Gapless spinons and a field-induced soliton gap in the hyper-honeycomb Cu oxalate framework compound [(C$_{2}$H$_{5}$)$_{3}$NH]$_{2}$Cu$_{2}$(C$_{2}$O$_{4}$)$_{3}$

C. Dissanayake; A. C. Jacko; K. Kumarasinghe; R. Munir; H. Siddiquee; W. J. Newsome; F. J. Uribe-Romo; E. S. Choi; S. Yadav; X. -Z. Hu; Y. Takano; S. Pakhira; D. C. Johnston; Q. -P. Ding; Y. Furukawa; B. J. Powell; Y. Nakajima

doi:10.1103/PhysRevB.108.134418

paper

Gapless spinons and a field-induced soliton gap in the hyper-honeycomb Cu oxalate framework compound [(C $_{2}$ H $_{5}$ ) $_{3}$ NH] $_{2}$ Cu $_{2}$ (C $_{2}$ O $_{4}$ ) $_{3}$

arXiv:2306.13598 · doi:10.1103/PhysRevB.108.134418

Abstract

We report a detailed study of the specific heat and magnetic susceptibility of single crystals of a spin liquid candidate: the hyper-honeycomb Cu oxalate framework compound [(C $_{2}$ H $_{5}$ ) $_{3}$ NH] $_{2}$ Cu $_{2}$ (C $_{2}$ O $_{4}$ ) $_{3}$ . The specific heat shows no anomaly associated with a magnetic transition at low temperatures down to $T \sim$ 180 mK in zero magnetic field. We observe a large linear-in- $T$ contribution to the specific heat $I^^{3} T$ , $I^^{3} = 98 (1)$ mK/mol K $^{2}$ , at low temperatures, indicative of the presence of fermionic excitations despite the Mott insulating state. The low- $T$ specific heat is strongly suppressed by applied magnetic fields $H$ , which induce an energy gap, $I^ (H)$ , in the spin-excitation spectrum. We use the four-component relativistic density-functional theory (DFT) to calculate the magnetic interactions, including the Dzyaloshinskii-Moriya antisymmetric exchange, which causes an effective staggered field acting on one copper sublattice. The magnitude and field dependence of the field-induced gap, $I^ (H) \propto H^{2/3}$ , are accurately predicted by the soliton mass calculated from the sine-Gordon model of weakly coupled antiferromagnetic Heisenberg chains with all parameters determined by our DFT calculations. Thus our experiment and calculations are entirely consistent with a model of [(C $_{2}$ H $_{5}$ ) $_{3}$ NH] $_{2}$ Cu $_{2}$ (C $_{2}$ O $_{4}$ ) $_{3}$ in which anisotropic magnetic exchange interactions due to Jahn-Teller distortion cause one copper sublattice to dimerize, leaving a second sublattice of weakly coupled antiferromagnetic chains. We also show that this model quantitatively accounts for the measured temperature-dependent magnetic susceptibility. Thus [(C $_{2}$ H $_{5}$ ) $_{3}$ NH] $_{2}$ Cu $_{2}$ (C $_{2}$ O $_{4}$ ) $_{3}$ is a canonical example of a one-dimensional spin-1/2 Heisenberg antiferromagnet and not a resonating-valence-bond quantum spin liquid, as previously proposed.

8 pages, 6 figures

Gapless spinons and a field-induced soliton gap in the hyper-honeycomb Cu oxalate framework compound [(C2​H5​)3​NH]2​Cu2​(C2​O4​)3​

Abstract

Gapless spinons and a field-induced soliton gap in the hyper-honeycomb Cu oxalate framework compound [(C $_{2}$ H $_{5}$ ) $_{3}$ NH] $_{2}$ Cu $_{2}$ (C $_{2}$ O $_{4}$ ) $_{3}$