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Perturbation-assisted Observation of the Lowest Vibrational Level of the $\mathrm{b}^{3}Π_{0}$ State of Ultracold LiK Molecules
Authors:
Anbang Yang,
Xiaoyu Nie,
Hao Lin Yu,
Yiming Liu,
Victor Avalos,
Canming He,
Jacek Klos,
Svetlana Kotochigova,
Kai Dieckmann
Abstract:
The narrow transition from the lowest rovibrational level of the $\mathrm{X}^{1}Σ^{+}$ electronic ground state to the lowest vibrational level of the $\mathrm{b}^{3}Π_{0}$ potential provides opportunities for achieving magic-wavelength trapping of ultracold bialkali molecules for enhancing their rotational coherence times. Guided by existing spectroscopic data of several perturbed and deeply-bound…
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The narrow transition from the lowest rovibrational level of the $\mathrm{X}^{1}Σ^{+}$ electronic ground state to the lowest vibrational level of the $\mathrm{b}^{3}Π_{0}$ potential provides opportunities for achieving magic-wavelength trapping of ultracold bialkali molecules for enhancing their rotational coherence times. Guided by existing spectroscopic data of several perturbed and deeply-bound rovibrational states of the $\mathrm{A}^{1}Σ^{+}$ potential [Grochola et al., Chem. Phys. Lett., 2012, 535, 17-20], we conducted a targeted spectroscopic search and report the first observation of the lowest vibrational level of the $\mathrm{b}^{3}Π_{0}$ state in $^{6}\mathrm{Li}^{40}\mathrm{K}$. The transition frequency from $|\mathrm{X}^{1}Σ^{+},\,v=0,\,J=0>$ to $|\mathrm{b}^{3}Π_{0},\,v'=0,\,J'=1>$ is determined to be 314,230.5(5)GHz. Assisted by microwave spectroscopy, we resolved the rotational structure of $|\mathrm{b}^{3}Π_{0},\,v'=0>$ and extracted a rotational constant of $h\times8.576(44)$ GHz for the $\mathrm{b}^{3}Π_{0}$ state. From this, we deducted an energy separation between $|\mathrm{b}^{3}Π_{0},v'=0,J'=0>$ and $|\mathrm{X}^{1}Σ^{+},v=0,J=0>$ of $hc\times$10,481.03(2) $\mathrm{cm}^{-1}$. Our work provides timely and precise information on the deeply-bound region of the $\mathrm{b}^{3}Π_{0}$ triplet excited potential of LiK, and benefits future applications of ultracold LiK isotopologues in quantum simulation and quantum computation that demand long coherence times.
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Submitted 6 December, 2025; v1 submitted 20 October, 2025;
originally announced October 2025.
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Unraveling Magneto-Phononic Coupling and Photoinduced Magnetic Control in Antiferromagnetic Kondo Semimetal CeBi
Authors:
Xu-Chen Nie,
Chen Zhang,
Qi-Yi Wu,
Hao Liu,
Jie Pang,
You-Guo Shi,
Zhi-An Xu,
Yan-Feng Guo,
Ya-Hua Yuan,
H. Y. Liu,
Yu-Xia Duan,
Jian-Qiao Meng
Abstract:
We report an ultrafast optical spectroscopy study on the coherent phonon dynamics in the topological semimetal CeBi and its nonmagnetic isostructural compound LaBi, revealing profound insights into their electronic and magnetic interactions. Both materials exhibit prominent $A_{1g}$ longitudinal optical phonons with characteristic anharmonic temperature dependencies. However, in CeBi, the…
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We report an ultrafast optical spectroscopy study on the coherent phonon dynamics in the topological semimetal CeBi and its nonmagnetic isostructural compound LaBi, revealing profound insights into their electronic and magnetic interactions. Both materials exhibit prominent $A_{1g}$ longitudinal optical phonons with characteristic anharmonic temperature dependencies. However, in CeBi, the $A_{1g}$ phonon frequency and amplitude show clear anomalies near its antiferromagnetic (AFM) ordering temperatures ($T_{N1}$ $\simeq$ 25 K and $T_{N2}$ $\simeq$ 12 K), which unequivocally demonstrate strong magneto-phononic coupling. Crucially, in the AFM state at 4 K, CeBi exhibits a pump fluence threshold of $F_C$ $\approx$ 44 $μ$J/cm$^2$, above which the rate of phonon softening accelerates and the amplitude increases sharply. This unique threshold, absent in paramagnetic CeBi and LaBi, points to a photoinduced, non-thermal quenching of the AFM order. Our findings establish coherent phonons as highly sensitive probes of intertwined orders in heavy fermion systems, highlighting the transformative potential of ultrafast pulses in dynamically controlling magnetic states in correlated electron materials and paving the way for the manipulation of emergent quantum phases.
