paper

Quantum magnetism in molecular spin ladders probed with muon-spin spectroscopy

arXiv:1806.09402 · doi:10.1088/1367-2630/aae21a

Abstract

We present the results of muon-spin spectroscopy ( $I^¼^{+}$ SR) measurements on the molecular spin ladder system (Hpip) $_{2}$ CuBr $_{4 (1 - x)}$ Cl $_{4 x}$ , [Hpip=(C $_{5}$ H $_{12}$ N)]. Using transverse field $I^¼^{+}$ SR we are able to identify characteristic behaviour in each of the regions of the phase diagram of the $x = 0$ strong-rung spin ladder system (Hpip) $_{2}$ CuBr $_{4}$ . Comparison of our results to those of the dimer-based molecular magnet Cu(pyz)(gly)(ClO $_{4}$ ) shows several common features. We locate the crossovers in partially disordered (Hpip) $_{2}$ CuBr $_{4 (1 - x)}$ Cl $_{4 x}$ ( $x = 0.05$ ), where a region of behaviour intermediate between quantum disordered and Luttinger liquid-like is identified. Our interpretation of the results incorporates an analysis of the probable muon stopping states in (Hpip) $_{2}$ CuBr $_{4}$ based on density functional calculations and suggests how the muon plus its local distortion can lead to a local probe unit with good sensitivity to the magnetic state. Using longitudinal field $I^¼^{+}$ SR we compare the dynamic response of the $x = 1$ strong-rung material (Hpip) $_{2}$ CuCl $_{4}$ to that of the strong-leg material (C $_{7}$ H $_{10}$ N) $_{2}$ CuBr $_{4}$ (known as DIMPY) and demonstrate that our results are in agreement with predictions based on interacting fermionic quasiparticle excitations in these materials.

16 pages, 13 figures