WTe2

/Tag: WTe2

Nonlinear magnetotransport shaped by Fermi surface topology and convexity

2019-03-20T10:34:26+00:00March 20th, 2019|Categories: Publications|Tags: |

Nonlinear magnetotransport shaped by Fermi surface topology and convexityNonlinear magnetotransport shaped by Fermi surface topology and convexity, Published online: 20 March 2019; doi:10.1038/s41467-019-09208-8The nature of non-saturating magnetoresistance (MR) in topological materials is an important issue in condensed matter research but remains elusive. The authors here report the nonlinear MR at room temperature in WTe2 with temperature-driven inversion due to the temperature-induced changes in Fermi surface convexity.

Published in: "Nature Communications".

Superconductivity in Potassium-intercalated Td-WTe2. (arXiv:1903.00639v1 [cond-mat.supr-con])

2019-03-05T02:29:29+00:00March 5th, 2019|Categories: Publications|Tags: |

To realize topological superconductor is one of the most attracting topics because of its great potential in quantum computation. In this study, we successfully intercalate potassium (K) into the van der Waals gap of type II Weyl semimetal WTe2, and discover the superconducting state in KxWTe2 through both electrical transport and scanning tunneling spectroscopy measurements. The superconductivity exhibits an evident anisotropic behavior. Moreover, we also uncover the coexistence of superconductivity and the positive magneto-resistance state. Structural analysis substantiates the negligible lattice expansion induced by the intercalation, therefore suggesting K-intercalated WTe2 still hosts the topological nontrivial state. These results indicate that the K-intercalated WTe2 may be a promising candidate to explore the topological superconductor.

Published in: "arXiv Material Science".

Yanson point-contact spectroscopy of Weyl semimetal WTe2. (arXiv:1902.11037v1 [cond-mat.mes-hall])

2019-03-01T04:30:31+00:00March 1st, 2019|Categories: Publications|Tags: , |

We carried out point contact (PC) investigation of WTe2 single crystals. We measured Yanson d2V/dI2 PC spectra of the electron-phonon interaction (EPI) in WTe2. The spectra demonstrate a main phonon peak around 8 meV and a shallow second maximum near 16 meV. Their position is in line with the calculation of the EPI spectra of WTe2 in the literature, albeit phonons with higher energy are not resolved in our PC spectra. An additional contribution to the spectra is present above the phonon energy, what may be connected with the peculiar electronic band structure and need to be clarified. We detected tiny superconducting features in d2V/dI2 close to zero bias, which broadens by increasing temperature and blurs above 6K. Thus, (surface) superconductivity may exist in WTe2 with a topologically nontrivial state. We found a broad maximum in dV/dI at large voltages (>200 mV) indicating change of conductivity from metallic to semiconducting type. The latter might be induced by the high current density (~10^8 A/cm^2) in the PC and/or local heating, thus enabling the manipulation of the quantum electronic states at the interface in the PC core.

Published : "arXiv Mesoscale and Nanoscale Physics".

Raman spectrum of 1T’-WTe2 under tensile strain: A first-principles prediction. (arXiv:1902.04676v1 [cond-mat.mtrl-sci])

2019-02-14T02:29:28+00:00February 14th, 2019|Categories: Publications|Tags: |

Monolayer WTe2 attracts rapidly growing interests for its large-gap quantum spin Hall effect,which enables promising apllications in flexible logic devices. Due to one-dimensional W-W chains,1T’-WTe2 exhibits unique anisotropic structure and promising properties, which can be modified by simply applying strains. Based on the first-principles simulations, we show that phonon branch undergoes soft down to negative frequency at special q points under different critical strains, i.e., epsilon_a = 11.55 percent along a-axis (with W-W chains) direction, epsilon_b = 7.0 percent along b-axis direction and epsilon_ab = 8.44 percent along biaxial direction. Before each critical strain, the Raman-shift of A1_g, A3_g, and A4_g modes, corresponding to the main peaks in Raman spectra of 1T’-WTe2 , shows anisotropic response to uniaxial strain but most sensitive to biaxial strain. Interestingly, we find that the frequency shift of A3_g mode show parabolic characters of strained 1T’-WTe2, then we split it into two parts and it shows a Raman-shift transition at about 5 percent strains. While for the A1_g and A4_g modes,the frequencies change linearly. Through careful structure and vibration analysis, we try to explain these Raman irregularity in strained 1T’-WTe2.

