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Edited by Zachary Fisk, University of California, Irvine, CA, and approved September 18, 2014 (received for review June 6, 2014)
Significance
Topological insulators form a novel state of matter that open up new opportunities to create unique quantum particles. Although theoretical studies have proposed an abundance of new phenomena, many of the predictions still await their experimental verification, not to mention their implementation into applications. The main obstacle is material quality and cleanliness of the experimental conditions. The presence of tiny amounts of defects in the bulk or contaminants at the surface masks these phenomena. Here we show that for Bi2Te3, it is possible to obtain the desired quality by carrying out the preparation and characterization all under ultra-high-vacuum conditions. In situ four-point conductance measurements revealed the charge carriers moving on the surface with very high values of mobility.
Abstract
Topological insulators represent a novel state of matter with surface charge carriers having a massless Dirac dispersion and locked helical spin polarization. Many exciting experiments have been proposed by theory, yet their execution has been hampered by the extrinsic conductivity associated with the unavoidable presence of defects in Bi2Te3 and Bi2Se3 bulk single crystals, as well as impurities on their surfaces. Here we present the preparation of Bi2Te3 thin films that are insulating in the bulk and the four-point probe measurement of the conductivity of the Dirac states on surfaces that are intrinsically clean. The total amount of charge carriers in the experiment is of the order of 1012 cm−2 only, and mobilities up to 4,600 cm2/Vs have been observed. These values are achieved by carrying out the preparation, structural characterization, angle-resolved and X-ray photoemission analysis, and temperature-dependent four-point probe conductivity measurement all in situ under ultra-high-vacuum conditions. This experimental approach opens the way to prepare devices that can exploit the intrinsic topological properties of the Dirac surface states.
Footnotes
- ↵1To whom correspondence should be addressed. Email: katharina.hoefer{at}cpfs.mpg.de.
Author contributions: K.H. and L.H.T. designed research; K.H., C.B., D.R., and J.S. performed research; K.H., C.B., and J.S. contributed new reagents/analytic tools; K.H., P.T., and L.H.T. analyzed data; and K.H., P.T., and L.H.T. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1410591111/-/DCSupplemental.
Freely available online through the PNAS open access option.
Intrinsic conduction of topological insulator Bi2Te3
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