Yi Liu

Zhejiang University of Technology

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Qiuyun Chen

Science and Technology on Surface Physics and Chemistry Laboratory

Xinchun Lai

Science and Technology on Surface Physics and Chemistry Laboratory

S. Y. Tan

Sun Yat-sen University

Xiegang Zhu

Science and Technology on Surface Physics and Chemistry Laboratory

Y. Zhang

Science and Technology on Surface Physics and Chemistry Laboratory

Dong Xie

Guangdong Academy of Sciences

Wei Feng

Science and Technology on Surface Physics and Chemistry Laboratory

Qunqing Hao

Science and Technology on Surface Physics and Chemistry Laboratory

Q. Liu

Science and Technology on Surface Physics and Chemistry Laboratory

Xingyu Ji

Science and Technology on Surface Physics and Chemistry Laboratory

Cooperative Institutions

Zhejiang University

Chinese Academy of Sciences

Science and Technology on Surface Physics and Chemistry Laboratory

University of Chinese Academy of Sciences

Tsinghua University

Zhejiang University of Technology

Institute of Physics

Sun Yat-sen University

Hangzhou Dianzi University

Fudan University

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STS MICCAI 2023 Challenge: Grand challenge on 2D and 3D semi-supervised tooth segmentation

arXiv (Cornell University) (2024)

Yaqi Wang Yifan Zhang Xiao-Diao Chen Shuai Wang Dahong Qian

Computer-aided design (CAD) tools are increasingly popular in modern dental practice, particularly for treatment planning or comprehensive prognosis evaluation. In particular, the 2D panoramic X-ray image efficiently detects invisible caries, impacted teeth and supernumerary teeth in children, while the 3D dental cone beam computed tomography (CBCT) is widely used in orthodontics and endodontics due to its low radiation dose. However, there is no open-access 2D public dataset for children's teeth and no open 3D dental CBCT dataset, which limits the development of automatic algorithms for segmenting teeth and analyzing diseases. The Semi-supervised Teeth Segmentation (STS) Challenge, a pioneering event in tooth segmentation, was held as a part of the MICCAI 2023 ToothFairy Workshop on the Alibaba Tianchi platform. This challenge aims to investigate effective semi-supervised tooth segmentation algorithms to advance the field of dentistry. In this challenge, we provide two modalities including the 2D panoramic X-ray images and the 3D CBCT tooth volumes. In Task 1, the goal was to segment tooth regions in panoramic X-ray images of both adult and pediatric teeth. Task 2 involved segmenting tooth sections using CBCT volumes. Limited labelled images with mostly unlabelled ones were provided in this challenge prompt using semi-supervised algorithms for training. In the preliminary round, the challenge received registration and result submission by 434 teams, with 64 advancing to the final round. This paper summarizes the diverse methods employed by the top-ranking teams in the STS MICCAI 2023 Challenge.

Grand Challenges

10.48550/arxiv.2407.13246

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CeCu₂Si₂ and YbRh₂Si₂: Strange Cases of Heavy-Fermion Superconductivity

Zhongyan Shan M. Smidman O. Stockert Yi Liu Huiqiu Yuan

The heavy-fermion superconductor CeCu$_{2}$Si$_{2}$ exhibits two-band, $d$-wave superconductivity with a finite energy gap over the whole Fermi surface around the magnetic instability where 4$f$ antiferrerromagnetic order is suppressed. In contrast, in YbRh$_{2}$Si$_{2}$ heavy-fermion superconductivity appears only when 4$f$-electronic antiferromagnetic order is replaced at ultra-low temperatures by a combined nuclear and 4$f$-spin order. Whereas both compounds exhibit different variants of antiferromagnetic instabilities, i.e., a spin-density-wave quantum critical point in CeCu$_{2}$Si$_{2}$ and one of "partial-Mott" type in YbRh$_{2}$Si$_{2}$, in both cases the Cooper pairing, as well as the pronounced "strange-metal" behavior in YbRh$_{2}$Si$_{2}$, appear to be driven by large-to-small Fermi surface fluctuations. The transport properties and scanning tunneling spectroscopy (STS) for these materials are dominated by single-ion Kondo scatterings down to very low temperatures. Further open problems of the Kondo lattice include both the interplay between superconductivity and antiferromagnetic order as well as the onset of lattice coherence. While microscopic coexistence of superconductivity and antiferromagnetism seems to require a sufficiently large staggered moment, the onset of lattice coherence in transport measurements and STS is associated solely with the crystal-field-doublet ground state, while it involves the fully degenerate Hund's rule multiplet in ARPES.

