Three-dimensional topological insulators are a phase of matter that hosts unique spin-polarized gapless surface states that are protected by time-reversal symmetry. They exhibit unconventional charge ...and spin transport properties1,2. Intense laser fields can drive ballistic charge dynamics in Dirac bands3,4 or they can coherently steer spin5 and valley pseudospin6. Similarly, high-harmonic generation (HHG) in solids provides insights into the dynamics of the electrons in topological insulators7–13. Despite several theoretical attempts to identify a topological signature in the high-harmonic spectrum14–16, a unique fingerprint has yet to be found experimentally. Here, we observe HHG that arises from topological surface states in the intrinsic topological insulator BiSbTeSe2. The components of the even-order harmonics that are polarized along the pump polarization stem from the spin current in helical surface states, whereas the perpendicular components originate from the out-of-plane spin polarization related to the hexagonal wrapping effect17. The dependence of HHG on surface doping in ambient air also suggests the presence of a Rashba-split two-dimensional electron gas, whose strength can be enhanced by an increase in the intensity of the mid-infrared pump.High-harmonic generation up to the seventh harmonic is observed from the intrinsic three-dimensional topological insulator BiSbTeSe2. The parallel components of the even-order harmonics arise directly from the topological surface states.
Abstract
Magnetic topological insulators (MTIs) offer a combination of topologically nontrivial characteristics and magnetic order and show promise in terms of potentially interesting physical ...phenomena such as the quantum anomalous Hall (QAH) effect and topological axion insulating states. However, the understanding of their properties and potential applications have been limited due to a lack of suitable candidates for MTIs. Here, we grow two-dimensional single crystals of Mn(Sb
x
Bi
(1-
x
)
)
2
Te
4
bulk and exfoliate them into thin flakes in order to search for intrinsic MTIs. We perform angle-resolved photoemission spectroscopy, low-temperature transport measurements, and first-principles calculations to investigate the band structure, transport properties, and magnetism of this family of materials, as well as the evolution of their topological properties. We find that there exists an optimized MTI zone in the Mn(Sb
x
Bi
(1-
x
)
)
2
Te
4
phase diagram, which could possibly host a high-temperature QAH phase, offering a promising avenue for new device applications.
A topological insulator (TI) is a kind of novel material hosting a topological band structure and plenty of exotic topological quantum effects. Achieving quantized electrical transport, including the ...quantum Hall effect (QHE) and the quantum anomalous Hall effect (QAHE), is an important aspect of realizing quantum devices based on TI materials. Intense efforts are made in this field, in which the most essential research is based on the optimization of realistic TI materials. Herein, the TI material development process is reviewed, focusing on the realization of quantized transport. Especially, for QHE, the strategies to increase the surface transport ratio and decrease the threshold magnetic field of QHE are examined. For QAHE, the evolution history of magnetic TIs is introduced, and the recently discovered magnetic TI candidates with intrinsic magnetizations are discussed in detail. Moreover, future research perspectives on these novel topological quantum effects are also evaluated.
Topological insulators (TIs) are materials hosting exotic topological quantum effects including the quantum Hall effect and the quantum anomalous Hall effect. The material development history of TIs and magnetic TIs and recent research progress are reviewed, focusing on the realization of these quantized transports, which will promote fundamental research and potential applications in the future.
Magnetic topological insulator, a platform for realizing quantum anomalous Hall effect, axion state, and other novel quantum transport phenomena, has attracted a lot of interest. Recently, it is ...proposed that MnBi2Te4 is an intrinsic magnetic topological insulator, which may overcome the disadvantages in the magnetic doped topological insulator, such as disorder. Here we report on the gate-reserved anomalous Hall effect (AHE) in the MnBi2Te4 thin film. By tuning the Fermi level using the top/bottom gate, the AHE loop gradually decreases to zero and the sign is reversed. The positive AHE exhibits distinct coercive fields compared with the negative AHE. It reaches a maximum inside the gap of the Dirac cone, and its amplitude exhibits a linear scaling with the longitudinal conductance. The positive AHE is attributed to the competition of the intrinsic Berry curvature and the extrinsic skew scattering. Its gate-controlled switching contributes a scheme for the topological spin field-effect transistors.
