Joseph Checkelsky

A tunable topological insulator in the spin helical Dirac transport regime

Helical Dirac fermions—charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum—are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose–Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene or bismuth. It has recently been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators—materials with a bulk insulating gap of spin–orbit origin and surface states protected against scattering by time-reversal symmetry—and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime. However, helical Dirac fermions have not been observed in existing topological insulators. Here we report the realization and characterization of a tunable topological insulator in a bismuth-based class of material by combining spin-imaging and momentum-resolved spectroscopies, bulk charge compensation, Hall transport measurements and surface quantum control. Our results reveal a spin-momentum locked Dirac cone carrying a non-trivial Berry’s phase that is nearly 100 per cent spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers point and can be driven to the long-sought topological spin transport regime. The observed topological nodal state is shown to be protected even up to 300 K. Our demonstration of room-temperature topological order and non-trivial spin-texture in stoichiometric Bi2Se3.Mx (Mx indicates surface doping or gating control) paves the way for future graphene-like studies of topological insulators, and applications of the observed spin-polarized edge channels in spintronic and computing technologies possibly at room temperature.Princeton University, Princeton, NJ 08544, USA Department of Physics, Shanghai Jiao Tong University, Shanghai 200030, China Swiss Light Source, Paul Scherrer Institute, CH-5232, Villigen, Switzerland Physik-Institut, Universität Zürich-Irchel, 8057 Zürich, Switzerland Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA Department of Physics, Northeastern University, Boston, MA 02115, USA Department of Chemistry, Princeton University, Princeton, NJ 08544, USA Princeton Center for Complex Materials, Princeton University, Princeton NJ 08544, USA

Superconductivity in CuxBi2Se3 and its Implications for Pairing in the Undoped Topological Insulator

Bi2Se3 is one of a handful of known topological insulators. Here we show that copper intercalation in the van der Waals gaps between the Bi2Se3 layers, yielding an electron concentration of approximately 2x10{20} cm{-3}, results in superconductivity at 3.8 K in CuxBi2Se3 for 0.12<or=x<or=0.15. This demonstrates that Cooper pairing is possible in Bi2Se3 at accessible temperatures, with implications for studying the physics of topological insulators and potential devices.

p -type Bi 2 Se 3 for topological insulator and low-temperature thermoelectric applications

The growth and elementary properties of

Extreme sensitivity of superconductivity to stoichiometry in Fe1+δSe

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Bulk band gap and surface state conduction observed in voltage-tuned crystals of the topological insulator Bi2Se3.

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Quantum Interference in Macroscopic Crystals of Nonmetallic Bi2Se3

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Development of ferromagnetism in the doped topological insulator Bi 2 − x Mn x Te 3

single crystals are reported. Based on a hypothesis about the defect chemistry of

Trajectory of the anomalous Hall effect towards the quantized state in a ferromagnetic topological insulator

{\text{Bi}}_{2}{\text{Se}}_{3}

Thermopower and Nernst effect in graphene in a magnetic field

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Zero-Energy State in Graphene in a High Magnetic Field

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