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Raman spectroscopic Signatures of fractionalized Excitations in the Honeycomb Iridates beta- and gamma-Li2IrO3

Speaker:Prof. Peter Lemmens
Affiliation:Inst. Condensed Matter Physics, TU Braunschweig, Braunschweig, Germany
Organizer:Amit Keren
Location:Lidow Nathan Rosen (300)

The fractionalization of elementary excitations is a central theme of current condensed matter physics and has previously been mainly limited to 1D systems (see the Luttinger liquid, the resonance valence bond (RVB) state, or the fractional quantum Hall effect). The 2D Kitaev honeycomb spin model provides a prominent example of exotic fractionalized quasiparticles, composed of itinerant Majorana fermions and gapped gauge fluxes. However, the identification of such Majorana fermions in a material (-RuCl3) realizing a honeycomb lattice remains rare [1]. Here we report spectroscopic signatures of fractional excitations even in the 3D harmonic-honeycomb iridates [2]. Using polarization-resolved Raman spectroscopy [3,4], we find that the dynamical Raman response of beta- and gamma-Li2IrO3 features a broad scattering continuum with distinct polarization and temperature dependencies. The later temperature dependence of the Raman spectral weight can be decomposed into fermionic and bosonic components and is dominated by a thermal damping of fermionic excitations. These results suggest the emergence of Majorana fermions from spin fractionalization in a three-dimensional Kitaev–Heisenberg system. 


We acknowledge support by German-Israeli Foundation (GIF, 1171-486 189.14/2011), the NTH-School Contacts in Nanosystems: Interactions, Control and Quantum Dynamics, the Braunschweig International Graduate School of Metrology funded by the State of Lower Saxony, and DFG-RTG 1952/1, Metrology for Complex Nanosystems. 


[1] L. J. Sandilands, Y. Tian, K. W. Plumb, Y.-J. Kim, and K. S. Burch, Phys. Rev. Lett. 114, 147201 (2015).

[2] A. Glamazda, P. Lemmens, S.-H. Do, K.-Y. Choi, Nature Commun. 7, 12286 (2016). 

[3] D. Wulferding, M. Shay, G. Drachuck, Z. Salman, P. Lemmens, and A. Keren, Phys. Rev. B 90, 104511 (2014).

[4] V. Gnezdilov, P. Lemmens, D. Wulferding, A. Möller, P. Recher, H. Berger, R. Sankar, F. C. Chou, Phys. Rev. B 89, 195117 (2014).