Showing 1–50 of 156 results for author: Zhou, Q

Collective Electrostatics and Band Alignment in Janus MoSTe nanotubes

Authors: Adithya Sadanandan, Tyson Karl, Rahil Shaik, Qunfei Zhou

Abstract: In this work, we investigate the collective electrostatic effects of one-dimensional (1D) Janus MoSTe nanotubes and their impacts on the band alignment of nanotube heterostructures. Using first-principles calculations based on Density Functional Theory, we find that the Janus nanotube generates a large and uniform electrostatic potential of over 1.3 V within the nanotube pores, which is accumulati… ▽ More In this work, we investigate the collective electrostatic effects of one-dimensional (1D) Janus MoSTe nanotubes and their impacts on the band alignment of nanotube heterostructures. Using first-principles calculations based on Density Functional Theory, we find that the Janus nanotube generates a large and uniform electrostatic potential of over 1.3 V within the nanotube pores, which is accumulative for double wall nanotubes. We develop an analytical model to provide a quantitative understanding of the electrostatic potential and its dependence on the quadrupole moment and nanotube radius. For double wall MoSTe nanotube, we find a substantial band edge shift of about 1.0 eV for the inner tube originated from the electrostatic effects, leading to a type-II band alignment. These results demonstrate that the electrostatic effects of 1D nanotubes can be used to tune the electronic properties and band alignment of 1D nanotube heterostructures for optoelectronic and catalytic applications. △ Less

Submitted 6 April, 2026; originally announced April 2026.

Realization of a Synthetic Hall Torus with a Spinor Bose-Einstein Condensate

Authors: T. -H. Chien, S. -C. Wu, Y. -H. Su, L. -R. Liu, N. -C. Chiu, M. Sarkar, Q. Zhou, Y. -J. Lin

Abstract: We report the first experimental realization of a synthetic Hall torus using a spinor Bose-Einstein condensate confined in a ring-shaped trap with in situ imaging. By cyclically coupling three hyperfine spin states via Raman and microwave fields, we impose a periodic boundary condition in the synthetic dimension, which together with a real-space ring trap, realizes a toroidal geometry with a synth… ▽ More We report the first experimental realization of a synthetic Hall torus using a spinor Bose-Einstein condensate confined in a ring-shaped trap with in situ imaging. By cyclically coupling three hyperfine spin states via Raman and microwave fields, we impose a periodic boundary condition in the synthetic dimension, which together with a real-space ring trap, realizes a toroidal geometry with a synthetic magnetic flux. This flux induces azimuthal density modulations in the condensate, whose periodicity is uniquely determined by the quantized toroidal magnetic flux-a hallmark of the Hall torus geometry. By varying the relative phase between the couplings across repeated experimental runs, we control the location of the density extrema, emulating the behavior of Thouless charge pump in a toroidal geometry. We further investigate the onset of these modulations as the system transitions from a cylindrical to a toroidal topology. Our results establish a versatile platform for investigating quantum Hall physics and topological phenomena in synthetic curved spaces. △ Less

Submitted 16 February, 2026; originally announced February 2026.

Correlation between superfluid density and transition temperature in infinite-layer nickelate superconductor $Nd_{1-x}Sr_xNiO_2$

Authors: Z. J. Li, R . Z. Zhang, M. H. Xu, K. Y. Liang, Y. Zhao, Q. S. He, Q. Z. Zhou, B. R. Chen, P. H. Zhang, K. Z. Yao, H. X. Yao, L. Qiao, Y. H. Wang

Abstract: A strong correlation between zero-temperature superfluid density ($ρ_{s0}$) and transition temperature ($T_c$) is considered as a hallmark of unconventional superconductivity. However, their relationship has yet to be unveiled in nickelates due to sample inhomogeneity. Here we perform local susceptometry on an infinite-layer nickelate superconductor $Nd_{0.8}Sr_{0.2}NiO_2$. The sample shows inhomo… ▽ More A strong correlation between zero-temperature superfluid density ($ρ_{s0}$) and transition temperature ($T_c$) is considered as a hallmark of unconventional superconductivity. However, their relationship has yet to be unveiled in nickelates due to sample inhomogeneity. Here we perform local susceptometry on an infinite-layer nickelate superconductor $Nd_{0.8}Sr_{0.2}NiO_2$. The sample shows inhomogeneous superfluid density and $T_c$ on micron-scale. The spatial statistics for different scan areas reveal a linear dependence of local $T_c$ on $ρ_{s0}$ for $T_c$>8 K and a sub-linear one for $T_c$<8 K. Remarkably, the overall relationship is reminiscent of that reported in overdoped cuprate superconductors, hinting at a close connection between them. △ Less

Submitted 18 January, 2026; originally announced January 2026.

Symmetry-driven giant magneto-optical Kerr effects in altermagnet hematite

Authors: Jiaxin Luo, Xiaodong Zhou, Jinxuan Liang, Ledong Wang, Qiuyun Zhou, Yong Jiang, Wenhong Wang, Yugui Yao, Luyi Yang, Wanjun Jiang

Abstract: Altermagnets have attracted tremendous interest for revealing intriguing physics and promising spintronics applications. In contrast to conventional antiferromagnets, altermagnets break both PT and Tt symmetries, and simultaneously exhibit spin-split band structures with a vanishing net magnetization. To quantify insulating altermagnets without conduction electron, we propose to use magneto-optica… ▽ More Altermagnets have attracted tremendous interest for revealing intriguing physics and promising spintronics applications. In contrast to conventional antiferromagnets, altermagnets break both PT and Tt symmetries, and simultaneously exhibit spin-split band structures with a vanishing net magnetization. To quantify insulating altermagnets without conduction electron, we propose to use magneto-optical Kerr effect (MOKE) to identify the altermagnetic fingerprints. In particular, we demonstrate not only the giant MOKE responses, but also their connection with the orientations of Neel vectors at room temperature in altermagnet hematite alpha-Fe_2O_3. Specifically, under the Neel vector along the [1-100] axis, we find a giant polar Kerr rotation angle 93.4 mdeg in the (11-20) plane, which is allowed by the magnetic space group C2'/c'. Under the Neel vector along the [11-20] axis, we find a longitudinal Kerr angle 9.6 mdeg in the (0001) plane, which is allowed by the magnetic space group C2/c. Further, we show that such pronounced MOKE effects directly enable an optical imaging of altermagnetic domains, together with their reversible domain wall (DW) motion. Our studies not only suggest MOKE can be used to identify altermagnet candidates, but also signify the feasibility of exploring altermagnetic optical and DW spintronics, which could largely expand the current research paradigm of altermagnetism. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Multi-pole solitons and breathers with spatially periodic modulation induced by the helicoidal spin-orbit coupling

Authors: Cui-Cui Ding, Qin Zhou, B. A. Malomed

Abstract: We report analytical solutions for diverse multi-pole (MP) soliton and breather states in spatially inhomogeneous binary Bose-Einstein condensates (BECs) with the helicoidally shaped spin-orbit coupling (SOC), including MP stripe solitons on zero background, MP beating stripe solitons on a nonzero plane-wave background, as well as MP beating stripe solitons and MP breathers on periodic backgrounds… ▽ More We report analytical solutions for diverse multi-pole (MP) soliton and breather states in spatially inhomogeneous binary Bose-Einstein condensates (BECs) with the helicoidally shaped spin-orbit coupling (SOC), including MP stripe solitons on zero background, MP beating stripe solitons on a nonzero plane-wave background, as well as MP beating stripe solitons and MP breathers on periodic backgrounds. The results indicate that modulation effects produced by the helicoidal SOC not only induce stripe patterns in MP solitons, but also generate the spatially-periodic background for the MP beating stripe solitons and breathers. An asymptotic analysis reveals curved trajectories with a logarithmically increasing soliton/breather separation for these MP excitations, fundamentally distinguishing them from periodic trajectories of bound-state solitons/breathers or straight trajectories of conventional multi-soliton/breather sets. With complex periodic structures in individual components, the total density distribution is nonperiodic, due to their configurations which are out-of-phase with respect to the two components. We further examine several degenerate structures of MP solitons and breathers under varying SOC and spectral parameters. Numerical simulations validate the analytical results and demonstrate stability of these MP excitations. These findings may facilitate deeper understanding of soliton/breather interactions beyond conventional multi-soliton systems and bound-state complexes in SOC BEC. △ Less

Submitted 27 November, 2025; originally announced December 2025.

Comments: To be published in Physica D

Lead-Free Europium Halide Perovskite Nanoplatelets

Authors: Sebastian Fernández, Divine Mbachu, Manchen Hu, Han Cui, William Michaels, Pournima Narayanan, Tyler K. Colenbrander, Qi Zhou, Da Lin, Ona Segura Lecina, Guosong Hong, Daniel N. Congreve

Abstract: Metal halide perovskites possess desirable optical, material, and electrical properties which have had substantial impact on next-generation optoelectronics. However, given the toxicity of lead, alternative lead-free perovskite semiconductors are needed. By fully replacing lead with rare-earth elements, one can simultaneously address toxicity concerns and achieve comparable optoelectronic performa… ▽ More Metal halide perovskites possess desirable optical, material, and electrical properties which have had substantial impact on next-generation optoelectronics. However, given the toxicity of lead, alternative lead-free perovskite semiconductors are needed. By fully replacing lead with rare-earth elements, one can simultaneously address toxicity concerns and achieve comparable optoelectronic performance. Here, we demonstrate the synthesis of two-dimensional europium halide perovskite nanoplatelets governed by the formula $\mathrm{L_{2}EuX_{4}}$ where L is an organic ligand and X is a halide anion. The structure, morphology, and composition of the nanoplatelets are confirmed by XRD, AFM, and XPS. Deep blue-emitting $\mathrm{PEA_{2}EuBr_{4}}$ perovskite nanoplatelets are synthesized in both the solution- and solid-states with photoluminescence emission centered at 446 nm and CIE color coordinates of (0.1515, 0.0327) and (0.1515, 0.0342), respectively. Additionally, near-ultraviolet $\mathrm{PEA_{2}EuCl_{4}}$ perovskite nanoplatelets are synthesized in both the solution- and solid-states with photoluminescence emission centered at 400 nm and 401 nm, respectively. Overall, europium halide perovskite nanoplatelets offer a lead-free alternative for deep blue, violet, and near-ultraviolet light emission $\unicode{x2013}$ charting new pathways for optoelectronics in this energy regime. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Lossy phononic metamaterials for valley manipulation

Authors: Shunda Yin, Qiuyan Zhou, Yuxiang Xi, Weiyin Deng, Wei Chen, Jiuyang Lu, Manzhu Ke, Zhengyou Liu

Abstract: Non-Hermitian physics characterized by complex band spectra has established a new paradigm in condensed matter systems and metamaterials. Recently, non-Hermitian gain and nonreciprocity are deliberately introduced to valley manipulation, leading to various phenomena beyond the Hermitian scenarios, such as the amplified topological whispering gallery modes as an acoustic laser. In contrast, pure lo… ▽ More Non-Hermitian physics characterized by complex band spectra has established a new paradigm in condensed matter systems and metamaterials. Recently, non-Hermitian gain and nonreciprocity are deliberately introduced to valley manipulation, leading to various phenomena beyond the Hermitian scenarios, such as the amplified topological whispering gallery modes as an acoustic laser. In contrast, pure loss is inevitable in practice and generally regarded as a detrimental factor. Here, we reveal that the coupling loss can manipulate valley degrees of freedom in a phononic metamaterial. Three distinct valley-related effects, including valley-resolved nonreciprocity that functions as a valley filter, valley-dependent skin effects where bulk states from different valleys localize at opposite boundaries, and valley-projected edge states with boundary-dependent lifetimes that leads to an anomalous beam splitting, are demonstrated through theoretical analysis and airborne sound experiments. Owing to the easy preparation of loss, our findings shed light on both non-Hermitian and valley physics and may facilitate innovative applications of valley-related devices. △ Less

Submitted 24 October, 2025; originally announced October 2025.

