Realization of a Valley Superlattice

Pseudospin Quantum Hall Ferromagnetism Probed by Electron Spin Resonance

We study the effect of the pseudospin ferromagnetism with the aid of an electrically detected electron spin resonance in a wide AlAs quantum well containing a high quality two-dimensional electron system. Here, pseudospin emerges as a two-component degree of freedom, that labels degenerate energy minima in momentum space populated by electrons. The built-in mechanical strain in the sample studied imposes a finite "Zeeman" splitting between the pseudospin "up" and "down" states. Because of the anisotropy of the electron spin splitting we were able to independently measure the electron spin resonances originating from the two in-plane valleys. By analyzing the relative resonance amplitudes, we were able to investigate the ferromagnetic phase transitions taking place at integer filling factors of the quantum Hall effect when the magnetic field is tilted. The pseudospin nature of these transitions is demonstrated.

Ferroelectrovalley in Two-Dimensional Multiferroic Lattices

Engineering the valley index is essential and highly sought for valley physics, but currently, it is exclusively based on the paradigm of the challenging ferrovalley with spin-orientation reversal under a magnetic field. Here, an alternative strategy, i.e., the so-called ferroelectrovalley, is proposed to tackle the insurmountable spin-orientation reversal, which reverses the valley index with the feasible ferroelectricity. Using symmetry arguments and the tight-binding model, the C2z rotation is unveiled to be able to take the place of time reversal for operating the valley index in two-dimensional multiferroic kagome lattices, which enables a ferroelectricity-engineered valley index, thereby generating the concept of a ferroelectrovalley. Based on first-principles calculations, this concept is further demonstrated in the breathing kagome lattice of single-layer Ti3Br8, wherein ferroelectricity couples with the breathing process. These findings open a new direction for valleytronics and 2D materials research.

Dirac wave transmission in Lévy-disordered systems

We investigate the propagation of electronic waves described by the Dirac equation subject to a Lévy-type disorder distribution. Our numerical calculations, based on the transfer matrix method, in a system with a distribution of potential barriers show that it presents a phase transition from anomalous to standard to anomalous localization as the incidence energy increases. In contrast, electronic waves described by the Schrödinger equation do not present such transitions. Moreover, we obtain the phase diagram delimiting anomalous and standard localization regimes, in the form of an incidence angle versus incidence energy diagram, and argue that transitions can also be characterized by the behavior of the dispersion of the transmission. We attribute this transition to an abrupt reduction in the transmittance of the system when the incidence angle is higher than a critical value which induces a decrease in the transmission fluctuations.

Successes and Issues in the Growth of Moad and MoSe2 on Ag(111) by the E-ALD Method

This paper explores the conditions for the electrodeposition of Moad (molybdenum adlayer) on Ag(111) from alkaline aqueous solution. Moreover, the first stages of the growth of MoSe2 are also presented, performing the deposition of Sead on the deposited Moad. The deposition of Moad on Sead/Ag(111) was also explored. MoSe2 is of interest due to its peculiar optoelectronic properties, making it suitable for solar energy conversion and nanoelectronics. In this study, electrodeposition techniques were exploited for the synthesis process as more sustainable alternatives to vacuum based techniques. The electrochemical atomic layer deposition (E-ALD) method emerges as a suitable technique to grow inorganic semiconductor thin films thanks to its fulfillment of the green energy predicament and a strict structural and morphological control, and this approach has gathered the attention of the scientific community. Indeed, E-ALD exploits surface limited reactions (SLRs) to alternate the deposition of chemically different atomic layers constituting a compound semiconductor. Thus, E-ALD is one of the most promising electrodeposition techniques for the growth of thin-film of compound semiconductors under a strict structural and morphological control. On this ground, E-ALD can be considered an ideal technique for the growth of 2D materials.