arXiv subjects

P. Khuntia

Publications and source records attributed to P. Khuntia.

At least 19 recordsLinked to original sources

arXiv2026

Magnetic properties of a quasi-two-dimensional spin-1/2 antiferromagnet Y2CuGe4O12

Competing magnetic interactions and frustration-induced quantum fluctuations in spatially anisotropic low-dimensional magnets often give rise to exotic magnetic phenomena, including field-induced phases. Here, we present crystal structure, magnetic susceptibility, specific heat, and electron spin resonance (ESR) measurements on polycrystalline Y$2$CuGe$4$O${12}$, supported by density functional theory (DFT) calculations. In this compound, the Cu$^{2+}$ ions form a distorted triangular lattice with competing intraplanar ferromagnetic ($J_1 \approx 0.138$ K and $J_2 \approx 0.01$ K) and antiferromagnetic ($J_3 \approx -3.22$ K) exchange interactions, together with a weaker interplanar antiferromagnetic coupling ($J_4 \approx -1.56$ K). These interactions account for the small Curie--Weiss temperature, $θ{\rm CW}=-1.8$ K. Despite the dominant antiferromagnetic interactions, no signature of long-range magnetic ordering is observed down to 0.4 K. Instead, broad maxima in both the magnetic susceptibility and magnetic specific heat reveal the development of short-range spin correlations, further supported by the critical ESR linewidth broadening characteristic of low-dimensional frustrated magnets. Application of an external magnetic field progressively suppresses the broad maximum in the magnetic specific heat, reflecting competition between the Zeeman and exchange energy scales, and drives the system into a field-polarized state above the saturation field, $μ_0H_{\rm s}=2.6$ T. In this regime, the magnetic specific heat exhibits an exponential temperature dependence, consistent with gapped magnon excitations. These results establish Y$_2$CuGe$4$O${12}$ as a rare distorted triangular-lattice magnet in which further-neighbor exchange interactions dominate the magnetic behavior, providing a promising platform for exploring frustration-driven quantum phenomena.

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arXiv2026

Coexistence of static order and spin dynamics in an S = 5/2 frustrated triangular antiferromagnet

Frustrated triangular-lattice antiferromagnets in the classical high-spin limit provide a paradigmatic setting in which the interplay of competing exchange interactions, anisotropy, and collective degrees of freedom can lead to unconventional low-energy excitations, anomalous criticality, and persistent dynamical responses. Here, we present comprehensive thermodynamic, $μ$SR, and neutron diffraction experiments, along with first-principles calculations, on a triangular-lattice antiferromagnet, MnSnB$_2$O$_6$, where Mn$^{2+}$ ($S=5/2$) moments form a nearly perfect 2D triangular network without any anti-site disorder. The Curie-Weiss fit to the magnetic susceptibility yields a moderate Curie-Weiss temperature of $-12$ K, indicating dominant antiferromagnetic interactions between Mn$^{2+}$ moments, which is supported by first-principles calculations. Specific-heat measurements reveal the onset of long-range magnetic order at $T_{\rm N}\approx 1$ K, which is ascribed to intraplane exchange interactions. The specific heat exhibits pronounced short-range correlations above $T_{\rm N}$ and an unconventional power-law behavior, $C\propto T^{1.37}$, deep in the ordered state, suggesting the presence of non-trivial low-energy excitations. Zero-field $μ$SR experiments down to 50~mK confirm the presence of magnetic ordering below $T_{\rm N}$, in agreement with thermodynamic and neutron diffraction experiments. The $μ$SR measurements detect persistent spin dynamics coexisting with static magnetic order. The temperature evolution of the order parameter down to 50~mK from neutron diffraction suggests that the ordered state is consistent with a 3D Ising-like antiferromagnet. This family of archetypal frustrated magnets offers a promising venue for the experimental realization of emergent phenomena governed by competing exchange interactions and exotic low-energy excitations.

