arXiv subjects

Jian-Keng Yuan

Publications and source records attributed to Jian-Keng Yuan.

6 recordsLinked to original sources

arXiv2026

Spin Quadrupolar orders in $d$-wave Unconventional Magnetism

Unconventional magnetism represents a class of metallic states whose Fermi surfaces exhibit spin-dependent splittings under the non-trivial representations of the rotation group. The $d$-wave $α$-phase unconventional magnetic state, commonly known as altermagnet, recently, has attracted significant attention. While these systems exhibit distinct anisotropic $d$-wave characteristics in momentum space, how this microscopic topology translates into the spin distributions in real space remains a question. In this work, we bridge the intrinsic spin quadrupolar ordering in momentum space to the real-space staggered magnetic distribution. By introducing a weak, non-magnetic periodic crystal potential into a $d$-wave unconventional magnetic state, the spin-charge cross susceptibility is calculated by using the linear response theory. We reveal that the interplay between the crystal potential and the intrinsic $d$-wave spin-splitting naturally induces a spatial spin quadrupole distribution without enlarging the unit cell. Our study thus provides a physical connection between momentum-space multipoles in the even partial wave channel and real-space spin multipole orders.

cond-mat.str-el↗

arXiv2025

Unconventional magnetism in spin-orbit coupled systems

``Unconventional magnetism" was proposed to describe the exotic states arising from Landau-Pomeranchuk instabilities in the spin channel nearly two decades ago. Its odd-partial-wave-channel (e.g. $p$-wave) states break parity giving rise to the dynamic generation of spin-orbit coupling, while its even-partial-wave-channel (e.g. $d$-wave) states break time-reversal symmetry. Both types of states can exhibit collinear and non-collinear spin configurations over Fermi surfaces with the former and latter termed as the $α$ and $β$-phases, respectively. The collinear states in even partial-wave channels are in the same symmetry class of ``altermagnetism". In this work, we investigate unconventional magnetism in both $p$- and $d$-wave channels within spin-orbit coupled systems with parity and time-reversal symmetries maintained. Based on the Ginzburg-Landau free energy analysis, the $p$-wave channel yields the gyrotropic, Rashba, Dresselhaus-type spin-orbit couplings. They compete and mix evolving from the $β$-phase to the $α$-phase with various types of spin-momentum lockings. Analyses are performed in parallel for the $d$-wave unconventional magnetism. We emphasize that the single-particle dispersion is not sufficient to justify the spin-group type symmetry of the full Hamiltonian. Furthermore, Goldstone manifolds and excitations are examined in each unconventional magnetic phase.

cond-mat.str-el↗

arXiv2022

Hierarchical Proliferation of Higher-Rank Symmetry Defects in Fractonic Superfluids

Symmetry defects, e.g., vortices in conventional superfluids, play a critical role in a complete description of symmetry-breaking phases. In this paper, we develop the theory of symmetry defects in fractonic superfluids, i.e., spontaneously higher-rank symmetry (HRS) breaking phases. By Noether's theorem, HRS is associated with the conservation law of higher moments, e.g. dipoles, quadrupoles, and angular moments. We establish finite-temperature phase diagrams by identifying a series of topological phase transitions via the renormalization group flow equations and Debye-Hückel approximation. Accordingly, a series of Kosterlitz-Thouless topological transitions are found to occur successively at different temperatures, which are triggered by proliferation of defects, defect bound states, and so on. Such a \emph{hierarchical proliferation} brings rich phase structures. Meanwhile, a screening effect from sufficiently high density of defect bound states leads to instability and collapse of the intermediate temperature phases, which further enriches the phase diagrams. For concreteness, we consider a fractonic superfluid in which ``angular moments'' are conserved. We then present the general theory, in which other types of HRS can be analyzed in a similar manner. Further directions are present at the end of the paper.

cond-mat.str-el↗

arXiv2022

Quantum Hydrodynamics of Fractonic Superfluids with Lineon Condensate: from Navier-Stokes-like Equations to Landau-like Criterion

Fractonic superfluids are exotic states of matter with spontaneously broken higher-rank $U(1)$ symmetry. The latter is associated with conserved quantities that include not only particle number (i.e. charge) but also higher moments, such as dipoles, quadrupoles, and angular moments. Due to the presence of such conserved quantities, the mobility of particles is restricted either completely or partially. In this work, we systematically study hydrodynamical properties of fractonic superfluids, especially focusing on the fractonic superfluids with conserved angular moments. The constituent bosons are called "lineons" with $d$-components in $d$-dimensional space. From Euler-Lagrange equation, we derive the continuity equation and Navier-Stokes-like equations, in which the angular moment conservation introduces extra terms. Furthermore, we discuss the current configurations that are related to the defects. Like the conventional superfluid, we study the critical values of velocity fields and density currents, which gives rise to a Landau-like criterion. At the end of this work, several future directions are discussed.

cond-mat.supr-con↗

arXiv2021

Fractonic superfluids. (II). Condensing subdimensional particles

In this paper, we develop an exotic fractonic superfluid phase in $d$-dimensional space where subdimensional particles -- their mobility is \emph{partially} restricted -- are condensed. The off-diagonal long range order (ODLRO) is investigated. To demonstrate, we consider "lineons" -- a subdimensional particle whose mobility is free only in certain one-dimensional directions. We start with a $d$-component microscopic Hamiltonian model. The model respects a higher-rank symmetry such that both particle numbers of each component and angular charge moments are conserved quantities. By performing the Hartree-Fock-Bogoliubov approximation, we derive a set of Gross-Pitaevskii equations and a Bogoliubov-de Gennes (BdG) Hamiltonian, which leads to a unified description of gapless phonons and gapped rotons. With the coherent-path-integral representation, we also derive the long-wavelength effective field theory of gapless Goldstone modes and analyze quantum fluctuations around classical ground states. The Euler-Lagrange equations and Noether charges/currents are also studied. In two spatial dimensions and higher, such an ODLRO stays stable against quantum fluctuations. Finally, we study vortex configurations. The higher-rank symmetry enforces a hierarchy of point vortex excitations whose structure is dominated by two guiding statements. Specially, we construct two types of vortex excitations, the conventional and dipole vortices. The latter carries a charge with dimension as a momentum. The two statements can be more generally applicable. Several future directions are discussed.

cond-mat.str-el↗

arXiv2020

Fractonic Superfluids

We propose a superfluid phase of ``many-fracton system'' in which charge and total dipole moments are conserved quantities. In this work, both microscopic model and long-wavelength effective theory are analyzed. We start with a second quantized microscopic model and formulate the coherent-state path-integral representation. With repulsive interactions and positive chemical potential, we calculate various properties of the resulting superfluid state and make comparison with a conventional superfluid. We deduce a highly nonlinear Euler-Lagrange equation as well as two Noether currents. We also formulate time-dependent Gross-Pitaevskii-type equations that govern hydrodynamical behaviors. We study the classical ground state wavefunction, the associated off-diagonal long range order (ODLRO), supercurrents, critical current, and unconventional topological vortices. At length scale much larger than coherence length $ξ_{\mathrm{coh}}$, we derive the effective theory of our microscopic model. Based on the effective theory, we analyze gapless Goldstone modes and specific heat capacity at low temperatures as well as the fate of ODLRO against quantum fluctuations. Several future directions, e.g., numerical analysis of Gross-Pitaevskii equations, fermionic fractons, fractonic superconductors, and cold-atom experimental realization, are discussed.

cond-mat.str-el↗