Wenshan Hong

Peking University

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Shiliang Li

National Laboratory for Superconductivity

Huiqian Luo

Chinese Academy of Sciences

Hai‐Hu Wen

Nanjing University

Xingjiang Zhou

Chinese Academy of Sciences

Kailun Chen

Affiliated Hospital of Hangzhou Normal University

Qi Wu

Kiel University

Liling Sun

Chinese Academy of Sciences

Huan Yang

Nanjing University

Jinyu Han

Institute of Physics

Jing Guo

Institute of Physics

Cooperative Institutions

Chinese Academy of Sciences

119

Institute of Physics

University of Chinese Academy of Sciences

National Laboratory for Superconductivity

Czech Academy of Sciences, Institute of Physics

Songshan Lake Materials Laboratory

Peking University

Central South University

Collaborative Innovation Center of Advanced Microstructures

Technical Institute of Physics and Chemistry

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Deconfined quantum critical point lost in pressurized SrCu2(BO3)2

Communications Physics (2025)

Jing Guo Pengyu Wang Cheng Huang Bin-Bin Chen Wenshan Hong

Critical point (mathematics)

10.1038/s42005-025-01976-8

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Influences of quenching treatment and cobalt-doping on the thermally activated flux-flow behavior in KCa₂(Fe 1−x Co_x)₄As₄F₂

Superconductor Science and Technology (2023)

Yixin Liu Teng Wang Zulei Xu Wenshan Hong Wei Peng

Abstract Owing to the unique double-FeAs-layered structure between neighboring insulating layers, the 12442-type Fe-based superconductors are expected to host rich vortex phenomena in the mixed state. Here, we report a systematic investigation on the influences of quenching treatment and cobalt-doping on the magnetic vortex dynamics of KCa 2 (Fe 1 − x Co x ) 4 As 4 F 2 ( x = 0, 0.1) single crystals via electrical transport measurements. It is found that the slopes of the upper critical field near T c , d μ 0 H / d T | T c along both directions ( H ⊥ c and H ∥ c ), are doubled by the cobalt-doping with x = 0.1. The activation energy is acquired by analyzing the Arrhenius plots, which shows a H − α dependence with a change in the exponent α at around 3 T, indicating the evolution of the dominant pinning mechanisms in different field regions. Importantly, the quenching treatment obviously enhances the magnitude of activation energy and critical current density J c , which can be suppressed by the introduction of cobalt-doping. Possible mechanisms for such evolutions of these important parameters are discussed. Our results emphasize the important role of quenching treatment in enhancing the activation energy and critical current density in 12442 system.

10.1088/1361-6668/ace661

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The effect of non-superconducting dopants (Mn, V, Cr and Cu) on the nematic fluctuations in iron-based superconductors

arXiv (Cornell University) (2019)

Yanhong Gu Wei Yuan Dongliang Gong Wenliang Zhang Wenshan Hong

We have systematically studied the nematic susceptibility in non-superconducting Ba(Fe$_{1-x}$TM$_{x}$)$_2$As$_2$ (TM = Cr, Mn, V and Cu) by measuring the uniaxial pressure dependence of the resistivity along the Fe-As-Fe direction. The nematic susceptibilities in all samples show the Curie-Weiss-like behavior at high temperatures, where the nematic Curie constant $A_n$ can be derived, similar to the Curie constant in a paramagnetism. While all these dopants do not introduce superconductivity in BaFe$_2$As$_2$, their effects on nematic fluctuations are different. In Mn, Cr and V doped samples, $|A_n|$ decreases significantly with the increasing doping level. On the other hand, $|A_n|$ increases dramatically with Cu doping, similar to the superconducting Ni-doped BaFe$_2$As$_2$. However, the nematic susceptibility is suppressed at low temperatures for $x$ larger than $0.04$, which may be related to the short-range antiferromagnetic order that survives up to very high doping level. Doping Mn, Cr and Cu into the optimally-doped superconducting BaFe$_2$(As$_{0.69}$P$_{0.31}$)$_2$ also strongly reduces $|A_n|$. Compared with those systems that clearly exhibit superconductivity, such as Ni, K or P doped samples, our results suggest a strong connection between the nematic and spin degrees of freedom. Moreover, the reason of the suppression of superconductivity by dopants such as Cr, Mn, V and Cu may be correlated with the suppression of nematic fluctuations.