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arXiv2026

Exotic magnetism and persistent spin dynamics in a frustrated Jeff = 1/2 triangular lattice antiferromagnet

The delicate interplay between competing degrees of freedom, anisotropy, and frustration-induced strong quantum fluctuations in pseudospin-$J_{\rm eff}=1/2$ rare-earth triangular-lattice antiferromagnets offers a promising platform for the experimental realization of exotic states with nontrivial low-energy excitations. Here, we present thermodynamic, inelastic neutron scattering (INS), and muon spin relaxation ($μ$SR) investigations of the frustrated magnet K$_3$NdTe$_2$O$9$, in which Nd$^{3+}$ ions constitute a structurally perfect triangular lattice with no detectable site disorder. The experiments reveal the realization of a Kramers doublet ground state with $J{\rm eff}=1/2$ moments, well separated from the first excited state, which interact antiferromagnetically with an exchange interaction of $\sim$0.6 K between the Nd$^{3+}$ moments in the triangular plane. The absence of oscillations and the so-called 1/3 plateau in the zero-field $μ$SR asymmetry down to 50 mK rules out long-range magnetic ordering and spin freezing on the $μ$SR time scale, respectively. The temperature dependence of the zero-field $μ$SR relaxation rate is well described by the Orbach relaxation mechanism, indicating the existence of fluctuating moments in the ground state of this frustrated magnet. Our results demonstrate exotic magnetism and persistent spin dynamics down to 50 mK. These observations establish this new family of frustrated rare-earth triangular-lattice antiferromagnets as a promising venue for the experimental realization of nontrivial quantum states with exotic low-energy excitations.

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arXiv2026

Signature of spin liquid state in a frustrated 3D antiferromagnet

Frustrated pyrochlore lattices in transition-metal oxides provide an ideal platform for realizing exotic quantum states, including spin liquids with unconventional low-energy excitations arising from the macroscopic ground-state degeneracy of corner-sharing tetrahedral networks. Here, we report the synthesis and comprehensive characterization of ZnCrGaO$4$, a frustrated three-dimensional pyrochlore-like magnet in which intrinsic cation ordering gives rise to unavoidable atomic-site disorder. A Curie--Weiss analysis of the high-temperature magnetic susceptibility yields a large negative Curie--Weiss temperature, $θ{\mathrm{CW}} \approx -205$ K, indicating dominant antiferromagnetic exchange interactions ($J/k_{\mathrm{B}} \sim 55$ K) between Cr$^{3+}$ ($S = 3/2$) moments. Despite the presence of strong antiferromagnetic interactions, no signature of long-range magnetic ordering is observed down to 125 mK, as evidenced by specific-heat and ac-susceptibility measurements. Furthermore, the absence of bifurcation between zero-field-cooled and field-cooled dc magnetic susceptibilities measured at 0.01 T indicates the absence of spin freezing, which is further supported by the frequency-independent ac susceptibility down to 250 mK. The presence of broad maxima in the magnetic specific heat and ac susceptibility at low temperatures suggests the development of short-range spin correlations within a dynamic magnetic state. In addition, the low-temperature specific heat follows a power-law behavior below 1 K, indicating the presence of unconventional low-energy excitations and algebraic spin correlations. These results provide compelling evidence for a dynamic correlated ground state in ZnCrGaO$_4$, establishing it as a promising platform for exploring highly frustrated $S > 1/2$ three-dimensional quantum magnets and potential spin-liquid behavior.

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arXiv2026

Topological spin freezing in frustrated quantum materials

Competing interactions, non-trivial electronic band topology, quantum fluctuations, and the interplay between emergent degrees of freedom in frustrated quantum materials can give rise to a wide range of exotic phenomena. Glassy dynamics, originally studied in amorphous materials and biological systems, has recently attracted considerable interest in quantum condensed matter, particularly in relation to the collective behavior of spins, quasiparticle excitations, and topological spin textures. Here, we investigate the emergence of unconventional glassy spin dynamics in a broad class of frustrated quantum materials, where spin freezing exhibit distinct signatures in both thermodynamic and microscopic measurements. Using a comprehensive set of experimental probes, including thermodynamic, NMR, ($μ$SR), and neutron scattering, we identify characteristic signatures of topological spin-glass behavior and these complementary techniques reveal unconventional spin dynamics, short-range spin correlations, emergent low-energy excitations, and glassy behavior of topological origins, distinguishing these states from conventional spin glasses and disordered magnets. Furthermore, we discuss the role of hydrodynamic spin modes in governing glassy dynamics and the emergence of spin-jam states in frustrated lattices, providing a unified framework for understanding unconventional spin freezing of topological origin and bridging experimental observations with theoretical models. This review aims to advance our understanding of collective many-body phenomena arising from competing interactions, topological defects, collective excitations, quantum entanglement, and symmetry constraints. Such insights may facilitate the discovery and design of novel quantum materials and help address fundamental questions in contemporary condensed matter physics, with potential implications for future quantum technologies.