Comments: 18 pages,4 figures

Dipole condensates in synthetic rank-2 electric fields

Authors: Jiali Zhang, Wenhui Xu, Qi Zhou, Shaoliang Zhang

Abstract: Dipole condensates, formed from particle-hole pairs, represent a unique class of charge-neutral quantum fluids that evade conventional vector gauge fields, making their electrodynamic responses difficult to probe in natural materials. Here, we propose a tunable platform using strongly interacting two-component ultracold atoms to realize dipole condensates and probe their coupling to rank-2 electri… ▽ More Dipole condensates, formed from particle-hole pairs, represent a unique class of charge-neutral quantum fluids that evade conventional vector gauge fields, making their electrodynamic responses difficult to probe in natural materials. Here, we propose a tunable platform using strongly interacting two-component ultracold atoms to realize dipole condensates and probe their coupling to rank-2 electric fields. By applying spin-dependent forces and treating spin as a synthetic dimension, we engineer a synthetic rank-2 electric field that induces measurable electrodynamic responses. We identify the atomic analog of perfect Coulomb drag: increasing intercomponent interactions leads to equal and opposite displacements of the centers of mass of the two spin components. Furthermore, a rank-2 electric field imprints a phase twist in the dipole condensate and generates a supercurrent of dipoles that obeys the dipolar Josephson relation -- a smoking gun for dipole condensation. Our results establish a powerful platform for exploring dipolar superfluidity under tensor gauge fields. △ Less

Submitted 17 September, 2025; originally announced September 2025.

Comments: 7 pages, 5 figures

Excitonic skin effect

Authors: Wenhui Xu, Qi Zhou

Abstract: We show that strong interactions combined with band-dependent imaginary vector potentials give rise to boundary localization of particle-hole pairs, which we term the excitonic skin effect. In a bilayer system with layer-specific gain/loss and an in-plane magnetic field, excitons experience a net imaginary vector potential, resulting in directional amplification of particle-hole pairs. Including n… ▽ More We show that strong interactions combined with band-dependent imaginary vector potentials give rise to boundary localization of particle-hole pairs, which we term the excitonic skin effect. In a bilayer system with layer-specific gain/loss and an in-plane magnetic field, excitons experience a net imaginary vector potential, resulting in directional amplification of particle-hole pairs. Including nearest-neighbor interactions leads to a non-Hermitian bosonic Kitaev model, where the pairing effects grow exponentially with the size of the system, revealing a unique form of critical skin effect in interacting systems. Our framework applies to both atomic and electronic platforms and is directly testable in current experiments. These results also provide a route to explore non-Hermitian analogs of tensor gauge fields. △ Less

Submitted 27 August, 2025; originally announced August 2025.

Polarization-dependent chiral transport and chiral solitons in spin Kitaev models

Authors: Chenwei Lv, Thomas Bilitewski, Ana Maria Rey, Qi Zhou

Abstract: Recent advances in synthetic quantum matter allow researchers to design quantum models inaccessible in traditional materials. Here, we propose protocols to engineer a new class of quantum spin models, which we call spin Kitaev models. The building blocks are basic spin-exchange interactions combined with locally selective Floquet pulses, a capability recently demonstrated in a range of experimenta… ▽ More Recent advances in synthetic quantum matter allow researchers to design quantum models inaccessible in traditional materials. Here, we propose protocols to engineer a new class of quantum spin models, which we call spin Kitaev models. The building blocks are basic spin-exchange interactions combined with locally selective Floquet pulses, a capability recently demonstrated in a range of experimental platforms. The resulting flip-flip and flop-flop terms lead to intriguing quantum transport dynamics beyond conventional spin models. For instance, in the absence of a magnetic field, spin excitations polarized along the $x$ and $y$ axes propagate chirally in opposite directions, producing polarization-dependent spin transport. In the large-spin limit, the spin Kitaev model maps to a nonlinear Hatano-Nelson model, where the interplay of nonlinearity and the underlying curvature yields polarization-dependent chiral solitons. A magnetic field binds two oppositely polarized chiral solitons into a chiral solitonic molecule, whose travel direction depends on its orientation. Our results, directly accessible in current experiments, open new opportunities for simulating transport in curved spaces and for applications in spintronics, information processing, and quantum sensing. △ Less

Submitted 23 August, 2025; originally announced August 2025.

Comments: 7+9 pages, 3+7 figures

Low Power, Scalable Nanofabrication via Photon Upconversion

Authors: Qi Zhou, Hao-Chi Yen, Qizhen Lan, Arynn O. Gallegos, Manchen Hu, Kyle Frohna, Hannah Niese, Da Lin, Natalia Murrietta, Pournima Narayanan, Tracy H. Schloemer, Linda Pucurimay, Sebastian Fernández, Michael Seitz, Daniel N. Congreve

Abstract: Micro- and nanoscale fabrication, which enables precise construction of intricate three-dimensional structures, is of foundational importance for advancing innovation in plasmonics, nanophotonics, and biomedical applications. However, scaling fabrication to industrially relevant levels remains a significant challenge. We demonstrate that triplet-triplet annihilation upconversion (TTA-UC) offers a… ▽ More Micro- and nanoscale fabrication, which enables precise construction of intricate three-dimensional structures, is of foundational importance for advancing innovation in plasmonics, nanophotonics, and biomedical applications. However, scaling fabrication to industrially relevant levels remains a significant challenge. We demonstrate that triplet-triplet annihilation upconversion (TTA-UC) offers a unique opportunity to increase fabrication speeds and scalability of micro- and nanoscale 3D structures. Due to its nonlinearity and low power requirements, TTA-UC enables localized polymerization with nanoscale resolutions while simultaneously printing millions of voxels per second through optical parallelization using off-the-shelf light-emitting diodes and digital micromirror devices. Our system design and component integration empower fabrication with a minimum lateral feature size down to 230 nm and speeds up to 112 million voxels per second at a power of 7.0 nW per voxel. This combination of high resolution and fast print speed demonstrates that TTA-UC is a significant advancement in nanofabrication technique, evidenced by the fabrication of hydrophobic nanostructures on a square-centimeter scale, paving the way for industrial nanomanufacturing. △ Less

Submitted 20 August, 2025; originally announced August 2025.

Observation of Metal-Insulator and Spectral Phase Transitions in Aubry-André-Harper Models

Authors: Quan Lin, Christopher Cedzich, Qi Zhou, Peng Xue

Abstract: Non-Hermitian extensions of the Aubry-André-Harper (AAH) model reveal a rich variety of phase transitions arising from the interplay of quasiperiodicity and non-Hermiticity. Despite their theoretical significance, experimental explorations remain challenging due to complexities in realizing controlled non-Hermiticity. Here, we present the first experimental realization of the unitary almost-Mathie… ▽ More Non-Hermitian extensions of the Aubry-André-Harper (AAH) model reveal a rich variety of phase transitions arising from the interplay of quasiperiodicity and non-Hermiticity. Despite their theoretical significance, experimental explorations remain challenging due to complexities in realizing controlled non-Hermiticity. Here, we present the first experimental realization of the unitary almost-Mathieu operator (UAMO) which simulates the AAH model by employing single-photon quantum walks. Through precise control of quasiperiodicity, we systematically explore the phase diagram displaying a phase transition between localized and delocalized regimes in the Hermitian limit. Subsequently, by introducing non-reciprocal hopping, we experimentally probe the parity-time (PT) symmetry-breaking transition that is characterized by the emergence of complex quasienergies. Moreover, we identify a novel spectral transition exclusive to discrete-time settings, where all quasienergies become purely imaginary. Both transitions are connected to changes in the spectral winding number, demonstrating their topological origins. These results clarify the interplay between localization, symmetry breaking, and topology in non-Hermitian quasicrystals, paving the way for future exploration of synthetic quantum matter. △ Less

Submitted 11 August, 2025; originally announced August 2025.

Comments: 9+3 pages, 7 figures

Stability and Symmetry-Assured Crystal Structure Generation for Inverse Design of Photocatalysts in Water Splitting

Authors: Zhilong Song, Chongyi Ling, Qiang Li, Qionghua Zhou, Jinlan Wang

Abstract: Generative models are revolutionizing materials discovery by enabling inverse design-direct generation of structures from desired properties. However, existing approaches often struggle to ensure inherent stability and symmetry while precisely generating structures with target compositions, space groups, and lattices without fine-tuning. Here, we present SSAGEN (Stability and Symmetry-Assured GENe… ▽ More Generative models are revolutionizing materials discovery by enabling inverse design-direct generation of structures from desired properties. However, existing approaches often struggle to ensure inherent stability and symmetry while precisely generating structures with target compositions, space groups, and lattices without fine-tuning. Here, we present SSAGEN (Stability and Symmetry-Assured GENerative framework), which overcomes these limitations by decoupling structure generation into two distinct stages: crystal information (lattice, composition, and space group) generation and coordinate optimization. SSAGEN first generates diverse yet physically plausible crystal information, then derives stable and metastable atomic positions through universal machine learning potentials, combined global and local optimization with symmetry and Wyckoff position constraints, and dynamically refined search spaces. Compared to prior generative models such as CDVAE, SSAGEN improves the thermodynamic and kinetic stability of generated structures by 148% and 180%, respectively, while inherently satisfying target compositions, space groups, and lattices. Applied to photocatalytic water splitting (PWS), SSAGEN generates 200,000 structures-81.2% novel-with 3,318 meeting all stability and band gap criteria. Density functional theory (DFT) validation confirms 95.6% structures satisfy PWS requirements, with 24 optimal candidates identified through comprehensive screening based on electronic structure, thermodynamic, kinetic, and aqueous stability criteria. SSAGEN not only precisely generates materials with desired crystal information but also ensures inherent stability and symmetry, establishing a new paradigm for targeted inverse design of functional materials. △ Less

Submitted 25 July, 2025; originally announced July 2025.

