arXiv subjects

Zhe-Ning Xiang

Publications and source records attributed to Zhe-Ning Xiang.

7 recordsLinked to original sources

arXiv2026

Heavily Sr-Doped La$_{2}$SrNi$_{2}$O$_{7-δ}$ as a Tetragonal Ruddlesden-Popper Phase at Ambient Pressure

High-temperature superconductivity has been found in bilayer Ruddlesden-Popper (RP) nickelates in bulk samples under high pressure, or in thin films via compressive strain. In the superconducting state, a tetragonal structure with a straight Ni-O-Ni bond along c-axis has been commonly observed, together with the suppression or diminishing of the density-wave orders. Therefore, it remains an open question whether these factors are sufficient for achieving superconductivity at ambient pressure. Here we report the first successful synthesis of heavily Sr-doped La$_{2}$SrNi$_{2}$O$_{7-δ}$ under high-pressure and high-temperature (HPHT) conditions with a flux method. X-ray diffraction and scanning transmission electron microscopy (STEM) confirm that the material adopts a tetragonal (I4/mmm) structure with an 180$^{\circ}$ Ni-O-Ni bond angle along c-axis. Resistance measurements reveal metallic behavior with a low-temperature upturn and no density-wave features are observed. However, neither pressure nor oxygen variation induces superconductivity. Density functional theory calculations indicate that the holes introduced by Sr doping are predominantly doped into the Ni-3d$_{z^2}$ orbital, leading to the appearance of a very large $γ$ pocket on the Fermi surface at ambient pressure and significantly reducing the occupation of the Ni-3d$_{z^2 }$ orbital. Combining the experimental observations with theoretical calculations, we attribute the absence of superconductivity to the serious deviation from the half-filling state of the Ni-3d$_{z^2 }$ band, which is crucial for the interlayer antiferromagnetic interaction and thus for pairing. Our work unravels important issues for achieving superconductivity in bilayer nickelate system.

cond-mat.supr-con↗

arXiv2026

Pressure-induced Structural Phase Transition, Metallization, and Superconductivity in layered metalloid dichalcogenide 1T-SiTe$_2$

Layered transition-metal dichalcogenides (TMDs) have attracted considerable attention as promising platforms for exploring emergent physics and potential device applications. In contrast, metalloid-based dichalcogenide counterparts remain largely underexplored. Here, we report the pressure-induced structural phase transition, metallization, and superconductivity in the layered metalloid dichalcogenide 1T-SiTe$_2$. At ambient pressure, 1T-SiTe$_2$ crystallizes in a trigonal crystal structure (space group: $P\bar{3}m1$) and exhibits intrinsic semiconducting transport characteristics. Upon pressurization, in concomitant with the suppression of semiconducting behavior in resistance, superconductivity emerges at around 6.7 GPa. The superconducting transition temperature (T$_c$) rises continuously with increasing pressure and finally saturates at approximately 5.5 K for pressures above 30 GPa. During the compression, 1T-SiTe$_2$ experiences three structural phase transitions, and the phase transition pressures are highly consistent with the anomalous transport responses observed experimentally, indicating that the changes of transport behavior of 1T-SiTe$_2$ under pressure are structurally-driven. Our work extends TMD superconductors into the realm of metalloid systems and provides a new platform for exploring novel physics in quasi two-dimensional materials without transition-metal elements.

cond-mat.supr-con↗

arXiv2025

Enhanced superconductivity in the compressively strained bilayer nickelate thin films by pressure

The discovery of high temperature superconductivity in the nickelate system has stimulated enormous interest in the community of condensed matter physics. Recently, superconductivity with an onset transition temperature (Tc^onset) over 40 K was achieved in La3Ni2O7 and (La,Pr)3Ni2O7 thin films at ambient pressure due to in-plane compressive strain. This observation has sparked enormous attention because measurements on superconducting properties can be accessible with many commonly used experimental tools. On the other hand, the Tc in these thin films is much lower than that of the bulk bilayer nickelates under pressure. Here we report the enhancement of Tc^onset to over 60 K by applying hydrostatic pressure on the compressively strained superconducting bilayer nickelate thin films. The Tc^onset firstly ramps up with pressure, then it slightly drops down after reaching the maximum Tc^onset at about 61.5 K under a pressure of 9 GPa, showing a dome-like phase diagram. Hall effect measurements reveal that the dominant charge carriers are hole-like with a slight enhancement of charge carrier density with pressure in accompanying with the increase of Tc. Our theoretical results demonstrate that the enhancement of Tc arises from a cooperative amplification of magnetic fluctuations within and between the layers and increased metallicity under pressure. However, this enhancement exhibits saturation at higher pressures. These findings highlight the critical role of the interplay between interlayer and intralayer electronic correlations in bilayer nickelate superconductors and point to the potential of tuning Tc through controlled manipulation of the electronic structure and interactions.

cond-mat.supr-con↗

arXiv2024

Unconventional superconductivity emerging along with the strange-metal behavior in UAs2 under pressure