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arXiv2026

Quantum spin liquid on a 3D bipartite lattice of spin trimers stabilized by enhanced effective anisotropy

Quantum spin liquids (QSLs) represent highly entangled states of matter in which frustration-induced quantum fluctuations suppress any symmetry-breaking phase transition down to absolute zero, giving rise to fractionalized excitations and emergent gauge fields. Theoretically, bond anisotropy can stabilize QSLs even on bipartite lattices, as exemplified by the Kitaev honeycomb model; however, no material has so far been established to realize such a state as its true ground state. Here we identify the three-dimensional spin-trimer magnet KBa$_3$Ca$_4$Cu$_3$V$_7$O$_{28}$ as a promising candidate for a bipartite quantum spin liquid persisting to the lowest temperatures. Strongly coupled Cu$^{2+}$ trimers form effective pseudospin-1/2 degrees of freedom upon cooling, which in turn constitute a three-dimensional bipartite network. Bulk thermodynamic measurements, neutron scattering, $μ$SR, and NMR detect no spin freezing or symmetry-breaking phase transition down to 20 mK, but instead reveal a gapless dynamical ground state with algebraic spin autocorrelations. Complementary Monte Carlo and exact-diagonalization calculations show that this state is stabilized by a strong enhancement of effective anisotropy: a weak microscopic Cu-Cu exchange anisotropy of approximately 15 percent is generically amplified at the trimer level, producing effective pseudospin-pseudospin interaction anisotropies of 60 to 100 percent. Our results establish trimer-based networks as a promising platform for realizing anisotropy-stabilized quantum entangled states, even in three-dimensional bipartite systems with only weak microscopic anisotropy.

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arXiv2026

Melting upon cooling in a quantum magnet

Heating enhances thermal fluctuations and typically leads to melting of solids, but in exceptional cases, heating can also cause liquids to solidify. The paradigm of this counterintuitive phenomenon is solidification of liquid $^3$He upon increasing temperature, known as the Pomeranchuk effect. Here we show that such inverse melting also appears in quantum magnetism. We find that, on cooling, the Ising-like triangular-lattice antiferromagnet erbium heptatantalate first develops a three-sublattice long-range magnetic order -- analogous to a solid -- which then, unexpectedly, melts at even lower temperatures into a short-range correlated spin-stripe state -- analogous to a liquid. We propose that such an unprecedented ``spin Pomeranchuk effect" can generically arise from strong competition between spin-spin interactions in frustrated magnets, and provides a novel avenue to transformations between exotic magnetic phases.

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arXiv2026

Exotic magnetism and persistent short-range spin correlations in a frustrated honeycomb lattice antiferromagnet

Two-dimensional high-spin bipartite honeycomb networks, where anisotropy, competing exchange interactions, and spin fluctuations interplay, provide an alternative platform to test theoretical models that distinguish between classical and quantum magnetism in the context of emergent many-body phenomena and exotic excitations. Here, we report the crystal structure, magnetization, specific heat, and inelastic neutron scattering measurements of the $S = 5/2$ distorted honeycomb magnet $\mathrm{CaZn_2Fe(PO_4)_3}$. Magnetization measurements reveal dominant antiferromagnetic interactions between the $\mathrm{Fe^{3+}}$ ($S = 5/2$) moments. The development and field evolution of a dip in the magnetic susceptibility under an external magnetic field indicate an unconventional field-induced transition, further supported by anomalies observed in magnetization isotherms. Zero-field specific heat measurements show an antiferromagnetic transition at $T_N \approx 1.67 \mathrm{K}$, which evolves under applied magnetic field, suggesting stabilization of a field-induced spin-canted state. Thermodynamic measurements reveal short-range spin correlations above the transition temperature. Inelastic neutron scattering results further corroborate antiferromagnetic ordering, consistent with specific heat data. Spin-wave calculations indicate competing exchange interactions that introduce magnetic frustration, along with weak Ising-like anisotropy. The interplay of competing interactions and anisotropy gives rise to exotic field-induced behavior and places the system in close proximity to a mean-field tricritical point in the $J_2/J_1$--$J_3/J_1$ phase diagram, opening a route to unconventional states in high-spin frustrated honeycomb magnets.

