Showing 1–50 of 270 results for author: Lin, T

Equivalence of residual entropy of hexagonal and cubic ices from tensor network methods

Authors: Xia-Ze Xu, Tong-Yu Lin, Guang-Ming Zhang

Abstract: The long-standing question of whether the residual entropy of hexagonal ice ($S_h$) equals that of cubic ice ($S_c$) remains unresolved despite decades of research on ice-type models. While analytical studies have established the inequality $S_h \geq S_c$, numerical investigations suggest that the two values are very close. In this work, we revisit this problem using high-precision tensor-network… ▽ More The long-standing question of whether the residual entropy of hexagonal ice ($S_h$) equals that of cubic ice ($S_c$) remains unresolved despite decades of research on ice-type models. While analytical studies have established the inequality $S_h \geq S_c$, numerical investigations suggest that the two values are very close. In this work, we revisit this problem using high-precision tensor-network methods. In Monte Carlo approaches the residual entropy cannot be directly obtained by sampling the ground-state degeneracy space, however, the tensor-network framework enables an explicit encoding of the "ice rule'' into local tensors, and then the residual entropy is transformed into finding the largest eigenvalue of a transfer operator in the form of a projected entangled-pair operator, which allows high-accuracy numerical evaluation. Meanwhile, we propose a new perspective based on analyzing the normality of the transfer operator, and demonstrate that if the operator is normal, the equality $S_h = S_c$ follows directly. Then the variational tensor network methods are employed to numerically verify this normality. Finally both residual entropies are directly computed by using our recently developed split corner transfer matrix renormalization group algorithm, providing a rigorous evidence supporting the equality between $S_h$ and $S_c$. △ Less

Submitted 27 November, 2025; originally announced November 2025.

Comments: 10 pages, 6 figures, two tables

Chiral gapped states are universally non-topological

Authors: Xiang Li, Ting-Chun Lin, Yahya Alavirad, John McGreevy

Abstract: We propose an operator generalization of the Li-Haldane conjecture regarding the entanglement Hamiltonian of a disk in a 2+1D chiral gapped groundstate. The logic applies to regions with sharp corners, from which we derive several universal properties regarding corner entanglement. These universal properties follow from a set of locally-checkable conditions on the wavefunction. We also define a qu… ▽ More We propose an operator generalization of the Li-Haldane conjecture regarding the entanglement Hamiltonian of a disk in a 2+1D chiral gapped groundstate. The logic applies to regions with sharp corners, from which we derive several universal properties regarding corner entanglement. These universal properties follow from a set of locally-checkable conditions on the wavefunction. We also define a quantity $(\mathfrak{c}_{\text{tot}})_{\text{min}}$ that reflects the robustness of corner entanglement contributions, and show that it provides an obstruction to a gapped boundary. One reward from our analysis is that we can construct a local gapped Hamiltonian within the same chiral gapped phase from a given wavefunction; we conjecture that it is closer to the low-energy renormalization group fixed point than the original parent Hamiltonian. Our analysis of corner entanglement reveals the emergence of a universal conformal geometry encoded in the entanglement structure of bulk regions of chiral gapped states that is not visible in topological field theory. △ Less

Submitted 27 October, 2025; originally announced October 2025.

Comments: 38+14 pages, 39 figures

Floquet engineering enabled by charge density wave transition

Authors: Fei Wang, Xuanxi Cai, Teng Xiao, Changhua Bao, Haoyuan Zhong, Wanying Chen, Tianyun Lin, Tianshuang Sheng, Xiao Tang, Hongyun Zhang, Pu Yu, Zhiyuan Sun, Shuyun Zhou

Abstract: Floquet engineering has emerged as a powerful approach for dynamically tailoring the electronic structures of quantum materials through time-periodic light fields generated by ultrafast laser pulses. The light fields can transiently dress Bloch electrons, creating novel electronic states inaccessible in equilibrium. While such temporal modulation provides dynamic control, spatially periodic modula… ▽ More Floquet engineering has emerged as a powerful approach for dynamically tailoring the electronic structures of quantum materials through time-periodic light fields generated by ultrafast laser pulses. The light fields can transiently dress Bloch electrons, creating novel electronic states inaccessible in equilibrium. While such temporal modulation provides dynamic control, spatially periodic modulations, such as those arising from charge density wave (CDW) order, can also dramatically reconstruct the band structure through real-space symmetry breaking. The interplay between these two distinct forms of modulation-temporal and spatial-opens a new frontier in electronic-phase-dependent Floquet engineering. Here we demonstrate this concept experimentally in the prototypical CDW material 1T-TiSe$_2$. Using time- and angle-resolved photoemission spectroscopy (TrARPES) with mid-infrared pumping, we observe a striking pump-induced instantaneous downshift of the valence band maximum (VBM), which is in sharp contrast to the subsequent upward shift on picosecond timescale associated with CDW melting. Most remarkably, the light-induced VBM downshift is observed exclusively in the CDW phase and only when the pump pulse is present, reaching maximum when pumping near resonance with the CDW gap. These observations unequivocally reveal the critical role of CDW in the Floquet engineering of TiSe$_2$. Our work demonstrates how time-periodic drives can synergistically couple to spatially periodic modulations to create non-equilibrium electronic states, establishing a new paradigm for Floquet engineering enabled by spontaneous symmetry breaking. △ Less

Submitted 21 October, 2025; originally announced October 2025.

High harmonic generation light source with polarization selectivity and sub-100-$μ$m beam size for time- and angle-resolved photoemission spectroscopy

Authors: Haoyuan Zhong, Xuanxi Cai, Changhua Bao, Fei Wang, Tianyun Lin, Yudong Chen, Sainan Peng, Lin Tang, Chen Gu, Zhensheng Tao, Hongyun Zhang, Shuyun Zhou

Abstract: High-quality ultrafast light sources are critical for developing advanced time- and angle-resolved photoemission spectroscopy (TrARPES). While the application of high harmonic generation (HHG) light sources in TrARPES has increased significantly over the past decade, the optimization of the HHG probe beam size and selective control of the light polarization, which are important for TrARPES measure… ▽ More High-quality ultrafast light sources are critical for developing advanced time- and angle-resolved photoemission spectroscopy (TrARPES). While the application of high harmonic generation (HHG) light sources in TrARPES has increased significantly over the past decade, the optimization of the HHG probe beam size and selective control of the light polarization, which are important for TrARPES measurements, have been rarely explored. In this work, we report the implementation of high-quality HHG probe source with an optimum beam size down to 57 $μ$m $\times$ 90 $μ$m and selective light polarization control, together with mid-infrared (MIR) pumping source for TrARPES measurements using a 10 kHz amplifier laser. The selective polarization control of the HHG probe source allows to enhance bands with different orbital contributions or symmetries, as demonstrated by experimental data measured on a few representative transition metal dichalcogenide materials (TMDCs) as well as topological insulator Bi$_2$Se$_3$. Furthermore, by combining the HHG probe source with MIR pumping at 2 $μ$m wavelength, TrARPES on a bilayer graphene shows a time resolution of 140 fs, allowing to distinguish two different relaxation processes in graphene. Such high-quality HHG probe source together with the MIR pumping expands the capability of TrARPES in revealing the ultrafast dynamics and light-induced emerging phenomena in quantum materials. △ Less

Submitted 18 October, 2025; originally announced October 2025.

Comments: 15 pages, 5 figures

Journal ref: Ultrafast Sci. 4, 0063 (2024)

In-plane polar domains enhanced energy storage

Authors: Yu Lei, Xiaoming Shi, Sihan Yan, Qinghua Zhang, Jiecheng Liu, Sixu Wang, Yu Chen, Jiaou Wang, He Qi, Qian Li, Ting Lin, Jingfen Li, Qing Zhu, Haoyu Wang, Jing Chen, Lincong Shu, Linkun Wang, Han Wu, Xianran Xing

Abstract: Relaxor ferroelectric thin films are recognized for their ultrahigh power density, rendering them highly promising for energy storage applications in electrical and electronic systems. However, achieving high energy storage performance with chemically homogeneous, environmentally friendly and compositionally stable materials remains challenging. In this work, we present a design of dielectrics wit… ▽ More Relaxor ferroelectric thin films are recognized for their ultrahigh power density, rendering them highly promising for energy storage applications in electrical and electronic systems. However, achieving high energy storage performance with chemically homogeneous, environmentally friendly and compositionally stable materials remains challenging. In this work, we present a design of dielectrics with high energy storage performance via an in-plane polar domains incorporating polar nanoregions mechanism. Guided by phase-field simulations, we synthesized La/Si co-doping BaTiO3 solid-solution thin films with high chemical homogeneity to realize high energy storage performance. Given that, we achieve a high energy density of 203.7J/cm3 and an energy efficiency of approximately 80% at an electric field of 6.15MV/cm. This mechanism holds significant promise for the design of next-generation high-performance dielectric materials for energy storage and other advanced functional materials. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Anisotropic linear magnetoresistance in nanoflakes of Dirac semimetal NiTe2

Authors: Ding Bang Zhou, Kuang Hong Gao, Tie Lin, Yang Yang, Meng Fan Zhao, Zhi Yan Jia, Xiao Xia Hu, Qian Jin Guo, Zhi Qing Li

Abstract: This work investigates the magneto-transport properties of exfoliated NiTe2 nano-flakes with varying thicknesses and disorder levels, unveiling two distinct physical mechanisms governing the observed anisotropic linear magnetoresistance (MR). For the perpendicular magnetic field configuration, the well-defined linear MR in high fields is unambiguously attributed to a classical origin. This conclus… ▽ More This work investigates the magneto-transport properties of exfoliated NiTe2 nano-flakes with varying thicknesses and disorder levels, unveiling two distinct physical mechanisms governing the observed anisotropic linear magnetoresistance (MR). For the perpendicular magnetic field configuration, the well-defined linear MR in high fields is unambiguously attributed to a classical origin. This conclusion is supported by the proportionality between the MR slope and the carrier mobility, and between the crossover field and the inverse of mobility. In stark contrast, the linear MR under parallel magnetic fields exhibits a non-classical character. It shows a pronounced enhancement with decreasing flake thickness, which correlates with an increasing hole-to-electron concentration ratio. This distinctive thickness dependence suggests an origin in the nonlinear band effects near the Dirac point, likely driven by the shift of the Fermi level. Furthermore, the strengthening of MR anisotropic with enhanced inter-layer transport contradicts the prediction of the guiding-center diffusion model for three-dimensional systems. Our findings highlight the critical roles of band topology and structural dimensional in the anomalous magneto-transport of Dirac semi-metals. △ Less

Submitted 6 December, 2025; v1 submitted 1 October, 2025; originally announced October 2025.

