Domenico Di Sante

Tuning the ferroelectric polarization in a multiferroic metal-organic framework.

We perform density functional theory calculations on a recently synthesized metal-organic framework (MOF) with a perovskite-like topology ABX3, i.e., [CH3CH2NH3]Mn(HCOO)3, and predict a multiferroic behavior, i.e., a coexistence of ferroelectricity and ferromagnetism. A peculiar canted ordering of the organic A-cation dipole moments gives rise to a ferroelectric polarization of ~2 μC/cm(2). Starting from these findings, we show that by choosing different organic A cations, it is possible to tune the ferroelectric polarization and increase it up to 6 μC/cm(2). The possibility of changing the magnitude and/or the canting of the organic molecular dipole opens new routes toward engineering ferroelectric polarization in the new class of multiferroic metal-organic frameworks.

Electric Control of the Giant Rashba Effect in Bulk GeTe

Relativistic effects, including the Rashba effect, are increasingly seen as key ingredients in spintronics. A link between Rashba physics and the field of ferroelectrics is established by predicting giant Rashba spin-splitting in bulk GeTe (see the Figure showing the band-structure as well as in-plane and out- of-plane spin polarization for a constant energy cut).

Giant Rashba‐Type Spin Splitting in Ferroelectric GeTe(111)

Photoelectron spectroscopy in combination with piezoforce microscopy reveals that the helicity of Rashba bands is coupled to the nonvolatile ferroelectric polarization of GeTe(111). A novel surface Rashba band is found and fingerprints of a bulk Rashba band are identified by comparison with density functional theory calculations.

Layer-dependent quantum cooperation of electron and hole states in the anomalous semimetal WTe2

The behaviour of electrons and holes in a crystal lattice is a fundamental quantum phenomenon, accounting for a rich variety of material properties. Boosted by the remarkable electronic and physical properties of two-dimensional materials such as graphene and topological insulators, transition metal dichalcogenides have recently received renewed attention. In this context, the anomalous bulk properties of semimetallic WTe2 have attracted considerable interest. Here we report angle- and spin-resolved photoemission spectroscopy of WTe2 single crystals, through which we disentangle the role of W and Te atoms in the formation of the band structure and identify the interplay of charge, spin and orbital degrees of freedom. Supported by first-principles calculations and high-resolution surface topography, we reveal the existence of a layer-dependent behaviour. The balance of electron and hole states is found only when considering at least three Te–W–Te layers, showing that the behaviour of WTe2 is not strictly two dimensional.

Emergence of ferroelectricity and spin-valley properties in two-dimensional honeycomb binary compounds.

By means of density functional theory calculations, we predict that several two dimensional AB binary monolayers, where A and B atoms belong to group IV or III-V, are ferroelectric. Dipoles arise from the buckled structure, where the A and B ions are located on the sites of a bipartite corrugated honeycomb lattice with trigonal symmetry. We discuss the emerging valley-dependent properties and the coupling of spin and valley physics, which arise from the loss of inversion symmetry, and explore the interplay between ferroelectricity and Rashba spin-spitting phenomena. We show that valleyrelated properties originate mainly from the binary nature of AB monolayers, while the Rashba spintexture developing around valleys is fully controllable and switchable by reversing the ferroelectric polarization.

Polar distortions in hydrogen bonded organic ferroelectrics

Although ferroelectric compounds containing hydrogen bonds were among the first to be discovered, organic ferroelectrics are relatively rare. The discovery of high polarization at room temperature in croconic acid [Nature \textbf{463}, 789 (2010)] has led to a renewed interest in organic ferroelectrics. We present an ab-initio study of two ferroelectric organic molecular crystals, 1-cyclobutene-1,2-dicarboxylic acid (CBDC) and 2-phenylmalondialdehyde (PhMDA). By using a distortion-mode analysis we shed light on the microscopic mechanisms contributing to the polarization, which we find to be as large as 14.3 and 7.0\,

Robust spin-polarized midgap states at step edges of topological crystalline insulators

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Topological Tuning in Three-Dimensional Dirac Semimetals

C/cm

Strain engineering of topological properties in lead‐salt semiconductors

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Three-Dimensional Electronic Structure of the Type-II Weyl Semimetal WTe2

for CBDC and PhMDA respectively. These results suggest that it may be fruitful to search among known but poorly characterized organic compounds for organic ferroelectrics with enhanced polar properties suitable for device applications.