6 research outputs found
From Half-metal to Semiconductor: Electron-correlation Effects in Zigzag SiC Nanoribbons From First Principles
We performed electronic structure calculations based on the first-principles
many-body theory approach in order to study quasiparticle band gaps, and
optical absorption spectra of hydrogen-passivated zigzag SiC nanoribbons.
Self-energy corrections are included using the GW approximation, and excitonic
effects are included using the Bethe-Salpeter equation. We have systematically
studied nanoribbons that have widths between 0.6 and 2.2
. Quasiparticle corrections widened the Kohn-Sham band gaps because
of enhanced interaction effects, caused by reduced dimensionality. Zigzag SiC
nanoribbons with widths larger than 1 nm, exhibit half-metallicity at the
mean-field level. The self-energy corrections increased band gaps
substantially, thereby transforming the half-metallic zigzag SiC nanoribbons,
to narrow gap spin-polarized semiconductors. Optical absorption spectra of
these nanoribbons get dramatically modified upon inclusion of electron-hole
interactions, and the narrowest ribbon exhibits strongly bound excitons, with
binding energy of 2.1 eV. Thus, the narrowest zigzag SiC nanoribbon has the
potential to be used in optoelectronic devices operating in the IR region of
the spectrum, while the broader ones, exhibiting spin polarization, can be
utilized in spintronic applications.Comment: 22 pages, 6 figures (included
Field-induced quantum critical point in the new itinerant antiferromagnet TiCu
New phases of matter emerge at the edge of magnetic instabilities. In local
moment systems, such as heavy fermions, the magnetism can be destabilized by
pressure, chemical doping, and, rarely, by magnetic field, towards a
zero-temperature transition at a quantum critical point (QCP). Even more rare
are instances of QCPs induced by pressure or doping in itinerant moment
systems, with no known examples of analogous field-induced \textit{T} = 0
transitions. Here we report the discovery of a new itinerant antiferromagnet
with no magnetic constituents, in single crystals of TiCu with =
11.3 K. Band structure calculations point to an orbital-selective, spin density
wave ground state, a consequence of the square net structural motif in
TiCu. A small magnetic field, = 4.87 T, suppresses the long-range
order via a continuous second-order transition, resulting in a field-induced
QCP. The magnetic Gr\"uneisen ratio diverges as and
, with a sign change at and scaling at ,
providing evidence from thermodynamic measurements for quantum criticality for
. Non-Fermi liquid (NFL) to Fermi liquid (FL) crossover is
observed close to the QCP, as revealed by the power law behavior of the
electrical resistivity
Nonsymmorphic symmetry-protected band crossings in a square-net metal PtPb4
Topological semimetals with symmetry-protected band crossings have emerged as a rich landscape to explore intriguing electronic phenomena. Nonsymmorphic symmetries in particular have been shown to play an important role in protecting the crossings along a line (rather than a point) in momentum space. Here we report experimental and theoretical evidence for Dirac nodal line crossings along the Brillouin zone boundaries in PtPb4, arising from the nonsymmorphic symmetry of its crystal structure. Interestingly, while the nodal lines would remain gapless in the absence of spin–orbit coupling (SOC), the SOC, in this case, plays a detrimental role to topology by lifting the band degeneracy everywhere except at a set of isolated points. Nevertheless, the nodal line is observed to have a bandwidth much smaller than that found in density functional theory (DFT). Our findings reveal PtPb4 to be a material system with narrow crossings approximately protected by nonsymmorphic crystalline symmetries