Abstract
Pressure represents a clean tuning parameter for traversing the complex phase diagrams of interacting electron systems, and as such has proved of key importance in the study of quantum ...materials. Application of controlled uniaxial pressure has recently been shown to more than double the transition temperature of the unconventional superconductor Sr
2
RuO
4
, leading to a pronounced peak in
T
c
versus strain whose origin is still under active debate. Here we develop a simple and compact method to passively apply large uniaxial pressures in restricted sample environments, and utilise this to study the evolution of the electronic structure of Sr
2
RuO
4
using angle-resolved photoemission. We directly visualise how uniaxial stress drives a Lifshitz transition of the γ-band Fermi surface, pointing to the key role of strain-tuning its associated van Hove singularity to the Fermi level in mediating the peak in
T
c
. Our measurements provide stringent constraints for theoretical models of the strain-tuned electronic structure evolution of Sr
2
RuO
4
. More generally, our experimental approach opens the door to future studies of strain-tuned phase transitions not only using photoemission but also other experimental techniques where large pressure cells or piezoelectric-based devices may be difficult to implement.
The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such ...studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca3Ru2O7, a 4d oxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spin-reorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin–orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.
Self-powered photodetectors operating in the UV–visible–NIR window made of environmentally friendly, earth abundant, and cheap materials are appealing systems to exploit natural solar radiation ...without external power sources. In this study, we propose a new p–n junction nanostructure, based on a ZnO–Co3O4 core–shell nanowire (NW) system, with a suitable electronic band structure and improved light absorption, charge transport, and charge collection, to build an efficient UV–visible–NIR p–n heterojunction photodetector. Ultrathin Co3O4 films (in the range 1–15 nm) were sputter-deposited on hydrothermally grown ZnO NW arrays. The effect of a thin layer of the Al2O3 buffer layer between ZnO and Co3O4 was investigated, which may inhibit charge recombination, boosting device performance. The photoresponse of the ZnO–Al2O3–Co3O4 system at zero bias is 6 times higher compared to that of ZnO–Co3O4. The responsivity (R) and specific detectivity (D*) of the best device were 21.80 mA W–1 and 4.12 × 1012 Jones, respectively. These results suggest a novel p–n junction structure to develop all-oxide UV–vis photodetectors based on stable, nontoxic, low-cost materials.
Abstract
Reducing the thickness of a material to its two-dimensional (2D) limit can have dramatic consequences for its collective electronic states, including magnetism, superconductivity, and charge ...and spin ordering. An extreme case is TiTe
2
, where a charge density wave (CDW) emerges in the single-layer, which is absent for the bulk compound, and whose origin is still poorly understood. Here, we investigate the electronic band structure evolution across this CDW transition using temperature-dependent angle-resolved photoemission spectroscopy. Our study reveals an orbital-selective band hybridisation between the backfolded conduction and valence bands occurring at the CDW phase transition, which in turn leads to a significant electronic energy gain, underpinning the CDW transition. For the bulk compound, we show how this energy gain is almost completely suppressed due to the three-dimensionality of the electronic band structure, including via a
k
z
-dependent band inversion which switches the orbital character of the valence states. Our study thus sheds new light on how control of the electronic dimensionality can be used to trigger the emergence of new collective states in 2D materials.
Abstract Van Hove singularities (VHss) in the vicinity of the Fermi energy often play a dramatic role in the physics of strongly correlated electron materials. The divergence of the density of states ...generated by VHss can trigger the emergence of phases such as superconductivity, ferromagnetism, metamagnetism, and density wave orders. A detailed understanding of the electronic structure of these VHss is therefore essential for an accurate description of such instabilities. Here, we study the low-energy electronic structure of the trilayer strontium ruthenate Sr 4 Ru 3 O 10 , identifying a rich hierarchy of VHss using angle-resolved photoemission spectroscopy and millikelvin scanning tunneling microscopy. Comparison of k -resolved electron spectroscopy and quasiparticle interference allows us to determine the structure of the VHss and demonstrate the crucial role of spin-orbit coupling in shaping them. We use this to develop a minimal model from which we identify a mechanism for driving a field-induced Lifshitz transition in ferromagnetic metals.
Abstract
In half-metallic systems, electronic conduction is mediated by a single spin species, offering enormous potential for spintronic devices. Here, using microscopic-area angle-resolved ...photoemission, we show that a spin-polarised two-dimensional hole gas is naturally realised in the polar magnetic semiconductor AgCrSe
2
by an intrinsic self-doping at its CrSe
2
-terminated surface. Through comparison with first-principles calculations, we unveil a striking role of spin-orbit coupling for the surface hole gas, unlocked by both bulk and surface inversion symmetry breaking, suggesting routes for stabilising complex magnetic textures in the surface layer of AgCrSe
2
.
The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such ...studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca₃Ru₂O₇, a 4d oxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spinreorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin–orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.
Self-powered photodetectors operating in the UV-visible-NIR window made of environmentally friendly, earth abundant, and cheap materials are appealing systems to exploit natural solar radiation ...without external power sources. In this study, we propose a new p-n junction nanostructure, based on a ZnO-Co
O
core-shell nanowire (NW) system, with a suitable electronic band structure and improved light absorption, charge transport, and charge collection, to build an efficient UV-visible-NIR p-n heterojunction photodetector. Ultrathin Co
O
films (in the range 1-15 nm) were sputter-deposited on hydrothermally grown ZnO NW arrays. The effect of a thin layer of the Al
O
buffer layer between ZnO and Co
O
was investigated, which may inhibit charge recombination, boosting device performance. The photoresponse of the ZnO-Al
O
-Co
O
system at zero bias is 6 times higher compared to that of ZnO-Co
O
. The responsivity ( R) and specific detectivity ( D*) of the best device were 21.80 mA W
and 4.12 × 10
Jones, respectively. These results suggest a novel p-n junction structure to develop all-oxide UV-vis photodetectors based on stable, nontoxic, low-cost materials.
Direct functionalization of prefabricated free-standing graphene oxide paper (GOP) is the only approach suitable for systematic tuning of its mechanical, thermal and electronic characteristics. ...However, the traditional liquid-phase functionalization can compromise physical integrity of the paper-like material up to its total disintegration. In the present paper, we attempted to apply an alternative, solvent-free strategy for facile and nondestructive functionalization of GOP with 1-octadecylamine (ODA) and 1,12-diaminododecane (DAD) as representatives of aliphatic amines, and with 1-aminopyrene (AP) and 1,5-diaminonaphthalene (DAN) as examples of aromatic amines. The functionalization can be carried out under moderate heating at 150-180 °C for 2 h in vacuum, and proceeds through both amidation and epoxy ring opening reactions. Comparative characterization of pristine and amine-modified GOP samples was carried out by means of Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopy, thermogravimetric and differential thermal analysis, scanning electron and atomic force microscopy. In addition, we compared stability in water, wettability, electrical conductivity and elastic (Young's) modulus of GOP samples before and after functionalization. The highest content of amine species was obtained in the case of GOP-ODA, followed by GOP-DAD, GOP-AP and GOP-DAN. The functionalization increased mechanical and thermal stability, as well as the electrical conductivity of GOP. The magnitude of each effect depends on the structure of amine employed, which allows for tuning a given GOP characteristic. Morphological characterization showed that, compared to pristine graphene oxide paper, amine-modified mats become relatively ordered layered structures, in which individual GO sheets are organized in a near-parallel fashion.
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