183 research outputs found
a variational approach to niche construction
In evolutionary biology, niche construction is sometimes described as a genuine evolutionary process whereby organisms, through their activities and regulatory mechanisms, modify their environment such as to steer their own evolutionary trajectory, and that of other species. There is ongoing debate, however, on the extent to which niche construction ought to be considered a bona fide evolutionary force, on a par with natural selection. Recent formulations of the variational free-energy principle as applied to the life sciences describe the properties of living systems, and their selection in evolution, in terms of variational inference. We argue that niche construction can be described using a variational approach. We propose new arguments to support the niche construction perspective, and to extend the variational approach to niche construction to current perspectives in various scientific fields
Interplay between optical emission and magnetism in the van der Waals magnetic semiconductor CrSBr in the two-dimensional limit
The Van der Waals semiconductor metamagnet CrSBr offers an ideal platform for
studying the interplay between optical and magnetic properties in the
two-dimensional limit. Here, we carried out an exhaustive optical
characterization of this material by means of temperature and magnetic field
dependent photoluminescence (PL) on flakes of different thicknesses down to the
monolayer. We found a characteristic emission peak that is quenched upon
switching the ferromagnetic layers from an antiparallel to a parallel
configuration and exhibits a different temperature dependence from that of the
peaks commonly ascribed to excitons. The contribution of this peak to the PL is
boosted around 30-40 K, coinciding with the hidden order magnetic transition
temperature. Our findings reveal the connection between the optical and
magnetic properties via the ionization of magnetic donor vacancies. This
behavior enables a useful tool for the optical reading of the magnetic states
in atomically thin layers of CrSBr and shows the potential of the design of
two-dimensional heterostructures with magnetic and excitonic properties.Comment: 20 pages, 5 figure
Enantio- and regioselective CpRu-catalyzed Carroll rearrangement
The addition of unstabilized carbonyl nucleophiles to allyl-metal fragments still represents a challenge for generating stereoselectively tertiary (and quaternary) stereogenic centers. In this context, the decarboxylative Carroll rearrangement of secondary and tertiary allyl β-ketoesters is particularly interesting since chiral γ,δ-unsaturated ketones are obtained. Herein, we show that CpRu half-sandwich complexes can, in the presence of selected enantiopure diimine ligands, catalyze this transformation and afford complete conversions and decent level of enantiomeric excess. Zwitterionic adducts of a hexacoordinated phosphorus anion and CpRu moieties were also associated and shown to generate air-, moisture-, and microwave-stable catalysts that can be readily purified and recycled. Carroll rearrangements of allylic β-ketoesters performed with these zwitterionic species occur with better regio- and enantioselectivit
Interplay between optical emission and magnetism in the van der Waals magnetic semiconductor CrSBr in the two-dimensional limit
The van der Waals semiconductor metamagnet CrSBr offers an ideal platform for studying the interplay between optical and magnetic properties in the two-dimensional limit. Here, we carried out an exhaustive optical characterization of this material by means of temperature- and magnetic-field-dependent photoluminescence (PL) on flakes of different thicknesses down to the monolayer. We found a characteristic emission peak that is quenched upon switching the ferromagnetic layers from an antiparallel to a parallel configuration and exhibits a temperature dependence different from that of the peaks commonly ascribed to excitons. The contribution of this peak to the PL is boosted around 30-40 K, coinciding with the hidden order magnetic transition temperature. Our findings reveal the connection between the optical and magnetic properties via the ionization of magnetic donor vacancies. This behavior enables a useful tool for the optical reading of the magnetic states in atomically thin layers of CrSBr and shows the potential of the design of 2D heterostructures with magnetic and excitonic properties
Out-of-Plane Transport of 1T-TaS2/Graphene-Based van der Waals Heterostructures
Due to their anisotropy, layered materials are excellent candidates for studying the interplay between the in-plane and out-of-plane entanglement in strongly correlated systems. A relevant example is provided by 1T-TaS2, which exhibits a multifaceted electronic and magnetic scenario due to the existence of several charge density wave (CDW) configurations. It includes quantum hidden phases, superconductivity and exotic quantum spin liquid (QSL) states, which are highly dependent on the out-of-plane stacking of the CDW. In this system, the interlayer stacking of the CDW is crucial for interpreting the underlying electronic and magnetic phase diagram. Here, atomically thin-layers of 1T-TaS2 are integrated in vertical van der Waals heterostructures based on few-layers graphene contacts and their electrical transport properties are measured. Different activation energies in the conductance and a gap at the Fermi level are clearly observed. Our experimental findings are supported by fully self-consistent DFT+U calculations, which evidence the presence of an energy gap in the few-layer limit, not necessarily coming from the formation of out-of-plane spin-paired bilayers at low temperatures, as previously proposed for the bulk. These results highlight dimensionality as a key effect for understanding quantum materials as 1T-TaS2, enabling the possible experimental realization of low-dimensional QSLs
Multistep magnetization switching in orthogonally twisted ferromagnetic monolayers
The advent of twist-engineering in two-dimensional (2D) crystals enables the
design of van der Waals (vdW) heterostructures exhibiting emergent properties.
In the case of magnets, this approach can afford artificial antiferromagnets
with tailored spin arrangements. Here, we fabricate an orthogonally-twisted
bilayer by twisting 90 degrees two CrSBr ferromagnetic monolayers with an
easy-axis in-plane anisotropy. The magneto-transport properties reveal
multistep magnetization switching with a magnetic hysteresis opening, that is
absent in the pristine case. By tuning the magnetic field, we modulate the
remanent state and coercivity and select between hysteretic and non-hysteretic
magneto-resistance scenarios. This complexity pinpoints spin anisotropy as a
key aspect in twisted magnetic superlattices. Our results highlight the control
over the magnetic properties in vdW heterostructures, leading to a variety of
field-induced phenomena and opening a fruitful playground for creating desired
magnetic symmetries and manipulating non-collinear magnetic configurations.Comment: Main Text + Supplementary Informatio
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