Abstract
A remarkable feature of vanadium dioxide is that it can be synthesized in a number of polymorphs. The conductivity mechanism in the metastable layered polymorph VO2(B) thin films has been investigated by terahertz time-domain spectroscopy (THz-TDS). In VO2(B), a critical temperature of 240 K marks the appearance of a non-zero Drude term in the observed complex conductivity, indicating the evolution from a pure insulating state towards a metallic state. In contrast, the THz conductivity of the well-known VO2(M1) is well fitted only by a modification of the Drude model to include backscattering. We also identified two different THz conductivity regimes separated by temperature in these two polymorphs. The electronic phase diagram is constructed, revealing that the width and onset of the metal-insulator transition in the B phase develop differently from the M1 phase.
Highlights
New Insights into the Diverse Electronic Phases of a Novel Vanadium Dioxide Polymorph: A Terahertz Spectroscopy Study
The conductivity mechanism in the metastable layered polymorph VO2(B) thin films has been investigated by terahertz time-domain spectroscopy (THz-TDS)
While metalinsulator transition (MIT) in VO2(M1) is associated with a corresponding reversible structural phase transition from a room temperature monoclinic to a high temperature tetragonal phase[9,13,14,15,16], currently there is little understanding of the nature of the semimetal-to-insulator transition in VO2(B) which remains monoclinic with MIT10
Summary
New Insights into the Diverse Electronic Phases of a Novel Vanadium Dioxide Polymorph: A Terahertz Spectroscopy Study. M ulti-polymorphic materials – compounds that can assume numerous, different crystal symmetries with the same chemical composition, show great promise as future electronic materials. This is because their structural diversity can give rise to a variety of electrical and optical responses that can be tuned for technological applications such as optical switches, batteries, solar cells, optical filters, spintronic devices, memory devices etc[1,2,3,4]. The drastic changes in conductivity with temperature for these VO2 polymorphs are accompanied by a corresponding change in optical response, thereby making terahertz (THz) spectroscopy a viable technique to probe the nature of electronic properties in these systems. THz spectroscopy has been used to make comprehensive optical investigations in a host of materials rich in exotic conducting phases including graphene[36,37], toplogical insulators[34,38], superconductors[39,40,41], oxide semiconductors[32,33], quantum-confined semiconductors[42], and percolating systems[43]
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