arXiv subjects

Huibo Cao

Publications and source records attributed to Huibo Cao.

At least 19 recordsLinked to original sources

arXiv2026

Anomalous Hall Response Induced by Correlated Disorder in the Breathing Kagome Lattice Mn$_{3}$Sn

Macroscopic transport tensors are generally constrained by the average crystallographic and magnetic symmetries of a material. In the kagome antiferromagnetic Weyl semimetals Mn$_{3+\delta}X$ ($X=$~Sn or Ge), previous studies showed that the anomalous Hall conductivity $\sigma_{yx}$ is forbidden by the average \hexsg{} structure and coplanar inverse-triangular magnetic order. Here we report that nearly stoichiometric Mn$_3$Sn nevertheless exhibits a finite $\sigma_{yx}$ with large hysteresis, together with enhanced $\sigma_{zx}$ and $\sigma_{yz}$, in the inverse-triangular phase below $T_{\mathrm{N1}}\approx 440~\mathrm{K}$, whereas all AHE components vanish in the amplitude-modulated conical phase below $T_{\mathrm{N2}}\approx 280~\mathrm{K}$. Total scattering and magnetic pair distribution function analysis reveal correlated orthorhombic distortions and noncoplanar Mn moments. First-principles calculations show that this coupled lattice-spin distortion activates the average symmetry forbidden $\sigma_{yx}$ within the inverse-triangular phase. Its disappearance below $T_{\mathrm{N2}}$ indicates that the correlated disorder must cooperate with a long-range inverse-triangular antiferromagnetic order capable of supporting Berry curvature. Our results establish correlated disorder as an active symmetry-breaking degree of freedom that enables topological transport inaccessible from the Bragg-average structure alone.

cond-mat.str-el↗

arXiv2026

Spin nematic liquid crystal and scalar spin chirality in tetragonal lattice YbMnBi$_2$

A spin nematic order, analogous to the nematic liquid crystal, characterizes the spontaneous breaking of spin-space rotational symmetry while preserving time-reversal ($T$) symmetry. In contrast, scalar spin chirality (SSC), a composite three-spin order, breaks $T$ symmetry and is known to induce an anomalous Hall effect (AHE). Although a spin nematic phase has been suggested in frustrated magnets and the square-lattice iridate, how it might affect magnetotransport properties is unknown. Here we use polarized neutron scattering to show that tetragonal $A$MnBi$_2$ ($A$ = Ca, Yb) is a strictly $c$-axis-aligned collinear antiferromagnet (C-type), with $T_N \approx 270$ K and 290 K, respectively. On cooling from 450 K to $T_N$, low-energy spin excitations in YbMnBi$_2$ spontaneously change from isotropic to anisotropic in spin space within the tetragonal plane, forming a dynamic spin nematic phase around 400 K due to heavy Yb-induced spin-orbit coupling, before gapping out below $T_N$. Similar measurements on CaMnBi$_2$ reveal isotropic paramagnetic scattering without a spin nematic phase above $T_N$. Under an in-plane magnetic field, the Yb$^{3+}$ moments may interact with the dynamic spin nematic phase to induce nonzero SSC, giving rise to AHE and an anomalous Nernst effect (ANE) in YbMnBi$_2$ that are absent in CaMnBi$_2$ above $T_N$. A symmetry-based Ginzburg-Landau analysis shows that coupling terms between the nematic order and SSC are allowed under an external magnetic field, which could explain the rapid increase of AHE with field in YbMnBi$_2$. Our results provide compelling evidence for dynamic SSC-induced AHE and ANE in the paramagnetic phase of a compensated collinear antiferromagnet, opening a new avenue for the physics of composite spin orders and room-temperature spintronics without magnetic order.

