PT-Symmetry-Enabled Spin Circular Photogalvanic Effect in Antiferromagnetic Insulators.

The short timescale spin dynamics in antiferromagnets is an attractive feature from the standpoint of ultrafast spintronics. Yet generating highly polarized spin current at room temperature remains a fundamental challenge for antiferromagnets. We propose a spin circular photogalvanic effect (spin CPGE), in which circularly polarized light can produce a highly spin-polarized current at room temperature, through an "injection-current-like" mechanism in parity-time (PT)-symmetric antiferromagnetic (AFM) insulators.

Switchable Enhanced Spin Photocurrent in Rashba and Cubic Dresselhaus Ferroelectric Semiconductors.

Generating and controlling spin current (SC) are of central interest in spin physics and applications. To date, the spin-orbit interaction (SOI) is an established pathway to generate SC through the spin-charge current conversion. We predict an efficient spin-light conversion via the Rashba and higher-order cubic Dresselhaus SOIs in ferroelectrics.

Meron-like topological spin defects in monolayer CrCl.

Noncollinear spin textures in low-dimensional magnetic systems have been studied for decades because of their extraordinary properties and promising applications derived from the chirality and topological nature. However, material realizations of topological spin states are still limited. Employing first-principles and Monte Carlo simulations, we propose that monolayer chromium trichloride (CrCl) can be a promising candidate for observing the vortex/antivortex type of topological defects, so-called merons.

Mechanism of Extreme Optical Nonlinearities in Spiral WS above the Bandgap.

Layered two-dimensional transition-metal dichalcogenides (2D-TMDs) are promising building blocks for ultracompact optoelectronic applications. Recently, a strong second harmonic generation (SHG) was observed in spiral stacked TMD nanostructures which was explained by its low crystal symmetry. However, the relationship between the efficiency of SHG signals and the electronic band structure remains unclear.

Artificial Multiferroics and Enhanced Magnetoelectric Effect in van der Waals Heterostructures.

Multiferroic materials with coupled ferroelectric (FE) and ferromagnetic (FM) properties are important for multifunctional devices because of their potential ability of controlling magnetism via electric field and vice versa. The recent discoveries of two-dimensional (2D) FM and FE materials have ignited tremendous research interest and aroused hope to search for 2D multiferroics. However, intrinsic 2D multiferroic materials and, particularly, those with strong magnetoelectric couplings are still rare to date.

Many-Body Effect and Device Performance Limit of Monolayer InSe.

Due to a higher environmental stability than few-layer black phosphorus and a higher carrier mobility than few-layer dichalcogenides, two-dimensional (2D) semiconductor InSe has become quite a promising channel material for the next-generation field-effect transistors (FETs). Here, we provide the investigation of the many-body effect and transistor performance scaling of monolayer (ML) InSe based on ab initio GW-Bethe-Salpeter equation approaches and quantum transport simulations, respectively. The fundamental band gap of ML InSe is indirect and 2.

Ferroelectricity and Phase Transitions in Monolayer Group-IV Monochalcogenides.

Ferroelectricity usually fades away as materials are thinned down below a critical value. We reveal that the unique ionic-potential anharmonicity can induce spontaneous in-plane electrical polarization and ferroelectricity in monolayer group-IV monochalcogenides MX (M=Ge, Sn; X=S, Se). An effective Hamiltonian has been successfully extracted from the parametrized energy space, making it possible to study the ferroelectric phase transitions in a single-atom layer.

Quantum oscillations in a two-dimensional electron gas in black phosphorus thin films.

For decades, two-dimensional electron gases (2DEG) have allowed important experimental discoveries and conceptual developments in condensed-matter physics. When combined with the unique electronic properties of two-dimensional crystals, they allow rich physical phenomena to be probed at the quantum level. Here, we create a 2DEG in black phosphorus--a recently added member of the two-dimensional atomic crystal family--using a gate electric field.

Enhanced thermoelectric efficiency via orthogonal electrical and thermal conductances in phosphorene.

Thermoelectric devices that utilize the Seebeck effect convert heat flow into electrical energy and are highly desirable for the development of portable, solid state, passively powered electronic systems. The conversion efficiencies of such devices are quantified by the dimensionless thermoelectric figure of merit (ZT), which is proportional to the ratio of a device's electrical conductance to its thermal conductance. In this paper, a recently fabricated two-dimensional (2D) semiconductor called phosphorene (monolayer black phosphorus) is assessed for its thermoelectric capabilities.

Strain-engineering the anisotropic electrical conductance of few-layer black phosphorus.

Newly fabricated few-layer black phosphorus and its monolayer structure, phosphorene, are expected to be promising for electronic and optical applications because of their finite direct band gaps and sizable but anisotropic electronic mobility. By first-principles simulations, we show that this unique anisotropic free-carrier mobility can be controlled by using simple strain conditions. With the appropriate biaxial or uniaxial strain (4-6%), we can rotate the preferred conducting direction by 90°.

Tunable and sizable band gap in silicene by surface adsorption.

Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.