arXiv subjects

Haidong Zhou

Publications and source records attributed to Haidong Zhou.

At least 19 recordsLinked to original sources

arXiv2026

High-pressure phase transitions in the quantum spin liquid candidate Na2Co2TeO6 probed by Raman spectroscopy

The quasi-2D magnet Na2Co2TeO6 (NCTO) is a candidate for a Kitaev Quantum Spin Liquid (KQSL) state. Pressure-tuning in such materials is of interest as a potential method to tune the Kitaev exchange interactions, which are strongly dependent on bond geometry. Here we report a Raman spectroscopic study of NCTO inside a diamond anvil cell (DAC) with pressure applied up to 16.3 GPa. Based on the changes in the Raman modes, this pressure range is divided into three regions. The appearance and disappearance of several modes and changes in the polarization dependence of the representative modes, most prominently above 13.8 GPa, point to pressure-induced phase transitions in this material.

cond-mat.str-el↗

arXiv2026

Local magnetic order in vacancy-disrupted spin ice Ho2TiO5

We investigate how local magnetic correlations evolve when the classical pyrochlore spin-ice Ho2Ti2O7 is transformed into the partially disordered stuffed compound Ho2TiO5. Neutron scattering measurements were analyzed using real-space magnetic pair distribution function, reciprocal-space reverse Monte Carlo, and half-polarized neutron powder diffraction methods to connect the average crystal structure with local magnetic correlations. Both compounds retain long-range $Fd-3m symmetry, but in Ho2TiO5 this average structure distorts locally through Ho-O, Ti-O and O-O bond-length disorder associated with partial Ho/Ti occupancy. Despite this disorder, half-polarized neutron powder diffraction shows that the Ho moments retain local <111> rangle Ising anisotropy and form spin-in/spin-out configurations on the tetrahedral network. In Ho2Ti2O7, real- and reciprocal-space analyses reveal a nearly ideal two-in/two-out spin-ice state at 0.3K, with 95% of tetrahedra satisfying the ice rule, followed by progressive thermal disordering on warming. In Ho2TiO5, most tetrahedra are magnetically incomplete because some tetrahedral vertices are occupied by nonmagnetic Ti rather than Ho; nevertheless, the dominant incomplete configurations are 2-in/1-out and 1-in/2-out, which are locally compatible with the ice rule if the missing Ho spin is restored. The single-ion <111> Ising anisotropy is therefore retained throughout, while the collective ice ordering is strongly disrupted: Ho2TiO5 is a vacancy-disrupted spin ice in which a local ice-rule tendency persists on a topologically incomplete magnetic network.

cond-mat.str-el↗

arXiv2026

Revealing Intrinsic Anisotropy of Collective Magnetic Excitations in Twinned Crystals of a Kitaev-Heisenberg Quantum Magnet

Quantum magnets with competing interactions often emerge from delicate balances among microscopic parameters, making it essential to disentangle intrinsic spin dynamics from extrinsic disorder effects. Here, we introduce a multimodal optical approach combining magneto-infrared spectroscopy with domain-resolved micro-Raman spectroscopy at high magnetic fields to reconstruct the intrinsic magnetic excitation spectrum of twinned crystals of the Kitaev-Heisenberg quantum magnet Na$_3$Co$_2$SbO$_6$. Far-infrared spectroscopy reveals multiple field-tunable magnetic excitations, but the intrinsic response is obscured by replica features arising from twin domains. By correlating magneto-infrared and domain-resolved Raman spectra, we isolate the single-domain magnon response and uncover a pronounced twofold in-plane magnon anisotropy. This anisotropy far exceeds that expected from the measured in-plane g-factor anisotropy and is instead dominated by anisotropic bond-dependent exchange interactions. By unifying high-field, high-resolution and spatially selective optical probes, our work establishes a broadly applicable framework for revealing intrinsic spin dynamics and constraining the spin Hamiltonian in multidomain quantum magnets.

cond-mat.mtrl-sci↗

arXiv2026

Intertwined magnetoresistance and Hall multifunctionality in a non-coplanar magnetic Weyl semimetal DyB4

