Searcharxiv⌕ Search

arXiv subjects

Zhijia Zhang

Publications and source records attributed to Zhijia Zhang.

29 records · Page 2Linked to original sources
arXiv2024

Spin waves and orbital contribution to ferromagnetism in a topological metal

Special arrangements of atoms with more than one atom per unit cell, including honeycomb or kagome (woven bamboo mat) lattices, can host propagating excitations with non-trivial topology as defined by their evolution along closed paths in momentum space. Excitations on such lattices can also be momentum-independent, meaning that they are localized notwithstanding strong hopping of the underlying disturbances between neighbouring sites. The associated flat bands are interesting because the interactions between the heavy quasiparticles inhabiting them will become much more important than for strong dispersion, resulting in novel quantum solid and liquid states. Different stackings of two-dimensional lattices, for example twisted graphene bilayers, provide routes to further engineer topology and many-body effects. Here, we report the discovery, using circularly polarized x-rays for the unambiguous isolation of magnetic signals, of a nearly flat spin wave band and large (compared to elemental iron) orbital moment for the metallic ferromagnet Fe3Sn2, built from compact AB-stacked kagome bilayers and which has a topologically non-trivial electronic band structure controllable by modest external magnetic fields. As a function of out-of-plane momentum, the nearly flat optical mode and the global rotation symmetry-restoring acoustic mode are out of phase, consistent with a bilayer exchange coupling that is larger than the already large in-plane couplings. The defining units of this topological metal are therefore a triangular lattice of octahedral iron clusters rather than weakly coupled kagome planes. The spin waves are strongly damped when compared to elemental iron, opening the topic of interactions of topological bosons (spin waves) and fermions (electrons) with the very specific target of explaining boson lifetimes.

cond-mat.str-el↗
arXiv2024

Birational invariants of volume preserving maps

We study the group of birational automorphisms of the $n$-dimensional projective space that preserve the standard torus invariant volume form with logarithmic poles. We prove that this group is not generated by pseudo-regularizable maps for $n\geq 4$ over $\mathbb{C}$, and for $n\geq 3$ over number fields. As a corollary, we show that this group is not simple in these cases.

math.AG↗
arXiv2024

Computing the equivariant Brauer group

Let X be a smooth projective rational variety carrying a regular action of a finite abelian group G. We give examples of effective computation of the Brauer group of the quotient stack [X/G] in dimensions 2 and 3 using residues in Galois cohomology and the geometry of fixed loci. In particular, we compute Br([X/G]) for all G-minimal del Pezzo surfaces.

math.AG↗
arXiv2023

Opening long-time investigation window of living matter by nonbleaching phase intensity nanoscope: PINE

Fundamental to all living organisms and living soft matter are emergent processes in which the reorganization of individual constituents at the nanoscale drives group-level movements and shape changes at the macroscale over time. However, light-induced degradation of fluorophores, photobleaching, is a significant problem in extended live cell imaging in life science, and excellent prior arts of STED, MINSTED, or MINFLUX intentionally apply photobleaching optics for super-resolution, yet lack extended live-cell imaging capability as fluorophores reach an irreversible photobleaching limit. Here, we report an innovative way of opening a long-time investigation window of living matter by a nonbleaching phase intensity nanoscope: PINE. We accomplish phase-intensity separation to obtain phase differences between electric field components, such that nanoprobes within a diffraction limited region are distinguished from one another by an integrated phase-intensity multilayer thin film (polyvinyl alcohol/liquid crystal). We obtain distributional patterns of precisely localized nanoprobes to overcome a physical limit to resolve sub-10 nm cellular architectures, and achieve the first dynamic imaging of nanoscopic reorganization over 250 hours using nonbleaching PINE. Since PINE allows a long-time investigation window, we discover nanoscopic rearrangements synchronized with the emergence of group-level movements and shape changes at the macroscale according to a set of interaction rules. We believe that PINE and its application presented here provide a mechanistic understanding of emergent dynamics important in cellular and soft matter reorganization, self-organization, and pattern formation.

physics.bio-ph↗
arXiv2021

Combinatorial Burnside groups

We study the structure of combinatorial Burnside groups, which receive equivariant birational invariants of actions of finite groups on algebraic varieties.

math.AG↗