Quantum materials under extreme conditions

Project Information

ExtremeQuantum

Grant agreement ID: 681260

DOI

10.3030/681260

Project closed

EC signature date 7 March 2016

Start date 1 September 2016

End date 28 February 2022

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 840 513,00

EU contribution

€ 1 840 513,00

Coordinated by

UNIVERSITY OF WARWICK
United Kingdom

Periodic Reporting for period 4 - ExtremeQuantum (Quantum materials under extreme conditions)

Reporting period: 2021-03-01 to 2022-02-28

Summary of the context and overall objectives of the project

The exploration of new and exotic states of matter is as fundamental to our understanding of the universe as is the detection of elementary particles or the discovery of celestial objects. What is more, many of these states exhibit properties that could have significant impact upon future technologies. States of particular current interest include unconventional superconductors, low-dimensional ordered magnets, spin liquids and ices, topological insulators and bosonic superfluids. All of these examples emerge from a complex soup of many-body quantum interactions, making them difficult to understand. Nevertheless, finding out how the states arise is the first, but essential step towards fully harnessing their capacity for application.

Two key factors governing these states are crystal symmetry and cooperative electronic or magnetic interactions. It is, however, apparent that other ingredients are likely playing an equally vital role: quantum mechanical fluctuations, the underlying topology, and random configurational disorder are all suspected of deep involvement in these so-called quantum materials.

This project seeks to advance our knowledge of these issues by using extreme conditions of magnetic field and pressure to enable a continuous, clean and reversible tuning of quantum interactions, thereby shedding light on the building blocks of exotic magnetism and unconventional superconductivity. By developing the materials and methodology to achieve this, we intend to push our understanding of quantum systems beyond current limitations and open a route for exploiting the untapped potential of these materials to underpin future technology.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

A) Spin-1/2 chains and other morphologies

In our papers "Magnetic order and enhanced exchange in the quasi-one-dimensional molecule-based antiferromagnet Cu(NO3)2(pyrazine)3" (Phys. Chem. Chem. Phys., 2019) and "Extremely well isolated two-dimensional spin-1/2 antiferromagnetic Heisenberg layers with a small exchange coupling in the molecular-based magnet CuPOF" (PRB, 2020), we report thorough experimental investigations of new examples of highly 1D and 2D, respectively, examples of S = 1/2 magnets.

Our publication, "Magnetic order and disorder in a quasi-two-dimensional quantum Heisenberg antiferromagnet with randomized exchange" (PRB, 2020) is a complete systematic investigation of a 2D quantum Heisenberg AFM with randomized exchange strengths. We find evidence for the formation of small clusters of fluctuating quantum spins that act to destabilize magnetic order, a situation that has been predicted theoretically.

The paper "Unconventional Field-Induced Spin Gap in an S = 1/2 Chiral Staggered Chain" (PRL, 2019) describes the remarkable properties of a new quantum spin chain that appears to be one of the most 1D spin-1/2 chains yet found and also exhibits an unusual energy gap in applied field which does not fit with the existing theories.

The paper "Magnetic order and ballistic spin transport in a sine-Gordon spin chain" (PRB, 2021) reports results probing the nature of the spin transport and staggered and chiral chains.

B) Spin-1 chains and other morphologies

Phase diagrams of 1D and 2D spin-1 AFMs are yet to be fully explored experimentally. There are barriers: (i) many of the newest materials are only available in powdered form, leading to difficulties in determining magnetic parameters, and (ii) methods to chemically control the parameters of new materials remain incomplete.

Addressing item (i): "Combining microscopic and macroscopic probes to untangle the single-ion anisotropy and exchange energies in an S=1 quantum antiferromagnet" in (PRB, 2017) and "Determining the anisotropy and exchange parameters of polycrystalline spin-1 magnets" (NJP, 2019).

Item (ii): "Enhancing easy-plane anisotropy in bespoke Ni(II) quantum magnets" (Polyhedron 2020) and "Magneto-structural Correlations in Ni2+—Halide···Halide—Ni2+ Chains" (Inorg. Chem., 2022).