Designing artificial zinc phosphate tribofilms with tailored mechanical properties by altering the chain length

Authors: Sebastian Lellig, Subisha Balakumar, Peter Schweizer, Eva P. Mayer, Simon Evertz, Marcus Hans, Damian M. Holzapfel, Yin Du, Qing Zhou, Martin Dienwiebel, Johann Michler, Jochen M. Schneider

Abstract: Zinc dialkyldithiophosphate (ZDDP), as the most prominent lubrication additive, forms tribofilms consisting primarily of zinc phosphate glasses containing sulfides. As sulfur is linked to environmental concerns, sulfur-free zinc phosphate coatings have been sputtered from a Zn3(PO4)2 target and investigated here. Based on the bridging to non-bridging oxygen ratio, determined by X-ray photoelectron… ▽ More Zinc dialkyldithiophosphate (ZDDP), as the most prominent lubrication additive, forms tribofilms consisting primarily of zinc phosphate glasses containing sulfides. As sulfur is linked to environmental concerns, sulfur-free zinc phosphate coatings have been sputtered from a Zn3(PO4)2 target and investigated here. Based on the bridging to non-bridging oxygen ratio, determined by X-ray photoelectron spectroscopy (XPS), the as deposited coatings are classified as metaphosphates. As the annealing temperature is increased, the chain lengths are reduced, as witnessed by XPS data indicated by a loss of phosphorus and oxygen of the coating surface, likely due to hydrolysis with water from the atmosphere. Transmission electron microscopy energy-dispersive X-ray spectroscopy line scans show that the XPS-revealed composition change of the coating surface upon annealing occurs over the whole thickness of the coating. This alteration in composition and chain length reductions causes a rise in hardness, reduced Young's modulus, and wear resistance. Therefore, the properties of the artificial zinc phosphate tribofilms can be tailored via a thermally stimulated composition change, causing an alternation in chain length from meta- to orthophosphate and thereby enabling the design of coatings with desired mechanical properties. △ Less

Submitted 13 June, 2025; originally announced June 2025.

Comments: Manuscript: 19 pages, 6 figures. Supplementary information: 2 pages, 3 figures

Unusual Electron-Phonon Interactions in Highly Anisotropic Two-Dimensional $Ta_2$$Ni_3$$Te_5$

Authors: Fei Wang, Qiaohui Zhou, Hong Tang, Fan Zhang, Yanxing Li, Ana M Sanchez, Keyuan Bai, Sidra Younus, Chih-Kang Shih, Adrienn Ruzsinszky, Xin Lu, Jiang Wei

Abstract: Electron-phonon interactions (EPIs) represent a fundamental cornerstone of condensed matter physics, commanding persistent attention due to their pivotal role in driving novel quantum phenomena within low-dimensional materials. Here, we unveil unusual anisotropic electron-phonon coupling behaviors in quasi-one-dimensional $Ta_2$$Ni_3$$Te_5$ nano-flakes through a powerful combination of angle-resol… ▽ More Electron-phonon interactions (EPIs) represent a fundamental cornerstone of condensed matter physics, commanding persistent attention due to their pivotal role in driving novel quantum phenomena within low-dimensional materials. Here, we unveil unusual anisotropic electron-phonon coupling behaviors in quasi-one-dimensional $Ta_2$$Ni_3$$Te_5$ nano-flakes through a powerful combination of angle-resolved polarized Raman spectroscopy and density functional perturbation theory (DFPT). High-resolution transmission electron microscopy and scanning tunneling microscopy directly visualize the pronounced quasi-one-dimensional atomic chains within the crystal structure, establishing a structural foundation for the observed anisotropic interactions. Our Raman investigations reveal remarkable polarization-dependent responses in $A_g$ phonon modes that deviate significantly from conventional behavior, which our theoretical analyses attribute to complex anisotropic electron-photon and electron-phonon interactions. Temperature-dependent Raman measurements further uncover an intriguing phonon decay mechanism involving both three- and four-phonon processes, with the latter showing significant contributions in some modes - a possible manifestation of strong anisotropic electron-phonon interactions. Beyond revealing $Ta_2$$Ni_3$$Te_5$ as an exceptional platform for exploring anisotropic EPIs, this work demonstrates that integrating angle-resolved polarized Raman spectroscopy with DFPT calculations offers a powerful methodology for investigating electron-phonon interactions in emerging low-dimensional quantum materials. △ Less

Submitted 19 July, 2025; v1 submitted 6 June, 2025; originally announced June 2025.

Pure nematic transition inside the superconducting dome of iron chalcogenide superconductor FeSe$_{1-x}$Te$_x$

Authors: K. Y. Liang, R . Z. Zhang, Z. F. Lin, Z. J. Li, B. R. Chen, P. H. Zhang, K. Z. Yao, Q. S. He, Q. Z. Zhou, H. X. Yao, K. Jin, Y. H. Wang

Abstract: Nematicity and magnetism are prevalent orders in high transition temperature (Tc) superconductors, coexisting in the parent compound of most material families. Quantum fluctuations of nematicity or spin orders are both plausible candidates for mediating unconventional Cooper pairing. Identifying the sole effect of a nematic quantum critical point (QCP) on the emergence of superconducting dome with… ▽ More Nematicity and magnetism are prevalent orders in high transition temperature (Tc) superconductors, coexisting in the parent compound of most material families. Quantum fluctuations of nematicity or spin orders are both plausible candidates for mediating unconventional Cooper pairing. Identifying the sole effect of a nematic quantum critical point (QCP) on the emergence of superconducting dome without interference of spin fluctuations is therefore highly desirable. The iron chalcogenide superconductor FeSe exhibits pure nematicity without any magnetic ordering. A nematic quantum phase transition can be induced by Te substitution but experimental study of such transition is so far limited to its normal state. By performing local susceptometry on composition-spread FeSe$_{1-x}$Te$_x$ films ($0 < x < 1$) using scanning Superconducting Quantum Interference Device (sSQUID) microscopy, we investigate the superfluid density ($ρ_s$) across the pure nematic transition in extremely fine steps of $Δx$ = 0.0008. The temperature dependence of $ρ_s$ changes from the form of anisotropic pairing on the nematic side to an isotropic one across the critical doping $x_c$. The power-law dependence of gap anisotropy on $|x - x_c|$ provides evidence for nematic quantum criticality under the superconducting dome. The low-temperature $ρ_s$ scales linearly with Tc in the nematic phase $x < x_c$, whereas the gap amplitude, maximized at $x_c$, determines the Tc for $x>x_c$. Our results establish a pure nematic QCP in FeSe$_{1-x}$Te$_x$, separating two superconducting orders with distinct pairing boosted by nematic quantum fluctuations. △ Less

Submitted 21 May, 2025; originally announced May 2025.

The fundamental localization phases in quasiperiodic systems: A unified framework and exact results

Authors: Xin-Chi Zhou, Bing-Chen Yao, Yongjian Wang, Yucheng Wang, Yudong Wei, Qi Zhou, Xiong-Jun Liu

Abstract: The disordered quantum systems host three classes of quantum states, the extended, localized, and critical, which bring up seven distinct fundamental phases in nature: three pure phases and four coexisting ones with mobility edges, yet a unified theory built on universal mechanism and full realization of all these phases has not been developed. Here we propose a unified framework based on a spinfu… ▽ More The disordered quantum systems host three classes of quantum states, the extended, localized, and critical, which bring up seven distinct fundamental phases in nature: three pure phases and four coexisting ones with mobility edges, yet a unified theory built on universal mechanism and full realization of all these phases has not been developed. Here we propose a unified framework based on a spinful quasiperiodic (QP) system which realizes all the fundamental localization phases, with the exact and universal results being obtained for their characterization. First, we show that the pure phases are obtained when the chiral(-like) symmetry preserves in the proposed spinful QP model, giving a criterion for emergence of the pure phases and otherwise the coexisting ones. Further, we uncover a novel mechanism for the critical states that their emergence is protected by the generalized incommensurate matrix element zeros in the spinful QP model, which considerably broadens rigorous realizations of the exotic critical states. We then show criteria of exact solvability for the present spinful QP system, with which we construct various exactly solvable models for all distinct localization phases. In particular, we propose two novel models, dubbed spin-selective QP lattice model and QP optical Raman lattice model, to achieve all basic types of mobility edges and all the seven fundamental phases of Anderson localization physics, respectively. The experimental scheme is proposed and studied in detail to realize these models with high feasibility. This study establishes a complete and profound theoretical framework which enables an in-depth exploration of the broad classes of all fundamental localization phenomena in QP systems, and offers key insights for constructing their exactly solvable models with experimental feasibility. △ Less

Submitted 14 February, 2026; v1 submitted 31 March, 2025; originally announced March 2025.

Comments: 32 pages, 12 figures. Substantially improved according to referees' reports

Beating stripe solitons arising from helicoidal spin-orbit coupling in Bose-Einstein condensates

Authors: Cui-Cui Ding, Qin Zhou, B. A. Malomed

Abstract: We demonstrate that the model of a spatially non-uniform two-component Bose-Einstein condensate (BEC) featuring the helicoidal spin-orbit coupling (SOC), gives rise to dark-bright soliton complexes characterized by spatiotemporal periodic oscillations in each component. These solitons are formed by the superposition of dark and bright ones, and exhibit a beating state over time and a striped state… ▽ More We demonstrate that the model of a spatially non-uniform two-component Bose-Einstein condensate (BEC) featuring the helicoidal spin-orbit coupling (SOC), gives rise to dark-bright soliton complexes characterized by spatiotemporal periodic oscillations in each component. These solitons are formed by the superposition of dark and bright ones, and exhibit a beating state over time and a striped state across space, earning them the designation of beating stripe solitons. Our analysis demonstrates that helicoidal SOC significantly affects the formation and dynamical properties of these solitons, also serving as the primary driver for spin oscillations. Through the nonlinear superposition of the beating stripe solitons, a range of intricate scenarios of the interaction between multiple solitons emerges, including head-on collisions, bound states, and parallel states. △ Less

Submitted 19 March, 2025; originally announced March 2025.

