## Superconductivity

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### X H Chen - One of the best experts on this subject based on the ideXlab platform.

• ##### evolution of high temperature Superconductivity from a low t_ c phase tuned by carrier concentration in fese thin flakes
Physical Review Letters, 2016
Co-Authors: B Lei, J H Cui, Z J Xiang, C Shang, N Z Wang, X G Luo, Zhe Sun, X H Chen
Abstract:

We report the evolution of Superconductivity in an FeSe thin flake with systematically regulated carrier concentrations by the liquid-gating technique. With electron doping tuned by the gate voltage, high-temperature Superconductivity with an onset at 48 K can be achieved in an FeSe thin flake with T_{c} less than 10 K. This is the first time such high temperature Superconductivity in FeSe is achieved without either an epitaxial interface or external pressure, and it definitely proves that the simple electron-doping process is able to induce high-temperature Superconductivity with T_{c}^{onset} as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the Superconductivity is suddenly changed from a low-T_{c} phase to a high-T_{c} phase with a Lifshitz transition at a certain carrier concentration. These results help to build a unified picture to understand the high-temperature Superconductivity among all FeSe-derived superconductors and shed light on the further pursuit of a higher T_{c} in these materials.

• ##### evolution of high temperature Superconductivity from a low t_ c phase tuned by carrier concentration in fese thin flakes
Physical Review Letters, 2016
Co-Authors: B Lei, J H Cui, C Shang, N Z Wang, Ziji Xiang, Xiaoguang Luo, Zhengzong Sun, X H Chen
Abstract:

We report the evolution of Superconductivity in an FeSe thin flake with systematically regulated carrier concentrations by the liquid-gating technique. With electron doping tuned by the gate voltage, high-temperature Superconductivity with an onset at 48 K can be achieved in an FeSe thin flake with ${T}_{c}$ less than 10 K. This is the first time such high temperature Superconductivity in FeSe is achieved without either an epitaxial interface or external pressure, and it definitely proves that the simple electron-doping process is able to induce high-temperature Superconductivity with ${T}_{c}^{\text{onset}}$ as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the Superconductivity is suddenly changed from a low-${T}_{c}$ phase to a high-${T}_{c}$ phase with a Lifshitz transition at a certain carrier concentration. These results help to build a unified picture to understand the high-temperature Superconductivity among all FeSe-derived superconductors and shed light on the further pursuit of a higher ${T}_{c}$ in these materials.

• ##### coexistence of static magnetism and Superconductivity in smfeaso 1 x f x as revealed by muon spin rotation
Nature Materials, 2009
Co-Authors: X H Chen, A J Drew, Ch Niedermayer, P J Baker, F L Pratt, Stephen J Blundell, Tom Lancaster, R H Liu, Isao Watanabe
Abstract:

In non-conventional superconductors, the competition of magnetic order and Superconductivity seems to be a key element for the origin of Superconductivity. Investigation of the newly discovered iron-pnictides superconductors challenges this picture, showing a coexistence of Superconductivity and magnetism.

• ##### Superconductivity at 43 k in smfeaso1 xfx
Nature, 2008
Co-Authors: X H Chen, T Wu, G Wu, H F Chen, D F Fang
Abstract:

