PHYSICAL REVIEW B 112, 035128 (2025)
Disorder-induced spin excitation continuum and spin-glass ground state
in the inverse spinel CuGa
2
O
4
Zhentao Huang ,
1,*
Zhijun Xu,
2,*
Shuaiwei Li ,
3
Qingchen Duan,
4
Junbo Liao ,
1
Song Bao ,
1
Yanyan Shangguan ,
1
Bo Zhang ,
1
Hao Xu,
1
Shufan Cheng,
1
Zihang Song,
1
Shuai Dong,
1
Maofeng Wu,
1
M. B. Stone,
5
Yiming Qiu ,
2
Ruidan Zhong,
4
Guangyong Xu ,
2
Zhen Ma ,
1,3,†
G. D. Gu,
6,‡
J. M. Tranquada ,
6,§
and Jinsheng Wen
1,7,
1
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
2
NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
3
Hubei Key Laboratory of Photoelectric Materials and Devices, School of Materials Science and Engineering,
Hubei Normal University, Huangshi 435002, China
4
Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
5
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
6
Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
7
Collaborative Innovation Center of Advanced Microstructures and Jiangsu Physical Science Research Center,
Nanjing University, Nanjing 210093, China
(Received 7 April 2025; revised 11 June 2025; accepted 24 June 2025; published 10 July 2025)
Spinel-structured compounds serve as prototypical examples of highly frustrated systems and are promising
candidates for realizing the long-sought quantum spin liquid (QSL) state. However, structural disorder is
inevitable in many real QSL candidates and its impact remains a topic of intense debate. In this work, we conduct
comprehensive investigations on CuGa
2
O
4
, a spinel compound with significant structural disorder, focusing on
its thermodynamic properties and spectroscopic behaviors. No long-range magnetic order is observed down to
∼80 mK, as evidenced by magnetic susceptibility, specific-heat, and elastic neutron scattering measurements.
More intriguingly, inelastic neutron scattering experiments reveal a broad gapless continuum of magnetic
excitations around the Brillouin zone boundary, resembling the magnetic excitation spectra expected for a QSL.
Nevertheless, a spin-freezing transition at T
f
≈ 0.88 K is identified from the cusp in the dc susceptibility curves,
where a bifurcation between zero-field-cooling and field-cooling curves occurs. Furthermore, ac susceptibility
measurements show a peak close to T
f
at low frequency, which shifts to higher temperature with increasing
frequency. These results show that CuGa
2
O
4
has a spin-glass ground state, consistent with the establishment of
short-range order inferred from the specific-heat measurements. Collectively, these results illustrate the crucial
role of disorder in defining the excitation spectrum out of the disordered ground state. Our findings shed light
onto the broader class of AB
2
O
4
spinels and advance our understanding of the spin dynamics in magnetically
disordered systems.
DOI: 10.1103/1xtf-wg3q
I. INTRODUCTION
Frustrated systems represent a fascinating frontier in con-
densed matter physics, where competing interactions give rise
to quantum fluctuations, resulting in rich emergent phenom-
ena [1–3]. Of particular interest are quantum spin liquids
(QSLs), in which strong quantum fluctuations prevent the
establishment of conventional long-range magnetic order, but
can also give rise to fractionalized quasiparticle excitations
such as spinons [3–8]. Frustration typically arises from ge-
ometrical constraints, as in triangular or kagome lattices
[9,10], or from competing exchange interactions, as in the
*
These authors contributed equally to this work.
†
Contact author: zma@hbnu.edu.cn
‡
Contact author: ggu@bnl.gov
§
Contact author: jtran@bnl.gov
Contact author: jwen@nju.edu.cn
honeycomb lattice [11–13]. Within the landscape of frustrated
systems, the compounds with a AB
2
X
4
(A = transition metal,
B = Al, Ga, Sc; X = O, S) spinel structure stand out as
prototypical examples due to their inherent geometrical and
magnetic structures [14–18]. These materials have attracted
significant attention for their potential to host novel quantum
states [16,19–21].
The AB
2
X
4
family of compounds crystallizes in the cubic
spinel structure (space group Fd
¯
3m), where A-site cations
occupy tetrahedral coordination sites, while B-site cations
reside at the octahedral coordination sites. If the magnetic
ions are located at the A sites, such compounds are termed
A-site magnetic spinels. Here, the magnetic ions at the A
sites form a diamondlike magnetic lattice, resulting in various
exotic phenomena depending on the ratio of the next-nearest-
neighbor interaction (J
2
) to the nearest-neighbor interaction
(J
1
)[16]. This has been the subject of extensive investiga-
tions in recent years [17,18,20,22–24]. A notable example is
the spiral spin liquid state observed in the highly frustrated
2469-9950/2025/112(3)/035128(10) 035128-1 ©2025 American Physical Society
