/Tag: MoTe2

Electron Transport in Dirac and Weyl Semimetals. (arXiv:1809.03282v1 [cond-mat.mtrl-sci])

2018-09-11T02:29:19+00:00 September 11th, 2018|Categories: Publications|Tags: |

Recently, the Dirac and Weyl semimetals have attracted extensive attention in condensed matter physics due to both the fundamental interest and the potential application of a new generation of electronic devices. Here we review the exotic electrical transport phenomena in Dirac and Weyl semimetals. Section 1 is a brief introduction to the topological semimetals (TSMs). In Section 2 and Section 3, the intriguing transport phenomena in Dirac semimetals (DSMs) and Weyl semimetals (WSMs) are reviewed, respectively. The most widely studied Cd3As2 and the TaAs family are selected as representatives to show the typical properties of DSMs and WSMs, respectively. Beyond these systems, the advances in other TSM materials, such as ZrTe5 and the MoTe2 family, are also introduced. In Section 4, we provide perspectives on the study of TSMs especially on the magnetotransport investigations.

Published in: "arXiv Material Science".

Origin of planar Hall effect in type-II Weyl semimetal MoTe2. (arXiv:1809.01290v1 [cond-mat.mtrl-sci])

2018-09-06T02:29:38+00:00 September 6th, 2018|Categories: Publications|Tags: |

Besides the negative longitudinal magnetoresistance (MR), planar Hall effect (PHE) is a newly emerging experimental tool to test the chiral anomaly or nontrivial Berry curvature in Weyl semimetals (WSMs). However, the origins of PHE in various systems are not fully distinguished and understood. Here we perform a systematic study on the PHE and anisotropic MR (AMR) of Td-MoTe2, a type-II WSM. Although the PHE and AMR curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity arises from the orbital MR (OMR), instead of the negative MR as expected in the chiral anomaly effect. In contrast, the absence of negative MR indicates that the large OMR dominates over the chiral anomaly effect. This explains why it is difficult to measure negative MR in type-II WSMs. We argue that the measured PHE can be related with the chiral anomaly only when the negative MR is simultaneously observed.

Published in: "arXiv Material Science".

Controlled Layer-by-Layer Oxidation of MoTe2 via O3 Exposure. (arXiv:1809.00119v1 [cond-mat.mtrl-sci])

2018-09-05T02:29:26+00:00 September 5th, 2018|Categories: Publications|Tags: |

Growing uniform oxides with various thickness on TMDs is one of the biggest challenges to integrate TMDs into complementary metal oxide semiconductor (CMOS) logic circuits. Here, we report a layer-by-layer oxidation of atomically thin MoTe2 flakes via ozone (O3) exposure. The thickness of MoOx oxide film could be tuning with atomic-level accuracy simply by varying O3 exposure time. Additionally, MoOx-covered MoTe2 shows a hole-dominated transport behavior. Our findings point to a simple and effective strategy for growing homogenous surface oxide film on MoTe2, which is promising for several purposes in metal-oxide-semiconductor transistor, ranging from surface passivation to dielectric layers.

Published in: "arXiv Material Science".

Nontrivial superconductivity in topological MoTe2-xSx crystals [Physics]

2018-08-31T02:31:50+00:00 August 31st, 2018|Categories: Publications|Tags: |

Topological Weyl semimetals (TWSs) with pairs of Weyl points and topologically protected Fermi arc states have broadened the classification of topological phases and provide superior platform for study of topological superconductivity. Here we report the nontrivial superconductivity and topological features of sulfur-doped Td-phase MoTe2 with enhanced Tc compared with type-II…

Published in: "PNAS (Ahead)".

Evidence of Coulomb interaction induced Lifshitz transition and robust hybrid Weyl semimetal in Td MoTe2. (arXiv:1808.08816v1 [cond-mat.str-el])

2018-08-28T02:29:38+00:00 August 28th, 2018|Categories: Publications|Tags: , |

Using soft x-ray angle-resolved photoemission spectroscopy we probed the bulk electronic structure of Td MoTe2. We found that on-site Coulomb interaction leads to a Lifshitz transition, which is essential for a precise description of the electronic structure. A hybrid Weyl semimetal state with a pair of energy bands touching at both type-I and type-II Weyl nodes is indicated by comparing the experimental data with theoretical calculations. Unveiling the importance of Coulomb interaction opens up a new route to comprehend the unique properties of MoTe2, and is significant for understanding the interplay between correlation effects, strong spin-orbit coupling and superconductivity in this van der Waals material.

