Compositional tuning in sputter-grown highly-oriented Bi-Te films and their optical and electronic structures

Phase-change behavior of RuSbTe thin film for photonic applications with amplitude-only modulation

Ge2Sb2Te5 (GST), the most mature phase-change materials (PCM), functions as a recoding layer in nonvolatile memory and optical discs by contrasting the physical properties upon phase transition between amorphous and crystalline phases. However, GST faces challenges such as a large extinction coefficient (k) and low thermal stability of the amorphous phase. In this study, we introduce RuSbTe as a new PCM to address the GST concerns. Notably, the crystallization temperature of the amorphous RuSbTe is approximately 350 °C, significantly higher than GST. A one-order-of-magnitude increase in the resistivity contrast was observed upon phase transition. The crystalline (0.35-0.50 eV) and amorphous (0.26-0.37 eV) phases exhibit relatively small band gap values, resulting in substantial k. Although RuSbTe demonstrates a k difference of approximately 1 upon crystallization at the telecommunications C-band, the refractive index (n) difference is negligible. Unlike GST, which induces both phase retardation and amplitude modulation in its optical switch device, RuSbTe exhibits amplitude-only modulation. This study suggests that RuSbTe has the potential to enable new photonic computing devices that can independently control the phase and amplitude. Combining RuSbTe with phase-only modulators could open avenues for advanced applications.

Supercurrent in Bi4Te3 Topological Material-Based Three-Terminal Junctions

In this paper, in an in situ prepared three-terminal Josephson junction based on the topological insulator Bi4Te3 and the superconductor Nb the transport properties are studied. The differential resistance maps as a function of two bias currents reveal extended areas of Josephson supercurrent, including coupling effects between adjacent superconducting electrodes. The observed dynamics for the coupling of the junctions is interpreted using a numerical simulation of a similar geometry based on a resistively and capacitively shunted Josephson junction model. The temperature dependency indicates that the device behaves similar to prior experiments with single Josephson junctions comprising topological insulators' weak links. Irradiating radio frequencies to the junction, we find a spectrum of integer Shapiro steps and an additional fractional step, which is interpreted with a skewed current-phase relationship. In a perpendicular magnetic field, we observe Fraunhofer-like interference patterns in the switching currents.

Polymorphism in Post-Dichalcogenide Two-Dimensional Materials

Two-dimensional (2D) materials exhibit a wide range of atomic structures, compositions, and associated versatility of properties. Furthermore, for a given composition, a variety of different crystal structures (i.e., polymorphs) can be observed. Polymorphism in 2D materials presents a fertile landscape for designing novel architectures and imparting new functionalities. The objective of this Review is to identify the polymorphs of emerging 2D materials, describe their polymorph-dependent properties, and outline methods used for polymorph control. Since traditional 2D materials (e.g., graphene, hexagonal boron nitride, and transition metal dichalcogenides) have already been studied extensively, the focus here is on polymorphism in post-dichalcogenide 2D materials including group III, IV, and V elemental 2D materials, layered group III, IV, and V metal chalcogenides, and 2D transition metal halides. In addition to providing a comprehensive survey of recent experimental and theoretical literature, this Review identifies the most promising opportunities for future research including how 2D polymorph engineering can provide a pathway to materials by design.