Mechanisms of Matter: Language Inferential Benchmark on Physicochemical Hypothesis in Materials Synthesis

Authors: Yingming Pu, Tao Lin, Hongyu Chen

Abstract: The capacity of Large Language Models (LLMs) to generate valid scientific hypotheses for materials synthesis remains largely unquantified, hindered by the absence of benchmarks probing physicochemical logics reasoning. To address this, we introduce MatterMech, a benchmark for evaluating LLM-generated hypotheses across eight nanomaterial synthesis domains. Our analysis reveals a critical disconnect… ▽ More The capacity of Large Language Models (LLMs) to generate valid scientific hypotheses for materials synthesis remains largely unquantified, hindered by the absence of benchmarks probing physicochemical logics reasoning. To address this, we introduce MatterMech, a benchmark for evaluating LLM-generated hypotheses across eight nanomaterial synthesis domains. Our analysis reveals a critical disconnect: LLMs are proficient in abstract logic yet fail to ground their reasoning in fundamental physicochemical principles. We demonstrate that our proposed principle-aware prompting methodology substantially outperforms standard Chain-of-Thought, enhancing both hypothesis accuracy and computational efficiency. This work provides a methodological framework to advance LLMs toward reliable scientific hypothesis generation in materials science. The MatterMech benchmark and associated code is publicly available at \href{https://github.com/amair-lab/MatterMech}{GitHub}. △ Less

Submitted 29 September, 2025; originally announced September 2025.

A systematic search for conformal field theories in very small spaces

Authors: Xiang Li, Ting-Chun Lin, John McGreevy

Abstract: Groundstates of 1+1d conformal field theories (CFTs) satisfy a local entropic condition called the vector fixed point equation. This condition is surprisingly well satisfied by groundstates of quantum critical lattice models even at small system sizes. We perform a search in the space of states of very small systems (four qubits and four qutrits) and examine the states that satisfy this condition.… ▽ More Groundstates of 1+1d conformal field theories (CFTs) satisfy a local entropic condition called the vector fixed point equation. This condition is surprisingly well satisfied by groundstates of quantum critical lattice models even at small system sizes. We perform a search in the space of states of very small systems (four qubits and four qutrits) and examine the states that satisfy this condition. By reconstructing a local Hamiltonian from each state, we are able to identify many of these solutions with known CFTs; others are gapped fixed points, or involve large relevant perturbations, and others are CFTs we have not yet identified. These ideas are also useful for identifying continuous quantum phase transitions in a given family of Hamiltonians, and for identifying the nature of the critical theory in small systems. △ Less

Submitted 4 September, 2025; originally announced September 2025.

Comments: 5+5 pages + many tables

Lattice-induced spin dynamics in Dirac magnet CoTiO3

Authors: Andrey Baydin, Jiaming Luo, Zhiren He, Jacques Doumani, Tong Lin, Fuyang Tay, Jiaming He, Jianshi Zhou, Guru Khalsa, Junichiro Kono, Hanyu Zhu

Abstract: Spin-lattice coupling is crucial for understanding the spin transport and dynamics for spintronics and magnonics applications. Recently, cobalt titanate (CoTiO3), an easy-plane antiferromagnet, has been found to host axial phonons with a large magnetic moment, which may originate from spin-lattice coupling. Here, we investigate the effect of light-driven lattice dynamics on the magnetic properties… ▽ More Spin-lattice coupling is crucial for understanding the spin transport and dynamics for spintronics and magnonics applications. Recently, cobalt titanate (CoTiO3), an easy-plane antiferromagnet, has been found to host axial phonons with a large magnetic moment, which may originate from spin-lattice coupling. Here, we investigate the effect of light-driven lattice dynamics on the magnetic properties of CoTiO3 using time-resolved spectroscopy with a THz pump and a magneto-optic probe. We found resonantly driven Raman active phonons, phonon-polariton-induced excitation of the antiferromagnetic magnons, and a slow increase in the polarization rotation of the probe, all indicating symmetry breaking that is not intrinsic to the magnetic space group. The temperature dependence confirmed that the observed spin dynamics is related to the magnetic order, and we suggest surface effects as a possible mechanism. Our results of THz-induced spin-lattice dynamics signify that extrinsic symmetry breaking may contribute strongly and unexpectedly to light-driven phenomena in bulk complex oxides. △ Less

Submitted 27 August, 2025; originally announced August 2025.

Ensemble nonlinear optical learner by electrically tunable linear scattering

Authors: Tunan Xia, Cheng-Kuan Wu, Duan-Yi Guo, Lidan Zhang, Bofeng Liu, Tsung-Hsien Lin, Xingjie Ni, Iam-Choon Khoo, Zhiwen Liu

Abstract: Recent progress in effective nonlinearity, achieved by exploiting multiple scatterings within the linear optical regime, has been demonstrated to be a promising approach to enable nonlinear optical processing without relying on actual material nonlinearity. Here we introduce an ensemble nonlinear optical learner, via electrically tunable linear scattering in a liquid-crystal-polymer composite film… ▽ More Recent progress in effective nonlinearity, achieved by exploiting multiple scatterings within the linear optical regime, has been demonstrated to be a promising approach to enable nonlinear optical processing without relying on actual material nonlinearity. Here we introduce an ensemble nonlinear optical learner, via electrically tunable linear scattering in a liquid-crystal-polymer composite film under low optical power and low applied electrical voltages. We demonstrate, through several image classification tasks, that by combining inference results from an ensemble of nonlinear optical learners realized at different applied voltages, the ensemble optical learning significantly outperforms the classification performance of individual processors. With very low-level optical power and electrical voltage requirements, and ease in reconfiguration simply by varying applied voltages, the ensemble nonlinear optical learning offers a cost-effective and flexible way to improve computing performance and enhance inference accuracy. △ Less

Submitted 24 June, 2025; originally announced June 2025.

Efficient optimization of variational tensor-network approach to three-dimensional statistical systems

Authors: Xia-Ze Xu, Tong-Yu Lin, Guang-Ming Zhang

Abstract: Variational tensor network optimization has become a powerful tool for studying classical statistical models in two dimensions. However, its application to three-dimensional systems remains limited, primarily due to the high computational cost associated with evaluating the free energy density and its gradient. This process requires contracting a triple-layer tensor network composed of a projected… ▽ More Variational tensor network optimization has become a powerful tool for studying classical statistical models in two dimensions. However, its application to three-dimensional systems remains limited, primarily due to the high computational cost associated with evaluating the free energy density and its gradient. This process requires contracting a triple-layer tensor network composed of a projected entangled pair operator and projected entangled pair states. In this paper, we employ a split corner-transfer renormalization group scheme tailored for the contraction of such a triple-layer network, which reduces the computational complexity while keeping high accuracy. Through numerical benchmarks on the three-dimensional classical Ising model, we demonstrate that the proposed scheme achieves numerical results comparable to the most recent Monte Carlo simulations, providing a substantial speedup over previous variational tensor network approaches. This makes this method well-suited for efficient gradient-based optimization in three-dimensional tensor network simulations. △ Less

Submitted 13 October, 2025; v1 submitted 24 June, 2025; originally announced June 2025.

Comments: 13 pages, 16 figures

Journal ref: Phys. Rev. B 112, 134403 (2025)

Discrete Spatial Diffusion: Intensity-Preserving Diffusion Modeling

Authors: Javier E. Santos, Agnese Marcato, Roman Colman, Nicholas Lubbers, Yen Ting Lin

Abstract: Generative diffusion models have achieved remarkable success in producing high-quality images. However, these models typically operate in continuous intensity spaces, diffusing independently across pixels and color channels. As a result, they are fundamentally ill-suited for applications involving inherently discrete quantities-such as particle counts or material units-that are constrained by stri… ▽ More Generative diffusion models have achieved remarkable success in producing high-quality images. However, these models typically operate in continuous intensity spaces, diffusing independently across pixels and color channels. As a result, they are fundamentally ill-suited for applications involving inherently discrete quantities-such as particle counts or material units-that are constrained by strict conservation laws like mass conservation, limiting their applicability in scientific workflows. To address this limitation, we propose Discrete Spatial Diffusion (DSD), a framework based on a continuous-time, discrete-state jump stochastic process that operates directly in discrete spatial domains while strictly preserving particle counts in both forward and reverse diffusion processes. By using spatial diffusion to achieve particle conservation, we introduce stochasticity naturally through a discrete formulation. We demonstrate the expressive flexibility of DSD by performing image synthesis, class conditioning, and image inpainting across standard image benchmarks, while exactly conditioning total image intensity. We validate DSD on two challenging scientific applications: porous rock microstructures and lithium-ion battery electrodes, demonstrating its ability to generate structurally realistic samples under strict mass conservation constraints, with quantitative evaluation using state-of-the-art metrics for transport and electrochemical performance. △ Less

Submitted 16 May, 2025; v1 submitted 3 May, 2025; originally announced May 2025.

Electric-field independent spin-orbit coupling gap in hBN-encapsulated bilayer graphene

Authors: Fang-Ming Jing, Zhen-Xiong Shen, Guo-Quan Qin, Wei-Kang Zhang, Ting Lin, Ranran Cai, Zhuo-Zhi Zhang, Gang Cao, Lixin He, Xiang-Xiang Song, Guo-Ping Guo

Abstract: The weak spin-orbit coupling (SOC) in bilayer graphene (BLG) is essential for encoding spin qubits while bringing technical challenges for extracting the opened small SOC gap Δ_SO in experiments. Moreover, in addition to the intrinsic Kane-Mele term, extrinsic mechanisms also contribute to SOC in BLG, especially under experimental conditions including encapsulation of BLG with hexagonal boron nitr… ▽ More The weak spin-orbit coupling (SOC) in bilayer graphene (BLG) is essential for encoding spin qubits while bringing technical challenges for extracting the opened small SOC gap Δ_SO in experiments. Moreover, in addition to the intrinsic Kane-Mele term, extrinsic mechanisms also contribute to SOC in BLG, especially under experimental conditions including encapsulation of BLG with hexagonal boron nitride (hBN) and applying an external out-of-plane electric displacement field D. Although measurements of Δ_SO in hBN-encapsulated BLG have been reported, the relatively large experimental variations and existing experimental controversy make it difficult to fully understand the physical origin of Δ_SO. Here, we report a combined experimental and theoretical study on Δ_SO in hBN-encapsulated BLG. We use an averaging method to extract Δ_SO in gate-defined single quantum dot devices. Under D fields as large as 0.57-0.90 V/nm, Δ_SO=53.4-61.8 μeV is obtained from two devices. Benchmarked with values reported at lower D field regime, our results support a D field-independent Δ_SO. This behavior is confirmed by our first-principle calculations, based on which Δ_SO is found to be independent of D field, regardless of different hBN/BLG/hBN stacking configurations. Our calculations also suggest a weak proximity effect from hBN, indicating that SOC in hBN-encapsulated BLG is dominated by the intrinsic Kane-Mele mechanism. Our results offer insightful understandings of SOC in BLG, which benefit SOC engineering and spin manipulations in BLG. △ Less

Submitted 25 April, 2025; originally announced April 2025.

