Tunable electronic properties of GaS-SnS2 heterostructure by strain and electric field

Vertically stacked heterostructures have received extensive attention because of their tunable electronic structures and outstanding optical properties. In this work, we have studied the structural, electronic and optical properties of vertically stacked GaS-SnS2 heterostructure under the frame of density functional theory. We find that the stacked GaS-SnS2 heterostructure is a semiconductor with suitable indirect band gaps of 1.82 eV, exhibiting a type-II band alignment for easily separating the photo-generated carriers. The electronic properties of GaS-SnS2 heterostructure can be effectively tuned by external strain and electric field. The optical absorption of GaS-SnS2 heterostructure is more enhanced by comparison with the GaS monolayer and SnS2 monolayer in the visible light. Our results suggest that GaS-SnS2 heterostructure is a promising candidate for the photocatalyst and photoelectronic devices in visible light.

Elastic Slow Dynamics in Polycrystalline Metal Alloys

Elastic slow dynamics, consisting in a reversible softening of materials when an external strain is applied, was experimentally observed in polycrystalline metals and presents analogies with the same phenomenon more widely observed in consolidated granular media. Since the effect is extremely small in metals, precise experimental techniques are needed. Reliable measurement of relative velocity variations of the order of 10−7 is crucial to perform the analysis. In addition, the grain structure and the nature of grain boundaries in metals is very different from that in rocks or concrete. Therefore, linking relaxation elastic effects to the microstructure is needed to understand the physical origin of slow dynamics in metals. Here, interpreting the relaxation phenomenon as a multirelaxation process, we show that it is sensitive to the spatial scale at the microstructural level, up to the point of allowing the identification of the existence of features at different spatial scales, particularly distinguishing damage from microstructural inhomogeneities.

Universality of ultrasonic attenuation coefficient of amorphous systems at low temperatures

The competition between unretarded dispersion interactions between molecules prevailing at medium range order length scales and their phonon induced coupling at larger scales leads to appearance of nano-scale sub structures in amorphous systems. The complexity of intermolecular interactions gives rise to randomization of their operators. Based on a random matrix modelling of the Hamiltonian and its linear response to an external strain field, we show that the ultrasonic attenuation coefficient can be expressed as a ratio of two crucial length-scales related to molecular dynamics. A nearly constant value of the ratio for a wide range of materials then provides a theoretical explanation of the experimentally observed qualitative universality of the ultrasonic attenuation coefficient at low temperatures.

A First-Principle Study of Monolayer Transition Metal Carbon Trichalcogenides

Monolayer MnCX3 metal–carbon trichalcogenides have been investigated by using the first-principle calculations. The compounds show half-metallic ferromagnetic characters. Our results reveal that their electronic and magnetic properties can be altered by applying uniaxial or biaxial strain. By tuning the strength of the external strain, the electronic bandgap and magnetic ordering of the compounds change and result in a phase transition from the half-metallic to the semiconducting phase. Furthermore, the vibrational and thermodynamic stability of the two-dimensional structure has been verified by calculating the phonon dispersion and molecular dynamics. Our study paves guidance for the potential applications of these two mono-layers in the future for spintronics and straintronics devices.

Global strain-induced scalar potential in graphene devices

By mechanically distorting a crystal lattice it is possible to engineer the electronic and optical properties of a material. In graphene, one of the major effects of such a distortion is an energy shift of the Dirac point, often described as a scalar potential. We demonstrate how such a scalar potential can be generated systematically over an entire electronic device and how the resulting changes in the graphene work function can be detected in transport experiments. Combined with Raman spectroscopy, we obtain a characteristic scalar potential consistent with recent theoretical estimates. This direct evidence for a scalar potential on a macroscopic scale due to deterministically generated strain in graphene paves the way for engineering the optical and electronic properties of graphene and similar materials by using external strain.

Highly tunable magneto-optical response from magnesium-vacancy color centers in diamond

Defect quantum bits (qubits) constitute an important emerging technology. However, it is necessary to explore new types of defects to enable large-scale applications. In this article, we examine the potential of magnesium-vacancy (MgV) in diamond to operate as a qubit by computing the key electronic- and spin properties with robust theoretical methods. We find that the electronic structure of MgV permits the coexistence of two loosely separated spin-states, where both can emerge as a ground state and be interconverted depending on the temperature and external strain. These results demonstrate a route to control the magneto-optical response of a qubit by modulating the operational conditions.