Quadrupolar magnetic excitations in an isotropic spin-1 antiferromagnet

Abstract

The microscopic origins of emergent behaviours in condensed matter systems are encoded in their excitations. In ordinary magnetic materials, single spin-flips give rise to collective dipolar magnetic excitations called magnons. Likewise, multiple spin-flips can give rise to multipolar magnetic excitations in magnetic materials with spin S ≥ 1. Unfortunately, since most experimental probes are governed by dipolar selection rules, collective multipolar excitations have generally remained elusive. For instance, only dipolar magnetic excitations have been observed in isotropic S = 1 Haldane spin systems. Here, we unveil a hidden quadrupolar constituent of the spin dynamics in antiferromagnetic S = 1 Haldane chain material Y2BaNiO5 using Ni L3-edge resonant inelastic x-ray scattering. Our results demonstrate that pure quadrupolar magnetic excitations can be probed without direct interactions with dipolar excitations or anisotropic perturbations. Originating from on-site double spin-flip processes, the quadrupolar magnetic excitations in Y2BaNiO5 show a remarkable dual nature of collective dispersion. While one component propagates as non-interacting entities, the other behaves as a bound quadrupolar magnetic wave. This result highlights the rich and largely unexplored physics of higher-order magnetic excitations.

Magnetic excitations beyond the single- and double-magnons

“…It is inevitable to conclude that the higher-rank magnons have a different origin compared to the single- and double-magnons reported in previous works 12 , 13 , 20 , and a mechanism that allows the exchange of higher angular momenta is needed. This apparent contradiction can be reconciled by realizing that the angular momenta of electrons only is not a conserved quantum number in real crystals 21 .…”

Verdazyl–Nitroxide Diradical with S = 1 Ground State: Observation of Long-Range Ordering and Haldane Gap in a Highly Isotropic S = 1 Antiferromagnetic Heisenberg Chain

“…The organic layer was dried over MgSO 4 , concentrated in vacuo, and purified by column chromatography on silica gel (eluent: n-hexane/CH 2 Cl 2 = from 20/80 to 70/30) to give 4 (400 mg, 1.3 mmol, 23%) as a brown oil. 1 H NMR (400 MHz, CDCl 3 ): δ/ppm 9.94 (1H, s), 7.76 (2H, d, J = 8.8 Hz), 7.39 (2H, d, J = 8.0 Hz), 1.13 (9H, s), 0.92 (9H, s), −0.12 (6H, br s); 13 (5). A mixture of 4 (400 mg, 1.3 mmol) and 7 (315 mg, 1.3 mmol, 1.0 equiv) in a mixture of EtOH (5 mL) and CH 2 Cl 2 (15 mL) was heated to reflux overnight.…”

“…Quantum fluctuations are strongly manifested in low-dimensional systems and lead to unique quantum states that cannot be expected from the classical picture. , The exotic quantum phase leads to nonclassical phenomena such as a resonating valence bond state and spin liquid, and the rich physics behind these remains unexplored . As a milestone of quantum magnetism, Haldane pointed out for a 1D antiferromagnetic (AFM) Heisenberg chain that whether the spin is half-integer or integer determines whether its excited spectrum is gapless or gapped, respectively .…”

“…1,2 The exotic quantum phase leads to nonclassical phenomena such as a resonating valence bond state 3 and spin liquid, 4 and the rich physics behind these remains unexplored. 5 As a milestone of quantum magnetism, Haldane pointed out for a 1D antiferromagnetic (AFM) Heisenberg chain that whether the spin is half-integer or integer determines whether its excited spectrum is gapless or gapped, respectively. 6 The Haldane phase has been characterized as a singlet state with large quantum fluctuations but with hidden nonlocal topological order.…”

A plausible investigation of low dimensional magnetism in a 3D spin system PrVO4

“…Exotic magnetic states ranging from the disordered ground state with excitations having quantum number S = 1 2 (known as spinons in case of half-integral spin systems) to Haldane spin gap in S = 1 are reported in such systems. [6][7][8][9][10][11][12][13][14] One of the most essential ingredients for low D magnetism is the presence of linear chains formed by magnetic ions, which are separated by a non-magnetic geometry such as tetrahedra. For S = 1 2 systems, there are numerous candidates, which include Cu 2+ , Ru 3+ , Ir 4+ , Ce 3+ , and Yb 3+ magnetic ions, whereas for Haldane spin gap systems, only Ni 2+ (S = 1) based systems are reported to be suitable candidates.…”