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Submitted 11 July, 2025;
originally announced July 2025.
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Non-adiabatic linear response in open quantum systems
Authors:
Xiaotian Nie,
Wei Zheng
Abstract:
Adiabatic theorem and non-adiabatic corrections have been widely applied in modern quantum technology. Recently, non-adiabatic linear response theory has been developed to probe the many-body correlations in closed systems. In this work, we generalize the non-adiabatic linear response theory to open quantum many-body systems. We show that, similar to the closed case, the first-order deviation from…
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Adiabatic theorem and non-adiabatic corrections have been widely applied in modern quantum technology. Recently, non-adiabatic linear response theory has been developed to probe the many-body correlations in closed systems. In this work, we generalize the non-adiabatic linear response theory to open quantum many-body systems. We show that, similar to the closed case, the first-order deviation from the instantaneous steady state is memoryless -- it depends only on the final parameters and not on the initial state or ramping path. When ramping the Hamiltonian, the linear response of observables is governed by the derivative of the retarded Green's function, as in closed systems. In contrast, ramping the dissipation gives rise to a different response, characterized by a high-order correlation function defined in the steady state. Our results offer a compact and physically transparent formulation of non-adiabatic response in open systems, and demonstrate that ramping dynamics can serve as a versatile tool for probing many-body correlations beyond equilibrium.
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Submitted 9 September, 2025; v1 submitted 15 January, 2025;
originally announced January 2025.
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Fate of the spatial-temporal order under quantum fluctuation
Authors:
Xiaotian Nie,
Wei Zheng
Abstract:
In a previous theoretical work [arXiv:2205.01461], T. Esslinger group proposed a scheme to realize a spatial-temporal lattice, which possesses dual periodicity on space and time, in a cavity-boson system pumped by a travelling wave laser. However, the prediction was made under the mean-field approximation. In this work, we investigate the dynamics beyond mean-field approximation. By including the…
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In a previous theoretical work [arXiv:2205.01461], T. Esslinger group proposed a scheme to realize a spatial-temporal lattice, which possesses dual periodicity on space and time, in a cavity-boson system pumped by a travelling wave laser. However, the prediction was made under the mean-field approximation. In this work, we investigate the dynamics beyond mean-field approximation. By including the fluctuation of the cavity field, we obtain a larger set of equations of motion. Numerical results show that the spatial-temporal lattice is melted in the mean-field level but survives in the quantum fluctuation.
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Submitted 7 November, 2024;
originally announced November 2024.
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Einstein-de Haas effect: a bridge linking mechanics, magnetism, and topology
Authors:
Xin Nie,
Dao-Xin Yao
Abstract:
The Einstein-de Haas (EdH) effect is a fascinating phenomenon that links mechanics and magnetism. Despite being discovered over a century ago, it remains significant in contemporary science, particularly within the fields of spintronics and ultrafast magnetism. Recent predictions suggest that the EdH effect may be realized in topological magnon systems, potentially leading to even richer propertie…
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The Einstein-de Haas (EdH) effect is a fascinating phenomenon that links mechanics and magnetism. Despite being discovered over a century ago, it remains significant in contemporary science, particularly within the fields of spintronics and ultrafast magnetism. Recent predictions suggest that the EdH effect may be realized in topological magnon systems, potentially leading to even richer properties. In this perspective, we introduce recent advancements in the EdH effect and discuss its developments in three key aspects: the microscopic mechanism, its manifestation in topological systems, and chirality-selective magnon-phonon coupling. Our discussions aim to inspire further explorations of the EdH effect and highlight its promising applications in different areas.
