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In this review, we consider the impact of magnetic field on the properties of strongly correlated heavy-fermion compounds such as heavy-fermion metals and frustrated insulators with quantum spin liquid. Magnetic field B can be considered a universal tool, allowing the exploration of the physics controlling the remarkable properties of heavy-fermion compounds. These vivid properties are T / B scaling, exhibited under the application of magnetic field B and at fixed temperature T, and the emergence of Landau Fermi liquid behavior under the application of magnetic field. We analyze the influence of quasiparticle–hole asymmetry on the properties of heavy-fermion (HF) compounds such as the universal scaling behavior of the thermopower S / T exhibited under the application of magnetic field B. We show that universal scaling is demonstrated by different HF compounds such as β - YbAlB 4 , YbRh 2 Si 2 , and strongly correlated layered cobalt oxide [ BiBa 0.66 K 0.36 O 2 ] CoO 2 . Analyzing YbRh 2 Si 2 , we show that the T / B scaling behavior of S / T is violated at the antiferromagnetic phase (AF) transition. The residual resistivity ρ 0 and the density of states N 0 experience jumps at the AF transition, causing two jumps in the thermopower and its sign reversal. Our consideration is based on the flattening of the single-particle spectrum that strongly affects ρ 0 and N 0 and leads to the violation of particle–hole symmetry. The particle–hole asymmetry generates the asymmetrical part Δ σ d (V) of tunneling differential conductivity σ d (V) , Δ σ d (V) = σ d (V) − σ d (− V) , where V is the voltage bias. We demonstrate that in the presence of magnetic field, the quasiparticle–hole asymmetry vanishes, the LFL behavior is restored, and the asymmetry disappears. Our calculations of the mentioned properties of HF compounds, based on the fermion condensation theory, are in good agreement with the experiment and support our conclusion that the fermion condensation theory is capable of describing the properties of HF compounds, including those exhibited under the application of magnetic field. [ABSTRACT FROM AUTHOR]

The search of quantum spin liquid (QSL), an exotic magnetic state with strongly fluctuating and highly entangled spins down to zero temperature, is a main theme in current condensed matter physics. However, there is no smoking gun evidence for deconfined spinons in any QSL candidate so far. The disorders and competing exchange interactions may prevent the formation of an ideal QSL state on frustrated spin lattices. Here we report comprehensive and systematic measurements of the magnetic susceptibility, ultralow-temperature specific heat, muon spin relaxation (μSR), nuclear magnetic resonance (NMR), and thermal conductivity for NaYbSe2 single crystals, in which Yb3+ ions with effective spin-1/2 form a perfect triangular lattice. All these complementary techniques find no evidence of long-range magnetic order down to their respective base temperatures. Instead, specific heat, μSR, and NMR measurements suggest the coexistence of quasi-static and dynamic spins in NaYbSe2. The scattering from these quasi-static spins may cause the absence of magnetic thermal conductivity. Thus, we propose a scenario of fluctuating ferrimagnetic droplets immersed in a sea of QSL. This may be quite common on the way pursuing an ideal QSL, and provides a brand new platform to study how a QSL state survives impurities and coexists with other magnetically ordered states.

The basis for our understanding of quantum magnetism has been the study of elegantly simple model systems. However, even for the antiferromagnetic honeycomb lattice with isotropic spin interactions–one of the simplest model systems–a detailed understanding of quantum effects is still lacking. Here, using inelastic neutron scattering measurements of the honeycomb lattice material YbCl3, we elucidate how quantum effects renormalize the single-magnon and multimagnon excitations and how this renormalization can be tuned and ultimately driven to the classical limit by applying a magnetic field. Additionally, our work reveals that the quantum effects tuned by the magnetic field not only renormalize the magnetic excitations but also induce a distinctive sharp feature inside the multimagnon continuum. From a more general perspective, this result demonstrates that structures within magnetic continua can occur over a wide experimental parameter space and can be used as a reliable means of identifying quantum phenomena. The honeycomb lattice is of fundamental importance for understanding quantum spin liquids and frustrated magnetism more generally. Here, the authors use inelastic neutron scattering to investigate the honeycomb antiferromagnet YbCl3 showing how quantum effects renormalize the single-magnon and multimagnon excitations, shedding further light on the mechanisms of quantum magnetism in honeycomb-lattice compounds. [ABSTRACT FROM AUTHOR]

The basis for our understanding of quantum magnetism has been the study of elegantly simple model systems. However, even for the antiferromagnetic honeycomb lattice with isotropic spin interactions–one of the simplest model systems–a detailed understanding of quantum effects is still lacking. Here, using inelastic neutron scattering measurements of the honeycomb lattice material YbCl3, we elucidate how quantum effects renormalize the single-magnon and multimagnon excitations and how this renormalization can be tuned and ultimately driven to the classical limit by applying a magnetic field. Additionally, our work reveals that the quantum effects tuned by the magnetic field not only renormalize the magnetic excitations but also induce a distinctive sharp feature inside the multimagnon continuum. From a more general perspective, this result demonstrates that structures within magnetic continua can occur over a wide experimental parameter space and can be used as a reliable means of identifying quantum phenomena. The honeycomb lattice is of fundamental importance for understanding quantum spin liquids and frustrated magnetism more generally. Here, the authors use inelastic neutron scattering to investigate the honeycomb antiferromagnet YbCl3 showing how quantum effects renormalize the single-magnon and multimagnon excitations, shedding further light on the mechanisms of quantum magnetism in honeycomb-lattice compounds. [ABSTRACT FROM AUTHOR]

Understanding the interplay between the inherent disorder and the correlated fluctuating-spin ground state is a key element in the search for quantum spin liquids. H3LiIr2O6 is considered to be a spin liquid that is proximate to the Kitaev-limit quantum spin liquid. Its ground state shows no magnetic order or spin freezing as expected for the spin liquid state. However, hydrogen zero-point motion and stacking faults are known to be present. The resulting bond disorder has been invoked to explain the existence of unexpected low-energy spin excitations, although data interpretation remains challenging. Here, we use resonant X-ray spectroscopies to map the collective excitations in H3LiIr2O6 and characterize its magnetic state. In the low-temperature correlated state, we reveal a broad bandwidth of magnetic excitations. The central energy and the high-energy tail of the continuum are consistent with expectations for dominant ferromagnetic Kitaev interactions between dynamically fluctuating spins. Furthermore, the absence of a momentum dependence to these excitations are consistent with disorder-induced broken translational invariance. Our low-energy data and the energy and width of the crystal field excitations support an interpretation of H3LiIr2O6 as a disordered topological spin liquid in close proximity to bond-disordered versions of the Kitaev quantum spin liquid. Kitaev quantum spin liquids are an exciting potential platform for hosting rich condensed matter physics. Here, the authors characterize the most promising material candidate, the honeycomb iridate H3LiIr2O6 and reveal a broad continuum of collective excitations absent of a momentum dependence–suggestive of a disordered topological spin liquid. [ABSTRACT FROM AUTHOR]

