Bachelor of Science, Tsinghua University (2008)
Doctor of Philosophy, Tsinghua University (2014)
Yi Cui, Postdoctoral Faculty Sponsor
Experimental Observation of the Quantum Anomalous Hall Effect in a Magnetic Topological Insulator
2013; 340 (6129): 167-170
The quantized version of the anomalous Hall effect has been predicted to occur in magnetic topological insulators, but the experimental realization has been challenging. Here, we report the observation of the quantum anomalous Hall (QAH) effect in thin films of chromium-doped (Bi,Sb)2Te3, a magnetic topological insulator. At zero magnetic field, the gate-tuned anomalous Hall resistance reaches the predicted quantized value of h/e(2), accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect may lead to the development of low-power-consumption electronics.
View details for DOI 10.1126/science.1234414
View details for Web of Science ID 000317341400047
View details for PubMedID 23493424
Topology-Driven Magnetic Quantum Phase Transition in Topological Insulators
2013; 339 (6127): 1582-1586
The breaking of time reversal symmetry in topological insulators may create previously unknown quantum effects. We observed a magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 topological insulator films grown by means of molecular beam epitaxy. Across the critical point, a topological quantum phase transition is revealed through both angle-resolved photoemission measurements and density functional theory calculations. We present strong evidence that the bulk band topology is the fundamental driving force for the magnetic quantum phase transition. The tunable topological and magnetic properties in this system are well suited for realizing the exotic topological quantum phenomena in magnetic topological insulators.
View details for DOI 10.1126/science.1230905
View details for Web of Science ID 000316731600042
View details for PubMedID 23539598
Thin Films of Magnetically Doped Topological Insulator with Carrier-Independent Long-Range Ferromagnetic Order
2013; 25 (7): 1065-1070
Thin films of magnetically doped topological insulators Cr(0.22) (Bi(x) Sb(1-x) )(1.78) Te(3) are found to possess carrier-independent long-range ferromagnetic order with perpendicular magnetic anisotropy. The anomalous Hall resistance is greatly enhanced, up to one quarter of quantum Hall resistance, by depletion of the carriers. The results demonstrate this material as a promising system to realize the quantized anomalous Hall effect.
View details for DOI 10.1002/adma.201203493
View details for Web of Science ID 000315091800019
View details for PubMedID 23334936
Crossover between Weak Antilocalization and Weak Localization in a Magnetically Doped Topological Insulator
PHYSICAL REVIEW LETTERS
2012; 108 (3)
We report transport studies on magnetically doped Bi(2)Se(3) topological insulator ultrathin films grown by molecular beam epitaxy. The magnetotransport behavior exhibits a systematic crossover between weak antilocalization and weak localization with the change of magnetic impurity concentration, temperature, and magnetic field. We show that the localization property is closely related to the magnetization of the sample, and the complex crossover is due to the transformation of Bi(2)Se(3) from a topological insulator to a topologically trivial dilute magnetic semiconductor driven by magnetic impurities. This work demonstrates an effective way to manipulate the quantum transport properties of the topological insulators by breaking time-reversal symmetry.
View details for DOI 10.1103/PhysRevLett.108.036805
View details for Web of Science ID 000299329100024
View details for PubMedID 22400773
Band structure engineering in (Bi1-xSbx)(2)Te-3 ternary topological insulators
Topological insulators (TIs) are quantum materials with insulating bulk and topologically protected metallic surfaces with Dirac-like band structure. The most challenging problem faced by current investigations of these materials is to establish the existence of significant bulk conduction. Here we show how the band structure of topological insulators can be engineered by molecular beam epitaxy growth of (Bi(1-x)Sb(x))(2)Te(3) ternary compounds. The topological surface states are shown to exist over the entire composition range of (Bi(1-x)Sb(x))(2)Te(3), indicating the robustness of bulk Z(2) topology. Most remarkably, the band engineering leads to ideal TIs with truly insulating bulk and tunable surface states across the Dirac point that behaves like one-quarter of graphene. This work demonstrates a new route to achieving intrinsic quantum transport of the topological surface states and designing conceptually new topologically insulating devices based on well-established semiconductor technology.
View details for DOI 10.1038/ncomms1588
View details for Web of Science ID 000299159900006
View details for PubMedID 22146393
- Disentangling the magnetoelectric and thermoelectric transport in topological insulator thin films PHYSICAL REVIEW B 2015; 91 (7)
Simultaneous Electrical-Field-Effect Modulation of Both Top and Bottom Dirac Surface States of Epitaxial Thin Films of Three-Dimensional Topological Insulators
2015; 15 (2): 1090-1094
It is crucial for the studies of the transport properties and quantum effects related to Dirac surface states of three-dimensional topological insulators (3D TIs) to be able to simultaneously tune the chemical potentials of both top and bottom surfaces of a 3D TI thin film. We have realized this in molecular beam epitaxy-grown thin films of 3D TIs, as well as magnetic 3D TIs, by fabricating dual-gate structures on them. The films could be tuned between n-type and p-type by each gate alone. Combined application of two gates can reduce the carrier density of a TI film to a much lower level than with only one of them and enhance the film resistance by 10,000%, implying that Fermi level is tuned very close to the Dirac points of both top and bottom surface states without crossing any bulk band. The result promises applications of 3D TIs in field effect devices.
View details for DOI 10.1021/nl504047c
View details for Web of Science ID 000349578000045
View details for PubMedID 25594485
- Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping PHYSICAL REVIEW B 2013; 88 (8)
- Transport properties of Sb2Te3/Bi2Te3 topological insulator heterostructures PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 2013; 7 (1-2): 142-144
- Interface-Induced High-Temperature Superconductivity in Single Unit-Cell FeSe Films on SrTiO3 CHINESE PHYSICS LETTERS 2012; 29 (3)
Li(Zn,Mn)As as a new generation ferromagnet based on a I-II-V semiconductor
In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li(1+y)(Zn(1-x)Mn(x))As in bulk materials. Ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess (y=0.05-0.2) compounds with Mn concentrations of x=0.02-0.15, which have p-type metallic carriers. This is presumably due to excess Li in substitutional Zn sites. Semiconducting LiZnAs, ferromagnetic Li(Zn,Mn)As, antiferromagnetic LiMnAs, and superconducting LiFeAs systems share square lattice As layers, which may enable development of novel junction devices in the future.
View details for DOI 10.1038/ncomms1425
View details for Web of Science ID 000294806500015
View details for PubMedID 21829184