Published in: "arXiv Material Science".

Barkhausen effect in the first order structural phase transition in type-II Weyl semimetal MoTe2. (arXiv:1808.05735v1 [cond-mat.mtrl-sci])

2018-08-20T02:29:14+00:00 August 20th, 2018|Categories: Publications|Tags: |

We report the first observation of the non-magnetic Barkhausen effect in van der Waals layered crystals, specifically, between the Td and 1T’ phases in type-II Weyl semimetal MoTe2. Thinning down the MoTe2 crystal from bulk material to about 25nm results in a drastic strengthening of the hysteresis in the phase transition, with the difference in critical temperature increasing from 40K to more than 300K. The Barkhausen effect appears for thin samples and the temperature range of the Barkhausen zone grows approximately linearly with reducing sample thickness, pointing to a surface origin of the phase pinning defects. The distribution of the Barkhausen jumps shows a power law behavior, with its critical exponent {alpha} = 1.27, in good agreement with existing scaling theory. Temperature-dependent Raman spectroscopy on MoTe2 crystals of various thicknesses shows results consistent with our transport measurements.

Published in: "arXiv Material Science".

Ultrafast Dynamics of Electron-phonon Coupling in Transition-metal Dichalcogenides. (arXiv:1807.10879v1 [cond-mat.mtrl-sci])

2018-07-31T02:29:17+00:00 July 31st, 2018|Categories: Publications|Tags: |

Time-domain femtosecond laser spectroscopic measurements of the ultrafast lattice dynamics in 2H-MoTe2 bulk crystals were carried out to understand the carrier-phonon interactions that govern electronic transport properties. An unusually long lifetime coherent A1g phonon mode was observed even in the presence of very large density of photo-excited carriers at room temperature. The decay rate was observed to decrease with increasing excitation laser fluence. Based on the laser fluence dependence including the inducement of significant phonon softening and a peculiar decrease in phonon decay rate, we attribute the long lifetime lattice dynamics to weak anharmonic phonon-phonon coupling and a carrier-density-dependent deformation potential electron-phonon coupling.

Published in: "arXiv Material Science".

Transport properties of semimetallic transition metal dichalcogenides. (arXiv:1807.08227v1 [cond-mat.mtrl-sci])

2018-07-24T02:29:16+00:00 July 24th, 2018|Categories: Publications|Tags: |

The Weyl semimetal requires the breaking of either the time-reversal symmetry (TRS) or the lattice inversion symmetry. When the TRS and inversion symmetry coexist, a pair of degenerate Weyl points may exist, leading to the related Dirac semimetal phase. In other words, a Dirac semimetallic state can be regarded as two copies of Weyl semimetal states. In this dissertation, we study tellurium based compounds like the Weyl semimetal candidate MoTe2 and the Dirac semimetal candidate PtTe2 within the transition metal dichalcogenides family.

Published in: "arXiv Material Science".

High performance Tunnel Field Effect Transistors based on in-plane transition metal dichalcogenide heterojunctions. (arXiv:1807.07128v1 [cond-mat.mes-hall])

2018-07-20T00:30:24+00:00 July 20th, 2018|Categories: Publications|Tags: , , |

In-plane heterojunction tunnel field effect transistors based on monolayer transition metal dichalcogenides are studied by means of self-consistent non-equilibrium Green’s functions simulations and an atomistic tight-binding Hamiltonian. We start by comparing several heterojunctions before focusing on the most promising ones, i.e WTe2-MoS2 and MoTe2-MoS2. The scalability of those devices as a function of channel length is studied, and the influence of backgate voltages on device performance is analysed. Our results indicate that, by fine-tuning the design parameters, those devices can yield extremely low sub-threshold swings (below 5mV/decade) and Ion/Ioff ratios higher than 1e8 at a supply voltage of 0.3V, making them ideal for ultra-low power consumption.

Published : "arXiv Mesoscale and Nanoscale Physics".

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