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Journal ArticleDOI: 10.1021/ACS.JPCLETT.1C00378

Temperature Dependence of Spin-Orbit Torques in Nearly Compensated Tb21Co79 Films by a Topological Insulator Sb2Te3.

04 Mar 2021-Journal of Physical Chemistry Letters (American Chemical Society)-Vol. 12, Iss: 9, pp 2394-2399
Abstract: Topological insulators (TIs) with spin-momentum-locked metallic surface states can exert giant spin-orbit torques, offering great potential in energy-efficient magnetic memory devices. In this work, temperature (T)-dependent SOT efficiencies are investigated in Sb2Te3/Ta/TbCo heterostructures with perpendicular magnetic anisotropy. The spin Hall angle θSH is around 0.16 at room temperature (RT), which is much higher than that of the control sample without TI. Moreover, as T decreases from RT down to 10 K, θSH exhibits a conspicuous 5-fold enhancement. Detailed analysis indicates that the θSH enhancement at reduced temperatures mainly results from the improved spin-polarized surface states, as evidenced from the continuously increased ratio of surface-to-bulk conduction. The θSH difference between 20 and 10 nm Sb2Te3 gradually shrinks with the increase of T, which is due to the increase of bulk state contribution. Our findings provide a deep insight into the spin transport mechanisms and robust charge-spin conversion in TIs.

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Topics: Topological insulator (57%), Surface states (51%)
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5 results found



Journal ArticleDOI: 10.1021/ACS.JPCLETT.1C01249
F. Liu1, Fanyao Qu1, I. Žutić2, Shijie Xie3  +3 moreInstitutions (3)
Abstract: A nodal-line semimetal (NLSM) is suppressed in the presence of spin-orbit coupling unless it is protected by a nonsymmorphic symmetry. We show that two-dimensional (2D) materials can realize robust NLSMs when vacancies are introduced on the lattice. As a case study we investigate borophene, a boron honeycomb-like sheet. While the Dirac cones of pristine borophene are shown to be gapped out by spin-orbit coupling and by magnetic exchange, robust nodal lines (NLs) emerge in the spectrum when selected atoms are removed. We propose an effective 2D model and a symmetry analysis to demonstrate that these NLs are topological and protected by a nonsymmorphic glide plane. Our findings offer a paradigm shift to the design of NLSMs: instead of searching for nonsymmorphic materials, robust NLSMs may be realized simply by removing atoms from ordinary symmorphic crystals.

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Topics: Borophene (58%)

2 Citations


Journal ArticleDOI: 10.1021/ACS.JPCLETT.1C00869
Rikizo Yano1, Andrei Kudriashov2, Hishiro T. Hirose3, Taiki Tsuda1  +5 moreInstitutions (4)
Abstract: Topological insulators with broken time-reversal symmetry and the Fermi level within the magnetic gap at the Dirac cone provides exotic topological magneto-electronic phenomena. Here, we introduce an improved magnetically doped topological insulator, Fe-doped BiSbTe2Se (Fe-BSTS) bulk single crystal, with an ideal Fermi level. Scanning tunneling microscopy and spectroscopy (STM/STS) measurements revealed that the surface state possesses a Dirac cone with the Dirac point just below the Fermi level by 12 meV. The normalized dI/dV spectra suggest a gap opening with Δmag ∼55 meV, resulting in the Fermi level within the opened gap. Ionic-liquid gated-transport measurements also support the Dirac point just below the Fermi level and the presence of the magnetic gap. The chemical potential of the surface state can be fully tuned by ionic-liquid gating, and thus the Fe-doped BSTS provides an ideal platform to investigate exotic quantum topological phenomena.

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1 Citations


Journal ArticleDOI: 10.1021/ACS.JPCLETT.1C02257
Abstract: We report on structural and electronic properties of superconducting nanohybrids made of Pb grown in the ultrahigh vacuum on the atomically clean surface of single crystals of topological Bi2Te3. In situ scanning tunneling microscopy and spectroscopy demonstrated that the resulting network is composed of Pb-nanoislands dispersed on the surface and linked together by an amorphous atomic layer of Pb, which wets Bi2Te3. As a result, the superconducting state of the system is characterized by a thickness-dependent superconducting gap of Pb-islands and by a very unusual position-independent proximity gap between them. Furthermore, the data analysis and DFT calculations demonstrate that the Pb-wetting layer leads to significant modifications of both topological and trivial electronic states of Bi2Te3, which are responsible for the observed long-range proximity effect.

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1 Citations


Open accessPosted Content
Abstract: The emergent two-dimensional (2D) ferromagnetic materials with unique magnetic properties have endowed great potential for next-generation spintronic devices with extraordinary merits of high flexibility, easy controllability, and high heretointegrability, which is expected to promote the development of Moore's Law continuously. However, it is extremely challenging to realize magnetic switching with ultra-low power consumption at room temperature. Here, we demonstrate the room-temperature spin-orbit torque (SOT) driven magnetization switching in a well-epitaxial all-van der Waals (vdW) heterostructure. The topological insulator Bi2Te3 not only helps to elevate the Curie temperature of Fe3GeTe2 (FGT) through interfacial exchange coupling but also works as a spin current source allowing to switch FGT at a low current density of 2.2 * 106 A cm2. A large SOT efficiency of 0.7 is measured at room temperature, and the thickness of FGT is further adjusted to reduce the influence of the thermal contribution on the second-harmonic signal. Furthermore, the temperature and thickness-dependent SOT efficiency prove that the large SOT in our system mainly originates from the nontrivial origin of topological materials. Our experiment has enabled an all-vdW SOT structure and lays a solid foundation for the implementation of room-temperature all-vdW spintronic devices in the future.