Comments: To be published in Phys. Rev. E

LLM-Feynman: Leveraging Large Language Models for Universal Scientific Formula and Theory Discovery

Authors: Zhilong Song, Qionghua Zhou, Chunjin Ren, Chongyi Ling, Minggang Ju, Jinlan Wang

Abstract: Distilling underlying principles from data has historically driven scientific breakthroughs. However, conventional data-driven machine learning often produces complex models that lack interpretability and generalization due to insufficient domain expertise. Here, we present LLM-Feynman, a novel framework that leverages large language models (LLMs) alongside systematic optimization to derive concis… ▽ More Distilling underlying principles from data has historically driven scientific breakthroughs. However, conventional data-driven machine learning often produces complex models that lack interpretability and generalization due to insufficient domain expertise. Here, we present LLM-Feynman, a novel framework that leverages large language models (LLMs) alongside systematic optimization to derive concise, interpretable formulas from data and domain knowledge. Our method integrates automated feature engineering, LLM-guided symbolic regression with self-evaluation, and Monte Carlo tree search to enhance formula discovery and clarity. The embedding of domain knowledge simplifies the formula, while self-evaluation based on this knowledge further minimizes prediction errors, surpassing conventional symbolic regression in accuracy and interpretability. Our LLM-Feynman successfully rediscovered over 90% of fundamental physical formulas and demonstrated its efficacy in key materials science applications, including classification of two-dimensional material and perovskite synthesizability and determination of the Green's function and screened Coulomb interaction bandgaps, and prediction of ionic conductivity in lithium solid-state electrolytes. By transcending mere data fitting through the integration of deep domain knowledge, this LLM-Feynman offers a transformative paradigm for the automated discovery of generalizable scientific formulas and theories across disciplines. △ Less

Submitted 25 July, 2025; v1 submitted 9 March, 2025; originally announced March 2025.

Phase Transitions in Quasi-Periodically Driven Quantum Critical Systems: Analytical Results

Authors: Jiyuan Fang, Qi Zhou, Xueda Wen

Abstract: In this work, we study analytically the phase transitions in quasi-periodically driven one dimensional quantum critical systems that are described by conformal field theories (CFTs). The phase diagrams and phase transitions can be analytically obtained by using Avila's global theory in one-frequency quasiperiodic cocycles. Compared to the previous works where the quasiperiodicity was introduced in… ▽ More In this work, we study analytically the phase transitions in quasi-periodically driven one dimensional quantum critical systems that are described by conformal field theories (CFTs). The phase diagrams and phase transitions can be analytically obtained by using Avila's global theory in one-frequency quasiperiodic cocycles. Compared to the previous works where the quasiperiodicity was introduced in the driving time and no phase transitions were observed [1], here we propose a setup where the quasiperiodicity is introduced in the driving Hamiltonians. In our setup, one can observe the heating phases, non-heating phases, and the phase transitions. The phase diagram as well as the Lyapunov exponents that determine the entanglement entropy evolution can be analytically obtained. In addition, based on Avila's theory, we prove there is no phase transition in the previously proposed setup of quasi-periodically driven CFTs [1]. We verify our field theory results by studying the time evolution of entanglement entropy on lattice models. △ Less

Submitted 8 January, 2025; originally announced January 2025.

Comments: 20 pages, many figures

Journal ref: Phys. Rev. B 111, 094304 (2025)

Robust topological interface states in a lateral magnetic-topological heterostructure

Authors: Qun Niu, Jie Yao, Quanchao Song, Humaira Akber, Qin Zhou, Xiaofang Zhai, Aidi Zhao

Abstract: Introducing uniform magnetic order in two-dimensional topological insulators (2D TIs) by constructing heterostructures of TI and magnet is a promising way to realize the high-temperature Quantum Anomalous Hall effect. However, the topological properties of 2D materials are susceptible to several factors that make them difficult to maintain, and whether topological interfacial states (TISs) can exi… ▽ More Introducing uniform magnetic order in two-dimensional topological insulators (2D TIs) by constructing heterostructures of TI and magnet is a promising way to realize the high-temperature Quantum Anomalous Hall effect. However, the topological properties of 2D materials are susceptible to several factors that make them difficult to maintain, and whether topological interfacial states (TISs) can exist at magnetic-topological heterostructure interfaces is largely unknown. Here, we experimentally show that TISs in a lateral heterostructure of CrTe_{2}/Bi(110) are robust against disorder, defects, high magnetic fields (time-reversal symmetry breaking perturbations), and elevated temperature (77 K). The lateral heterostructure is realized by lateral epitaxial growth of bilayer (BL) Bi to monolayer CrTe_{2} grown on HOPG. Scanning Tunneling Microscopy and non-contact Atomic Force Microscopy demonstrate a black phosphorus-like structure with low atomic buckling (less than 0.1 Å) of the BL Bi(110), indicating the presence of its topological properties. Scanning tunneling spectroscopy and energy-dependent dI/dV mapping further confirm the existence of topologically induced one-dimensional in-gap states localized at the interface. These results demonstrate the robustness of TISs in lateral magnetic-topological heterostructures, which is competitive with those in vertically stacked magnetic-topological heterostructures, and provides a promising route for constructing planar high-density non-dissipative devices using TISs. △ Less

Submitted 20 October, 2024; originally announced October 2024.

Recovering dark states by non-Hermiticity

Authors: Qi Zhou

Abstract: Dark states, which are incapable of absorbing and emitting light, have been widely applied in multiple disciplines of physics. However, the existence of dark states relies on certain strict constraints on the system. For instance, in the fundamental Λ system, a perturbation breaking the degeneracy between two energy levels may destroy the destructive interference and demolish the dark state. Here,… ▽ More Dark states, which are incapable of absorbing and emitting light, have been widely applied in multiple disciplines of physics. However, the existence of dark states relies on certain strict constraints on the system. For instance, in the fundamental Λ system, a perturbation breaking the degeneracy between two energy levels may destroy the destructive interference and demolish the dark state. Here, we show that non-Hermiticity can be exploited as a constructive means to restore a dark state. By compensating for the undesired perturbations, non-Hermiticity produces unidirectional couplings such that the dark state remains decoupled from the rest of the system. Implementing this scheme in many-body systems, flat bands and edge states can be recovered by losses and gains. Further taking into account interactions, a range of novel quantum phases could arise in such non-Hermitian systems. △ Less

Submitted 18 October, 2024; originally announced October 2024.

Comments: Submitted to a special collection of AAPPS in memory of Professor Lee Chang

Enhanced Polarizability and Tunable Diamagnetic Shifts from Charged Localized Emitters in WSe2 on a Relaxor Ferroelectric

Authors: Qiaohui Zhou, Fei Wang, Ali Soleymani, Kenji Watanabe, Takashi Taniguchi, Jiang Wei, Xin Lu

Abstract: Strain modulation is a crucial way in engineering nanoscale materials. It is even more important for single photon emitters in layered materials, where strain can create quantum emitters and control their energies. Here we report the localized, charge-enhanced coupling between the charged localized emitters in monolayer tungsten diselenide (WSe2) to the piezoelectric relaxor ferroelectric substrat… ▽ More Strain modulation is a crucial way in engineering nanoscale materials. It is even more important for single photon emitters in layered materials, where strain can create quantum emitters and control their energies. Here we report the localized, charge-enhanced coupling between the charged localized emitters in monolayer tungsten diselenide (WSe2) to the piezoelectric relaxor ferroelectric substrate. In addition to the strain effect, we observe a gigantic polarizability volume with the enhancement factor up to 1010. The enormous polarizability leads to a large Quantum-confined Stark shift under a small variation of electric field, indicating the potential of integrating layered materials with functional substrates for quantum sensing. We further demonstrate the tunable diamagnetic shift and g-factor with strain varying by ~0.05%, which confirms the existence of enhanced interaction between the localized oscillating dipoles and the ferroelectric domains. Our results signify the prospect of charged quantum emitters in layered materials for quantum sciences and technology. △ Less

Submitted 27 December, 2024; v1 submitted 11 September, 2024; originally announced September 2024.

Comments: 19 pages, 4 figures

Observation of vortex stripes in UTe$_2$

Authors: Y. F. Wang, H. X. Yao, T. Winyard, Christopher Broyles, Shannon Gould, Q. S. He, P. H. Zhang, K. Z. Yao, J. J. Zhu, B. K. Xiang, K. Y. Liang, Z. J. Li, B. R. Chen, Q. Z. Zhou, D. F. Agterberg, E. Babaev, S. Ran, Y. H. Wang

Abstract: Quantum vortices are fundamentally important for properties of superconductors. In conventional type-II superconductor they determine the magnetic response of the system and tend to form regular lattices. UTe$_2$ is a recently discovered heavy fermion superconductor exhibiting many anomalous macroscopic behaviors. However, the question whether it has a multicomponent order parameter remains open.… ▽ More Quantum vortices are fundamentally important for properties of superconductors. In conventional type-II superconductor they determine the magnetic response of the system and tend to form regular lattices. UTe$_2$ is a recently discovered heavy fermion superconductor exhibiting many anomalous macroscopic behaviors. However, the question whether it has a multicomponent order parameter remains open. Here, we study magnetic properties of UTe$_2$ by employing scanning superconducting quantum interference device microscopy. We find vortex behavior which is very different from that in ordinary superconductors. We imaged vortices generated by cooling in magnetic field applied along different crystalline directions. While a small out-of-plane magnetic field produces typical isolated vortices, higher field generates vortex stripe patterns which evolve with vortex density. The stripes form at different locations and along different directions in the surface plane when the vortices are crystalized along the crystalline b or c axes. The behavior is reproduced by our simulation based on an anisotropic two-component order parameter. This study shows that UTe$_2$ has a nontrivial disparity of multiple length scales, placing constraints on multicomponent superconductivity. The tendency of vortex stripe formation and their control by external field may be useful in fluxonics applications. △ Less

Submitted 1 September, 2024; v1 submitted 12 August, 2024; originally announced August 2024.

