NMR; Molecular magnetism; Spin liquid; Quantum criticality; Neutron scattering
Sørensen Mikkel A., Hansen Ursula B., Perfetti Mauro, Pedersen Kasper S., Bartolomé Elena, Simeoni Giovanna G., Mutka Hannu, Rols Stéphane, Jeong Minki, Zivkovic Ivica, Retuerto Maria, Arauzo Ana, Bartolomé Juan, Piligkos Stergios, Weihe Høgni, Doerrer Linda H., van Slageren Joris, Rønnow Henrik M., Lefmann Kim, Bendix Jesper (2018), Chemical tunnel-splitting-engineering in a dysprosium-based molecular nanomagnet, in Nature Communications
, 9, 1292.
Vennemann Tarek, Jeong Minki, Yoon Dongyoung, Magrez Arnaud, Berger Helmuth, Yang Lin, Živković Ivica, Babkevich Peter, Rønnow Henrik (2018), Note: Commercial SQUID magnetometer-compatible NMR probe and its application for studying a quantum magnet, in Review of Scientiic Instruments
, 89, 046101.
Jeong M., Mayaffre H., Berthier C., Schmidiger D., Zheludev A., Horvatić M. (2017), Magnetic-Order Crossover in Coupled Spin Ladders, in Physical Review Letters
, 118(16), 167206-167206.
Matheoud Alessandro V, Gualco Gabriele, Jeong Minki, Zivkovic Ivica, Brugger Jürgen, Rønnow Henrik M, Anders Jens, Boero Giovanni (2017), Single-chip electron spin resonance detectors operating at 50GHz, 92GHz, and 146GHz., in Journal of magnetic resonance (San Diego, Calif. : 1997)
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.