Anomalous magneto-transport responses provide complementary probes of orbital motion, momentum-space topology, and real-space spin chirality, yet their integration into a single material remains rare because their underlying requirements often compete. A promising materials-design strategy is to realize a magnetic Weyl semimetal that combines linearly dispersive high-mobility bands with tunable non-coplanar magnetism while limiting spin-dependent scattering. Here we identify DyB4, a frustrated rare-earth tetraboride, as a magnetic Weyl semimetal candidate that embodies this strategy and hosts intertwined magnetoresistance and Hall multifunctionality. Neutron diffraction reveals a sequence of field-tunable magnetic states, including non-coplanar spin configurations and PT-symmetry-broken phases. First-principles calculations identify steep linear dispersions and field-induced Weyl points near the Fermi level. Magneto-transport measurements establish a rare fourfold combination of extremely large magnetoresistance, chiral-anomaly-like negative magnetoresistance, large anomalous Hall conductivity arising from cooperative intrinsic Berry curvature and skew scattering, and scalar-spin-chirality-driven topological Hall responses. This multifunctionality arises from the distinct yet weakly coupled roles of itinerant carriers and localized 4f moments, which enable high-mobility transport, field-induced Weyl topology, and non-coplanar magnetism. DyB4 therefore provides a 4f-electron platform for correlating orbital transport, momentum-space Berry curvature, and real-space spin chirality, suggesting a route toward multifunctional magnetic topological materials.

cond-mat.mtrl-sci↗

arXiv2026

Revealing Charge Transfer in Defect-Engineered 4H$_\mathrm{b}$-TaS$_2$

We present a comprehensive first-principles investigation of defects in 4$H_b$-TaS$_2$. In this layered transition metal dichalcogenide, charge transfer between alternating Mott-insulating 1T and metallic 1H layers gives rise to exotic quantum phases such as the Kondo effect and topological superconductivity. Motivated by recent defect manipulation in 4$H_b$-TaS$_2$ via STM, we address their microscopic nature and impact on interlayer charge transfer. To this end, we systematically analyze over 90 defects using large-scale density functional theory (DFT) calculations. Our extensive dataset, compiled from STM simulations, defect formation energies, work functions, and charge transfer, establishes a foundational resource for future theoretical and experimental studies on defect engineering in 4$H_b$-TaS$_2$.

cond-mat.mtrl-sci↗

arXiv2026

One-to-one quantum simulation of a frustrated magnet with 256 qubits

Analog quantum simulators offer a powerful microscopic probe of quantum many-body systems, yet have largely been benchmarked against model Hamiltonians rather than real materials. Here, we use a 256-qubit Rydberg simulator to implement the effective Hamiltonian of the frustrated triangular-lattice magnet TmMgGaO$_4$. Simulated magnetization curves agree quantitatively with susceptibility measurements on single crystals, and both platforms consistently determine the antiferromagnetic phase transition. Snapshot-resolved analysis confirms that quantum fluctuations, rather than disorder, govern the intermediate paramagnetic regime. Having established this correspondence, we access non-equilibrium dynamics following a sudden quench, a regime at picosecond material timescales where entanglement growth places the problem beyond classical reach. The simulator reveals thermalization of local observables, demonstrating that analog quantum simulation can reproduce and extend the physics of a real material.

quant-ph↗

arXiv2026

Pressure-Induced Structural and Magnetic Evolution in Layered Antiferromagnet YbMn$_2$Sb$_2$

Electronic states under pressure exhibit unconventional spin and charge dynamics that provide a powerful route to uncover exotic phases in quantum materials. Here, we present the structural, magnetic, and electronic evolution of YbMn$_2$Sb$_2$ under pressure. Single-crystal X-ray diffraction reveals a pressure-induced structural transition from the space group trigonal $P\bar{3}m1$ to the monoclinic $P2_1$/$m$ phase near 3.5 GPa, which remains stable up to 10 GPa. Magnetization measurements display an anomalously weak net magnetic moment and the absence of Curie-Weiss behavior up to 400 K, suggesting the formation of short-range Mn moment pairs that cancel macroscopically and subsequently evolve into long-range order upon cooling. Temperature-dependent resistivity shows semiconducting behavior with a transition at ~119 K at ambient pressure, while pressure induces a dramatic suppression of resistance and the emergence of metallic-like temperature dependence, stabilized beyond 5 GPa. This pressure-driven semiconductor-metal transition is consistent with our density functional theory calculations, confirming the closing of the band gap under compression. Neutron diffraction under pressure identifies an incommensurate magnetic structure with antiparallel correlations between paired spins. Together, these results demonstrate how pressure-driven structural tuning and competing exchange interactions stabilize unconventional magnetic states in this low-dimensional magnetic semiconductor.