Interests in organic quantum materials (OQMs) have been explosively growing in the field of condensed physics of matter due to their rich chemistry and unique quantum properties. They are strongly correlated systems and show novel electromagnetic performance such as high‐temperature superconducting, quantum sensing, spin electronics, quantum dots, topological insulating, quantum Hall effects, spin liquids, qubits, and so forth, which exhibit promising prospects in information communication and thus facilitate the construction of a modern intelligent society. This article reviews recent developments in the research on the electromagnetic characteristics of OQMs. We mainly give an overview on the progress of superconductors and quantum spin liquids based on organic materials and describe their possible mechanisms. Numerous experimental findings exhibit new exciton interactions and provide insights into exotic electronic properties. Finally, their association and strategies for realizing multiple quantum states in one system are discussed. [ABSTRACT FROM AUTHOR]

Flat bands are rare in pristine solids and are unstable against electronic correlations or other types of long-range order. Unlike atomic-scale Hubbard systems or Moiré materials, where electronic correlations are either localized or long-ranged, pristine flat band systems with short-range interactions that do not break symmetry spontaneously are less known and intriguing. These systems could bridge the gap between atomic Mott insulators and Moiré correlated insulators, offering a unique platform to explore their mysterious relation. Using an analytical analysis, further verified by numerical calculations, we show that monolayer Nb3Cl8 is a unique flat band system with short-range interactions. We present clear evidence that it is a cluster Mott insulator, which nicely explains the electronic structure observed in angle-resolved photoemission spectroscopy. We further propose that monolayer Nb3Cl8 may constitute a rare example of molecular quantum spin liquid with flat bands. Flat bands are dispersionless band structures where the strength of electron-electron interactions increases giving rise to phenomena that cannot be described using theories based on weakly interacting electrons. Here, the authors use many-body calculations to show that Nb3Cl8 exhibits a correlated flat-band state and could potentially house a molecular quantum spin liquid phase. [ABSTRACT FROM AUTHOR]

Kagome lattices of various transition metals are versatile platforms for achieving anomalous Hall effects, unconventional charge-density wave orders and quantum spin liquid phenomena due to the strong correlations, spin-orbit coupling and/or magnetic interactions involved in such a lattice. Here, we use laser-based angle-resolved photoemission spectroscopy in combination with density functional theory calculations to investigate the electronic structure of the newly discovered kagome superconductor CsTi3Bi5, which is isostructural to the AV3Sb5 (A = K, Rb or Cs) kagome superconductor family and possesses a two-dimensional kagome network of titanium. We directly observe a striking flat band derived from the local destructive interference of Bloch wave functions within the kagome lattice. In agreement with calculations, we identify type-II and type-III Dirac nodal lines and their momentum distribution in CsTi3Bi5 from the measured electronic structures. In addition, around the Brillouin zone centre, Z 2 nontrivial topological surface states are also observed due to band inversion mediated by strong spin-orbit coupling. Kagome superconductors host a panoply of condensed matter phenomena, some of which are mediated by band topology. Here, authors use ARPES and DFT to identify type-II and type-III Dirac nodal lines, flat bands and topological surface states in the kagome metal CsTi3Bi5. [ABSTRACT FROM AUTHOR]

A case showing quantum spin liquid (QSL) behavior remains extremely scarce until now. To this end, it is suggested that the geometrical spin-frustrated lattices may be a potential platform for the study of QSL phenomena. In this work, we present an unprecedented geometrical spin-frustrated lattice with a three-dimensional five-connected CaB6-type topological matrix for the U(IV) centers in a novel uranium-fluorine compound, [U6F31] [NH4]7. Impressively, as evidenced by both the magnetic susceptibility and heat capacity measurements, this uranium-fluorine compound performs strong antiferromagnetic interactions without magnetic ordering, or spin freezing, or nonmagnetic singlet ground state down to 2 K, however appearing to be a QSL candidate. Moreover, [U6F31][NH4]7 also enables remarkable proton conductivity of 1.87 × 10−4 S/cm rather than electrical insulator as observed in the literature for all reported uranium-fluorine compounds, mainly resulted from the long-range hydrogen bond pathway between NH4+ and F−. More importantly, [U6F31][NH4]7 can be also used as ionic channel through solid–liquid reaction of cation exchange between NH4+ and Li+, leading to high lithium-ion conduction of 2.48 × 10−3 S/cm. [ABSTRACT FROM AUTHOR]

Among the family of transition metal dichalcogenides, 1T-TaS2 stands out for several peculiar physical properties including a rich charge density wave phase diagram, quantum spin liquid candidacy and low temperature Mott insulator phase. As 1T-TaS2 is thinned down to the few-layer limit, interesting physics emerges in this quasi 2D material. Here, using scanning near-field optical microscopy, we perform a spatial- and temperature-dependent study on the phase transitions of a few-layer thick microcrystal of 1T-TaS2. We investigate encapsulated air-sensitive 1T-TaS2 prepared under inert conditions down to cryogenic temperatures. We find an abrupt metal-to-insulator transition in this few-layer limit. Our results provide new insight in contrast to previous transport studies on thin 1T-TaS2 where the resistivity jump became undetectable, and to spatially resolved studies on non-encapsulated samples which found a gradual, spatially inhomogeneous transition. A statistical analysis suggests bimodal high and low temperature phases, and that the characteristic phase transition hysteresis is preserved down to a few-layer limit. [ABSTRACT FROM AUTHOR]

