Quantum Spin Liquids in Kagome Mateirals – LINK

The model materials issued from most refined synthesis worldwide will be studied in depth by using a unique combination of cutting-edge local resonance techniques (nuclear magnetic resonance, muon spin resonance) and reciprocal-space technique as inelastic neutron scattering. We will further modify these materials either through physical conditions or through the well-controlled synthesis of variants to better understand their physical properties along a new ”perturb-to-reveal” strategy: there local techniques give ubiquitous insight due to their spatial resolution.
On the theory side, we will expand our numerical skills to the stage where thermodynamical quantitites can be computed, defect-induced spin textures can be predicted, thus opening the comparison to experimental results gained in this project.

1- Aqueous solution growth at 200 degrees C and characterizations of pure, O-17- or D-based herbertsmithite ZnxCu4-x(OH)(6)Cl-2 single crystals

2- Gapless ground state in the archetypal quantum kagome antiferromagnet ZnCu3(OH)(6)Cl2

3- Local study of the insulating quantum kagome antiferromagnets YCu3(OH)(6)OxCl3-x (x=0, 1/3)

4- Effect of perturbations on the kagome S=1/2 antiferromagnet at all temperatures

- Discovery of new quantum kagome materials
- Outsanding progress in the understanding of the spin liquid ground state of the kagome Heisenberg antiferromagnet.
- New numercial tools to compute thermodynamic quantitties and spin textures

1. “Aqueous solution growth at 200 degrees C and characterizations of pure, O-17- or D-based herbertsmithite ZnxCu4-x(OH)(6)Cl-2 single crystals”
M. Velazquez, F. Bert, P. Mendels, D. Denux, P. Veber, M. Lahaye, C. Labrugere, J. Crystal Growth, 531, 125372 (2020).

2. “Gapless ground state in the archetypal quantum kagome antiferromagnet ZnCu3(OH)(6)Cl2”
P. Khuntia, P., M. Velazquez, Q. Barthelémy, F. Bert, E. Kermarrec, A. Legros, B. Bernu, L. Messio, A. Zorko, P. Mendels, Nature Physics 16, 460 (2020).

3. Local study of the insulating quantum kagome antiferromagnets YCu3(OH)(6)OxCl3-x (x=0, 1/3)
Q. Barthelémy, P. Puphal, K.M. Zoch, C. Krellner, H. Luetkens, C. Baines, D. Sheptyakov, E. Kermarrec, P. Mendels, F. Bert, Phys. Rev. Materials 3, 074401 (2019).

4. Effect of perturbations on the kagome S=1/2 antiferromagnet at all temperatures
B. Bernu, L. Pierre, K. Essafi, L. Messio, Phys. Rev. B 101, 140403 (2020).

This proposal, at the frontier of our knowledge in quantum magnetism, aims at exploring both experimentally and theoretically the properties of quantum spin liquids (QSL) induced by the frustration of magnetic interactions on a regular lattice. QSL states have remained quite elusive in dimensions higher than one but recent progress in materials science have brought into the spotlight the very first examples of two-dimensional triangular-based kagome materials, which are the best candidates to probe this novel physics. The nearest-neighbor kagome Heisenberg antiferromagnet (KHAF) is one of the most enduring theoretical problems in quantum magnetism. New theories are currently being developed and it is now becoming possible to confront their predictions with experiments. We can foresee key progress in this field with the opening of new concepts and unexpected experimental phenomena.

The proposal covers within the same consortium the domains of materials, experiments, and theory, and explores four main areas:
(i) Bringing single crystals synthesis of the emblematic herbertsmithite and related systems to an unprecedented level of control of intrinsic built-in exchange defects and extrinsic substitutions, with the aim to reveal the ultimate properties of the kagome physics;
(ii) In the framework of international collaborations, measure physical properties of recently discovered materials which are expected to open new avenues for QSL studies, especially in connection with the KHAF problem;
(iii) Explore new tracks, in particular the S=1 KHAF, based on novel ideas in materials synthesis within our consortium;
(iv) Theory wise, go beyond existing frontiers and develop new theoretical approaches to calculate low-temperature thermodynamic quantities and dynamical spectra that will be compared to experimental data, a bottleneck in the field, and also address the response to spinless or spin-1 impurities in a spin-½ kagome lattice, in close relation with (i), (ii), and (iii).

The model materials issued from the most refined synthesis worldwide will be studied in depth by using a unique combination of cutting-edge local resonance techniques (nuclear magnetic resonance, muon spin resonance) and reciprocal-space techniques such as inelastic neutron scattering. We will further modify these materials either through external conditions (such as pressure and magnetic field) or through well-controlled chemical tuning to better understand their physical properties, following a ”perturb-to-reveal” strategy. Here, local techniques give ubiquitous insights due to their spatial resolution.

The central idea of our project is to master all steps of these studies from materials design and synthesis via physical measurements to theory, still profiting from well-established international collaborations. Our project brings together knowledgeable scientists in several fields with complementary skills: Institut des Matériaux de Nantes and Institut de Chimie de la Matière Condensée de Bordeaux for materials synthesis and single crystal growth, the NMR-µSR-neutron Orsay team strongly linked with B. Fåk (ILL Grenoble) for inelastic neutron scattering, and the novel collaboration between complementary theory teams from LPTMC, Paris and LPT, Toulouse.

We plan to publish our scientific results in joint publications in peer-reviewed high-impact international journals. Our studies will also be disseminated at various levels through the participation in international conferences, organization of national or international events, advertising selected highlights, and organizing teaching seminars. We also aim at popularizing “Quantum Spin Liquids” to a broader audience within a large scale action led by J. Bobroff (“Physics reimagined”) at LPS.