cond-mat.mtrl-sci↗

arXiv2026

Spin dynamics of the spin-1 triangular lattice Heisenberg antiferromagnet K$_2$Ni(SeO$_3$)$_2$

Strong quantum fluctuations and unconventional spin dynamics are well established in the spin-1/2 triangular lattice Heisenberg antiferromagnet. However, their survival in the spin-1 case remains an open question. We investigate the spin dynamics of K$_2$Ni(SeO$_3$)$_2$, a nearly ideal spin-1 triangular lattice Heisenberg antiferromagnet, using inelastic neutron scattering. Below the ordering temperature $T_{\rm N}$, we observe coherent one-magnon excitations coexisting with a broad high-energy continuum. Two complementary approaches, a spectrally consistent $1/S$-corrected spin wave theory and a beyond-mean-field Schwinger boson theory, reproduce different facets of the continuum. Neither alone is complete, demonstrating substantial quantum fluctuations survive for $S\!=\!1$ and are reflected primarily in the spectral distribution of the continuum. Above $T_{\rm N}$, the continuum bandwidth is conserved while spectral weight is redistributed as magnons lose spatial coherence. Our results establish K$_2$Ni(SeO$_3$)$_2$ as a model triangular antiferromagnet, identifying bandwidth conservation and the distribution of spectral weight within the continuum as organizing principles to understand the spin dynamics of ordered quantum magnets beyond spin-1/2. Our results highlight the need for controlled calculations of the interacting multi-magnon sector of 2D antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2026

diffpy.morph: Python tools for model independent comparisons between sets of 1D functions

diffpy$.$morph addresses a need to gain scientific insights from 1D scientific spectra in model independent ways. A powerful approach for this is to take differences between pairs of spectra and look for meaningful changes that might indicate underlying chemical, structural, or other modifications. The challenge is that the difference curve may contain uninteresting differences such as experimental inconsistencies and benign physical changes such as the effects of thermal expansion. diffpy$.$morph allows researchers to apply simple transformations, or "morphs", to one of the datasets to remove the unwanted differences revealing, when they are present, non-trivial differences. diffpy$.$morph is an open-source Python package available on the Python Package Index and conda-forge. Here, we describe its functionality and apply it to solve a range of experimental challenges on diffraction and PDF data from x-rays and neutrons, though we note that it may be applied to any 1D function in principle.

physics.comp-ph↗

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

Probing ice-rule-breaking transition in $\rm{Dy_2Ti_2O_7}$ thin film by proximitized transport and magnetic torque

While the spin ice state of bulk pyrochlores such as $\rm{Dy_2Ti_2O_7}$ and $\rm{Ho_2Ti_2O_7}$ has been extensively studied in the last several decades due to its unique degenerate ground state and emergent monopole excitation, whether it survives in the thin-film form remains a mystery. The limited volume of thin-film sample makes it challenging to study the intrinsic magnetic properties. Here, we synthesized 18nm-thick $\rm{Dy_2Ti_2O_7}$ thin film on YSZ (Yttria-stabilized Zirconia with 9.5 mol% $\rm{Y_2O_3}$) substrate and capped it by a thin conductive $\rm{Bi_2Ir_2O_7}$ layer, and performed the proximitized magnetoresistance measurements. Our study found that the ice-rule-breaking phase transition survives but with a modified effective nearest-neighbor interaction ($\rm{J_{eff}}=$ 1.054 K) and distorted Ising spin axes ($\rmε=+0.051)$ compared to the bulk crystal. The results are supported by the simultaneously measured capacitive torque magnetometry. Our study demonstrates that proximitized transport is an effective tool for thin films of insulating frustrated magnets.

