Showing 1–50 of 86 results for author: Jia, W

Control of Extraordinary Optical Transmission in Resonant Terahertz Gratings via Lateral Depletion in an AlGaN-GaN Heterostructure

Authors: Geofrey Nyabere, Hunter Ellis, Miguel Gomez, Wei Jia, Yizheng Liu, Karli Ann Higley, Sriram Krishnamoorthy, Steve Blair, Kai Fu, Berardi Sensale-Rodriguez

Abstract: Periodic metallic gratings on substrates can support a range of electromagnetic modes, such as leaky waveguide, guided-resonant, and Fabry-Perot (FP) cavity modes, which can strongly modulate optical transmission under resonant excitation. Here, we investigate how this coupling can be dynamically manipulated through charge-density control in a laterally patterned AlGaN/GaN heterostructure. The str… ▽ More Periodic metallic gratings on substrates can support a range of electromagnetic modes, such as leaky waveguide, guided-resonant, and Fabry-Perot (FP) cavity modes, which can strongly modulate optical transmission under resonant excitation. Here, we investigate how this coupling can be dynamically manipulated through charge-density control in a laterally patterned AlGaN/GaN heterostructure. The structure comprises metallic stripes separated by regions containing a two-dimensional electron gas (2DEG), forming a periodically modulated interface whose electromagnetic response is governed by the charge density between the stripes. In the unbiased state, the conductive 2DEG screens the incident terahertz field and suppresses excitation of guided modes. When the 2DEG is depleted, the change in boundary conditions allows efficient coupling into substrate resonances, producing a strong modulation at particular frequencies where extraordinary optical transmission (EOT) through the structure takes place. The results highlight the sensitive dependence of guided-mode-resonance (GMR) mediated EOT on inter-stripe charge distribution and demonstrate a direct interplay between carrier dynamics and resonant electromagnetic phenomena in the terahertz regime. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 12 pages, 4 figures

Spatial organization of biomass controls intrinsic permeability of porous systems

Authors: Wenqiao Jiao, David Scheidweiler, Nolwenn Delouche, Alberto Guadagnini, Pietro de Anna

Abstract: Biofilms in porous media critically influence hydraulic properties in environmental and engineered systems. However, a mechanistic understanding of how microbial life controls permeability remains elusive. By combining microfluidics, controlled pressure gradient and time-lapse microscopy, we quantify how motile and non-motile bacteria colonize a porous landscape and alter its resistance to flow. W… ▽ More Biofilms in porous media critically influence hydraulic properties in environmental and engineered systems. However, a mechanistic understanding of how microbial life controls permeability remains elusive. By combining microfluidics, controlled pressure gradient and time-lapse microscopy, we quantify how motile and non-motile bacteria colonize a porous landscape and alter its resistance to flow. We find that while both strains achieve nearly identical total biomass, they cause drastically different permeability reductions - 78% for motile cells versus 94% for non-motile cells. This divergence stems from motility, which limits biomass spatial accumulation, whereas non-motile cells clog the entire system. We develop a mechanistic model that accurately predicts permeability dynamics from the pore-scale biomass distribution. We conclude that the spatial organization of biomass, not its total amount, is the primary factor controlling permeability. △ Less

Submitted 31 October, 2025; originally announced October 2025.

Probing the Critical Point (CritPt) of AI Reasoning: a Frontier Physics Research Benchmark

Authors: Minhui Zhu, Minyang Tian, Xiaocheng Yang, Tianci Zhou, Lifan Yuan, Penghao Zhu, Eli Chertkov, Shengyan Liu, Yufeng Du, Ziming Ji, Indranil Das, Junyi Cao, Yufeng Du, Jiabin Yu, Peixue Wu, Jinchen He, Yifan Su, Yikun Jiang, Yujie Zhang, Chang Liu, Ze-Min Huang, Weizhen Jia, Yunkai Wang, Farshid Jafarpour, Yong Zhao , et al. (39 additional authors not shown)

Abstract: While large language models (LLMs) with reasoning capabilities are progressing rapidly on high-school math competitions and coding, can they reason effectively through complex, open-ended challenges found in frontier physics research? And crucially, what kinds of reasoning tasks do physicists want LLMs to assist with? To address these questions, we present the CritPt (Complex Research using Integr… ▽ More While large language models (LLMs) with reasoning capabilities are progressing rapidly on high-school math competitions and coding, can they reason effectively through complex, open-ended challenges found in frontier physics research? And crucially, what kinds of reasoning tasks do physicists want LLMs to assist with? To address these questions, we present the CritPt (Complex Research using Integrated Thinking - Physics Test, pronounced "critical point"), the first benchmark designed to test LLMs on unpublished, research-level reasoning tasks that broadly covers modern physics research areas, including condensed matter, quantum physics, atomic, molecular & optical physics, astrophysics, high energy physics, mathematical physics, statistical physics, nuclear physics, nonlinear dynamics, fluid dynamics and biophysics. CritPt consists of 71 composite research challenges designed to simulate full-scale research projects at the entry level, which are also decomposed to 190 simpler checkpoint tasks for more fine-grained insights. All problems are newly created by 50+ active physics researchers based on their own research. Every problem is hand-curated to admit a guess-resistant and machine-verifiable answer and is evaluated by an automated grading pipeline heavily customized for advanced physics-specific output formats. We find that while current state-of-the-art LLMs show early promise on isolated checkpoints, they remain far from being able to reliably solve full research-scale challenges: the best average accuracy among base models is only 5.7%, achieved by GPT-5 (high), moderately rising to around 10% when equipped with coding tools. Through the realistic yet standardized evaluation offered by CritPt, we highlight a large disconnect between current model capabilities and realistic physics research demands, offering a foundation to guide the development of scientifically grounded AI tools. △ Less

Submitted 20 November, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: 39 pages, 6 figures, 6 tables

Oscillating bound states in waveguide-QED system with two giant atoms

Authors: F. J. Lü, W. Z. Jia

Abstract: We study the bound states in the continuum (BIC) in a system of two identical two-level giant atoms coupled to a one-dimensional waveguide. By deriving general dark-state conditions, we clarify how coupling configurations and atomic parameters influence decay suppression. Through analysis of the long-time dynamical behaviors of atoms and bound photons, we carry out a detailed classification of bou… ▽ More We study the bound states in the continuum (BIC) in a system of two identical two-level giant atoms coupled to a one-dimensional waveguide. By deriving general dark-state conditions, we clarify how coupling configurations and atomic parameters influence decay suppression. Through analysis of the long-time dynamical behaviors of atoms and bound photons, we carry out a detailed classification of bound states and explore the connections between these dynamical behaviors and the system's intrinsic light-matter interactions. The system supports static bound states with persistent atomic excitations, and oscillating bound states with periodic atom-photon or atom-atom excitation exchange. Under certain conditions, oscillating bound states can contain more harmonic components owing to the emergence of additional quasi-dark modes, rendering them promising platforms for high-capacity quantum information processing. These findings advance the understanding of BIC in waveguide quantum electrodynamics with multiple giant atoms and reveal their prospective applications in quantum technologies. △ Less

Submitted 12 August, 2025; originally announced August 2025.

Comments: 21 pages, 9 figures

Unconventional hybrid-order topological insulators

Authors: Wei Jia, Yuping Tian, Huanhuan Yang, Xiangru Kong, Zhi-Hao Huang, Wei-Jiang Gong, Jun-Hong An

Abstract: Exploring novel topological matters with exotic quantum states has always been a core issue in the field of condensed matter physics, which can update the understanding of topological phases and broaden the classification of topological materials. Here, we report a class of unconventional hybrid-order topological insulators (HyOTIs), which simultaneously host various different higher-order topolog… ▽ More Exploring novel topological matters with exotic quantum states has always been a core issue in the field of condensed matter physics, which can update the understanding of topological phases and broaden the classification of topological materials. Here, we report a class of unconventional hybrid-order topological insulators (HyOTIs), which simultaneously host various different higher-order topological states in a single band gap. Such topological states exhibit a unique bulk-boundary correspondence that is different from the well-known first-order topological states, higher-order topological states, and the coexistence of both. Particularly, we develop a generic surface theory to precisely capture them and discover a three-dimensional unconventional HyOTI protected by inversion symmetry, which renders both helical and corner topological states and exhibits an unprecedented bulk-edge-corner correspondence. By adjusting the parameters of the system, we also observe the nontrivial phase transitions between the inversion-symmetric HyOTI and other conventional phases. We further propose a circuit-based experimental scheme to detect these interesting results. Remarkably, we demonstrate that a modified tight-binding model of bismuth can support the unconventional HyOTI, suggesting a possible route for its material realization. This work shall significantly advance the research of hybrid topological states in both theory and experiment. △ Less

Submitted 6 December, 2025; v1 submitted 30 July, 2025; originally announced July 2025.

Comments: 7+7 pages, 4+4 figures

Journal ref: Phys. Rev. B 112, L241103 (2025)

In-Plane Magnetic Anisotropy and Large topological Hall Effect in Self-Intercalated Ferromagnet Cr1.61Te2

Authors: Yalei Huang, Na Zuo, Zheyi Zhang, Xiangzhuo Xing, Xinyu Yao, Anlei Zhang, Haowei Ma, Chunqiang Xu, Wenhe Jiao, Wei Zhou, Raman Sankar, Dong Qian, Xiaofeng Xu

Abstract: Self-intercalated chromium tellurides Cr1+xTe2 have garnered growing attention due to their high-temperature ferromagnetism, tunable spin structures and air stability, all of which are vital for versatile applications in next-generation memory and information technology. Here, we report strong magnetic anisotropy and a large topological Hall effect (THE) in self-intercalated Cr1.61Te2 single cryst… ▽ More Self-intercalated chromium tellurides Cr1+xTe2 have garnered growing attention due to their high-temperature ferromagnetism, tunable spin structures and air stability, all of which are vital for versatile applications in next-generation memory and information technology. Here, we report strong magnetic anisotropy and a large topological Hall effect (THE) in self-intercalated Cr1.61Te2 single crystals, which are both highly desirable properties for future spintronic applications. Our results demonstrate that Cr1.61Te2 is a soft ferromagnet with strong in-plane magnetic anisotropy. Remarkably, distinct THE behaviors are observed in different temperature regimes, reflecting the intricate spin structures and competing exchange interactions. More interestingly, a large topological Hall resistivity, induced by microscopic non-coplanar spin structures, emerges in the temperature range 70-240 K, reaching a maximum value of 0.93 μΩ cm at 150 K. Moreover, a sign-reversed and weak THE is observed at low temperatures below ~70 K, indicating the emergence of an additional topological spin structure with opposite topological charges. This work not only offers valuable insights into the correlation between magnetocrystalline anisotropy and topological phenomena in Cr1+xTe2 systems, but also provides a robust platform for engineering the evolution of complex spin textures that can be leveraged in diverse spintronic device applications. △ Less

Submitted 30 July, 2025; originally announced July 2025.

