Several studies propose two-dimensional (2D) materials as candidates for spintronic and valleytronic devices. The capability to access two well-defined spin-valley polarization states is the main factor for a good spin-valleytronic device. Each 2D material possesses certain characteristics that can improve the spin-valley polarization. Here, we study the spin and valley transport properties in single ferromagnetic 1T'-MoS2 junctions. The transmission probabilities are calculated with the transfer matrix method. The Landauer-B & uuml;ttiker formalism is used to compute the conductance. We take into account an external electric field to modulate the band gap of the 1T'-MoS2 monolayer. Also, the proximity effect originating from the ferromagnetic layer interaction with the 1T'-MoS2 monolayer is considered. The combination of both the external electric field and the proximity effect gives rise to two well-defined positive and negative spin-valley polarization states. These findings indicate that the proposed system can be suitable for spintronic and valleytronic devices.
Conventional Peierls theory cannot fully capture the thermal transport in strongly anharmonic compounds (e.g., lead-free halide double perovskites) because it does not account for the significant wavelike behavior of phonons-a consequence of their inherent capability to interfere and tunnel. Here, we elucidate the mechanism behind the ultralow lattice thermal conductivity in model systems Cs2AgInCl6 and Cs2AgInBr6 through a combined evaluation of the particlelike and wavelike thermal transport channels. The rattling vibrations of Cs atoms suppress the particlelike channel through enhanced anharmonicity and promote the wavelike channel by flattening phonon branches to enhance coherence. Furthermore, the T1g rotational mode of the InX6 octahedron induces stronger quartic anharmonicity in Cs2AgInBr6 than in Cs2AgInCl6, which primarily enhances four-phonon scattering processes to further suppress the particlelike channel. In contrast, the wavelike contributions in both compounds remain comparable due to a compensating effect between the stronger coherent coupling in Cs2AgInBr6 and the larger group velocities in Cs2AgInCl6. Overall, the dominance of the wavelike channel is more pronounced in Cs2AgInBr6. Finally, the dominant wavelike contribution leads to a markedly weaker temperature dependence of the total thermal conductivity in both compounds, which is more notable in Cs2AgInBr6 with a scaling exponent of T-0.19 compared to T-0.52 in Cs2AgInCl6. Our work establishes the wavelike channel as a vital mechanism for thermal transport in lead-free halide double perovskites, providing novel insights into their fundamental thermal properties.
Contrary to traditional approaches, high entropy oxides (HEOs) strategically employ cationic disorder to engineer tunable functionalities. This disorder, stemming from multiple elements at the same crystallographic site, disrupts local symmetry and induces local distortions. By investigating a series of single-crystalline [La0.2Pr0.2Nd0.2Sm0.2Eu0.2]NiO3-delta thin films, grown by pulsed laser deposition, we demonstrate herein that the creation of oxygen vacancies (OVs) further offers a powerful means of tailoring electronic behavior of HEOs by concurrently introducing disorder and doping electrons into the system. Increasing OV concentration via changing the oxygen partial pressure during the ablation leads to a monotonic increase in room-temperature sheet resistance. A striking feature is the Janus-faced response of the metal-insulator transition (MIT) due to the interplay among correlation energy scales, electron doping, and disorder. Unlike the monotonous influence of OV observed for the MIT in VO2 and V2O3, initial OV doping lowers the MIT temperature here, whereas higher OV levels completely suppress the metallic phase. Magnetotransport measurements further reveal weak localization, and strong localization as a function of relative change in delta. Moreover, the disorder on both RE and oxygen sublattices is responsible for the Mott-Anderson insulator state. These findings surpass the scope of the recently featured "electron antidoping" effect.
The study of electron hydrodynamics provides a powerful framework for understanding transport in ultraclean conductors, yet experimental evidence has thus far been largely restricted to the linear response regime. Here, we report the direct observation of a strongly nonlinear transport regime in a high-mobility two-dimensional electron system. By engineering devices in a Venturi-shaped (wedge) geometry specifically designed to enhance convective nonlinearities, we uncover a pronounced nonlinear voltage response and a large diodicity in the current-voltage characteristics. Our experimental findings show quantitative agreement with a theoretical model that attributes the observed nonlinearity to the convective acceleration of the electron fluid, analogous to the Bernoulli effect. These results provide compelling evidence for the applicability of the hydrodynamic framework to electron transport in two dimensions and open avenues for exploring nonlinear and preturbulent phenomena in solid-state systems.
The current through a small contact between two 2D regions is theoretically studied. The electron gas viscosity that arises due to electron-electron and electron-impurity scattering is considered. It is found the electron flow corresponds to the ideal Fermi-liquid model rather than the ideal gas one at strong viscosity. It is shown that an electron density inhomogeneity results in the finite contact resistance of the almost ideal flow of the electron gas. The temperature dependence of the resistance is found. The agreement between theory and experiment is discussed.
