Dirac surface plasmons in photoexcited bismuth telluride nanowires: Optical pump-terahertz probe spectroscopy

Mithun, KP and Kar, S and Kumar, A and Muthu, DVS and Ravishankar, N and Sood, AK (2021) Dirac surface plasmons in photoexcited bismuth telluride nanowires: Optical pump-terahertz probe spectroscopy. In: Nanoscale, 13 (17). pp. 8283-8292.

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Abstract

Collective excitation of Dirac plasmons in graphene and topological insulators has opened new possibilities of tunable plasmonic materials ranging from THz to mid-infrared regions. Using time resolved Optical Pump-Terahertz Probe (OPTP) spectroscopy, we demonstrate the presence of plasmonic oscillations in bismuth telluride nanowires (Bi2Te3 NWs) after photoexcitation using an 800 nm pump pulse. In the frequency domain, the differential conductivity (�� = �pump on - �pump off) spectrum shows a Lorentzian response where the resonance frequency (�p), attributed to surface plasmon oscillations, shifts with photogenerated carrier density (n) as. This dependence establishes the absorption of THz radiation by the Dirac surface plasmon oscillations of the charge carriers in the Topological Surface States (TSS) of Bi2Te3 NWs. Moreover, we obtain a modulation depth, tunable by pump fluence, of �40 over the spectral range of 0.5 to 2.5 THz. In addition, the time evolution of ��(t) represents a long relaxation channel lasting for more than 50 ps. We model the decay dynamics of ��(t) using coupled second order rate equations, highlighting the contributions from surface recombination as well as from trap mediated relaxation channels of the photoinjected carriers. This journal is © The Royal Society of Chemistry.

Item Type:	Journal Article
Publication:	Nanoscale
Publisher:	Royal Society of Chemistry
Additional Information:	The copyright for this article belongs to Royal Society of Chemistry
Keywords:	Bismuth compounds; Bismuth metallography; Carrier mobility; Frequency domain analysis; Nanowires; Optical pumping; Probes; Surface plasmon resonance; Terahertz spectroscopy; Terahertz waves, Collective excitations; Differential conductivity; Optical pump-terahertz probe; Optical-pump terahertz-probe spectroscopy; Photogenerated carriers; Photoinjected carriers; Surface plasmon oscillation; Surface recombinations, Surface plasmons
Department/Centre:	Division of Chemical Sciences > Materials Research Centre Division of Physical & Mathematical Sciences > Physics
Date Deposited:	03 Aug 2021 09:17
Last Modified:	03 Aug 2021 09:17
URI:	http://eprints.iisc.ac.in/id/eprint/68920

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