Comments: 5 figures, 1 table

Journal ref: Adv. Funct. Mater. 2025, e10351

Torsional Hall Viscosity of Massive Chern Insulators: Magnetic Field and Momentum Deformations

Authors: Ioannis Matthaiakakis, Weizhen Jia, Raffael L. Klees, David Rodríguez Fernández, Zhuo-Yu Xian, René Meyer, Johanna Erdmenger, Ewelina M. Hankiewicz

Abstract: This work focuses on the non-dissipative, parity-odd spin transport of (2 + 1)-dimensional relativistic electrons, generated by torsion, and the torsional Hall viscosity $ζ_{\mathrm{H}}$. We first determine $ζ_{\mathrm{H}}$ for massive Dirac fermions in the presence of a constant electromagnetic field. We predict that the magnetic field induces a contribution to $ζ_{\mathrm{H}}$ competing with the… ▽ More This work focuses on the non-dissipative, parity-odd spin transport of (2 + 1)-dimensional relativistic electrons, generated by torsion, and the torsional Hall viscosity $ζ_{\mathrm{H}}$. We first determine $ζ_{\mathrm{H}}$ for massive Dirac fermions in the presence of a constant electromagnetic field. We predict that the magnetic field induces a contribution to $ζ_{\mathrm{H}}$ competing with the one originating from the Dirac mass. Moreover, we quantify the impact on $ζ_{\mathrm{H}}$ originating from the band structure deformation quadratic in momentum terms that was proposed by Bernevig-Hughes-Zhang (BHZ). We find that the BHZ deformation enhances $ζ_{\mathrm{H}}$ in magnitude, but reverses its sign as compared to the standard massive Dirac fermion, indicating a Hall response in opposite direction to the typical Hall viscous force. Nevertheless, the torsional Hall viscosity still discriminates between topologically trivial and non-trivial regimes. Our results, hence, pave the way for a deeper understanding of hydrodynamic spin transport and its possible verification in experiments. △ Less

Submitted 17 April, 2025; originally announced April 2025.

Comments: 14+6pages, 5 figures

Multiple topological corner states in the continuum of extended kagome lattice

Authors: Shun-Peng Zhang, Ming-Jian Gao, Wei Jia, Jun-Hong An

Abstract: The kagome lattice is renowned for its exotic electronic properties, such as flat bands, Dirac points, and Van Hove singularities. These features have provided a fertile ground for exploring exotic quantum phenomena. Here, we discover that a breathing kagome lattice with long-range hoppings can host multiple zero-energy corner states, which emerge as topologically protected bound states in the con… ▽ More The kagome lattice is renowned for its exotic electronic properties, such as flat bands, Dirac points, and Van Hove singularities. These features have provided a fertile ground for exploring exotic quantum phenomena. Here, we discover that a breathing kagome lattice with long-range hoppings can host multiple zero-energy corner states, which emerge as topologically protected bound states in the continuum (BICs). This result demonstrates that additional hopping control can induce further non-trivial physics of the kagome lattice. Since the zero-energy corner states in the continuum are intertwined with a substantial number of zero-energy bulk states, we also develop a momentum-space topological characterization theory to precisely quantify the number of corner states, revealing a general bulk-corner correspondence. Furthermore, we uncover three distinct types of topological phase transitions (TPTs) for the BICs driven by shifts in the spatial localization of zero-energy bulk and/or edge states. These TPTs are exactly captured by our characterization theory. This work provides deep insights into the topological physics of the kagome lattice and broadens the understanding of its electronic properties △ Less

Submitted 18 September, 2025; v1 submitted 1 April, 2025; originally announced April 2025.

Comments: 8+6 pages,4+1 figures

Journal ref: Phys. Rev. B 112, L121106 (2025)

Opening and closing a bandgap via alternating softening and hardening nonlinearities

Authors: Weijian Jiao

Abstract: Recent studies have shown some unusual nonlinear dispersion behaviors that are disconnected from the linear regime. However, existing analytical techniques, such as perturbation methods, fail to correctly capture these behaviors. Here we propose a general theoretical approach that converts the nonlinear wave equation to an equivalent linear eigenvalue problem, which directly gives the nonlinear di… ▽ More Recent studies have shown some unusual nonlinear dispersion behaviors that are disconnected from the linear regime. However, existing analytical techniques, such as perturbation methods, fail to correctly capture these behaviors. Here we propose a general theoretical approach that converts the nonlinear wave equation to an equivalent linear eigenvalue problem, which directly gives the nonlinear dispersion relation and modal vectors. The theoretical approach is employed to 1D phononic chains and 2D hexagonal lattices with alternating softening and hardening nonlinearities, revealing amplitude-induced bandgap opening and closing phenomena. The theoretical results are validated via full-scale simulations with periodic boundary conditions, in which steady-state nonlinear plane wave responses are numerically obtained. Moreover, we leverage these nonlinear phenomena to achieve tunable frequency splitting and focusing effects. Thus, our work opens new paradigms for understanding nonlinear wave physics and for achieving novel wave control capabilities. △ Less

Submitted 20 March, 2025; originally announced March 2025.

Degradation of 2.4-kV $Ga_{2}O_{3}$ Schottky Barrier Diode at High Temperatures up to 500 °C

Authors: Hunter Ellis, Wei Jia, Imteaz Rahaman, Apostoli Hillas, Botong Li, Michael A. Scarpulla, Berardi Sensale Rodriguez, Kai Fu

Abstract: Ga2O3 Schottky barrier diodes featuring a field plate and a composite SiO2/SiNx dielectric layer beneath the field plate were fabricated, achieving a breakdown voltage of 2.4 kV at room temperature. Electrical performance and degradation were analyzed via I-V and C-V measurements from 25 °C to 500 °C, revealing temperature-dependent transport, interface stability, and device stability. Upon return… ▽ More Ga2O3 Schottky barrier diodes featuring a field plate and a composite SiO2/SiNx dielectric layer beneath the field plate were fabricated, achieving a breakdown voltage of 2.4 kV at room temperature. Electrical performance and degradation were analyzed via I-V and C-V measurements from 25 °C to 500 °C, revealing temperature-dependent transport, interface stability, and device stability. Upon returning to room temperature, the diodes exhibited nearly unchanged forward characteristics, while the breakdown voltage declined significantly from 2.4 kV to 700 V. This behavior indicates a temperature-induced reduction in the barrier height. Detailed analysis revealed that variable range hopping (VRH) dominated the leakage mechanism at moderate temperatures, while thermal emission (TE) became increasingly significant at temperatures exceeding 400 °C. △ Less

Submitted 18 March, 2025; originally announced March 2025.

Comments: 7 Pages, 9 Figures

Pressure-driven superconductivity in the topological insulator GeBi4Te7

Authors: Yalei Huang, Na Zuo, Zheyi Zhang, Chunqiang Xu, Xiangzhuo Xing, Wen-He Jiao, Bin Li, Wei Zhou, Xiaobing Liu, Dong Qian, Xiaofeng Xu

Abstract: The van der Waals, pseudo-binary chalcogenides (ACh)m(Pn2Ch3)n (A = Ge, Mn, Pb, etc.; Pn = Sb or Bi; Ch = Te, Se) have recently been reported to host a vast landscape of topological phases of matter, including the quantum anomalous Hall state and topological axion state with quantized magnetoelectric effect. A subgroup in this series, like MnSb4Te7 and GeSb4Te7, can be driven to a superconducting… ▽ More The van der Waals, pseudo-binary chalcogenides (ACh)m(Pn2Ch3)n (A = Ge, Mn, Pb, etc.; Pn = Sb or Bi; Ch = Te, Se) have recently been reported to host a vast landscape of topological phases of matter, including the quantum anomalous Hall state and topological axion state with quantized magnetoelectric effect. A subgroup in this series, like MnSb4Te7 and GeSb4Te7, can be driven to a superconducting state by applying a physical pressure, making them viable candidates to realize so-called topological superconductivity. However, the role of magnetic fluctuations in this pressure-induced superconductivity remains unclear. Here, we report the pressure-induced multiple superconducting phases in the nonmagnetic GeBi4Te7, accompanied by corresponding structural transitions evidenced from the high-pressure Raman scattering. In comparison with other members in this family, we find the superconducting transition temperature of the nonmagnetic subgroup is significantly higher than their magnetic homologues, possibly hinting at the detrimental role played by the magnetic fluctuations in the superconductivity formation, at least in this pseudo-binary chalcogenide family. △ Less

Submitted 5 March, 2025; originally announced March 2025.

Journal ref: Physical Review B, 2025, 112(1): 014515

Abnormal Normal State and Pressure-driven Reentrant Superconductivity in the Heavy $d$-electron Superconductor Rh$_{17}$S$_{15}$

Authors: Xiaofeng Xu, J. Y. Nie, C. Q. Xu, Z. M. Zhu, Xiangzhuo Xing, Y. L. Huang, C. T. Zhang, N. Zuo, C. C. Zhao, Z. Y. Zhang, W. Zhou, W. H. Jiao, S. Xu, Q. Zhang, Zhu-An Xu, X. B. Liu, Dong Qian, Shiyan Li

Abstract: Superconductivity beyond the conventional Bardeen-Cooper-Schrieffer (BCS) framework often emerges out of a normal state that is accompanied by exotic magnetism and thereby displays many exceptional transport and thermodynamic properties. Here we report that the normal state of the heavy $d$-electron superconductor Rh$_{17}$S$_{15}$ is characterized by a weak \textit{ferromagnetism} that persists u… ▽ More Superconductivity beyond the conventional Bardeen-Cooper-Schrieffer (BCS) framework often emerges out of a normal state that is accompanied by exotic magnetism and thereby displays many exceptional transport and thermodynamic properties. Here we report that the normal state of the heavy $d$-electron superconductor Rh$_{17}$S$_{15}$ is characterized by a weak \textit{ferromagnetism} that persists up to room temperature. We show that the broad hump in its resistivity likely results from the Kondo interaction of the conduction electrons with this novel magnetism. By applying pressure, superconductivity is fully suppressed first. In the high-pressure regime, however, we observe a second dome of superconductivity with its maximum $T_c$ greater than the ambient pressure value, highlighting the possible \textit{unconventional} superconductivity in this heavy $d$-electron sulfide. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Comments: 4 figures

Journal ref: Phys. Rev. B 111, L161113 (2025)

Large Scale Finite-Temperature Real-time Time Dependent Density Functional Theory Calculation with Hybrid Functional on ARM and GPU Systems

Authors: Rongrong Liu, Zhuoqiang Guo, Qiuchen Sha, Tong Zhao, Haibo Li, Wei Hu, Lijun Liu, Guangming Tan, Weile Jia

Abstract: Ultra-fast electronic phenomena originating from finite temperature, such as nonlinear optical excitation, can be simulated with high fidelity via real-time time dependent density functional theory (rt-TDDFT) calculations with hybrid functional. However, previous rt-TDDFT simulations of real materials using the optimal gauge--known as the parallel transport gauge--have been limited to low-temperat… ▽ More Ultra-fast electronic phenomena originating from finite temperature, such as nonlinear optical excitation, can be simulated with high fidelity via real-time time dependent density functional theory (rt-TDDFT) calculations with hybrid functional. However, previous rt-TDDFT simulations of real materials using the optimal gauge--known as the parallel transport gauge--have been limited to low-temperature systems with band gaps. In this paper, we introduce the parallel transport-implicit midpoint (PT-IM) method, which significantly accelerates finite-temperature rt-TDDFT calculations of real materials with hybrid function. We first implement PT-IM with hybrid functional in our plane wave code PWDFT, and optimized it on both GPU and ARM platforms to build a solid baseline code. Next, we propose a diagonalization method to reduce computation and communication complexity, and then, we employ adaptively compressed exchange (ACE) method to reduce the frequency of the most expensive Fock exchange operator. Finally, we adopt the ring\_based method and the shared memory mechanism to overlap computation and communication and alleviate memory consumption respectively. Numerical results show that our optimized code can reach 3072 atoms for rt-TDDFT simulation with hybrid functional at finite temperature on 192 computing nodes, the time-to-solution for one time step is 429.3s, which is 41.4 times faster compared to the baseline. △ Less

Submitted 6 January, 2025; originally announced January 2025.

