Showing 1–9 of 9 results for author: Zhen, X

Stochastic Similarity Renormalization Group

Authors: Rongzhe Hu, Xin Zhen, Furong Xu, Junchen Pei

Abstract: By integrating the quantum Monte Carlo technique into the similarity renormalization group (SRG), we have developed a stochastic SRG framework (SRGQMC) capable of both free-space two-body and in-medium many-body evolutions. This approach circumvents the combinatorial tensor-space explosion of many-body flow equations by mapping continuous unitary transformations onto an ensemble of signed random w… ▽ More By integrating the quantum Monte Carlo technique into the similarity renormalization group (SRG), we have developed a stochastic SRG framework (SRGQMC) capable of both free-space two-body and in-medium many-body evolutions. This approach circumvents the combinatorial tensor-space explosion of many-body flow equations by mapping continuous unitary transformations onto an ensemble of signed random walkers. We benchmark the SRGQMC against deterministic free-space SRG evolutions of realistic nucleon-nucleon (NN) interactions, as well as against in-medium SRG (IMSRG) many-body calculations with the Richardson pairing model at two- and three-body levels [IMSRG(2)/(3)]. While a deterministic extension to the four-body level [IMSRG(4)] remains unfeasible due to prohibitive computational costs, we have achieved the first IMSRG(4) calculation by using the stochastic technique, demonstrating a substantial improvement toward the full configuration-interaction limit. This stochastic framework provides a practical pathway to higher-order IMSRG calculations. △ Less

Submitted 9 July, 2026; originally announced July 2026.

Comments: 5 pages, 3 figures; with Supplemental Material

Coalescence of multiple topological orders in quasi-one-dimensional bismuth halide chains

Authors: Jingyuan Zhong, Ming Yang, Wenxuan Zhao, Kaiyi Zhai, Xuan Zhen, Lifu Zhang, Dan Mu, Yundan Liu, Zhijian Shi, Ningyan Cheng, Wei Zhou, Jianfeng Wang, Weichang Hao, Zhenpeng Hu, Jincheng Zhuang, Jinhu Lü, Yi Du

Abstract: Topology is being widely adopted to understand and to categorize quantum matter in modern physics. The nexus of topology orders, which engenders distinct quantum phases with benefits to both fundamental research and practical applications for future quantum devices, can be driven by topological phase transition through modulating intrinsic or extrinsic ordering parameters. The conjoined topology,… ▽ More Topology is being widely adopted to understand and to categorize quantum matter in modern physics. The nexus of topology orders, which engenders distinct quantum phases with benefits to both fundamental research and practical applications for future quantum devices, can be driven by topological phase transition through modulating intrinsic or extrinsic ordering parameters. The conjoined topology, however, is still elusive in experiments due to the lack of suitable material platforms. Here we use scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and theoretical calculations to investigate the doping-driven band structure evolution of a quasi-one-dimensional material system, bismuth halide, which contains rare multiple band inversions in two time-reversal-invariant momenta. According to the unique bulk-boundary correspondence in topological matter, we unveil a composite topological phase, the coexistence of a strong topological phase and a high-order topological phase, evoked by the band inversion associated with topological phase transition in this system. Moreover, we reveal multiple-stage topological phase transitions by varying the halide element ratio: from high-order topology to weak topology, the unusual dual topology, and trivial/weak topology subsequently. Our results not only realize an ideal material platform with composite topology, but also provide an insightful pathway to establish abundant topological phases in the framework of band inversion theory. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Journal ref: Nat Commun 16, 1163 (2025)

Fully-gapped superconductivity and topological aspects of the noncentrosymmetric TaReSi superconductor

Authors: T. Shang, J. Z. Zhao, Lun-Hui Hu, D. J. Gawryluk, X. Y. Zhu, H. Zhang, J. Meng, Z. X. Zhen, B. C. Yu, Z. Zhou, Y. Xu, Q. F. Zhan, E. Pomjakushina, T. Shiroka