Progress allows us to explore specific, novel S = 1 systems:
—"Implications of bond disorder in a S=1 kagome lattice" (Sci. Rep., 2018) reports interplay between order, disorder and geometric frustration.
—"Magnetic ground state of the one-dimensional ferromagnetic chain compounds M(NCS)2(thiourea)2 (M = Ni, Co)" (PRM, 2021) investigates isostructural S = 1 and 3/2 ferromagnetic chains.
—"A Near-Ideal Molecule-Based Haldane Spin-Chain" (PRR, 2020) reports a new material which promises to be an important testbed of issues of topology and low-dimensionality.
—"Controlling Magnetic Anisotropy in a Zero-Dimensional S = 1 Magnet Using Isotropic Cation Substitution" (JACS, 2021) reports a novel form of symmetry breaking; an anisotropic change in magnetic properties induced by ionic substitution of an isotropic species.

C) Spin-1/2 dimers

"Adiabatic physics of a magnetic quantum fluid: magnetocaloric effect, zero-point fluctuations, and two-dimensional universal behavior" (Physical Review B, 2017) describes the effect of ultra-high magnetic fields on quantum magnets and shows that quantum fluctuations play a significant role. "Anomalous magnetic exchange in a dimerized quantum magnet composed of unlike spin species" (PRB, 2021) presents the magnetic properties of a unique material, in which dimer units are composed of two different S = 1/2 species.

D) Unconventional superconductors

We published two groundbreaking articles on high-temperature superconductors: "Linear-in temperature resistivity from an isotropic Planckian scattering rate" (Nature, 2021) and "Fermi surface transformation at the pseudogap critical point of a cuprate superconductor" (Nat. Phys., 2022).

The team has also published: "Multigap superconductivity in chiral non-centrosymmetric TaRh2B2" (Phys. Rev. B, 2018) and "Superconductivity and the upper critical field in the chiral non-centrosymmetric superconductor NbRh2B2" (J. Phys. CM 31, 465601, 2019)

E) Strongly correlated and topological systems

"Unusual phase boundary of the magnetic-field-tuned valence transition in CeOs4Sb12" (PRB, 2020) reports ultra-high magnetic field work suggests a strong influence on the properties of this semimetal from quantum fluctuations and the proximity of a topological phase of matter.

"Magnetic monopole density and antiferromagnetic domain control in spin-ice iridates" (Nat. Commun. 2022) describes results showing a direct link between magnetic monopoles and charge carriers in frustrated pyrochlore iridates, as well as the ability to tune AFM domains with an external magnetic field.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

These results are significant steps forward in our understanding of quantum materials.
This project has made significant progress in: (i) creating and measuring tuneable molecular magnets, which pushes back the boundaries of our understanding of interacting spin systems; and (ii) the exploration of strongly correlated electron systems, including the high-temperature superconducting state using ultra-high fields. Additional data taken during the project is currently being prepared for publication.

Kagome structure of the molecule-based S = 1 system [H2F]2[Ni3F6(3-fluoropyridine)12][SbF6]2

Logo for SQUIDLab programme from Review of Scientific Instruments 91, 023901 (2020)

Crystal structure of the chiral spin-1/2 chain [Cu(pyrazine)(H2O)4]SiF6.H2O

Zero-field magnetic structure of the spin-1 chain [Ni(pyridine)2(HF2)]SbF6

Simulation of disorder in (QuinH)2Cu(ClxBr1−x)4⋅2H2O. Black = Br–Br, yellow = Br–Cl, red = Cl–Cl.

Cartoon showing effect of a [111] applied field on monopoles density and domain size in Ho2Ir2O7.

Phase diagram of molecular dimer system. The extended dome is measured in pulsed fields.

45 T angle-dependent magnetoresistance and simulations for a high-temperature superconductor.

Cover art for Polyhedron 180, 114379 (2020).