29 research outputs found
One-dimensional electronic states in a natural misfit structure
Misfit compounds are thermodynamically stable stacks of two-dimensional
materials, forming a three-dimensional structure that remains incommensurate in
one direction parallel to the layers. As a consequence, no true bonding is
expected between the layers, with their interaction being dominated by charge
transfer. In contrast to this well-established picture, we show that interlayer
coupling can strongly influence the electronic properties of one type of layer
in a misfit structure, in a similar way to the creation of modified band
structures in an artificial moir\'e structure between two-dimensional
materials. Using angle-resolved photoemission spectroscopy with a micron-scale
light focus, we selectively probe the electronic properties of hexagonal
NbSe and square BiSe layers that terminate the surface of the
(BiSe)NbSe misfit compound. We show that the band structure in
the BiSe layers is strongly affected by the presence of the hexagonal NbSe
layers, leading to quasi one-dimensional electronic features. The electronic
structure of the NbSe layers, on the other hand, is hardly influenced by
the presence of the BiSe. Using density functional theory calculations of the
unfolded band structures, we argue that the preferred modification of one type
of bands is mainly due to the atomic and orbital character of the states
involved, opening a promising way to design novel electronic states that
exploit the partially incommensurate character of the misfit compounds
Divalent EuRh2Si2 as a reference for the Luttinger theorem and antiferromagnetism in trivalent heavy-fermion YbRh2Si2
Application of the Luttinger theorem to the Kondo lattice YbRh2Si2 suggests that its large 4f-derived Fermi surface (FS) in the paramagnetic (PM) regime should be similar in shape and volume to that of the divalent local-moment antiferromagnet (AFM) EuRh2Si2 in its PM regime. Here we show by angle-resolved photoemission spectroscopy that paramagnetic EuRh2Si2 has a large FS essentially similar to the one seen in YbRh2Si2 down to 1 K. In EuRh2Si2 the onset of AFM order below 24.5 K induces an extensive fragmentation of the FS due to Brillouin zone folding, intersection and resulting hybridization of the Fermi-surface sheets. Our results on EuRh2Si2 indicate that the formation of the AFM state in YbRh2Si2 is very likely also connected with similar changes in the FS, which have to be taken into account in the controversial analysis and discussion of anomalies observed at the quantum critical point in this system
Provoking topology by octahedral tilting in strained SrNbO
Transition metal oxides with a wide variety of electronic and magnetic
properties offer an extraordinary possibility to be a platform for developing
future electronics based on unconventional quantum phenomena, for instance, the
topology. The formation of topologically non-trivial states is related to
crystalline symmetry, spin-orbit coupling, and magnetic ordering. Here, we
demonstrate how lattice distortions and octahedral rotation in SrNbO films
induce the band topology. By employing angle-resolved photoemission
spectroscopy (ARPES) and density functional theory (DFT) calculations, we
verify the presence of in-phase octahedral rotation in ultra-thin
SrNbO films, which causes the formation of topologically-protected Dirac
band crossings. Our study illustrates that octahedral engineering can be
effectively exploited for implanting and controlling quantum topological phases
in transition metal oxides.Comment: 6 pages, 4 figure
Octahedral distortions in SrNbO<sub>3</sub>:Unraveling the structure-property relation
Strontium niobate has triggered a lot of interest as a transparent conductor
and as a possible realization of a correlated Dirac semi-metal. Using the
lattice parameters as a tunable knob, the energy landscape of octahedral
tilting was mapped using density functional theory calculations. We find that
biaxial compressive strain induces tilting around the out-of-plane axis, while
tensile strain induces tilting around the two in-plane axes. The two competing
distorted structures for compressive strain show semi-Dirac dispersions above
the Fermi level in their electronic structure. Our density functional theory
calculations combined with dynamical mean field theory (DFT+DMFT) reveals that
dynamical correlations downshift these semi-Dirac like cones towards the Fermi
energy. More generally, our study reveals that the competition between the
in-phase and out-of-phase tilting in SrNbO provides a new degree of freedom
which allows for tuning the thermoelectric and optical properties. We show how
the tilt angle and mode is reflected in the behavior of the Seebeck coefficient
and the plasma frequency, due to changes in the band structure
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Publisher Correction: Turning charge-density waves into Cooper pairs (npj Quantum Materials, (2020), 5, 1, (22), 10.1038/s41535-020-0225-5)
[ no abstract available] Correction to: npj Quantum Materials https://doi.org/10.1038/s41535-020-0225-5, published online 14 April 202