cond-mat.mtrl-sci↗

arXiv2025

Nanoscale Modulation of Flat Bands via Controllable Charge-Density-Waves Defects in 4Hb-TaS2

Electron correlation is a main driver of exotic quantum phases and their interplay. The 4Hb-TaS2 system, possessing intrinsic heterostructure of 1T- and 1H-TaS2 monolayers, offers a unique opportunity to control electron correlation by distorting the atomic lattice or tuning interlayer coupling. Here, we investigated intrinsically deformed charge-density-waves (CDW) in the 1T layer of 4Hb-TaS2 to elucidate and control their effects on flat bands using scanning tunneling microscopy and spectroscopy (STM/S) combined with first-principles calculations. We identified two types of CDW defects: Type 1 has structural distortion and locally suppressed flat bands, while Type 2 features an increased flat band filling factor of intact CDW structure. Density functional theory calculations indicate that a sulfur vacancy in the 1T layer distorts the CDW structure and gives rise to a Type 1, whereas a sulfur vacancy in the 1H layer reduces the interlayer charge transfer and lead to a Type 2. Furthermore, we demonstrated creating and erasing individual CDW defects via STM manipulation. Our findings provide a pathway to not only tune flat bands but also selectively manipulate the interaction between CDW, the atomic lattice, and interlayer coupling in strongly correlated systems with atomic precision.

cond-mat.str-el↗

arXiv2025

Sharp spectroscopic fingerprints of disorder in an incompressible magnetic state

Disorder significantly impacts the electronic properties of conducting quantum materials by inducing electron localization and thus altering the local density of states and electric transport. In insulating quantum magnetic materials, the effects of disorder are less understood and can drastically impact fluctuating spin states like quantum spin liquids. In the absence of transport tools, disorder is typically characterized using chemical methods or by semi-classical modeling of spin dynamics. This requires high magnetic fields that may not always be accessible. Here, we show that magnetization plateaus -- incompressible states found in many quantum magnets -- provide an exquisite platform to uncover small amounts of disorder, regardless of the origin of the plateau. Using optical magneto-spectroscopy on the Ising-Heisenberg triangular-lattice antiferromagnet K$_2$Co(SeO$_3$)$_2$ exhibiting a 1/3 magnetization plateau, we identify sharp spectroscopic lines, the fine structure of which serves as a hallmark signature of disorder. Through analytical and numerical modeling, we show that these fingerprints not only enable us to quantify minute amounts of disorder but also reveal its nature -- as dilute vacancies. Remarkably, this model explains all details of the thermomagnetic response of our system, including the existence of multiple plateaus. Our findings provide a new approach to identifying disorder in quantum magnets.

cond-mat.mtrl-sci↗

arXiv2025

Constraints on magnetism and correlations in RuO$_2$ from lattice dynamics and Mössbauer spectroscopy

We provide experimental evidence for the absence of a magnetic moment in bulk RuO$_2$, a candidate altermagnetic material, by using a combination of Mössbauer spectroscopy, nuclear forward scattering, inelastic X-ray and neutron scattering, and density functional theory calculations. Using complementary Mössbauer and nuclear forward scattering we determine the $^{99}$Ru magnetic hyperfine splitting to be negligible. Inelastic X-ray and neutron scattering derived lattice dynamics of RuO$_2$ are compared to density functional theory calculations of varying flavors. Comparisons among theory with experiments indicate that electronic correlations, rather than magnetic order, are key in describing the lattice dynamics.