Published in: "arXiv Material Science".

Imaging quantum spin Hall edges in monolayer WTe2

2019-02-09T12:36:27+00:00February 9th, 2019|Categories: Publications|Tags: |

A two-dimensional (2D) topological insulator exhibits the quantum spin Hall (QSH) effect, in which topologically protected conducting channels exist at the sample edges. Experimental signatures of the QSH effect have recently been reported in an atomically thin material, monolayer WTe2. Here, we directly image the local conductivity of monolayer WTe2

Published in: "Science Advances".

Antimonene: Van der Waals Heteroepitaxial Growth of Monolayer Sb in a Puckered Honeycomb Structure (Adv. Mater. 5/2019)

2019-02-04T02:38:46+00:00February 4th, 2019|Categories: Publications|Tags: , |

In article number 1806130, Wenguang Zhu, Shao‐Chun Li, and co‐workers describe the fabrication of monolayer α‐phase antimonene, a structural analog to black phosphorous, on a WTe2 substrate by molecular beam epitaxy. The α‐antimonene exhibits great stability upon exposure to air. Its electron band, crossing the Fermi level, exhibits a linear dispersion with a fairly small effective mass, and thus, a good electrical conductivity. All of these properties make α‐antimonene promising for future electronic applications.

Published in: "Advanced Materials".

Antimonene: Van der Waals Heteroepitaxial Growth of Monolayer Sb in a Puckered Honeycomb Structure (Adv. Mater. 5/2019)

2019-02-02T22:36:40+00:00February 2nd, 2019|Categories: Publications|Tags: , |

In article number 1806130, Wenguang Zhu, Shao‐Chun Li, and co‐workers describe the fabrication of monolayer α‐phase antimonene, a structural analog to black phosphorous, on a WTe2 substrate by molecular beam epitaxy. The α‐antimonene exhibits great stability upon exposure to air. Its electron band, crossing the Fermi level, exhibits a linear dispersion with a fairly small effective mass, and thus, a good electrical conductivity. All of these properties make α‐antimonene promising for future electronic applications.

Published in: "Advanced Materials".

Antimonene: Van der Waals Heteroepitaxial Growth of Monolayer Sb in a Puckered Honeycomb Structure (Adv. Mater. 5/2019)

2019-02-02T08:37:03+00:00February 2nd, 2019|Categories: Publications|Tags: , |

In article number 1806130, Wenguang Zhu, Shao‐Chun Li, and co‐workers describe the fabrication of monolayer α‐phase antimonene, a structural analog to black phosphorous, on a WTe2 substrate by molecular beam epitaxy. The α‐antimonene exhibits great stability upon exposure to air. Its electron band, crossing the Fermi level, exhibits a linear dispersion with a fairly small effective mass, and thus, a good electrical conductivity. All of these properties make α‐antimonene promising for future electronic applications.

Published in: "Advanced Materials".

An ultrafast symmetry switch in a Weyl semimetal

2019-01-02T18:33:47+00:00January 2nd, 2019|Categories: Publications|Tags: |

An ultrafast symmetry switch in a Weyl semimetalAn ultrafast symmetry switch in a Weyl semimetal, Published online: 02 January 2019; doi:10.1038/s41586-018-0809-4Terahertz light pulses induce transitions between a topological and a trivial phase in the Weyl semimetal WTe2 through an interlayer shear strain.

Published in: "Nature".

In‐Plane Anisotropic Thermal Conductivity of Few‐Layered Transition Metal Dichalcogenide Td‐WTe2

