/Tag: VSe2

Pseudogap, Fermi arc, and Peierls-insulating phase induced by 3D-2D crossover in monolayer VSe2. (arXiv:1810.02511v1 [cond-mat.mtrl-sci])

2018-10-08T02:29:16+00:00October 8th, 2018|Categories: Publications|Tags: , , |

One of important challenges in condensed-matter physics is to realize new quantum states of matter by manipulating the dimensionality of materials, as represented by the discovery of high-temperature superconductivity in atomic-layer pnictides and room-temperature quantum Hall effect in graphene. Transition-metal dichalcogenides (TMDs) provide a fertile platform for exploring novel quantum phenomena accompanied by the dimensionality change, since they exhibit a variety of electronic/magnetic states owing to quantum confinement. Here we report an anomalous metal-insulator transition induced by 3D-2D crossover in monolayer 1T-VSe2 grown on bilayer graphene. We observed a complete insulating state with a finite energy gap on the entire Fermi surface in monolayer 1T-VSe2 at low temperatures, in sharp contrast to metallic nature of bulk. More surprisingly, monolayer 1T-VSe2 exhibits a pseudogap with Fermi arc at temperatures above the charge-density-wave temperature, showing a close resemblance to high-temperature cuprates. This similarity suggests a common underlying physics between two apparently different systems, pointing to the importance of charge/spin fluctuations to create the novel electronic states, such as pseudogap and Fermi arc, in these materials.

Published in: "arXiv Material Science".

Emergence of a Metal-Insulator Transition and High Temperature Charge Density Waves in VSe2 at the Monolayer Limit. (arXiv:1808.03034v1 [cond-mat.str-el])

2018-08-10T02:29:19+00:00August 10th, 2018|Categories: Publications|Tags: , , |

Emergent phenomena driven by electronic reconstructions in oxide heterostructures have been intensively discussed. However, the role of these phenomena in shaping the electronic properties in van der Waals heterointerfaces has hitherto not been established. By reducing the material thickness and forming a heterointerface, we find two types of charge-ordering transitions in monolayer VSe2 on graphene substrates. Angle-resolved photoemission spectroscopy (ARPES) uncovers that Fermi-surface nesting becomes perfect in ML VSe2. Renormalization group analysis confirms that imperfect nesting in three dimensions universally flows into perfect nesting in two dimensions. As a result, the charge density wave transition temperature is dramatically enhanced to a value of 350 K compared to the 105 K in bulk VSe2. More interestingly, ARPES and scanning tunneling microscopy measurements confirm an unexpected metal-insulator transition at 135 K, driven by lattice distortions. The heterointerface plays an important role in driving this novel metal-insulator transition in the family of monolayered transition metal dichalcogenides.

Published in: "arXiv Material Science".

Absence of ferromagnetism in VSe2 caused by its charge density wave phase. (arXiv:1804.07102v1 [cond-mat.mtrl-sci])

2018-04-20T19:59:09+00:00April 20th, 2018|Categories: Publications|Tags: |

In this study we present a detailed ab initio analysis of the magnetic properties of VSe2 . Ab initio calculations in the so-called 1T structure yield a ferromagnetic phase as most stable, with a magnetic moment of about 0.6 {mu} B /V. According to our calculations, and based on the Stoner criterion for itinerant ferromagnets, this ferromagnetic state is on the verge of instability. We have modeled ab initio the charge density wave state reported in the literature. This introduces a periodic lattice distortion leading to a supercell with periodicity 4a x 4a x 3c (4a x 4a for the monolayer) in which we have fully relaxed the atomic positions. We demonstrate that this structural rearrangement causes a strong reduction in the density of states at the Fermi level and the ground state of the system becomes non-magnetic. Experimental evidences that report a magnetic signal need to be understood on the light of this finding.

Published in: "arXiv Material Science".

Metallic few-layered VSe2 nanosheets: high two-dimensional conductivity for flexible in-plane solid-state supercapacitor

2018-03-07T01:18:02+00:00March 7th, 2018|Categories: Publications|Tags: , |

J. Mater. Chem. A, 2018, Accepted ManuscriptDOI: 10.1039/C8TA00089A, PaperChaolun Wang, Xing Wu, Yonghui Ma, Gang Mu, Yaoyi Li, Luo Chen, Hejun Xu, Yuanyuan Zhang, Jing Yang, Xiaodong Tang, Jian Zhang, Wenzhong Bao, Chun-Gang DuanMetallic two-dimensional (2D) 1T-VSe2 with high conductivity and large specific

Published in: "Journal of Materials Chemistry A".

