Quantized Signature of Majorana Fermion: Particle being its own Anti-particle

In 1937, Ettore Majorana proposed a particle being its antiparticle. Since its inception, Majorana has been under intensive pursuit both theoretically and in experiments. Recent interest in robust topologically protected quantum computing has accelerated the experimental quest of Majorana. Among various proposals, I will discuss the scenario when a topological insulator meets a superconductor. This system offers a possible host for Majorana. The talk will begin from the experimental efforts of the quest of dissipationless transport: quantum Hall without magnetic field, quantum spin Hall to quantum anomalous Hall (QAH). The latter was enabled by a long term effort in the materials growth of topological insulator - magnetic (Cr) doped BiSbTe to achieve reliably QAH. I will discuss the topological transitions of Dirac electrons for TI in QAH. When the QAH edge states interface with a superconductor, the Dirac electron space is transformed to the Nambu space, hosting Majorana fermions via pairing energy. We will describe our experimental efforts to show the convincing evidence of quantized signature of the one-dimensional chiral Majorana fermion [1]. A half-integer quantized conductance plateau (0.5 e²/h) gives a firm signature of the elusive Majorana fermion for the first time by scanning topological phase transitions under the reversal of the magnetization. This finding gives a new direction for topological quantum computing, for which I will discuss several possible paths for realizing the elemental qubits and operations.

[1]. Science, July 21, 2017