Heavy fermion superconductor

10.7566/jpscp.38.011020

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Crossover behavior of the localized to itinerant transition of 5f electrons in the antiferromagnetic Kondo lattice USb2

Physical review. B./Physical review. B (2021)

Wei Feng Dong Xie Xuebing Luo S. Y. Tan Yi Liu

In Uranium-based heavy fermion system, the 5f electrons display an intermediate character between partial localization and partial itinerancy, which makes the Kondo problem more complicated. Here we use scanning tunneling microscopy/spectroscopy to investigate the (001) surface of the Kondo lattice antiferromagnet USb2. Temperature-dependent dI/dV spectra from 4.7 K up to 140 K reveal several peak structures around the Fermi level. Two pronounced peaks are originated from the hybridization between the conduction and 5f electrons. We did not observe the mysteriously abrupt change of the electronic state at 45 K, which is previously reported by another STM group and attributed to a novel first-order like transition. Instead, we only observe continuous evolution of the dI/dV spectra with temperature. Furthermore, in some scanning regions, we find significant Sb atoms missing from the top layer, which gives us the opportunity to investigate the electronic structure of the U-terminated surface. For the U-terminated surface, an additional sharp peak emerges, which is closely related to the magnetic order.

10.1103/physrevb.104.235103

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Orbital-Selective Kondo Entanglement and Antiferromagnetic Order in USb2

Physical Review Letters (2019)

Qiuyun Chen Xuebing Luo Dong Xie M. L. Li Xiaoying Ji

In heavy-fermion compounds, the dual character of f electrons underlies their rich and often exotic properties like fragile heavy quasiparticles, a variety of magnetic orders and unconventional superconductivity. 5f-electron actinide materials provide a rich setting to elucidate the larger and outstanding issue of the competition between magnetic order and Kondo entanglement and, more generally, the interplay among different channels of interactions in correlated electron systems. Here, by using angle-resolved photoemission spectroscopy, we present the detailed electronic structure of USb_{2} and observe two different kinds of nearly flat bands in the antiferromagnetic state of USb_{2}. Polarization-dependent measurements show that these electronic states are derived from 5f orbitals with different characters; in addition, further temperature-dependent measurements reveal that one of them is driven by the Kondo correlations between the 5f electrons and conduction electrons, while the other reflects the dominant role of the magnetic order. Our results on the low-energy electronic excitations of USb_{2} implicate orbital selectivity as an important new ingredient for the competition between Kondo correlations and magnetic order and, by extension, in the rich landscape of quantum phases for strongly correlated f electron systems.

Strongly correlated material

Mott insulator

10.1103/physrevlett.123.106402

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Strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe ₂

Chinese Physics B (2018)

Wen Zhang Yi Liu Xiaoying Wang Yun Zhang Donghua Xie

10.1088/1674-1056/27/3/037501

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Griffiths phase-like exponents in the hidden-order state of URu2Si2

Journal of Magnetism and Magnetic Materials (2020)

Xingyu Ji Yun Zhang Xiaoying Wang Yi Liu

10.1016/j.jmmm.2020.167455

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Superconductivity modulated by structural phase transitions in pressurized vanadium-based kagome metals

Physical review. B./Physical review. B (2022)

Feng Du Rui Li Shuaishuai Luo Yu Gong Yanchun Li

The interplay of superconductivity with electronic and structural instabilities on the kagome lattice provides a fertile ground for emergent phenomena. The vanadium-based kagome metals $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ ($A=$ K, Rb, Cs) exhibit superconductivity on an almost ideal kagome lattice, with the superconducting transition temperature ${T}_{\mathrm{c}}$ forming two domes upon pressure tuning. The first dome arises from the competition between superconductivity and a charge-density wave, whereas the origin for the second dome remains unclear. Herein, we show that the appearance of the second superconducting dome in ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ and ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$ is associated with transitions from hexagonal to monoclinic structures, evidenced by the splitting of structural peaks from synchrotron powder x-ray diffraction experiments and imaginary phonon frequencies in first-principles calculations. In ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$, the transition to an orthorhombic structure is further observed for pressure $p\ensuremath{\gtrsim}20$ GPa, and is correlated with the strong suppression of ${T}_{\mathrm{c}}$ in the second superconducting dome. Our findings indicate that distortions of the crystal structure modulate superconductivity in $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ under pressure, providing a platform to study kagome lattice superconductivity in the presence of multiple electronic and structural instabilities.

