Probing signatures of fractionalization in the candidate quantum spin liquid Cu2IrO3 via anomalous Raman scattering

Abstract

Long-range entanglement in quantum spin liquids (QSLs) leads to novel low-energy excitations with fractionalized quantum numbers and (in two dimensions) statistics. Experimental detection and manipulation of these excitations present a challenge particularly in view of diverse candidate magnets. A promising probe of fractionalization is their coupling to phonons. Here, we present Raman scattering results for the S = 1/2 honeycomb iridate Cu 2 IrO 3 , a candidate Kitaev QSL with fractionalized Majorana fermions and Ising flux excitations. We observe anomalous low-temperature frequency shift and linewidth broadening of the Raman intensities in addition to a broad magnetic continuum, both of which, as we derive, are naturally attributed to the phonon decaying into itinerant Majoranas. The dynamic Raman susceptibility marks a crossover from the QSL to a thermal paramagnet at ∼120 K. The phonon anomalies below this temperature demonstrate a strong phonon-Majorana coupling. These results provide evidence of spin fractionalization in Cu 2 IrO 3 .

Metastable Kitaev Magnets

“…Single crystals will also enable accurate determination of the interlayer and intra-layer exchange couplings. Both Raman and nuclear magnetic resonance (NMR) experiments can provide information about the fractionalized (Majorana) excitations in single crystals [ 23 , 43 ].…”

Probing emergent QED in quantum spin ice via Raman scattering of phonons: shallow inelastic scattering and pair production

“…A related probe for the spin physics are optical phonons, via infrared and Raman scattering experiments where phonon energy and linewidth encode such effects [15,[28][29][30][31][32]. Notably, such phonon spectroscopy can sensitively detect magnetic, superconducting, or chargedensity wave ordering, as well as couples to the resultant low-energy quasi-particles in these conventional phases [33][34][35].…”

“…The spin-phonon effects are expected to be particularly strong in spin-orbit coupled magnets where the magnetic moment is sensitive to the real space geometry due to an interlocking of spin and real space [36][37][38][39]. Indeed such spin-phonon coupling has recently been explored both experimentally and theoretically in candidate Kitaev QSLs such as α-RuCl 3 [15,19,40], Cu 2 IrO 3 [28], β-and γ-Li 2 IrO 3 [30,41] etc. In particular, for Cu 2 IrO 3 [28], the anomalous broadening of the phonon peaks and frequency softening at low temperatures is accounted for by the low-energy Majorana fermions that the spin fractionalises into [5].…”

“…Indeed such spin-phonon coupling has recently been explored both experimentally and theoretically in candidate Kitaev QSLs such as α-RuCl 3 [15,19,40], Cu 2 IrO 3 [28], β-and γ-Li 2 IrO 3 [30,41] etc. In particular, for Cu 2 IrO 3 [28], the anomalous broadening of the phonon peaks and frequency softening at low temperatures is accounted for by the low-energy Majorana fermions that the spin fractionalises into [5].…”

Raman fingerprints of fractionalized Majorana excitations in honeycomb iridate Ag$_3$LiIr$_2$O$_6$

“…Recently, a new set of Kitaev materials like H 3 LiIr 2 O 6 [16], Cu 2 IrO 3 [17], and Ag 3 LiIr 2 O 6 have been synthesized from the parent compounds A 2 IrO 3 (A = Na, Li) with the caveat that these compounds are susceptible to quenched disorders in their structure. In fact, the nature of disorder in these candidates becomes a key precursor in controlling the fate of their QSL ground state [18][19][20][21].…”