cond-mat.str-el↗

arXiv2026

Stacking-dependent anisotropic altermagnetism in V$_{1/3}$NbS$_2$

We report profound impacts of the stacking sequence of triangular lattices of magnetic transition metal ions intercalated between the layers of the van der Waals material NbS$_2$. Using single crystal x-ray and neutron diffraction, and transport and magnetization measurements, we show there are two distinct polytypes of $\rm V_{1/3}NbS_2$ with disparate easy axes of magnetization and different anomalous Hall responses. Self-consistent analysis of inelastic neutron scattering data provides evidence for oscillatory RKKY interactions that extend to 1 nm and stabilize quasi-collinear A-type altermagnetic orders in both polytypes though with perpendicular easy axes. The detailed stacking sequence of a bulk polytype crystal dramatically impact its macroscopic anomalous Hall response and magnetism, which suggests a new path to engineer the bulk properties of a layered three dimensional solid.

cond-mat.str-el↗

arXiv2026

Atomic-scale visualization of the toroidal order in a trimeric Dy(III) single-molecule toroic

Single-molecule toroics (SMTs) offer a unique platform for next-generation quantum devices utilizing head-to-tail spin alignments in the compounds. Presence of toroidal moments in SMTs has been essentially based on magnetometry and ab initio calculations. Here, we report observation and probe of the toroidal moment in [Dy3(OH)(teaH2)3(paa)3]Cl(OMe) [teaH3: triethanolamine; paaH: N-(2-pyridyl)-acetoacetamide] from mapping of Dy3+ magnetic susceptibility tensors by polarized neutron diffraction (PND). Neutron diffraction under variable magnetic fields demonstrates field-induced magnetization along the c-axis with toroidal moments anti-parallelly stacked, providing definite proof of the toroidal moment. Magnetometry studies confirm the toroidal ground state. For the first time, the combined use of PND, variable-field neutron diffraction, ab initio calculations, and magnetometry is introduced as a robust and quantitative methodology to probe molecular-scale toroidal magnetism. This integrated approach overcomes limitations of earlier indirect methods, establishes a benchmark framework for investigating SMTs, and provides valuable insights for the design of molecular quantum materials.

cond-mat.str-el↗

arXiv2026

Field-rigid Ising antiferromagnetism with giant spin-flip fields in Van der Waals UOTe

Van der Waals antiferromagnets provide a route to thickness-controlled magnetic order, but few combine high-temperature Ising order with conducting, correlated, and topological electronic structure. Here we show that UOTe realizes this combination. Magnetic susceptibility reveals a strongly anisotropic paramagnetic response, while neutron diffraction establishes c-axis antiferromagnetic order below $T_N \simeq 150$ K with an order-parameter exponent $\beta = 0.14$, close to the two-dimensional Ising value. Torque magnetometry further shows that the ordered state remains well described by a uniaxial antiferromagnet below the high-field transition. Pulsed-field magnetization up to 73 T shows that the ordered state survives to very large fields applied along the c axis before entering a broad metamagnetic regime that begins near 50 T, and remains unsaturated at the highest measured field. Angle-dependent proximity detector oscillator measurements show that the metamagnetic instability is set by the field component along the ordered moment direction, providing direct evidence for Ising-like field rigidity. UOTe therefore establishes a field-rigid Ising antiferromagnet with giant spin-flip fields in a compensated Van der Waals metal, where high-temperature c-axis order, quasi-two-dimensional magnetic criticality, Kondo-associated uranium 5f hybridization, metallic transport, and symmetry-enabled topology coexist in a single material.

cond-mat.str-el↗

arXiv2026

Near-degenerate competing magnetic orders in EuAgAs: a tunable route to altermagnetism