Quantum spin liquid is a nontrivial magnetic state of longstanding interest, in which spins are strongly correlated and entangled but do not order; further intriguing is its doped version, which possibly hosts strange metal and unconventional superconductivity. A promising candidate of the doped spin liquid is a triangular-lattice organic conductor, κ-(BEDT-TTF)4Hg2.89Br8, recently found to hold metallicity, spin-liquid-like magnetism, and BEC-like superconductivity. The nature of the metallic state with the spin-liquid behaviour is awaiting to be further clarified. Here, we report the thermoelectric signature that mobile holes in the spin liquid background are in a quantum critical state and it pertains to the BEC-like superconductivity. The Seebeck coefficient divided by temperature, S/T, is enhanced on cooling with logarithmic divergence indicative of quantum criticality. Furthermore, the logarithmic enhancement is correlated with the superconducting transition temperature under pressure variation, and the temperature and magnetic field profile of S/T upon the superconducting transition change with pressure in a consistent way with the previously suggested BEC-BCS crossover. The present results reveal that the quantum criticality in a doped spin liquid emerges in a phase, not at a point, and is involved in the unconventional BEC-like nature. A triangular-lattice organic conductor κ-(BEDT-TTF)4Hg2.89 Br8 is a promising doped spin liquid candidate which also exhibits superconductivity. Here the authors report thermoelectric measurements under pressure and find a quantum critical phase that could be correlated to BEC-like superconductivity. [ABSTRACT FROM AUTHOR]

α-RuCl3 is considered to be the top candidate material for the experimental realization of the celebrated Kitaev model, where ground states are quantum spin liquids with interesting fractionalized excitations. It is, however, known that additional interactions beyond the Kitaev model trigger in α-RuCl3 a long-range zigzag antiferromagnetic ground state. In this work, we investigate a nanoflake of α-RuCl3 through guarded high impedance measurements aimed at reaching the regime where the system turns into a zigzag antiferromagnet. We investigated a variety of temperatures (1.45–175 K) and out-of-plane magnetic fields (up to 11 T), finding a clear signature of a structural phase transition at ≈ 160 K as reported for thin crystals of α-RuCl3, as well as a thermally activated behavior at temperatures above ≈ 30 K, with a characteristic activation energy significantly smaller than the energy gap that we observe for α-RuCl3 bulk crystals through our angle resolved photoemission spectroscopy (ARPES) experiments. Additionally, we found that below ≈ 30 K, transport is ruled by Efros–Shklovskii variable range hopping (VRH). Most importantly, our data show that below the magnetic ordering transition known for bulk α-RuCl3 in the frame of the Kitaev–Heisenberg model (≈ 7 K), there is a clear deviation from VRH or thermal activation transport mechanisms. Our work demonstrates the possibility of reaching, through specialized high impedance measurements, the thrilling ground states predicted for α-RuCl3 at low temperatures in the frame of the Kitaev–Heisenberg model and informs about the transport mechanisms in this material in a wide temperature range. [ABSTRACT FROM AUTHOR]

We report a quantum criticality crossover representing two different universal scaling behaviors in a Kitaev quantum magnetic material α-RuCl3. α-RuCl3 presents both a symmetry-breaking antiferromagnetic order and a long-range entangled topological order of a quantum spin liquid, and thus could be a candidate system for a unique universality class involving deconfined fractionalized excitations of the local Z2 fluxes and itinerant Majorana fermions. Theoretical analyses on the inelastic neutron scattering, ac-magnetic susceptibility, and specific heat results demonstrate that Wilson–Fisher-Yukawa-type 'conventional' weak-coupling quantum criticality in high-energy scales crosses over to heavy-fermion-type 'local' strong-coupling one in low-energy scales. Our findings provide deep insight on how quantum criticality evolves in fermion-boson coupled topological systems with different types of deconfined fermions. [ABSTRACT FROM AUTHOR]

Gauge fields coupled to dynamical matter are ubiquitous in many disciplines of physics, ranging from particle to condensed matter physics, but their implementation in large-scale quantum simulators remains challenging. Here we propose a realistic scheme for Rydberg atom array experiments in which a Z 2 gauge structure with dynamical charges emerges on experimentally relevant timescales from only local two-body interactions and one-body terms in two spatial dimensions. The scheme enables the experimental study of a variety of models, including (2 + 1)D Z 2 lattice gauge theories coupled to different types of dynamical matter and quantum dimer models on the honeycomb lattice, for which we derive effective Hamiltonians. We discuss ground-state phase diagrams of the experimentally most relevant effective Z 2 lattice gauge theories with dynamical matter featuring various confined and deconfined, quantum spin liquid phases. Further, we present selected probes with immediate experimental relevance, including signatures of disorder-free localization and a thermal deconfinement transition of two charges. The robust implementation of gauge fields coupled to dynamical matter in large-scale quantum simulators is limited by the ever-present gauge-breaking errors. The authors propose an experimentally suitable scheme combining two-body interactions with weak fields, demonstrating its robustness against gauge breaking errors and its flexibility in the study of various models with Z2 gauge symmetry. [ABSTRACT FROM AUTHOR]

A glance at recent research on magnetism turns up a curious set of articles discussing, or claiming evidence for, a state of matter called a quantum spin liquid (QSL). These articles are notable in their invocation of exotic notions of topological physics, quantum entanglement, fractional quantum numbers, anyon statistics and gauge field theories. So what is a QSL and why do we need this complicated technical vocabulary to describe it? Our aim in this article is to introduce some of these concepts and provide a discussion of what a QSL is, where it might occur in Nature and why it is of interest. As we'll see, this is a rich subject which is still in development, and unambiguous evidence for the realisation of the QSL state in a magnetic material remains hotly debated. However, the payoff in terms of the special nature of quantum entanglement in the QSL, and its diverse spectrum of unusual excitations and topological status will (at least to some extent) justify the need to engage with some powerful, occasionally abstract, technical material. [ABSTRACT FROM AUTHOR]

We describe the confining instabilities of a proposed quantum spin liquid underlying the pseudogap metal state of the hole-doped cuprates. The spin liquid can be described by a SU(2) gauge theory of Nf = 2 massless Dirac fermions carrying fundamental gauge charges--this is the low-energy theory of a mean-field state of fermionic spinons moving on the square lattice with π-flux per plaquette in the Z2 center of SU(2). This theory has an emergent SO(5)f global symmetry and is presumed to confine at low energies to the Néel state. At nonzero doping (or smaller Hubbard repulsion U at half-filling), we argue that confinement occurs via the Higgs condensation of bosonic chargons carrying fundamental SU(2) gauge charges also moving in π Z2-flux. At halffilling, the low-energy theory of the Higgs sector has Nb = 2 relativistic bosons with a possible emergent SO(5)b global symmetry describing rotations between a d-wave superconductor, period-2 charge stripes, and the time-reversal breaking "d-density wave" state. We propose a conformal SU(2) gauge theory with Nf = 2 fundamental fermions, Nb = 2 fundamental bosons, and a SO(5)f × SO(5)b global symmetry, which describes a deconfined quantum critical point between a confining state which breaks SO(5)f and a confining state which breaks SO(5)b. The pattern of symmetry breaking within both SO(5)s is determined by terms likely irrelevant at the critical point, which can be chosen to obtain a transition between Néel order and d-wave superconductivity. A similar theory applies at nonzero doping and large U, with longer-range couplings of the chargons leading to charge order with longer periods. [ABSTRACT FROM AUTHOR]

