arXiv subjects

Binbin Ruan

Publications and source records attributed to Binbin Ruan.

7 recordsLinked to original sources

arXiv2026

Two distinct superconducting regimes in Ti4Co2O under pressures

We report on the pressure dependence of superconducting transition temperature Tc and upper critical field Bc2(0) through electrical transport of the Ti4Co2O superconductor (eg.,the superconducting transition temperature Tc = 2.5 K and the Bc2(0)=7.2T=2.9Tc). We find that the Tc exhibits non-monotonic pressure dependence:it rises monotonically at first with a pressure coefficient of dTc/dP=0.034 K/GPa, but rapidly decreases around 10-20 GPa, and then increases with the dTc/dP = 0.023 K/GPa, up to= 4.31 K at 69.7 GPa. Concurrently, the Bc2(0)exhibits a dome shaped pressure dependence, with its maximum at 5 GPa of almost twice the value at ambient pressure, exceeding the weak-coupling Pauli paramagnetic limit Bp throughout the whole pressure range. By comparing the normal-state and superconducting properties, we identify two distinct superconducting regimes, with a low-pressure superconducting phase characterized by an enhanced Bc2(0)values and Fermi-liquid normal-state electrical transport (the exponent n = 2), and a high-pressure superconducting phase with a monotonically increased Tc and an enhancement in phonon scatterings (the exponent n = 4). Room-temperature synchrotron X-ray diffraction indicates that there is no structural transition up to 55.8 GPa, which gives a relatively large bulk modulus of 192 GPa in comparison with other alloy superconductors. First-principles calculations suggest that the nonmonotonic Tc maybe closely related to the evolution of the density of states of Ti4Co2O upon compression, which is different from those of isostructural superconductors Ti4Ir2O and Nb4Rh2C. Our results show that even in the Ti4Co2O with weak spin-orbit coupling, superconductivity remains highly sensitive to the external stimuli such as pressure.

cond-mat.supr-con↗

arXiv2024

Crystal growth and characterization of Fe$_{1+\delta}$Se$_{1-x}$Te$_x$ (0.5 $\leq$ $x$ $\leq$ 1) from LiCl/KCl flux

An eutectic LiCl/KCl flux method in a horizontal configuration has been used to grow a series of homogeneous Fe$_{1+\delta}$Se$_{1-x}$Te$_x$ single crystals of high quality with 0.5 $\leq$ $x$ $\leq$ 1. Compared with previously used melt-growth method, the stable crystallization process in LiCl/KCl flux below their peritectic temperatures results in better homogeneity and crystalline perfection identified by energy dispersive spectrometer and x-ray diffraction. The interstitial Fe value $\delta$ remains small within 0.5 $\leq$ $x$ $\leq$ 0.85 where the superconducting temperature $T_C$ is not sensitive to the Te content with sharp superconducting transition widths $\Delta$$T_C$ < 1 K and a maximum of $T_C$ = 14.3 K at $x$ = 0.61. The value $\delta$ starts to increase quickly accompanied by a deviation of linear behavior of crystal lattice parameters as well as the broadening of $\Delta$$T_C$ = 2.1 K at $x$ = 0.91, then suddenly rises up to $\delta$ > 0.1 followed by the disappearance of superconductivity and emergence of antiferromagnetic order at x $\geq$ 0.96. We also observed a metallic to semiconducting transition in the normal state resistivity of Fe$_{1+\delta}$Se$_{1-x}$Te$_x$ with increasing Te content which is related to a localized electronic state induced by the interstitial Fe. The interstitial Fe value $\delta$ might be a key physical parameter to understand various properties of Fe$_{1+\delta}$Se$_{1-x}$Te$_x$ system.

cond-mat.supr-con↗

arXiv2024

Superconductivity in a layered cobalt oxychalcogenide Na$_{2}$CoSe$_{2}$O with a triangular lattice

