Project

NMR; Molecular magnetism; Spin liquid; Quantum criticality; Neutron scattering

Lead
Cette collaboration Swiss-coréenne exploite cristaux moléculaires d'origine organique et organo-métallique pour une meilleure compréhension des états émergents dans les systèmes de spins quantiques.
Lay summary
Un point critique quantique est une singularité à température nulle dans le diagramme de phase de la matière quantique provenant de fluctuations quantiques intenses. C’est un thème central dans la recherche de la matière condensée courant. Un aspect surprenant en ce qui concerne un point critique quantique est que les fortes fluctuations quantiques critiques effectivement persistent jusqu'à des températures relativement élevées conduisant à un comportement universel observables physiques. Établir des catégories universalité d'une variété de transitions de phase quantique est d'une importance fondamentale rappelant qu'une tâche similaire pour les transitions thermiques classiques marque l'un des triomphes de l'histoire de la physique moderne. Un autre aspect très attractif, et potentiellement pratique, est qu’un point critique quantique est considéré comme une source probable de nouvelles phases telles que le métal étrange ou les supraconducteurs non conventionnels. Ces aspects motive naturellement au rêve de la classification expérimentale de divers points critiques quantiques et leur comportement critique, et d'appliquer ces connaissances pour découvrir phases quantiques exotiques de propriétés ou fonctionnalités nouvelles. Ici, nous abordons cette tâche difficile en exploitant les cristaux moléculaires, des composés organo-métalliques et les isolants organiques – des aimants quantiques qui sont représentés par les spins interagissant localisées sur un réseau. Un aspect convaincant d'aimants quantiques pour l'étude de criticité quantique est qu’un modelle simple et bien définie, sans complication d'électrons itinérants ou les fluctuations de charge, permet une comparaison étroite entre les expériences et théories.

Direct link to Lay Summary

Last update: 11.02.2016

Lead
This Swiss-Korean collaboration exploits molecular crystals of organic and meatal-organic origin to further understanding of emerging states in quantum spin systems.
Lay summary
A quantum critical point is a zero-temperature singularity in phase diagram of quantum matter originating from intense quantum fluctuations, and is a central theme in current condensed-matter research. One surprising aspect regarding a quantum critical point is that strong quantum critical fluctuations actually persist up to relatively high temperatures leading to universal behaviour in physical observables. Establishing universality classes of a variety of quantum phase transitions is of fundamental importance recalling that a similar task for classical thermal transitions marks one of the triumphs in the history of modern physics. Another highly attractive, and potentially practical, aspect is that a quantum critical point is considered a probable source of novel phases such as strange metal or unconventional superconducting ones. These aspects naturally motivates one to dream of experimental classification of various quantum critical points and their critical behaviour, and to apply those insights for discovering exotic quantum phases of novel properties or functionalities. Here we tackle this challenging task by harnessing molecular crystals, metal-organic compounds and organic insulators, for quantum magnets which are represented by the interacting spins localized on a lattice. A compelling aspect of quantum magnets for studying quantum criticality is that a simple and well-defined Hamiltonian, without complication from itinerant electrons or charge fluctuations, allows close comparison between experiments and theories.

Direct link to Lay Summary

Last update: 11.02.2016

Natural persons

Number	Title	Start	Funding scheme

A quantum critical point is a zero-temperature singularity in phase diagram of quantum matter originating from intense quantum fluctuations, and is a central theme in current condensed-matter research. One surprising aspect regarding a quantum critical point is that strong quantum critical fluctuations actually persist up to relatively high temperatures leading to universal behaviour in physical observables. Establishing universality classes of a variety of quantum phase transitions is of fundamental importance recalling that a similar task for classical thermal transitions marks one of the triumphs in the history of modern physics. Another highly attractive, and potentially practical, aspect is that a quantum critical point is considered a probable source of novel phases such as strange metal or unconventional superconducting ones. These aspects naturally motivates one to dream of experimental classification of various quantum critical points and their critical behaviour, and to apply those insights for discovering exotic quantum phases of novel properties or functionalities.Here we tackle this challenging task by harnessing molecular crystals, metal-organic compounds and organic insulators, for quantum magnets which are represented by the interacting spins localized on a lattice. A compelling aspect of quantum magnets for studying quantum criticality is that a simple and well-defined Hamiltonian, without complication from itinerant electrons or charge fluctuations, allows close comparison between experiments and theories. Being more specific, we aim at •Experimentally establishing classification of quantum critical points using metal-organic compounds,•Assessing quantum-spin-liquid candidates of triangular-lattice organic antiferromagnets.Recent advent of metal-organic compounds as an ideal quantum-magnet platform capable of fine tuning of geometry and dimensionality of magnetic lattices has made possible controlled realization of generic many-body phenomena like the formation of Bose-Einstein condensation or Tomonaga-Luttinger liquid. Moreover, relatively small energy scale in their magnetic exchange interactions allows access to various field-induced transitions and criticality that cannot be reached with traditional oxides. We will take advantage of these features of metal-organic compounds for the first systematic attempt toward experimental establishment of the universality classes of quantum critical points.Organic insulators featuring a triangular-lattice S=1/2 Heisenberg antiferromagnet are known promising for realization of a long-sought quantum spin liquid owing to strong quantum fluctuations and high geometrical frustration. However, much of their properties such as the nature of low-energy excitations remain controversial both theoretically and experimentally. Recently, controlled synthesis of organic crystals of triangular-lattice antiferromagnets with varying degrees of frustration has opened the possibility for tuning between the ground states that may include a spin liquid. We will track the ground states of this series of frustrated organic systems with local probes and map out the phase diagram to shed light on the origin for a putative spin liquid and the impact of quantum critical fluctuations.Our unique strategy is to combine the recently developed, state-of-art techniques such as magnetic resonance force microscopy and magnetic resonance using coplanar resonators with the established techniques such as neutron scattering and conventional NMR, and utilize them as powerful and complementary local probes. This guarantees pushing experimental boundary by allowing us to address very low temperature, a strong magnetic field, and tiny samples.Through this project, we lay the foundation for building a bottom-up understanding of very timely issue of quantum criticality, and put a step forward to utilizing those insights for discovering or designing novel phases like a spin liquid. The impact must be far-reaching in so much as the broad interest in the subject in neighbouring or larger communities of strongly correlated electron systems, cold atoms, and quantum information.