117 research outputs found
An adsorbed gas estimation model for shale gas reservoirs via statistical learning
Shale gas plays an important role in reducing pollution and adjusting the
structure of world energy. Gas content estimation is particularly significant
in shale gas resource evaluation. There exist various estimation methods, such
as first principle methods and empirical models. However, resource evaluation
presents many challenges, especially the insufficient accuracy of existing
models and the high cost resulting from time-consuming adsorption experiments.
In this research, a low-cost and high-accuracy model based on geological
parameters is constructed through statistical learning methods to estimate
adsorbed shale gas conten
Universal theory of spin-momentum-orbital-site locking
Spin textures, i.e., the distribution of spin polarization vectors in
reciprocal space, exhibit diverse patterns determined by symmetry constraints,
resulting in a variety of spintronic phenomena. Here, we propose a universal
theory to comprehensively describe the nature of spin textures by incorporating
three symmetry flavors of reciprocal wavevector, atomic orbital and atomic
site. Such approach enables us to establish a complete classification of spin
textures constrained by the little co-group and predict unprecedentedly
reported spin texture types, such as Zeeman-type spin splitting in
antiferromagnets and quadratic spin texture. To examine the impact of atomic
orbitals and sites, we predict orbital-dependent spin texture and anisotropic
spin-momentum-site locking effects and corresponding material candidates
validated through first-principles calculations. Our theory not only covers all
possible spin textures in crystal solids described by magnetic space groups,
but also introduces new possibilities for designing innovative spin textures by
the coupling of multiple degrees of freedom
Spin Space Group Theory and Unconventional Magnons in Collinear Magnets
Topological magnons have received substantial interest for their potential in
both fundamental research and device applications due to their exotic uncharged
yet topologically protected boundary modes. However, their understanding has
been impeded by the lack of fundamental symmetry descriptions of magnetic
materials, of which the spin Hamiltonians are essentially determined by the
isotropic Heisenberg interaction. The corresponding magnon band structures
allows for more symmetry operations with separated spin and spatial operations,
forming spin space groups (SSGs), than the conventional magnetic space groups.
Here we developed spin space group (SSG) theory to describe collinear magnetic
configurations, identifying all the 1421 collinear SSGs and categorizing them
into four types, constructing band representations for these SSGs, and
providing a full tabulation of SSGs with exotic nodal topology. Our
representation theory perfectly explains the band degeneracies of previous
experiments and identifies new magnons beyond magnetic space groups with
topological charges, including duodecuple point, octuple nodal line and
charge-4 octuple point. With an efficient algorithm that diagnoses topological
magnons in collinear magnets, our work offers new pathways to exploring exotic
phenomena of magnonic systems, with the potential to advance the
next-generation spintronic devices
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