FeSe

/Tag: FeSe

The stability of exfoliated FeSe nanosheets during in-air device fabrication process. (arXiv:1805.02805v1 [cond-mat.mtrl-sci])

2018-05-09T19:59:00+00:00May 9th, 2018|Categories: Publications|Tags: |

We studied the stability and superconductivity of FeSe nanosheets during an in-air device fabrication process. Methods were developed to improve the exfoliation yield and to maintain the superconductivity of FeSe. Raman spectroscopy, atomic force microscopy, optical microscopy and time-of-flight-secondary-ion-mass-spectroscopy measurements show that FeSe nanosheets decayed in air. Precipitation of Se particles and iron oxidation likely occurred during the decay process. Transport measurements revealed that the superconductivity of FeSe disappeared during a conventional electron beam lithography process. Shadow mask evaporation and transfer onto pre-defined electrodes methods were shown to be effective in maintaining the superconductivity after the in-air device fabrication process. These methods developed provide a way of making high quality FeSe nano-devices.

Published : "arXiv Mesoscale and Nanoscale Physics".

Direct imaging of electron transfer and its influence on superconducting pairing at FeSe/SrTiO3 interface

2018-03-16T20:32:30+00:00March 16th, 2018|Categories: Publications|Tags: , |

The exact mechanism responsible for the significant enhancement of the superconducting transition temperature (Tc) of monolayer iron selenide (FeSe) films on SrTiO3 (STO) over that of bulk FeSe is an open issue. We present the results of a coordinated study of electrical transport, low temperature electron energy-loss spectroscopy (EELS), and

Published in: "Science Advances".

Coexistence of multiphase superconductivity and ferromagnetism in lithiated iron selenide hydroxide $[(mathrm{L}{mathrm{i}}_{1−x}mathrm{F}{mathrm{e}}_{x})mathrm{OH}]mathrm{FeSe}$

2018-01-25T14:30:35+00:00January 25th, 2018|Categories: Publications|Tags: |

Author(s): Christian Urban, Ilya Valmianski, Ursula Pachmayr, Ali C. Basaran, Dirk Johrendt, and Ivan K. SchullerWe present experimental evidence for (a) multiphase superconductivity and (b) coexistence of magnetism and superconductivity in a single structural phase of lithiated iron selenide hydroxide [(Li1−xFex)OH]FeSe. Magnetic field modulated microwave spectroscopy data confirms superconductivity with at l…[Phys. Rev. B 97, 024516] Published Thu Jan 25, 2018

Published in: "Physical Review B".

Liquid phase mass production of air-stable black phosphorus/phospholipids nanocomposite with ultralow tunneling barrier. (arXiv:1801.06997v1 [cond-mat.mtrl-sci])

2018-01-23T20:00:54+00:00January 23rd, 2018|Categories: Publications|Tags: , , , |

Few-layer black phosphorus (FLBP), a recently discovered two-dimensional semiconductor, has attracted substantial attention in the scientific and technical communities due to its great potential in electronic and optoelectronic applications. However, reactivity of FLBP flakes with ambient species limits its direct applications. Among various methods to passivate FLBP in ambient environment, nanocomposites mixing FLBP flakes with stable matrix may be one of the most promising approaches for industry applications. Here, we report a simple one-step procedure to mass produce air-stable FLBP/phospholipids nanocomposite in liquid phase. The resultant nanocomposite is found to have ultralow tunneling barrier for charge carriers which can be described by an Efros-Shklovskii variable range hopping mechanism. Devices made from such mass-produced FLBP/phospholipids nanocomposite show highly stable electrical conductivity and opto-electrical response in ambient conditions, indicating its promising applications in both electronic and optoelectronic applications. This method could also be generalized to the mass production of nanocomposites consisting of other air-sensitive two-dimensional materials, such as FeSe, NbSe2, WTe2, etc.

Published in: "arXiv Material Science".