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Submitted 14 February, 2025; v1 submitted 25 September, 2024;
originally announced September 2024.
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Density-Dependent Gauge Field with Raman Lattices
Authors:
Xiang-Can Cheng,
Zong-Yao Wang,
Jinyi Zhang,
Shuai Chen,
Xiaotian Nie
Abstract:
The study of the gauge field is an everlasting topic in modern physics. Spin-orbit coupling is a powerful tool in ultracold atomic systems, resulting in an artificial gauge field that can be easily manipulated and observed in a tabletop environment. Combining optical Raman lattices and atom-atom interaction, the artificial gauge field can be made density-dependent. In this work, we propose a strai…
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The study of the gauge field is an everlasting topic in modern physics. Spin-orbit coupling is a powerful tool in ultracold atomic systems, resulting in an artificial gauge field that can be easily manipulated and observed in a tabletop environment. Combining optical Raman lattices and atom-atom interaction, the artificial gauge field can be made density-dependent. In this work, we propose a straightforward way to engineer one-dimensional density-dependent gauge field in a Bose-Hubbard model in spin-orbit coupled Raman lattices. Next, we study the model from two perspectives: few-body quantum walk dynamics and many-body ground state. In the first perspective, we show that large spin-flipped tunneling can lead to a deep two-body bound state. In the second perspective, mean-field and density matrix renormalization group (DMRG) calculations consistently reveal three different phases, i.e. the Mott insulator phase, the superfluid phase, and the magnetic superfluid phase. Finally, we discuss the experimental protocol with Raman lattices based on existing experimental platforms.
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Submitted 3 February, 2025; v1 submitted 13 August, 2024;
originally announced August 2024.
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Kibble-Zurek behavior in a topological phase transition with a quadratic band crossing
Authors:
Huan Yuan,
Jinyi Zhang,
Shuai Chen,
Xiaotian Nie
Abstract:
Kibble-Zurek (KZ) mechanism describes the scaling behavior when driving a system across a continuous symmetry-breaking transition. Previous studies have shown that the KZ-like scaling behavior also lies in the topological transitions in the Qi-Wu-Zhang model (2D) and the Su-Schrieffer-Heeger model (1D), although symmetry breaking does not exist here. Both models with linear band crossings give tha…
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Kibble-Zurek (KZ) mechanism describes the scaling behavior when driving a system across a continuous symmetry-breaking transition. Previous studies have shown that the KZ-like scaling behavior also lies in the topological transitions in the Qi-Wu-Zhang model (2D) and the Su-Schrieffer-Heeger model (1D), although symmetry breaking does not exist here. Both models with linear band crossings give that $ν=1$ and $z=1$. We wonder whether different critical exponents can be acquired in topological transitions beyond linear band crossing. In this work, we look into the KZ behavior in a topological 2D checkerboard lattice with a quadratic band crossing. We investigate from dual perspectives: momentum distribution of the Berry curvature in clean systems for simplicity, and real-space analysis of domain-like local Chern marker configurations in disordered systems, which is a more intuitive analog to conventional KZ description. In equilibrium, we find the correlation length diverges with a power $ν\simeq 1/2$. Then, by slowly quenching the system across the topological phase transition, we find that the freeze-out time $t_\mathrm{f}$ and the unfrozen length scale $ξ(t_\mathrm{f})$ both satisfy the KZ scaling, verifying $z\simeq 2$. We subsequently explore KZ behavior in topological phase transitions with other higher-order band crossing and find the relationship between the critical exponents and the order. Our results extend the understanding of the KZ mechanism and non-equilibrium topological phase transitions.
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Submitted 18 October, 2024; v1 submitted 29 July, 2024;
originally announced July 2024.