Journal ref: Phys. Rev. Applied 23, 044053 (2025)

Light-field dressing of transient photo-excited states above $E_F$

Authors: Fei Wang, Wanying Chen, Changhua Bao, Tianyun Lin, Haoyuan Zhong, Hongyun Zhang, Shuyun Zhou

Abstract: Time-periodic light-field provides an emerging pathway for dynamically engineering quantum materials by forming hybrid states between photons and Bloch electrons. So far, experimental progress on light-field dressed states has been mainly focused on the occupied states, however, it is unclear if the transient photo-excited states above the Fermi energy $E_F$ can also be dressed, leaving the dynami… ▽ More Time-periodic light-field provides an emerging pathway for dynamically engineering quantum materials by forming hybrid states between photons and Bloch electrons. So far, experimental progress on light-field dressed states has been mainly focused on the occupied states, however, it is unclear if the transient photo-excited states above the Fermi energy $E_F$ can also be dressed, leaving the dynamical interplay between photo-excitation and light-field dressing elusive. Here, we provide direct experimental evidence for light-field dressing of the transient photo-excited surface states above $E_F$, which exhibits distinct dynamics with a delay response as compared to light-field dressed states below $E_F$. Our work reveals the dual roles of the pump pulse in both photo-excitation and light-field dressing, providing a more comprehensive picture with new insights on the light-induced manipulation of transient electronic states. △ Less

Submitted 9 April, 2025; originally announced April 2025.

Journal ref: Phys. Rev. Lett. 134, 146401 (2025)

Floquet-Volkov interference in a semiconductor

Authors: Changhua Bao, Haoyuan Zhong, Benshu Fan, Xuanxi Cai, Fei Wang, Shaohua Zhou, Tianyun Lin, Hongyun Zhang, Pu Yu, Peizhe Tang, Wenhui Duan, Shuyun Zhou

Abstract: Intense light-field can dress both Bloch electrons inside crystals and photo-emitted free electrons in the vacuum, dubbed as Floquet and Volkov states respectively. These quantum states can further interfere coherently, modulating light-field dressed states. Here, we report experimental evidence of the Floquet-Volkov interference in a semiconductor - black phosphorus. A highly asymmetric modulatio… ▽ More Intense light-field can dress both Bloch electrons inside crystals and photo-emitted free electrons in the vacuum, dubbed as Floquet and Volkov states respectively. These quantum states can further interfere coherently, modulating light-field dressed states. Here, we report experimental evidence of the Floquet-Volkov interference in a semiconductor - black phosphorus. A highly asymmetric modulation of the spectral weight is observed for the Floquet-Volkov states, and such asymmetry can be further controlled by rotating the pump polarization. Our work reveals the quantum interference between different light-field dressed electronic states, providing insights for material engineering on the ultrafast timescale. △ Less

Submitted 11 February, 2025; originally announced February 2025.

Journal ref: Phys. Rev. B 111, L081106 (2025)

Light-induced ultrafast glide-mirror symmetry breaking in black phosphorus

Authors: Changhua Bao, Fei Wang, Haoyuan Zhong, Shaohua Zhou, Tianyun Lin, Hongyun Zhang, Xuanxi Cai, Wenhui Duan, Shuyun Zhou

Abstract: Symmetry breaking plays an important role in fields of physics, ranging from particle physics to condensed matter physics. In solid-state materials, phase transitions are deeply linked to the underlying symmetry breakings, resulting in a rich variety of emergent phases. Such symmetry breakings are often induced by controlling the chemical composition and temperature or applying an electric field a… ▽ More Symmetry breaking plays an important role in fields of physics, ranging from particle physics to condensed matter physics. In solid-state materials, phase transitions are deeply linked to the underlying symmetry breakings, resulting in a rich variety of emergent phases. Such symmetry breakings are often induced by controlling the chemical composition and temperature or applying an electric field and strain, etc. In this work, we demonstrate an ultrafast glide-mirror symmetry breaking in black phosphorus through Floquet engineering. Upon near-resonance pumping, a light-induced full gap opening is observed at the glide-mirror symmetry protected nodal ring, suggesting light-induced breaking of the glide-mirror symmetry. Moreover, the full gap is observed only in the presence of the light-field and disappears almost instantaneously ($\ll$100 fs) when the light-field is turned off, suggesting the ultrafast manipulation of the symmetry and its Floquet engineering origin. This work not only demonstrates light-matter interaction as an effective way to realize ultrafast symmetry breaking in solid-state materials, but also moves forward towards the long-sought Floquet topological phases. △ Less

Submitted 9 December, 2024; originally announced December 2024.

Journal ref: ACS Nano 18, 32038 (2024)

Manipulating the symmetry of photon-dressed electronic states

Authors: Changhua Bao, Michael Schüler, Teng Xiao, Fei Wang, Haoyuan Zhong, Tianyun Lin, Xuanxi Cai, Tianshuang Sheng, Xiao Tang, Hongyun Zhang, Pu Yu, Zhiyuan Sun, Wenhui Duan, Shuyun Zhou

Abstract: Strong light-matter interaction provides opportunities for tailoring the physical properties of quantum materials on the ultrafast timescale by forming photon-dressed electronic states, i.e., Floquet-Bloch states. While the light field can in principle imprint its symmetry properties onto the photon-dressed electronic states, so far, how to experimentally detect and further engineer the symmetry o… ▽ More Strong light-matter interaction provides opportunities for tailoring the physical properties of quantum materials on the ultrafast timescale by forming photon-dressed electronic states, i.e., Floquet-Bloch states. While the light field can in principle imprint its symmetry properties onto the photon-dressed electronic states, so far, how to experimentally detect and further engineer the symmetry of photon-dressed electronic states remains elusive. Here by utilizing time- and angle-resolved photoemission spectroscopy (TrARPES) with polarization-dependent study, we directly visualize the parity symmetry of Floquet-Bloch states in black phosphorus. The photon-dressed sideband exhibits opposite photoemission intensity to the valence band at the $Γ$ point,suggesting a switch of the parity induced by the light field. Moreover, a "hot spot" with strong intensity confined near $Γ$ is observed, indicating a momentum-dependent modulation beyond the parity switch. Combining with theoretical calculations, we reveal the light-induced engineering of the wave function of the Floquet-Bloch states as a result of the hybridization between the conduction and valence bands with opposite parities, and show that the "hot spot" is intrinsically dictated by the symmetry properties of black phosphorus. Our work suggests TrARPES as a direct probe for the parity of the photon-dressed electronic states with energy- and momentum-resolved information, providing an example for engineering the wave function and symmetry of such photon-dressed electronic states via Floquet engineering. △ Less

Submitted 9 December, 2024; originally announced December 2024.

Journal ref: Nature Communications 15, 10535 (2024)

Confined Magnetization at the Sublattice-Matched Ruthenium Oxide Heterointerface

Authors: Yiyan Fan, Qinghua Zhang, Ting Lin, He Bai, Chuanrui Huo, Qiao Jin, Tielong Deng, Songhee Choi, Shengru Chen, Haitao Hong, Ting Cui, Qianying Wang, Dongke Rong, Chen Liu, Chen Ge, Tao Zhu, Lin Gu, Kuijuan Jin, Jun Chen, Er-Jia Guo

Abstract: Creating a heterostructure by combining two magnetically and structurally distinct ruthenium oxides is a crucial approach for investigating their emergent magnetic states and interactions. Previously, research has predominantly concentrated on the intrinsic properties of the ferromagnet SrRuO3 and recently discovered altermagnet RuO2 solely. Here, we engineered an ultrasharp sublattice-matched het… ▽ More Creating a heterostructure by combining two magnetically and structurally distinct ruthenium oxides is a crucial approach for investigating their emergent magnetic states and interactions. Previously, research has predominantly concentrated on the intrinsic properties of the ferromagnet SrRuO3 and recently discovered altermagnet RuO2 solely. Here, we engineered an ultrasharp sublattice-matched heterointerface using pseudo-cubic SrRuO3 and rutile RuO2, conducting an in-depth analysis of their spin interactions. Structurally, to accommodate the lattice symmetry mismatch, the inverted RuO2 layer undergoes an in-plane rotation of 18 degrees during epitaxial growth on SrRuO3 layer, resulting in an interesting and rotational interface with perfect crystallinity and negligible chemical intermixing. Performance-wise, the interfacial layer of 6 nm in RuO2 adjacent to SrRuO3 exhibits a nonzero magnetic moment, contributing to an enhanced anomalous Hall effect (AHE) at low temperatures. Furthermore, our observations indicate that, in contrast to SrRuO3 single layers, the AHE of [(RuO2)15/(SrRuO3)n] heterostructures shows nonlinear behavior and reaches its maximum when the SrRuO3 thickness reaches tens of nm. These results suggest that the interfacial magnetic interaction surpasses that of all-perovskite oxides (~5-unit cells). This study underscores the significance and potential applications of magnetic interactions based on the crystallographic asymmetric interfaces in the design of spintronic devices. △ Less

Submitted 4 December, 2024; originally announced December 2024.

Comments: 30 pages/5 figures

Proposals for 3D self-correcting quantum memory

Authors: Ting-Chun Lin, Hsin-Po Wang, Min-Hsiu Hsieh

Abstract: A self-correcting quantum memory is a type of quantum error correcting code that can correct errors passively through cooling. A major open question in the field is whether self-correcting quantum memories can exist in 3D. In this work, we propose two candidate constructions for 3D self-correcting quantum memories. The first construction is an extension of Haah's code, which retains translation in… ▽ More A self-correcting quantum memory is a type of quantum error correcting code that can correct errors passively through cooling. A major open question in the field is whether self-correcting quantum memories can exist in 3D. In this work, we propose two candidate constructions for 3D self-correcting quantum memories. The first construction is an extension of Haah's code, which retains translation invariance. The second construction is based on fractals with greater flexibility in its design. Additionally, we review existing 3D quantum codes and suggest that they are not self-correcting. △ Less

Submitted 5 November, 2024; originally announced November 2024.

Strict area law entanglement versus chirality

Authors: Xiang Li, Ting-Chun Lin, John McGreevy, Bowen Shi

Abstract: Chirality is a property of a gapped phase of matter in two spatial dimensions that can be manifested through non-zero thermal or electrical Hall conductance. In this paper, we prove two no-go theorems that forbid such chirality for a quantum state in a finite dimensional local Hilbert space with strict area law entanglement entropies. As a crucial ingredient in the proofs, we introduce a new quant… ▽ More Chirality is a property of a gapped phase of matter in two spatial dimensions that can be manifested through non-zero thermal or electrical Hall conductance. In this paper, we prove two no-go theorems that forbid such chirality for a quantum state in a finite dimensional local Hilbert space with strict area law entanglement entropies. As a crucial ingredient in the proofs, we introduce a new quantum information-theoretic primitive called instantaneous modular flow, which has many other potential applications. △ Less

Submitted 1 November, 2025; v1 submitted 19 August, 2024; originally announced August 2024.