Some IFM initiatives IFM has co-organised a physics conference or symposium annually since 1975. These are (1) to promote physics and elevate the profession of physicists, (2) to educate and train those who wish to practice as physicists, and those who are interested in physics, (3) to hold meetings/conferences, workshops and to deliver lectures, and (4) to organize activities of interest to IFM members related to research, education, and outreach programs. This article briefly traces the formation of IFM against the backdrop of physics in Malaysia, highlights some of the achievements and sketches possible future directions of IFM. Introduction This year, 2023, marks a significant milestone in the history of physics in Malaysia. [Extracted from the article]

The quest for entangled spin excitations has stimulated intense research on frustrated magnetic systems. For almost two decades, the triangular-lattice Mott insulator κ-(BEDT-TTF)2Cu2(CN)3 has been one of the hottest candidates for a gapless quantum spin liquid with itinerant spinons. Very recently, however, this scenario was overturned as electron-spin-resonance (ESR) studies unveiled a spin gap, calling for reevaluation of the magnetic ground state. Here we achieve a precise mapping of this spin-gapped phase through the Mott transition by ultrahigh-resolution strain tuning. Our transport experiments reveal a reentrance of charge localization below T⋆ = 6 K associated with a gap size of 30–50 K. The negative slope of the insulator-metal boundary, dT⋆/dp < 0, evidences the low-entropy nature of the spin-singlet ground state. By tuning the enigmatic '6K anomaly' through the phase diagram of κ-(BEDT-TTF)2Cu2(CN)3, we identify it as the transition to a valence-bond-solid phase, in agreement with previous thermal expansion and magnetic resonance studies. This spin-gapped insulating state persists at T → 0 until unconventional superconductivity and metallic transport proliferate. The Mott insulator κ-(BEDT-TTF)2Cu2(CN)3 has been a strong candidate for a gapless quantum spin liquid, but recent experiments suggested a spin-gapped phase below 6 K. Pustogow et al. study the entropy of this phase by driving the system through the metal-insulator transition with a strain engineering approach. [ABSTRACT FROM AUTHOR]

We determine the phase diagram of a bilayer, Yao-Lee spin-orbital model with inter-layer interactions (J), for several stackings and moiré superlattices. For AA stacking, a gapped Z 2 quantum spin liquid phase emerges at a finite Jc. We show that this phase survives in the well-controlled large-J limit, where an isotropic honeycomb toric code emerges. For moiré superlattices, a finite-q inter-layer hybridization is stabilized. This connects inequivalent Dirac points, effectively 'untwisting' the system. Our study thus provides insight into the spin-liquid phases of bilayer spin-orbital Kitaev materials. [ABSTRACT FROM AUTHOR]

We report on the largest open‐shell graphenic bilayer and also the first example of triply negatively charged radical π‐dimer. Upon three‐electron reduction, bilayer nanographene fragment molecule (C96H24Ar6)2 (Ar=2,6‐dimethylphenyl) (12) was transformed to a triply negatively charged species 123.−, which has been characterized by single‐crystal X‐ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and magnetic properties on a superconducting quantum interference device (SQUID). 123.− features a 96‐center‐3‐electron (96c/3e) pancake bond with a doublet ground state, which can be thermally excited to a quartet state. It consists of 34 π‐fused rings with 96 conjugated sp2 carbon atoms. Spin frustration is observed with the frustration parameter f>31.8 at low temperatures in 123.−, which indicates graphene upon reduction doping may behave as a quantum spin liquid. [ABSTRACT FROM AUTHOR]

As shown, the formation and destruction of 2D Majorana flat zones in frustrated La0.15Sm0.85MnO3+δ manganites occur as a result of Landau quantization of the spectrum of magnetic excitations of the Z2-quantum spin liquid with magnetic flux in the form of composite quasi-particles ‘spinon–gauge field’. In this work, the dynamics of the formation and destruction of 2D Majorana flat zones in frustrated manganites is also studied by analysing of the dc field M(H) dependences measured in the zero-field-cooled (ZFC) and field-cooled (FC) measurement modes. As shown, in the processes of magnetization reversal of La0.15Sm0.85MnO3+δ at 4.2 K, a superposition of the hump-like asymmetric features of the M(H) plots is formed in the range of magnetic fields of ±500 Oe, and non-dispersive ultra-narrow 2D Majorana flat zones of excited states of Z2-chiral quantum spin liquid are formed in the range of weak magnetic fields of 100–200 Oe near the zero field, similarly to flat bands in the low-dimensional topological superconductors. [ABSTRACT FROM AUTHOR]

The article presents a study which explores about the anomalously field-susceptible spin clusters emerging in the electric-dipole liquid molecular dimers. It mentions the analysis of the nuclear magnetic resonance (NMR) relaxation rate signifies that the moments fluctuate at a characteristic frequency slowing down to below megahertz at low temperatures.

Triangular lattice, with each site coordinating with six neighbors, is one most common network in two-dimensional (2D) limit. Manifestations of peculiar properties in the lattice, including magnetic frustration and quantum spin liquid, have been restricted to single-orbital tight-binding (TB) model so far, while the orbital degree of freedom is largely overlooked. Here, by combining TB modeling with first-principles calculations, we demonstrate the rich electronic structures of triangular lattice with multiple (p x , p y , p z) orbitals. Type I/II Dirac point, quadratic nodal point and nodal-loops are observed, and the topological phase diagram is mapped out by manipulating the horizontal mirror symmetry, spin-orbit coupling and energy position of relevant orbitals. Remarkably, we show that large-gap quantum spin Hall phase (∼0.2 eV) can be realized in experimentally achievable systems by growing indium monolayer on a series of semiconducting substrates, such as C/Si/Ge(111) and SiC(0001) surfaces, and the proposed materials capture the TB parameter space well. Our work not only provides physical insights into the orbital physics in 2D lattices, but also sheds light on the integration of novel quantum states with conventional semiconductor technology for potential applications, such as dissipationless interconnects for electronic circuits. [ABSTRACT FROM AUTHOR]