Altermagnets (AMs) have recently emerged as a distinct magnetic class bridging central features of ferromagnets (FMs) and antiferromagnets (AFMs), offering new opportunities for spin-based electronics. While they possess zero net magnetization like collinear AFMs, they simultaneously exhibit momentum-dependent spin splitting long thought exclusive to FMs. Despite intense theoretical interest, experimentally accessible materials hosting both altermagnetism and nontrivial band topology remain scarce. EuAgAs, crystallizing in space group $P6_3/mmc$, was previously identified via density functional theory (DFT) as a bulk altermagnetic Dirac semimetal. Contrary to these predictions, our neutron diffraction experiments reveal that the bulk ground state adopts a $\mathbf{q} = (0,0,\tfrac{1}{2})$ AFM structure with an in-plane $\uparrow\uparrow\downarrow\downarrow$ spin sequence. Systematic DFT calculations, however, uncover a remarkable near-degeneracy among competing magnetic orders: the FM and AM configurations lie only $0.11$ and $0.40~\text{meV/f.u.}$ above the AFM ground state, respectively. We further show that while a simple Heisenberg model favors a spin-spiral ground state, the inclusion of non-Heisenberg biquadratic coupling stabilizes the observed commensurate AFM phase. This near-degeneracy renders the magnetic state highly tunable, with DFT predicting a transition to the altermagnetic phase under hydrostatic pressure at approximately $14 \text{ GPa}$, establishing EuAgAs as a controllable platform for accessing topological altermagnetism.

cond-mat.mtrl-sci↗

arXiv2026

Experimental investigation of altermagnetic order in Cr-doped FeSb2

Altermagnets are a class of materials with compensated magnetic moments, in which spin sublattices are related by specific rotational symmetries other than inversion or translation. This allows time-reversal symmetry to be broken without a net magnetization. Cr-doped FeSb2 has been theoretically proposed as a candidate d-wave altermagnetic system, yet its magnetic ground state has remained unresolved. Here, we synthesize single crystals of Fe1-xCrxSb2 and investigate their electrical transport and magnetic properties, with a focus on Fe0.85Cr0.15Sb2. Magnetization measurements suggest spin-compensated ordering below ~3.5 K, where magnetic moments align along the crystallographic b-direction. Transport measurements reveal a crossover from large positive to negative magnetoresistance, while an anomalous Hall response emerges below 5 K, indicating time-reversal symmetry breaking. Muon spin relaxation measurements confirm that the magnetic ordering below 3.5 K is bulk in nature. The absence of coherent oscillations in zero-field {\mu}SR spectra and of magnetic Bragg intensity in single-crystal neutron diffraction establishes that the magnetically ordered state is short-range or disordered, rather than collinear altermagnetic order. These results demonstrate that Cr-doping alone breaks time-reversal symmetry without stabilizing long-range altermagnetic order in FeSb2.

cond-mat.mtrl-sci↗

arXiv2026

K$_2$Co$_2$(TeO$_{3}$)$_{3}$ $\cdot$ 2.5 H$_2$O : A mineral-inspired pseudo-honeycomb cobalt dimer antiferromagnet

In recent years, magnetically-frustrated triangular and honeycomb lattice cobaltates have seen extensive study in the pursuit of a quantum spin liquid (QSL) state in a real material. In this work, we describe the hydroflux synthesis of K$_2$Co$_2$(TeO$_{3}$)$_{3}$ $\cdot$ 2.5 H$_2$O (KCoTOH), a novel zemannite-type antiferromagnet (AFM) possessing structural elements of both triangular dimer and honeycomb structural motifs. Bulk magnetometry and specific heat data support the onset of long-range AFM order below $T_\text{N}$ = 7.6(1) K, with neutron diffraction and muon spin relaxation ($\mu$SR) measurements placing the majority of the ordered moment within the pseudo-honeycomb plane. We resolve three unique oscillation frequencies from the zero-field $\mu$SR spectra, additionally suggesting a remarkably low level of structural disorder in as-grown KCoTOH crystals. Whereas interactions between dimerized chains of Co$^{2+}$ cations are typically observed to be negligible or ferromagnetic in nature, the largely planar ordering motif observed in KCoTOH is instead stabilized by net antiferromagnetic interactions through bridging tellurite groups. This work highlights the potential of hydroflux synthesis methods in the stabilization of magnetic materials possessing novel and potentially more frustrated lattice geometries.

cond-mat.str-el↗

arXiv2026

Kondo driven suppression of charge density wave in Van der Waals material UTe$_3$