Anisotropic transport properties and topological Hall effect in the annealed kagome antiferromagnet FeGe

Authors: Jiajun Ma, Chenfei Shi, Yantao Cao, YuWei Zhang, Yazhou Li, Jiaxing Liao, Jialu Wang, Wenhe Jiao, Hanjie Guo, Chenchao Xu, Shixun Cao, Jianhui Dai, Jin-Ke Bao, Yuke Li

Abstract: Electron correlation often gives birth to various orders in quantum materials. Recently, a strongly correlated kagome antiferromagnet FeGe is discovered to undergo a charge density wave transition inside the A-type antiferromagnetic state, providing an opportunity to explore the interplay between charge order and magnetism. Here, we reported the observation of anisotropic resistivity and Hall effe… ▽ More Electron correlation often gives birth to various orders in quantum materials. Recently, a strongly correlated kagome antiferromagnet FeGe is discovered to undergo a charge density wave transition inside the A-type antiferromagnetic state, providing an opportunity to explore the interplay between charge order and magnetism. Here, we reported the observation of anisotropic resistivity and Hall effect, along with a topological Hall effect, in the annealed FeGe crystals. As the current flows along the \emph{ab}-plane, the temperature dependence of $ρ_{ab}$ exhibits a distinct resistivity loop related to a first-order transition at $T_{cdw}$. The applied magnetic fields do not alter $T_{cdw}$ but can induce a spin-flop transition at $H_{sf}$. Consequently, a field-induced large topological Hall effect is observed in the canting antiferromagnetic (CAFM) state below $T_{cant}$, which is possibly attributed to the non-trivial spin texture during the spin-flop process. Whereas, as current is parallel to \emph{c}-axis, both the field-induced transitions in $ρ_{c}$ and $χ_{c}$ disappear. Instead, the Hall resistivity in the annealed FeGe significantly exhibits a deviation from the linear field-dependent. These findings provide valuable insight into revealing the interplay among magnetism, charge order and topology in the kagome magnets. △ Less

Submitted 25 December, 2024; originally announced December 2024.

Comments: 8 pages, 5 figures

Journal ref: SCIENCE CHINA Physics, Mechanics & Astronomy 68, 237412 (2025)

Weak antilocalization in the transition metal telluride Ta$_2$Pd$_3$Te$_5$

Authors: Wen-He Jiao, Hang-Qiang Qiu, Wuzhang Yang, Jin-Ke Bao, Shaozhu Xiao, Yi Liu, Yuke Li, Guang-Han Cao, Xiaofeng Xu, Zhi Ren, Peng Zhang

Abstract: We report transport studies on the layered van der Waals topological crystalline insulator Ta$_2$Pd$_3$Te$_5$. The temperature-dependent resistance at high temperature is dominated by a bulk insulating gap and tend to saturate at low temperatures. Low temperature magnetotransport shows that Ta$_2$Pd$_3$Te$_5$ exhibits weak antilocatization (WAL) effect in both perpendicular orientation and paralle… ▽ More We report transport studies on the layered van der Waals topological crystalline insulator Ta$_2$Pd$_3$Te$_5$. The temperature-dependent resistance at high temperature is dominated by a bulk insulating gap and tend to saturate at low temperatures. Low temperature magnetotransport shows that Ta$_2$Pd$_3$Te$_5$ exhibits weak antilocatization (WAL) effect in both perpendicular orientation and parallel orientation, suggesting an contribution of the WAL effect from both topological edge states and bulk states. By measuring the anisotropic magnetoconductance and then subtracting the contribution of bulk states, the WAL effect associated with topological edge states can be revealed and analyzed quantitatively based on the two-dimensional Hikami-Larkin-Nagaoka model. Our results have important implications in understanding the WAL phenomena in Ta$_2$Pd$_3$Te$_5$. △ Less

Submitted 6 November, 2024; originally announced November 2024.

Comments: 8 pages, 5 figures

Journal ref: PhysRevB 108 (2023) 8

On the superconducting gap structure of the miassite Rh17S15: Nodal or nodeless?

Authors: J. Y. Nie, C. C. Zhao, C. Q. Xu, B. Li, C. P. Tu, X. Zhang, D. Z. Dai, H. R. Wang, S. Xu, Wenhe Jiao, B. M. Wang, Zhu'an Xu, Xiaofeng Xu, S. Y. Li

Abstract: Recent penetration depth measurement claimed the observation of unconventional superconductivity in the miassite Rh$_{17}$S$_{15}$ single crystals, evidenced by the linear-in-temperature penetration depth at low temperatures, thereby arguing for the presence of the lines of node in its superconducting gap structure. Here we measure the thermal conductivity of Rh$_{17}$S$_{15}$ single crystals down… ▽ More Recent penetration depth measurement claimed the observation of unconventional superconductivity in the miassite Rh$_{17}$S$_{15}$ single crystals, evidenced by the linear-in-temperature penetration depth at low temperatures, thereby arguing for the presence of the lines of node in its superconducting gap structure. Here we measure the thermal conductivity of Rh$_{17}$S$_{15}$ single crystals down to 110 mK and up to a field of 8 T ($\simeq 0.4H{\rm_{c2}}$). In marked contrast to the penetration depth measurement, we observe a negligible residual linear term $κ_0/T$ in zero field, in line with the nodeless gap structure. The field dependence of $κ_0(H)/T$ shows a profile that is more consistent with either a highly anisotropic gap structure or multiple nodeless gaps with significantly different magnitudes. Moreover, first-principles calculations give two electronic bands with complex shape of Fermi surfaces. These results suggest multigap nodeless superconductivity in this multiband Rh$_{17}$S$_{15}$ superconductor. △ Less

Submitted 14 May, 2024; originally announced May 2024.

Comments: 7 pages, 6 figures

Unveiling Higher-Order Topology via Polarized Topological Charges

Authors: Wei Jia, Bao-Zong Wang, Ming-Jian Gao, Jun-Hong An

Abstract: Higher-order topological phases (HOTPs) host exotic topological states that go beyond the traditional bulk-boundary correspondence. Up to now, there is still a lack of experimentally measurable momentum-space topological characterization for the HOTPs, which is not conducive to revealing the essential properties of these topological states and also restricts their detection in quantum simulation s… ▽ More Higher-order topological phases (HOTPs) host exotic topological states that go beyond the traditional bulk-boundary correspondence. Up to now, there is still a lack of experimentally measurable momentum-space topological characterization for the HOTPs, which is not conducive to revealing the essential properties of these topological states and also restricts their detection in quantum simulation systems. Here, we propose a concept of polarized topological charges to characterize chiral-symmetric HOTPs in momentum space, which further facilitates a feasible experimental scheme to detect the HOTPs in $^{87}$Rb cold atomic system. Remarkably, our characterization theory not only shows that the second-order (third-order) topological phases are determined by a quarter (negative eighth) of the total polarized topological charges, but also reveals that the higher-order topological phase transitions are identified by the creation or annihilation of polarized topological charges. Particularly, these polarized topological charges can be measured by pseudospin structures of the systems. Due to theoretical simplicity and observational intuitiveness, this work shall advance the broad studies of the HOTPs in both theory and experiment. △ Less

Submitted 3 December, 2024; v1 submitted 8 May, 2024; originally announced May 2024.

Comments: 8+9 pages, 4+3 figures. References are updated.Typos are corrected

Journal ref: Phys. Rev. B 110, L201117 (2024)

Generic reduction theory for Fermi sea topology in metallic systems

Authors: Wei Jia

Abstract: The Fermi sea of a metal can host exotic quantum topology, which governs its conductance quantization and is characterized by the Euler characteristic ($χ_F$). In contrast to the well-known band topology, which is determined by the global features of wave functions, the topology of such metallic systems is intrinsically linked to the geometry of the Fermi sea. As a result, probing and identifying… ▽ More The Fermi sea of a metal can host exotic quantum topology, which governs its conductance quantization and is characterized by the Euler characteristic ($χ_F$). In contrast to the well-known band topology, which is determined by the global features of wave functions, the topology of such metallic systems is intrinsically linked to the geometry of the Fermi sea. As a result, probing and identifying $χ_F$ in high-dimensional systems presents a challenge. Here, we propose a generic dimensional reduction theory for the Fermi sea topology in $d$-dimensional metallic systems, showing that $χ_F$ can be determined by the features of so-called reduced critical points on Fermi surfaces. Moreover, we reveal that $χ_F$ can be interpreted as a topological invariant of band topology by mapping a metallic system to a gapped system. Building on this nontrivial result, we identify a broad class of topological superconductors (SCs) whose topological numbers are precisely determined by the $χ_F$ of their normally filled bands. This provides an indirect method to capture $χ_F$ by measuring the (pseudo)spin polarizations of these topological SCs. Our findings are expected to significantly advance research into Fermi sea topology. △ Less

Submitted 16 February, 2025; v1 submitted 27 March, 2024; originally announced March 2024.

Comments: 11 pages, 7 figures, 1 table, References are updated

Journal ref: Phys. Rev. B 111, 155115 (2025)

Superconductivity in kagome metal ThRu3Si2

Authors: Yi Liu, Jing Li, Wu-Zhang Yang, Jia-Yi Lu, Bo-Ya Cao, Hua-Xun Li, Wan-Li Chai, Si-Qi Wu, Bai-Zhuo Li, Yun-Lei Sun, Wen-He Jiao, Wang Cao, Xiao-Feng Xu, Ren Zhi, Guang-Han Cao

Abstract: We report the physical properties of ThRu$_3$Si$_2$ featured with distorted Ru kagome lattice. The combined experiments of resistivity, magnetization and specific heat reveal bulk superconductivity with $T_{\rm{c}}$ = 3.8 K. The specific heat jump and calculated electron-phonon coupling indicate a moderate coupled BCS superconductor. In comparison with LaRu$_3$Si$_2$, the calculated electronic str… ▽ More We report the physical properties of ThRu$_3$Si$_2$ featured with distorted Ru kagome lattice. The combined experiments of resistivity, magnetization and specific heat reveal bulk superconductivity with $T_{\rm{c}}$ = 3.8 K. The specific heat jump and calculated electron-phonon coupling indicate a moderate coupled BCS superconductor. In comparison with LaRu$_3$Si$_2$, the calculated electronic structure in ThRu$_3$Si$_2$ shows an electron-doping effect with electron filling lifted from 100 meV below flat bands to 300 meV above it. This explains the lower superconducting transition temperature and weaker electron correlations observed in ThRu$_3$Si$_2$. Our work suggests the $T_{\rm{c}}$ and electronic correlations in kagome superconductor could have intimate connection with the flat bands. △ Less

Submitted 8 March, 2024; originally announced March 2024.

