arXiv subjects

E. B. Guedes

Publications and source records attributed to E. B. Guedes.

3 recordsLinked to original sources

arXiv2021

Orbital selective switching of ferromagnetism in an oxide quasi two-dimensional electron gas

Multi-orbital physics in quasi-two-dimensional electron gases (q2DEGs) triggers unique phenomena not observed in bulk materials, such as unconventional superconductivity and magnetism. Here, we investigate the mechanism of orbital selective switching of the spin-polarization in the oxide q2DEG formed at the (001) interface between the LaAlO$_{3}$, EuTiO$_{3}$ and SrTiO$_{3}$ band insulators. By using density functional theory calculations, transport, magnetic and x-ray spectroscopy measurements, we find that the filling of titanium-bands with 3d$_{xz,yz}$ orbital character in the EuTiO3 layer and at the interface with SrTiO$_{3}$ induces an antiferromagnetic to ferromagnetic switching of the exchange interaction between Eu-4f$^{7}$ magnetic moments. The results explain the observation of the carrier density dependent ferromagnetic correlations and anomalous Hall effect in this q2DEG, and demonstrate how combined theoretical and experimental approaches can lead to a deeper understanding of novel electronic phases and serve as a guide for the materials design for advanced electronic applications.

cond-mat.mtrl-sci↗

arXiv2021

Observation of a singular Weyl point surrounded by charged nodal walls in PtGa

Constrained by the Nielsen-Ninomiya no-go theorem, in all so-far experimentally determined Weyl semimetals (WSMs) the Weyl points (WPs) always appear in pairs in the momentum space with no exception. As a consequence, Fermi arcs occur on surfaces which connect the projections of the WPs with opposite chiral charges. However, this situation can be circumvented in the case of unpaired WP, without relevant surface Fermi arc connecting its surface projection, appearing singularly, while its Berry curvature field is absorbed by nontrivial charged nodal walls. Here, combining angle-resolved photoemission spectroscopy with density functional theory calculations, we show experimentally that a singular Weyl point emerges in PtGa at the center of the Brillouin zone (BZ), which is surrounded by closed Weyl nodal walls located at the BZ boundaries and there is no Fermi arc connecting its surface projection. Our results reveal that nontrivial band crossings of different dimensionalities can emerge concomitantly in condensed matter, while their coexistence ensures the net topological charge of different dimensional topological objects to be zero. Our observation extends the applicable range of the original Nielsen-Ninomiya no-go theorem which was derived from zero dimensional paired WPs with opposite chirality.

cond-mat.str-el↗

arXiv2021

A two-dimensional electron gas at the (001) surface of ferromagnetic EuTiO$_{3}$(001)

Studies on oxide quasi-two dimensional electron gas (q2DEG) have been a playground for the discovery of novel and sometimes unexpected phenomena, like the reported magnetism at the surface and at the interface between LaAlO$_{3}$ and SrTiO$_{3}$ non-magnetic materials. However, magnetism in this system is weak and there are evidences of a not intrinsic origin. Here, by using in-situ high-resolution angle resolved photoemission we demonstrate that ferromagnetic EuTiO$_{3}$, the magnetic counterpart of SrTiO$_{3}$ in the bulk, hosts a q2DEG at its (001) surface. This is confirmed by density functional theory calculations with Hubbard U terms in the presence of oxygen divacancies in various configurations, all of them leading to a spin-polarized q2DEG related to the ferromagnetic order of Eu-4f magnetic moments. The results suggest EuTiO$_{3}$(001) as a new material platform for oxide q2DEGs, characterized by broken inversion and time reversal symmetries.

cond-mat.mtrl-sci↗