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arXiv2026

Spin-liquid-like spin dynamics in the frustrated antiferromagnet TbBO3

The synergistic interplay between spin correlations, spin-orbit coupling, and competing exchange interactions provides a promising route to realize exotic quantum states with nontrivial excitations in rare-earth based frustrated magnets. Here, by using thermodynamic and local-probe measurements down to 16 mK, we demonstrate the exotic magnetism and spin dynamics in the distorted triangular lattice TbBO3. Thermodynamic experiments reveal the presence of dominant antiferromagnetic exchange and subdominant dipolar interactions. Despite sizable antiferromagnetic exchange interactions between the Tb3+ moments, muon-spin relaxation experiment does not detect any signatures of long-range magnetic order or spin-freezing down to 16 mK, corroborating the specific heat and ac magnetic susceptibility down to 45 mK that suggests a persistent spin dynamics in this frustrated triangular lattice. The scaling of muon relaxation rate as a function of the characteristic energy scale for several spin-liquid candidates, including TbBO3, demonstrates that a common underlying mechanism is at play. The persistent dynamics in this frustrated triangular lattice antiferromagnet is reminiscent of a universal spin-liquid-like spin fluctuations, here attributed to dominant two dimensional (2D) antiferromagnetic short-range spin correlations, confirmed by the presence of a broad magnetic diffuse scattering in the elastic and low-energy inelastic neutron scattering channels at Q ~ 1.03 Ang**$^{-1}$** at low temperatures. Our results demonstrate that non-Kramers ion based triangular lattice hosts spin-liquid-like dynamics of local moments arising from the admixture of excited crystal electric field states into the ground state and intertwining of frustration and spin-orbit interaction.

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arXiv2026

Magnetic properties of a buckled honeycomb lattice antiferromagnet

The intriguing interplay between competing degrees of freedom in frustrated magnets can lead to non-trivial magnetic phenomena with exotic low-energy excitations that are highly relevant for addressing some of the fundamental questions in quantum condensed matter as well as potential technological applications. Herein, we report the synthesis and thermodynamic results on a frustrated magnet Co3ZnNb2O9. The Co2+ moments constitute buckled AB-type honeycomb layers in the ab-plane. The temperature-dependent magnetic susceptibility shows a sharp anomaly at 14 K, indicating the onset of long-range magnetic ordering. The Curie-Weiss fit of the magnetic susceptibility above 100 K, yields a Curie-Weiss temperature of -70 K, suggesting strong antiferromagnetic (AFM) interactions between the Co2+ spins and an effective magnetic moment of 5.54 muB, indicating the presence of unquenched orbital angular momentum. A field-induced spin-flop-like metamagnetic transition below the ordering temperature is characterized by a critical magnetic field of 1.2 T. The specific heat shows a lambda-type anomaly at 14 K, confirming the presence of long-range magnetic ordering, due to finite interlayer interaction. Interestingly, our study of the magnetocaloric effect near the transition temperature revealed an entropy change of 2.81 J/kg.K, which is ascribed to competing interactions, underlying anisotropy, and reduced net magnetization lead to relatively small isothermal entropy changes that suggest that frustrated honeycomb magnets are promising contenders for field-induced exotic phases and magnetocaloric response.