The recently discovered layered rare-earth metal oxypnictides have reinvigorated research into high-temperature Superconductivity. The first of these, found only a few months ago, had a transition temperature of 26 K. A recent paper in Nature reported an iron–arsenic-based material superconducting at 43 K with the application of pressure. Previously only copper oxides superconductors had beaten the 40 K barrier. Now Chen et al. report bulk Superconductivity in the samarium–arsenide oxide SmFeAsO1−xFx with a transition temperature of 43 K without this pressure. A report on the discovery of bulk Superconductivity in samarium-arsenide oxides SmFeAsO1−xFx with a transition temperature as high as 43 K. Since the discovery of high-transition-temperature (high-Tc) Superconductivity in layered copper oxides, extensive effort has been devoted to exploring the origins of this phenomenon. A Tc higher than 40 K (about the theoretical maximum predicted from Bardeen–Cooper–Schrieffer theory1), however, has been obtained only in the copper oxide superconductors. The highest reported value for non-copper-oxide bulk Superconductivity is Tc = 39 K in MgB2 (ref. 2). The layered rare-earth metal oxypnictides LnOFeAs (where Ln is La–Nd, Sm and Gd) are now attracting attention following the discovery of Superconductivity at 26 K in the iron-based LaO1-xF x FeAs (ref. 3). Here we report the discovery of bulk Superconductivity in the related compound SmFeAsO1-xF x , which has a ZrCuSiAs-type structure. Resistivity and magnetization measurements reveal a transition temperature as high as 43 K. This provides a new material base for studying the origin of high-temperature Superconductivity.

• ##### Superconductivity at 43 k in samarium arsenide oxides smfeaso_ 1 x f_x
Nature, 2008
Co-Authors: X H Chen, T Wu, G Wu, H F Chen, D F Fang
Abstract:

Since the discovery of high-transition temperature ($T_c$) Superconductivity in layered copper oxides, extensive efforts have been devoted to explore the higher $T_c$ Superconductivity. However, the $T_c$ higher than 40 K can be obtained only in the copper oxide superconductors so far. The highest reported value of $T_c$ for non-copper-oxide bulk Superconductivity is 39 K in $MgB_2$.\cite{jun} The $T_c$ of about 40 K is close to or above the theoretical value predicted from BCS theory.\cite{mcmillan} Therefore, it is very significant to search for non-copper oxide superconductor with the transition temperature higher than 40 K to understand the mechanism of high-$T_c$ Superconductivity. Here we report the discovery of bulk Superconductivity in samarium-arsenide oxides $SmFeAsO_{1-x}F_x$ with ZrCuAiAs type structure. Resistivity and magnetization measurements show strong evidences for transition temperature as high as 43 K. $SmFeAsO_{1-x}F_x$ is the first non-copper oxide superconductor with $T_c$ higher than 40 K. The $T_c$ higher than 40 K may be a strong argument to consider $SmFeAsO_{1-x}F_x$ as an unconventional superconductor.

### Qi Kun Xue - One of the best experts on this subject based on the ideXlab platform.

• ##### high temperature Superconductivity in single unit cell fese films on anatase tio 2 001
Physical Review Letters, 2016
Co-Authors: Hao Ding, Lili Wang, Kun Zhao, Wenlin Wang, Canli Song, Xi Chen, Qi Kun Xue
Abstract:

We report on the observation of high-temperature (T_{c}) Superconductivity and magnetic vortices in single-unit-cell FeSe films on anatase TiO_{2}(001) substrate by using scanning tunneling microscopy. A systematic study and engineering of interfacial properties has clarified the essential roles of substrate in realizing the high-T_{c} Superconductivity, probably via interface-induced electron-phonon coupling enhancement and charge transfer. By visualizing and tuning the oxygen vacancies at the interface, we find their very limited effect on the Superconductivity, which excludes interfacial oxygen vacancies as the primary source for charge transfer between the substrate and FeSe films. Our findings have placed severe constraints on any microscopic model for the high-T_{c} Superconductivity in FeSe-related heterostructures.