Observation of single-quantum vortex splitting in the Ba$_{1-x}$K$_x$Fe$_2$As$_2$ superconductor

Authors: Q. Z. Zhou, B. R. Chen, B. K. Xiang, I. Timoshuk, J. Garaud, Y. Li, K. Y. Liang, Q. S. He, Z. J. Li, P. H. Zhang, K. Z. Yao, H. X. Yao, E. Babaev, V. Grinenko, Y. H. Wang

Abstract: Since their theoretical discovery more than a half-century ago, vortices observed in bulk superconductors have carried a quantized value of magnetic flux determined only by fundamental constants. A recent experiment reported 'unquantized' quantum vortices carrying the same fraction of flux quantum in Ba$_{0.23}$K$_{0.77}$Fe$_2$As$_2$ in a small temperature range below its superconducting critical… ▽ More Since their theoretical discovery more than a half-century ago, vortices observed in bulk superconductors have carried a quantized value of magnetic flux determined only by fundamental constants. A recent experiment reported 'unquantized' quantum vortices carrying the same fraction of flux quantum in Ba$_{0.23}$K$_{0.77}$Fe$_2$As$_2$ in a small temperature range below its superconducting critical temperature ($T_C$). Here, we use scanning superconducting quantum interference device (sSQUID) microscopy with improved sensitivity to investigate the genesis of fractional vortices in Ba$_{0.23}$K$_{0.77}$Fe$_2$As$_2$. We report the direct observation of a single-flux quantum vortex splitting into two different fractions with increasing temperature. The flux of the two fractions has opposite dependence on temperature, while the total flux sums up to one flux quantum despite their spatial separation. Overall, our study shows the existence of different fractional vortices and their stability in temperature ranging from 0.1 to 0.99 $T_C$. Besides the implications of this observation for the fundamental question of quantum vorticity, the discovery of these objects paves the way for the new platform for anyon quasiparticles and applications for fractional fluxonics. △ Less

Submitted 27 August, 2024; v1 submitted 11 August, 2024; originally announced August 2024.

Hidden curved spaces in Bosonic Kitaev model

Authors: Chenwei Lv, Qi Zhou

Abstract: Quantum matter in curved spaces exhibits remarkable properties unattainable in flat spaces. To access curved spaces in laboratories, the conventional wisdom is that physical distortions need to be implemented into a system. In contrast to this belief, here, we show that two hyperbolic surfaces readily exist in bosonic Kitaev model in the absence of any physical distortions and give rise to a range… ▽ More Quantum matter in curved spaces exhibits remarkable properties unattainable in flat spaces. To access curved spaces in laboratories, the conventional wisdom is that physical distortions need to be implemented into a system. In contrast to this belief, here, we show that two hyperbolic surfaces readily exist in bosonic Kitaev model in the absence of any physical distortions and give rise to a range of intriguing phenomena, such as chiral quantum transport or chiral reaction-diffusion. A finite chemical potential couples these two hyperbolic surfaces, delivering a quantum sensor whose sensitivity grows exponentially with the size of the system. Our results provide experimentalists with an unprecedented opportunity to explore intriguing quantum phenomena in curve spaces without distortion or access non-Hermitian phenomena without dissipation. Our work also suggests a new class of quantum sensors in which geometry amplifies small signals. △ Less

Submitted 9 August, 2024; originally announced August 2024.

Comments: 7 pages, 3 figures

Ultra-high-amplitude Peregrine solitons induced by helicoidal spin-orbit coupling

Authors: Cui-Cui Ding, Qin Zhou, B. A. Malomed

Abstract: In the framework of the model of a spatially non-uniform Bose-Einstein condensate with helicoidal spin-orbit (SO) coupling, we find abnormal Peregrine solitons (PSs) on top of flat and periodic backgrounds, with ultra-high amplitudes. We explore the roles of the SO coupling strength and helicity pitch in the creation of these anomalously tall PSs and find that their amplitude, normalized to the ba… ▽ More In the framework of the model of a spatially non-uniform Bose-Einstein condensate with helicoidal spin-orbit (SO) coupling, we find abnormal Peregrine solitons (PSs) on top of flat and periodic backgrounds, with ultra-high amplitudes. We explore the roles of the SO coupling strength and helicity pitch in the creation of these anomalously tall PSs and find that their amplitude, normalized to the background height, attains indefinitely large values. The investigation of the modulation instability (MI) in the same system demonstrates that these PSs exist in a range of relatively weak MI, maintaining the feasibility of their experimental observation. △ Less

Submitted 1 August, 2024; originally announced August 2024.

Comments: To be published as a Letter in Phys. Rev. Research

Is Large Language Model All You Need to Predict the Synthesizability and Precursors of Crystal Structures?

Authors: Zhilong Song, Shuaihua Lu, Minggang Ju, Qionghua Zhou, Jinlan Wang

Abstract: Accessing the synthesizability of crystal structures is pivotal for advancing the practical application of theoretical material structures designed by machine learning or high-throughput screening. However, a significant gap exists between the actual synthesizability and thermodynamic or kinetic stability, which is commonly used for screening theoretical structures for experiments. To address this… ▽ More Accessing the synthesizability of crystal structures is pivotal for advancing the practical application of theoretical material structures designed by machine learning or high-throughput screening. However, a significant gap exists between the actual synthesizability and thermodynamic or kinetic stability, which is commonly used for screening theoretical structures for experiments. To address this, we develop the Crystal Synthesis Large Language Models (CSLLM) framework, which includes three LLMs for predicting the synthesizability, synthesis methods, and precursors. We create a comprehensive synthesizability dataset including 140,120 crystal structures and develop an efficient text representation method for crystal structures to fine-tune the LLMs. The Synthesizability LLM achieves a remarkable 98.6% accuracy, significantly outperforming traditional synthesizability screening based on thermodynamic and kinetic stability by 106.1% and 44.5%, respectively. The Methods LLM achieves a classification accuracy of 91.02%, and the Precursors LLM has an 80.2% success rate in predicting synthesis precursors. Furthermore, we develop a user-friendly graphical interface that enables automatic predictions of synthesizability and precursors from uploaded crystal structure files. Through these contributions, CSLLM bridges the gap between theoretical material design and experimental synthesis, paving the way for the rapid discovery of novel and synthesizable functional materials. △ Less

Submitted 9 July, 2024; originally announced July 2024.

T2MAT (text-to-materials): A universal agent for generating material structures with goal properties from a single sentence

Authors: Zhilong Song, Shuaihua Lu, Qionghua Zhou, Jinlan Wang

Abstract: Artificial Intelligence-Generated Content (AIGC)-content autonomously produced by AI systems without human intervention-has significantly boosted efficiency across various fields. However, AIGC in material science faces challenges in efficiently discovering novel materials that surpass existing databases, while simultaneously addressing the invariance and stability of crystal structures. To addres… ▽ More Artificial Intelligence-Generated Content (AIGC)-content autonomously produced by AI systems without human intervention-has significantly boosted efficiency across various fields. However, AIGC in material science faces challenges in efficiently discovering novel materials that surpass existing databases, while simultaneously addressing the invariance and stability of crystal structures. To address these challenges, we develop T2MAT (text-to-material), a comprehensive agent processing from a user-input sentence to inverse design material structures with goal properties beyond the existing database via globally exploring chemical space, followed by an entirely automated workflow of first-principles validation. Furthermore, we propose CGTNet (Crystal Graph Transformer NETwork), a graph neural network model that captures long-range interactions, to enhance the accuracy and data utilization efficiency of property prediction and thereby strengthen the reliability of inverse design. Through these contributions, T2MAT minimizes the dependency on human expertise and significantly improves the efficiency of discovering novel, high-performance functional materials, offering a robust way toward more autonomous materials design. △ Less

Submitted 25 July, 2025; v1 submitted 8 July, 2024; originally announced July 2024.

Inverse Design of Promising Alloys for Electrocatalytic CO$_2$ Reduction via Generative Graph Neural Networks Combined with Bird Swarm Algorithm

Authors: Zhilong Song, Linfeng Fan, Shuaihua Lu, Qionghua Zhou, Chongyi Ling, Jinlan Wang

Abstract: Directly generating material structures with optimal properties is a long-standing goal in material design. One of the fundamental challenges lies in how to overcome the limitation of traditional generative models to efficiently explore the global chemical space rather than a small localized space. Herein, we develop a framework named MAGECS to address this dilemma, by integrating the bird swarm a… ▽ More Directly generating material structures with optimal properties is a long-standing goal in material design. One of the fundamental challenges lies in how to overcome the limitation of traditional generative models to efficiently explore the global chemical space rather than a small localized space. Herein, we develop a framework named MAGECS to address this dilemma, by integrating the bird swarm algorithm and supervised graph neural network to effectively navigate the generative model in the immense chemical space towards materials with target properties. As a demonstration, MAGECS is applied to design compelling alloy electrocatalysts for CO$_2$ reduction reaction (CO$_2$RR) and works extremely well. Specifically, the chemical space of CO$_2$RR is effectively explored, where over 250,000 promising structures with high activity have been generated and notably, the proportion of desired structures is 2.5-fold increased. Moreover, five predicted alloys, i.e., CuAl, AlPd, Sn$_2$Pd$_5$, Sn$_9$Pd$_7$, and CuAlSe$_2$ are successfully synthesized and characterized experimentally, two of which exhibit about 90% Faraday efficiency of CO$_2$RR, and CuAl achieved 76% efficiency for C$_2$ products. This pioneering application of inverse design in CO$_2$RR catalysis showcases the potential of MAGECS to dramatically accelerate the development of functional materials, paving the way for fully automated, artificial intelligence-driven material design. △ Less

Submitted 29 May, 2024; originally announced May 2024.

Elucidating Structure Formation in Highly Oriented Triple Cation Perovskite Films

Authors: Oscar Telschow, Niels Scheffczyk, Alexander Hinderhofer, Lena Merten, Ekaterina Kneschaurek, Florian Bertram, Qi Zhou, Markus Löffler, Frank Schreiber, Fabian Paulus, Yana Vaynzof

Abstract: Metal halide perovskites are an emerging class of crystalline semiconductors of great interest for application in optoelectronics. Their properties are dictated not only by their composition, but also by their crystalline structure and microstructure. While significant efforts were dedicated to the development of strategies for microstructural control, significantly less is known about the process… ▽ More Metal halide perovskites are an emerging class of crystalline semiconductors of great interest for application in optoelectronics. Their properties are dictated not only by their composition, but also by their crystalline structure and microstructure. While significant efforts were dedicated to the development of strategies for microstructural control, significantly less is known about the processes that govern the formation of their crystalline structure in thin films, in particular in the context of crystalline orientation. In this work, we investigate the formation of highly oriented triple cation perovskite films fabricated by utilizing a range of alcohols as an antisolvent. Examining the film formation by in-situ grazing-incidence wide-angle X-ray scattering reveals the presence of a short-lived highly oriented crystalline intermediate, which we identify as FAI-PbI2-xDMSO. The intermediate phase templates the crystallisation of the perovskite layer, resulting in highly oriented perovskite layers. The formation of this DMSO containing intermediate is triggered by the selective removal of DMF when alcohols are used as an antisolvent, consequently leading to differing degrees of orientation depending on the antisolvent properties. Finally, we demonstrate that photovoltaic devices fabricated from the highly oriented films, are superior to those with a random polycrystalline structure in terms of both performance and stability. △ Less

Submitted 17 April, 2024; originally announced April 2024.