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Efficient Creation of Ultracold Ground State $^{6}\textrm{Li}^{40}\textrm{K}$ Polar Molecules
Authors:
Canming He,
Xiaoyu Nie,
Victor Avalos,
Sofia Botsi,
Sunil Kumar,
Anbang Yang,
Kai Dieckmann
Abstract:
We report the creation of ultracold ground state $^{6}\textrm{Li}^{40}\textrm{K}$ polar molecules with high efficiency. Starting from weakly-bound molecules state, stimulated Raman adiabatic passage (STIRAP) is adopted to coherently transfer the molecules to their singlet ro-vibrational ground state $|\textrm{X}^{1}Σ^{+},v=0,J=0>$. By employing a singlet STIRAP pathway and low-phase-noise narrow-l…
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We report the creation of ultracold ground state $^{6}\textrm{Li}^{40}\textrm{K}$ polar molecules with high efficiency. Starting from weakly-bound molecules state, stimulated Raman adiabatic passage (STIRAP) is adopted to coherently transfer the molecules to their singlet ro-vibrational ground state $|\textrm{X}^{1}Σ^{+},v=0,J=0>$. By employing a singlet STIRAP pathway and low-phase-noise narrow-linewidth lasers, we observed a one-way transfer efficiency of 96(4)\,\%. Held in an optical dipole trap, the lifetime of the ground-state molecules is measured to be 5.0(3)\,ms. The large permanent dipole moment of LiK is confirmed by applying a DC electric field on the molecules and performing Stark shift spectroscopy of the ground state. With recent advances in the quantum control of collisions, our work paves the way for exploring quantum many-body physics with strongly-interacting $^{6}\textrm{Li}^{40}\textrm{K}$ molecules.
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Submitted 5 October, 2023;
originally announced October 2023.
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A spin-rotation mechanism of Einstein-de Haas effect based on a ferromagnetic disk
Authors:
Xin Nie,
Jun Li,
Trinanjan Datta,
Dao-Xin Yao
Abstract:
Spin-rotation coupling (SRC) is a fundamental phenomenon that connects electronic spins with the rotational motion of a medium. We elucidate the Einstein-de Haas (EdH) effect and its inverse with SRC as the microscopic mechanism using the dynamic spin-lattice equations derived by elasticity theory and Lagrangian formalism. By applying the coupling equations to an iron disk in a magnetic field, we…
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Spin-rotation coupling (SRC) is a fundamental phenomenon that connects electronic spins with the rotational motion of a medium. We elucidate the Einstein-de Haas (EdH) effect and its inverse with SRC as the microscopic mechanism using the dynamic spin-lattice equations derived by elasticity theory and Lagrangian formalism. By applying the coupling equations to an iron disk in a magnetic field, we exhibit the transfer of angular momentum and energy between spins and lattice, with or without damping. The timescale of the angular momentum transfer from spins to the entire lattice is estimated by our theory to be on the order of 0.01 ns, for the disk with a radius of 100 nm. Moreover, we discover a linear relationship between the magnetic field strength and the rotation frequency, which is also enhanced by a higher ratio of Young's modulus to Poisson's coefficient. In the presence of damping, we notice that the spin-lattice relaxation time is nearly inversely proportional to the magnetic field. Our explorations will contribute to a better understanding of the EdH effect and provide valuable insights for magneto-mechanical manufacturing.
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Submitted 8 April, 2024; v1 submitted 19 July, 2023;
originally announced July 2023.
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Non-equilibrium phases of Fermi gas inside a cavity with imbalanced pumping
Authors:
Xiaotian Nie,
Wei Zheng
Abstract:
In this work, we investigate the non-equilibrium dynamics of one-dimensional spinless fermions loaded in a cavity with imbalanced pumping lasers. Our study is motivated by previous work on a similar setup using bosons, and we explore the unique properties of fermionic systems in this context. By considering the imbalance in the pumping, we find that the system exhibits multiple superradiant steady…
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In this work, we investigate the non-equilibrium dynamics of one-dimensional spinless fermions loaded in a cavity with imbalanced pumping lasers. Our study is motivated by previous work on a similar setup using bosons, and we explore the unique properties of fermionic systems in this context. By considering the imbalance in the pumping, we find that the system exhibits multiple superradiant steady phases and an unstable phase. Furthermore, by making use of the hysteresis structure of superradiant phases, we propose a unidirectional topological pumping. Unlike the usual topological pumping in which the driving protocol breaks time reversal symmetry, the driving protocol can be time reversal invariant in our proposal.