Competing electronic instabilities lie at the heart of emergent phenomena in quantum materials. In low-dimensional metals, Fermi-surface nesting can drive charge density wave (CDW) formation through a Peierls-like mechanism, while in strongly correlated systems, Kondo hybridization reconstructs the electronic structure by entangling localized moments with itinerant electrons. How these two fundamentally different instabilities interact$-$whether they coexist, compete, or mutually exclude each other$-$remains an open question. Here, we present suppression of charge density wave via the Kondo interaction in van der Waals material UTe$_3$. The angle-resolved photoemission spectroscopy (ARPES) data reveals Fermi surface nesting under similar conditions as seen in RETe$_3$ compounds. Despite that, no CDW is found in UTe$_3$ after an extensive search. We demonstrate that strong hybridization between U 5$f$ electrons and Te $p$ states reconstructs the low-energy electronic structure, removes the instability, and preempts CDW formation. Our results reveal a rare example where Kondo hybridization preempts density wave formation, offering a new route to controlling ordering phenomena in correlated 2D materials.

cond-mat.str-el↗

arXiv2026

Atomically-sharp magnetic soliton in the square-net lattice EuRhAl$_{4}$Si$_{2}$

Topological spin textures are hallmark manifestations of competing interactions in magnetic matter. Their effective description by nonlinear field theories reflects an energetic frustration that destabilizes uniform order while selecting finite-size, topologically nontrivial configurations as stationary states. Among the most extreme realizations are atomically-sharp domain wall excitations, namely one-dimensional (1D) magnetic solitons, which represent the ultimate scaling limit of magnetic textures. Such solitons may emerge in magnetic systems where effective exchange interactions compete directly with uniaxial magnetic anisotropy. Here we show that the square-net rare earth compound EuRhAl$_{4}$Si$_{2}$ realizes a very susceptible regime where the magnetic anisotropy competes with highly frustrated exchange interactions stabilizing a rare ferrimagnetic $\uparrow\uparrow\downarrow$ state that, under applied magnetic field, supports the formation of atomically-sharp soliton defects. We confirm the bulk response of the 1D magnetic solitons via magnetization and electrical transport measurements. We establish both the zero- and in-field $\uparrow\uparrow\downarrow$ order via neutron diffraction, while magnetic force microscopy visualizes its real-space evolution into a stripe-like array. To elucidate the microscopic origin of the soliton, we relate the Ruderman-Kittel-Kasuya-Yosida (RKKY)-driven exchange interactions and the magnetic anisotropy through density functional theory, and we construct an effective 1D $J_{1}$-$J_{2}$-$K$ model whose atomistic spin dynamics simulations reproduce the observed soliton states as a function of external field. Our results demonstrate that EuRhAl$_{4}$Si$_{2}$ hosts atomically-sharp, field-driven 1D magnetic solitons, providing a new platform for studying 1D topological excitations at the atomic length scale.

cond-mat.str-el↗

arXiv2026

Frustrated Magnetism in FeGe$_3$O$_4$ with a Chiral Trillium Network

The discovery of new magnetic ground states in geometrically frustrated lattices remains a central challenge in materials science. Here, we report the synthesis, structural characterization, and frustrated magnetic properties of FeGe$_3$O$_4$, a newly identified compound that crystallizes in the noncentrosymmetric cubic space group $P2_13$. In this structure, Fe atoms form an intricate double-trillium lattice with nearest-neighbor Fe--Fe distances of $\sim$4.2~\AA{}, while Ge$^{2+}$ ions mediate magnetic interactions through Fe-Ge-Fe pathways. Field-dependent magnetization at 2~K shows a pronounced nonlinearity, reaching a maximum moment of 2.55(3)~$\mu_\mathrm{B}$/Fe$^{2+}$ at 70~kOe without evidence of saturation. Magnetic susceptibility, heat capacity, and neutron scattering collectively reveal the onset of short-range magnetic interactions near 5~K, with no long-range ordering detected down to 0.06~K. Specific heat measurements demonstrate strong frustration: only $\sim$34\% of the expected magnetic entropy is recovered at 2.4~K. Taken together, these results establish FeGe$_3$O$_4$ as a rare example of a geometrically frustrated trillium-lattice magnet, offering a promising platform for exploring exotic quantum magnetic phenomena.

