DIMPY
Chemical formula:
(C7H10N)2CuBr4
Lattice type:
Monoclinic, space group P21/n
How to grow:
Wet chemistry synthesis
Magnetic model:
Heisenberg S = 1/2 spin ladder with strong legs
Why is it cool:
Unique multi-magnon bound states, and spinon deconfinement at a field-induced quantum phase transition into the first known attractive Tomonaga-Luttinger spin liquid
DIMPY is the Heisenberg S = 1/2 spin ladder in the strong-leg limit: good antiferromagnetic spin chains weakly welded together in pairs. It remains the only clean material realization of this regime, the opposite of the strong-rung ladder BPCB and much closer to the physics of individual chains. The ground state is a gapped spin liquid whose excitations we have mapped in their entirety: long-lived triplet magnons survive throughout the Brillouin zone [1], and on top of them the spectrum, resolved into its symmetric and asymmetric rung-parity channels, reveals exotic composite excitations including a genuine two-magnon bound state [2,3]. Everything is reproduced quantitatively by DMRG calculations for the simple two-parameter Hamiltonian.
An applied magnetic field closes the spin gap at a quantum phase transition, and there the very nature of the excitations changes: the coherent magnons deconfine into continua of fractional spinon-like excitations, in both commensurate and incommensurate sectors [4]. The magnetized phase is a Tomonaga-Luttinger spin liquid, and a very special one: it corresponds to one-dimensional fermions with attractive interactions, the first such realization in any spin system. We measured the scaling of its temporal spin correlations directly by neutron spectroscopy: the extracted Luttinger parameter K ≈ 1.25 and the entire scaling function agree quantitatively with theory [5].
The material has one more trick: the magnetic copper is easily replaced by non-magnetic zinc during crystal growth, which turns DIMPY into our platform of choice for studying defects in quantum magnets, with emergent interacting "spin islands" nucleating around every impurity [6].
Magnetic excitations in DIMPY and their evolution in an applied magnetic field: from the gapped spin liquid to the Tomonaga-Luttinger spin-liquid phase [4].
- [1] D. Schmidiger, S. Mühlbauer, S. N. Gvasaliya, T. Yankova, A. Zheludev, Long-lived magnons throughout the Brillouin zone of the strong-leg spin ladder (C7D10N)2CuBr4 , Phys. Rev. B 84, 144421 (2011); arXiv:1105.4832.
- [2] D. Schmidiger, P. Bouillot, S. Mühlbauer, S. Gvasaliya, C. Kollath, T. Giamarchi, A. Zheludev, Spectral and thermodynamic properties of a strong-leg quantum spin ladder , Phys. Rev. Lett. 108, 167201 (2012); arXiv:1112.4307.
- [3] D. Schmidiger, P. Bouillot, G. Ehlers, S. Mühlbauer, A. M. Tsvelik, C. Kollath, T. Giamarchi, A. Zheludev, Symmetric and asymmetric excitations of a strong-leg quantum spin ladder , Phys. Rev. B 88, 094411 (2013); arXiv:1306.1671.
- [4] D. Schmidiger, P. Bouillot, T. Guidi, R. Bewley, C. Kollath, T. Giamarchi, A. Zheludev, Spectrum of a magnetized strong-leg quantum spin ladder , Phys. Rev. Lett. 111, 107202 (2013); arXiv:1306.4216.
- [5] K. Yu. Povarov, D. Schmidiger, N. Reynolds, A. Zheludev, R. Bewley, Scaling of temporal correlations in an attractive Tomonaga-Luttinger spin liquid , Phys. Rev. B 91, 020406(R) (2015); arXiv:1406.6876.
- [6] D. Schmidiger, K. Yu. Povarov, S. Galeski, N. Reynolds, R. Bewley, T. Guidi, J. Ollivier, A. Zheludev, Emergent interacting spin islands in a depleted strong-leg Heisenberg ladder , Phys. Rev. Lett. 116, 257203 (2016); arXiv:1603.00070.