arXiv subjects

Jin-Tao Jin

Publications and source records attributed to Jin-Tao Jin.

6 recordsLinked to original sources

arXiv2026

Charge-4e Superconducting Ground State without Pair Condensation: Exact Quartet Dynamics, Rigorous Order, and a Microscopic Route

A direct charge-$4e$ superconductor exhibits coherent four-electron order while every charge-$2e$ pairing channel remains uncondensed. We establish three complementary results. First, building on the $η$-clustering states and bipartite parent of Yoshida and Katsura, we formulate and exactly solve a minimal two-term parent on any connected graph. Its fixed-number ground states have quartet off-diagonal long-range order (ODLRO) without charge-$2e$ ODLRO, while an exact mapping to classical hard-core exclusion dynamics yields the full fixed-sector gap and a branch of quartet-density modes. Nonzero quartet stiffness and vanishing inverse quartet compressibility identify this $z=2$ parent as a phase-separation boundary. Second, for a finite-range fermionic family with explicit quartet transfer and sufficiently large onsite penalty, we rigorously prove quartet ODLRO without charge-$2e$ ODLRO at half quartet filling, both at the hypercubic XY point for $d\geq2$ and throughout a finite XXZ interval on the square lattice. Third, we derive a strong-coupling realization using only electron hopping and two-body interactions. With local gap $U_0$, pair hopping $K$ generates quartet motion at order $K^2/U_0$, whereas electron hopping $t$ first contributes at order $t^4/U_0^3$; charge-$2e$ excitations remain gapped at $O(U_0)$. On bipartite lattices, positive inverse quartet compressibility opens an asymptotically controlled homogeneous $z=1$ regime with short-ranged pair correlations, while negative curvature drives phase separation.

cond-mat.str-el↗

arXiv2026

Gauge-covariant magnetic Bloch sums for general multiorbital Hofstadter models

We formulate a unified treatment of the Hofstadter problem for general two-dimensional multiorbital Peierls tight-binding Hamiltonians using a gauge-covariant magnetic Bloch-sum basis. The construction retains the full Bravais geometry, arbitrary intracell orbital positions, and the original hopping table, so lattice geometry, orbital embedding, hopping range, and orbital content can all be handled within the same framework. At rational flux $Φ/Φ_0=p/q$, commuting magnetic translations reduce the Peierls Hamiltonian to minimal $qN_{\rm orb}\times qN_{\rm orb}$ blocks. Their dimension depends only on the flux through the primitive cell, even when the fractional orbital coordinates are irrational. Electromagnetic gauge transformations act by unitary conjugation within the construction and do not alter the required magnetic supercell. We derive an explicit sparse matrix in an oblique Landau gauge and establish the associated band counting, spectral redundancy, Chern-number formulation, magnetic spatial constraints, and flux periodicity. Numerical examples include elementary lattices, topological and flat-band models, and a spinful 22-band Wannier Hamiltonian of monolayer $\mathrm{MoS}_2$, demonstrating a direct interface with first-principles electronic-structure calculations. As a complementary representation, we also derive exact generalized Harper equations from the same hopping data and relate them to the finite magnetic-Bloch blocks.

cond-mat.mes-hall↗

arXiv2026

Topological Defects in Triple-$Q$ Magnetic Orders: A Fixed-Lattice Homotopy Classification

