Direct measurement of the spin gap in a quasi-one-dimensional clinopyroxene:NaTiSi2O6

Milestones of low-D quantum magnetism

“…The condensation of the system in either one of these states explains the appearance of a large singlet-triplet spin gap. The value of gap Δ = 620 K was estimated in time-of-flight neutron spectroscopy 65 in good correspondence with the first principles calculations. 66…”

Dual Orbital Degeneracy Lifting in a Strongly Correlated Electron System

“…The PDF observations establish that the ODL phenomenology does extend to materials with strong electron correlations, reinforcing the notion of its ubiquity. The results account for a number of high temperature anomalies reported in previous studies of this system [36,43,44], and provide new insight into the understanding of the transition mechanism.…”

“…1(a), (b)), with Ti 3+ in d 1 (S = 1/2) nominally triply degenerate 2g orbital configuration. A nonmagnetic ground state of NaTiSi 2 O 6 with a 53 meV spin gap [36] establishes on cooling through a 210 K [37] structural transition where orbital ordering stabilizes intrachain Ti-Ti spin singlet dimerization [38]. Once thought to host Haldane S = 1 chains [35,39,40], NaTiSi 2 O 6 is considered a candidate for quantum liquid with strong orbital fluctuations [41].…”

“…Polycrystalline NaTiSi 2 O 6 used in powder diffraction measurements was obtained via a solid state route [36,37,45] and shows a transition to a nonmagnetic state below T s = 210 K, Fig. 1(e).…”

“…5). Partial degeneracy alleviation is expected from slight trigonal distortion of TiO 6 [43], placing the single electron into a two fold degenerate low lying t 2g -derived (zx, xy) doublet [41] and rendering the third (yz) orbital inert [36,43,48]. The edge-sharing topology fosters direct (xy, xy) and (zx, zx) overlaps of t 2g orbitals belonging to neighboring Ti along the chains.…”