In 1991 the layered organic compound κ-(BEDT-TTF)2Cu2(CN)3 with a triangular lattice was synthesized for the first time. Although, originally, the focus was on the superconducting properties under pressure, this frustrated Mott insulator has been the most promising quantum-spin-liquid candidate for almost two decades, widely believed to host gapless spin excitations down to T→0. The recent observation of a spin gap rules out a gapless spin liquid with itinerant spinons and puts severe constraints on the magnetic ground state. This review evaluates magnetic, thermal transport, and structural anomalies around T⋆=6 K. The opening of a spin gap yields a rapid drop of spin susceptibility, NMR Knight shift, spin-lattice relaxation rate, and μ-SR spin fluctuation rate, but is often concealed by impurity spins. The concomitant structural transition at T⋆ manifests in thermal expansion, THz phonons and 63Cu NQR relaxation. Based on the field dependence of T⋆, a critical field of 30–60 T is estimated for the underlying spin-singlet state. Overall, the physical properties are remarkably similar to those of spin-Peierls compounds. Thus, a strong case is made that the ‘6K anomaly’ in κ-(BEDT-TTF)2Cu2(CN)3 is the transition to a valence-bond-solid state and it is suggested that such a scenario is rather the rule than the exception in materials with strong magnetic frustration.

The search for the experimental evidence of quantum spin liquid (QSL) states is critical but extremely challenging, as the quenched interaction randomness introduced by structural imperfection is usually inevitable in real materials. YCu3(OH)6.5Br2.5 (YCOB) is a spin-1/2 kagome Heisenberg antiferromagnet (KHA) with strong coupling of 〈J1〉 ~ 51 K but without conventional magnetic freezing down to 50 mK ~ 0.001〈J1〉. Here, we report a Br nuclear magnetic resonance (NMR) study of the local spin susceptibility and dynamics on the single crystal of YCOB. The temperature dependence of NMR main-line shifts and broadening can be well understood within the frame of the KHA model with randomly distributed hexagons of alternate exchanges, compatible with the formation of a randomness-induced QSL state at low temperatures. The in-plane spin fluctuations as measured by the spin-lattice relaxation rates (1/T1) exhibit a weak temperature dependence down to T ~ 0.03〈J1〉. Our results demonstrate that the majority of spins remain highly fluctuating at low temperatures despite the quenched disorder in YCOB. In search of a quantum spin liquid, spin dynamics in a recently proposed candidate, kagome material YCu3(OH)6.5Br2.5 was investigated by nuclear magnetic resonance. The work highlights the role of quantum fluctuations in the presence of random disorder in relation to gapless quantum spin liquids. [ABSTRACT FROM AUTHOR]

Quantum spin liquids realize massive entanglement and fractional quasiparticles from localized spins, proposed as an avenue for quantum science and technology. In particular, topological quantum computations are suggested in the non-abelian phase of Kitaev quantum spin liquid with Majorana fermions, and detection of Majorana fermions is one of the most outstanding problems in modern condensed matter physics. Here, we propose a concrete way to identify the non-abelian Kitaev quantum spin liquid by magnetic field angle dependence. Topologically protected critical lines exist on a plane of magnetic field angles, and their shapes are determined by microscopic spin interactions. A chirality operator plays a key role in demonstrating microscopic dependences of the critical lines. We also show that the chirality operator can be used to evaluate topological properties of the non-abelian Kitaev quantum spin liquid without relying on Majorana fermion descriptions. Experimental criteria for the non-abelian spin liquid state are provided for future experiments. Non-Abelian phase of Kitaev quantum spin liquid is promising for topological quantum computation. Here, the authors propose a way to identify the non-abelian Kitaev quantum spin liquid by magnetic field angle dependence, providing criteria for such a state for future experiments. [ABSTRACT FROM AUTHOR]

Thermal Hall effect (THE) is to describe the phenomenon where heat carriers are deflected by an external magnetic field applied perpendicular to the heat flow, and thus the carriers gain transverse velocity, leading to a finite temperature gradient on the two sides orthogonal to the heat flow and field. THE is predicted to occur in systems with nontrivial Berry curvatures and thus can reveal topological properties, similar to the electrical Hall effect. However, THE is not limited to charge excitations as in the electrical Hall effect, but rather, to all kinds of excitations that are able to conduct heat, making it possible to explore the exotic properties in strongly correlated electronic systems, which are typically insulators. Therefore, THE is more universal than the electrical form and has become a powerful probe in detecting charge-neutral excitations, such as phonons and magnons. Moreover, there are some sources such as chiral phonons, which are beyond a simple nontrivial-Berry-curvature scenario, that can also give rise to THE; examining THE wherein will shed light on the complex microscopic mechanism hidden in materials. Despite these, heat signals are much weaker than electrical ones. Especially for measurements of the thermal Hall conductivity, it is often needed to collect weak signals on top of a large background. This makes measuring the THE challenging一but thanks to the sustained efforts of the community, this field is developing rapidly in recent years, with many interesting results on the measurements of the thermal Hall conductivity. In this review article, we try to summarize some of these exciting accomplishments, point out remaining outstanding issues, and suggest possible future directions. [ABSTRACT FROM AUTHOR]

Quantum dimer models are known to host topological quantum spin liquid phases, and it has recently become possible to simulate such models with Rydberg atoms trapped in arrays of optical tweezers. Here, we present large-scale quantum Monte Carlo simulation results on an extension of the triangular lattice quantum dimer model with terms in the Hamiltonian annihilating and creating single dimers. We find distinct odd and even Z 2 spin liquids, along with several phases with no topological order: a staggered crystal, a nematic phase, and a trivial symmetric phase with no obvious broken symmetry. We also present dynamic spectra of the phases, and note implications for experiments on Rydberg atoms. Quantum dimer models are known to host topological quantum spin liquid phases, and it has recently become possible to simulate related Z 2 gauge theories with Rydberg atoms. Yan et al. compute the phase diagram of an experimentally motivated quantum dimer model on a triangular lattice with fluctuating dimer density. [ABSTRACT FROM AUTHOR]