Abstract: We report a study of the noncentrosymmetric TaReSi superconductor by means of muon-spin rotation and relaxation ($μ$SR) technique, complemented by electronic band-structure calculations. Its superconductivity, with $T_c$ = 5.5 K and upper critical field $μ_0H_\mathrm{c2}(0)$ $\sim$ 3.4 T, was characterized via electrical-resistivity- and magnetic-susceptibility measurements. The temperature-depend… ▽ More We report a study of the noncentrosymmetric TaReSi superconductor by means of muon-spin rotation and relaxation ($μ$SR) technique, complemented by electronic band-structure calculations. Its superconductivity, with $T_c$ = 5.5 K and upper critical field $μ_0H_\mathrm{c2}(0)$ $\sim$ 3.4 T, was characterized via electrical-resistivity- and magnetic-susceptibility measurements. The temperature-dependent superfluid density, obtained from transverse-field $μ$SR, suggests a fully-gapped superconducting state in TaReSi, with an energy gap $Δ_0$ = 0.79 meV and a magnetic penetration depth $λ_0$ = 562 nm. The absence of a spontaneous magnetization below $T_c$, as confirmed by zero-field $μ$SR, indicates a preserved time-reversal symmetry in the superconducting state. The density of states near the Fermi level is dominated by the Ta- and Re-5$d$ orbitals, which account for the relatively large band splitting due to the antisymmetric spin-orbit coupling. In its normal state, TaReSi behaves as a three-dimensional Kramers nodal-line semimetal, characterized by an hourglass-shaped dispersion protected by glide reflection. By combining non\-triv\-i\-al electronic bands with intrinsic superconductivity, TaReSi is a promising material for investigating the topological aspects of noncentrosymmetric superconductors. △ Less

Submitted 27 May, 2023; originally announced May 2023.

Comments: 9 pages, 9 figures; accepted by Phys. Rev. B

Journal ref: Phys. Rev. B 107, 224504 (2023)

Fully-gapped superconductivity with preserved time-reversal symmetry in NiBi$_3$ single crystals

Authors: T. Shang, J. Meng, X. Y. Zhu, H. Zhang, B. C. Yu, Z. X. Zhen, Y. H. Wang, Y. Xu, Q. F. Zhan, D. J. Gawryluk, T. Shiroka

Abstract: We report a study of NiBi$_3$ single crystals by means of electrical-resistivity-, magnetization-, and muon-spin rotation and relaxation ($μ$SR) measurements. As a single crystal, NiBi$_3$ adopts a needle-like shape and exhibits bulk superconductivity with $T_c \approx 4.1$ K. By applying magnetic fields parallel and perpendicular to the $b$-axis of NiBi$_3$, we establish that its lower- and upper… ▽ More We report a study of NiBi$_3$ single crystals by means of electrical-resistivity-, magnetization-, and muon-spin rotation and relaxation ($μ$SR) measurements. As a single crystal, NiBi$_3$ adopts a needle-like shape and exhibits bulk superconductivity with $T_c \approx 4.1$ K. By applying magnetic fields parallel and perpendicular to the $b$-axis of NiBi$_3$, we establish that its lower- and upper critical fields, as well as the magnetic penetration depths show slightly different values, suggesting a weakly anisotropic superconductivity. In both cases, the zero-temperature upper critical fields are much smaller than the Pauli-limit value, indicating that the superconducting state is constrained by the orbital pair breaking. The temperature evolution of the superfluid density, obtained from transverse-field $μ$SR, reveals a fully-gapped superconductivity in NiBi$_3$, with a shared superconducting gap $Δ_0$ = 2.1 $k_\mathrm{B}$$T_c$ and magnetic penetration depths $λ_0$ = 223 and 210 nm for $H \parallel b$- and $H \perp b$, respectively. The lack of spontaneous fields below $T_c$ indicates that time-reversal symmetry is preserved in NiBi$_3$. The absence of a fast muon-spin relaxation and/or precession in the zero-field $μ$SR spectra definitely rules out any type of magnetic ordering in NiBi$_3$ single crystals. Overall, our investigation suggests that NiBi$_3$ behaves as a conventional $s$-type superconductor. △ Less

Submitted 5 May, 2023; originally announced May 2023.

