
Line-Graph Approach to Spiral Spin Liquids∗
Shang Gao,1, 2, †Ganesh Pokharel,2, 3 Andrew F. May,2Joseph A. M. Paddison,2Chris Pasco,2Yaohua Liu,1Keith
M. Taddei,1Stuart Calder,1David G. Mandrus,2, 3, 4 Matthew B. Stone,1and Andrew D. Christianson2
1Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
2Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
3Department of Physics & Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
4Department of Material Science & Engineering,
University of Tennessee, Knoxville, Tennessee 37996, USA
(Dated: October 24, 2022)
Competition among exchange interactions is able to induce novel spin correlations on a bipar-
tite lattice without geometrical frustration. A prototype example is the spiral spin liquid, which
is a correlated paramagnetic state characterized by sub-dimensional degenerate propagation vec-
tors. Here, using spectral graph theory, we show that spiral spin liquids on a bipartite lattice can
be approximated by a further-neighbor model on the corresponding line-graph lattice that is non-
bipartite, thus broadening the space of candidate materials that may support the spiral spin liquid
phases. As illustrations, we examine neutron scattering experiments performed on two spinel com-
pounds, ZnCr2Se4and CuInCr4Se8, to demonstrate the feasibility of this new approach and expose
its possible limitations in experimental realizations.
Introduction.— A spiral spin liquid (SSL) is an ex-
otic correlated paramagnetic state of sub-dimensional
degeneracy, meaning that the propagation vectors qof
the ground states form a continuous manifold, or spiral
surface, in a dimension that is reduced from the orig-
inal system [1–14]. Similar to geometrically frustrated
magnets [15, 16], a SSL may host topological spin tex-
tures [17–19] and quantum spin liquid states [3–5, 20–22].
What differentiates a SSL from a conventional frustrated
magnet is the sub-dimensional degeneracy, which induces
highly distinctive dynamics since the spins are confined
to fluctuate collectively as nonlocal spirals [23]. Recent
calculations on a square lattice reveal that the low-energy
fluctuations in a SSL may behave as topological vortices
in momentum space [23], leading to an effective tensor
gauge theory with unconventional fracton quadrupole ex-
citations that are deeply connected to theories of quan-
tum information, elasticity, and gravity [24–29].
To date, bipartite lattices have been the primary av-
enue through which SSLs are studied. This is because
the ground state degeneracy on a bipartite lattice can
be exact, so that all spin spirals with qover the spi-
ral surface have exactly the same energy [5]. Although
this degeneracy stabilizes the SSL down to very low tem-
∗This manuscript has been authored by UT-Battelle, LLC un-
der Contract No. DE-AC05-00OR22725 with the U.S. Depart-
ment of Energy. The United States Government retains and the
publisher, by accepting the article for publication, acknowledges
that the United States Government retains a non-exclusive, paid-
up, irrevocable, world-wide license to publish or reproduce the
published form of this manuscript, or allow others to do so, for
United States Government purposes. The Department of En-
ergy will provide public access to these results of federally spon-
sored research in accordance with the DOE Public Access Plan
(http://energy.gov/downloads/doe-public-access-plan).
†sgao.physics@gmail.com
peratures [1, 3], it also imposes a strong constraint on
real materials because most of the known bipartite-lattice
compounds are dominated by the nearest-neighbor inter-
actions J1[30–44]. Even for the established model com-
pounds where the second-neighbor interactions J2are rel-
atively strong [17, 45, 46], the degeneracy over the spiral
surface is only approximate due to the existence of fur-
ther perturbations [14]. This degeneracy lifting results
in an approximate SSL state at elevated temperatures
where thermal fluctuations overcome the slight energy
difference among the spirals.
Inspired by recent density functional theory (DFT)
calculations for the breathing pyrochlore lattice com-
pounds [47], here we seek the realization of an approx-
imate SSL, i.e. a SSL with an approximate degener-
acy, beyond the bipartite lattices. According to the
Luttinger-Tisza theory [48, 49], the degeneracy of a SSL
model is encoded in the minimum manifold of the in-
teraction matrix. Using graph theory [50, 51], we show
that the J1-J2model on a bipartite lattice shares the
same minimum manifold with a J1-J3model on the cor-
responding line-graph lattice, where J3denotes the third-
neighbor interaction. Thus an approximate SSL state is
achieved in the latter case when J3is sufficiently strong,
which greatly expands the range of materials that may
support a SSL state. This line-graph approach to SSL
is vetted through neutron scattering experiments per-
formed on two Cr-based chalcogenide spinels ZnCr2Se4
and CuInCr4Se8.
Line-graph approach.— Our starting point is a Heisen-
berg model on a l-regular lattice, where lcounts the num-
ber of the nearest-neighbor (NN) sites. In the presence of
a uniform NN exchange interaction J1, the coupled spins
form a undirected graph G= (V, D), with Vdenoting the
set of vertices (i.e. the spin sites) and Ddenoting the set
of edges (i.e. the NN bonds). Two vertices iand jare
arXiv:2210.11781v1 [cond-mat.str-el] 21 Oct 2022