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arXiv2026

Magnetic ground state of a Jeff = 1/2 based frustrated triangular lattice antiferromagnet

The subtle interplay between competing degrees of freedom, crystal electric fields, and spin correlations can lead to exotic quantum states in 4f ion-based frustrated triangular lattice antiferromagnets. We present the crystal structure, thermodynamic and muon spin relaxation (μSR) studies of the 4f ion-based frustrated magnet Ba4YbReWO12, wherein Yb3+ ions constitute a triangular lattice. The magnetic susceptibility does not show any signature of spin freezing down to 1.9 K or long-range magnetic ordering down to 0.4 K. The low-temperature Curie-Weiss fit to the inverse magnetic susceptibility data reveals a weak antiferromagnetic exchange interaction, which is corroborated by the fit of magnetic specific heat data following the J1-J2 model with the nearest neighbor exchange interaction of J1 = -0.197 K between the Jeff = 1/2 states of the Yb3+ moments in the lowest Kramers doublet. The lowest Kramers ground state doublet is well separated from the first excited state with a gap of 278 K, as evidenced by our μSR experiments that support the realization of Jeff = 1/2 at low temperatures. The specific heat experiments do not detect a phase transition down to 56 mK. The magnetic specific heat shows a broad maximum 90 mK suggesting a disordered ground state with short range spin correlations. The associated magnetic entropy release at low temperatures is consistent with that expected for the Jeff = 1/2 state. The zero-field μSR measurements show neither the signature of spin freezing nor a phase transition, at least down to 43 mK. Our results suggest a dynamic, disordered ground state in this Jeff = 1/2 frustrated triangular lattice antiferromagnet. Ba4RReWO12 (R=rare earth) offers a viable platform to realize intriguing quantum states borne out of spin-orbit coupling and frustration

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arXiv2025

Spin liquid state in a three-dimensional pyrochlore-like frustrated magnet

The three-dimensional frustrated spin lattice in MgCrGaO4, where Cr3+ ions occupy a pyrochlore-like network, exemplifies a quantum magnet with competing interactions, macroscopic degeneracy, and exotic low-energy excitations. Using thermodynamic, electron spin resonance (ESR), muon spin relaxation (muSR), and inelastic neutron scattering (INS) techniques, we observe no magnetic order or spin freezing down to 57 mK, despite a sizable exchange interaction (J= 58 K) between Cr3+ (S=3/2) moments and inherent site disorder. Below the characteristic exchange energy scale, all experimental probes detect the emergence of antiferromagnetic short-range spin correlations, corroborated by magnetic diffuse scattering in the wave vector dependence of low-energy magnetic excitations centered on Q = 1.5 A^-1 in inelastic neutron scattering experiments. The low-temperature specific heat follows a near-quadratic dependence without a gap, consistent with algebraic spin correlations. These results establish MgCrGaO4 as a rare three-dimensional classical spin liquid featuring a highly degenerate ground-state manifold and gapless excitations, offering a strong impetus for the experimental realization of spin liquids in higher-dimensional frustrated quantum magnets.

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arXiv2025

Coexistence of static and dynamic local magnetic fields in an S = 3/2 honeycomb lattice antiferromagnet Co2Te3O8

Two-dimensional honeycomb lattices, characterized by their low coordination numbers, provide a fertile platform for exploring various quantum phenomena due to the intricate interplay between competing magnetic interactions, spin-orbit coupling, and crystal electric fields. Beyond the widely studied Jeff= 1/2 honeycomb systems, S = 3/2 honeycomb lattices present a promising alternative route to realizing the classical spin liquid-like state within the spin-S Kitaev models. Herein, we present crystal structure, thermodynamic, neutron diffraction and muon spin relaxation (muSR) measurements, complemented by density functional theory (DFT) calculations on an unexplored 3d transition metal based compound Co2Te3O8, where Co2+ (S = 3/2) ions form a distorted honeycomb lattice in the crystallographic bc-plane without any anti-side disorder between constituent atoms. A clear lambda type anomaly around 55 K in both magnetic susceptibility and specific heat data indicates the onset of a long-range ordered state below TN= 55 K. The dominant antiferromagnetic interaction between S = 3/2 moments is evidenced by a relatively large negative Curie-Weiss temperature of -103 K derived from magnetic susceptibility data and supported by DFT calculations. The signature of long-range antiferomagnetic order state in the thermodynamic data is corroborated by neutron diffraction and muSR results. Furthermore, muSR experiments reveal the coexistence of static and dynamic local magnetic fields below TN, along with a complex magnetic structure that can be associated with XY-like antiferromagnet, as confirmed by neutron diffraction experiments.