The recently discovered spin-triplet superconductor candidate UTe2 with Tc = 2 K has attracted enormous attention because it possesses many interesting properties, such as the extremely high upper critical field Hc2(0), chiral superconductivity and spontaneous time-reversal symmetry breaking, etc., all these suggest that it may be the long-sought spin-triplet superconductor. Here we report the discovery of superconductivity up to Tc = 4K in one of its siblings, i.e., UAs2 under high pressures. Interestingly, the UAs2 shows metallic behavior with an antiferromagnetic (AFM) transition at about 274 K under ambient pressure. Upon applying pressure, this transition is pushed down to lower temperatures with improved electric conductivity. When the pressure rises to about 20-22 GPa, superconductivity occurs together with the emergence of a linear temperature dependence of normal state resistance, the latter is a hallmark of the strange-metal state. The superconductivity with the highest Tc = 4 K is reached under a pressure of about 26.8 GPa, and it is robust against magnetic field with the upper critical field μ0Hc2(0) ~ 12 T, far beyond the Pauli limit. Higher pressures will suppress the superconductivity and bring back the Fermi liquid behavior, showing a clear signature of quantum criticality. Our results open a new avenue for investigating the unconventional superconductivity concerning the mysterious 5f-band electrons in this uranium-based system.

cond-mat.supr-con↗

arXiv2024

Superconductivity up to 14.2 K in MnB$_4$ under pressure

The discovery of superconductivity in 3$d$-transition metal compounds with strong magnetism is interesting but rare. Especially for Mn-based compounds, there exist only very limited materials that show superconductivity. Here, we report the discovery of superconductivity up to 14.2 K in a Mn-based material MnB$_4$. By applying high pressures, we found the continuous suppression of a weak insulating behavior and the occurrence of superconductivity after about 30 GPa. With further increasing pressure, $T_\text{c}$ is gradually enhanced and reaches the maximum value of about 14.2 K at 150 GPa with a Fermi-Liquid behavior in the normal states. The synchrotron X-ray diffraction data reveal the unchanged monoclinic (S.G: $P2_1/c$) symmetry but an unusual crossover of the lattice parameters $b$ and $c$. Theoretical calculations based on the electron-phonon coupling picture reveal a very low $T_\text{c}$ (less than 1 K), manifesting an exotic pairing mechanism beyond the Bardeen-Cooper-Schrieffer (BCS) theory. Our findings show a promising way to explore high $T_\text{c}$ superconductivity by combining the 3d-transition metal magnetic elements and light elements.

cond-mat.supr-con↗

arXiv2024

Record high superconducting transition temperature in Ti$_{1-x}$Mn$_x$ alloy with rich magnetic element Mn

It is well-known that magnetic moments are very harmful to superconductivity. A typical example is the element Mn whose compounds usually exhibit strong magnetism. Thus, it is very hard to achieve superconductivity in materials containing Mn. Here, we report enhanced superconductivity with the superconducting transition temperature ($T_\text{c}$) up to a record high-value of about 26 K in a beta-phase Ti$_{1-x}$Mn$_x$ alloy containing rich magnetic element Mn under high pressures. This is contrary to the intuition that the magnetic moments always suppress superconductivity. Under high pressures, we also found that in the middle-pressure regime, the Pauli limit of the upper critical field is surpassed. The synchrotron X-ray diffraction data shows an unchanged beta-phase with a continuous contraction of the cell volume, which is well supported by the first-principles calculations. Although the theoretical results based on electron-phonon coupling (EPC) can interpret the $T_\text{c}$ value in a certain pressure region, the monotonic enhancement of superconductivity by pressure cannot seek support from the theory. Our results show a surprising enhancement of superconductivity in Ti$_{1-x}$Mn$_x$ alloy with a considerable Mn content.

cond-mat.supr-con↗

arXiv2023

Signature of superconductivity in pressurized La$_4$Ni$_3$O$_{10}$

The discovery of high-temperature superconductivity near 80 K in bilayer nickelate La$_3$Ni$_2$O$_7$ under high pressures has renewed the exploration of superconducting nickelate in bulk materials. The extension of superconductivity in other nickelates in a broader family is also essential. Here, we report the experimental observation of superconducting signature in trilayer nickelate La$_4$Ni$_3$O$_{10}$ under high pressures. By using a modified sol-gel method and post-annealing treatment under high oxygen pressure, we successfully obtained polycrystalline La$_4$Ni$_3$O$_{10}$ samples with different transport behaviors at ambient pressure. Then we performed high-pressure electrical resistance measurements on these samples in a diamond-anvil-cell (DAC) apparatus. Surprisingly, the signature of possible superconducting transition with a maximum transition temperature ($T_\text{c}$) of about 20 K under high pressures is observed, as evidenced by a clear drop of resistance and the suppression of resistance drops under magnetic fields. Although the resistance drop is sample-dependent and relatively small, it appears in all of our measured samples. We argue that the observed superconducting signal is most likely to originate from the main phase of La$_4$Ni$_3$O$_{10}$. Our findings will motivate the exploration of superconductivity in a broader family of nickelates and shed light on the understanding of the underlying mechanisms of high-$T_\text{c}$ superconductivity in nickelates.

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