2019-01-01T22:34:33+00:00January 1st, 2019|Categories: Publications|Tags: |

In‐plane anisotropic thermal conductivities are experimentally demonstrated in suspended Td‐WTe2 of different thicknesses. Theoretical calculation implies that the in‐plane anisotropy is attributed to the different mean free paths along the two orientations. As the thickness decreases, the phonon‐boundary scattering increases faster along the armchair direction, resulting in the stronger anisotropy. Abstract 2D Td‐WTe2 has attracted increasing attention due to its promising applications in spintronic, field‐effect chiral, and high‐efficiency thermoelectric devices. It is known that thermal conductivity plays a crucial role in condensed matter devices, especially in 2D systems where phonons, electrons, and magnons are highly confined and coupled. This work reports the first experimental evidence of in‐plane anisotropic thermal conductivities in suspended Td‐WTe2 samples of different thicknesses, and is also the first demonstration of such anisotropy in 2D transition metal dichalcogenides. The results reveal an obvious anisotropy in the thermal conductivities between the zigzag and armchair axes. The theoretical calculation implies that the in‐plane anisotropy is attributed to the different mean free paths along the two orientations. As thickness decreases, the phonon‐boundary scattering increases faster along the armchair direction, resulting in stronger anisotropy. The findings here are crucial for developing efficient thermal management schemes when engineering thermal‐related applications of a 2D system.

Published in: "Advanced Materials".

In‐Plane Anisotropic Thermal Conductivity of Few‐Layered Transition Metal Dichalcogenide Td‐WTe2

2018-12-29T22:35:20+00:00December 29th, 2018|Categories: Publications|Tags: |

In‐plane anisotropic thermal conductivities are experimentally demonstrated in suspended Td‐WTe2 of different thicknesses. Theoretical calculation implies that the in‐plane anisotropy is attributed to the different mean free paths along the two orientations. As the thickness decreases, the phonon‐boundary scattering increases faster along the armchair direction, resulting in the stronger anisotropy. Abstract 2D Td‐WTe2 has attracted increasing attention due to its promising applications in spintronic, field‐effect chiral, and high‐efficiency thermoelectric devices. It is known that thermal conductivity plays a crucial role in condensed matter devices, especially in 2D systems where phonons, electrons, and magnons are highly confined and coupled. This work reports the first experimental evidence of in‐plane anisotropic thermal conductivities in suspended Td‐WTe2 samples of different thicknesses, and is also the first demonstration of such anisotropy in 2D transition metal dichalcogenides. The results reveal an obvious anisotropy in the thermal conductivities between the zigzag and armchair axes. The theoretical calculation implies that the in‐plane anisotropy is attributed to the different mean free paths along the two orientations. As thickness decreases, the phonon‐boundary scattering increases faster along the armchair direction, resulting in stronger anisotropy. The findings here are crucial for developing efficient thermal management schemes when engineering thermal‐related applications of a 2D system.

Published in: "Advanced Materials".

In‐Plane Anisotropic Thermal Conductivity of Few‐Layered Transition Metal Dichalcogenide Td‐WTe2

2018-12-28T08:34:21+00:00December 28th, 2018|Categories: Publications|Tags: |

In‐plane anisotropic thermal conductivities are experimentally demonstrated in suspended Td‐WTe2 of different thicknesses. Theoretical calculation implies that the in‐plane anisotropy is attributed to the different mean free paths along the two orientations. As the thickness decreases, the phonon‐boundary scattering increases faster along the armchair direction, resulting in the stronger anisotropy. Abstract 2D Td‐WTe2 has attracted increasing attention due to its promising applications in spintronic, field‐effect chiral, and high‐efficiency thermoelectric devices. It is known that thermal conductivity plays a crucial role in condensed matter devices, especially in 2D systems where phonons, electrons, and magnons are highly confined and coupled. This work reports the first experimental evidence of in‐plane anisotropic thermal conductivities in suspended Td‐WTe2 samples of different thicknesses, and is also the first demonstration of such anisotropy in 2D transition metal dichalcogenides. The results reveal an obvious anisotropy in the thermal conductivities between the zigzag and armchair axes. The theoretical calculation implies that the in‐plane anisotropy is attributed to the different mean free paths along the two orientations. As thickness decreases, the phonon‐boundary scattering increases faster along the armchair direction, resulting in stronger anisotropy. The findings here are crucial for developing efficient thermal management schemes when engineering thermal‐related applications of a 2D system.

Published in: "Advanced Materials".