cond-mat.mtrl-sci↗

arXiv2025

Determining the Nature of Magnetism in Altermagnetic Candidate RuO$_2$

The terminology "altermagnetism" has recently been adopted to describe collinear magnetic order with no net magnetization and non-relativisitic, momentum-dependent spin-splitting. The archetypal material used to theoretically explore altermagnetism is RuO$_2$, but there has been significant debate as to whether RuO$_2$ possesses magnetic, let alone altermagnetic, order. To address questions surrounding the nature of magnetism in RuO$_2$, we combine symmetry-sensitive torque magnetometry and magnetization measurements in single crystals. The data are inconsistent with collinear magnetic order possessing a Néel vector along the $c-$axis. Torque magnetometry further demonstrates an isotropic magnetic susceptibility within the $ab-$plane, indicative of neither a Néel vector within the $ab-$plane nor a field-induced Néel vector reorientation. Magnetic quantum oscillations from both techniques reveal a nearly spherical Fermi surface pocket at the Brillouin zone center, in agreement with paramagnetic electronic structure calculations. Taken together, these data indicate no detectable long-range magnetic order and, by extension, suggest no altermagnetism in high-quality RuO$_2$ single crystals.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic Pair Distribution Function and Half Polarized Neutron Powder Diffraction at the HB-2A Powder Diffractometer

Local magnetic order and anisotropy are often central for understanding fundamental behavior and emergent functional properties in quantum materials and beyond. Advances in neutron powder diffraction experiments and analysis tools now allow for quantitative determination. We demonstrate this here with complementary total neutron scattering and polarized neutron measurements on the HB-2A neutron powder diffractometer at the High Flux Isotope Reactor (HFIR). In recent years, magnetic pair distribution function (mPDF) analysis has emerged as a powerful technique for probing local magnetic spin ordering of magnetic materials. This method can be broadly applied to any magnetic material but is particularly effective for studying systems with short-range magnetic order, such as materials with reduced dimensionality, geometrically frustrated magnets, thermoelectrics, multiferroics, and correlated paramagnets. Magnetic anisotropy often underpins the short-range order adopted. Half-polarized neutron powder diffraction (pNPD) can be used to determine the local susceptibility tensor on the magnetic sites to quantify the magnetic anisotropy. Combining the techniques of mPDF and pNPD can therefore provide valuable insights into local magnetic behavior. A series of measurements optimized for these techniques are presented as exemplar cases focused on frustrated materials where short-range order dominates, these include measurements to ultra-low temperature (<100 mK) not typically accessible for such experiments.

cond-mat.str-el↗

arXiv2025

NMR study of supersolid phases in the triangular-lattice antiferromagnet Na2BaCo(PO4)2

We report ultra-low-temperature $^{23}$Na NMR measurements on the Ising triangular lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$, which precisely resolve the phase diagram under magnetic field applied along the crystalline $c$ axis. With increasing field, the NMR spectra resolve three ordered phases with distinct spin configurations: the Y, up-up-down (UUD), and V phases. The spin-lattice relaxation rate $1/T_1$ data demonstrate gapless excitations in the Y and V phases, strongly supporting their supersolid nature. However, the phase transitions from the UUD phase to the two supersolid phases exhibit dramatically different behaviors upon cooling. Prior to entering the Y phase, $1/T_1$ identifies a gapless regime within the UUD phase, suggesting a Berezinskii-Kosterlitz-Thouless phase above a second-order phase transition. In contrast, the coexistence of the UUD and V phases observed in our experiments provides direct evidence of a first-order phase transition between these phases.

cond-mat.str-el↗

arXiv2025

Strain-tunable anomalous Hall plateau in antiferromagnet CoNb$_3$S$_6$

Antiferromagnets exhibiting the anomalous Hall effect represent a fascinating convergence of magnetism, topology, and electronic structure. Identifying antiferromagnets with large and tunable anomalous Hall effects is crucial for the development of spintronic applications. Here, we report a strain-tunable anomalous Hall plateau in CoNb$_3$S$_6$, which is a prime candidate for altermagnetism. The plateau emerges as a flat extended intermediate step of the anomalous Hall hysteresis loop with a controllable step height with temperature and strain. The remarkable tunability of the plateau position is in contrast with typical magnetic plateau associated with a field-induced metastable magnetic structure, but indicates the existence of a hidden phase transition that significantly alters the magnetic anisotropy energy without changing the magnetic order. The symmetry analysis of the strain tuning suggests that the hidden phase preserves the rotational symmetry of the ab-plane. Our results show the plateau reflects the phase coexistence during the hidden transition, and anomalous Hall resistivity of the plateau is thus non-volatile, enabling a novel four-state switching of the anomalous Hall effect.

cond-mat.mtrl-sci↗