Compression of Wannier functions into Gaussian-type orbitals. (arXiv:1712.02996v1 [cond-mat.mtrl-sci])

2017-12-11T19:59:54+00:00December 11th, 2017|Categories: Publications|Tags: , |

We propose a greedy algorithm for the compression of Wannier functions into Gaussian-polynomials orbitals. The so-obtained compressed Wannier functions can be stored in a very compact form, and can be used to efficiently parameterize effective tight-binding Hamiltonians for multilayer 2D materials for instance. The compression method preserves the symmetries (if any) of the original Wannier function. We provide algorithmic details, and illustrate the performance of our implementation on several examples, including graphene, hexagonal boron-nitride, single-layer FeSe, and bulk silicon in the diamond cubic structure.

Published in: "arXiv Material Science".

Sign reversal of the order parameter in (Li<sub>1−<i>x</i></sub>Fe<sub><i>x</i></sub>)OHFe<sub>1−<i>y</i></sub>Zn<sub><i>y</i></sub>Se

2017-10-24T18:30:26+00:00October 24th, 2017|Categories: Publications|Tags: |

Sign reversal of the order parameter in (Li1−xFex)OHFe1−yZnySeNature Physics, Published online: 23 October 2017; doi:10.1038/nphys4299A scanning tunnelling microscopy study of an intercalated iron selenide-based superconductor reveals a sign change in its superconducting gap function, providing indirect evidence for the origin of the pairing mechanism in this system.

Published in: "Nature Physics".

Stripes developed at the strong limit of nematicity in FeSe film

2017-10-05T14:30:46+00:00October 5th, 2017|Categories: Publications|Tags: |

Nature Physics 13, 957 (2017). doi:10.1038/nphys4186 Authors: Wei Li, Yan Zhang, Peng Deng, Zhilin Xu, S.-K. Mo, Ming Yi, Hao Ding, M. Hashimoto, R. G. Moore, D.-H. Lu, Xi Chen, Z.-X. Shen & Qi-Kun Xue A single monolayer of iron selenide grown on strontium titanate shows an impressive enhancement of superconductivity compared with the bulk, as well as a novel Fermi surface topology, extreme two-dimensionality, and the possibility of phonon-enhanced electron pairing. For films thicker than one unit cell, however, the electronic structure is markedly different, with a drastically suppressed superconductivity and strong nematicity appearing. The physics driving this extraordinary dichotomy of superconducting behaviour is far from clear. Here, we use low-temperature scanning tunnelling microscopy to study multilayers of iron selenide grown by molecular beam epitaxy, and find a stripe-type charge ordering instability that develops beneath the nematic state. The charge ordering is visible and pinned in the vicinity of impurities. And as it emerges in the strong limit of nematicity, it suggests that a magnetic fluctuation with a rather small wavevector may be competing with the ordinary collinear antiferromagnetic ordering in multilayer films. The existence of stripes in iron-based superconductors, which resemble the stripe order in cuprates, not only suggests that electronic anisotropy and correlation are playing an important role, but also provides a platform for probing the complex interactions between nematicity, charge ordering, magnetism and superconductivity in high-temperature superconductors.

Published in: "Nature Physics".

Basic electronic properties of iron selenide under variation of structural parameters. (arXiv:1706.03543v2 [cond-mat.supr-con] UPDATED)

2017-09-07T19:59:01+00:00September 7th, 2017|Categories: Publications|Tags: |

Since the discovery of high-temperature superconductivity in the thin-film FeSe/SrTiO$_3$ system, iron selenide and its derivates have been intensively scrutinized. Using ab initio density functional theory calculations we review the electronic structures that could be realized in iron-selenide if the structural parameters could be tuned at liberty. We calculate the momentum-dependence of the susceptibility and investigate the symmetry of electron pairing within the random phase approximation. Both the susceptibility and the symmetry of electron pairing depend on the structural parameters in a nontrivial way. These results are consistent with the known experimental behavior of binary iron chalcogenides and, at the same time, reveal two promising new ways of tuning superconducting transition temperatures in these materials. On the one hand by expanding the iron lattice of FeSe at constant iron-selenium distance and, on the other hand, by increasing the iron-selenium distance with unchanged iron lattice.