Dynamic instabilities in strongly correlated ${text{VSe}}_{2}$ monolayers and bilayers

2017-12-27T18:30:43+00:00December 27th, 2017|Categories: Publications|Tags: , |

Author(s): Marco Esters, Richard G. Hennig, and David C. JohnsonWith the emergence of graphene and other two-dimensional (2D) materials, transition-metal dichalcogenides have been investigated intensely as potential 2D materials using experimental and theoretical methods. VSe2 is an especially interesting material since its bulk modification exhibits a charge-de…[Phys. Rev. B 96, 235147] Published Wed Dec 27, 2017

Published in: "Physical Review B".

Signatures of the Kondo effect in VSe2. (arXiv:1709.00594v1 [cond-mat.mtrl-sci])

2017-09-05T19:59:09+00:00September 5th, 2017|Categories: Publications|Tags: |

VSe2 is a transition metal dichaclogenide which has a charge-density wave transition that has been well studied. We report on a low-temperature upturn in the resistivity and, at temperatures below this resistivity minimum, an unusual magnetoresistance which is negative at low fields and positive at higher fields, in single crystals of VSe2. The negative magnetoresistance has a parabolic dependence on the magnetic field and shows little angular dependence. The magnetoresistance at temperatures above the resistivity minimum is always positive. We interpret these results as signatures of the Kondo effect in VSe2. An upturn in the susceptibility indicates the presence of interlayer V ions which can provide the localized magnetic moments required for scattering the conduction electrons in the Kondo effect. The low-temperature behaviour of the heat capacity, including a high value of gamma, along with a deviation from a Curie-Weiss law observed in the low-temperature magnetic susceptibility, are consistent with the presence of magnetic interactions between the paramagnetic interlayer V ions and a Kondo screening of these V moments.

Published in: "arXiv Material Science".

Van der Waals Epitaxial Growth of 2D Metallic Vanadium Diselenide Single Crystals and their Extra-High Electrical Conductivity

2017-08-14T08:31:12+00:00August 14th, 2017|Categories: Publications|Tags: |

2D metallic transition-metal dichalcogenides (MTMDs) have recently emerged as a new class of materials for the engineering of novel electronic phases, 2D superconductors, magnets, as well as novel electronic applications. However, the mechanical exfoliation route is predominantly used to obtain such metallic 2D flakes, but the batch production remains challenging. Herein, the van der Waals epitaxial growth of monocrystalline, 1T-phase, few-layer metallic VSe2 nanosheets on an atomically flat mica substrate via a “one-step” chemical vapor deposition method is reported. The thickness of the VSe2 nanosheets is precisely tuned from several nanometers to several tenths of nanometers. More significantly, the 2D VSe2 single crystals are found to present an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 106 S m−1, 1–4 orders of magnitude higher than that of various conductive 2D materials. The thickness-dependent charge-density-wave phase transitions are also examined through low-temperature transport measurements, which reveal that the synthesized 2D metallic 1T-VSe2 nanosheets should serve as good research platforms for the detecting novel many-body states. These results open a new path for the synthesis and property investigations of nanoscale-thickness 2D MTMDs crystals. 2D metallic 1T-VSe2 single crystals are synthesized on a mica substrate by a van der Waals epitaxial strategy via a chemical vapor deposition method. The synthesized few-layer 1T-VSe2 nanosheets present extremely high electrical conductivity and excellent stability. The charge-density-wave phase transition is also detected, to show a similar feature to that of exfoliated VSe2 nanosheets.

Published in: "Advanced Materials".

Thickness dependence of the charge-density-wave transition temperature in VSe2

2016-10-15T13:01:06+00:00August 12th, 2014|Categories: Publications|Tags: |

By Jiyong Yang, Weike Wang, Yan Liu, Haifeng Du, Wei Ning, Guolin Zheng, Chiming Jin, Yuyan Han, Ning Wang, Zhaorong Yang, Mingliang Tian and Yuheng Zhang

A set of three-dimensional charge-density-wave (3D CDW) VSe2 nano-flakes with different thicknesses were obtained by the scotch tape-based micro-mechanical exfoliation method. Resistivity measurements showed that the 3D CDW transition temperature Tp decreases systematically from 105 K in bulk to 81.8 K in the 11.6 nm thick flake. The Hall resistivity ρxy of all the flakes …read more

Via: Applied Physics Letters

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