arXiv subjects

Yeyang Zhang

Publications and source records attributed to Yeyang Zhang.

5 recordsLinked to original sources

arXiv2024

Topological effect on the Anderson transition in chiral symmetry classes

In this Letter, we propose a mechanism of an emergent quasi-localized phase in chiral symmetry classes, where wave function along a spatial direction with weak topology is delocalized but exponentially localized along the other directions. The Anderson transition in 2D chiral symmetry classes is induced by the proliferation of vortex-antivortex pairs of a U(1) phase degree of freedom, while the weak topology endows the pair with the Berry phase. We argue that the Berry phase induces spatial polarizations of the pairs along the topological direction through the quantum interference effect, and the proliferation of the polarized vortex pairs results in the quasi-localized phase.

cond-mat.dis-nn↗

arXiv2024

Lattice-induced wavefunction effects on trapped superfluids

Wavefunction effects in uncorrelated systems are characterized by the Berry curvature and quantum metric. Beyond those, we propose gauge-independent tensors describing Bloch wavefunction effects on local interaction between correlated particles. We derive an effective hydrodynamic theory for ultracold bosons in optical lattices. Ground states and collective modes of superfluids in isotropic harmonic traps are solved for highly symmetric lattices. In a dynamic process, the wavefunction effects are featured by the eigenfrequency, amplitude, and phase shift of an excited breathing mode and can be observed in experiments. We also give a tight-binding model of a bipartite square lattice with nontrivial wavefunction effects, where results are estimated with typical experimental parameters. Our discovery advances the connections between the modern band theory and quantum many-body physics.

cond-mat.quant-gas↗

arXiv2024

Superfluidity of Total Angular Momentum

Spontaneous symmetry breaking of a U(1) symmetry in interacting systems leads to superfluidity of a corresponding conserved charge. We generalize the superfluidity to systems with U(1) symmetries acting on both matter fields and 2D spatial coordinates. Such systems can be effectively realized in easy-plane ferromagnetic systems with spin-orbit coupling where the conserved charge is a total angular momentum. We clarify that under a steady injection of spin angular momentum, the superfluid of the total angular momentum shows spacetime oscillations of the spin density and geometry-dependent spin hydrodynamics. We also demonstrate that the steady spin injection destabilizes the superfluid of total angular momentum, causing a dissipation effect in its spin hydrodynamic properties. Although a stability analysis shows that the superfluid under the spin injection is nonideal, the unique spin-transport features persist with weak dissipation of the spin angular momentum. Our study broadens the comprehension of superfluidity and sheds new light on the interplay between symmetries and phases of matter.

cond-mat.quant-gas↗

arXiv2022

Antiparticle of exciton in semimetals

An emergent quantized field enriches quantum many-body systems. We propose an antiparticle analog of the exciton in semimetals as an emergent collective mode in interacting electron systems. We show that inter-band excitations in semimetals are generally comprised of both excitons and antiparticles of excitons. These two stand for two distinct inter-band collective modes in semimetals, having different energies and opposite conserved charges. The conserved charge here is a quantity conjugate to a joint U(1) symmetry of two electron's bands associated with the inter-band excitations. The opposite charges foster fertile scattering processes among the inter-band collective modes. In spin-polarized systems, they also suggest possible experimental detections of the antiparticles. We clarify that the effective theory of the inter-band excitations is given by a generalized Klein-Gordon theory. Our theory provides a comprehensive understanding of excitonic spectra in generic semimetals, bringing a new insight into electronic collective phenomena in solids.

cond-mat.mes-hall↗

arXiv2021

Dissipationless Spin-Charge Conversion in Excitonic Pseudospin Superfluid

Spin-charge conversion by inverse spin Hall effect or inverse Rashba-Edelstein effect is prevalent in spintronics but dissipative. We propose a dissipationless spin-charge conversion mechanism by an excitonic pseudospin superfluid in an electron-hole double layer system. Magnetic exchange fields lift singlet-triplet degeneracy of interlayer exciton levels in the double layer system. Condensation of the singlet-triplet hybridized excitons breaks both a U(1) gauge symmetry and a pseudospin rotational symmetry around the fields, leading to spin-charge coupled superflow in the system. We demonstrate the mechanism by deriving spin-charge coupled Josephson equations for the excitonic superflow from a coupled quantum-dot model.

cond-mat.supr-con↗