2D transition metal dichalcogenides are promising platforms for next‐generation electronics and spintronics. The layered Weyl semimetal (W,Mo)Te2 series features structural phase transition, ...nonsaturated magnetoresistance, superconductivity, and exotic topological physics. However, the superconducting critical temperature of the bulk (W,Mo)Te2 remains ultralow without applying a high pressure. Here, the significantly enhanced superconductivity is observed with a transition temperature as large as about 7.5 K in bulk Mo1−xTaxTe2 single crystals upon Ta doping (0 ≤ x ≤ 0.22), which is attributed to an enrichment of density of states at the Fermi level. In addition, an enhanced perpendicular upper critical field of 14.5 T exceeding the Pauli limit is also observed in Td‐phase Mo1−xTaxTe2 (x = 0.08), indicating the possible emergence of unconventional mixed singlet–triplet superconductivity owing to the inversion symmetry breaking. This work provides a new pathway for exploring the exotic superconductivity and topological physics in transition metal dichalcogenides.
The superconducting transition temperature is greatly enhanced to be as large as 7.5 K in bulk Mo1−xTaxTe2 single crystals, which is attributed to an enrichment of density of states at the Fermi level. We also find the enhanced upper critical field beyond the Pauli limit in Ta‐doped Weyl semimetal Td‐MoTe2, which is likely due to the mixed singlet–triplet superconductivity.
Exotic Superconductivity
In article number 2207841, Fucong Fei, Zhicheng Zhong, Fengqi Song, Xuefeng Wang, and co‐workers report boosted superconductivity with a transition temperature of about 7.5 K ...in Ta‐doped MoTe2 single crystals under ambient pressure. An enhanced upper critical field beyond the Pauli limit is also observed in Ta‐doped Weyl semimetal Td‐MoTe2, which is likely due to the mixed singlet–triplet superconductivity.
The discovery of a new type‐II Dirac semimetal in Ir1−xPtxTe2 with optimized band structure is described. Pt dopants protect the crystal structure holding the Dirac cones and tune the Fermi level ...close to the Dirac point. The type‐II Dirac dispersion in Ir1−xPtxTe2 is confirmed by angle‐resolved photoemission spectroscopy and first‐principles calculations. Superconductivity is also observed and persists when the Fermi level aligns with the Dirac points. Ir1−xPtxTe2 is an ideal platform for further studies on the exotic properties and potential applications of type‐II DSMs, and opens up a new route for the investigation of the possible topological superconductivity and Majorana physics.
A type‐II Dirac semimetal in Ir1−xPtxTe2 with optimized Dirac dispersions is experimentally discovered by angle‐resolved photoemission spectroscopy. The Pt dopant protects the crystal structure holding the Dirac cones and tunes the Fermi level close to the Dirac point. Combining the type‐II Dirac cone, Fermi level tunability, and superconductivity together, Ir1−xPtxTe2 provides an ideal platform for more in‐depth research of type‐II DSMs.
Crystalline and amorphous structures are two of the most common solid‐state phases. Crystals having orientational and periodic translation symmetries are usually both short‐range and long‐range ...ordered, while amorphous materials have no long‐range order. Short‐range ordered but long‐range disordered materials are generally categorized into amorphous phases. In contrast to the extensively studied crystalline and amorphous phases, the combination of short‐range disordered and long‐range ordered structures at the atomic level is extremely rare and so far has only been reported for solvated fullerenes under compression. Here, a report on the creation and investigation of a superconducting quasi‐1D material with long‐range ordered amorphous building blocks is presented. Using a diamond anvil cell, monocrystalline (TaSe4)2I is compressed and a system is created where the TaSe4 atomic chains are in amorphous state without breaking the orientational and periodic translation symmetries of the chain lattice. Strikingly, along with the amorphization of the atomic chains, the insulating (TaSe4)2I becomes a superconductor. The data provide critical insight into a new phase of solid‐state materials. The findings demonstrate a first ever case where superconductivity is hosted by a lattice with periodic but amorphous constituent atomic chains.
Combination of long‐range ordered and short‐range disordered structures at the atomic level is demonstrated for a quasi‐1D linear chain compound. Under compression, the constituent atomic chains of the material are amorphized without breaking the orientational and periodic translation symmetries of the chain lattice. This lattice of amorphous atomic chains hosts a quantum condensate of Cooper pairs.
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