Monoclinic crystal system

Orthorhombic crystal system

Lattice (music)

10.1103/physrevb.106.024516

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Inter-cation charge transfer mediated antiferromagnetism in Co1+xIr2−xS4

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

Liang-Wen Ji Siqi Wu Bai-Zhuo Li Wuzhang Yang Shijie Song

The antiferromagnetism in transition metal compounds is mostly mediated by the bridging anions through a so-called superexchange mechanism. However, in materials like normal spinels $AB_2X_4$ with local moments only at the $A$ site, such an anion-mediated superexchange needs to be modified. Here we report a new spinel compound Co$_{1+x}$Ir$_{2-x}$S$_4$ ($x$ = 0.3). The physical property measurements strongly suggest an antiferromagnetic-like transition at 292 K in the Co($A$) diamond sublattice. The first-principle calculations reveal that the nearest-neighbor Co($A$) spins align antiferromagnetically with an ordered magnetic moment of 1.67 $\mu_\mathrm{B}$, smaller than the expected $S = 3/2$ for Co$^{2+}$. In the antiferromagnetic state, there exists an inter-cation charge-transfer gap between the non-bonding Ir-$t_\mathrm{2g}$ orbitals at the valence band maximum and the Co-S antibonding molecular orbitals at the conduction band minimum. The small charge transfer energy significantly enhances the virtual hopping between these two states, facilitating a robust long-range superexchange interaction between two neighboring CoS$_4$ complexes, which accounts for the high N\'{e}el temperature in Co$_{1+x}$Ir$_{2-x}$S$_4$. This inter-cation charge transfer mediated magnetic interaction expands the traditional superexchange theory, which could be applicable in complex magnetic materials with multiple cations.

10.1103/physrevb.110.155139

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Structures and Physical Properties of Rare-Earth Zinc Antimonides Pr₆Zn_1+xSb_14+y and RE₆Zn_1+xSb₁₄ (RE = Sm, Gd−Ho)

Inorganic Chemistry (2008)

Yi Liu Ling Chen Long-Hua Li Li‐Ming Wu Oksana Ya. Zelinska

A new series of isostructural ternary rare-earth zinc antimonides RE(6)Zn(1+x)Sb(14+y) (RE = Pr, Sm, Gd-Ho) has been obtained by direct reaction of the elements at 1050-1100 degrees C. Single-crystal X-ray diffraction studies revealed that these compounds adopt an orthorhombic structure type (space group Immm (no. 71), Z = 2, a = 4.28-4.11 A, b = 15.15-14.73 A, c = 19.13-18.56 A in the progression from RE = Pr to Ho) that may be regarded as stuffed variants of a (U(0.5)Ho(0.5))(3)Sb(7)-type host structure. Columns of face-sharing RE(6) trigonal prisms, centered by Sb atoms, occupy channels defined by an extensive polyanionic Sb network. This network is constructed from three-atom-wide and four-atom-wide Sb strips, the latter being linked together by single Sb atoms in RE(6)Zn(1+x)Sb(14) (RE = Sm, Gd-Ho; y = 0), but also by additional Sb-Sb pairs in a disordered fashion in Pr(6)Zn(1+x)Sb(14+y) (y = approximately 0.6). Interstitial Zn atoms then partially fill tetrahedral sites (occupancy of 0.5-0.7) and, to a lesser extent, square pyramidal sites (occupancy of 0.04-0.12), accounting for the observed nonstoichiometry with variable x. Except for the Gd member, these compounds undergo antiferromagnetic ordering below T(N) < 9 K, with the magnetic susceptibilities of the Tb, Dy, and Ho members following the Curie-Weiss law above T(N). For the Ho member, the thermal conductivities are low and the Seebeck coefficients are small and positive, implying p-type character consistent with the occurrence of partial Zn occupancies. At low temperatures (down to 5 K), electrical resistivity measurements for the Tb, Dy, and Ho members indicated metallic behavior, which persists at high temperatures (up to 560 K) for the Ho member. Band structure calculations on an idealized "Gd(6)Zn(2)Sb(14)" model revealed the existence of a pseudogap near the Fermi level.

Isostructural

Orthorhombic crystal system

10.1021/ic800524d

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Quantitatively determining the degree of spin fluctuations in actinide metals and compounds

Journal of Physics Communications (2020)

Yi Liu Xingyu Ji Qifa Pan Yun Zhang Xiaoying Wang

Abstract Actinide materials are well-documented for nuclear properties, but their 5f electrons that produce exotic phenomena are not, due to the complexity of a dual localized and itinerant nature that remains a mystery. Particular interest is given to the electronic correlations at the localized and itinerant boundary where strong spin fluctuations are present. We report the identification of an intensity defined by integrating the normalized resistivity that approximately provides a quantitative measure of spin fluctuations. The intensity is very sensitive to the tuning of non-thermal parameters such as pressure and chemical doping, probing the anomalies in the evolution of spin fluctuations close to a valence or magnetic instability. In this way, our results are not only connected with the long-standing controversy on the anomalous low-temperature resistivity behavior of actinide metals, but also highlight an unconventional type of superconducting pairing, mediated by valence and/or spin fluctuations, for a wealth of 4f and 5f-electron systems. In an unified picture proposed, it is helpful to determine the degree of spin fluctuations for understanding the origin of the emergent superconductivity in systems with correlated electrons.

Valence electron

Thermal fluctuations

10.1088/2399-6528/abbcdd

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