Comments: 8 pages, 8 figures, accepted by Phys. Rev. B

Journal ref: Phys. Rev. B 107, 174513 (2023)

Evidence of unconventional pairing in the quasi two-dimensional CuIr$_2$Te$_4$ superconductor

Authors: T. Shang, Y. Chen, W. Xie, D. J. Gawryluk, R. Gupta, R. Khasanov, X. Y. Zhu, H. Zhang, Z. X. Zhen, B. C. Yu, Z. Zhou, Y. Xu, Q. F. Zhan, E. Pomjakushina, H. Q. Yuan, T. Shiroka

Abstract: The CuIr$_{2-x}$Ru$_x$Te$_4$ superconductors (with a $T_c$ around 2.8 K) can host charge-density waves, whose onset and interplay with superconductivity are not well known at a microscopic level. Here, we report a comprehensive study of the $x$ = 0 and 0.05 cases, whose superconductivity was characterized via electrical-resistivity-, magnetization-, and heat-capacity measurements, while their micr… ▽ More The CuIr$_{2-x}$Ru$_x$Te$_4$ superconductors (with a $T_c$ around 2.8 K) can host charge-density waves, whose onset and interplay with superconductivity are not well known at a microscopic level. Here, we report a comprehensive study of the $x$ = 0 and 0.05 cases, whose superconductivity was characterized via electrical-resistivity-, magnetization-, and heat-capacity measurements, while their microscopic superconducting properties were studied via muon-spin rotation and relaxation ($μ$SR). In CuIr$_{2-x}$Ru$_x$Te$_4$, both the temperature-dependent electronic specific heat and the superfluid density (determined via transverse-field $μ$SR) are best described by a two-gap (s+d)-wave model, comprising a nodeless gap and a gap with nodes. The multigap superconductivity is also supported by the temperature dependence of the upper critical field $H_\mathrm{c2}(T)$. However, under applied pressure, a charge-density-wave order starts to develop and, as a consequence, the superconductivity of CuIr$_2$Te$_4$ achieves a more conventional s-wave character. From a series of experiments, we provide ample evidence that the CuIr$_{2-x}$Ru$_x$Te$_4$ family belongs to the rare cases, where an unconventional superconducting pairing is found near a charge-density-wave quantum critical point. △ Less

Submitted 13 October, 2022; originally announced October 2022.

Comments: 10 pages, 12 figures

Journal ref: Phys. Rev. B 106, 144505 (2022)

Fully-gapped superconducting state in interstitial-carbon-doped Zr5Pt3

Authors: T. Shang, J. Philippe, X. Y. Zhu, H. Zhang, B. C. Yu, Z. X. Zhen, H. -R. Ott, J. Kitagawa, T. Shiroka

Abstract: We report a comprehensive study of the Zr$_5$Pt$_3$C$_x$ superconductors, with interstitial carbon comprised between 0 and 0.3. At a macroscopic level, their superconductivity, with $T_c$ ranging from 4.5 to 6.3 K, was investigated via electrical-resistivity-, magnetic-susceptibility-, and specific-heat measurements. The upper critical fields $μ_0H_\mathrm{c2}$ $\sim$ 7 T were determined mostly fr… ▽ More We report a comprehensive study of the Zr$_5$Pt$_3$C$_x$ superconductors, with interstitial carbon comprised between 0 and 0.3. At a macroscopic level, their superconductivity, with $T_c$ ranging from 4.5 to 6.3 K, was investigated via electrical-resistivity-, magnetic-susceptibility-, and specific-heat measurements. The upper critical fields $μ_0H_\mathrm{c2}$ $\sim$ 7 T were determined mostly from measurements of the electrical resistivity in applied magnetic fields. The microscopic electronic properties were investigated by means of muon-spin rotation and relaxation ($μ$SR) and nuclear magnetic resonance (NMR) techniques. In the normal state, NMR relaxation data indicate an almost ideal metallic behavior, confirmed by band-structure calculations, which suggest a relatively high electronic density of states at the Fermi level, dominated by the Zr 4$d$ orbitals. The low-temperature superfluid density, obtained via transverse-field $μ$SR, suggests a fully-gapped superconducting state in Zr$_5$Pt$_3$ and Zr$_5$Pt$_3$C$_{0.3}$, with a zero-temperature gap $Δ_0$ = 1.20 and 0.60 meV and a magnetic penetration depth $λ_0$ = 333 and 493 nm, respectively. The exponential dependence of the NMR relaxation rates below $T_c$ further supports a nodeless superconductivity. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined from zero-field $μ$SR measurements, confirms a preserved time-reversal symmetry in the superconducting state of Zr$_5$Pt$_3$C$_x$. In contrast to a previous study, our $μ$SR and NMR results suggest a conventional superconductivity in the Zr$_5$Pt$_3$C$_x$ family, independent of the C content. △ Less