Comments: 6+10 pages, 4 figures

A Microscopic Estimation of the Splay Elastic Constant K11 for Nematic Liquid Crystals

Authors: Tien-Lun Ting, Tsung-Hsien Lin

Abstract: A theory of the relationship between splay elastic constant K11 and permanent molecular moment of liquid crystals is developed. The theory gives a microscopic estimation of K11 with a correct order of magnitude by calculating the electrostatic energy density between the adjacent molecules. A theory of the relationship between splay elastic constant K11 and permanent molecular moment of liquid crystals is developed. The theory gives a microscopic estimation of K11 with a correct order of magnitude by calculating the electrostatic energy density between the adjacent molecules. △ Less

Submitted 26 June, 2024; originally announced June 2024.

Electric-field control of the perpendicular magnetization switching in ferroelectric/ferrimagnet heterostructures

Authors: Pengfei Liu, Tao Xu, Qi Liu, Juncai Dong, Ting Lin, Qinhua Zhang, Xiukai Lan, Yu Sheng, Chunyu Wang, Jiajing Pei, Hongxin Yang, Lin Gu, Kaiyou Wang

Abstract: Electric field control of the magnetic state in ferrimagnets holds great promise for developing spintronic devices due to low power consumption. Here, we demonstrate a non-volatile reversal of perpendicular net magnetization in a ferrimagnet by manipulating the electric-field driven polarization within the Pb (Zr0.2Ti0.8) O3 (PZT)/CoGd heterostructure. Electron energy loss spectra and X-ray absorp… ▽ More Electric field control of the magnetic state in ferrimagnets holds great promise for developing spintronic devices due to low power consumption. Here, we demonstrate a non-volatile reversal of perpendicular net magnetization in a ferrimagnet by manipulating the electric-field driven polarization within the Pb (Zr0.2Ti0.8) O3 (PZT)/CoGd heterostructure. Electron energy loss spectra and X-ray absorption spectrum directly verify that the oxygen ion migration at the PZT/CoGd interface associated with reversing the polarization causes the enhanced/reduced oxidation in CoGd. Ab initio calculations further substantiate that the migrated oxygen ions can modulate the relative magnetization of Co/Gd sublattices, facilitating perpendicular net magnetization switching. Our findings offer an approach to effectively control ferrimagnetic net magnetization, holding significant implications for ferrimagnetic spintronic applications. △ Less

Submitted 26 June, 2024; originally announced June 2024.

Comments: 21 pages,4 figures

Theory of charge-6e condensed phase in Kagome lattice superconductors

Authors: Tong-Yu Lin, Feng-Feng Song, Guang-Ming Zhang

Abstract: We develop a Ginzburg-Landau theory for commensurate pair density wave (PDW) states in a hexagonal lattice system, relevant to the kagome superconductors $\rm{AV_3Sb_5}$. Compared to previous theoretical frameworks, the commensurate wave vectors permit additional symmetric terms in the free energy, altering the system's ground state and its degeneracy. In particular, we analyze topological defects… ▽ More We develop a Ginzburg-Landau theory for commensurate pair density wave (PDW) states in a hexagonal lattice system, relevant to the kagome superconductors $\rm{AV_3Sb_5}$. Compared to previous theoretical frameworks, the commensurate wave vectors permit additional symmetric terms in the free energy, altering the system's ground state and its degeneracy. In particular, we analyze topological defects in the energetically favorable $ψ_{\text{kagome}}$ ground state and find that kinks on domain walls can carry $1/3$ topological charges. We further establish a correspondence between the SC fluctuations in these states and an effective $J_1-J_2$ frustrated XY model on the emergent kagome lattice. By employing a state-of-the-art numerical tensor network method, we rigorously solve this effective model at finite temperatures and confirm the existence of a vestigial phase characterized by $1/3$ vortex-antivortex pairs in low temperatures with the absence of phase coherence of Cooper pairs, which is dual to the charge-$6e$ condensed phase. Our theory provides a potential explanation for the vestigial charge-$6e$ magnetoresistance oscillations observed in recent experiments [J. Ge, et. al., Phys. Rev. X 14, 021025 (2024)]. △ Less

Submitted 25 November, 2024; v1 submitted 17 June, 2024; originally announced June 2024.

Comments: 16 pages, 11 figures; revised version and another author included

Journal ref: Physical Review B, 111, 054508 (2025)

The regulation of symmetry-breaking-dependent electronic structures in ReSeS monolayer

Authors: Texture Lin

Abstract: Due to the excellent physical properties, two dimensional materials have attracted widespread attention from researchers. In this article, we discuss a transition metal dichalcogenide, ReSeS monolayer with 1T" phase, with extremely low symmetry through the first principles calculation. It belongs to the space group P1 and has Jauns structure. Due to the broken of the central inversion symmetry. Ra… ▽ More Due to the excellent physical properties, two dimensional materials have attracted widespread attention from researchers. In this article, we discuss a transition metal dichalcogenide, ReSeS monolayer with 1T" phase, with extremely low symmetry through the first principles calculation. It belongs to the space group P1 and has Jauns structure. Due to the broken of the central inversion symmetry. Raman and infrared active modes in the vibrational spectrum no longer mutually exclusive, which has become a spectral fingerprint of this material. First principles calculation indicates that the bandgap decreases when the material has geometric deformation, and we propose two models to explain this phenomenon and provide the physical pictures. The first model requires constructing a low symmetry Wannier analytically simplify Hamiltonian to obtain 4 energy levels of mixed orbital, Then the changes of bandgap can be qualitatively described through the difference between these energy levels; The second model analyzes the variations of bandgap through the bonding or antibonding characteristics of the valence and conduction band. We point out that it is a "saturation effect", where the energy of the valence and conduction band has difficulties in further changing under the deformation, resulting in the reduction of the bandgap under both compression and tensile deformation. Meanwhile, we discuss a metallic phase of ReSeS, called 1T' phase, to explain the formation of the bandgap. Compared to the 1T" phase, it has higher symmetry. Semi-filled d-orbital bands in 1T' phases will become unstable and split into bonding and antibonding bands, leading to the opening of bandgap. This process is also known as Peierls phase transition. Finally, we calculated the effective mass of electron and the absorption spectrum. Results point out the potential of ReSeS in the preparation of electrical or optical devices. △ Less

Submitted 28 May, 2024; originally announced June 2024.

Comments: 47 pages, 17 figures, in Chinese

Ultrafast Carrier Relaxation Dynamics in a Nodal-Line Semimetal PtSn$_4$

Authors: Tianyun Lin, Yongkang Ju, Haoyuan Zhong, Xiangyu Zeng, Xue Dong, Changhua Bao, Hongyun Zhang, Tian-Long Xia, Peizhe Tang, Shuyun Zhou

Abstract: Topological Dirac nodal-line semimetals host topologically nontrivial electronic structure with nodal-line crossings around the Fermi level, which could affect the photocarrier dynamics and lead to novel relaxation mechanisms. Herein, by using time- and angle-resolved photoemission spectroscopy, we reveal the previously-inaccessible linear dispersions of the bulk conduction bands above the Fermi l… ▽ More Topological Dirac nodal-line semimetals host topologically nontrivial electronic structure with nodal-line crossings around the Fermi level, which could affect the photocarrier dynamics and lead to novel relaxation mechanisms. Herein, by using time- and angle-resolved photoemission spectroscopy, we reveal the previously-inaccessible linear dispersions of the bulk conduction bands above the Fermi level in a Dirac nodal-line semimetal PtSn$_4$, as well as the momentum and temporal evolution of the gapless nodal lines. A surprisingly ultrafast relaxation dynamics within a few hundred femtoseconds is revealed for photoexcited carriers in the nodal line. Theoretical calculations suggest that such ultrafast carrier relaxation is attributed to the multichannel scatterings among the complex metallic bands of PtSn$_4$ via electron-phonon coupling. In addition, a unique dynamic relaxation mechanism contributed by the highly anisotropic Dirac nodal-line electronic structure is also identified. Our work provides a comprehensive understanding of the ultrafast carrier dynamics in a Dirac nodal-line semimetal. △ Less

Submitted 20 May, 2024; originally announced May 2024.

Strict area law implies commuting parent Hamiltonian

Authors: Isaac H. Kim, Ting-Chun Lin, Daniel Ranard, Bowen Shi

Abstract: We show that in two spatial dimensions, when a quantum state has entanglement entropy obeying a strict area law, meaning $S(A)=α|\partial A| - γ$ for constants $α, γ$ independent of lattice region $A$, then it admits a commuting parent Hamiltonian. More generally, we prove that the entanglement bootstrap axioms in 2D imply the existence of a commuting, local parent Hamiltonian with a stable spectr… ▽ More We show that in two spatial dimensions, when a quantum state has entanglement entropy obeying a strict area law, meaning $S(A)=α|\partial A| - γ$ for constants $α, γ$ independent of lattice region $A$, then it admits a commuting parent Hamiltonian. More generally, we prove that the entanglement bootstrap axioms in 2D imply the existence of a commuting, local parent Hamiltonian with a stable spectral gap. We also extend our proof to states that describe gapped domain walls. Physically, these results imply that the states studied in the entanglement bootstrap program correspond to ground states of some local Hamiltonian, describing a stable phase of matter. Our result also suggests that systems with chiral gapless edge modes cannot obey a strict area law provided they have finite local Hilbert space. △ Less

Submitted 8 April, 2024; originally announced April 2024.