• ##### Interface high-temperature Superconductivity
Superconductor Science and Technology, 2016
Co-Authors: Lili Wang, Xucun Ma, Qi Kun Xue
Abstract:

Cuprate high temperature superconductors consist of two quasi-two-dimensional (2D) substructures: CuO2 superconducting layers and charge reservoir layers. The Superconductivity is realized by charge transfer from the charge reservoir layers into the superconducting layers without chemical dopants and defects being introduced into the latter, similar to modulation-doping in semiconductor superlattices of AlGaAs/GaAs. Inspired by this scheme, we have been searching for high temperature Superconductivity in ultrathin films of superconductors epitaxially grown on semiconductor/oxide substrates since 2008. We have observed interface enhanced Superconductivity in both conventional and unconventional superconducting films, including single atomic layer films of Pb and In on Si substrates and single unit cell (UC) films of FeSe on SrTiO3 (STO) substrates. The discovery of high temperature Superconductivity with a superconducting gap of ~20 meV in 1UC-FeSe/STO has stimulated tremendous interest in Superconductivity community, for it opens new avenue for both raising superconducting transition temperature and understanding the pairing mechanism of unconventional high temperature Superconductivity. Here, we review mainly the experimental progress on interface enhanced Superconductivity in the three systems mentioned above with emphasis on 1UC-FeSe/STO, studied by scanning tunneling microscopy/spectroscopy, angle-resolved photoemission spectroscopy and transport experiments. We discuss the roles of interfaces and possible pairing mechanism inferred from those studies.

### Yasuna Kawasaki - One of the best experts on this subject based on the ideXlab platform.

• ##### clarification as to why alcoholic beverages have the ability to induce Superconductivity in fe1 dte1 xsx
Superconductor Science and Technology, 2012
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Dan Sato, Masahiro Sugimoto, Hiroshi Hara, Tohru Watanabe
Abstract:

To elucidate the mechanism as to why alcoholic beverages can induce Superconductivity in Fe1+dTe1?xSx samples, we performed component analysis and found that a weak acid such as an organic acid has the ability to induce Superconductivity. Inductively coupled plasma spectroscopy was performed on weak acid solutions post-annealing. We found that the mechanism of inducement of Superconductivity in Fe1+dTe1?xSx is the deintercalation of excess Fe from the interlayer sites.

• ##### phase diagram and oxygen annealing effect of fete1 xsex iron based superconductor
Solid State Communications, 2012
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Tohru Watanabe, Hiroyuki Okazaki, Toshinori Ozaki
Abstract:

Abstract Phase diagrams of as-grown and O 2 -annealed FeTe 1− x Se x determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x ≥0.15, and weak Superconductivity appeared when x ≥0.1. Beginning at x =0.5, weak Superconductivity was found to evolve into bulk Superconductivity. Interestingly, for O 2 -annealed samples, complete suppression of magnetic order and the occurrence of bulk Superconductivity were observed when x ≥0.1. We found that O 2 -annealing induces bulk Superconductivity for FeTe 1− x Se x . Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk Superconductivity.

• ##### phase diagram and oxygen annealing effect of fete1 xsex iron based superconductor
arXiv: Superconductivity, 2011
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Tohru Watanabe, Hiroyuki Okazaki, Toshinori Ozaki
Abstract:

Phase diagrams of as-grown and O2-annealed FeTe1-xSex determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x \geq 0.15, and weak Superconductivity appeared when x \geq 0.1. Beginning at x = 0.5, weak Superconductivity was found to evolve into bulk Superconductivity. Interestingly, for O2-annealed samples, complete suppression of magnetic order and the occurrence of bulk Superconductivity were observed when x \geq 0.1. We found that O2-annealing induces bulk Superconductivity for FeTe1-xSex. Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk Superconductivity.

### Keita Deguchi - One of the best experts on this subject based on the ideXlab platform.

• ##### clarification as to why alcoholic beverages have the ability to induce Superconductivity in fe1 dte1 xsx
Superconductor Science and Technology, 2012
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Dan Sato, Masahiro Sugimoto, Hiroshi Hara, Tohru Watanabe
Abstract:

To elucidate the mechanism as to why alcoholic beverages can induce Superconductivity in Fe1+dTe1?xSx samples, we performed component analysis and found that a weak acid such as an organic acid has the ability to induce Superconductivity. Inductively coupled plasma spectroscopy was performed on weak acid solutions post-annealing. We found that the mechanism of inducement of Superconductivity in Fe1+dTe1?xSx is the deintercalation of excess Fe from the interlayer sites.