Submitted 30 June, 2022; originally announced July 2022.

Comments: 9 pages, 11 figures, accepted by Phys. Rev. B

Journal ref: Phys. Rev. B 106, 014507 (2022)

Emerging negative Poisson's ratio driven by strong intralayer interaction response in rectangular transition metal chalcogenides

Authors: Linfeng Yu, Yancong Wang, Xiong Zhen, Huiming Wang, Zhenzhen Qin, Guangzhao Qin

Abstract: Auxetic behavior quantified by the negative Poisson's ratio (NPR) is commonly attributed to geometry evolution with re-entrant mechanism or other mechanical factors, which is thought to be independent of electronic structures. Thus, searching for electronic effect dominated auxetic behavior is challenging. Herein, from state-of-the-art first-principles calculations, by studying a class of two-dime… ▽ More Auxetic behavior quantified by the negative Poisson's ratio (NPR) is commonly attributed to geometry evolution with re-entrant mechanism or other mechanical factors, which is thought to be independent of electronic structures. Thus, searching for electronic effect dominated auxetic behavior is challenging. Herein, from state-of-the-art first-principles calculations, by studying a class of two-dimensional (2D) transition metal chalcogenides (TMCs), namely X2Y2-type (X=Cu, Ag, Au; Y=O, S, Se) rectangular TMCs (R-TMCs), we identify that the monolayer R-Cu2Se2 unconventionally demonstrates a structure-independent anisotropic NPR. In contrast, the NPR is absent in other R-TMCs. The emerging NPR is attributed to the strong strain response of intralayer interaction in R-Cu2Se2, which can be traced to the lone pair electrons and weak electronegativity of Se atoms under multi-orbital hybridization. The emerging NPR would make R-Cu2Se2 a promising candidate in electronics protection, and our study would provide valuable clues and useful guidance for designing advanced auxetic materials. △ Less

Submitted 16 April, 2022; v1 submitted 3 February, 2022; originally announced February 2022.

Spin order and fluctuations in the EuAl$_4$ and EuGa$_4$ topological antiferromagnets: A $μ$SR study

Authors: X. Y. Zhu, H. Zhang, D. J. Gawryluk, Z. X. Zhen, B. C. Yu, S. L. Ju, W. Xie, D. M. Jiang, W. J. Cheng, Y. Xu, M. Shi, E. Pomjakushina, Q. F. Zhan, T. Shiroka, T. Shang