Comments: 7 pages, 5 figures

Journal ref: Chinese Physics B (2024)

Single photon scattering from a chain of giant atoms coupled to a one-dimensional waveguide

Authors: Y. P. Peng, W. Z. Jia

Abstract: We investigate coherent single-photon transport in a waveguide quantum electrodynamics structure containing multiple giant atoms. The single-photon scattering amplitudes are solved using a real-space method. The results give rise to a clear picture of the multi-channel scattering process. In the case of identical and equally-spaced giant atoms in a separate configuration, we also use the transfer-… ▽ More We investigate coherent single-photon transport in a waveguide quantum electrodynamics structure containing multiple giant atoms. The single-photon scattering amplitudes are solved using a real-space method. The results give rise to a clear picture of the multi-channel scattering process. In the case of identical and equally-spaced giant atoms in a separate configuration, we also use the transfer-matrix method to express the scattering amplitudes in terms of compact analytical expressions, which allow us to conveniently analyze the properties of the scattering spectra. Based on these theoretical results, we find that the non-dipole effects of giant atoms, which are relevant to the design of the setup, can strongly manipulate several types of collective properties of the output fields, including the superradiant phenomenon, the multiple Fano interference, and the photonic band gap. This makes it possible to manipulate the photon transport in a more versatile way than with small atoms. We also make a proposal to probe the topological states of a chain of braided giant atoms by using photon scattering spectra, showing that waveguide quantum electrodynamics systems with giant atoms are ideal platforms to merge topological physics and on-chip quantum optics. △ Less

Submitted 2 March, 2024; originally announced March 2024.

Comments: 19 pages, 11 figures

Journal ref: Phys. Rev. A 108, 043709 (2023)

Surface Chern-Simons theory for third-order topological insulators and superconductors

Authors: Zhi-Hao Huang, Yi Tan, Wei Jia, Long Zhang, Xiong-Jun Liu

Abstract: Three-dimensional 3rd-order topological insulators (TOTIs) and superconductors (TOTSCs), as the highestorder topological phases hosting zero corner modes in physical dimension, has sparked extensive research interest. However, such topological states have not been discovered in reality due to the lack of experimental schemes of realization. Here, we propose a novel surface Chern-Simons (CS) theory… ▽ More Three-dimensional 3rd-order topological insulators (TOTIs) and superconductors (TOTSCs), as the highestorder topological phases hosting zero corner modes in physical dimension, has sparked extensive research interest. However, such topological states have not been discovered in reality due to the lack of experimental schemes of realization. Here, we propose a novel surface Chern-Simons (CS) theory for 3rd-order topological phases, and show that the theory enables a feasible and systematic design of TOTIs and TOTSCs. We show that the emergence of zero Dirac (Majorana) corner modes is entirely captured by an emergent $\mathbb{Z}_{2}$ CS term that can be further characterized by a novel two-particle Wess-Zumino (WZ) term uncovered here in the surfaces of three-dimensional topological materials. Importantly, our proposed CS term characterization and two-particle WZ term mechanism provide a unique perspective to design TOTIs (TOTSCs) in terms of minimal ingredients, feasibly guiding the search for underlying materials, with promising candidates being discussed. This work shall advance both the theoretical and experimental research for highest-order topological matters. △ Less

Submitted 1 March, 2024; originally announced March 2024.

Comments: 5+11 pages, 4+5 figures

DPA-2: a large atomic model as a multi-task learner

Authors: Duo Zhang, Xinzijian Liu, Xiangyu Zhang, Chengqian Zhang, Chun Cai, Hangrui Bi, Yiming Du, Xuejian Qin, Anyang Peng, Jiameng Huang, Bowen Li, Yifan Shan, Jinzhe Zeng, Yuzhi Zhang, Siyuan Liu, Yifan Li, Junhan Chang, Xinyan Wang, Shuo Zhou, Jianchuan Liu, Xiaoshan Luo, Zhenyu Wang, Wanrun Jiang, Jing Wu, Yudi Yang , et al. (18 additional authors not shown)

Abstract: The rapid advancements in artificial intelligence (AI) are catalyzing transformative changes in atomic modeling, simulation, and design. AI-driven potential energy models have demonstrated the capability to conduct large-scale, long-duration simulations with the accuracy of ab initio electronic structure methods. However, the model generation process remains a bottleneck for large-scale applicatio… ▽ More The rapid advancements in artificial intelligence (AI) are catalyzing transformative changes in atomic modeling, simulation, and design. AI-driven potential energy models have demonstrated the capability to conduct large-scale, long-duration simulations with the accuracy of ab initio electronic structure methods. However, the model generation process remains a bottleneck for large-scale applications. We propose a shift towards a model-centric ecosystem, wherein a large atomic model (LAM), pre-trained across multiple disciplines, can be efficiently fine-tuned and distilled for various downstream tasks, thereby establishing a new framework for molecular modeling. In this study, we introduce the DPA-2 architecture as a prototype for LAMs. Pre-trained on a diverse array of chemical and materials systems using a multi-task approach, DPA-2 demonstrates superior generalization capabilities across multiple downstream tasks compared to the traditional single-task pre-training and fine-tuning methodologies. Our approach sets the stage for the development and broad application of LAMs in molecular and materials simulation research. △ Less

Submitted 16 August, 2024; v1 submitted 24 December, 2023; originally announced December 2023.

Journal ref: npj Comput Mater 10, 293 (2024)

Spontaneous gap opening and potential excitonic states in an ideal Dirac semimetal Ta$_2$Pd$_3$Te$_5$

Authors: Peng Zhang, Yuyang Dong, Dayu Yan, Bei Jiang, Tao Yang, Jun Li, Zhaopeng Guo, Yong Huang, Bo Hao, Qing Li, Yupeng Li, Kifu Kurokawa, Rui Wang, Yuefeng Nie, Makoto Hashimoto, Donghui Lu, Wen-He Jiao, Jie Shen, Tian Qian, Zhijun Wang, Youguo Shi, Takeshi Kondo

Abstract: The opening of an energy gap in the electronic structure generally indicates the presence of interactions. In materials with low carrier density and short screening length, long-range Coulomb interaction favors the spontaneous formation of electron-hole pairs, so-called excitons, opening an excitonic gap at the Fermi level. Excitonic materials host unique phenomenons associated with pair excitatio… ▽ More The opening of an energy gap in the electronic structure generally indicates the presence of interactions. In materials with low carrier density and short screening length, long-range Coulomb interaction favors the spontaneous formation of electron-hole pairs, so-called excitons, opening an excitonic gap at the Fermi level. Excitonic materials host unique phenomenons associated with pair excitations. However, there is still no generally recognized single-crystal material with excitonic order, which is, therefore, awaited in condensed matter physics. Here, we show that excitonic states may exist in the quasi-one-dimensional material Ta$_2$Pd$_3$Te$_5$, which has an almost ideal Dirac-like band structure, with Dirac point located exactly at Fermi level. We find that an energy gap appears at 350 K, and it grows with decreasing temperature. The spontaneous gap opening is absent in a similar material Ta$_2$Ni$_3$Te$_5$. Intriguingly, the gap is destroyed by the potassium deposition on the crystal, likely due to extra-doped carriers. Furthermore, we observe a pair of in-gap flat bands, which is an analog of the impurity states in a superconducting gap. All these observations can be properly explained by an excitonic order, providing Ta$_2$Pd$_3$Te$_5$ as a new and promising candidate realizing excitonic states. △ Less

Submitted 15 March, 2024; v1 submitted 22 December, 2023; originally announced December 2023.

Comments: 9 pages, 5 figures

Journal ref: Phys. Rev. X 14, 011047 (2024)

Self-doping effect in confined copper selenide semiconducting quantum dots for efficient photoelectrocatalytic oxygen evolution

Authors: Jie Ren, Chenya Zhao, Lanshan He, Congcong Wu, Wenting Jia, Shengwen Xu, Daojian Ye, Weiyang Xu, Fujin Huang, Hang Zhou, Chengwu Zou, Ce Hu, Ting Yu, Xingfang Luo, Cailei Yuan

Abstract: Self-doping can not only suppress the photogenerated charge recombination of semiconducting quantum dots by self-introducing trapping states within the bandgap, but also provide high-density catalytic active sites as the consequence of abundant non-saturated bonds associated with the defects. Here, we successfully prepared semiconducting copper selenide (CuSe) confined quantum dots with abundant v… ▽ More Self-doping can not only suppress the photogenerated charge recombination of semiconducting quantum dots by self-introducing trapping states within the bandgap, but also provide high-density catalytic active sites as the consequence of abundant non-saturated bonds associated with the defects. Here, we successfully prepared semiconducting copper selenide (CuSe) confined quantum dots with abundant vacancies and systematically investigated their photoelectrochemical characteristics. Photoluminescence characterizations reveal that the presence of vacancies reduces the emission intensity dramatically, indicating a low recombination rate of photogenerated charge carriers due to the self-introduced trapping states within the bandgap. In addition, the ultra-low charge transfer resistance measured by electrochemical impedance spectroscopy implies the efficient charge transfer of CuSe semiconducting quantum dots-based photoelectrocatalysts, which is guaranteed by the high conductivity of their confined structure as revealed by room-temperature electrical transport measurements. Such high conductivity and low photogenerated charge carriers recombination rate, combined with high-density active sites and confined structure, guaranteeing the remarkable photoelectrocatalytic performance and stability as manifested by photoelectrocatalysis characterizations. This work promotes the development of semiconducting quantum dots-based photoelectrocatalysis and demonstrates CuSe semiconducting quantum confined catalysts as an advanced photoelectrocatalysts for oxygen evolution reaction. △ Less

Submitted 13 April, 2023; originally announced April 2023.

Unified characterization for higher-order topological phase transitions

Authors: Wei Jia, Xin-Chi Zhou, Lin Zhang, Long Zhang, Xiong-Jun Liu

Abstract: Higher-order topological phase transitions (HOTPTs) are associated with closing either the bulk energy gap (type-I) or boundary energy gap (type-II) without changing symmetry, and conventionally the both transitions are captured in real space and characterized separately. Here we propose a momentum-space topological characterization of the HOTPTs, which unifies the both types of topological transi… ▽ More Higher-order topological phase transitions (HOTPTs) are associated with closing either the bulk energy gap (type-I) or boundary energy gap (type-II) without changing symmetry, and conventionally the both transitions are captured in real space and characterized separately. Here we propose a momentum-space topological characterization of the HOTPTs, which unifies the both types of topological transitions and enables a precise detection by quench dynamics. Our unified characterization is based on a novel correspondence between the mass domain walls on real-space boundaries and the higher-order band-inversion surfaces (BIS) which are characteristic interfaces in the momentum subspace. The topological transitions occur when momentum-space topological nodes, dubbed higher-order topological charges, cross the higher-order BISs after proper projection. Particularly, the bulk (boundary) gap closes when all (part of) topological charges cross the BISs, characterizing the type-I (type-II) HOTPTs. These distinct dynamical behaviours of higher-order topological charges can be feasibly measured from quench dynamics driven with control in experiments. Our work opens an avenue to characterize and detect the two types of HOTPTs within a unified framework, and shall advance the research in both theory and experiment. △ Less

Submitted 13 April, 2023; v1 submitted 21 September, 2022; originally announced September 2022.