• ##### phase diagram and oxygen annealing effect of fete1 xsex iron based superconductor
Solid State Communications, 2012
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Tohru Watanabe, Hiroyuki Okazaki, Toshinori Ozaki
Abstract:

Abstract Phase diagrams of as-grown and O 2 -annealed FeTe 1− x Se x determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x ≥0.15, and weak Superconductivity appeared when x ≥0.1. Beginning at x =0.5, weak Superconductivity was found to evolve into bulk Superconductivity. Interestingly, for O 2 -annealed samples, complete suppression of magnetic order and the occurrence of bulk Superconductivity were observed when x ≥0.1. We found that O 2 -annealing induces bulk Superconductivity for FeTe 1− x Se x . Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk Superconductivity.

• ##### phase diagram and oxygen annealing effect of fete1 xsex iron based superconductor
arXiv: Superconductivity, 2011
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Tohru Watanabe, Hiroyuki Okazaki, Toshinori Ozaki
Abstract:

Phase diagrams of as-grown and O2-annealed FeTe1-xSex determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x \geq 0.15, and weak Superconductivity appeared when x \geq 0.1. Beginning at x = 0.5, weak Superconductivity was found to evolve into bulk Superconductivity. Interestingly, for O2-annealed samples, complete suppression of magnetic order and the occurrence of bulk Superconductivity were observed when x \geq 0.1. We found that O2-annealing induces bulk Superconductivity for FeTe1-xSex. Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk Superconductivity.

### Tohru Watanabe - One of the best experts on this subject based on the ideXlab platform.

• ##### clarification as to why alcoholic beverages have the ability to induce Superconductivity in fe1 dte1 xsx
Superconductor Science and Technology, 2012
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Dan Sato, Masahiro Sugimoto, Hiroshi Hara, Tohru Watanabe
Abstract:

To elucidate the mechanism as to why alcoholic beverages can induce Superconductivity in Fe1+dTe1?xSx samples, we performed component analysis and found that a weak acid such as an organic acid has the ability to induce Superconductivity. Inductively coupled plasma spectroscopy was performed on weak acid solutions post-annealing. We found that the mechanism of inducement of Superconductivity in Fe1+dTe1?xSx is the deintercalation of excess Fe from the interlayer sites.

• ##### phase diagram and oxygen annealing effect of fete1 xsex iron based superconductor
Solid State Communications, 2012
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Tohru Watanabe, Hiroyuki Okazaki, Toshinori Ozaki
Abstract:

Abstract Phase diagrams of as-grown and O 2 -annealed FeTe 1− x Se x determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x ≥0.15, and weak Superconductivity appeared when x ≥0.1. Beginning at x =0.5, weak Superconductivity was found to evolve into bulk Superconductivity. Interestingly, for O 2 -annealed samples, complete suppression of magnetic order and the occurrence of bulk Superconductivity were observed when x ≥0.1. We found that O 2 -annealing induces bulk Superconductivity for FeTe 1− x Se x . Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk Superconductivity.

• ##### phase diagram and oxygen annealing effect of fete1 xsex iron based superconductor
arXiv: Superconductivity, 2011
Co-Authors: Yasuna Kawasaki, Keita Deguchi, Satoshi Demura, Tohru Watanabe, Hiroyuki Okazaki, Toshinori Ozaki
Abstract:

Phase diagrams of as-grown and O2-annealed FeTe1-xSex determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x \geq 0.15, and weak Superconductivity appeared when x \geq 0.1. Beginning at x = 0.5, weak Superconductivity was found to evolve into bulk Superconductivity. Interestingly, for O2-annealed samples, complete suppression of magnetic order and the occurrence of bulk Superconductivity were observed when x \geq 0.1. We found that O2-annealing induces bulk Superconductivity for FeTe1-xSex. Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk Superconductivity.