Comments: 19+2 pages, 10 figures

Hidden charge density wave induced shadow bands and ultrafast dynamics of CuTe investigated using time-resolved ARPES

Authors: Haoyuan Zhong, Changhua Bao, Tianyun Lin, Fei Wang, Xuanxi Cai, Pu Yu, Shuyun Zhou

Abstract: Revealing the fine electronic structure is critical for understanding the underlying physics of low-dimensional materials. Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique for mapping out the experimental electronic structure. By reducing the photon energy (e.g. to 6 eV) using laser sources, a greatly improved momentum resolution can be achieved, thereby provi… ▽ More Revealing the fine electronic structure is critical for understanding the underlying physics of low-dimensional materials. Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique for mapping out the experimental electronic structure. By reducing the photon energy (e.g. to 6 eV) using laser sources, a greatly improved momentum resolution can be achieved, thereby providing opportunities for ``zooming in'' the fine electronic structure and even revealing the previously unresolvable bands near the Brillouin zone center. Here, by using quasi-one-dimensional material CuTe as an example, we demonstrate the unique capability of laser-based ARPES in revealing the fine electronic structures of ``hidden'' charge density wave induced shadow bands near the Brillouin zone center, which are previously unresolvable using synchrotron sources. The observation of the shadow bands reveals the CDW phase from the aspect of band folding, and the unpredicted CDW band hybridization strongly modifies the electronic structure and Fermi surface, which suggests that such hybridization must be taken into account for studying the CDW transition. Moreover, the ultrafast non-equilibrium carrier dynamics are captured by time-resolved ARPES, revealing the relaxation dynamics through electron-phonon scattering. Our work demonstrates the advantages of laser-based ARPES in zooming in the fine electronic structures, as well as capturing the ultrafast dynamics of low-dimensional materials. △ Less

Submitted 8 April, 2024; originally announced April 2024.

Comments: 8 pages, 5 figures

Journal ref: Phys. Rev. B 109, 165411 (2024)

Conformal geometry from entanglement

Authors: Isaac H. Kim, Xiang Li, Ting-Chun Lin, John McGreevy, Bowen Shi

Abstract: In a physical system with conformal symmetry, observables depend on cross-ratios, measures of distance invariant under global conformal transformations (conformal geometry for short). We identify a quantum information-theoretic mechanism by which the conformal geometry emerges at the gapless edge of a 2+1D quantum many-body system with a bulk energy gap. We introduce a novel pair of information-th… ▽ More In a physical system with conformal symmetry, observables depend on cross-ratios, measures of distance invariant under global conformal transformations (conformal geometry for short). We identify a quantum information-theoretic mechanism by which the conformal geometry emerges at the gapless edge of a 2+1D quantum many-body system with a bulk energy gap. We introduce a novel pair of information-theoretic quantities $(\mathfrak{c}_{\mathrm{tot}}, η)$ that can be defined locally on the edge from the wavefunction of the many-body system, without prior knowledge of any distance measure. We posit that, for a topological groundstate, the quantity $\mathfrak{c}_{\mathrm{tot}}$ is stationary under arbitrary variations of the quantum state, and study the logical consequences. We show that stationarity, modulo an entanglement-based assumption about the bulk, implies (i) $\mathfrak{c}_{\mathrm{tot}}$ is a non-negative constant that can be interpreted as the total central charge of the edge theory. (ii) $η$ is a cross-ratio, obeying the full set of mathematical consistency rules, which further indicates the existence of a distance measure of the edge with global conformal invariance. Thus, the conformal geometry emerges from a simple assumption on groundstate entanglement. We show that stationarity of $\mathfrak{c}_{\mathrm{tot}}$ is equivalent to a vector fixed-point equation involving $η$, making our assumption locally checkable. We also derive similar results for 1+1D systems under a suitable set of assumptions. △ Less

Submitted 3 February, 2025; v1 submitted 4 April, 2024; originally announced April 2024.

Comments: 48+31 pages, 25 figures

Journal ref: SciPost Phys. 18, 102 (2025)

Chiral Virasoro algebra from a single wavefunction

Authors: Isaac H. Kim, Xiang Li, Ting-Chun Lin, John McGreevy, Bowen Shi

Abstract: Chiral edges of 2+1D systems can have very robust emergent conformal symmetry. When the edge is purely chiral, the Hilbert space of low-energy edge excitations can form a representation of a single Virasoro algebra. We propose a method to systematically extract the generators of the Virasoro algebra from a single ground state wavefunction, using entanglement bootstrap and an input from the edge co… ▽ More Chiral edges of 2+1D systems can have very robust emergent conformal symmetry. When the edge is purely chiral, the Hilbert space of low-energy edge excitations can form a representation of a single Virasoro algebra. We propose a method to systematically extract the generators of the Virasoro algebra from a single ground state wavefunction, using entanglement bootstrap and an input from the edge conformal field theory. We corroborate our construction by numerically verifying the commutation relations of the generators. We also study the unitary flows generated by these operators, whose properties (such as energy and state overlap) are shown numerically to agree with our analytical predictions. △ Less

Submitted 3 January, 2025; v1 submitted 27 March, 2024; originally announced March 2024.

Comments: 60+20 pages, 28 figures

Journal ref: Ann. Phys., vol 471, 169849 (2024)

Evolution of flat band and role of lattice relaxations in twisted bilayer graphene

Authors: Qian Li, Hongyun Zhang, Yijie Wang, Wanying Chen, Changhua Bao, Qinxin Liu, Tianyun Lin, Shuai Zhang, Haoxiong Zhang, Kenji Watanabe, Takashi Taniguchi, Jose Avila, Pavel Dudin, Qunyang Li, Pu Yu, Wenhui Duan, Zhida Song, Shuyun Zhou

Abstract: Magic-angle twisted bilayer graphene (MATBG) exhibits correlated phenomena such as superconductivity and Mott insulating state related to the weakly dispersing flat band near the Fermi energy. Beyond its moiré period, such flat band is expected to be sensitive to lattice relaxations. Thus, clarifying the evolution of the electronic structure with twist angle is critical for understanding the physi… ▽ More Magic-angle twisted bilayer graphene (MATBG) exhibits correlated phenomena such as superconductivity and Mott insulating state related to the weakly dispersing flat band near the Fermi energy. Beyond its moiré period, such flat band is expected to be sensitive to lattice relaxations. Thus, clarifying the evolution of the electronic structure with twist angle is critical for understanding the physics of MATBG. Here, we combine nanospot angle-resolved photoemission spectroscopy and atomic force microscopy to resolve the fine electronic structure of the flat band and remote bands, and their evolution with twist angles from 1.07$^\circ$ to 2.60$^\circ$. Near the magic angle, dispersion is characterized by a flat band near the Fermi energy with a strongly reduced bandwidth. Moreover, near 1.07$^\circ$, we observe a spectral weight transfer between remote bands at higher binding energy and extract the modulated interlayer spacing near the magic angle. Our work provides direct spectroscopic information on flat band physics and highlights the role of lattice relaxations. △ Less

Submitted 20 March, 2024; originally announced March 2024.

Comments: 22 pages, 5 figures, Nature Materials, in press

Data-Driven Modeling of Dislocation Mobility from Atomistics using Physics-Informed Machine Learning

Authors: Yifeng Tian, Soumendu Bagchi, Liam Myhill, Giacomo Po, Enrique Martinez, Yen Ting Lin, Nithin Mathew, Danny Perez

Abstract: Dislocation mobility, which dictates the response of dislocations to an applied stress, is a fundamental property of crystalline materials that governs the evolution of plastic deformation. Traditional approaches for deriving mobility laws rely on phenomenological models of the underlying physics, whose free parameters are in turn fitted to a small number of intuition-driven atomic scale simulatio… ▽ More Dislocation mobility, which dictates the response of dislocations to an applied stress, is a fundamental property of crystalline materials that governs the evolution of plastic deformation. Traditional approaches for deriving mobility laws rely on phenomenological models of the underlying physics, whose free parameters are in turn fitted to a small number of intuition-driven atomic scale simulations under varying conditions of temperature and stress. This tedious and time-consuming approach becomes particularly cumbersome for materials with complex dependencies on stress, temperature, and local environment, such as body-centered cubic crystals (BCC) metals and alloys. In this paper, we present a novel, uncertainty quantification-driven active learning paradigm for learning dislocation mobility laws from automated high-throughput large-scale molecular dynamics simulations, using Graph Neural Networks (GNN) with a physics-informed architecture. We demonstrate that this Physics-informed Graph Neural Network (PI-GNN) framework captures the underlying physics more accurately compared to existing phenomenological mobility laws in BCC metals. △ Less

Submitted 20 March, 2024; originally announced March 2024.

Regulation of electronic structures in ReSeS monolayer with anisotropic deformations

Authors: T. T. Lin, J. W. Ma, H. C. Deng, L. Z. Liu

Abstract: Because of their unique and rich physical properties, transition metal dichalcogenides (TMDs) materials have attracted much interest. Many studies suggest that introducing the degree of freedom of anisotropy, which may be brought about by low structural symmetry, might further optimize their applications in industry and manufacturing. However, most currently reported TMDs do not achieve the theore… ▽ More Because of their unique and rich physical properties, transition metal dichalcogenides (TMDs) materials have attracted much interest. Many studies suggest that introducing the degree of freedom of anisotropy, which may be brought about by low structural symmetry, might further optimize their applications in industry and manufacturing. However, most currently reported TMDs do not achieve the theoretical minimum symmetry. Utilizing the first principles calculation, we present ReSeS monolayer with a Janus structure. Results indicate that its electronic dispersion is sensitive to structural distortions, which increases metallicity. Our reduction-Hamiltonian can provide a qualitative description, but further analyses reveal that bonding/antibonding properties near the Fermi surface are the more fundamental cause of the variations. Furthermore, geometric deformations can regulate the effective mass of electrons as well as the spectroscopic response, resulting in anisotropic behaviors. Our ideas serve as a foundation for developing new regulable optoelectronic devices. △ Less

Submitted 8 February, 2025; v1 submitted 2 March, 2024; originally announced March 2024.

Forming Long-range Order of Semiconducting Polymers through Liquid-phase Directional Molecular Assemblies

Authors: Minh Nhat Pham, Chun-Jen Su, Yu-Ching Huang, Kun-Ta Lin, Ting-Yu Huang, Yu-Ying Lai, Chen-An Wang, Yong-Kang Liaw, Ting-Han Lin, U-Ser Jeng, Jrjeng Ruan, Chan Luo, Ye Huang, Guillermo C. Bazan, Ben B. Y. Hsu

Abstract: Intermolecular interactions are crucial in determining the morphology of solution-processed semiconducting polymer thin films. However, these random interactions often lead to disordered or short-range ordered structures. Achieving long-range order in these films has been a challenge due to limited control over microscopic interactions in current techniques. Here, we present a molecular-level meth… ▽ More Intermolecular interactions are crucial in determining the morphology of solution-processed semiconducting polymer thin films. However, these random interactions often lead to disordered or short-range ordered structures. Achieving long-range order in these films has been a challenge due to limited control over microscopic interactions in current techniques. Here, we present a molecular-level methodology that leverages spatial matching of intermolecular dynamics among solutes, solvents, and substrates to induce directional molecular assembly in weakly bonded polymers. Within the optimized dynamic scale of 2.5 Å between polymer side chains and self-assembled monolayers (SAMs) on nanogrooved substrates, our approach transforms random aggregates into unidirectional fibers with a remarkable increase in the anisotropic stacking ratio from 1 to 11. The Flory-Huggins-based molecular stacking model accurately predicts the transitioning order on various SAMs, validated by morphologic and spectroscopic observations. The enhanced structural ordering spans over 3 orders of magnitude in length, raising from the smallest 7.3 nm random crystallites to >14 um unidirectional fibers on sub-millimeter areas. Overall, this study provides insights into the control of complex intermolecular interactions and offers enhanced molecular-level controllability in solution-based processes. △ Less

Submitted 19 February, 2024; originally announced February 2024.