The quantum spin liquid (QSL) states with no long-range magnetic order even down to zero temperature have recently raised intensive research interest. Here we propose that the spin frustration characteristic of the QSL candidates also make them superior magnetocaloric materials that exhibit prominent cooling effect, especially near the quantum critical points. By simulating the highly frustrated kagome and triangular lattice models, we reveal a significant magnetothermal pumping effect when combing quantum magnets with paramagnetic salts, which can be exploited to design a high-performance cascade demagnetization refrigerator. Moreover, with realistic magnetic compounds YbAlO3 and Na2BaCo(PO4)2, we find a giant enhancement in the cooling capacity characterized by a great increment rate, e.g., more than 200% when working between 3 K heat sink and 30 mK load. Our work thus paves a promising and viable way for the quantum spin cooling to promote the helium-free refrigeration useful in space applications and quantum technologies. Quantum spin liquids are a series of materials which exhibit an absence of magnetic order down to absolute zero and may have applications for data storage and memory. Here, using numerical simulations, the authors propose that the magnetic frustration in a quantum spin liquid may also lead to pronounced magnetocaloric effects near the quantum critical point with potential application as materials for refrigerants. [ABSTRACT FROM AUTHOR]

The layered honeycomb magnet α-RuCl3 has been suggested to exhibit a field-induced quantum spin liquid state, in which the reported large thermal Hall effect close to the half-quantized value still remains a subject of debate. Recently, oscillatory structures of the magnetothermal conductivity were reported and interpreted as quantum oscillations of charge-neutral particles. To investigate the origin of these oscillatory structures, we performed a comprehensive measurement of the in-plane magnetothermal conductivity κ(H) down to low temperature (100 mK), as well as magnetization M, for single crystals grown by two different techniques: Bridgman and chemical vapor transport. The results show a series of dips in κ(H) and peaks in the field derivative of M located at the same fields independent of the growth method. We argue that these structures originate from the field-induced phase transitions rather than from quantum oscillations. The positions of several of these features are temperature-dependent and connected to the magnetic phase transitions in zero field: the main transition at 7 K and weaker additional transitions, which likely arise from secondary phases at 10 K and 13 K. In contrast to what is expected for quantum oscillations, the magnitude of the structure in κ(H) is smaller for the higher conductivity crystal and decreases rapidly upon cooling below 1 K. [ABSTRACT FROM AUTHOR]

We study the dynamical response functions relevant for electric field induced two-dimensional (2D) coherent nonlinear optical spectroscopy in a Kitaev magnet at finite temperature. We show that these response functions are susceptible to both types of fractional quasiparticles of this quantum spin-liquid, i.e. fermions and flux visons. Focusing on the second order response, we find a strong antidiagonal feature in the 2D frequency plane, related to the galvanoelectric effect of the fractional fermions. Perpendicular to the antidiagonal, the width of this feature is set by quasiparticle relaxation rates beyond the bare Kitaev magnet, thereby providing access to single-particle characteristics within a multi-particle continuum. While the 2D spectrum of the response is set by the fermionic quasiparticles and displays Fermi blocking versus temperature, the emergent bond randomness which arises due to thermally populated visons strongly modifies the fermionic spectrum. Therefore also the presence of gauge excitations is manifest in the 2D nonlinear response as the temperature is increased beyond the flux proliferation crossover., (Creative Commons Attribution license.)

Topological order in strongly correlated systems, including quantum spin liquids, quantum Hall states in lattices and topological superconductivity, is treated. Various metallic non-Fermi-liquid states are discussed, including fractionalized Fermi-liquid (FL ∗ ) and phase string theories. Classification of topological states and differences between quantum and classical topology is considered. [ABSTRACT FROM AUTHOR]

Quantum spin liquids have been drawing much attention in recent years as a platform to develop future quantum technologies, such as topological quantum computing. In particular, Kitaev's honeycomb model has provided a blueprint to realize a quantum spin liquid that has Majorana fermions as its elementary excitation. While numerous theoretical studies have shown intriguing properties of quantum spin liquids, an experimental realization remains elusive. The recent observation of the quantized thermal Hall effect in α-RuCl3 has brought us tantalizingly close to an experimental realization of Kitaev quantum spin liquids. However, various groups report conflicting results, indicating that the Kitaev quantum spin liquid phase might be very fragile and its properties strongly depend on the sample. Here, we present a short overview of the rise of α-RuCl3 as a prime candidate material for realizing Kitaev quantum spin liquids. There are already many excellent review papers on this topic, so the emphasis will be on the materials aspect, comparing different crystal growth methods and crystal morphologies. We also discuss current research attempts to find other candidate materials to realize Kitaev quantum spin liquids, mostly focused on 3d transition-metal compounds, such as transition-metal halides and layered cobalt compounds. [ABSTRACT FROM AUTHOR]

In this article, we review the recent progress of the scanning tunneling microscopy studies of 1T-TaS2 and 1T-TaSe2 for bulk single crystals and molecular beam epitaxy monolayer films. We focus on how to understand the Mott insulating state in the whole set of materials, even when the stacking order takes effect. Based on this understanding, we discuss tuning the Mott insulator to a metallic state with different techniques, with Mott physics information revealed from the tuning process. The Kondo physics and quantum spin liquid state of 1T-TaS2 and 1T-TaSe2 are further discussed. This good platform of strong correlation must bring more intriguing phenomenon and physics in the future. [ABSTRACT FROM AUTHOR]

Motivated by reports of metallic behavior in the recently synthesized RuI3, in contrast to the Mott-insulating nature of the actively discussed α-RuCl3, as well as RuBr3, we present a detailed comparative analysis of the electronic and magnetic properties of this family of trihalides. Using a combination of first-principles calculations and effective-model considerations, we conclude that RuI3, similarly to the other two members, is most probably on the verge of a Mott insulator, but with much smaller magnetic moments and strong magnetic frustration. We predict the ideal pristine crystal of RuI3 to have a nearly vanishing conventional nearest-neighbor Heisenberg interaction and to be a quantum spin liquid candidate of a possibly different kind than the Kitaev spin liquid. In order to understand the apparent contradiction to the reported resistivity ρ, we analyze the experimental evidence for all three compounds and propose a scenario for the observed metallicity in existing samples of RuI3. Furthermore, for the Mott insulator RuBr3, we obtain a magnetic Hamiltonian of a similar form to that in the much-discussed α-RuCl3 and show that this Hamiltonian is in agreement with experimental evidence in RuBr3. [ABSTRACT FROM AUTHOR]

B-site ordered 4d1 and 5d1 double perovskites have a number of potential exotic ground states including multipolar order, quantum spin liquids and valence bond glass states. These arise from the complex interactions of spin-orbital entangled Jeff = 3/2 pseudospins on the geometrically frustrated fcc lattice. The 4d1 Mo5+ perovskite Ba2YMoO6 has been suggested to have a valence bond glass ground state. Here we report on the low temperature properties of powder samples of isostructural Ba2LuMoO6: the only other known cubic 4d1 perovskite with one magnetic cation. Our muon spectroscopy experiments show that magnetism in this material remains dynamic down to 60 mK without any spin freezing or magnetic order. A singlet-triplet excitation with a gap of Δ = 28 meV is observed in inelastic neutron scattering. These results are interpreted as a disordered valence bond glass ground state similar to Ba2YMoO6. Our results highlight the differences of the 4d1 double perovskites in comparison to cubic 5d1 analogues, which have both magnetic and multipolar order. [ABSTRACT FROM AUTHOR]