Rapid state-recrossing kinetics in non-Markovian systems

Authors: Qingyuan Zhou, Roland R. Netz, Benjamin A. Dalton

Abstract: The mean first-passage time (MFPT) is one standard measure for the reaction time in thermally activated barrier-crossing processes. While the relationship between MFPTs and phenomenological rate coefficients is known for systems that satisfy Markovian dynamics, it is not clear how to interpret MFPTs for experimental and simulation time-series data generated by non-Markovian systems. Here, we simul… ▽ More The mean first-passage time (MFPT) is one standard measure for the reaction time in thermally activated barrier-crossing processes. While the relationship between MFPTs and phenomenological rate coefficients is known for systems that satisfy Markovian dynamics, it is not clear how to interpret MFPTs for experimental and simulation time-series data generated by non-Markovian systems. Here, we simulate a one-dimensional generalized Langevin equation (GLE) in a bistable potential and compare two related numerical methods for evaluating MFPTs: one that only incorporates information about first arrivals between subsequent states and is equivalent to calculating the waiting time, or dwell time, and one that incorporates information about all first-passages associated with a given barrier-crossing event and is therefore typically employed to enhance numerical sampling. In the Markovian limit, the two methods are equivalent. However, for significant memory times, the two methods suggest dramatically different reaction kinetics. By focusing on first-passage distributions, we systematically reveal the influence of memory-induced rapid state-recrossing on the MFPTs, which we compare to various other numerical or theoretical descriptions of reaction times. Overall, we demonstrate that it is necessary to consider full first-passage distributions, rather than just the mean barrier-crossing kinetics when analyzing non-Markovian time series data. △ Less

Submitted 11 March, 2024; originally announced March 2024.

Comments: 7 pages, 5 figures

Real-projective-plane hybrid-order topological insulator realized in phononic crystals

Authors: Pengtao Lai, Jien Wu, Zhenhang Pu, Qiuyan Zhou, Jiuyang Lu, Hui Liu, Weiyin Deng, Hua Cheng, Shuqi Chen, Zhengyou Liu

Abstract: The manifold of the fundamental domain of the Brillouin zone is always considered to be a torus. However, under the synthetic gauge field, the Brillouin manifold can be modified by the projective symmetries, resulting in unprecedented topological properties. Here, we realize a real-projective-plane hybrid-order topological insulator in a phononic crystal by introducing the Z_2 gauge field. Such in… ▽ More The manifold of the fundamental domain of the Brillouin zone is always considered to be a torus. However, under the synthetic gauge field, the Brillouin manifold can be modified by the projective symmetries, resulting in unprecedented topological properties. Here, we realize a real-projective-plane hybrid-order topological insulator in a phononic crystal by introducing the Z_2 gauge field. Such insulator hosts two momentum-space non-symmorphic reflection symmetries, which change the Brillouin manifold from a torus to a real projective plane. These symmetries can simultaneously lead to Klein-bottle and quadrupole topologies in different bulk gaps. The non-symmorphic reflection symmetries on Brillouin real projective plane, edge states of Klein-bottle insulator, and corner states of quadrupole insulator are observed. These results evidence the hybrid-order topology on Brillouin manifold beyond the torus, and enrich the topological physics. △ Less

Submitted 28 November, 2023; originally announced November 2023.

Comments: 4 figures

Three-dimensional solitons in Rydberg-Dressed cold atomic gases with spin-orbit coupling

Authors: Yuan Zhao, Heng-Jie Hu, Qian-Qian Zhou, Zhang-Cai Qiu, Li Xue, Si-Liu Xu, Qin Zhou, Boris A. Malomed

Abstract: We present numerical results for three-dimensional (3D) solitons with symmetries of the semi-vortex (SV) and mixed-mode (MM) types, which can be created in spinor Bose-Einstein condensates of Rydberg atoms under the action of the spin-orbit coupling (SOC). By means of systematic numerical computations, we demonstrate that the interplay of SOC and long-range spherically symmetric Rydberg interactio… ▽ More We present numerical results for three-dimensional (3D) solitons with symmetries of the semi-vortex (SV) and mixed-mode (MM) types, which can be created in spinor Bose-Einstein condensates of Rydberg atoms under the action of the spin-orbit coupling (SOC). By means of systematic numerical computations, we demonstrate that the interplay of SOC and long-range spherically symmetric Rydberg interactions stabilize the 3D solitons, improving their resistance to collapse. We find how the stability range depends on the strengths of the SOC and Rydberg interactions and the soft-core atomic radius. △ Less

Submitted 11 October, 2023; originally announced October 2023.

Comments: to be published in Scientific Reports

Journal ref: Scientific Reports 13(2023) 18079

Synthetic tensor gauge fields

Authors: Shaoliang Zhang, Chenwei Lv, Qi Zhou

Abstract: Synthetic gauge fields have provided physicists with a unique tool to explore a wide range of fundamentally important phenomena. However, most experiments have been focusing on synthetic vector gauge fields. The very rich physics brought by coupling tensor gauge fields to fracton phase of matter remain unexplored in laboratories. Here, we propose schemes to realize synthetic tensor gauge fields th… ▽ More Synthetic gauge fields have provided physicists with a unique tool to explore a wide range of fundamentally important phenomena. However, most experiments have been focusing on synthetic vector gauge fields. The very rich physics brought by coupling tensor gauge fields to fracton phase of matter remain unexplored in laboratories. Here, we propose schemes to realize synthetic tensor gauge fields that address dipoles instead of single-particles. A lattice tilted by a strong linear potential and a weak quadratic potential yields a rank-2 electric field for a lineon formed by a particle-hole pair. Such a rank-2 electric field leads to a new type of Bloch oscillations, which modulate the quadrupole moment and preserve the dipole moment of the system. In higher dimensions, the interplay between interactions and vector gauge potentials imprints a phase to the ring-exchange interaction and thus generates synthetic tensor gauge fields for planons. Such tensor gauge fields make it possible to realize a dipolar Harper-Hofstadter model in laboratories. The resultant dipolar Chern insulators feature chiral edge currents of dipoles in the absence of net charge currents. △ Less

Submitted 28 March, 2024; v1 submitted 27 June, 2023; originally announced June 2023.

Comments: 6+5 pages, 4+5 figures

Multipolar condensates and multipolar Josephson effects

Authors: Wenhui Xu, Chenwei Lv, Qi Zhou

Abstract: When single-particle dynamics are suppressed in certain strongly correlated systems, dipoles arise as elementary carriers of quantum kinetics. These dipoles can further condense, providing physicists with a rich realm to study fracton phases of matter. Whereas recent theoretical discoveries have shown that an unconventional lattice model may host a dipole condensate as the ground state, fundamenta… ▽ More When single-particle dynamics are suppressed in certain strongly correlated systems, dipoles arise as elementary carriers of quantum kinetics. These dipoles can further condense, providing physicists with a rich realm to study fracton phases of matter. Whereas recent theoretical discoveries have shown that an unconventional lattice model may host a dipole condensate as the ground state, fundamental questions arise as to whether dipole condensation is a generic phenomenon rather than a specific one unique to a particular model and what new quantum macroscopic phenomena a dipole condensate may bring us with. Here, we show that dipole condensates prevail in bosonic systems. Because of a self-proximity effect, where single-particle kinetics inevitably induces a finite order parameter of dipoles, dipole condensation readily occurs in conventional normal phases of bosons. Our findings allow experimentalists to manipulate the phase of a dipole condensate and deliver dipolar Josephson effects, where supercurrents of dipoles arise in the absence of particle flows. The self-proximity effects can also be utilized to produce a generic multipolar condensate. The kinetics of the $n$-th order multipoles unavoidably creates a condensate of the $(n+1)$-th order multipoles, forming a hierarchy of multipolar condensates that will offer physicists a whole new class of macroscopic quantum phenomena. △ Less

Submitted 3 October, 2023; v1 submitted 25 June, 2023; originally announced June 2023.

Robust 3.7 V-Na$_{2/3}$[Cu$_{1/3}$Mn$_{2/3}$]O$_2$ Cathode for Na-ion Batteries

Authors: Xiaohui Rong, Xingguo Qi, Quan Zhou, Libin Kang, Dongdong Xiao, Ruijuan Xiao, Feixiang Ding, Yang Yang, Yuan Liu, Yun Su, Shiguang Zhang, Lunhua He, Yaxiang Lu, Liquan Chen, Yong-Sheng Hu

Abstract: Na-ion batteries (NIBs), which are recognized as a next-generation alternative technology for energy storage, still suffer from commercialization constraints due to the lack of low-cost, high-performance cathode materials. Since our first discovery of Cu$^{3+}$/Cu$^{2+}$ electrochemistry in 2014, numerous Cu-substituted/doped materials have been designed for NIBs. However for almost ten years, the… ▽ More Na-ion batteries (NIBs), which are recognized as a next-generation alternative technology for energy storage, still suffer from commercialization constraints due to the lack of low-cost, high-performance cathode materials. Since our first discovery of Cu$^{3+}$/Cu$^{2+}$ electrochemistry in 2014, numerous Cu-substituted/doped materials have been designed for NIBs. However for almost ten years, the potential of Cu$^{3+}$/Cu$^{2+}$ electrochemistry has been grossly underappreciated and normally regarded as a semielectrochemically active redox. Here, we re-synthesized P2-Na$_{2/3}$[Cu$_{1/3}$Mn$_{2/3}$]O$_2$ and reinterpreted it as a high-voltage, cost-efficient, air-stable, long-life, and high-rate cathode material for NIBs, which demonstrates a high operating voltage of 3.7 V and a completely active Cu$^{3+}$/Cu$^{2+}$ redox reaction. The 2.3 Ah cylindrical cells exhibit excellent cycling (93.1% capacity after 2000 cycles), high rate (97.2% capacity at 10C rate), good low-temperature performance (86.6% capacity at -30$^\circ$C), and high safety, based on which, a 56 V-11.5 Ah battery pack for E-bikes is successfully constructed, exhibiting stable cycling (96.5% capacity at the 800th cycle) and a long driving distance (36 km, tester weight 65 kg). This work offers a commercially feasible cathode material for low-cost, high-voltage NIBs, paving the way for advanced NIBs in power and stationary energy storage applications. △ Less

Submitted 27 March, 2023; originally announced March 2023.