Comments: 40 pages, 6 figures, 2 tables

Using Ornstein-Uhlenbeck Process to understand Denoising Diffusion Probabilistic Model and its Noise Schedules

Authors: Javier E. Santos, Yen Ting Lin

Abstract: The aim of this short note is to show that Denoising Diffusion Probabilistic Model DDPM, a non-homogeneous discrete-time Markov process, can be represented by a time-homogeneous continuous-time Markov process observed at non-uniformly sampled discrete times. Surprisingly, this continuous-time Markov process is the well-known and well-studied Ornstein-Ohlenbeck (OU) process, which was developed in… ▽ More The aim of this short note is to show that Denoising Diffusion Probabilistic Model DDPM, a non-homogeneous discrete-time Markov process, can be represented by a time-homogeneous continuous-time Markov process observed at non-uniformly sampled discrete times. Surprisingly, this continuous-time Markov process is the well-known and well-studied Ornstein-Ohlenbeck (OU) process, which was developed in 1930's for studying Brownian particles in Harmonic potentials. We establish the formal equivalence between DDPM and the OU process using its analytical solution. We further demonstrate that the design problem of the noise scheduler for non-homogeneous DDPM is equivalent to designing observation times for the OU process. We present several heuristic designs for observation times based on principled quantities such as auto-variance and Fisher Information and connect them to ad hoc noise schedules for DDPM. Interestingly, we show that the Fisher-Information-motivated schedule corresponds exactly the cosine schedule, which was developed without any theoretical foundation but is the current state-of-the-art noise schedule. △ Less

Submitted 29 November, 2023; originally announced November 2023.

Strain mediated phase crossover in Ruddlesden Popper nickelates

Authors: Ting Cui, Songhee Choi, Ting Lin, Chen Liu, Gang Wang, Ningning Wang, Shengru Chen, Haitao Hong, Dongke Rong, Qianying Wang, Qiao Jin, Jia-Ou Wang, Lin Gu, Chen Ge, Can Wang, Jin Guang Cheng, Qinghua Zhang, Liang Si, Kui-juan Jin, Er-Jia Guo

Abstract: Recent progress on the signatures of pressure-induced high temperature superconductivity in Ruddlesden Popper (RP) nickelates (Lan+1NinO3n+1) has attracted growing interest in both theoretical calculations and experimental efforts. The fabrication of high-quality single crystalline RP nickelate thin films is critical for possible reducing the superconducting transition pressure and advancing appli… ▽ More Recent progress on the signatures of pressure-induced high temperature superconductivity in Ruddlesden Popper (RP) nickelates (Lan+1NinO3n+1) has attracted growing interest in both theoretical calculations and experimental efforts. The fabrication of high-quality single crystalline RP nickelate thin films is critical for possible reducing the superconducting transition pressure and advancing applications in microelectronics in the future. In this study, we report the observations of an active phase transition in RP nickelate films induced by misfit strain. We found that RP nickelate films favor the perovskite structure (n = infinite) under tensile strains, while compressive strains stabilize the La3Ni2O7 (n = 2) phase. The selection of distinct phases is governed by the strain dependent formation energy and electronic configuration. In compressively strained La3Ni2O7, we experimentally determined splitting energy is ~0.2 eV and electrons prefer to occupy in-plane orbitals. First principles calculations unveil a robust coupling between strain effects and the valence state of Ni ions in RP nickelates, suggesting a dual driving force for the inevitable phase co-existence transition in RP nickelates. Our work underscores the sensitivity of RP nickelate formation to epitaxial strain, presenting a significant challenge in fabricating pure-phase RP nickelate films. Therefore, special attention to stacking defects and grain boundaries between different RP phases is essential when discussing the pressure-induced superconductivity in RP nickelates. △ Less

Submitted 22 November, 2023; originally announced November 2023.

Comments: 29 pages, 5 figures, one supplementary materials

Unified tensor network theory for frustrated classical spin models in two dimensions

Authors: Feng-Feng Song, Tong-Yu Lin, Guang-Ming Zhang

Abstract: Frustration is a ubiquitous phenomenon in many-body physics that influences the nature of the system in a profound way with exotic emergent behavior. Despite its long research history, the analytical or numerical investigations on frustrated spin models remain a formidable challenge due to their extensive ground state degeneracy. In this work, we propose a unified tensor network theory to numerica… ▽ More Frustration is a ubiquitous phenomenon in many-body physics that influences the nature of the system in a profound way with exotic emergent behavior. Despite its long research history, the analytical or numerical investigations on frustrated spin models remain a formidable challenge due to their extensive ground state degeneracy. In this work, we propose a unified tensor network theory to numerically solve the frustrated classical spin models on various two-dimensional (2D) lattice geometry with high efficiency. We show that the appropriate encoding of emergent degrees of freedom in each local tensor is of crucial importance in the construction of the infinite tensor network representation of the partition function. The frustrations are thus relieved through the effective interactions between emergent local degrees of freedom. Then the partition function is written as a product of a one-dimensional (1D) transfer operator, whose eigen-equation can be solved by the standard algorithm of matrix product states rigorously, and various phase transitions can be accurately determined from the singularities of the entanglement entropy of the 1D quantum correspondence. We demonstrated the power of our unified theory by numerically solving 2D fully frustrated XY spin models on the kagome, square and triangular lattices, giving rise to a variety of thermal phase transitions from infinite-order Brezinskii-Kosterlitz-Thouless transitions, second-order transitions, to first-order phase transitions. Our approach holds the potential application to other types of frustrated classical systems like Heisenberg spin antiferromagnets. △ Less

Submitted 11 September, 2023; originally announced September 2023.

Comments: 20 pages, 19 figures

Journal ref: Physical Review B 108, 224404 (2023)

Magnetism and berry phase manipulation in an emergent structure of perovskite ruthenate by (111) strain engineering

Authors: Zhaoqing Ding, Xuejiao Chen, Zhenzhen Wang, Qinghua Zhang, Fang Yang, Jiachang Bi, Ting Lin, Zhen Wang, Xiaofeng Wu, Minghui Gu, Meng Meng, Yanwei Cao, Lin Gu, Jiandi Zhang, Zhicheng Zhong, Xiaoran Liu, Jiandong Guo

Abstract: The interplay among symmetry of lattices, electronic correlations, and Berry phase of the Bloch states in solids has led to fascinating quantum phases of matter. A prototypical system is the magnetic Weyl candidate SrRuO3, where designing and creating electronic and topological properties on artificial lattice geometry is highly demanded yet remains elusive. Here, we establish an emergent trigonal… ▽ More The interplay among symmetry of lattices, electronic correlations, and Berry phase of the Bloch states in solids has led to fascinating quantum phases of matter. A prototypical system is the magnetic Weyl candidate SrRuO3, where designing and creating electronic and topological properties on artificial lattice geometry is highly demanded yet remains elusive. Here, we establish an emergent trigonal structure of SrRuO3 by means of heteroepitaxial strain engineering along the [111] crystallographic axis. Distinctive from bulk, the trigonal SrRuO3 exhibits a peculiar XY-type ferromagnetic ground state, with the coexistence of high-mobility holes likely from linear Weyl bands and low-mobility electrons from normal quadratic bands as carriers. The presence of Weyl nodes are further corroborated by capturing intrinsic anomalous Hall effect, acting as momentum-space sources of Berry curvatures. The experimental observations are consistent with our first-principles calculations, shedding light on the detailed band topology of trigonal SrRuO3 with multiple pairs of Weyl nodes near the Fermi level. Our findings signify the essence of magnetism and Berry phase manipulation via lattice design and pave the way towards unveiling nontrivial correlated topological phenomena. △ Less

Submitted 26 August, 2023; originally announced August 2023.

On the combinatorics of Lotka-Volterra equations

Authors: Francesco Caravelli, Yen Ting Lin

Abstract: We study an approach to obtaining the exact formal solution of the 2-species Lotka-Volterra equation based on combinatorics and generating functions. By employing a combination of Carleman linearization and Mori-Zwanzig reduction techniques, we transform the nonlinear equations into a linear system, allowing for the derivation of a formal solution. The Mori-Zwanzig reduction reduces to an expansio… ▽ More We study an approach to obtaining the exact formal solution of the 2-species Lotka-Volterra equation based on combinatorics and generating functions. By employing a combination of Carleman linearization and Mori-Zwanzig reduction techniques, we transform the nonlinear equations into a linear system, allowing for the derivation of a formal solution. The Mori-Zwanzig reduction reduces to an expansion which we show can be interpreted as a directed and weighted lattice path walk, which we use to obtain a representation of the system dynamics as walks of fixed length. The exact solution is then shown to be dependent on the generator of weighted walks. We show that the generator can be obtained by the solution of PDE which in turn is equivalent to a particular Koopman evolution of nonlinear observables. △ Less

Submitted 25 August, 2023; originally announced August 2023.

Comments: 27 single column pages+epsilon, 3 figures

Journal ref: Physica A, Volume 670, 15 July 2025, 130484

Super-tetragonal Sr4Al2O7: a versatile sacrificial layer for high-integrity freestanding oxide membranes

Authors: Jinfeng Zhang, Ting Lin, Ao Wang, Xiaochao Wang, Qingyu He, Huan Ye, Jingdi Lu, Qing Wang, Zhengguo Liang, Feng Jin, Shengru Chen, Minghui Fan, Er-Jia Guo, Qinghua Zhang, Lin Gu, Zhenlin Luo, Liang Si, Wenbin Wu, Lingfei Wang

Abstract: Releasing the epitaxial oxide heterostructures from substrate constraints leads to the emergence of various correlated electronic phases and paves the way for integrations with advanced semiconductor technologies. Identifying a suitable water-soluble sacrificial layer, compatible with the high-quality epitaxial growth of oxide heterostructures, is currently the key to the development of large-scal… ▽ More Releasing the epitaxial oxide heterostructures from substrate constraints leads to the emergence of various correlated electronic phases and paves the way for integrations with advanced semiconductor technologies. Identifying a suitable water-soluble sacrificial layer, compatible with the high-quality epitaxial growth of oxide heterostructures, is currently the key to the development of large-scale freestanding oxide membranes. In this study, we unveil the super-tetragonal Sr4Al2O7 (SAOT) as a promising water-soluble sacrificial layer. The distinct low-symmetric crystal structure of SAOT enables a superior capability to sustain epitaxial strain, thus allowing for broad tunability in lattice constants. The resultant structural coherency and defect-free interface in perovskite ABO3/SAOT heterostructures effectively restrain crack formations during the water-assisted release of freestanding oxide membranes. For a variety of non-ferroelectric oxide membranes, the crack-free areas can span up to a few millimeters in length scale. These compelling features, combined with the inherent high-water solubility, make SAOT a versatile and feasible sacrificial layer for producing high-quality freestanding oxide membranes, thereby boosting their potential for innovative oxide electronics and flexible device designs. △ Less

Submitted 6 October, 2023; v1 submitted 27 July, 2023; originally announced July 2023.

