Speaker
Description
Chasing new states of quantum matter is a central element in condensed matter physics, motivated both by fundamental curiosity but also by the need for a better understanding of many-body quantum effects for future technologies. Of particular interest are frustrated systems such as the Shastry-Sutherland (SS) model consisting of spin pairs (dimers) embedded in a square lattice. The model has an exact dimer product ground state when the ratio, $J’/J$, between the inter-dimer coupling, $J$, and intra-dimer coupling, $J’$, is less than 0.675 [1]. The network of Cu$^{2+}$ ions in SrCu$_2$(BO$_3$)$_2$ (SCBO) is topologically equivalent to the SS lattice and with $J’/J \sim 0.6$ close to the critical point, this compound presents unique experimental testing grounds for the model. Upon applying a magnetic field, SCBO exhibits a series of phase transitions [3,4] and we study the magnetic excitations upon approaching the first transition at 27T to the 1/8 magnetization plateau using inelastic neutron scattering. At field values much below the transition a novel and unexpected mode shows up. We use state-of-the-art model calculations to identify the nature of this mode: Is it a bound state or a triplet excitation? And why does it appear before the transition?
[1] B. S. Shastry and B. Sutherland, Physica 108B, 1069-1070 (1981)
[2] S. Miyahara and K. Ueda, Phys. Rev. Lett. 82, 3701 (1999)
[3] M. Takigawa et al., Phys. Rev. Lett. 110, 067210 (2013)
[4] P. Corboz and F. Mila, Phys. Rev. Lett. 112, 147203 (2014)