Comments: 8+15 pages, 3+7 figures; Discussions are updated. References are updated

Journal ref: Phys. Rev. Research 5, L022032 (2023)

Dynamical detection of mean-field topological phases in an interacting Chern insulator

Authors: Wei Jia, Long Zhang, Lin Zhang, Xiong-Jun Liu

Abstract: Interactions generically have important effects on the topological quantum phases. For a quantum anomalous Hall (QAH) insulator, the presence of interactions can qualitatively change the topological phase diagram which, however, is typically hard to measure in the experiment. Here we propose a novel scheme based on quench dynamics to detect the mean-field topological phase diagram of an interactin… ▽ More Interactions generically have important effects on the topological quantum phases. For a quantum anomalous Hall (QAH) insulator, the presence of interactions can qualitatively change the topological phase diagram which, however, is typically hard to measure in the experiment. Here we propose a novel scheme based on quench dynamics to detect the mean-field topological phase diagram of an interacting Chern insulator described by QAH-Hubbard model, with nontrivial dynamical quantum physics being uncovered. We focus on the dynamical properties of the system at a weak to intermediate Hubbard interaction which mainly induces a ferromagnetic order under the mean-field level. Remarkably, three characteristic times $t_s$, $t_c$, and $t^*$ are found in the quench dynamics. The first two capture the emergence of dynamical self-consistent particle density and dynamical topological phase transition respectively, while the last one gives a linear scaling time on the topological phase boundaries. A more interesting result is that $t_s>t^*>t_c$ ($t^*<t_s<t_c$) occurs in repulsive (attractive) interaction and the Chern number is determined by any two characteristic time scales when the system is quenched from an initial nearly fully polarized state to the topologically nontrivial regimes, showing a dynamical way to determine equilibrium mean-field topological phase diagram via the time scales. Experimentally,the measurement of $t_s$ is challenging while $t_c$ and $t^*$ can be directly readout by measuring the spin polarizations of four Dirac points and the time-dependent particle density, respectively. Our work reveals the novel interacting effects on the topological phases and shall promote the experimental observation. △ Less

Submitted 7 March, 2023; v1 submitted 22 June, 2022; originally announced June 2022.

Comments: 14 pages, 7 figures.Typos are corrected and References are updated. To appear in Phys. Rev. B

Journal ref: Phys. Rev. B 107, 125132 (2023)

Dirac nodal lines in the quasi-one-dimensional ternary telluride TaPtTe$_5$

Authors: Shaozhu Xiao, Wen-He Jiao, Yu Lin, Qi Jiang, Xiufu Yang, Yunpeng He, Zhicheng Jiang, Yichen Yang, Zhengtai Liu, Mao Ye, Dawei Shen, Shaolong He

Abstract: A Dirac nodal-line phase, as a quantum state of topological materials, usually occur in three-dimensional or at least two-dimensional materials with sufficient symmetry operations that could protect the Dirac band crossings. Here, we report a combined theoretical and experimental study on the electronic structure of the quasi-one-dimensional ternary telluride TaPtTe$_5$, which is corroborated as b… ▽ More A Dirac nodal-line phase, as a quantum state of topological materials, usually occur in three-dimensional or at least two-dimensional materials with sufficient symmetry operations that could protect the Dirac band crossings. Here, we report a combined theoretical and experimental study on the electronic structure of the quasi-one-dimensional ternary telluride TaPtTe$_5$, which is corroborated as being in a robust nodal-line phase with fourfold degeneracy. Our angle-resolved photoemission spectroscopy measurements show that two pairs of linearly dispersive Dirac-like bands exist in a very large energy window, which extend from a binding energy of $\sim$ 0.75 eV to across the Fermi level. The crossing points are at the boundary of Brillouin zone and form Dirac-like nodal lines. Using first-principles calculations, we demonstrate the existing of nodal surfaces on the $k_y = \pm π$ plane in the absence of spin-orbit coupling (SOC), which are protected by nonsymmorphic symmetry in TaPtTe$_5$. When SOC is included, the nodal surfaces are broken into several nodal lines. By theoretical analysis, we conclude that the nodal lines along $Y$-$T$ and the ones connecting the $R$ points are non-trivial and protected by nonsymmorphic symmetry against SOC. △ Less

Submitted 11 May, 2022; originally announced May 2022.

Comments: 17 pages, 5 figures, accepted for publication as a Regular Article in Physical Review B

Journal ref: Phys. Rev. B 105, 195145 (2022)

de Haas-van Alphen effect and the first-principles study of the possible topological stannide Cu$_3$Sn

Authors: Chengxu Liu, Bin Li, Yongheng Ge, Wen-He Jiao, Chuanying Xi, Yi Liu, Chunqiang Xu, Qi Lu, Yunlong Li, Hang-Qiang Qiu, Qin-Qing Zhu, Zhi Ren, Ziming Zhu, Dong Qian, Xianglin Ke, Xiaofeng Xu

Abstract: The quest for quantum materials with diverse symmetry-protected topological states has been the focus of recent research interest, primarily due to their fascinating physical properties and the potential technological utility. In this work, we report on the magnetotransport, de Haas-van Alphen (dHvA) oscillations, and the first-principles calculations of the stannide Cu$_3$Sn that is isostructural… ▽ More The quest for quantum materials with diverse symmetry-protected topological states has been the focus of recent research interest, primarily due to their fascinating physical properties and the potential technological utility. In this work, we report on the magnetotransport, de Haas-van Alphen (dHvA) oscillations, and the first-principles calculations of the stannide Cu$_3$Sn that is isostructural with the recently reported topological semimetal Ag$_3$Sn. The magnetoresistance was found to vary quasi-linearly in field. Clear dHvA oscillations were observed under a field as low as 1 Tesla at 2 K, with three major oscillation frequencies $F_α$=8.74 T, $F_β$=150.19 T and $F_γ$=229.66 T and extremely small effective masses. The analysis of dHvA quantum oscillations revealed a possible nonzero Berry phase, suggestive of the nontrivial band topology. The corroborating evidence for the nontrivial electronic topology also comes from the first-principles calculations which yield a nonzero $\mathbb{Z}_2$ topological index. These results collectively suggest that Cu$_3$Sn, in analogy to its homologue Ag$_3$Sn, may be another intermetallic stannide hosting topological Dirac fermions. △ Less

Submitted 9 May, 2022; originally announced May 2022.

Comments: 4 figures, 1 table

Journal ref: Journal of Alloys and Compounds 928 (2022) 167017

Spectrum of Single-Photon Scattering in a Strong-Coupling Hybrid Optomechanical System

Authors: S. Y. Yang, W. Z. Jia, H. Yuan

Abstract: We analyze theoretically the single-photon excitation and transmission spectra of a strong-coupling hybrid optomechanics, where a two-level system (TLS) is coupled to the mechanical resonator (MR), generating the Jaynes-Cummings-type polariton doublets. In our model, both the optomichanical coupling and the TLS-MR coupling are strong. In this parameter region, the polaron-assisted excitation and r… ▽ More We analyze theoretically the single-photon excitation and transmission spectra of a strong-coupling hybrid optomechanics, where a two-level system (TLS) is coupled to the mechanical resonator (MR), generating the Jaynes-Cummings-type polariton doublets. In our model, both the optomichanical coupling and the TLS-MR coupling are strong. In this parameter region, the polaron-assisted excitation and reemission processes can strongly affect the single-photon excitation and output spectra of the cavity. We find that the fine structure around each sideband can be used to characterize the TLS-MR and the effective TLS-photon couplings, even at single-quantum level. Thus, the spectrum structures may make it possible to sensitively probe the quantum nature of a macroscopic mechanical element. We further provide a possible approach for tomographic reconstruction of the state of a TLS, utilizing the single-photon transmission spectra. △ Less

Submitted 14 January, 2022; originally announced January 2022.

Comments: 12 pages, 7 figures

Journal ref: Ann. Phys. (Berlin) 2020, 2000154

A Methodology for Thermal Simulation of Interconnects Enabled by Model Reduction with Material Property Variation

Authors: Wangkun Jia, Ming-C. Cheng

Abstract: A thermal simulation methodology is developed for interconnects enabled by a data-driven learning algorithm accounting for variations of material properties, heat sources and boundary conditions (BCs). The methodology is based on the concepts of model order reduction and domain decomposition to construct a multi-block approach. A generic block model is built to represent a group of interconnect bl… ▽ More A thermal simulation methodology is developed for interconnects enabled by a data-driven learning algorithm accounting for variations of material properties, heat sources and boundary conditions (BCs). The methodology is based on the concepts of model order reduction and domain decomposition to construct a multi-block approach. A generic block model is built to represent a group of interconnect blocks that are used to wire standard cells in the integrated circuits (ICs). The blocks in this group possess identical geometry with various metal/via routings. The data-driven model reduction method is thus applied to learn material property variations induced by different metal/via routings in the blocks, in addition to the variations of heat sources and BCs. The approach is investigated in two very different settings. It is first applied to thermal simulation of a single interconnect block with similar BCs to those in the training of the generic block. It is then implemented in multi-block thermal simulation of a FinFET IC, where the interconnect structure is partitioned into several blocks each modeled by the generic block model. Accuracy of the generic block model is examined in terms of the metal/via routings, BCs and thermal discontinuities at the block interfaces. △ Less

Submitted 1 December, 2021; originally announced December 2021.

Comments: 23 pages, 15 figures

Coupling between Antiferromagnetic and Spin Glass Orders in the Quasi-One-Dimensional Iron Telluride TaFe$_{1+x}$Te$_3$ ($x$=0.25)

Authors: Y. Liu, J. J. Bao, C. Q. Xu, W. H. Jiao, H. Zhang, L. C. Xu, Zengwei Zhu, H. Y. Yang, Yonghui. Zhou, Z. Ren, P. K. Biswas, S. K. Ghosh, Zhaorong Yang, X. Ke, G. H. Cao, Xiaofeng Xu

Abstract: Understanding the interplay among different magnetic exchange interactions and its physical consequences, especially in the presence of itinerant electrons and disorders, remains one of the central themes in condensed matter physics. In this vein, the coupling between antiferromagnetic and spin glass orders may lead to large exchange bias, a property of potential broad technological applications.… ▽ More Understanding the interplay among different magnetic exchange interactions and its physical consequences, especially in the presence of itinerant electrons and disorders, remains one of the central themes in condensed matter physics. In this vein, the coupling between antiferromagnetic and spin glass orders may lead to large exchange bias, a property of potential broad technological applications. In this article, we report the coexistence of antiferromagnetic order and spin glass behaviors in a quasi-one-dimensional iron telluride TaFe$_{1+x}$Te$_3$ ($x$=0.25). Its antiferromagnetism is believed to arise from the antiferromagnetic interchain coupling between the ferromagnetically aligned FeTe chains along the $b$-axis, while the spin glassy state stems from the disordered Fe interstitials. This dichotomic role of chain and interstitial sublattices is responsible for the large exchange bias observed at low temperatures, with the interstitial Fe acting as the uncompensated moment and its neighboring Fe chain providing the source for its pinning. This iron-based telluride may thereby represent a new paradigm to study the large family of transition metal chalcogenides whose magnetic order or even the dimensionality can be tuned to a large extent, forming a fertile playground to manipulate or switch the spin degrees of freedom thereof. △ Less

Submitted 22 September, 2021; originally announced September 2021.