Comments: 5 figures and SI, it is the second version of this manuscript

Versatile Method of Engineering the Band Alignment and the Electron Wavefunction Hybridization of Hybrid Quantum Devices

Authors: Guoan Li, Xiaofan Shi, Ting Lin, Guang Yang, Marco Rossi, Ghada Badawy, Zhiyuan Zhang, Jiayu Shi, Degui Qian, Fang Lu, Lin Gu, An-Qi Wang, Bingbing Tong, Peiling Li, Zhaozheng Lyu, Guangtong Liu, Fanming Qu, Ziwei Dou, Dong Pan, Jianhua Zhao, Qinghua Zhang, Erik P. A. M. Bakkers, Michał P. Nowak, Paweł Wójcik, Li Lu , et al. (1 additional authors not shown)

Abstract: With the development of quantum technology, hybrid devices that combine superconductors (S) and semiconductors (Sm) have attracted great attention due to the possibility of engineering structures that benefit from the integration of the properties of both materials. However, until now, none of the experiments have reported good control of band alignment at the interface, which determines the stren… ▽ More With the development of quantum technology, hybrid devices that combine superconductors (S) and semiconductors (Sm) have attracted great attention due to the possibility of engineering structures that benefit from the integration of the properties of both materials. However, until now, none of the experiments have reported good control of band alignment at the interface, which determines the strength of S-Sm coupling and the proximitized superconducting gap. Here, we fabricate hybrid devices in a generic way with argon milling to modify the interface while maintaining its high quality. First, after the milling the atomically connected S-Sm interfaces appear, resulting in a large induced gap, as well as the ballistic transport revealed by the multiple Andreev reflections and quantized above-gap conductance plateaus. Second, by comparing transport measurement with Schrödinger-Poisson (SP) calculations, we demonstrate that argon milling is capable of varying the band bending strength in the semiconducting wire as the electrons tend to accumulate on the etched surface for longer milling time. Finally, we perform nonlocal measurements on advanced devices to demonstrate the coexistence and tunability of crossed Andreev reflection (CAR) and elastic co-tunneling (ECT) -- key ingredients for building the prototype setup for realization of Kitaev chain and quantum entanglement probing. Such a versatile method, compatible with the standard fabrication process and accompanied by the well-controlled modification of the interface, will definitely boost the creation of more sophisticated hybrid devices for exploring physics in solid-state systems. △ Less

Submitted 24 July, 2024; v1 submitted 13 July, 2023; originally announced July 2023.

Comments: 41 pages, 16 figures

Large effective magnetic fields from chiral phonons in rare-earth halides

Authors: Jiaming Luo, Tong Lin, Junjie Zhang, Xiaotong Chen, Elizabeth R. Blackert, Rui Xu, Boris I. Yakobson, Hanyu Zhu

Abstract: Time-reversal symmetry (TRS) is pivotal for materials optical, magnetic, topological, and transport properties. Chiral phonons, characterized by atoms rotating unidirectionally around their equilibrium positions, generate dynamic lattice structures that break TRS. Here we report that coherent chiral phonons, driven by circularly polarized terahertz light pulses, can polarize the paramagnetic spins… ▽ More Time-reversal symmetry (TRS) is pivotal for materials optical, magnetic, topological, and transport properties. Chiral phonons, characterized by atoms rotating unidirectionally around their equilibrium positions, generate dynamic lattice structures that break TRS. Here we report that coherent chiral phonons, driven by circularly polarized terahertz light pulses, can polarize the paramagnetic spins in CeF3 like a quasi-static magnetic field on the order of 1 Tesla. Through time-resolved Faraday rotation and Kerr ellipticity, we found the transient magnetization is only excited by pulses resonant with phonons, proportional to the angular momentum of the phonons, and growing with magnetic susceptibility at cryogenic temperatures, as expected from the spin-phonon coupling model. The time-dependent effective magnetic field quantitatively agrees with that calculated from phonon dynamics. Our results may open a new route to directly investigate mode-specific spin-phonon interaction in ultrafast magnetism, energy-efficient spintronics, and non-equilibrium phases of matter with broken TRS. △ Less

Submitted 6 June, 2023; originally announced June 2023.

Journal ref: Science 382(6671), 698-702 (2023)

Conformal Field Theory Ground States as Critical Points of an Entropy Function

Authors: Ting-Chun Lin, John McGreevy

Abstract: We derive an entropy formula satisfied by the ground states of 1+1D conformal field theories. The formula implies that the ground state is the critical point of an entropy function. We conjecture that this formula may serve as an information-theoretic criterion for conformal field theories, which differs from the conventional algebraic definition. In addition to these findings, we use the same pro… ▽ More We derive an entropy formula satisfied by the ground states of 1+1D conformal field theories. The formula implies that the ground state is the critical point of an entropy function. We conjecture that this formula may serve as an information-theoretic criterion for conformal field theories, which differs from the conventional algebraic definition. In addition to these findings, we use the same proof method to extract the six global conformal generators of the conformal field theory from its ground state. We validate our results by testing them on different critical lattice models with excellent agreement. △ Less

Submitted 20 December, 2023; v1 submitted 9 March, 2023; originally announced March 2023.

Distinguishing and controlling Mottness in 1T-TaS$_2$ by ultrafast light

Authors: Changhua Bao, Haoyuan Zhong, Fei Wang, Tianyun Lin, Haoxiong Zhang, Zhiyuan Sun, Wenhui Duan, Shuyun Zhou

Abstract: Distinguishing and controlling the extent of Mottness is important for materials where the energy scales of the onsite Coulomb repulsion U and the bandwidth W are comparable. Here we report the ultrafast electronic dynamics of 1T-TaS$_2$ by ultrafast time- and angle-resolved photoemission spectroscopy. A comparison of the electron dynamics for the newly-discovered intermediate phase (I-phase) as w… ▽ More Distinguishing and controlling the extent of Mottness is important for materials where the energy scales of the onsite Coulomb repulsion U and the bandwidth W are comparable. Here we report the ultrafast electronic dynamics of 1T-TaS$_2$ by ultrafast time- and angle-resolved photoemission spectroscopy. A comparison of the electron dynamics for the newly-discovered intermediate phase (I-phase) as well as the low-temperature commensurate charge density wave (C-CDW) phase shows distinctive dynamics. While the I-phase is characterized by an instantaneous response and nearly time-resolution-limited fast relaxation (~200 fs), the C-CDW phase shows a delayed response and a slower relaxation (a few ps). Such distinctive dynamics refect the different relaxation mechanisms and provide nonequilibrium signatures to distinguish the Mott insulating I-phase from the C-CDW band insulating phase. Moreover, a light-induced bandwidth reduction is observed in the C-CDW phase, pushing it toward the Mott insulating phase. Our work demonstrates the power of ultrafast light-matter interaction in both distinguishing and controlling the extent of Mottness on the ultrafast timescale. △ Less

Submitted 3 March, 2023; originally announced March 2023.

Spin State Disproportionation in Insulating Ferromagnetic LaCoO3 Epitaxial Thin Films

Authors: Shanquan Chen, Jhong-Yi Chang, Qinghua Zhang, Qiuyue Li, Ting Lin, Fanqi Meng, Haoliang Huang, Shengwei Zeng, Xinmao Yin, My Ngoc Duong, Yalin Lu, Lang Chen, Er-Jia Guo, Hanghui Chen, Chun-Fu Chang, Chang-Yang Kuo, Zuhuang Chen

Abstract: The origin of insulating ferromagnetism in epitaxial LaCoO3 films under tensile strain remains elusive despite extensive research efforts have been devoted. Surprisingly, the spin state of its Co ions, the main parameter of its ferromagnetism, is still to be determined. Here, we have systematically investigated the spin state in epitaxial LaCoO3 thin films to clarify the mechanism of strain induce… ▽ More The origin of insulating ferromagnetism in epitaxial LaCoO3 films under tensile strain remains elusive despite extensive research efforts have been devoted. Surprisingly, the spin state of its Co ions, the main parameter of its ferromagnetism, is still to be determined. Here, we have systematically investigated the spin state in epitaxial LaCoO3 thin films to clarify the mechanism of strain induced ferromagnetism using element-specific x-ray absorption spectroscopy and dichroism. Combining with the configuration interaction cluster calculations, we unambiguously demonstrate that Co3+ in LaCoO3 films under compressive strain (on LaAlO3 substrate) are practically a low spin state, whereas Co3+ in LaCoO3 films under tensile strain (on SrTiO3 substrate) have mixed high spin and low spin states with a ratio close to 1:3. From the identification of this spin state ratio, we infer that the dark strips observed by high-resolution scanning transmission electron microscopy indicate the position of Co3+ high spin state, i.e., an observation of a spin state disproportionation in tensile-strained LaCoO3 films. This consequently explains the nature of ferromagnetism in LaCoO3 films. △ Less

Submitted 12 February, 2023; originally announced February 2023.

Journal ref: Advanced Science, 2303630 (2023)

Universal lower bound on topological entanglement entropy

Authors: Isaac H. Kim, Michael Levin, Ting-Chun Lin, Daniel Ranard, Bowen Shi

Abstract: Entanglement entropies of two-dimensional gapped ground states are expected to satisfy an area law, with a constant correction term known as the topological entanglement entropy (TEE). In many models, the TEE takes a universal value that characterizes the underlying topological phase. However, the TEE is not truly universal: it can differ even for two states related by constant-depth circuits, whi… ▽ More Entanglement entropies of two-dimensional gapped ground states are expected to satisfy an area law, with a constant correction term known as the topological entanglement entropy (TEE). In many models, the TEE takes a universal value that characterizes the underlying topological phase. However, the TEE is not truly universal: it can differ even for two states related by constant-depth circuits, which are necessarily in the same phase. The difference between the TEE and the value predicted by the anyon theory is often called the spurious topological entanglement entropy. We show that this spurious contribution is always nonnegative, thus the value predicted by the anyon theory provides a universal lower bound. This observation also leads to a definition of TEE that is invariant under constant-depth quantum circuits. △ Less

Submitted 31 October, 2023; v1 submitted 1 February, 2023; originally announced February 2023.

