Vanishing Wilson ratio as the hallmark of quantum spin-liquid models

Prelovšek, P.; Morita, Katsuhiro; Tohyama, Takami; Herbrych, Jacek

doi:10.1103/physrevresearch.2.023024

Cited by 22 publications

(24 citation statements)

References 79 publications

(175 reference statements)

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“…A striking property of Heisenberg spins on smaller icosahedral molecules [22,26], as well as for smaller fullerene geometries [35], is that the first excited state is not a triplet, but rather a singlet, a signature of frustration connected to spin-liquid behaviour [14,[50][51][52]. The icosidodecahedron has in fact a large amount of singlet states below the first triplet [22].…”

Section: Lowest Triplet and Singlet Excitationsmentioning

confidence: 99%

The antiferromagnetic $S=1/2$ Heisenberg model on the C$_{60}$ fullerene geometry

2021

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We solve the quantum-mechanical antiferromagnetic Heisenberg model with spins positioned on vertices of the truncated icosahedron using the density-matrix renormalization group (DMRG). This describes magnetic properties of the undoped C_{60}60 fullerene at half filling in the limit of strong on-site interaction UU. We calculate the ground state and correlation functions for all possible distances, the lowest singlet and triplet excited states, as well as thermodynamic properties, namely the specific heat and spin susceptibility. We find that unlike smaller C_{20}20 or C_{32}32 that are solvable by exact diagonalization, the lowest excited state is a triplet rather than a singlet, indicating a reduced frustration due to the presence of many hexagon faces and the separation of the pentagonal faces, similar to what is found for the truncated tetrahedron. This implies that frustration may be tuneable within the fullerenes by changing their size. The spin-spin correlations are much stronger along the hexagon bonds and exponentially decrease with distance, so that the molecule is large enough not to be correlated across its whole extent. The specific heat shows a high-temperature peak and a low-temperature shoulder reminiscent of the kagomé lattice, while the spin susceptibility shows a single broad peak and is very close to the one of C_{20}20.

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Section: Lowest Triplet and Singlet Excitationsmentioning

confidence: 99%

The antiferromagnetic $S=1/2$ Heisenberg model on the C$_{60}$ fullerene geometry

2021

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“…The Wilson ratio is also seen as an empirical indicator for the importance of spin-orbit coupling, which is commonly taken as a minor issue in organics; albeit this aspect has come under scrutiny in some systems recently [241,547,548]. Most theories on quantum spin liquids predict that R W 1, in contrast to measured ratios [500,549]. For all organic compounds, we find a slightly enhanced Wilson ratio compared to a free electron gas: R W = 1.4−1.6 [536], but significantly less than the anomalously large Wilson ratio (R W = 70) reported for the three-dimensional quantum spin liquid Na 4 Ir 3 O 8 [550,551].…”

Section: Gapless Quantum Spin Liquid?mentioning

confidence: 99%

Molecular quantum materials: electronic phases and charge dynamics in two-dimensional organic solids

Dressel

Tomić

2020

Advances in Physics

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This review provides a perspective on recent developments and their implications for our understanding of novel quantum phenomena in the physics of two-dimensional organic solids. We concentrate on the phase transitions and collective response in the charge sector, the importance of coupling of electronic and lattice degrees of freedom and stress an intriguing role of disorder. After a brief introduction to low-dimensional organic solids and their crystallographic structures, we focus on the dimensionality and interactions and emergent quantum phenomena. Important topics of current research in organic matter with sizeable electronic correlations are Mott metal-insulator phase transitions, charge order and ferroelectricity. Highly frustrated two-dimensional systems are established model compounds for studying the quantum spin liquid state and the competition with magnetic long-range order. There are also unique examples of quantum disordered state of magnetic and electric dipoles. Representative experimental results are complemented by current theoretical approaches.

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“…It measures the ratio of the density of magnetic excitations with M > 0 and the density of all excitations including singlet excitations with M = 0. As demonstrated for the kagome HAF [46,47], a vanishing P as temperature T → 0 is a hallmark of quantum spinliquid ground state with dominating singlet excitations at low T . On the other hand, for quantum spin models with semi-classical magnetic ground-state order, such as the square-lattice HAF the Wilson ratio diverges as P (T → 0) ∝ T η , η ≥ 1. practically coincide with the data for N = 42.…”

Section: A Zero-field Propertiesmentioning

confidence: 93%

Thermodynamics of the spin-half square-kagome lattice antiferromagnet

Richter,

Derzhko,

Schnack

2022

Preprint

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Over the last decade, the interest in the spin-1/2 Heisenberg antiferromagnet (HAF) on the squarekagome (also called shuriken) lattice has been growing as a model system of quantum magnetism with a quantum paramagnetic ground state, flat-band physics near the saturation field, and quantum scars. A further motivation to study this model comes from the recent discovery of a gapless spin liquid in the square-kagome magnet KCu6AlBiO4(SO4)5Cl [M. Fujihala et al., Nat. Commun. 11, 3429 (2020)]. Here, we present large-scale numerical investigations of the specific heat C(T ), the entropy S(T ) as well as the susceptibility χ(T ) by means of the finite-temperature Lanczos method for system sizes of N = 18, 24, 30, 36, 42, 48, and N = 54. We find that the specific heat exhibits a low-temperature shoulder below the major maximum which can be attributed to low-lying singlet excitations filling the singlet-triplet gap, which is significantly larger than the singlet-singlet gap. This observation is further supported by the behavior of the entropy S(T ), where a change in curvature is present just at about T /J = 0.2, the same temperature where the shoulder in C sets in. For the susceptibility the low-lying singlet excitations are irrelevant, and the singlet-triplet gap leads to an exponentially activated low-temperature behavior. The maximum in χ(T ) is found at a pretty low temperature Tmax/J = 0.146 (for N = 42) compared to Tmax/J = 0.935 for the unfrustrated square-lattice HAF signaling the crucial role of frustration also for the susceptibility. We find a striking similarity of our square-kagome data with the corresponding ones for the kagome HAF down to very low T . The magnetization process featuring plateaus and jumps and the field dependence of the specific heat that exhibits characteristic peculiarities attributed to the existence of a flat one-magnon band are as well discussed.

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Vanishing Wilson ratio as the hallmark of quantum spin-liquid models

Cited by 22 publications

References 79 publications

The antiferromagnetic $S=1/2$ Heisenberg model on the C$_{60}$ fullerene geometry

The antiferromagnetic $S=1/2$ Heisenberg model on the C$_{60}$ fullerene geometry

Molecular quantum materials: electronic phases and charge dynamics in two-dimensional organic solids

Thermodynamics of the spin-half square-kagome lattice antiferromagnet

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