cond-mat.str-el↗

arXiv2025

Structural transition and possible pressure-induced superconductivity in a suboxide La$_5$Pb$_3$O

Here we report a structural phase transition and its possible competition with superconductivity in the suboxide La$_5$Pb$_3$O. Upon cooling through $T_t$ = 225 K, La$_5$Pb$_3$O transforms from a high-temperature I4/mcm to a low-temperature P4/ncc structure in which La - Pb dimerization along the c-axis occurs. This transition is accompanied by anomalies in the temperature dependence of electrical resistivity and specific heat. High-pressure electrical transport measurements reveal that hydrostatic pressure suppresses the structural transition and possibly induces superconductivity with a maximum superconducting temperature of 10 K. Density functional theory calculations show minimal changes in the electronic density of states and no gap opening at $E_F$ across $T_t$, suggesting that the transition is driven by bonding effects rather than Fermi surface instability. These findings establish La$_5$Pb$_3$O as a promising platform for exploring the interplay between weak structural transitions and superconductivity.

cond-mat.supr-con↗

arXiv2025

Dichotomy of flat bands in the van der Waals ferromagnet Fe$_5$GeTe$_2$

Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantum destructive interference can quench the electronic kinetic energy. Although both have a narrow bandwidth, the two types of flat bands should exhibit very distinct spectral properties arising from their distinctive origins. So far, the two types of flat bands have only been realized in very different material settings and chemical environments, preventing a direct comparison. Here, we report the observation of the two types of flat bands within the same material system--an above-room-temperature van der Waals ferromagnet, Fe$_{5-x}$GeTe$_2$, distinguishable by a switchable iron site order. The contrasting nature of the flat bands is also identified by the remarkably distinctive temperature-evolution of the spectral features, indicating that one arises from electron correlations in the Fe(1) site-disordered phase, while the other geometrical frustration in the Fe(1) site-ordered phase. Our results therefore provide a direct juxtaposition of the distinct formation mechanism of flat bands in quantum materials, and an avenue for understanding the distinctive roles flat bands play in the presence of magnetism, topology, and lattice geometrical frustration, utilizing sublattice ordering as a key control parameter.

cond-mat.str-el↗

arXiv2025

Robust superzone gap opening in incommensurate antiferromagnetic semimetal EuAg$_4$Sb$_2$ under in-plane magnetic field

The interplay between magnetism and charge transport in semimetals has emerged as a fertile ground for discovering novel electronic phenomena. A notable example is the recent discovery of electronic commensuration arising from a spin moir\'e superlattice (SMS), realized as double-q spin modulation in the antiferromagnetic semimetal EuAg$_4$Sb$_2$. Here, we investigate the in-plane magnetic-field tunability of the SMS using neutron scattering, magnetic and transport measurements. We reveal an incommensurate noncollinear cycloidal magnetic ground state. Temperature-field phase diagrams constructed with field tilting uncover multiple spin-reoriented phases, suggesting the critical role of in-plane field components in driving magnetic transitions. Despite substantial spin reorientation of the double-q phase, we observe a persistent gap opening, evidenced by strong suppression in both Hall and longitudinal conductivities. Model calculations attribute this robustness to the stability of SMS under tilting fields. Our results establish EuAg$_4$Sb$_2$ as a tunable platform for exploring spin-texture-driven superzone gap opening in electronic states.

cond-mat.str-el↗

arXiv2025

Jeff = 1/2 Diamond Magnet CaCo2TeO6: A Pathway toward New Spin Physics and Quantum Functions

Diamond lattice magnets, formed by a framework of corner-sharing tetrahedra of magnetic cations, offer unique opportunities to realize novel states of matter for potential utility in information technology. However, research has mostly focused on AB2X4 spinels with Td magnetic ions. This hinders the atomically enabled tunability of competing interactions at different energy scales and the ability to harness many-body electronic states in quantum materials, making the discovery of quantum fluctuations and spin dynamics less accessible. We discover a new material CaCo2TeO6 featuring a diamond lattice of two distinct Oh-Co2+ sites. This material displays strong quantum fluctuations, increased competing magnetic exchange interactions, and field-induced tunability of magnetic structures. The results demonstrate how simple, fundamental refinements in ligand fields can profoundly influence the phase space of quantum matter.