Multiple-$Q$ magnetic orders combine continuous spin rotations with discrete crystalline sectors associated with translations and point-group transformations, producing a richer defect structure than conventional single-$Q$ magnets. We classify the bulk defects of all seven stable phases for $N=2$ and $3$ in the $M$-point triple-$Q$ Ginzburg--Landau theory with $(\Vfour\rtimes\Dthree)\times\OO(N)$ symmetry, where $\Vfour$ is the translation-generated Klein four-group. The atomic lattice is treated as a prescribed background, with lattice dislocations and disclinations excluded and the three Fourier fields retaining their physical $M$-point labels. The parent-group transformations continuously connected to the identity form $G_0=\{e\}\times\SO(N)$. For a reference-state stabilizer $H$, the connected component containing the reference state is $G_0/(H\cap G_0)$, not the quotient obtained by projecting $H$ onto spin space. This distinction gives the orthogonal triple-$Q$ phase the full manifold $\OO(3)$, with chirality walls and Abelian $\ZZ_2$ frame vortices rather than non-Abelian binary-polyhedral vortices. Every connected component of the $\OO(2)$ phases supports an integer $2π$ vortex, whereas fractional windings close only when attached to a discrete-domain wall and are linearly confined at nonzero wall tension. Translation symmetry further forbids cross-gradient bilinears, reducing the quadratic elastic sector to an isotropic and an $M$-point-locked anisotropic stiffness. The classification separates free internal defects, crystalline domain walls, and wall-bound composites in triple-$Q$ magnets.

cond-mat.str-el↗

arXiv2025

Phenomenological Ginzburg-Landau theory for triple-Q magnetic orders on a hexagonal lattice

We develop a comprehensive Ginzburg-Landau theory describing triple-Q magnetic orders on hexagonal lattices, focusing on $O(N)$ models with $N=2$ and $N=3$. Through systematic analysis of symmetry-allowed terms in the free energy, we establish complete phase diagrams governed by competing interaction parameters. Our theory reveals distinct magnetic configurations including single-Q, double-Q, and triple-Q states, each characterized by unique symmetry breaking patterns and collective excitations. The framework provides fundamental insights into complex magnetic orders recently observed in materials such as Na$_2$Co$_2$TeO$_6$, where the interplay between geometric frustration and multiple ordering vectors leads to exotic magnetic states. Our results establish clear connections between microscopic interactions, broken symmetries, and experimentally observable properties, offering a powerful tool for understanding and predicting novel magnetic phases in frustrated magnets.

cond-mat.str-el↗

arXiv2023

Lacing topological orders in two dimensions: exactly solvable models for Kitaev's sixteen-fold way

A family of two-dimensional (2D) spin-1/2 models have been constructed to realize Kitaev's sixteen-fold way of anyon theories. Defining a one-dimensional (1D) path through all the lattice sites, and performing the Jordan-Wigner transformation with the help of the 1D path, we find that such a spin-1/2 model is equivalent to a model with $ν$ species of Majorana fermions coupled to a static $\mathbb{Z}_2$ gauge field. Here each specie of Majorana fermions gives rise to an energy band that carries a Chern number $\mathcal{C}=1$, yielding a total Chern number $\mathcal{C}=ν$. It has been shown that the ground states are three (four)-fold topologically degenerate on a torus, when $ν$ is an odd (even) number. These exactly solvable models can be achieved by quantum simulations.

cond-mat.str-el↗

arXiv2022

Interplay between Pair Density Wave and a Nested Fermi Surface

We show that spontaneous time-reversal-symmetry (TRS) breaking can naturally arise from the interplay between pair density wave (PDW) ordering at multiple momenta and nesting of Fermi surfaces (FS). Concretely, we consider pair-density-wave superconductivity on a hexagonal lattice with nested FS at $3/4$ electron filling, which is related to a recently discovered superconductor CsV$_3$Sb$_5$. Because of nesting of the FS, each momentum $\bk$ on the FS has at least two counterparts $-\bk\pm\mathbf{Q}_α$ ($α=1,2,3$) on the FS to form finite momentum ($\pm\mathbf{Q}_α$) Cooper pairs, resulting in a TRS and inversion broken PDW state with stable Bogoliubov Fermi pockets. Various spectra, including (local) density of states, electron spectral function and the effect of quasi-particle interference, have been investigated. The partial melting of the PDW will give rise to $4\times{}4$ and $\frac{4}{\sqrt{3}}\times\frac{4}{\sqrt{3}}$ CDW orders, in addition to the $2\times2$ CDW. Possible implications to real materials such as CsV$_3$Sb$_5$ and future experiments have been further discussed.

cond-mat.supr-con↗