The S=3/2 Kitaev honeycomb model (KHM) is a quantum spin liquid (QSL) state coupled to a static Z2 gauge field. Employing an SO(6) Majorana representation of spin3/2's, we find an exact representation of the conserved plaquette fluxes in terms of static Z2 gauge fields akin to the S=1/2 KHM which enables us to treat the remaining interacting matter fermion sector in a parton mean-field theory. We uncover a ground-state phase diagram consisting of gapped and gapless QSLs. Our parton description is in quantitative agreement with numerical simulations, and is furthermore corroborated by the addition of a [001] single ion anisotropy (SIA) which continuously connects the gapless Dirac QSL of our model with that of the S=1/2 KHM. In the presence of a weak [111] SIA, we discuss an emergent chiral QSL within a perturbation theory. Recently, material realizations of the spin 3/2 Kitaev honeycomb model have been proposed, but the model has not been solved by either analytical or numerical methods. Here the authors report exact results for the spin 3/2 model consistent with numerical simulations, and find gapped and gapless quantum spin liquids. [ABSTRACT FROM AUTHOR]

We develop a nonequilibrium increment method in quantum Monte Carlo simulations to obtain the Rényi entanglement entropy of various quantum many-body systems with high efficiency and precision. To demonstrate its power, we show the results on a few important yet difficult (2 + 1)d quantum lattice models, ranging from the Heisenberg quantum antiferromagnet with spontaneous symmetry breaking, the quantum critical point with O(3) conformal field theory (CFT) to the toric code Z 2 topological ordered state and the Kagome Z 2 quantum spin liquid model with frustration and multi-spin interactions. In all these cases, our method either reveals the precise CFT data from the logarithmic correction or extracts the quantum dimension in topological order, from the dominant area law in finite-size scaling, with very large system sizes, controlled errorbars, and minimal computational costs. Our method, therefore, establishes a controlled and practical computation paradigm to obtain the difficult yet important universal properties in highly entangled quantum matter. [ABSTRACT FROM AUTHOR]

In the present work, we provide a comprehensive numerical investigation of the magnetic properties and phase spectra of three types of spin-1/2 branched chains consisting of one, two and three side spins per unit block with intra-chain interaction and a uniform inter-chain interaction in the presence of an external magnetic field. In a specific magnetic field interval, the low-temperature magnetization of these chains shows a step-like behavior with a pronounced plateau depending on the strength and the type of intra-chain interaction being ferromagnetic or antiferromagnetic. We demonstrate that when inter-chain interaction J 1 is antiferromagnetic and intra-chain interaction J 2 is ferromagnetic, the magnetization of the models manifests a smooth increase without a plateau, which is evidence of the existence of a Luttinger-like spin liquid phase before reaching its saturation value. On the other hand, when J 1 is ferromagnetic and J 2 is antiferromagnetic, the low-temperature magnetization of the chain with two branches shows an intermediate plateau at one-half of the saturation magnetization that breaks a quantum spin liquid phase into two regions. The magnetization of the chain with three branches exhibits two intermediate plateaus and two regions of a quantum spin liquid. We demonstrate that the chains with more than one side spin illustrate in their ground-state phase diagram a Kosterlitz–Thouless transition from a gapful phase to a gapless spin liquid phase. [ABSTRACT FROM AUTHOR]

In recent years, there has been an intense search for materials realizing the Kitaev quantum spin liquid model. A number of edge-shared compounds with strong spin-orbit coupling, such as RuCl3 and iridates, have been proposed to realize this model. Nevertheless, an effective spin Hamiltonian derived from the microscopic model relevant to these compounds generally contains terms that are antagonistic toward the quantum spin liquid. This is consistent with the fact that the zero magnetic field ground state of these materials is generally magnetically ordered. It is a pressing issue to identify protocols to drive the system to the limit of the Kitaev quantum spin model. In this work, we propose Floquet engineering of these Kitaev quantum magnets by coupling materials to a circularly polarized laser. We demonstrate that all the magnetic interactions can be tuned in situ by the amplitude and frequency of the laser, hence providing a route to stabilize the Kitaev quantum spin liquid phase. Kitaev materials are prime candidates to study quantum spin liquids but despite many known examples it is still a challenge to realize systems that have a total absence of magnetic ordering. Here, the authors propose Floquet engineering and the use of light-matter interactions to achieve a Kitaev quantum spin liquid phase. [ABSTRACT FROM AUTHOR]

A finite residual linear term in the thermal conductivity at zero temperature in insulating magnets indicates the presence of gapless excitations of itinerant quasiparticles, which has been observed in some candidate materials of quantum spin liquids (QSLs). In the organic triangular insulator β′–EtMe3Sb[Pd(dmit)2]2, a QSL candidate material, the low-temperature thermal conductivity depends on the cooling process and the finite residual term is observed only in samples with large thermal conductivity. Moreover, the cooling rate dependence is largely sample dependent. Here we find that, while the low-temperature thermal conductivity significantly depends on the cooling rate, the high-temperature resistivity is almost perfectly independent of the cooling rate. These results indicate that in the samples with the finite residual term, the mean free path of the quasiparticles that carry the heat at low temperatures is governed by disorders, whose characteristic length scale of the distribution is much longer than the electron mean free path that determines the high-temperature resistivity. This explains why recent X-ray diffraction and nuclear magnetic resonance measurements show no cooling rate dependence. Naturally, these measurements are unsuitable for detecting disorders of the length scale relevant for the thermal conductivity, just as they cannot determine the residual resistivity of metals. Present results indicate that very careful experiments are needed when discussing itinerant spin excitations in β′–EtMe3Sb[Pd(dmit)2]2. [ABSTRACT FROM AUTHOR]