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arXiv2025

Comment on "Neutron diffraction evidence of the 3-dimensional structure of Ba2MnTeO6 and misidentification of the triangular layers within the face-centred cubic lattice"

Frustrated magnetism continues to attract significant attention due to its potential to host novel quantum many-body phenomena and associated exotic excitations that transcend existing paradigms. Herein, we present our reply to the comment on our recent thermodynamic and muon spin relaxation studies on a frustrated double perovskite, Ba2MnTeO6 (henceforth BMTO). Previous studies by four independent groups, including our group, suggested a trigonal space group based on single-crystal and polycrystalline samples of BMTO, while the recent comment reports a cubic space group based on polycrystalline samples. We believe that the structure is fairly intricate because of the slight variations between the two space groups, refining the crystal structure of BMTO remains an unresolved problem that needs additional high-resolution XRD and neutron diffraction studies on high-quality single crystals. It is thought, however, that structural assignments will not greatly influence any of the primary findings related to the magnetism and spin dynamics of BMTO. These consist of a magnetic phase transition at around 21 K, the observation of antiferromagnetic magnon excitations exhibiting a gap of 1.4 K beneath the phase transition, the presence of short-range spin correlations well above the antiferromagnetic phase transition, and the persistence of spin dynamics even within the magnetically ordered phase. It is important to note that the magnetization, specific heat, and muon spin relaxation findings that constitute the core of our earlier study are independent; the interpretation of these findings did not rely on any specific space group. Concerning the final allocation of the symmetry of BMTO, a definitive differentiation in certain physical characteristics resulting from the symmetry is still necessary.

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arXiv2025

A novel Gapless Quantum Spin Liquid in the S = 1 4d4-honeycomb material Cu$_3$LiRu$_2$O$_6$

We report the discovery of a novel gapless quantum spin liquid in the S=1 honeycomb system Cu$_3$LiRu$_2$O$_6$ with Ru$^{4+}$ ($4d^4$) where moments remain dynamic down to 50 mK. Heat capacity measurements show no sign of magnetic ordering down to 60 mK in spite of a Curie-Weiss temperature = -222 K indicating a strong antiferromagnetic interaction. In zero field, magnetic heat capacity shows a linear T-dependence with Sommerfeld coefficient = 107 mJ/mol K$^2$ is much larger than that found in typical Fermi liquids. Our local probe $^7$Li nuclear magnetic resonance (NMR) measurements find a significant temperature-independent $^7$Li NMR shift (and hence a non-zero spin susceptibility) at low-T and a linear T-variation of the $^7$Li NMR spin-lattice relaxation rate 1/T$_1$ at low-T reminiscent of fermionic excitations. Muon spin relaxation measurements detect neither long-range ordering nor spin freezing down to 50 mK and the temperature variation of the muon depolarization rate shows a gradual increase with decreasing temperature and a leveling off below about 1 K evincing a persistent spin dynamics common to several spin liquid candidates. Our results provide strong signatures of a quantum spin liquid in the titled honeycomb material.

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arXiv2024

Magnetic properties and field-induced phenomena in the Jeff = 1/2 distorted kagome antiferromagnet