Iron-based superconductor

10.48550/arxiv.1905.03941

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Coevolution of superconductivity and Hall coefficient with anisotropic lattice shrinkage in compressed KCa₂Fe₄As₄F₂

Chinese Physics B (2024)

Jinyu Han Wenshan Hong Shu Cai Jinyu Zhao Jing Guo

Abstract The stability of superconductivity in superconductors is widely recognized to be determined by various factors, including charge, spin, orbit, lattice, and other related degrees of freedom. Here, we report our findings on the pressure-induced coevolution of superconductivity and Hall coefficient in KCa 2 Fe 4 As 4 F 2 , an iron-based superconductor possessing a hybrid crystal structure combining KFe 2 As 2 and CaFeAsF. Our investigation, involving high-pressure resistance, Hall effect and x-ray diffraction (XRD) measurements, allows us to observe the connection of the superconductivity and Hall coefficient with the anisotropic lattice shrinkage. We find that its ambient-pressure tetragonal (T) phase presents a collapse starting at around 18 GPa, where the sign of the Hall coefficient ( R H ) changes from positive to negative. Upon further compression, both superconducting transition temperature ( T c ) and R H exhibit a monotonous decrease. At around 41 GPa, the superconductivity is completely suppressed ( T c = 0), where the parameter a begins to decline again and the Hall coefficient remains nearly unchanged. Our experiment results clearly demonstrate that the pressure-induced anisotropic lattice collapse plays a crucial role in tuning the interplay among multiple degrees of freedom in the superconducting system and, correspondingly, the stability of the superconductivity.

Shrinkage

Lattice (music)

10.1088/1674-1056/ad4d65

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¹⁹F NMR Study of the Bilayer Iron-Based Superconductor KCa₂Fe₄As₄F₂ ^*

Chinese Physics Letters (2019)

Yuting Shao Wenshan Hong Shiliang Li Z. Li Jianlin Luo

We report a 19 F nuclear magnetic resonance (NMR) study on single-crystal KCa 2 Fe 4 As 4 F 2 ( T c ∼ 33.3 K). The 19 F NMR spectral shape of KCa 2 Fe 4 As 4 F 2 is weakly dependent on temperature and the Knight shift is small, which implies weak coupling between the CaF layer and the FeAs layer. The temperature dependence of 1/ 19 T 1 shows a hump below T c , however the 1/ 75 T 1 decreases just below T c , which implies that there are strong in-plane magnetic fluctuations in the CaF layers than in the FeAs layers. This may be caused by the motion of vortices. The absence of the coherence peak suggests unconventional superconductivity in KCa 2 Fe 4 As 4 F 2 .

Knight shift

Iron-based superconductor

10.1088/0256-307x/36/12/127401

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Proximate deconfined quantum critical point in SrCu ₂ ( BO ₃ ) ₂

Science (2023)

Yi Cui Lu Liu Huihang Lin Kai-Hsin Wu Wenshan Hong

The deconfined quantum critical point (DQCP) represents a paradigm shift in quantum matter studies, presenting a “beyond Landau” scenario for order-order transitions. Its experimental realization, however, has remained elusive. Using high-pressure 11 B nuclear magnetic resonance measurements on the quantum magnet SrCu 2 (BO 3 ) 2 , we here demonstrate a magnetic field–induced plaquette singlet to antiferromagnetic transition above 1.8 gigapascals at a notably low temperature, T c ≃ 0.07 kelvin. First-order signatures of the transition weaken with increasing pressure, and we observe quantum critical scaling at the highest pressure, 2.4 gigapascals. Supported by model calculations, we suggest that these observations can be explained by a proximate DQCP inducing critical quantum fluctuations and emergent O(3) symmetry of the order parameters. Our findings offer a concrete experimental platform for investigation of the DQCP.

10.1126/science.adc9487

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Scanning tunneling microscopy studies of the cuprate superconductor HgBa2Ca2Cu3O8+δ

Physical review. B./Physical review. B (2024)

Fan Zhang Xingyuan Hou Wenshan Hong Yubing Tu Tao Han

We report on scanning tunneling microscopy and spectroscopy studies of the slightly underdoped cuprate superconductor ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{8+\ensuremath{\delta}}$, which has an onset ${T}_{c}\ensuremath{\approx}120$ K. Disordered HgO-terminated surfaces were observed after sample cleaving in ultrahigh vacuum, revealing spatially inhomogeneous energy gaps with a low-lying $\mathsf{V}$-shaped structure and the ubiquitous mode features. Similar to Bi-family cuprate superconductors, vortex cores were identified by the suppression of superconducting coherence peaks and the emergence of in-gap features. Superconductivity near step edges is also strongly suppressed over several coherence lengths, forming an effective interface to the superconducting region, where the local spectra show a weak zero-bias conductance peak arising from the Andreev bound states. These results are expected from the widely believed $d$-wave nature in cuprates, demonstrating a platform for studying unconventional superconductivity.

