Yulong Huang

A magnetic protein biocompass

The notion that animals can detect the Earths magnetic field was once ridiculed, but is now well established. Yet the biological nature of such magnetosensing phenomenon remains unknown. Here, we report a putative magnetic receptor (Drosophila CG8198, here named MagR) and a multimeric magnetosensing rod-like protein complex, identified by theoretical postulation and genome-wide screening, and validated with cellular, biochemical, structural and biophysical methods. The magnetosensing complex consists of the identified putative magnetoreceptor and known magnetoreception-related photoreceptor cryptochromes (Cry), has the attributes of both Cry- and iron-based systems, and exhibits spontaneous alignment in magnetic fields, including that of the Earth. Such a protein complex may form the basis of magnetoreception in animals, and may lead to applications across multiple fields.

Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films

The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

(Li0.84Fe0.16)OHFe0.98Se superconductor: Ion-exchange synthesis of large single-crystal and highly two-dimensional electron properties

A large and high-quality single crystal (Li0.84Fe0.16)OHFe0.98Se, the optimal superconductor of a reported (Li1-xFex)OHFe1-ySe system, has been successfully synthesized via a hydrothermal ion-exchange technique. The superconducting transition temperature (T-c) of 42 K is determined by magnetic susceptibility and electric resistivity measurements, and the zero-temperature upper critical magnetic fields are evaluated as 79 and 313 T for the field along the c axis and the ab plane, respectively. The ratio of out-of-plane to in-plane electric resistivity rho(c)/rho(ab) is found to increase with decreasing temperature and to reach a high value of 2500 at 50 K, with an evident kink occurring at a characteristic temperature T* = 120 K. The negative in-plane Hall coefficient indicates that electron carriers dominate in the charge transport, and the hole contribution is significantly reduced as the temperature is lowered to approach T *. From T * down to T-c we observe the linear temperature dependencies of the in-plane electric resistivity and the magnetic susceptibility for the FeSe layers. Our findings thus reveal that the normal state of (Li0.84Fe0.16)OHFe0.98Se becomes highly two dimensional and anomalous prior to the superconducting transition, providing an insight into the mechanism of high-T-c superconductivity.

The upper critical field and its anisotropy in (Li1−x Fe x )OHFe1−y Se

The temperature dependence of the upper critical field (H c2) in a (Li1-x Fe x )OHFe1-y Se single crystal ([Formula: see text] K) has been determined by means of magnetotransport measurements down to 1.4 K both for inter-plane ([Formula: see text], [Formula: see text]) and in-plane ([Formula: see text], [Formula: see text]) field directions in static magnetic fields up to 14 T and pulsed magnetic fields up to 70 T. [Formula: see text] exhibits a quasilinear increase with decreasing temperature below the superconducting transition and can be described well by an effective two-band model with unbalanced diffusivity, while [Formula: see text] shows a flattening below 35 K and follows the Werthamer-Helfand-Hohenberg (WHH) model incorporating orbital pair-breaking and spin-paramagnetic effects, yielding zero-temperature critical fields of [Formula: see text] T and [Formula: see text] T. The anisotropy of the upper critical fields, [Formula: see text] monotonically decreases with decreasing temperature from about 7 near T c to 1.5 at 0 K. This reduced anisotropy, observed in most Fe-based superconductors, is caused by the Pauli limitation of [Formula: see text].

Synthesis of large FeSe superconductor crystals via ion release/introduction and property characterization*

Large superconducting FeSe crystals of (001) orientation have been prepared via a hydrothermal ion release/introduction route for the first time. The hydrothermally derived FeSe crystals are up to 10 mm×5 mm×0.3 mm in dimension. The pure tetragonal FeSe phase has been confirmed by x-ray diffraction (XRD) and the composition determined by both inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy dispersive x-ray spectroscopy (EDX). The superconducting transition of the FeSe samples has been characterized by magnetic and transport measurements. The zero-temperature upper critical field H c2 is calculated to be 13.2–16.7 T from a two-band model. The normal-state cooperative paramagnetism is found to be predominated by strong spin frustrations below the characteristic temperature T sn, where the Ising spin nematicity has been discerned in the FeSe superconductor crystals as reported elsewhere.