Journal ref: Physical Review B 104, 104418 (2021)

Coexistence of Ferroelectric-like Polarization and Dirac-like Surface State in TaNiTe5

Authors: Yunlong Li, Zhao Ran, Chaozhi Huang, Guanyong Wang, Peiyue Shen, Haili Huang, Chunqiang Xu, Yi Liu, Wenhe Jiao, Wenxiang Jiang, Jiayuan Hu, Gucheng Zhu, Chenhang Xu, Qi Lu, Guohua Wang, Qiang Jing, Shiyong Wang, Zhiwen Shi, Jinfeng Jia, Xiaofeng Xu, Wentao Zhang, Weidong Luo, Dong Qian

Abstract: By combining angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), piezoresponse force microscopy (PFM) and first-principles calculations, we have studied the low-energy band structure, atomic structure and charge polarization on the surface of a topological semimetal candidate TaNiTe5. Dirac-like surface states were observed on the (010) surface by ARPES, consist… ▽ More By combining angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), piezoresponse force microscopy (PFM) and first-principles calculations, we have studied the low-energy band structure, atomic structure and charge polarization on the surface of a topological semimetal candidate TaNiTe5. Dirac-like surface states were observed on the (010) surface by ARPES, consistent with the first-principles calculations. On the other hand, PFM reveals a switchable ferroelectric-like polarization on the same surface. We propose that the noncentrosymmetric surface reconstruction observed by STM could be the origin of the observed ferroelectric-like state in this novel material. Our findings provide a new platform with the coexistence of ferroelectric-like surface charge distribution and novel surface states. △ Less

Submitted 17 June, 2021; originally announced June 2021.

A new heat source model for selective laser melting simulations based on energy distribution on the powder layer and the surface of substrate

Authors: Zhi Huang, Weibo Jia, Haoming Wang, Zhengtong Yang, Chao Li, Jie Liang, Yue Zhong

Abstract: In order to predict the more accurate shape information of the melt pool in Selective Laser Melting (SLM), a new finite element temperature field simulations model is proposed. The simulations use a new heat source model that takes into account the influence of the powder layout, the surface of the substrate and the changes in the thickness of the powder layer after fusion on the energy distributi… ▽ More In order to predict the more accurate shape information of the melt pool in Selective Laser Melting (SLM), a new finite element temperature field simulations model is proposed. The simulations use a new heat source model that takes into account the influence of the powder layout, the surface of the substrate and the changes in the thickness of the powder layer after fusion on the energy distribution. In order to construct this new heat source model, firstly an improved optimization method based on the gradient descent and the univariate search technique is proposed to simulate the powder layout, and then the laser beam propagation between the powder and the surface of the substrate is tracked and recorded to obtain the energy distribution. Finally, according to the distribution of laser energy between the powder layer and the surface of the substrate, the heat source model is divided into two parts: one is the surface of substrate heat source model being the Gaussian distribution, the other one is the powder layer heat source model-satisfying the Gaussian distribution on the horizontal plane, changes in the depth direction according to the functional relationship obtained by the fitting. In addition, the thickness change of the powder layer after fusion is analyzed, and is taken into account in the heat source model. The powder simulation results are compared with the powder scattering experiment results to verify the effectiveness of the powder model. Comparing the temperature field simulation with the experiment, the results show that the predicted molten pool width relative error is 6.4%, and the connect width error is 9.6%, which has better accuracy and verifies the validity of the temperature field simulation model. △ Less

Submitted 7 June, 2021; originally announced June 2021.

Comments: 13pages,21figures

Universal topological quench dynamics: Altland-Zirnbauer tenfold classes

Authors: Lin Zhang, Wei Jia, Xiong-Jun Liu

Abstract: Topological phases of the famous Altland-Zirnbauer (AZ) tenfold classes are defined on the equilibrium ground states. Whether such equilibrium topological phases have universal correspondence to far-from-equilibrium quantum dynamics is a fundamental issue of both theoretical and experimental importance. Here we uncover the universal topological quench dynamics linking to the equilibrium topologica… ▽ More Topological phases of the famous Altland-Zirnbauer (AZ) tenfold classes are defined on the equilibrium ground states. Whether such equilibrium topological phases have universal correspondence to far-from-equilibrium quantum dynamics is a fundamental issue of both theoretical and experimental importance. Here we uncover the universal topological quench dynamics linking to the equilibrium topological phases for the complete AZ tenfold classes, with a general framework being established. We show a fundamental result that a $d$-dimensional topological phase of the tenfold class, with an integer invariant or $\mathbb{Z}_{2}$ index defined on high symmetry momenta, is generically characterized by topology reduced to the highest-order band-inversion surfaces located at arbitrary discrete momenta of Brillouin zone. Such dimension-reduced topology is further captured by universal topological patterns emerging in far-from-equilibrium quantum dynamics by quenching the system from trivial phase to the topological regime, rendering the dynamical hallmark of the equilibrium topological phase. This work establishes a universal dynamical characterization for the complete AZ symmetry classes of topological phases, which has broad applications in theory and experiment. △ Less

Submitted 7 April, 2021; v1 submitted 1 April, 2021; originally announced April 2021.

Comments: 6+11 pages; 3+6 figures; 2 tables; Discussions are improved and typos are corrected

Journal ref: Science Bulletin 67, 1236 (2022)

Anisotropic transport and de Haas$-$van Alphen oscillations in quasi-one-dimensional TaPtTe$_5$

Authors: Wen-He Jiao, Shaozhu Xiao, Bin Li, Chunqiang Xu, Xiao-Meng Xie, Hang-Qiang Qiu, Xiaofeng Xu, Yi Liu, Shi-Jie Song, Wei Zhou, Hui-Fei Zhai, X. Ke, Shaolong He, Guang-Han Cao

Abstract: Because of the unique physical properties and potential applications, the exploration of quantum materials with diverse symmetry-protected topological states has attracted considerable interest in the condensed-matter community in recent years. Most of the topologically nontirvial materials identified thus far have two-dimensional or three-dimensional structural characteristics, while the quasi-on… ▽ More Because of the unique physical properties and potential applications, the exploration of quantum materials with diverse symmetry-protected topological states has attracted considerable interest in the condensed-matter community in recent years. Most of the topologically nontirvial materials identified thus far have two-dimensional or three-dimensional structural characteristics, while the quasi-one-dimensional (quasi-1D) analogs are rare. Here we report on anisotropic magnetoresistance, Hall effect, and quantum de Haas$-$van Alphen (dHvA) oscillations in TaPtTe$_5$ single crystals, which possess a layered crystal structure with quasi-1D PtTe$_2$ chains. TaPtTe$_5$ manifests an anisotropic magnetoresistance and a nonlinear Hall effect at low temperatures. The analysis of the dHvA oscillations reveals two major oscillation frequencies (63.5 T and 95.2 T). The corresponding light effective masses and the nonzero Berry phases suggest the nontrivial band topology in TaPtTe$_5$, which is further corroborated by the first-principles calculations. Our results suggest that TaPtTe$_5$, in analogy with its sister compounds TaPdTe$_5$ and TaNiTe$_5$, is another quasi-1D material hosting topological Dirac fermions. △ Less

Submitted 28 March, 2021; v1 submitted 25 March, 2021; originally announced March 2021.

Comments: There are some errors in the current vertion. After proper modifications, updated manuscript will be resubmitted

Journal ref: Phys. Rev. B 103, 125150 (2021)

Tunable bandgaps and symmetry breaking in magneto-mechanical metastructures inspired by multi-layer 2D materials

Authors: Kuan Zhang, Weijian Jiao, Stefano Gonella

Abstract: In this Letter, we introduce a paradigm to realize magneto-mechanical metastructures inspired by multi-layer 2D materials, such as graphene bilayers. The metastructures are intended to capture two aspects of their nanoscale counterparts. One is the multi-layer geometry, which is implemented by stacking hexagonal lattice sheets. The other is the landscape of weak inter-layer forces, which is mimick… ▽ More In this Letter, we introduce a paradigm to realize magneto-mechanical metastructures inspired by multi-layer 2D materials, such as graphene bilayers. The metastructures are intended to capture two aspects of their nanoscale counterparts. One is the multi-layer geometry, which is implemented by stacking hexagonal lattice sheets. The other is the landscape of weak inter-layer forces, which is mimicked by the interactions between pairs of magnets located at corresponding lattice sites on adjacent layers. We illustrate the potential of this paradigm through a three-layer prototype. The two rigid outer lattices serve as control layers, while the thin inner layer is free to experience flexural motion under the confining action of the magnetic forces exchanged with the outer ones, thus behaving as a lattice on elastic foundation. The inner layer is free to rotate relatively to the others, giving rise to a rich spectrum of inter-layer interaction patterns. Our objective is to determine how the dynamical response can be tuned by changing the twist angle between the layers. Specifically, we demonstrate experimentally that switching between different stacking patterns has profound consequences on the phonon landscape, opening and closing bandgaps in different frequency regimes. △ Less

Submitted 2 March, 2021; v1 submitted 1 March, 2021; originally announced March 2021.

Journal ref: Phys. Rev. B 104, 020301 (2021)

Current-induced magnetization switching in a chemically disordered A1 CoPt single layer

Authors: Zehan Chen, Lin Liu, Zhixiang Ye, Zhiren Chen, Hongnan Zheng, Wei Jia, Qi Zeng, Ning Wang, Boyuan Xiang, Tao Lin, Jing Liu, Mingxia Qiu, Shunpu Li, Ji Shi, Peigang Han, Hongyu An

Abstract: We report the first demonstration of the current-induced magnetization switching in a perpendicularly magnetized A1 CoPt single layer. We show that good perpendicular magnetic anisotropy can be obtained in a wide composition range of the A1 Co1-xPtx single layers, which allows to fabricate perpendicularly magnetized CoPt single layer with composition gradient to break the inversion symmetry of the… ▽ More We report the first demonstration of the current-induced magnetization switching in a perpendicularly magnetized A1 CoPt single layer. We show that good perpendicular magnetic anisotropy can be obtained in a wide composition range of the A1 Co1-xPtx single layers, which allows to fabricate perpendicularly magnetized CoPt single layer with composition gradient to break the inversion symmetry of the structure. By fabricating the gradient CoPt single layer, we have evaluated the SOT efficiency and successfully realized the SOT-induced magnetization switching. Our study provides an approach to realize the current-induced magnetization in the ferromagnetic single layers without attaching SOT source materials. △ Less

Submitted 12 January, 2021; originally announced January 2021.

Dynamically characterizing topological phases by high-order topological charges

Authors: Wei Jia, Lin Zhang, Long Zhang, Xiong-Jun Liu

Abstract: We propose a new theory to characterize equilibrium topological phase with non-equilibrium quantum dynamics by introducing the concept of high-order topological charges, with novel phenomena being predicted. Through a dimension reduction approach, we can characterize a $d$-dimensional ($d$D) integer-invariant topological phase with lower-dimensional topological number quantified by high-order topo… ▽ More We propose a new theory to characterize equilibrium topological phase with non-equilibrium quantum dynamics by introducing the concept of high-order topological charges, with novel phenomena being predicted. Through a dimension reduction approach, we can characterize a $d$-dimensional ($d$D) integer-invariant topological phase with lower-dimensional topological number quantified by high-order topological charges, of which the $s$th-order topological charges denote the monopoles confined on the $(s-1)$th-order band inversion surfaces (BISs) that are $(d-s+1)$D momentum subspaces. The bulk topology is determined by the $s$th order topological charges enclosed by the $s$th-order BISs. By quenching the system from trivial phase to topological regime, we show that the bulk topology of post-quench Hamiltonian can be detected through a high-order dynamical bulk-surface correspondence, in which both the high-order topological charges and high-order BISs are identified from quench dynamics. This characterization theory has essential advantages in two aspects. First, the highest ($d$th) order topological charges are characterized by only discrete signs of spin-polarization in zero dimension (i.e. the $0$th Chern numbers), whose measurement is much easier than the $1$st-order topological charges that are characterized by the continuous charge-related spin texture in higher dimensional space. Secondly, a more striking result is that a first-order high integer-valued topological charge always reduces to multiple highest-order topological charges with unit charge value, and the latter can be readily detected in experiment. The two fundamental features greatly simplify the characterization and detection of the topological charges and also topological phases, which shall advance the experimental studies in the near future. △ Less

Submitted 24 December, 2020; originally announced December 2020.