Comments: 15 pages, 3 figures, 1 table

Building Krylov complexity from circuit complexity

Authors: Chenwei Lv, Ren Zhang, Qi Zhou

Abstract: Krylov complexity has emerged as a new probe of operator growth in a wide range of non-equilibrium quantum dynamics. However, a fundamental issue remains in such studies: the definition of the distance between basis states in Krylov space is ambiguous. Here, we show that Krylov complexity can be rigorously established from circuit complexity when dynamical symmetries exist. Whereas circuit complex… ▽ More Krylov complexity has emerged as a new probe of operator growth in a wide range of non-equilibrium quantum dynamics. However, a fundamental issue remains in such studies: the definition of the distance between basis states in Krylov space is ambiguous. Here, we show that Krylov complexity can be rigorously established from circuit complexity when dynamical symmetries exist. Whereas circuit complexity characterizes the geodesic distance in a multi-dimensional operator space, Krylov complexity measures the height of the final operator in a particular direction. The geometric representation of circuit complexity thus unambiguously designates the distance between basis states in Krylov space. This geometric approach also applies to time-dependent Liouvillian superoperators, where a single Krylov complexity is no longer sufficient. Multiple Krylov complexity may be exploited jointly to fully describe operator dynamics. △ Less

Submitted 13 March, 2023; originally announced March 2023.

Comments: 6 pages, 3 figures

Robust fabrication of ultra-soft tunable PDMS microcapsules as a biomimetic model for red blood cells

Authors: Qi Chen, Naval Singh, Kerstin Schirrmann, Qi Zhou, Igor Chernyavsky, Anne Juel

Abstract: Microcapsules with liquid cores encapsulated by thin membranes have many applications in science, medicine and industry. In this paper, we design a suspension of microcapsules which flow and deform like red blood cells (RBCs), as a valuable tool to investigate microhaemodynamics. A reconfigurable and easy-to-assemble 3D nested glass capillary device is used to robustly fabricate water-oil-water do… ▽ More Microcapsules with liquid cores encapsulated by thin membranes have many applications in science, medicine and industry. In this paper, we design a suspension of microcapsules which flow and deform like red blood cells (RBCs), as a valuable tool to investigate microhaemodynamics. A reconfigurable and easy-to-assemble 3D nested glass capillary device is used to robustly fabricate water-oil-water double emulsions which are then converted into spherical microcapsules with hyperelastic membranes by cross-linking the polydimethylsiloxane (PDMS) layer coating the droplets. The resulting capsules are monodisperse to within 1% and can be made in a wide range of size and membrane thickness. We use osmosis to deflate by 36% initially spherical capsules of diameter 350 μm and a membrane thickness of 4% of their radius, in order to match the reduced volume of biconcave RBCs. We compare the propagation of initially spherical and deflated capsules under constant volumetric flow in cylindrical capillaries of different confinements. We find that only deflated capsules deform broadly similarly to RBCs over a similar range of capillary numbers (Ca) -- the ratio of viscous to elastic forces. Similarly to the RBCs, the microcapsules transition from a symmetric 'parachute' to an asymmetric 'slipper'-like shape as Ca increases within the physiological range, demonstrating intriguing confinement-dependent dynamics. In addition to biomimetic RBC properties, high-throughput fabrication of tunable ultra-soft microcapsules could be further functionalized and find applications in other areas of science and engineering △ Less

Submitted 21 February, 2023; v1 submitted 19 February, 2023; originally announced February 2023.

Comments: 14 pages, 10 figures

Observation of exceptional points and skin effect correspondence in non-Hermitian phononic crystals

Authors: Qiuyan Zhou, Jien Wu, Zhenhang Pu, Jiuyang Lu, Xueqin Huang, Weiyin Deng, Manzhu Ke, Zhengyou Liu

Abstract: Exceptional points and skin effect, as the two distinct hallmark features unique to the non-Hermitian physics, have each attracted enormous interests. Recent theoretical works reveal that the topologically nontrivial exceptional points can give rise to the non-Hermitian skin effect, which is geometry-dependent. However, this kind of novel correspondence between the exceptional points and skin effe… ▽ More Exceptional points and skin effect, as the two distinct hallmark features unique to the non-Hermitian physics, have each attracted enormous interests. Recent theoretical works reveal that the topologically nontrivial exceptional points can give rise to the non-Hermitian skin effect, which is geometry-dependent. However, this kind of novel correspondence between the exceptional points and skin effect remains to be confirmed by experiments. Here, we corroborate the correspondence in a non-Hermitian phononic crystal. The exceptional points connected by the bulk Fermi arcs, and the skin effects with the geometry dependence, are evidenced in simulations and experiments. Our work, building an experimental bridge between the exceptional points and skin effect and uncovering the unconventional geometry-dependent skin effect, expands a horizon in non-Hermitian physics. △ Less

Submitted 8 February, 2023; originally announced February 2023.

Journal ref: Nat. Commun. 14, 4569 (2023)

Controlled non-autonomous matter-wave solitons in spinor Bose-Einstein condensates with spatiotemporal modulation

Authors: Cui-Cui Ding, Qin Zhou, Si-Liu Xu, Yun-Zhou Sun, Wen-Jun Liu, Dumitru Mihalache, Boris A. Malomed

Abstract: To study controlled evolution of non-autonomous matter-wave solitons in spinor Bose-Einstein condensates with spatiotemporal modulation, we focus on a system of three coupled Gross-Pitaevskii (GP) equations with space-time-dependent external potentials and temporally modulated gain/loss distributions. An integrability condition and a non-isospectral Lax pair for the coupled GP equations are obtain… ▽ More To study controlled evolution of non-autonomous matter-wave solitons in spinor Bose-Einstein condensates with spatiotemporal modulation, we focus on a system of three coupled Gross-Pitaevskii (GP) equations with space-time-dependent external potentials and temporally modulated gain/loss distributions. An integrability condition and a non-isospectral Lax pair for the coupled GP equations are obtained. Using it, we derive an infinite set of dynamical invariants, the first two of which are the mass and momentum. The Darboux transform is used to generate one- and two-soliton solutions. Under the action of different external potentials and gain/loss distributions, various solutions for controlled non-autonomous matter-wave solitons of both ferromagnetic and polar types are obtained, such as self-compressed, snake-like and stepwise solitons, and as well as breathers. In particular, the formation of states resembling rogue waves, under the action of a sign-reversible gain-loss distribution, is demonstrated too. Shape-preserving and changing interactions between two non-autonomous matter-wave solitons and bound states of solitons are addressed too. In this context, spin switching arises in the polar-ferromagnetic interaction. Stability of the non-autonomous matter-wave solitons is verified by means of systematic simulations of their perturbed evolution. △ Less

Submitted 8 February, 2023; originally announced February 2023.

Comments: to be published in Chaos, Solitons & Fractals

Collective excitations of the Chern-insulator states in commensurate double moiré superlattices of twisted bilayer graphene on hexagonal boron nitride

Authors: Xianqing Lin, Quan Zhou, Cheng Li, Jun Ni

Abstract: We study the collective excitation modes of the Chern insulator states in magic-angle twisted bilayer graphene aligned with hexagonal boron nitride (TBG/BN) at odd integer fillings ($ν$) of the flat bands. For the $1 \times 1$ commensurate double moiré superlattices in TBG/BN at three twist angles ($θ'$) between BN and graphene, self-consistent Hartree-Fock calculations show that the electron-elec… ▽ More We study the collective excitation modes of the Chern insulator states in magic-angle twisted bilayer graphene aligned with hexagonal boron nitride (TBG/BN) at odd integer fillings ($ν$) of the flat bands. For the $1 \times 1$ commensurate double moiré superlattices in TBG/BN at three twist angles ($θ'$) between BN and graphene, self-consistent Hartree-Fock calculations show that the electron-electron interaction and the broken $C_{2z}$ symmetry lead to the Chern-insulator ground states with valley-spin flavor polarized HF bands at odd $ν$. In the active-band approximation, the HF bands in the same flavor of TBG/BN are much more separated than those of the pristine TBG with TBG/BN having a larger intra-flavor band gap so that the energies of the lowest intra-flavor exciton modes of TBG/BN computed within the time-dependent HF method are much higher than those of TBG and reach about 20 meV, and the exciton wavefunctions of TBG/BN become less localized than those of TBG. The inter-flavor valley-wave modes in TBG/BN have excitation energies higher than 2.5 meV which is also much larger than that of TBG, while the spin-wave modes all have zero excitation gap. In contrast to TBG with particle-hole symmetric excitation modes for positive and negative $ν$, the excitation spectrums and gaps of TBG/BN at positive $ν$ are rather different from those at negative $ν$. The quantitative behavior of the excitation spectrum of TBG/BN also varies with $θ'$. Full HF calculations demonstrate that more HF bands besides the two central bands can have rather large contributions from the single-particle flat-band states, then the lowest exciton modes that determine the optical properties of the Chern insulator states in TBG/BN are generally the ones between the remote and flat-like bands, while the valley-wave modes have similar energies as those in the active-band approximation. △ Less

Submitted 12 January, 2023; originally announced January 2023.

Comments: 9 pages, 6 figures

Exact new mobility edges between critical and localized states

Authors: Xin-Chi Zhou, Yongjian Wang, Ting-Fung Jeffrey Poon, Qi Zhou, Xiong-Jun Liu

Abstract: The disorder systems host three types of fundamental quantum states, known as the extended, localized, and critical states, of which the critical states remain being much less explored. Here we propose a class of exactly solvable models which host a novel type of exact mobility edges (MEs) separating localized states from robust critical states, and propose experimental realization. Here the robus… ▽ More The disorder systems host three types of fundamental quantum states, known as the extended, localized, and critical states, of which the critical states remain being much less explored. Here we propose a class of exactly solvable models which host a novel type of exact mobility edges (MEs) separating localized states from robust critical states, and propose experimental realization. Here the robustness refers to the stability against both single-particle perturbation and interactions in the few-body regime. The exactly solvable one-dimensional models are featured by quasiperiodic mosaic type of both hopping terms and on-site potentials. The analytic results enable us to unambiguously obtain the critical states which otherwise require arduous numerical verification including the careful finite size scalings. The critical states and new MEs are shown to be robust, illustrating a generic mechanism unveiled here that the critical states are protected by zeros of quasiperiodic hopping terms in the thermodynamic limit. Further, we propose a novel experimental scheme to realize the exactly solvable model and the new MEs in an incommensurate Rydberg Raman superarray. This work may pave a way to precisely explore the critical states and new ME physics with experimental feasibility. △ Less

Submitted 20 August, 2023; v1 submitted 29 December, 2022; originally announced December 2022.

