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APS March Meeting 2011

## Volume 56, Number 1

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Monday–Friday, March 21–25, 2011;
Dallas, Texas

### Abstract: Y2.00001 : Quantum oscillations and Hall anomaly of surface electrons on Topological Insulators

8:00 AM–8:36 AM

Preview Abstract

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Author:

The investigation of Topological Insulators (TI) by transport
experiments is a challenge, because the surface currents cannot
be well-resolved when the bulk conductance is dominant, as in
most crystals. I will review the progress starting from Ca-doped
Bi$_2$Se$_3$, and proceeding to Bi$_2$Te$_3$ and to
Bi$_2$SeTe$_2$. Using Ca dopants in Bi$_2$Se$_3$, we succeeded
in lowering the Fermi energy $E_F$ into the bulk gap. However,
in non-metallic crystals, the substantial dopant-induced disorder
precluded observation of Shubnikov-de Haas (SdH) oscillations.
Fortunately, $E_F$ in undoped Bi$_2$Te$_3$ can be tuned into the
gap by heat treatment. The non-metallic samples display a bulk
resistivity $\rho$ = 4-12 m$\Omega$cm at 4 K. In these crystals,
weak SdH oscillations are observed below 10 K. We confirmed that
these oscillations arise from a 2D Fermi Surface by tilting the
magnetic field $\bf H$. From the behavior of the SdH amplitude
versus temperature $T$ and $H$, we infer a surface Fermi velocity
$v_F$ = 3.7-4.2 $\times 10^5$ m/s, and a high surface mobility
$\mu$ = 10,000 cm$^2$/Vs. The high mobility of the surface
electrons is confirmed by the appearance of an unusual weak-field
anomaly in the Hall conductance $G_{xy}$. I will discuss recent
progress in further lowering the bulk conductance in the new TI
Bi$_2$Se$_3$, in which a Se layer is sandwiched between two Te
layers in each quintuplet unit cell. In these crystals, $\rho$
at 4 K is a factor of 1000 larger (6 $\Omega$cm). The
interesting pattern of SdH oscillations in this new system will
be reported.\\[4pt]
Collaborators: D.X. Qu, J. M. Checkelsky, Y. S. Hor, J. Xiong, R.
J. Cava

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.Y2.1