Comments: 13 pages, 7 figures

Journal ref: Phys. Rev. A 103, 052213 (2021)

Intrinsic mechanism for anisotropic magnetoresistance and experimental confirmation in Co$_x$Fe$_{1-x}$ single-crystal films

Authors: F. L. Zeng, Z. Y. Ren, Y. Li, J. Y. Zeng, M. W. Jia, J. Miao, A. Hoffmann, W. Zhang, Y. Z. Wu, Z. Yuan

Abstract: Using first-principles transport calculations, we predict that the anisotropic magnetoresistance (AMR) of single-crystal Co$_x$Fe$_{1-x}$ alloys is strongly dependent on the current orientation and alloy concentration. An intrinsic mechanism for AMR is found to arise from the band crossing due to magnetization-dependent symmetry protection. These special $k$-points can be shifted towards or away f… ▽ More Using first-principles transport calculations, we predict that the anisotropic magnetoresistance (AMR) of single-crystal Co$_x$Fe$_{1-x}$ alloys is strongly dependent on the current orientation and alloy concentration. An intrinsic mechanism for AMR is found to arise from the band crossing due to magnetization-dependent symmetry protection. These special $k$-points can be shifted towards or away from the Fermi energy by varying the alloy composition and hence the exchange splitting, thus allowing AMR tunability. The prediction is confirmed by delicate transport measurements, which further reveal a reciprocal relationship of the longitudinal and transverse resistivities along different crystal axes. △ Less

Submitted 3 August, 2020; originally announced August 2020.

Comments: 6 pages, 4 figures, Supplemental Materials available

Journal ref: Phys. Rev. Lett. 125, 097201 (2020)

Anisotropic transport and quantum oscillations in the quasi-one-dimensional TaNiTe5: Evidence for the nontrivial band topology

Authors: C. Q. Xu, Y. Liu, P. G. Cai, B. Li, W. H. Jiao, Y. L. Li, J. Y. Zhang, W. Zhou, B. Qian, X. F. Jiang, Z. X. Shi, R. Sankar, J. L. Zhang, F. Yang, Zengwei Zhu, P. K. Biswas, Dong Qian, X. Ke, Xiaofeng Xu

Abstract: The past decade has witnessed the burgeoning discovery of a variety of topological states of matter with distinct nontrivial band topologies. Thus far, most of materials studied possess two-dimensional or three-dimensional electronic structures, with only a few exceptions that host quasi-one-dimensional (quasi-1D) topological electronic properties. Here we present the clear-cut evidence for Dirac… ▽ More The past decade has witnessed the burgeoning discovery of a variety of topological states of matter with distinct nontrivial band topologies. Thus far, most of materials studied possess two-dimensional or three-dimensional electronic structures, with only a few exceptions that host quasi-one-dimensional (quasi-1D) topological electronic properties. Here we present the clear-cut evidence for Dirac fermions in the quasi-1D telluride TaNiTe5. We show that its transport behaviors are highly anisotropic and we observe nontrivial Berry phases via the quantum oscillation measurements. The nontrivial band topology is further corroborated by first-principles calculations. Our results may help to guide the future quest for topological states in this new family of quasi-1D ternary chalcogenides. △ Less

Submitted 16 June, 2020; originally announced June 2020.

Comments: 5 figures, 1 table

Journal ref: J. Phys. Chem. Lett. 11, 7782 (2020)

Topological Dirac states in a layered telluride TaPdTe$_5$ with quasi-one-dimensional PdTe$_2$ chains

Authors: Wen-He Jiao, Xiao-Meng Xie, Yi Liu, Xiaofeng Xu, Bin Li, Chun-Qiang Xu, Ji-Yong Liu, Wei Zhou, Yu-Ke Li, Hai-Yang Yang, Shan Jiang, Yongkang Luo, Zeng-Wei Zhu, Guang-Han Cao

Abstract: We report the synthesis and systematic studies of a new layered ternary telluride TaPdTe5 with quasi-one-dimensional PdTe2 chains. This compound crystalizes in a layered orthorhombic structure with space group Cmcm. Analysis of its curved field-dependent Hall resistivity, using the two-band model, indicates the hole-dominated transport with a high mobility $μ_h$ = 2.38 $\times$ 10$^3$ cm$^2$ V… ▽ More We report the synthesis and systematic studies of a new layered ternary telluride TaPdTe5 with quasi-one-dimensional PdTe2 chains. This compound crystalizes in a layered orthorhombic structure with space group Cmcm. Analysis of its curved field-dependent Hall resistivity, using the two-band model, indicates the hole-dominated transport with a high mobility $μ_h$ = 2.38 $\times$ 10$^3$ cm$^2$ V$^{-1}$ s$^{-1}$ at low temperatures. The in-plane magnetoresistance (MR) displays significant anisotropy with field applied along the crystallographic $b$ axis. The MR with the current applied along the $c$-axis is also measured in high magnetic fields up to 51.7 T. Remarkably, it follows a power-law dependence and reaches (9.5 $\times$ 10$^3$)% at 2.1 K without any signature of saturation. The De Haas-van Alphen oscillations show a small Fermi-surface pocket with a nontrivial Berry phase. The Shubnikov-de Haas (SdH) oscillations are detected at low temperatures and under magnetic fields above 28.5 T. Two effective masses $m^*$ (0.26$m_e$ and 0.41$m_e$) are extracted from the oscillatory SdH data. Our first-principles calculations unveil a topological Dirac cone in its surface states, and, in particular, the topological index indicates that TaPdTe$_5$ is a topologically nontrivial material. △ Less

Submitted 14 August, 2020; v1 submitted 16 June, 2020; originally announced June 2020.

Comments: 12 pages,6 figures

Journal ref: Phys. Rev. B 102, 075141 (2020)

ELSI -- An Open Infrastructure for Electronic Structure Solvers

Authors: Victor Wen-zhe Yu, Carmen Campos, William Dawson, Alberto García, Ville Havu, Ben Hourahine, William P Huhn, Mathias Jacquelin, Weile Jia, Murat Keçeli, Raul Laasner, Yingzhou Li, Lin Lin, Jianfeng Lu, Jonathan Moussa, Jose E Roman, Álvaro Vázquez-Mayagoitia, Chao Yang, Volker Blum

Abstract: Routine applications of electronic structure theory to molecules and periodic systems need to compute the electron density from given Hamiltonian and, in case of non-orthogonal basis sets, overlap matrices. System sizes can range from few to thousands or, in some examples, millions of atoms. Different discretization schemes (basis sets) and different system geometries (finite non-periodic vs. infi… ▽ More Routine applications of electronic structure theory to molecules and periodic systems need to compute the electron density from given Hamiltonian and, in case of non-orthogonal basis sets, overlap matrices. System sizes can range from few to thousands or, in some examples, millions of atoms. Different discretization schemes (basis sets) and different system geometries (finite non-periodic vs. infinite periodic boundary conditions) yield matrices with different structures. The ELectronic Structure Infrastructure (ELSI) project provides an open-source software interface to facilitate the implementation and optimal use of high-performance solver libraries covering cubic scaling eigensolvers, linear scaling density-matrix-based algorithms, and other reduced scaling methods in between. In this paper, we present recent improvements and developments inside ELSI, mainly covering (1) new solvers connected to the interface, (2) matrix layout and communication adapted for parallel calculations of periodic and/or spin-polarized systems, (3) routines for density matrix extrapolation in geometry optimization and molecular dynamics calculations, and (4) general utilities such as parallel matrix I/O and JSON output. The ELSI interface has been integrated into four electronic structure code projects (DFTB+, DGDFT, FHI-aims, SIESTA), allowing us to rigorously benchmark the performance of the solvers on an equal footing. Based on results of a systematic set of large-scale benchmarks performed with Kohn-Sham density-functional theory and density-functional tight-binding theory, we identify factors that strongly affect the efficiency of the solvers, and propose a decision layer that assists with the solver selection process. Finally, we describe a reverse communication interface encoding matrix-free iterative solver strategies that are amenable, e.g., for use with planewave basis sets. △ Less

Submitted 4 July, 2020; v1 submitted 31 December, 2019; originally announced December 2019.

Journal ref: Computer Physics Communications 256 (2020) 107459

Electronic structure and $H$-$T$ phase diagram of Eu(Fe$_{1-x}$Rh$_x$)$_2$As$_2$

Authors: Shaozhu Xiao, Darren C. Peets, Wei Liu, Shiju Zhang, Ya Feng, Wen-He Jiao, Guang-Han Cao, Eike F. Schwier, Kenya Shimada, Cong Li, Xingjiang Zhou, Shaolong He

Abstract: The iron-based superconductors represent a promising platform for high-temperature superconductivity, but the interactions underpinning their pairing present a puzzle. The EuFe$_2$As$_2$ family is unique among these materials for having magnetic order which onsets within the superconducting state, just below the superconducting transition. Superconductivity and magnetic order are normally antagoni… ▽ More The iron-based superconductors represent a promising platform for high-temperature superconductivity, but the interactions underpinning their pairing present a puzzle. The EuFe$_2$As$_2$ family is unique among these materials for having magnetic order which onsets within the superconducting state, just below the superconducting transition. Superconductivity and magnetic order are normally antagonistic and often vie for the same unpaired electrons, but in this family the magnetism arises from largely localized Eu moments and they coexist, with the competition between these evenly-matched opponents leading to reentrant superconducting behavior. To help elucidate the physics in this family and the interactions between the magnetic order and superconductivity, we investigate the $H$--$T$ phase diagram near optimal Rh doping through specific heat, resistivity, and magnetization measurements, and study the electronic structure by angular-resolved photoemission spectroscopy. The competition between the Eu and FeAs layers may offer a route to directly accessing the electronic structure under effective magnetic fields via ARPES, which is ordinarily a strictly zero-field technique. △ Less

Submitted 1 August, 2019; v1 submitted 27 May, 2019; originally announced May 2019.

Comments: 11 pages, 8 figures, Supplementary included as an appendix

Journal ref: Phys. Rev. B 100, 054510 (2019)

Parallel Transport Time-Dependent Density Functional Theory Calculations with Hybrid Functional on Summit

Authors: Weile Jia, Lin-Wang Wang, Lin Lin

Abstract: Real-time time-dependent density functional theory (rt-TDDFT) with hybrid exchange-correlation functional has wide-ranging applications in chemistry and material science simulations. However, it can be thousands of times more expensive than a conventional ground state DFT simulation, hence is limited to small systems. In this paper, we accelerate hybrid functional rt-TDDFT calculations using the p… ▽ More Real-time time-dependent density functional theory (rt-TDDFT) with hybrid exchange-correlation functional has wide-ranging applications in chemistry and material science simulations. However, it can be thousands of times more expensive than a conventional ground state DFT simulation, hence is limited to small systems. In this paper, we accelerate hybrid functional rt-TDDFT calculations using the parallel transport gauge formalism, and the GPU implementation on Summit. Our implementation can efficiently scale to 786 GPUs for a large system with 1536 silicon atoms, and the wall clock time is only 1.5 hours per femtosecond. This unprecedented speed enables the simulation of large systems with more than 1000 atoms using rt-TDDFT and hybrid functional. △ Less

Submitted 3 May, 2019; originally announced May 2019.