Spontanous breaking of time-reversal symmetry at the edges of 1T’ monolayer transition metal dichalcogenides. (arXiv:1812.09082v1 [cond-mat.mes-hall])

2018-12-24T02:29:29+00:00December 24th, 2018|Categories: Publications|Tags: , , |

Using density functional theory calculations and the Greens’s function formalism, we report the existence of magnetic edge states with a non-collinear spin texture present on different edges of the 1T’ phase of the three monolayer transition metal dichalcogenides (TMDs): MoS2, MoTe2 and WTe2. The magnetic states are gapless and accompanied by a spontaneous breaking of the time-reversal symmetry. This may have an impact on the prospects of utilizing WTe2 as a quantum spin Hall insulator. It has previously been suggested that the topologically protected edge states of the 1T’ TMDs could be switched off by applying a perpendicular electric field. We confirm with fully self-consistent DFT calculations, that the topological edge states can be switched off. The investigated magnetic edge states are seen to be robust and remains gapless when applying a field.

Published in: "arXiv Material Science".

Intrinsic Spin Hall Conductivity of MoTe2 and WTe2 Semimetals. (arXiv:1812.06910v1 [cond-mat.mtrl-sci])

2018-12-18T02:29:22+00:00December 18th, 2018|Categories: Publications|Tags: , , |

We report a comprehensive study on the intrinsic spin Hall conductivity (SHC) of semimetals MoTe2 and WTe2 by ab initio calculation. Large SHC and desirable spin Hall angles have been discovered, due to the strong spin orbit coupling effect and low charge conductivity in semimetals. Diverse anisotropic SHC values, attributed to the unusual reduced-symmetry crystalline structure, have been revealed. We report an effective method on SHC optimization by electron doping, and exhibit the mechanism of SHC variation respect to the energy shifting by the spin Berry curvature. Our work provides insights into the realization of strong spin Hall effects in 2D systems.

Published in: "arXiv Material Science".

Observation of the nonlinear Hall effect under time-reversal-symmetric conditions

2018-12-17T16:35:06+00:00December 17th, 2018|Categories: Publications|Tags: |

Observation of the nonlinear Hall effect under time-reversal-symmetric conditionsObservation of the nonlinear Hall effect under time-reversal-symmetric conditions, Published online: 17 December 2018; doi:10.1038/s41586-018-0807-6The nonlinear Hall effect is observed in bilayer WTe2 in the absence of a magnetic field, providing a direct measure of the dipole moment of the Berry curvature.

Published in: "Nature".

Van der Waals Heteroepitaxial Growth of Monolayer Sb in a Puckered Honeycomb Structure

2018-12-15T22:33:29+00:00December 15th, 2018|Categories: Publications|Tags: , |

Monolayer α‐phase antimonene, a structural analog to black phosphorous, is fabricated on a WTe2 substrate. The α‐antimonene exhibits great stability upon exposure to air. Its electron band crossing the Fermi level exhibits a linear dispersion with a fairly small effective mass, and thus a good electrical conductivity. All of these properties make α‐antimonene promising in the future electronic applications. Abstract Atomically thin 2D crystals have gained tremendous attention owing to their potential impact on future electronics technologies, as well as the exotic phenomena emerging in these materials. Monolayers of α‐phase Sb (α‐antimonene), which shares the same puckered structure as black phosphorous, are predicted to be stable with precious properties. However, the experimental realization still remains challenging. Here, high‐quality monolayerα‐antimonene is successfully grown, with the thickness finely controlled. The α‐antimonene exhibits great stability upon exposure to air. Combining scanning tunneling microscopy, density functional theory calculations, and transport measurements, it is found that the electron band crossing the Fermi level exhibits a linear dispersion with a fairly small effective mass, and thus a good electrical conductivity. All of these properties make the α‐antimonene promising for future electronic applications.

Published in: "Advanced Materials".

Anomalous and Polarization‐Sensitive Photoresponse of Td‐WTe2 from Visible to Infrared Light