Published in: "arXiv Material Science".

Basic electronic properties of iron selenide under variation of structural parameters

2017-09-06T16:29:43+00:00September 6th, 2017|Categories: Publications|Tags: |

Author(s): Daniel Guterding, Harald O. Jeschke, and Roser ValentíSince the discovery of high-temperature superconductivity in the thin-film FeSe/SrTiO3 system, iron selenide and its derivates have been intensively scrutinized. Using ab initio density functional theory calculations we review the electronic structures that could be realized in iron selenide if the …[Phys. Rev. B 96, 125107] Published Wed Sep 06, 2017

Published in: "Physical Review B".

High-Tc Superconducting Phases in Organic Molecular Intercalated Iron Selenides: Synthesis and Crystal Structures

2017-07-31T10:29:42+00:00July 31st, 2017|Categories: Publications|Tags: |

Chem. Commun., 2017, Accepted ManuscriptDOI: 10.1039/C7CC05242A, CommunicationShifeng Jin, Xiao Fan, Ruijin Sun, Xiaozhi Wu, Hui Wu, Qingzhen Huang, Chenlong Shi, Xuiqui Xi, Zhilin Li, Xiaolong ChenHybrid iron-based superconductors were synthesized by sonochemical insertion of organic molecules into FeSe layers. High quality of the samples firstly enables reliable phase identifications and three structure types are discovered….The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li0.8Fe0.2OH)FeSe

2017-07-20T20:43:29+00:00July 20th, 2017|Categories: Publications|Tags: |

In iron-based superconductors, understanding the relation between superconductivity and electronic structure upon doping is crucial for exploring the pairing mechanism. Recently, it was found that, in iron selenide (FeSe), enhanced superconductivity (Tc of more than 40 K) can be achieved via electron doping, with the Fermi surface only comprising M-centered

Published in: "Science Advances".

From a Molecular 2Fe-2Se Precursor to a Highly Efficient Iron Diselenide Electrocatalyst for Overall Water Splitting

2017-07-20T20:25:47+00:00July 20th, 2017|Categories: Publications|Tags: |

Abstract A highly active FeSe2 electrocatalyst for durable overall water splitting was prepared from a molecular 2Fe-2Se precursor. The as-synthesized FeSe2 was electrophoretically deposited on nickel foam and applied to the oxygen and hydrogen evolution reactions (OER and HER, respectively) in alkaline media. When used as an oxygen-evolution electrode, a low 245 mV overpotential was achieved at a current density of 10 mA cm−2, representing outstanding catalytic activity and stability because of Fe(OH)2/FeOOH active sites formed at the surface of FeSe2. Remarkably, the system is also favorable for the HER. Moreover, an overall water-splitting setup was fabricated using a two-electrode cell, which displayed a low cell voltage and high stability. In summary, the first iron selenide material is reported that can be used as a bifunctional electrocatalyst for the OER and HER, as well as overall water splitting. Bridging the gap: A highly active iron diselenide electrocatalyst was prepared at low temperature from a bioinspired 2Fe-2Se molecular complex (Dep = diethylphenyl). The catalyst was applied to bifunctional oxygen and hydrogen evolution reactions, as well as overall water splitting. The nature of active sites and structure–activity relationships of the electrocatalyst were uncovered.

Published in: "Angewandte Chemie International Edition".