10.1103/physrevb.109.085132

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The Hidden Nematic Fluctuations in the Triclinic (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 Superconductor Revealed by Ultrafast Optical Spectroscopy

arXiv (Cornell University) (2023)

Qi-Yi Wu Chen Zhang Ze-Zhong Li Wenshan Hong Hao Liu

We reported the quasiparticle relaxation dynamics of an optimally doped triclinic iron-based superconductor (Ca$_{0.85}$La$_{0.15}$)$_{10}$(Pt$_3$As$_8$)(Fe$_2$As$_2$)$_5$ with bulk $T_c$ = 30 K using polarized ultrafast optical pump-probe spectroscopy. Our results reveal anisotropic transient reflectivity induced by nematic fluctuations develops below $T_{nem}$ $\approx$ 120 K and persists in the superconducting states. Measurements under high pump fluence reveal three distinct, coherent phonon modes at frequencies of 1.6, 3.5, and 4.7 THz, corresponding to $A_{1g}(1)$, $E_g$, and $A_{1g}(2)$ modes, respectively. The high-frequency $A_{1g}(2)$ mode corresponds to the $c$-axis polarized vibrations of FeAs planes with a nominal electron-phonon coupling constant $\lambda _{A_{1g}(2)}$ $\approx$ 0.139 $\pm$ 0.02. Our findings suggest that the superconductivity and nematic state are compatible but competitive at low temperatures, and the $A_{1g}$ phonons play an important role in the formation of Cooper pairs in (Ca$_{0.85}$La$_{0.15}$)$_{10}$(Pt$_3$As$_8$)(Fe$_2$As$_2$)$_5$.

Triclinic crystal system

10.48550/arxiv.2305.18763

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Necklacelike Pattern of Vortex Bound States

Physical Review X (2025)

Zhiyong Hou Kailun Chen Wenshan Hong Da Wang Wen Shan Duan

A vortex is a topological defect in the superconducting condensate when a magnetic field is applied to a type-II superconductor, as elucidated by the Ginzburg-Landau theory. Because of the confinement of the quasiparticles by a vortex, it exhibits a circular-shaped pattern of bound states with discrete energy levels, as predicted by the Caroli–de Gennes–Matricon theory in 1964. Here, however, we report a completely new type of vortex pattern which is necklacelike in an iron-based superconductor KCa2Fe4As4F2. Our theoretical analysis shows that this necklacelike vortex pattern arises primarily from selective off-shell interference between vortex bound states of opposite angular momenta in the presence of rotational symmetry breaking due to disorders. This fascinating effect can be observed in a system with a small Fermi energy and wave vector, conditions fortuitously met in our samples. Our results not only disclose a novel vortex structure, but also unravel a completely new quantum phenomenon in the superconducting condensate. Published by the American Physical Society 2025

10.1103/physrevx.15.011027

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Growth and characterization of superconducting Ca_1–xNa_xFe₂As₂ single crystals by NaAs-flux method

Chinese Physics B (2022)

Honglin Zhou Yuhao Zhang Yang Li Shiliang Li Wenshan Hong

High-quality superconducting Ca 1− x Na x Fe 2 As 2 single crystals have been successfully grown by the NaAs-flux method, with sodium doping level x = 0.4–0.64. The typical sizes of these crystals are more than 10 mm in ab -plane and ∼ 0.1 mm along c -axis in thickness. X-ray diffraction, resistance and magnetization measurements are carried out to characterize the quality of these crystals. While no signature of magnetic phase transitions is detected in the normal state, bulk superconductivity is found for these samples, with a sharp transition at T c ranging from 19.8 K ( x = 0.4) to 34.8 K ( x = 0.64). The doping dependences of the c -axis parameter and T c are consistent with previous reports, suggesting a possible connection between the lattice parameters and superconductivity.

Flux method

Lattice constant

Lattice (music)

10.1088/1674-1056/ac834a

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Citations (4)