Abstract: We report on systematic muon-spin rotation and relaxation ($μ$SR) studies of the magnetic properties of EuAl$_4$ and EuGa$_4$ single crystals at a microscopic level. Transverse-field $μ$SR measurements, spanning a wide temperature range (from 1.5 to 50 K), show clear bulk AFM transitions, with an almost 100% magnetic volume fraction in both cases. Zero-field $μ$SR measurements, covering both the A… ▽ More We report on systematic muon-spin rotation and relaxation ($μ$SR) studies of the magnetic properties of EuAl$_4$ and EuGa$_4$ single crystals at a microscopic level. Transverse-field $μ$SR measurements, spanning a wide temperature range (from 1.5 to 50 K), show clear bulk AFM transitions, with an almost 100% magnetic volume fraction in both cases. Zero-field $μ$SR measurements, covering both the AFM and the paramagnetic (PM) states, reveal internal magnetic fields $B_\mathrm{int}(0) = 0.33$ T and 0.89 T in EuAl$_4$ and EuGa$_4$, respectively. The transverse muon-spin relaxation rate $λ_\mathrm{T}$, a measure of the internal field distribution at the muon-stopping site, shows a contrasting behavior. In EuGa$_4$, it decreases with lowering the temperature, reaching its minimum at zero temperature, $λ_\mathrm{T}(0) = 0.71$ $μ$s$^{-1}$. In EuAl$_4$, it increases significantly below $T_\mathrm{N}$, to reach 58 $μ$s$^{-1}$ at 1.5 K, most likely reflecting the complex magnetic structure and the competing interactions in the AFM state of EuAl$_4$. In both compounds, the temperature-dependent longitudinal muon-spin relaxation $λ_\mathrm{L}(T)$, an indication of the rate of spin fluctuations, diverges near the onset of AFM order, followed by a significant drop at $T < T_\mathrm{N}$. In the AFM state, spin fluctuations are much stronger in EuAl$_4$ than in EuGa$_4$, while being comparable in the PM state. The evidence of robust spin fluctuations against the external magnetic fields provided by $μ$SR may offer new insights into the origin of the topological Hall effect and the possible magnetic skyrmions in the EuAl$_4$ and EuGa$_4$ compounds. △ Less

Submitted 6 January, 2022; originally announced January 2022.

Comments: 10 pages, 7 figures, accepted by Phys. Rev. B

Journal ref: Phys. Rev. B 105, 014423 (2022)

Lateral modulation of magnetic anisotropy in tricolor 3d-5d oxide superlattices

Authors: Zengxing Lu, Jingwu Liu, Lijie Wen, Jiatai Feng, Shuai Kong, Xuan Zhen, Sheng Li, Peiheng Jiang, Zhicheng Zhong, Junfa Zhu, Xianfeng Hao, Zhiming Wang, Run-Wei Li

Abstract: Manipulating magnetic anisotropy (MA) purposefully in transition metal oxides (TMOs) enables the development of oxide-based spintronic devices with practical applications. Here, we report a pathway to reversibly switch the lateral magnetic easy-axis via interfacial oxygen octahedral coupling (OOC) effects in 3d-5d tricolor superlattices, i.e. [SrIrO3,mRTiO3,SrIrO3,2La0.67Sr0.33MnO3]10 (RTiO3: SrTi… ▽ More Manipulating magnetic anisotropy (MA) purposefully in transition metal oxides (TMOs) enables the development of oxide-based spintronic devices with practical applications. Here, we report a pathway to reversibly switch the lateral magnetic easy-axis via interfacial oxygen octahedral coupling (OOC) effects in 3d-5d tricolor superlattices, i.e. [SrIrO3,mRTiO3,SrIrO3,2La0.67Sr0.33MnO3]10 (RTiO3: SrTiO3 and CaTiO3). In the heterostructures, the anisotropy energy (MAE) is enhanced over one magnitude to ~106 erg/cm3 compared to La0.67Sr0.33MnO3 films. Moreover, the magnetic easy-axis is reversibly reoriented between (100)- and (110)-directions by changing the RTiO3. Using first-principles density functional theory calculations, we find that the SrIrO3 owns a large single-ion anisotropy due to its strong spin-orbit interaction. This anisotropy can be reversibly controlled by the OOC, then reorient the easy-axis of the superlattices. Additionally, it enlarges the MAE of the films via the cooperation with a robust orbital hybridization between the Ir and Mn atoms. Our results indicate that the tricolor superlattices consisting of 3d and 5d oxides provide a powerful platform to study the MA and develop oxide-based spintronic devices. △ Less

Submitted 5 September, 2021; originally announced September 2021.

Journal ref: ACS Applied Electronic Materials 3, 4210 (2021)