Stripes developed at the strong limit of nematicity in FeSe film

2017-07-17T18:28:52+00:00July 17th, 2017|Categories: Publications|Tags: |

Nature Physics. doi:10.1038/nphys4186 Authors: Wei Li, Yan Zhang, Peng Deng, Zhilin Xu, S.-K. Mo, Ming Yi, Hao Ding, M. Hashimoto, R. G. Moore, D.-H. Lu, Xi Chen, Z.-X. Shen & Qi-Kun Xue A single monolayer of iron selenide grown on strontium titanate shows an impressive enhancement of superconductivity compared with the bulk, as well as a novel Fermi surface topology, extreme two-dimensionality, and the possibility of phonon-enhanced electron pairing. For films thicker than one unit cell, however, the electronic structure is markedly different, with a drastically suppressed superconductivity and strong nematicity appearing. The physics driving this extraordinary dichotomy of superconducting behaviour is far from clear. Here, we use low-temperature scanning tunnelling microscopy to study multilayers of iron selenide grown by molecular beam epitaxy, and find a stripe-type charge ordering instability that develops beneath the nematic state. The charge ordering is visible and pinned in the vicinity of impurities. And as it emerges in the strong limit of nematicity, it suggests that a magnetic fluctuation with a rather small wavevector may be competing with the ordinary collinear antiferromagnetic ordering in multilayer films. The existence of stripes in iron-based superconductors, which resemble the stripe order in cuprates, not only suggests that electronic anisotropy and correlation are playing an important role, but also provides a platform for probing the complex interactions between nematicity, charge ordering, magnetism and superconductivity in high-temperature superconductors.

Doping SrTiO_{3} supported FeSe by excess atoms and oxygen vacancies

2016-10-15T11:33:39+00:00July 24th, 2015|Categories: Publications|Tags: |

By K. V. Shanavas and David J. Singh Author(s): K. V. Shanavas and David J. SinghPhotoemission studies of FeSe monolayer films on SrTiO3 substrate have shown electronic structures that deviate from pristine FeSe, consistent with heavy electron doping. With the help of first-principles calculations we studied the effect of excess Fe and Se atoms on the monolayer and …read more

Published in: Physical Review B

Surface alloying and iron selenide formation in Fe/Bi_{2} Se_{3} (0001) observed by x-ray absorption fine structure experiments

2016-10-15T11:34:18+00:00July 23rd, 2015|Categories: Publications|Tags: , |

By A. Polyakov, Holger L. Meyerheim, E. Daryl Crozier, R. A. Gordon, K. Mohseni, S. Roy, A. Ernst, M. G. Vergniory, X. Zubizarreta, M. M. Otrokov, E. V. Chulkov, and J. Kirschner Author(s): A. Polyakov, Holger L. Meyerheim, E. Daryl Crozier, R. A. Gordon, K. Mohseni, S. Roy, A. Ernst, M. G. Vergniory, X. Zubizarreta, M. M. Otrokov, E. V. Chulkov, and J. KirschnerThe atomic structure of ultrathin iron films deposited on the (0001) surface of the topological insulator Bi2Se3 is analyzed …read more

Published in: Physical Review B

Superconductivity: The FeSe riddle

2016-10-15T11:34:19+00:00July 23rd, 2015|Categories: Publications|Tags: |

By I. I. Mazin Nature Materials 14, 755 (2015).
doi:10.1038/nmat4371

Author: I. I. Mazin
Electron–phonon coupling has been considered as a possible mechanism behind the high superconducting critical temperature of FeSe monolayers. The doping dependence of the superconductivity casts serious doubt that it …read more

Published in: Nature Materials

Large electron-phonon interactions from FeSe phonons in a monolayer. (arXiv:1407.5657v2 [cond-mat.supr-con] UPDATED)

2016-10-15T11:36:35+00:00July 14th, 2015|Categories: Publications|Tags: |

By Sinisa Coh, Marvin L. Cohen, Steven G. Louie We show that electron-phonon coupling can induce strong electron pairing in
an FeSe monolayer on a SrTiO3 substrate (experimental indications for
superconducting Tc are between 65 and 109K). The role of the SrTiO3 substrate
in increasing the coupling is two-fold. First, the interaction of the FeSe and
TiO2 terminated face of SrTiO3 prevents the …read more

Published in: arXiv Material Science

Some say, that 2D Research is the best website in the world.