2018-12-15T22:33:25+00:00December 15th, 2018|Categories: Publications|Tags: |

Semimetal Td‐WTe2 demonstrates broadband anomalous and polarization‐sensitive photoresponse. The giant photocurrent and responsivity reach 40 µA and 250 A W−1 for a 3.8 µm laser at 77 K, and the photocurrent anisotropic ratio of 4.9 for a 514.5 nm laser. Consistently, first‐principles calculations confirm angle sensitive bandgap opening of WTe2 by polarized light, showing its photodetection potential. Abstract Recently, an emergent layered material Td‐WTe2 was explored for its novel electron–hole overlapping band structure and anisotropic inplane crystal structure. Here, the photoresponse of mechanically exfoliated WTe2 flakes is investigated. A large anomalous current decrease for visible (514.5 nm), and mid‐ and far‐infrared (3.8 and 10.6 µm) laser irradiation is observed, which can be attributed to light‐induced surface bandgap opening from the first‐principles calculations. The photocurrent and responsivity can be as large as 40 µA and 250 A W−1 for a 3.8 µm laser at 77 K. Furthermore, the WTe2 anomalous photocurrent matches its in‐plane crystal structure and exhibits light polarization dependence, maximal for linear laser polarization along the W atom chain a direction and minimal for the perpendicular b direction, with the anisotropic ratio of 4.9. Consistently, first‐principles calculations confirm the angle‐dependent bandgap opening of WTe2 under polarized light irradiation. The anomalous and polarization‐sensitive photoresponses suggest that linearly polarized light can significantly tune the WTe2 surface electronic structure, providing a potential approach to detect polarized and broadband lights up to far infrared range.

Published in: "Advanced Materials".

Van der Waals Heteroepitaxial Growth of Monolayer Sb in a Puckered Honeycomb Structure

2018-12-13T00:34:12+00:00December 12th, 2018|Categories: Publications|Tags: , |

Monolayer α‐phase antimonene, a structural analog to black phosphorous, is fabricated on a WTe2 substrate. The α‐antimonene exhibits great stability upon exposure to air. Its electron band crossing the Fermi level exhibits a linear dispersion with a fairly small effective mass, and thus a good electrical conductivity. All of these properties make α‐antimonene promising in the future electronic applications. Abstract Atomically thin 2D crystals have gained tremendous attention owing to their potential impact on future electronics technologies, as well as the exotic phenomena emerging in these materials. Monolayers of α‐phase Sb (α‐antimonene), which shares the same puckered structure as black phosphorous, are predicted to be stable with precious properties. However, the experimental realization still remains challenging. Here, high‐quality monolayerα‐antimonene is successfully grown, with the thickness finely controlled. The α‐antimonene exhibits great stability upon exposure to air. Combining scanning tunneling microscopy, density functional theory calculations, and transport measurements, it is found that the electron band crossing the Fermi level exhibits a linear dispersion with a fairly small effective mass, and thus a good electrical conductivity. All of these properties make the α‐antimonene promising for future electronic applications.

Published in: "Advanced Materials".

Anomalous and Polarization‐Sensitive Photoresponse of Td‐WTe2 from Visible to Infrared Light

2018-12-13T00:33:58+00:00December 12th, 2018|Categories: Publications|Tags: |

Semimetal Td‐WTe2 demonstrates broadband anomalous and polarization‐sensitive photoresponse. The giant photocurrent and responsivity reach 40 µA and 250 A W−1 for a 3.8 µm laser at 77 K, and the photocurrent anisotropic ratio of 4.9 for a 514.5 nm laser. Consistently, first‐principles calculations confirm angle sensitive bandgap opening of WTe2 by polarized light, showing its photodetection potential. Abstract Recently, an emergent layered material Td‐WTe2 was explored for its novel electron–hole overlapping band structure and anisotropic inplane crystal structure. Here, the photoresponse of mechanically exfoliated WTe2 flakes is investigated. A large anomalous current decrease for visible (514.5 nm), and mid‐ and far‐infrared (3.8 and 10.6 µm) laser irradiation is observed, which can be attributed to light‐induced surface bandgap opening from the first‐principles calculations. The photocurrent and responsivity can be as large as 40 µA and 250 A W−1 for a 3.8 µm laser at 77 K. Furthermore, the WTe2 anomalous photocurrent matches its in‐plane crystal structure and exhibits light polarization dependence, maximal for linear laser polarization along the W atom chain a direction and minimal for the perpendicular b direction, with the anisotropic ratio of 4.9. Consistently, first‐principles calculations confirm the angle‐dependent bandgap opening of WTe2 under polarized light irradiation. The anomalous and polarization‐sensitive photoresponses suggest that linearly polarized light can significantly tune the WTe2 surface electronic structure, providing a potential approach to detect polarized and broadband lights up to far infrared range.

Published in: "Advanced Materials".

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