Comments: 5+6 pages, 4+5 figures. Discussions are updated. Under second round of review

Journal ref: Phys. Rev. Lett. 131, 176401 (2023)

Emergent spacetimes from Hermitian and non-Hermitian quantum dynamics

Authors: Chenwei Lv, Qi Zhou

Abstract: We show that quantum dynamics of any systems with $SU(1,1)$ symmetry give rise to emergent Anti-de Sitter spacetimes in 2+1 dimensions (AdS$_{2+1}$). Using the continuous circuit depth, a quantum evolution is mapped to a trajectory in AdS$_{2+1}$. Whereas the time measured in laboratories becomes either the proper time or the proper distance, quench dynamics follow geodesics of AdS$_{2+1}$. Such a… ▽ More We show that quantum dynamics of any systems with $SU(1,1)$ symmetry give rise to emergent Anti-de Sitter spacetimes in 2+1 dimensions (AdS$_{2+1}$). Using the continuous circuit depth, a quantum evolution is mapped to a trajectory in AdS$_{2+1}$. Whereas the time measured in laboratories becomes either the proper time or the proper distance, quench dynamics follow geodesics of AdS$_{2+1}$. Such a geometric approach provides a unified interpretation of a wide range of prototypical phenomena that appear disconnected. For instance, the light cone of AdS$_{2+1}$ underlies expansions of unitary fermions released from harmonic traps, the onsite of parametric amplifications, and the exceptional points that represent the $PT$ symmetry breaking in non-Hermitian systems. Our work provides a transparent means to optimize quantum controls by exploiting shortest paths in the emergent spacetimes. It also allows experimentalists to engineer emergent spacetimes and induce tunnelings between different AdS$_{2+1}$. △ Less

Submitted 13 November, 2023; v1 submitted 15 May, 2022; originally announced May 2022.

Comments: 6+3 pages, 3 figures

Analytical Theory of Near-Field Electrostatic Effects in Two-Dimensional Materials and van der Waals Heterojunctions

Authors: Qunfei Zhou, Michele Kotiuga, Pierre Darancet

Abstract: We derive and validate a quantitative analytical model of the near-field electrostatic effects in the vicinity (>=3Å) of two-dimensional (2D) materials. In solving the Poisson equation of a near-planar point charge ansatz for the electronic density of a 2D material, our formula quantitatively captures the out-of-plane decay and the in-plane modulation of density functional theory (DFT)-calculated… ▽ More We derive and validate a quantitative analytical model of the near-field electrostatic effects in the vicinity (>=3Å) of two-dimensional (2D) materials. In solving the Poisson equation of a near-planar point charge ansatz for the electronic density of a 2D material, our formula quantitatively captures the out-of-plane decay and the in-plane modulation of density functional theory (DFT)-calculated potentials. We provide a method for quickly constructing the electronic density ansatz, and apply it to the case of hexagonal monolayers (BN, AlN, GaN) and monochalcogenides (GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, PbTe) and their flexural and polar distortions. We demonstrate how our model can be straightforwardly applied to predict material-/angle-specific moiré potentials arising in twisted superlattices with periodicities beyond the reach of DFT calculations. △ Less

Submitted 9 May, 2022; originally announced May 2022.

Comments: 6 pages, 4 figures

Universal relations for dilute systems with two-body decays in reduced dimensions

Authors: Mingyuan He, Chenwei Lv, Qi Zhou

Abstract: Physical systems in reduced dimensions exhibit intriguing properties. For instance, the dependences of two-body and many-body physics on scattering lengths are distinct from their counterparts in three dimensions. Whereas many studies of ultracold atoms and molecules in reduced dimensions have been focusing on closed systems, two-body losses may occur in such systems. Here, we show that the two-bo… ▽ More Physical systems in reduced dimensions exhibit intriguing properties. For instance, the dependences of two-body and many-body physics on scattering lengths are distinct from their counterparts in three dimensions. Whereas many studies of ultracold atoms and molecules in reduced dimensions have been focusing on closed systems, two-body losses may occur in such systems. Here, we show that the two-body inelastic loss rate in reduced dimensions can be expressed in universal relations that are governed by contacts. These universal relations correlate the two-body decay rate with other physical observables at arbitrary temperatures and interaction strengths. Our results will provide experimentalists with a new protocol to study inelastic scatterings in both few- and many-body systems in reduced dimensions. △ Less

Submitted 17 May, 2024; v1 submitted 28 April, 2022; originally announced April 2022.

Comments: 11 pages, 3 tables

Analogue Black Holes in Reactive Molecules

Authors: Ren Zhang, Chenwei Lv, Qi Zhou

Abstract: We show that reactive molecules with a unit probability of reaction naturally provide a simulator of some intriguing black hole physics. The unit reaction at the short distance acts as an event horizon and delivers a one-way traffic for matter waves passing through the potential barrier when two molecules interact by high partial-wave scatterings or dipole-dipole interactions. In particular, the s… ▽ More We show that reactive molecules with a unit probability of reaction naturally provide a simulator of some intriguing black hole physics. The unit reaction at the short distance acts as an event horizon and delivers a one-way traffic for matter waves passing through the potential barrier when two molecules interact by high partial-wave scatterings or dipole-dipole interactions. In particular, the scattering rate as a function of the incident energy exhibits a thermal-like distribution near the maximum of the interaction energy in the same manner as a scalar field scatters with the potential barrier outside the event horizon of a black hole. Such a thermal-like scattering can be extracted from the temperature-dependent two-body loss rate measured in experiments on KRb and other molecules. △ Less

Submitted 9 October, 2022; v1 submitted 10 April, 2022; originally announced April 2022.

Comments: 6+5 pages, 4+2 figures

A Review of Sc-containing "Scandate" Thermionic Cathodes

Authors: Mujan N. Seif, Qunfei Zhou, Xiaotao Liu, T. John Balk, Matthew J. Beck

Abstract: Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g. higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing "scandate" cathodes have been widely reported to… ▽ More Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g. higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing "scandate" cathodes have been widely reported to exhibit superior emission properties compared to previous-generation thermionic cathodes, including oxide, B-, and M-type cathodes. Despite extensive study spanning several decades, the mechanism by which the addition of Sc enhances cathode emission remains ambiguous, and certain limitations -- non-uniform emission, low reproducibility, inconsistent longevity -- continue to prevent widespread commercial integration of scandate cathodes into electron devices. This review attempts to survey the literature to-date addressing the fabrication, structure, and properties of scandate cathodes, with particular attention to studies addressing the role of Sc in enhancing emission. △ Less

Submitted 9 February, 2022; originally announced February 2022.

Robust Dirac lines against Ge vacancy and possible spin-orbit Dirac points in nonsymmorphic HfGe0.92Te

Authors: L. Chen, L. Q. Zhou, Y. Zhou, C. Liu, Z. N. Guo, S. Y. Gao, W. H. Fan, J. F. Xu, Y. X. Guo, K, Liao, J. O. Wang, H. M. Weng, G. Wang

Abstract: Looking for new materials with Dirac points has been a fascinating subject of research. Here we report the growth, crystal structure, and band structure of HfGe0.92Te single crystals, featuring three different types of Dirac points. HfGe0.92Te crystalizes in a nonsymmorphic tetragonal space group P4/nmm (No. 129), having square Ge-atom plane with vacancies about 8%. Despite the vacancies on Ge sit… ▽ More Looking for new materials with Dirac points has been a fascinating subject of research. Here we report the growth, crystal structure, and band structure of HfGe0.92Te single crystals, featuring three different types of Dirac points. HfGe0.92Te crystalizes in a nonsymmorphic tetragonal space group P4/nmm (No. 129), having square Ge-atom plane with vacancies about 8%. Despite the vacancies on Ge site, the Dirac nodal line composed of conventional Dirac points vulnerable to spin-orbit coupling (SOC) is observed using angle-resolved photoemission spectroscopy, accompanied with the robust Dirac line protected by the nonsymmorphic symmetry against both SOC and vacancies. Specially, spin-orbit Dirac points (SDPs) originated from the surface formed under SOC are hinted to exist according to our experiments and calculations. Quasi-two-dimensional (quasi-2D) characters are observed and further confirmed by angular-resolved magnetoresistance. HfGe0.92Te is a good candidate to explore exotic topological phases or topological properties with three different types of Dirac points and a promising candidate to realize 2D SDPs. △ Less

Submitted 15 January, 2022; originally announced January 2022.

Comments: 16 pages, 9 figures

Journal ref: SCIENCE CHINA Physics, Mechanics & Astronomy, 66, 1, 2023, 217011

Single-crystal epitaxial europium iron garnet films with strain-induced perpendicular magnetic anisotropy: structural, strain, magnetic, and spin transport properties

Authors: M. X. Guo, C. K. Cheng, Y. C. Liu, C. N. Wu, W. N. Chen, T. Y Chen, C. T. Wu, C. H. Hsu, S. Q. Zhou, C. F. Chang, L. H. Tjeng, S. F. Lee, C. F. Pai, M. Hong, J. Kwo

Abstract: Single-crystal europium iron garnet (EuIG) thin films epitaxially strain-grown on gadolinium gallium garnet (GGG)(100) substrates using off-axis sputtering have strain-induced perpendicular magnetic anisotropy (PMA). By varying the sputtering conditions, we have tuned the europium/iron (Eu/Fe) composition ratios in the films to tailor the film strains. The films exhibited an extremely smooth, part… ▽ More Single-crystal europium iron garnet (EuIG) thin films epitaxially strain-grown on gadolinium gallium garnet (GGG)(100) substrates using off-axis sputtering have strain-induced perpendicular magnetic anisotropy (PMA). By varying the sputtering conditions, we have tuned the europium/iron (Eu/Fe) composition ratios in the films to tailor the film strains. The films exhibited an extremely smooth, particle-free surface with roughness as low as 0.1 nm as observed using atomic force microscopy. High-resolution x-ray diffraction analysis and reciprocal space maps showed in-plane epitaxial film growth, very smooth film/substrate interface, excellent film crystallinity with a small full width at half maximum of 0.012$^{\circ}$ in the rocking curve scans, and an in-plane compressive strain without relaxation. In addition, spherical aberration-corrected scanning transmission electron microscopy showed an atomically abrupt interface between the EuIG film and GGG. The measured squarish out-of-plane magnetization-field hysteresis loops by vibrating sample magnetometry in conjunction with the measurements from angle-dependent x-ray magnetic dichroism demonstrated the PMA in the films. We have tailored the magnetic properties of the EuIG thin films, including saturation magnetization ranging from 71.91 to 124.51 emu/c.c. (increase with the (Eu/Fe) ratios), coercive field from 27 to 157.64 Oe, and the strength of PMA field ($H_\bot$) increasing from 4.21 to 18.87 kOe with the in-plane compressive strain from -0.774 to -1.044%. We have also investigated spin transport in Pt/EuIG bi-layer structure and evaluated the real part of spin mixing conductance to be $3.48\times10^{14} Ω^{-1}m^{-2}$. We demonstrated the current-induced magnetization switching with a low critical switching current density of $3.5\times10^6 A/cm^2$, showing excellent potential for low-dissipation spintronic devices. △ Less

Submitted 11 January, 2022; originally announced January 2022.

Comments: 29 pages, 9 figures, 1 table