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Rüegg, Ch.; Furrer, A.; Sheptyakov, Denis; Strässle, Th.; Krämer, Karl; Güdel, Hans‐Ulrich; Mélési, L

doi:10.1103/physrevlett.93.257201

Cited by 111 publications

(51 citation statements)

References 30 publications

(49 reference statements)

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“…The magnetic excitation spectrum has again the nature of a gapless Goldstone mode (Matsumoto et al, 2004) which was experimentally confirmed in the pressure-induced ordered phase as shown in Fig. 57(b) (Rüegg et al, 2004a). In later INS experiments, it was demonstrated that only the longitudinal and one transverse triplet component soften at p c , whereas the other transverse triplet component retains a finite gap at p c .…”

Section: B Dimer-based Antiferromagnetsmentioning

confidence: 78%

Magnetic Cluster Excitations

Fürrer

2010

Int. J. Mod. Phys. B

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Magnetic clusters, i.e., assemblies of a finite number (between two or three and several hundred) of interacting spin centers which are magnetically decoupled from their environment, can be found in many materials ranging from inorganic compounds, magnetic molecules, artificial metal structures formed on surfaces to metalloproteins. The magnetic excitation spectra in them are determined by the nature of the spin centers, the nature of the magnetic interactions, and the particular arrangement of the mutual interaction paths between the spin centers. Small clusters of up to four magnetic ions are ideal model systems to examine the fundamental magnetic interactions which are usually dominated by Heisenberg exchange, but often complemented by anisotropic and/or higher-order interactions. In large magnetic clusters which may potentially deal with a dozen or more spin centers, the possibility of novel many-body quantum states and quantum phenomena are in focus. In this review the necessary theoretical concepts and experimental techniques to study the magnetic cluster excitations and the resulting characteristic magnetic properties are introduced, followed by examples of small clusters demonstrating the enormous amount of detailed physical information which can be retrieved. The current understanding of the excitations and their physical interpretation in the molecular nanomagnets which represent large magnetic clusters is then presented, with an own section devoted to the subclass of the singlemolecule magnets which are distinguished by displaying quantum tunneling of the magnetization. Finally, some quantum many-body states are summarized which evolve in magnetic insulators characterized by built-in or field-induced magnetic clusters. The review concludes addressing future perspectives in the field of magnetic cluster excitations.

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Section: B Dimer-based Antiferromagnetsmentioning

confidence: 78%

Magnetic Cluster Excitations

Fürrer

2010

Int. J. Mod. Phys. B

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“…At the transition between these two very different forms of order, the ground-state wavefunction is entangled over macroscopic length scales. Recent neutron scattering experiments have revealed the emergence of new bosonic quasiparticles at magnetic quantum-critical points [26][27][28] . Ordinary magnets exhibit well-defined spin waves that modulate the direction of the magnetization, but the longitudinal modes that modulate its amplitude (roughly analogous to the Higgs modes found in superconductors and in particle physics 29 ) are usually found at much higher energies and are strongly mixed with multimagnon excitations.…”

Section: Quantum Collective Phenomenamentioning

confidence: 99%

The physics of quantum materials

2017

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The physical description of all materials is rooted in quantum mechanics, which describes how atoms bond and electrons interact at a fundamental level. Although these quantum e ects can in many cases be approximated by a classical description at the macroscopic level, in recent years there has been growing interest in material systems where quantum e ects remain manifest over a wider range of energy and length scales. Such quantum materials include superconductors, graphene, topological insulators, Weyl semimetals, quantum spin liquids, and spin ices. Many of them derive their properties from reduced dimensionality, in particular from confinement of electrons to two-dimensional sheets. Moreover, they tend to be materials in which electrons cannot be considered as independent particles but interact strongly and give rise to collective excitations known as quasiparticles. In all cases, however, quantum-mechanical e ects fundamentally alter properties of the material. This Review surveys the electronic properties of quantum materials through the prism of the electron wavefunction, and examines how its entanglement and topology give rise to a rich variety of quantum states and phases; these are less classically describable than conventional ordered states also driven by quantum mechanics, such as ferromagnetism.T he way we think about manifestations of quantum physics in materials has recently undergone a profound change of perspective. Although materials scientists and engineers have long exploited quantum effects in a range of electronic deviceswell-known examples are the quantized electronic energy levels and optical selection rules at the heart of optoelectronics, and the tunnel effect that underlies the upcoming generation of harddisk drives 1,2 -the past decade has seen a dramatic increase in our understanding of how subtle quantum effects control the macroscopic behaviour of a whole range of different materials.Two strange and beautiful aspects of quantum mechanics have come to the fore. One is the topological nature of quantum wavefunctions. A familiar example is the existence of quantized vortices in superconductors. These vortices exist because of the requirement that the superconducting condensate have a well-defined phase, and gauge invariance fixes how this phase couples to magnetic flux. The phase can wind only by an integer multiple of 2π around a vortex, and this integer winding number is a simple example of a topological invariant: a quantity that remains fixed under smooth changes of a system. Similar topological quantities turn out to govern many other kinds of materials, not just superconductors, and these support phenomena ranging from dissipationless transport to novel quasiparticle excitations.Another deep feature of quantum mechanics is the non-local entanglement of some quantum states that is spectacularly highlighted in teleportation experiments with two photons separated over macroscopic distances 3 . Even the wavefunction of two spins in a singlet is entangled, in that the wavefunction of...

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“…Until recently only one good experimental realization of a pressure-induced QPT had been found, namely that in the three-dimensional dimer system TlCuCl 3 . [3][4][5] Further work has lead to fascinating insights, in particular to the observation of a massive amplitude mode, 6,7 the magnetic analog of the Higgs boson. 8 Quantum magnets built from organic molecules can be very susceptible to perturbation by external pressure due to their 'soft' molecular frameworks.…”

Section: Introductionmentioning

confidence: 99%

Spin dynamics in pressure-induced magnetically ordered phases in(C4H12N2)Cu2Cl<

et al. 2015

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We present inelastic neutron scattering experiments on the S = 1/2 frustrated gapped quantum magnet piperazinium hexachlorodicuprate (PHCC) under applied hydrostatic pressure. These results show that at 9 kbar the magnetic triplet excitations in the system are gapless, contrary to what was previously reported. Our results are in agreement with recent muon-spin relaxation experiments which found magnetic order above a quantum-critical point at 4.3 kbar. We show that the changes in the excitation spectrum can be primarily attributed to the change in a single exchange pathway.

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Pressure-Induced Quantum Phase Transition in the Spin-LiquidTlCuCl3

Cited by 111 publications

References 30 publications

Magnetic Cluster Excitations

Magnetic Cluster Excitations

The physics of quantum materials

Spin dynamics in pressure-induced magnetically ordered phases in(C4H12N2)Cu2Cl<

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