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Topics: Spintronics (51%), Topological insulator (51%)
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51 results found


Open accessJournal ArticleDOI: 10.1126/SCIENCE.1218197
Luqiao Liu1, Chi-Feng Pai1, Yulin Li1, Hsin-Wei Tseng1  +2 moreInstitutions (1)
04 May 2012-Science
Abstract: Spin currents can apply useful torques in spintronic devices. The spin Hall effect has been proposed as a source of spin current, but its modest strength has limited its usefulness. We report a giant spin Hall effect (SHE) in β-tantalum that generates spin currents intense enough to induce efficient spin-torque switching of ferromagnets at room temperature. We quantify this SHE by three independent methods and demonstrate spin-torque switching of both out-of-plane and in-plane magnetized layers. We furthermore implement a three-terminal device that uses current passing through a tantalum-ferromagnet bilayer to switch a nanomagnet, with a magnetic tunnel junction for read-out. This simple, reliable, and efficient design may eliminate the main obstacles to the development of magnetic memory and nonvolatile spin logic technologies.

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Topics: Spin Hall effect (72%), Spintronics (63%), Nanomagnet (61%) ... read more

2,740 Citations


Open accessJournal ArticleDOI: 10.1038/NPHYS1274
Yuqi Xia1, Dong Qian1, Dong Qian2, David Hsieh1  +8 moreInstitutions (3)
01 Jun 2009-Nature Physics
Abstract: Recent experiments and theories have suggested that strong spin–orbit coupling effects in certain band insulators can give rise to a new phase of quantum matter, the so-called topological insulator, which can show macroscopic quantum-entanglement effects. Such systems feature two-dimensional surface states whose electrodynamic properties are described not by the conventional Maxwell equations but rather by an attached axion field, originally proposed to describe interacting quarks. It has been proposed that a topological insulator with a single Dirac cone interfaced with a superconductor can form the most elementary unit for performing fault-tolerant quantum computation. Here we present an angle-resolved photoemission spectroscopy study that reveals the first observation of such a topological state of matter featuring a single surface Dirac cone realized in the naturally occurring Bi_2Se_3 class of materials. Our results, supported by our theoretical calculations, demonstrate that undoped Bi_2Se_3 can serve as the parent matrix compound for the long-sought topological device where in-plane carrier transport would have a purely quantum topological origin. Our study further suggests that the undoped compound reached via n-to-p doping should show topological transport phenomena even at room temperature.

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Topics: Topological insulator (70%), Topological order (69%), Topological quantum number (67%) ... read more

2,686 Citations


Open accessJournal ArticleDOI: 10.1103/PHYSREVLETT.109.096602
Luqiao Liu1, O. J. Lee1, Theodore Gudmundsen1, Daniel C. Ralph1  +1 moreInstitutions (1)
Abstract: We show that in a perpendicularly magnetized Pt/Co bilayer the spin-Hall effect (SHE) in Pt can produce a spin torque strong enough to efficiently rotate and switch the Co magnetization. We calculate the phase diagram of switching driven by this torque, finding quantitative agreement with experiments. When optimized, the SHE torque can enable memory and logic devices with similar critical currents and improved reliability compared to conventional spin-torque switching. We suggest that the SHE torque also affects current-driven magnetic domain wall motion in Pt/ferromagnet bilayers.

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Topics: Spin-transfer torque (66%), Spin Hall effect (58%), Magnetic domain (53%) ... read more

1,216 Citations


Open accessJournal ArticleDOI: 10.1103/PHYSREVLETT.106.036601
Abstract: We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance dynamics. The Oersted field from the current also generates a ferromagnetic resonance signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle.

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Topics: Spin Hall effect (73%), Spin polarization (72%), Ferromagnetic resonance (66%) ... read more

1,162 Citations


Open accessJournal ArticleDOI: 10.1103/PHYSREVLETT.103.146401
David Hsieh1, Yuqi Xia1, Dong Qian1, Lewis Wray1  +13 moreInstitutions (5)
Abstract: We show that the strongly spin-orbit coupled materials Bi_2Te_3 and Sb_2Te_3 and their derivatives belong to the Z_2 topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that Bi_2Te_3 is a large spin-orbit-induced indirect bulk band gap (δ∼150 meV) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped Sb_2Te_3 exhibits similar Z_2 topological properties. We demonstrate that the dynamics of spin-Dirac fermions can be controlled through systematic Mn doping, making these materials classes potentially suitable for topological device applications.

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Topics: Topological insulator (61%), Dirac fermion (52%)

764 Citations


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