Institute of Fundamental Technological Research
Polish Academy of Sciences

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Xiaofeng Xu


Recent publications
1.  Chudziński P., Berben M., Xu X., Wakeham N., Bernáth B., Duffy C., Hinlopen R., Hsu Y., Wiedmann S., Tinnemans P., Jin R., Greenblatt M., Hussey N., Emergent symmetry in a low-dimensional superconductor on the edge of Mottness, Science, ISSN: 0036-8075, DOI: 10.1126/science.abp8948, Vol.382, pp.792-796, 2023

Abstract:
Upon cooling, condensed-matter systems typically transition into states of lower symmetry. The converse—i.e., the emergence of higher symmetry at lower temperatures—is extremely rare. In this work, we show how an unusually isotropic magnetoresistance in the highly anisotropic, one-dimensional conductor Li0.9Mo6O17 and its temperature dependence can be interpreted as a renormalization group (RG) flow toward a so-called separatrix. This approach is equivalent to an emergent symmetry in the system. The existence of two distinct ground states, Mott insulator and superconductor, can then be traced back to two opposing RG trajectories. By establishing a direct link between quantum field theory and an experimentally measurable quantity, we uncover a path through which emergent symmetry might be identified in other candidate materials.

Affiliations:
Chudziński P. - IPPT PAN
Berben M. - other affiliation
Xu X. - other affiliation
Wakeham N. - other affiliation
Bernáth B. - other affiliation
Duffy C. - other affiliation
Hinlopen R. - other affiliation
Hsu Y. - other affiliation
Wiedmann S. - other affiliation
Tinnemans P. - other affiliation
Jin R. - other affiliation
Greenblatt M. - other affiliation
Hussey N. - other affiliation
2.  Chen R., Xue Yafei ., Xu X., Yang H., Qiu T., Shui Lingling ., Wang Xin ., Zhou G., Giersig M., Pidot S., Hutchison J.A ., Akinoglu E.M., Lithography-free synthesis of periodic, vertically-aligned, multi-walled carbon nanotube arrays, NANOTECHNOLOGY, ISSN: 0957-4484, DOI: 10.1088/1361-6528/ac345a, Vol.33, No.065304, pp.1-9, 2021

Abstract:
Until now, the growth of periodic vertically aligned multi-walled carbon nanotube (VA-
MWCNT) arrays was dependent on at least one lithography step during fabrication. Here, we demonstrate a lithography-free fabrication method to grow hexagonal arrays of self-standing VA-MWCNTs with tunable pitch and MWCNT size. The MWCNTs are synthesized by plasma enhanced chemical vapor deposition (PECVD) from Ni catalyst particles. Template guided dewetting of a thin Ni film on a hexagonally close-packed silica particle monolayer provides periodically distributed Ni catalyst particles as seeds for the growth of the periodic MWCNT arrays. The diameter of the silica particles directly controls the pitch of the periodic VA-MWCNT arrays from 600 nm to as small as 160 nm. The diameter and length of the individual MWCNTs can also be readily adjusted and are a function of the Ni particle size and PECVD time. This unique method of lithography-free growth of periodic VA-MWCNT arrays can be utilized for the fabrication of large-scale biomimetic materials

Keywords:
periodic, ithography free, nanofabrication, template guided, vertically-aligned multi- walled carbon nanotubes, self-standing

Affiliations:
Chen R. - other affiliation
Xue Yafei . - South China Normal Universit (CN)
Xu X. - other affiliation
Yang H. - South China Normal Universit (CN)
Qiu T. - other affiliation
Shui Lingling . - South China Normal Universit (CN)
Wang Xin . - other affiliation
Zhou G. - South China Normal Universit (CN)
Giersig M. - IPPT PAN
Pidot S. - other affiliation
Hutchison J.A . - other affiliation
Akinoglu E.M. - University of Melbourne (AU)
3.  Lu J., Xu X., Greenblatt M., Jin R., Tinnemans P., Licciardello S., van Delft M.R., Buhot J., Chudziński P., Hussey N.E., Emergence of a real-space symmetry axis in the magnetoresistance of the one-dimensional conductor Li0.9Mo6O17, Science Advances, ISSN: 2375-2548, DOI: 10.1126/sciadv.aar8027, Vol.5, No.7, pp.eaar8027-1-7, 2019

Abstract:
We report on an emerging symmetry axis in the magnetoresistance of bulk single crystals of quasi–one-dimensional Li0.9Mo6O17 below Tmin = 25 K, the temperature at which the electrical resistivity experiences a minimum. Detailed angle-dependent magnetoresistance sweeps reveal that this symmetry axis is induced by the development of a negative magnetoresistance, which is suppressed only for magnetic fields oriented along the poles of the MoO6 octahedra that form the conducting chains. We show that this unusual negative magnetoresistance is consistent with the melting of dark excitons, composed of previously omitted orbitals within the t2g manifold that order below Tmin. The unveiled symmetry axis in directional magnetic fields not only provides evidence for the crystallization of these dark excitons but also sheds new light on the long-standing mystery of the metal-insulator transition in Li0.9Mo6O17.

Affiliations:
Lu J. - other affiliation
Xu X. - other affiliation
Greenblatt M. - other affiliation
Jin R. - other affiliation
Tinnemans P. - other affiliation
Licciardello S. - other affiliation
van Delft M.R. - other affiliation
Buhot J. - other affiliation
Chudziński P. - other affiliation
Hussey N.E. - other affiliation

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