Compatible layers bring benefits
Related Articles
Ultrafast exciton-phonon coupling and energy transfer dynamics in quasi-2D layered Ruddlesden-Popper perovskites
Understanding the performance of perovskite solar cells is critical for advancing sustainable energy solutions. Hot-drop casted quasi-2D Ruddlesden-Popper perovskites (RPPs) exhibit remarkable efficiency and stability, making them promising for commercial applications. However, the ultrafast energy transfer and exciton-phonon interactions in these materials remain unclear. Here, we show that using advanced techniques like two-dimensional electronic spectroscopy (2DES) and transient grating (TG), we can unravel energy dynamics in hot-drop casted RPP films. Our study reveals rapid energy transfer between perovskite layers occurring within 100–220 femtoseconds and highlights how exciton-phonon coupling drives structural changes in the material. Coherent vibrational signals identify key lattice and organic cation modes, providing insights into their role in energy dissipation. These findings deepen our understanding of how 2D perovskites work and pave the way for improving the efficiency and stability of next-generation optoelectronic devices.
Neurophysiological insights into catecholamine-dependent tDCS modulation of cognitive control
Goal-directed behavior requires resolving both consciously and subconsciously induced response conflicts. Neuronal gain control, which enhances processing efficacy, is crucial for conflict resolution and can be increased through pharmacological or brain stimulation interventions, though it faces inherent physical limits. This study examined the effects of anodal transcranial direct current stimulation (atDCS) and methylphenidate (MPH) on conflict processing. Healthy adults (n = 105) performed a flanker task, with electroencephalography (EEG) used to assess alpha and theta band activity (ABA, TBA). Results showed that combining atDCS with MPH enhanced cognitive control and reduced response conflicts more effectively than atDCS alone, particularly when both conflict types co-occurred. Both atDCS and atDCS + MPH exhibited similar task-induced ABA and TBA modulations in the (pre)supplementary motor area, indicating heightened gain control. Overlapping neuroanatomical effects in mid-superior frontal areas suggest that atDCS and MPH share a common neuronal mechanism of gain control, especially in high-conflict/-demand situations.
Switching on and off the spin polarization of the conduction band in antiferromagnetic bilayer transistors
Antiferromagnetic conductors with suitably broken spatial symmetries host spin-polarized bands, which lead to transport phenomena commonly observed in metallic ferromagnets. In bulk materials, it is the given crystalline structure that determines whether symmetries are broken and spin-polarized bands are present. Here we show that, in the two-dimensional limit, an electric field can control the relevant symmetries. To this end, we fabricate a double-gate transistor based on bilayers of van der Waals antiferromagnetic semiconductor CrPS4 and show how a perpendicular electric displacement field can switch the spin polarization of the conduction band on and off. Because conduction band states with opposite spin polarizations are hosted in the different layers and are spatially separated, these devices also give control over the magnetization of the electrons that are accumulated electrostatically. Our experiments show that double-gated CrPS4 transistors provide a viable platform to create gate-induced conductors with near unity spin polarization at the Fermi level, as well as devices with a full electrostatic control of the total magnetization of the system.
Folded pseudochiral Fermi surface in 4Hb-TaSe2 from band hybridization with a charge density wave
Stacking of strongly-correlated 2D materials is opening the possibility to demonstrate novel electronic or magnetic ordering phenomena. In this regard the intrinsic polytypism of tantalum dichalcogenides has emerged as a platform to generate clean and controllable material interfaces. Here, we report on the Fermi surface of 4Hb-TaSe2, a polytype which consists of alternately stacked layers with octahedral (T) and trigonal prismatic (H) coordination of tantalum in the Se-Ta-Se layers. The material is known to host a charge density wave (CDW) phase with star clusters in the T-layers, intercalated by metallic H-layers, but its momentum resolved electronic structure remains undetermined. Using selective area angle resolved photoemission spectroscopy on the T termination combined with ab initio calculations, we unveil a finely structured Fermi surface arising from band folding in the reconstructed Brillouin zone caused by the CDW star clusters. The star-shaped Fermi surface is rotated away from the high-symmetry directions of the normal phase, and exhibits pseudochirality. Theoretical analysis supports the metallic nature of the system and interlayer interactions leading to hybridization. The work provides a detailed overview on the impact of band hybridization with the CDW on the Fermi surface of a material for new phases of quantum matter.
Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization
Magnetic random-access memory that uses magnetic tunnel junction memory cells is a high-performance, non-volatile memory technology that goes beyond traditional charge-based memories. Today, its speed is limited by the high magnetization of the memory storage layer. Here we prepare magnetic tunnel junction memory devices with a low magnetization ferrimagnetic Heusler alloy Mn3Ge as the memory storage layer on technologically relevant amorphous substrates using a combination of a nitride seed layer and a chemical templating layer. We switch the magnetic state of the storage layer with nanosecond long write pulses at a reliable write error rate of 10−7 and detect a tunnelling magnetoresistance of 87% at ambient temperature. These results provide a strategy towards lower write switching currents using ferrimagnetic Heusler materials and, therefore, to the scaling of high-performance magnetic random-access memories beyond those nodes possible with ferromagnetic memory layers.
Responses