DTN
The material DTN is one of the best prototype systems for studying various "magnon condensation" problems. Nickel S=1 ions with dominant single ion anisotropy ensure the singlet on-site ground state, and the antiferromagnetic exchange is not strong enough to change this. Thus, at zero field the material has quantum-disordered ground state and a doublet of bosonic excitations. These can be split by external field, or modified by tuning the "average" Hamiltonian parameters via slightly altering the chemical composition. Thanks to the exceptionally high symmetry of DTN, the Hamiltonian is guaranteed to be free of the annoying anisotropic exchange terms and is therefore an ideal playground for the wanted physics. In particular, the substitution of chlorine with bromine modifies the Hamiltonian without disrupting its symmetry, and may eventually lead to the chemically induced long range order.
T. A. Soldatov, A. I. Smirnov, K. Yu. Povarov, A. Paduan-Filho, A. Zheludev, Microwave dynamics of pure and doped anisotropic S=1 chain antiferromagnet NiCl2-4SC(NH2)2, external pagePhys. Rev. B 101, 104410 (2020); external pagearXiv:1912.00172
A. Mannig, K. Yu. Povarov, J. Ollivier, A. Zheludev, Spin waves near the edge of halogen substitution induced magnetic order in Ni(Cl1−xBrx)2⋅4SC(NH2)2, external pagePhys. Rev. B 98, 214419 (2018); external pagearXiv:1810.10912
K. Yu. Povarov, A. Mannig, G. Perren, J. S. Möller, E. Wulf, J. Ollivier, and A. Zheludev, Quantum criticality in a three-dimensional spin system at zero field and pressure, external pagePhys. Rev. B 96, 140414(R) (2017); external pagearXiv:1708.02776
K. Yu. Povarov, E. Wulf, D. Hüvonen, J. Ollivier, A. Paduan-Filho and A. Zheludev, Dynamics of a bond-disordered S=1 quantum magnet near z=1 criticality, external pagePhys. Rev. B 92, 024429 (2015); external pagearXiv:1505.07328
E. Wulf, D. Hüvonen, R. Schönemann, H. Kühne, T. Herrmannsdörfer, I. Glavatskyy, S. Gerischer, K. Kiefer, S. Gvasaliya and A. Zheludev, Critical exponents and intrinsic broadening of the field-induced transition in NiCl2·4SC(NH2)2, external pagePhys. Rev. B 91, 014406 (2015); external pagearXiv:1412.0545
E. Wulf, D. Hüvonen, J.-W. Kim, A. Paduan-Filho, E. Ressouche, S. Gvasaliya, V. Zapf, A. Zheludev, Criticality in a disordered quantum antiferromagnet by neutron diffraction, external pagePhys. Rev. B 88, 174418 (2013); external pagearXiv:1310.1023
L. Facheris, D. Blosser, R. Bewley, S. Gvasaliya, A. Zheludev, Finite-temperature dynamics and role of disorder in almost-critical Ni(Cl1−xBrx)2⋅4SC(NH2)2, external pagePhys. Rev. B 102, 224405 (2020), external pagearXiv:2008.04037 (2020).