A finite residual linear term in the thermal conductivity at zero temperature in insulating magnets indicates the presence of gapless excitations of itinerant quasiparticles, which has been observed in some candidate materials of quantum spin liquids (QSLs). In the organic triangular insulator β′–EtMe3Sb[Pd(dmit)2]2, a QSL candidate material, the low-temperature thermal conductivity depends on the cooling process and the finite residual term is observed only in samples with large thermal conductivity. Moreover, the cooling rate dependence is largely sample dependent. Here we find that, while the low-temperature thermal conductivity significantly depends on the cooling rate, the high-temperature resistivity is almost perfectly independent of the cooling rate. These results indicate that in the samples with the finite residual term, the mean free path of the quasiparticles that carry the heat at low temperatures is governed by disorders, whose characteristic length scale of the distribution is much longer than the electron mean free path that determines the high-temperature resistivity. This explains why recent X-ray diffraction and nuclear magnetic resonance measurements show no cooling rate dependence. Naturally, these measurements are unsuitable for detecting disorders of the length scale relevant for the thermal conductivity, just as they cannot determine the residual resistivity of metals. Present results indicate that very careful experiments are needed when discussing itinerant spin excitations in β′–EtMe3Sb[Pd(dmit)2]2. [ABSTRACT FROM AUTHOR]

This review considers the topological fermion condensation quantum phase transition (FCQPT) that explains the complex behavior of strongly correlated Fermi systems, such as frustrated insulators with quantum spin liquid and heavy fermion metals. The review contrasts theoretical consideration with recent experimental data collected on both heavy fermion metals (HF) and frustrated insulators. Such a method allows to understand experimental data. We also consider experimental data collected on quantum spin liquid in Lu 3 Cu 2 Sb 3 O 14 and quasi-one dimensional (1D) quantum spin liquid in both YbAlO 3 and Cu (C 4 H 4 N 2) (NO 3) 2 with the aim to establish a sound theoretical explanation for the observed scaling laws, Landau Fermi liquid (LFL) and non-Fermi-liquid (NFL) behavior exhibited by these frustrated insulators. The recent experimental data on the heavy-fermion metal α − YbAl 1 − x Fe x B 4 , with x = 0.014 , and on its sister compounds β − YbAlB 4 and YbCo 2 Ge 4 , carried out under the application of magnetic field as a control parameter are analyzed. We show that the thermodynamic and transport properties as well as the empirical scaling laws follow from the fermion condensation theory. We explain how both the similarity and the difference in the thermodynamic and transport properties of α − YbAl 1 − x Fe x B 4 and in its sister compounds β − YbAlB 4 and YbCo 2 Ge 4 emerge, as well as establish connection of these (HF) metals with insulators Lu 3 Cu 2 Sb 3 O 14 , Cu (C 4 H 4 N 2) (NO 3) 2 and YbAlO 3 . We demonstrate that the universal LFL and NFL behavior emerge because the HF compounds and the frustrated insulators are located near the topological FCQPT or are driven by the application of magnetic fields. [ABSTRACT FROM AUTHOR]

The evolution of quantum spin liquid states (QSL) of the anisotropic antiferromagnetic (AFM) Kitaev model with the [001] magnetic field by utilizing the finite‐temperature Lanczos method (FTLM) is investigated. In this anisotropic Kitaev model with KX=KY$K_{X}=K_{Y}$ and KX+KY+KZ=−3K$K_{X}+K_{Y}+K_{Z}=-3\text{ K}$ (K is the energy unit), due to the competition between anisotropy and magnetic field, the system emerges four exotic quantum phase transitions (QPTs) when KZ=−1.8$K_{Z}=-1.8$ and −1.4K$-1.4\text{ K}$, while only two QPTs when KZ=−0.6K$K_Z=-0.6\text{ K}$. At these magnetic‐field tuning quantum phase transition points, the low‐energy excitation spectrums appear level crossover, and the specific heat, magnetic susceptibility and Wilson ratio display anomalies; accordingly, the topological Chern number may also change. These results demonstrate that the anisotropic interacting Kitaev model with modulating magnetic field displays more rich phase diagrams, in comparison with the isotropic Kitaev model. [ABSTRACT FROM AUTHOR]

Quantum matter (novel phases of matter at zero temperature with exotic properties) is a growing field with applications in its own domain, and in providing foundational support to quantum sciences fields more generally. The ability to characterize and manipulate matter at the smallest scales continues to advance in fundamental ways. This review provides a plain-language, non-technical description of contemporary activity in quantum matter for a general science audience, and an example of these methods applied to quantum neuroscience. Quantum matter is the study of topologically governed phases of matter at absolute zero temperature that exhibit new kinds of emergent order and exotic properties related to topology and symmetry, entanglement, and electronic charge and magnetism, which may be orchestrated to create new classes of materials and computational devices (including in the areas of spintronics, valleytronics, and quantum computing). The paper is organized to discuss recent developments in quantum matter on the topics of short-range topologically protected materials (namely, topological semimetals), long-range entangled materials (quantum spin liquids and fractional quantum Hall states), and codes for characterizing and controlling quantum systems. A key finding is that a shift in the conceptualization of the field of quantum matter may be underway to expand the core focus on short-range topologically protected materials to also include geometry-based approaches and long-range entanglement as additionally important tools for the understanding, characterization, and manipulation of topological materials. [ABSTRACT FROM AUTHOR]

We investigate the recently identified Kitaev candidate, the unconventional two-dimensional (2D) crystalline material van der Waals CoI 2. Our approach involves employing ab-initio calculations to study the effects of applied pressure on its physical properties. CoI 2 was found to be a semiconductor with a band gap energy of 2.1 eV. By applying pressure up to 13 GPa, a transition from a semiconductor to a metallic state takes place. This transition was explained by the displacement of the initially filled 5p-iodide band, overlapping with partially filled Co-3d states, leading to the formation of a hybridized conduction band and the emergence of a metallic ground state. Furthermore, by subjecting the CoI 2 to pressure, a significant increase of the optical conductivity from 9900 to 11600 (Ω cm)−1, and the refractive index increases from 2.75 to 3.5. Our thermodynamic calculations reveal a captivating tale of CoI 2 ; detecting a peak at 55 K in the temperature-normalized heat capacity which suggests the presence of entropy variation in the material, indicating a shift in the spin configuration within CoI 2. In addition, a low thermal conductivity (ranging from 5 to 0.1 W m−1 K−1) underscores the strong interactions among quantum spins. • CoI 2 transitions from semiconductor to metal at 13 GPa. • Optical conductivity rises from 9900 to 11600 (Ω cm)−1 under pressure. • Refractive index increases from 2.75 to 3.5 with pressure. • Peak at 55 K in heat capacity suggests entropy variation. • Low thermal conductivity ranges from 5 to 0.1 W m−1 K−1. [ABSTRACT FROM AUTHOR]