Disordered ground state in the spin-orbit coupled <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>J</mml:mi><mml:mi>eff</mml:mi></mml:msub></mml:math> = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:math> distorted honeycomb magnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">BiYbGeO</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math>
S. Mohanty, S. S. Islam, N. Winterhalter-Stocker, Anton Jesche, G. Simutis, Chunhui Wang, Zurab Guguchia, J. Sichelschmidt, M. Baenitz, Alexander A. Tsirlin, P. Gegenwart, R. Nath
Abstract
We delineate quantum magnetism in the strongly spin-orbit coupled distorted honeycomb lattice antiferromagnet ${\mathrm{BiYbGeO}}_{5}$. Our magnetization and heat capacity measurements reveal that its low-temperature behavior is well described by an effective ${J}_{\mathrm{eff}}=\frac{1}{2}$ Kramers doublet of ${\mathrm{Yb}}^{3+}$. The ground state is nonmagnetic with a tiny spin gap. Temperature-dependent magnetic susceptibility, magnetization isotherm, and heat capacity can be modeled well assuming isolated spin dimers with anisotropic exchange interactions ${J}_{\mathrm{Z}}\ensuremath{\simeq}2.6$ K and ${J}_{\mathrm{XY}}\ensuremath{\simeq}1.3$ K. Heat capacity measurements backed by muon spin relaxation suggest the absence of magnetic long-range order down to at least 80 mK both in zero field and in applied fields. This sets ${\mathrm{BiYbGeO}}_{5}$ apart from ${\mathrm{Yb}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{7}$, with its unusual regime of magnon Bose-Einstein condensation, and suggests negligible interdimer couplings, despite only a weak structural deformation of the honeycomb lattice.