cond-mat.mtrl-sci↗

arXiv2025

Electromagnon signatures of a metastable multiferroic state

Magnetoelectric multiferroic materials, particularly type-II multiferroics where ferroelectric polarizations arise from magnetic order, offer significant potential for the simultaneous control of magnetic and electric properties. However, it remains an open question as to how the multiferroic ground states are stabilized on the free-energy landscape in the presence of intricate competition between the magnetoelectric coupling and thermal fluctuations. In this work, by using terahertz time-domain spectroscopy in combination with an applied magnetic field, photoexcitation, and single-shot detection, we reveal the spectroscopic signatures of a magnetic-field-induced metastable multiferroic state in a hexaferrite. This state remains robust until thermal influences cause the sample to revert to the original paraelectric state. Our findings shed light on the emergence of metastable multiferroicity and its interplay with thermal dynamics.

cond-mat.str-el↗

arXiv2025

Anomalous temperature-dependent magnetization in the nearly collinear antiferromagnet Y$_2$Co$_3$

Y$_2$Co$_3$ is a newly discovered antiferromagnetic (AFM) compound with distorted kagome layers. Previous investigations via bulk magnetization measurements suggested a complex noncollinear magnetic behavior, with magnetic moments primarily anti-aligned along the $b$ axis and some canting towards the $ac$ plane. In this study, we report the magnetic structure of Y$_2$Co$_3$ to be an A-type AFM structure with ferromagnetic (FM) interactions within the distorted kagome plane and an interplane antiferromagnetic interaction, as determined by single-crystal neutron diffraction. The magnetic moments align along the $b$ axis, with minimal canting towards the $c$ axis, at odds with the previous interpretation of bulk magnetization measurements. The magnetic moments on the two distinct Co sites are [0, -0.68(3), 0] $\mu_B$ and [0, 1.25(4), 0.07(1)] $\mu_B$. We attribute the previously reported "noncollinear" behavior to the considerable temperature dependence of itinerant AFM exchange interactions, induced by thermal contraction along the $b$ axis. Additionally, our examination of lattice constants through pressure studies reveals compensating effects on FM and AFM interactions, resulting in negligible pressure dependence of $T_\textrm{N}$.

cond-mat.str-el↗

arXiv2024

Coexistence of Commensurate and Incommensurate Antiferromagnetic Groundstates in Co$_x$NbSe$_2$ Single Crystal

In Co$_x$NbSe$_2$, crystal symmetry, and cobalt site occupation drive the formation of two distinct magnetic phases. At $x = 1/4$, the centrosymmetric structure ($P$6$_3$/$mmc$) promotes Co-Co interactions leading to the formation of an $A$-type antiferromagnetic structure phase with a transition temperature of $T_N^A$ = 169 K. At $x = 1/3$, the non-centrosymmetric structure ($P$6$_3$22) induces a lower-temperature magnetic phase with $T_N^S$ = 28 K. We report the coexistence of both substructures within a superlattice, with a nuclear propagation vector of (1/3, 1/3, 0) relative to the host lattice. Single crystals of Co$_{0.28}$NbSe$_2$ exhibit both magnetic transitions, with $T_N^A$ corresponding to the $x \sim 1/4$ phase and $T_N^S$ corresponding to the $x \sim 1/3$ phase. Magnetic susceptibility and specific heat measurements confirm these transitions, although only the high-temperature $T_N^A$ phase significantly affects resistivity. We successfully isolate each phase in powder samples, while single crystals with an intercalation ratio of $x = 0.28$ display the coexistence of both phases in a single sample. Using single-crystal neutron diffraction, we solved the magnetic structure of the high-temperature centrosymmetric phase ($T_N^A$), and neutron powder diffraction revealed the double-$q$ magnetic structure of the low-temperature noncentrosymmetric phase ($T_N^S$)

cond-mat.mtrl-sci↗