The intertwining between competing degrees of freedom, anisotropy, and frustration-induced quantum fluctuations offers an ideal ground to realize exotic quantum phenomena in the rare-earth-based kagome lattice. The magnetic susceptibility reveals the presence of two energy scales in agreement with the INS results. The higher energy state is dominated by CEF excitations, where the lowest Kramers ground-state doublet is well separated from the excited state suggesting that the compound realizes a low-energy state at low temperatures. The second energy scale is witnessed via thermodynamic results that reveal an anomaly at 0.3 K typical of a phase transition, which is attributed to the presence of complex magnetic ordering phenomena. The broad maximum in the specific heat well above 0.3 K indicates the presence of short-range spin correlations that is corroborated by muon spin relaxation rate results. The isothermal magnetization reveals a field-induced 1/3 magnetization plateau at low temperatures. muSR relaxation rate experiments, on the other hand, neither show the signature of a phase transition nor spin-freezing down to 34 mK. The ZF muSR relaxation is governed by the Orbach process and reveals the presence of a fluctuating state owing to the depopulation of crystal field levels reflected as a constant value of relaxation rate in the temperature range 0.4-10 K. NMR results indicate the presence of fluctuating Nd3+ moments down to 1.8 K consistent with muSR experiments. Our comprehensive results reveal that a field-induced quantum critical phenomenon is at play in this frustrated kagome magnet and enable us to construct a phase diagram exemplifying the proximity effect of competing magnetic states. This sets the stage to investigate the broad RE3BWO9 family of rare-earth kagome magnets promising to host exotic quantum states driven by spin-orbit coupling and geometrical frustration.

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arXiv2024

The nature of low-temperature spin-freezing in frustrated Kitaev magnets

The subtle interplay between competing degrees of freedom, anisotropy, and spin correlations in frustrated Kitaev quantum materials offers an ideal platform to host non-trivial quantum states with exotic fractional excitations. The signature of spin-freezing behavior of these spin-orbit-driven frustrated magnets is characterized by a bifurcation of zero-field-cooled and field-cooled magnetic susceptibility at low temperatures much below the characteristic interaction energy scale of spins. The temperature dependence of magnetic specific heat exhibits Cm~ T^2 dependence near the freezing temperature. The field-independent behavior of Cm below the freezing temperature implies the presence of exotic low-energy excitations. The aging and memory effect experiments in the Kitaev magnets suggest a non-hierarchical free energy distribution, which differs from the hierarchical organization of conventional spin-freezing. Furthermore, the NMR spin-lattice relaxation rate follows a power law behavior below the spin-freezing temperature, suggesting the persistence of unconventional spin excitation spectra. Herein, we demonstrate that the observed low-temperature spin-freezing phenomena in a few representative Kitaev quantum materials can be effectively explained by the Halperin and Saslow (HS) hydrodynamic modes relevant for non-trivial spin glass materials. The linearly dispersive HS modes are hypothesized to account for instigating non-abelian defect propagation, thereby inducing a spin jam state in the low-temperature regime in frustrated Kitaev magnets. Our investigation reveals that HS modes capture the essence of unconventional spin-freezing ascribed to topological origin in two-dimensional (2D) Kitaev magnets decorated on a honeycomb lattice and its 3D analog hyperhoneycomb that offers a viable ground to extend this framework to a large class of frustrated quantum materials.

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arXiv2024

Possible realization of a randomness-driven quantum disordered state in an S = 1/2 antiferromagnet Sr3CuTa2O9

Collective behavior of spins, frustration-induced strong quantum fluctuations, and subtle interplay between competing degrees of freedom in quantum materials can lead to correlated quantum states with exotic excitations that are essential ingredients for establishing paradigmatic models and have immense potential for quantum technologies. Disorder is ubiquitous in real materials, and the detailed insights into the role of disorder on the intriguing ground state borne out of quenched randomness provide a route toward the design and discovery of functional quantum materials. Herein, we report magnetization, specific heat, electron spin resonance, and muon spin resonance studies on a 3d-electron-based antiferromagnet Sr3CuTa2O9. The negative Curie- Weiss temperature value, obtained from the Curie-Weiss fit of high-temperature magnetic susceptibility data, indicates antiferromagnetic interaction between Cu2+ moments. Specific heat data show the absence of long-range magnetic ordering down to 64 mK despite a reasonably strong exchange interaction between Cu2+ (S =1/2) spins as reflected from a Curie-Weiss temperature of -27 K. The power-law behavior and the data collapse of specific heat and magnetization data evince the emergence of a random-singlet state in Sr3CuTa2O9. The power-law-like spin auto-correlation function and the data collapse of muon polarization asymmetry with longitudinal field dependence of t(μ0H)^γ further support credence to the presence of a randomness-induced quantum disordered state. Our results suggest that randomness induced by disorder is an alternate route to realize a quantum disordered state in this antiferromagnet.

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