Comparisons of phase times with tunnelling times based on absorption probabilities

The times spent by an electron in a scattering event or tunnelling through a potential barrier are investigated using a method based on the absorption probabilities. The reflection and transmission times derived from this method are equal to the local Larmor times if the transmission and reflection probability amplitudes are complex analytic functions of the complex potential. The numerical results show that they coincide with the phase times except as the incident electron energy approaches zero or when the transmission probability is too small. If the imaginary potential covers the whole space the tunnelling times are again equal to the phase times. The results show that the tunnelling times based on absorption probabilities are the best of the various candidates.

The effect of Cu doping in the NiO2 plane on the stripe phase in La1.67Sr0.33NiO4

The effect of Cu doping on the stripe-ordered state in La1.67Sr0.33NiO4 has been studied by means of electrical resistivity and magnetic measurements and transmission electron microscopy observation. The investigations reveal that Cu doping at Ni sites does not change the modulation pattern of the charge ordering, but clearly reduces the charge-ordered-transition and spin-ordering temperatures. Moreover, Cu on the NiO2 planes tends to melt the stripe lattice and reduce the charge and spin stripe correlation lengths. These effects could arise from the cooperative action of carrier mobility enhancement, strong interplay of Cu spins with the host Ni spin-lattice system, and the disordering effect of Cu dopants.

Tunable critical temperature for superconductivity in FeSe thin films by pulsed laser deposition

Stabilized FeSe thin films in ambient pressure with tunable superconducting critical temperature would be a promising candidate for superconducting electronic devices. By carefully controlling the depositions on twelve kinds of substrates using a pulsed laser deposition technique single crystalline FeSe thin films were fabricated. The high quality of the thin films was confirmed by X-ray diffraction with a full width at half maximum of 0.515° in the rocking curve and clear four-fold symmetry in φ-scan. The films have a maximum Tc ~ 15 K on the CaF2 substrate and were stable in ambient conditions air for more than half a year. Slightly tuning the stoichiometry of the FeSe targets, the superconducting critical temperature becomes adjustable below 15 K with quite narrow transition width less than 2 K. These FeSe thin films deposited on different substrates are optimized respectively. The Tc of these optimized films show a relation with the out-of-plane (c-axis) lattice parameter of the FeSe films.

Distinction between critical current effects and intrinsic anomalies in the point-contact Andreev reflection spectra of unconventional superconductors

Ge He(何格)1,2,†,‡, Zhong-Xu Wei(魏忠旭)1,2,†, Jérémy Brisbois3,†, Yan-Li Jia(贾艳丽)1,2, Yu-Long Huang(黄裕龙)1,2, Hua-Xue Zhou(周花雪)1,2, Shun-Li Ni(倪顺利)1,2, Alejandro V Silhanek3, Lei Shan(单磊)1,2,4, Bei-Yi Zhu(朱北沂)1, Jie Yuan(袁洁)1, Xiao-Li Dong(董晓莉)1,2,4, Fang Zhou(周放)1,2,4, Zhong-Xian Zhao(赵忠贤)1,2,4, and Kui Jin(金魁)1,2,4 1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 2School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China 3Experimental Physics of Nanostructured Materials, Q-MAT, CESAM, Université de Liège, B-4000 Sart Tilman, Belgium 4Collaborative Innovation Center of Quantum Matter, Beijing 100190, China

Superconducting (Li,Fe)OHFeSe Film of High Quality and High Critical Parameters

The superconducting film of (Li1-xFex)OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22 deg, in terms of the FWHM (full-width-at-half-maximum) of x-ray rocking curve, and an excellent out-of-plane orientation by x-ray phi-scan. Its bulk superconducting transition temperature (Tc) of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field (Hc2) is estimated to be 79.5 T and 443 T, respectively, for the magnetic field perpendicular and parallel to the ab plane. Moreover, a large critical current density (Jc) of a value over 0.5 MA/cm2 is achieved at ~20 K. Such a (Li1-xFex)OHFeSe film is therefore not only important to the fundamental research for understanding the high-Tc mechanism, but also promising in the field of high-Tc superconductivity application, especially in high-performance electronic devices and large scientific facilities such as superconducting accelerator.