Comments: 13 pages, 16 figures

Journal ref: Phys. Rev. Lett. 131, 16, 166601 (Oct 2023)

Pseudospin-selective Floquet band engineering in black phosphorus

Authors: Shaohua Zhou, Changhua Bao, Benshu Fan, Hui Zhou, Qixuan Gao, Haoyuan Zhong, Tianyun Lin, Hang Liu, Pu Yu, Peizhe Tang, Sheng Meng, Wenhui Duan, Shuyun Zhou

Abstract: Time-periodic light field has emerged as a control knob for manipulating quantum states in solid-state materials, cold atoms and photonic systems via hybridization with photon-dressed Floquet states in the strong coupling limit, dubbed as Floquet engineering. Such interaction leads to tailored properties of quantum materials, for example, modifications of the topological properties of Dirac materi… ▽ More Time-periodic light field has emerged as a control knob for manipulating quantum states in solid-state materials, cold atoms and photonic systems via hybridization with photon-dressed Floquet states in the strong coupling limit, dubbed as Floquet engineering. Such interaction leads to tailored properties of quantum materials, for example, modifications of the topological properties of Dirac materials and modulation of the optical response. Despite extensive research interests over the past decade, there is no experimental evidence of momentum-resolved Floquet band engineering of semiconductors, which is a crucial step to extend Floquet engineering to a wide range of solid-state materials. Here, based on time- and angle-resolved photoemission spectroscopy measurements, we report experimental signatures of Floquet band engineering in a model semiconductor - black phosphorus. Upon near-resonance pumping at photon energy of 340 to 440 meV, a strong band renormalization is observed near the band edges. In particular, light-induced dynamical gap opening is resolved at the resonance points, which emerges simultaneously with the Floquet sidebands. Moreover, the band renormalization shows a strong selection rule favoring pump polarization along the armchair direction, suggesting pseudospin selectivity for the Floquet band engineering as enforced by the lattice symmetry. Our work demonstrates pseudospin-selective Floquet band engineering in black phosphorus, and provides important guiding principles for Floquet engineering of semiconductors. △ Less

Submitted 1 February, 2023; originally announced February 2023.

Journal ref: Nature 614, 75-80 (2023)

A newly-designed femtosecond KBe$_2$BO$_3$F$_2$ device with pulse duration down to 55 fs for time- and angle-resolved photoemission spectroscopy

Authors: Haoyuan Zhong, Changhua Bao, Tianyun Lin, Shaohua Zhou, Shuyun Zhou

Abstract: Developing a widely tunable vacuum ultraviolet (VUV) source with sub-100 femtoseconds (fs) pulse duration is critical for ultrafast pump-probe techniques such as time- and angle-resolved photoemission spectroscopy (TrARPES). While a tunable probe source with photon energy of 5.3 - 7.0 eV has been recently implemented for TrARPES by using a KBe$_2$BO$_3$F$_2$ (KBBF) device, the time resolution of 2… ▽ More Developing a widely tunable vacuum ultraviolet (VUV) source with sub-100 femtoseconds (fs) pulse duration is critical for ultrafast pump-probe techniques such as time- and angle-resolved photoemission spectroscopy (TrARPES). While a tunable probe source with photon energy of 5.3 - 7.0 eV has been recently implemented for TrARPES by using a KBe$_2$BO$_3$F$_2$ (KBBF) device, the time resolution of 280 - 320 fs is still not ideal, which is mainly limited by the duration of the VUV probe pulse generated by the KBBF device. Here, by designing a new KBBF device which is specially optimized for fs applications, an optimum pulse duration of 55 fs is obtained after systematic diagnostics and optimization. More importantly, a high time resolution of 81 - 95 fs is achieved for TrARPES measurements covering the probe photon energy range of 5.3 - 7.0 eV, making it particularly useful for investigating the ultrafast dynamics of quantum materials. Our work extends the application of KBBF device to ultrafast pump-probe techniques with the advantages of both widely tunable VUV source and ultimate time resolution. △ Less

Submitted 1 February, 2023; originally announced February 2023.

Comments: 8 pages, 4 figures

Journal ref: Rev. Sci. Instrum. 93, 113910 (2022)

Simulation Study of the Effects of Polymer Network Dynamics and Mesh Confinement on the Diffusion and Structural Relaxation of Penetrants

Authors: Tsai-Wei Lin, Baicheng Mei, Kenneth S. Schweizer, Charles E. Sing

Abstract: The diffusion of small molecular penetrants through polymeric materials represents an important fundamental problem, relevant to the design of materials for applications such as coatings and membranes. Polymer networks hold promise in these applications, because dramatic differences in molecular diffusion can result from subtle changes in the network structure. In this paper, we use molecular simu… ▽ More The diffusion of small molecular penetrants through polymeric materials represents an important fundamental problem, relevant to the design of materials for applications such as coatings and membranes. Polymer networks hold promise in these applications, because dramatic differences in molecular diffusion can result from subtle changes in the network structure. In this paper, we use molecular simulation to understand the role that crosslinked network polymers have in governing the molecular motion of penetrants. By considering the local, activated alpha relaxation time of the penetrant and its long-time diffusive dynamics, we can determine the relative importance of activated glassy dynamics on penetrants at the segmental scale versus entropic mesh confinement on penetrant diffusion. We vary several parameters, such as the crosslinking density, temperature, and penetrant size, to show that crosslinks primarily affect molecular diffusion through modification of the matrix glass transition, with local penetrant hopping at least partially coupled to the segmental relaxation of the polymer network. This coupling is very sensitive to the local activated segmental dynamics of the surrounding matrix, and we also show that penetrant transport is affected by dynamic heterogeneity at low temperatures. To contrast, only at high temperatures and for large penetrants or when the dynamic heterogeneity effect is weak does the effect of mesh confinement become significant, even though penetrant diffusion more broadly empirically follows similar trends as established models of mesh confinement-based transport. △ Less

Submitted 27 February, 2023; v1 submitted 12 January, 2023; originally announced January 2023.

Comments: Including a main text and a supporting information, for main text: 33 pages, 1 table, and 9 figures; for supporting information: 3 figures and 1 table. Totally, 35 pages, 2 tables, and 12 figures

Journal ref: J.Chem.Phys. 159 (2023) 014904

Self-Consistent Hopping Theory of Activated Relaxation and Diffusion of Dilute Penetrants in Dense Crosslinked Polymer Networks

Authors: Baicheng Mei, Tsai-Wei Lin, Charles E. Sing, Kenneth S. Schweizer

Abstract: We generalize and apply a microscopic force-level statistical mechanical theory of the activated dynamics of dilute spherical penetrants in glass-forming liquids to study the influence of permanent crosslinking in polymer networks on the penetrant relaxation time and diffusivity over a wide range of temperature and crosslink density. Calculations are performed for model parameters relevant to rece… ▽ More We generalize and apply a microscopic force-level statistical mechanical theory of the activated dynamics of dilute spherical penetrants in glass-forming liquids to study the influence of permanent crosslinking in polymer networks on the penetrant relaxation time and diffusivity over a wide range of temperature and crosslink density. Calculations are performed for model parameters relevant to recent experimental studies of an nm-sized organic molecule diffusing in crosslinked PnBA networks. The theory predicts the penetrant alpha relaxation time increases exponentially with the crosslink fraction ($f_n$) dependent glass transition temperature, $T_g$, which grows roughly linearly with the square root of $f_n$. Moreover, $T_g$ is also found to be proportional to a geometric confinement parameter defined as the ratio of the penetrant diameter to the mean network mesh size. The decoupling ratio of the penetrant to polymer Kuhn segment alpha relaxation times displays a complex non-monotonic dependence on crosslink density and temperature that can be well collapsed based on the variable $T_g(f_n)/T$. The microscopic mechanism for activated penetrant relaxation is elucidated and a model for the penetrant diffusion constant that combines activated segmental dynamics and entropic mesh confinement is proposed which results in a significantly stronger suppression of mass transport with degree of effective supercooling than predicted for the penetrant alpha time. This behavior corresponds to a new polymer network-based type of decoupling of diffusion and relaxation. In contrast to the diffusion of larger nanoparticles in high temperature rubbery networks, our analysis in the deeply supercooled regime suggests that for the penetrants studied the mesh confinement effects are of secondary importance relative to the consequences of crosslink-induced slowing down of glassy activated relaxation. △ Less

Submitted 27 February, 2023; v1 submitted 12 January, 2023; originally announced January 2023.

Comments: 42 pages and 14 figures

Journal ref: J.Chem.Phys. 158 (2023) 184901

How Segmental Dynamics and Mesh Confinement Determine the Selective Diffusivity of Molecules in Crosslinked Dense Polymer Networks

Authors: Baicheng Mei, Tsai-Wei Lin, Grant S. Sheridan, Christopher M. Evans, Charles E. Sing, Kenneth S. Schweizer

Abstract: The diffusion of molecules (penetrants) of variable size, shape, and chemistry through dense crosslinked polymer networks is a fundamental scientific problem that is broadly relevant in materials, polymer, physical and biological chemistry. Relevant applications include molecular separations in membranes, barrier materials for coatings, drug delivery, and nanofiltration. A major open question is t… ▽ More The diffusion of molecules (penetrants) of variable size, shape, and chemistry through dense crosslinked polymer networks is a fundamental scientific problem that is broadly relevant in materials, polymer, physical and biological chemistry. Relevant applications include molecular separations in membranes, barrier materials for coatings, drug delivery, and nanofiltration. A major open question is the relationship between molecular transport, thermodynamic state, and chemical structure of the penetrant and polymeric media. Here we address this question by combining experiment, simulation, and theory to unravel the competing effects of penetrant chemistry on its transport in rubbery and supercooled polymer permanent networks over a wide range of crosslink densities, size ratios, and temperatures. The crucial importance of the coupling of local penetrant hopping to the polymer structural relaxation process, and the secondary importance of geometric mesh confinement effects, are established. Network crosslinks induce a large slowing down of nm-scale polymer relaxation which greatly retards the rate of penetrant activated relaxation. The demonstrated good agreement between experiment, simulation, and theory provides strong support for the size ratio variable (effective penetrant diameter to the polymer Kuhn length) as a key variable, and the usefulness of coarse-grained simulation and theoretical models that average over Angstrom scale chemical details. The developed microscopic theory provides a fundamental understanding of the physical processes underlying the behaviors observed in experiment and simulation. Penetrant transport is theoretically predicted to become even more size sensitive in a more deeply supercooled regime not probed in our present experiments or simulations, which suggests new strategies for enhancing selective polymer membrane design. △ Less

Submitted 7 January, 2023; originally announced January 2023.

Comments: including a main text and a supporting information. For the main text, 28 pages and 5 figures; For the supporting information, 23 pages and 14 figures. Totally, 51 pages and 19 figures

Journal ref: ACS Cent. Sci. 9 (2023) 508-518