Unconventional superconductivity in bulk materials under ambient pressure is extremely rare among the 3d transition metal compounds outside the layered cuprates and iron-based family. It is predominantly linked to highly anisotropic electronic properties and quasi-two-dimensional (2D) Fermi surfaces. To date, the only known example of a Co-based exotic superconductor is the hydrated layered cobaltate, Na$_{x}$CoO$_{2}\cdot$ yH$_{2}$O, and its superconductivity is realized in the vicinity of a spin-1/2 Mott state. However, the nature of the superconductivity in these materials is still a subject of intense debate, and therefore, finding a new class of superconductors will help unravel the mysteries of their unconventional superconductivity. Here we report the discovery of superconductivity at $\sim$ 6.3 K in our newly synthesized layered compound Na$_{2}$CoSe$_{2}$O, in which the edge-shared CoSe$_{6}$ octahedra form [CoSe$_{2}$] layers with a perfect triangular lattice of Co ions. It is the first 3d transition metal oxychalcogenide superconductor with distinct structural and chemical characteristics. Despite its relatively low $T_{c}$, this material exhibits very high superconducting upper critical fields, $μ_{0}H_{c2}(0)$, which far exceeds the Pauli paramagnetic limit by a factor of 3 - 4. First-principles calculations show that Na$_{2}$CoSe$_{2}$O is a rare example of a negative charge transfer superconductor. This cobalt oxychalcogenide with a geometrical frustration among Co spins shows great potential as a highly appealing candidate for the realization of unconventional and/or high-$T_{c}$ superconductivity beyond the well-established Cu- and Fe-based superconductor families and opens a new field in the physics and chemistry of low-dimensional superconductors.

cond-mat.supr-con↗

arXiv2024

Structural and resistivity properties of Fe$_{1-x}$Co${_x}$Se single crystals grown by the molten salt method

A series of tetragonal Fe$_{1-x}$Co${_x}$Se single crystals with a complete Co doping range (0$\leq$x$\leq$0.52) up to its solid solubility limit in FeSe have been grown by an eutectic AlCl${_3}$/KCl molten salt method. The typical lateral size of as-grown Fe$_{1-x}$Co${_x}$Se single crystals is 1$-$5 mm. The chemical composition and homogeneity of the crystals was examined by both inductively coupled plasma atomic emission spectroscopy and energy dispersive spectrometer. X-ray diffraction analysis demonstrates that the crystal lattice parameters $a$ and $c$ are both linearly decreased with increasing Co doping level x. In the whole doping range, all the samples show metallic behaviour in contrast to a metal insulator transition of Cu-doped FeSe according to the resistivity measurements

cond-mat.supr-con↗

arXiv2023

Growth of millimeter-sized high-quality CuFeSe$_2$ single crystals by the molten salt method and study of their semiconducting behavior

An eutectic AlCl$_3$/KCl molten salt method in a horizontal configuration was employed to grow millimeter-sized and composition homogeneous CuFeSe$_2$ single crystals due to the continuous growth process in a temperature gradient induced solution convection. The typical as-grown CuFeSe$_2$ single crystals in cubic forms are nearly 1.6$\times$1.2$\times$1.0 mm3 in size. The chemical composition and homogeneity of the crystals was examined by both inductively coupled plasma atomic emission spectroscopy and energy dispersive spectrometer with Cu:Fe:Se = 0.96:1.00:1.99 consistent with the stoichiometric composition of CuFeSe$_2$. The magnetic measurements suggest a ferrimagnetic or weak ferromagnetic transition below T$_C$ = 146 K and the resistivity reveals a semiconducting behavior and an abrupt increase below T$_C$.

cond-mat.mtrl-sci↗

arXiv2021

Large CaFeAsF single crystals of high quality grown by the oscillating temperature technique

The oscillating temperature technique was successfully employed to grow large and composition homogeneous CaFeAsF single crystals due to the reduction of nuclei number by temperature oscillation. The largest as-grown CaFeAsF single crystal was nearly 8 mm in lateral size and 0.27 mm in thickness which is far larger than previously reported in all dimensions. The full-width-at-half maximum (FWHM) of x-ray rocking curve is as small as 0.163° indicating the high quality of CaFeAsF single crystals.

cond-mat.supr-con↗

arXiv2021

Coexistence of ferromagnetism, antiferromagnetism, and superconductivity in magnetically anisotropic (Eu,La)FeAs2

Materials with exceptional magnetism and superconductivity usually conceive emergent physical phenomena. Here, we investigate the physical properties of the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2 shows anisotropy-associated magnetic behaviors, such as Eu-related moment canting and exchange bias. Through La doping, the magnetic anisotropy is enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a special exchange bias of the superposed ferromagnetic/superconducting loop revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows unusual robustness against La doping. Theoretical calculation and 57Fe Mössbauer spectroscopy investigation reveal a doping-tunable dual itinerant/localized nature of the Fe-related antiferromagnetism. Coexistence of the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform for further exploration of potential applications and emergent physics. Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the whole superconducting dome adjacent to the Fe-related antiferromagnetic phase, which is of benefit for seeking underlying clues to high-temperature superconductivity.

cond-mat.supr-con↗