arXiv subjects

Francesco Ricci

Publications and source records attributed to Francesco Ricci.

41 records · Page 3Linked to original sources

arXiv2015

Theoretical and experimental investigation of optical absorption anisotropy in $β$-Ga2O3

The question of optical bandgap anisotropy in the monoclinic semiconductor $β$-Ga2O3 was revisited by combining accurate optical absorption measurements with theoretical analysis, performed using different advanced computation methods. As expected, the bandgap edge of bulk $β$-Ga2O3 was found to be a function of light polarization and crystal orientation, with the lowest onset occurring at polarization in the ac crystal plane around 4.5-4.6 eV; polarization along b unambiguously shifts the onset up by 0.2 eV. The theoretical analysis clearly indicates that the shift of the b onset is due to a suppression of the transition matrix elements of the three top valence bands at $Γ$ point.

cond-mat.mtrl-sci↗

arXiv2014

Low In solubility and band offsets in the small-$x$ $β$-Ga$_2$O$_3$/(Ga$_{1-x}$In$_x$)$_2$O$_3$ system

Based on first-principles calculations, we show that the maximum reachable concentration $x$ in the (Ga$_{1-x}$In$_x$)$_2$O$_3$ alloy in the low-$x$ regime (i.e. In solubility in $β$-Ga$_2$O$_3$) is around 10%. We then calculate the band alignment at the (100) interface between $β$-Ga$_2$O$_3$ and (Ga$_{1-x}$In$_x$)$_2$O$_3$ at 12%, the nearest computationally treatable concentration. The alignment is strongly strain-dependent: it is of type-B staggered when the alloy is epitaxial on Ga$_2$O$_3$, and type-A straddling in a free-standing superlattice. Our results suggest a limited range of applicability of low-In-content GaInO alloys.

cond-mat.mtrl-sci↗

arXiv2014

Multi-gap absorption in CaCu$_{3}$Ti$_{4}$O$_{12}$ and the predictivity of ab initio methods

We report the electronic properties of the quadruple perovskite CaCu$_{3}$Ti$_{4}$O$_{12}$ as obtained via several density-functional based methods, and propose a new interpretation of optical experiments to the effect that four distinct transitions (centered around 0.7, 1.5, 2.5, and 3.5 eV) contribute to the spectrum. The comparison with experiment is satisfactory, especially after we account for the effects of spin disorder, which does not close the fundamental gap but suppresses the transition intensity. We find that some of the methods we employ tend to overestimate considerably the gaps for standard values of the respective adjustable parameters.

cond-mat.mtrl-sci↗

arXiv2013

Giant electroresistance and tunable magnetoelectricity in a multiferroic junction

First-principles density functional calculations show that the $\textrm{SrRuO}_{3}/\textrm{PbTiO}_{3}/\textrm{SrRuO}_{3}$ multiferroic junction with asymmetric (RuO$_{2}$/PbO and TiO$_{2}$/SrO) interfaces has a large ferroelectric depolarizing field, whose switching changes the interface transmission probabilities for tunneling electrons, leading to electroresistance modulation over several orders of magnitude. The switching further affects the interface spin density, naturally driving magnetoresistance as well as modulated spin-dependent in-plane resistivity, which may be exploited in field-effect devices.

cond-mat.mtrl-sci↗

arXiv2013

Multiferroicity in V-doped PbTiO$_{3}$

We report \emph{ab initio} predictions on the proper multiferroic (ferromagnetic, insulating and ferroelectric) character of PbTiO$_{3}$ doped with vanadium. V impurities coupled ferromagnetically carry a magnetization of 1 $μ_{\rm B}$ each. The coupling is expected to be strong, since the paramagnetic solution is higher by 150 meV/vanadium, and no stable antiferromagnetic solution was found. The electronic gap in the doped system is about 0.2-0.3 eV in GGA, hence the system is properly multiferroic. V doping increases the spontaneous polarization in PbTiO$_{3}$, with an approximate percentual rate of 0.7 $μ$C/cm$^{2}$.

cond-mat.mtrl-sci↗