgesia (IPA) compared to PCA with systemic opioids (PCA). Following ethics committee approval and informed consent, 45 thoracotomy patients were randomised for postoperative pain management: group 1: intravenous PCA with piritramide (PCA-control), group 2: intercostal blocks of the segments concerned with 5 ml bupivacaine 0.5% at the end of surgery and 6 hours thereafter (ICB), group 3: interpleural analgesia with 20 ml bupivacaine 0.25% applied every 4 hours using a catheter placed during surgery near the apex of the pleural space (IPA). Patients in the ICB and IPA groups were able to obtain additional pain relief by PCA with piritramide. Alternative medication for all groups in case of insufficient analgesia was metamizol. Both regional analgesia groups used significantly less piritramide up to the 3rd (IPA) or 7th (ICB) postoperative day than the control group (p < 0.05). The consumption of metamizol was lower as well (n. s.). No significant differences between the study groups were observed with regard to pain scores (visual analogue scale VAS) at rest, during deep inspiration, coughing or mobilisation. Respiratory parameters as forced vital capacity, forced expiratory volume (1 sec) and peak flow (FVC; FEV1; PF) were reduced significantly following thoracotomy and showed a slow restitution in all three study groups without major inter-group differences. Intercostal blocks and interpleural analgesia significantly reduce opioid demand following thoracotomy and are effective means of postoperative pain management. Nevertheless, in contrast to epidural analgesia, both methods have to be supplemented by, or combined with, systemic analgesics in most patients. On the other hand, compared to epidural analgesia, ICB and IPA are less invasive and easier to manage on general surgical wards.     

A Living‐Dead Magnetic Layer at the Surface of Ferrimagnetic DyTiO3 Thin Films

When ferromagnetic films become ultrathin, key properties such as the Curie temperature and the saturation magnetization are usually depressed. This effect is thoroughly investigated in magnetic oxides such as half‐metallic manganites, but much less in ferrimagnetic insulating perovskites such as rare‐earth titanates RTiO₃, despite their appeal to design correlated 2D electron gases. Here, the magnetic properties of epitaxial DyTiO₃ thin films are reported. While films thicker than about 50 nm show a bulk‐like response, at low thickness a surprising increase of the saturation magnetization is observed. This behavior is described using a classical model of a “dead layer” but assuming that this layer is actually “living,” that is, it responds to the magnetic field with a strong paramagnetic susceptibility. Through depth‐dependent X‐ray absorption and photoemission spectroscopy, it is shown that the “living‐dead layer” corresponds to surface regions where magnetic (S = 1/2) Ti³⁺ ions are replaced by nonmagnetic Ti⁴⁺ ions. Hysteresis cycles at the Dy M₅ and Ti L₃ edges indicate that the surface Ti⁴⁺ ions decouple the Dy³⁺ ions, thus unleashing their strong paramagnetic response. Finally, it is shown how capping the DyTiO₃ film can help increase the Ti³⁺ content near the surface and thus recover a better ferrimagnetic behavior.     

Accelerated MINFLUX Nanoscopy,through Spontaneously Fast-Blinking Fluorophores

The introduction of MINFLUX nanoscopy allows single molecules to be localized with one nanometer precision in as little as one millisecond. However, current applications have so far focused on increasing this precision by optimizing photon collection, rather than minimizing the localization time. Concurrently, commonly used fluorescent switches are specifically designed for stochastic methods (e.g., STORM), optimized for a high photon yield and rather long on-times (tens of milliseconds). Here, accelerated MINFLUX nanoscopy with up to a 30-fold gain in localization speed is presented. The improvement is attained by designing spontaneously blinking fluorescent markers with remarkably fast on-times, down to 1–3 ms, matching the iterative localization process used in a MINFLUX microscope. This design utilizes a silicon rhodamine amide core, shifting the spirocyclization equilibrium toward an uncharged closed form at physiological conditions and imparting intact live cell permeability, modified with a fused (benzo)thiophene spirolactam fragment. The best candidate for MINFLUX microscopy (also suitable for STORM imaging) is selected through detailed characterization of the blinking behavior of single fluorophores, bound to different protein tags. Finally, optimization of the localization routines, customized to the fast blinking times, renders a significant speed improvement on a commercial MINFLUX microscope.