Universal critical behavior in the ferromagnetic superconductor Eu(Fe$_{0.75}$Ru$_{0.25}$)$_{2}$As$_{2}$

Authors: Zheng Zhou, W. T. Jin, Wei Li, S. Nandi, B. Ouladdiaf, Zheng Yan, Xinyuan Wei, Xuguang Xu, W. H. Jiao, N. Qureshi, Y. Xiao, Y. Su, G. H. Cao, Th. Brueckel

Abstract: The study of universal critical behavior is a crucial issue in a continuous phase transition, which groups various critical phenomena into universality classes for revealing microscopic electronic behaviors. The understanding of the nature of magnetism in Eu-based ferromagnetic superconductors is largely impeded by the infeasibility of performing inelastic neutron scattering measurements to deduce… ▽ More The study of universal critical behavior is a crucial issue in a continuous phase transition, which groups various critical phenomena into universality classes for revealing microscopic electronic behaviors. The understanding of the nature of magnetism in Eu-based ferromagnetic superconductors is largely impeded by the infeasibility of performing inelastic neutron scattering measurements to deduce the microscopic magnetic behaviors and the effects on the superconductivity, due to the significant neutron absorption effect of natural $^{152}$Eu and unavailability of large single crystals. However, by systematically combining the neutron diffraction experiment, the first-principles calculations, and the quantum Monte Carlo simulations, we have obtained a perfectly consistent universal critical exponent value of $β=0.385(13)$ experimentally and theoretically for Eu(Fe$_{0.75}$Ru$_{0.25}$)$_{2}$As$_{2}$, from which the magnetism in the Eu-based ferromagnetic superconductors is identified as the universal class of a three-dimensional anisotropic quantum Heisenberg model with long-range magnetic exchange coupling. This study not only clarifies the nature of microscopic magnetic behaviors in the Eu-based ferromagnetic superconductors, but also opens a new avenue of systemic methodology for studying the universal critical behaviors associated with magnetic phase transitions in the area of magnetism and the spin fluctuations effects on the unconventional superconductivity. △ Less

Submitted 14 August, 2019; v1 submitted 15 April, 2019; originally announced April 2019.

Comments: 6 pages, 4 figures, 1 table

Journal ref: Phys. Rev. B 100, 060406 (2019)

Polarization-sensitive and broadband photodetection based on a mixed-dimensionality TiS3/Si p-n junction

Authors: Yue Niu, Riccardo Frisenda, Eduardo Flores, Jose R. Ares, Weicheng Jiao, David Perez de Lara, Carlos Sanchez, Rongguo Wang, Isabel J. Ferrer, Andres Castellanos-Gomez

Abstract: The capability to detect the polarization state of light is crucial in many day-life applications and scientific disciplines. Novel anisotropic two-dimensional materials such as TiS3 combine polarization sensitivity, given by the in-plane optical anisotropy, with excellent electrical properties. Here we demonstrate the fabrication of a monolithic polarization sensitive broadband photodetector base… ▽ More The capability to detect the polarization state of light is crucial in many day-life applications and scientific disciplines. Novel anisotropic two-dimensional materials such as TiS3 combine polarization sensitivity, given by the in-plane optical anisotropy, with excellent electrical properties. Here we demonstrate the fabrication of a monolithic polarization sensitive broadband photodetector based on a mixed-dimensionality TiS3/Si p-n junction. The fabricated devices show broadband responsivity up to 1050 nm, a strong sensitivity to linearly polarized illumination with difference between the two orthogonal polarization states up to 350 % and a good detectivity and fast response time. The discussed devices can be used as building blocks to fabricate more complex polarization sensitive systems such as polarimeters. △ Less

Submitted 22 September, 2020; v1 submitted 27 March, 2019; originally announced March 2019.

Comments: 6 main text figures, 1 figure. Includes the supporting information (18 supp. info. figures)

Journal ref: Advanced Optical Materials, 2018, vol. 6, no 19, p. 1800351

Metallic glasses for spintronics: anomalous temperature dependence and giant enhancement of inverse spin Hall effect

Authors: W. Jiao, D. Z. Hou, C. Chen, H. Wang, Y. Z. Zhang, Y. Tian, Z. Y. Qiu, S. Okamoto, K. Watanabe, A. Hirata, T. Egami, E. Saitoh, M. W. Chen

Abstract: Spin-charge conversion via inverse spin Hall effect (ISHE) is essential for enabling various applications of spintronics. The spin Hall response usually follows a universal scaling relation with longitudinal electric resistivity and has mild temperature dependence because elementary excitations play only a minor role in resistivity and hence ISHE. Here we report that the ISHE of metallic glasses s… ▽ More Spin-charge conversion via inverse spin Hall effect (ISHE) is essential for enabling various applications of spintronics. The spin Hall response usually follows a universal scaling relation with longitudinal electric resistivity and has mild temperature dependence because elementary excitations play only a minor role in resistivity and hence ISHE. Here we report that the ISHE of metallic glasses shows nearly two orders of magnitude enhancements with temperature increase from a threshold of 80-100 K to glass transition points. As electric resistivity changes only marginally in the temperature range, the anomalous temperature dependence is in defiance of the prevailing scaling law. Such a giant temperature enhancement can be well described by a two-level thermal excitation model of glasses and disappears after crystallization, suggesting a new mechanism which involves unique thermal excitations of glasses. This finding may pave new ways to achieve high spin-charge conversion efficiency at room and higher temperatures for spintronic devices and to detect structure and dynamics of glasses using spin currents. △ Less

Submitted 30 August, 2018; originally announced August 2018.

Topological Type-II Dirac Fermions Approaching the Fermi Level in a Transition Metal Dichalcogenide NiTe2

Authors: Chunqiang Xu, Bin Li, Wenhe Jiao, Wei Zhou, Bin Qian, Raman Sankar, Nikolai D. Zhigadlo, Yanpeng Qi, Dong Qian, Fang-Cheng Chou, Xiaofeng Xu

Abstract: Type-II Dirac/Weyl semimetals are characterized by strongly tilted Dirac cones such that the Dirac/Weyl node emerges at the boundary of electron and hole pockets as a new state of quantum matter, distinct from the standard Dirac/Weyl points with a point-like Fermi surface which are referred to as type-I nodes. The type-II Dirac fermions were recently predicted by theory and have since been confirm… ▽ More Type-II Dirac/Weyl semimetals are characterized by strongly tilted Dirac cones such that the Dirac/Weyl node emerges at the boundary of electron and hole pockets as a new state of quantum matter, distinct from the standard Dirac/Weyl points with a point-like Fermi surface which are referred to as type-I nodes. The type-II Dirac fermions were recently predicted by theory and have since been confirmed in experiments in the PtSe2-class of transition metal dichal-cogenides. However, the Dirac nodes observed in PtSe2, PdTe2 and PtTe2 candidates are quite far away from the Fermi level, making the signature of topological fermions obscure as the physical properties are still dominated by the non-Dirac quasiparticles. Here we report the synthesis of a new type-II Dirac semimetal NiTe2 in which a pair of type-II Dirac nodes are located very close to the Fermi level. The quantum oscillations in this material reveal a nontrivial Berry's phase associated with these Dirac fermions. Our first principles calculations further unveil a topological Dirac cone in its surface states. Therefore, NiTe2 may not only represent an improved system to formulate the theoretical understanding of the exotic consequences of type-II Dirac fermions, it also facilitates possible applications based on these topological carriers. △ Less

Submitted 22 August, 2018; originally announced August 2018.

Comments: 4 figures, 1 table

Journal ref: Chem. Mater. 30, 4823 (2018)

Magnetism and superconductivity in Eu(Fe$_{1-x}$Ni$_{x}$)As$_2$ ($x$ = 0, 0.04)

Authors: Ya-Bin Liu, Yi Liu, Wen-He Jiao, Zhi Ren, Guang-Han Cao

Abstract: We report Eu-local-spin magnetism and Ni-doping-induced superconductivity (SC) in a 112-type ferroarsenide system Eu(Fe$_{1-x}$Ni$_{x}$)As$_2$. The non-doped EuFeAs$_2$ exhibits two primary magnetic transitions at $\sim$100 and $\sim$ 40 K, probably associated with a spin-density-wave (SDW) transition and an antiferromagnetic ordering in the Fe and Eu sublattices, respectively. Two additional succ… ▽ More We report Eu-local-spin magnetism and Ni-doping-induced superconductivity (SC) in a 112-type ferroarsenide system Eu(Fe$_{1-x}$Ni$_{x}$)As$_2$. The non-doped EuFeAs$_2$ exhibits two primary magnetic transitions at $\sim$100 and $\sim$ 40 K, probably associated with a spin-density-wave (SDW) transition and an antiferromagnetic ordering in the Fe and Eu sublattices, respectively. Two additional successive transitions possibly related to Eu-spin modulations appear at 15.5 and 6.5 K. For the Ni-doped sample with $x$ = 0.04, the SDW transition disappears, and SC emerges at $T_\mathrm{c}$ = 17.5 K. The Eu-spin ordering remains at around 40 K, followed by the possible reentrant magnetic modulations with enhanced spin canting. Consequently, SC coexists with a weak spontaneous magnetization below 6.2 K in Eu(Fe$_{0.96}$Ni$_{0.04}$)As$_2$, which provides a complementary playground for the study of the interplay between SC and magnetism. △ Less

Submitted 17 August, 2018; originally announced August 2018.

Comments: 7 pages, 7 figures, 1 table

Journal ref: Sci. China-Phys. Mech. Astron. 61, 127405 (2018)

Broadband terahertz generation via the interface inverse Rashba-Edelstein effect

Authors: C. Zhou, Y. P. Liu, Z. Wang, S. J. Ma, M. W. Jia, R. Q. Wu, L. Zhou, W. Zhang, M. K. Liu, Y. Z. Wu, J. Qi

Abstract: Novel mechanisms for electromagnetic wave emission in the terahertz (THz) frequency regime emerging at the nanometer scale have recently attracted intense attention for the purpose of searching next-generation broadband THz emitters. Here, we report a new mechanism for broadband THz emission, utilizing the interface inverse Rashba-Edelstein effect. By engineering the symmetry of the Ag/Bi Rashba i… ▽ More Novel mechanisms for electromagnetic wave emission in the terahertz (THz) frequency regime emerging at the nanometer scale have recently attracted intense attention for the purpose of searching next-generation broadband THz emitters. Here, we report a new mechanism for broadband THz emission, utilizing the interface inverse Rashba-Edelstein effect. By engineering the symmetry of the Ag/Bi Rashba interface, we demonstrate a controllable THz radiation (~0.1-5 THz) waveform emitted from metallic Fe/Ag/Bi heterostructures following photo-excitation. We further reveal that this type of THz radiation can be selectively superimposed on the emission discovered recently due to the inverse Spin Hall effect, yielding a unique film thickness dependent emission pattern. Our results thus offer new opportunities for versatile broadband THz radiation using the interface quantum effects. △ Less

Submitted 12 April, 2018; originally announced April 2018.

Journal ref: Phys. Rev. Lett. 121, 086801 (2018)