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Submitted 14 July, 2023;
originally announced July 2023.
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Mode softening in time-crystalline transitions of open quantum systems
Authors:
Xiaotian Nie,
Wei Zheng
Abstract:
In this work, we generalize the concept of roton softening mechanism of spatial crystalline transition to time crystals in open quantum systems. We study a dissipative Dicke model as a prototypical example, which exhibits both continuous time crystal and discrete time crystal phases.We found that on approaching the time crystalline transition, the response function diverges at a finite frequency,…
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In this work, we generalize the concept of roton softening mechanism of spatial crystalline transition to time crystals in open quantum systems. We study a dissipative Dicke model as a prototypical example, which exhibits both continuous time crystal and discrete time crystal phases.We found that on approaching the time crystalline transition, the response function diverges at a finite frequency, which determines the period of the upcoming time crystal. This divergence can be understood as softening of the relaxation rate of the corresponding collective excitation, which can be clearly seen by the poles of the response function on the complex plane. Using this mode softening analysis, we predict a time quasi-crystal phase in our model, in which the self-organized period and the driving period are incommensurate.
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Submitted 15 March, 2023; v1 submitted 23 August, 2022;
originally announced August 2022.
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Observation of a symmetry-protected topological phase in external magnetic fields
Authors:
Zhihuang Luo,
Wenzhao Zhang,
Xinfang Nie,
Dawei Lu
Abstract:
Topological phases have greatly improved our understanding of modern conception of phases of matter that go beyond the paradigm of symmetry breaking and are not described by local order parameters. Instead, characterization of topological phases requires the robust topological invariants, whereas measuring these global quantities presents an outstanding challenge for experiments, especially in int…
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Topological phases have greatly improved our understanding of modern conception of phases of matter that go beyond the paradigm of symmetry breaking and are not described by local order parameters. Instead, characterization of topological phases requires the robust topological invariants, whereas measuring these global quantities presents an outstanding challenge for experiments, especially in interacting systems. Here we report the real-space observation of a symmetry-protected topological phase with interacting nuclear spins, and probe the interaction-induced transition between two topologically distinct phases, both of which are classified by many-body Chern numbers obtained from the dynamical response to the external magnetic fields. The resulting value of Chern number ($\bar{\mathcal{C}h} = 1.958 \pm 0.070$) demonstrates the robust ground state degeneracy, and also determines the number of nontrivial edge states. Our findings enable direct characterization of topological features of quantum many-body states through gradually decreasing the strength of the introduced external fields.
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Submitted 10 August, 2022; v1 submitted 10 August, 2022;
originally announced August 2022.
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Entangled Photons Enabled Time- and Frequency-Resolved Coherent Raman Spectroscopy in Condensed Phase Molecules
Authors:
Zhedong Zhang,
Tao Peng,
Xiaoyu Nie,
Girish S. Agarwal,
Marlan O. Scully
Abstract:
We develop an ultrafast frequency-resolved Raman spectroscopy with entangled photons for polyatomic molecules in condensed phases, to probe the electronic and vibrational coherences. Using quantum correlation between the photons, the signal shows the capability of both temporal and spectral resolutions that are not accessible by either classical pulses or the fields without entanglement. We develo…
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We develop an ultrafast frequency-resolved Raman spectroscopy with entangled photons for polyatomic molecules in condensed phases, to probe the electronic and vibrational coherences. Using quantum correlation between the photons, the signal shows the capability of both temporal and spectral resolutions that are not accessible by either classical pulses or the fields without entanglement. We develop a microscopic theory for this Raman spectroscopy, revealing the electronic coherence dynamics which often shows a rapid decay within $\sim$50fs. The heterodyne-detected Raman signal is further developed to capture the phases of electronic coherence and emission in real-time domain.
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Submitted 22 June, 2021; v1 submitted 21 June, 2021;
originally announced June 2021.
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Discovery of segmented Fermi surface induced by Cooper pair momentum
Authors:
Zhen Zhu,
Michał Papaj,
Xiao-Ang Nie,
Hao-Ke Xu,
Yi-Sheng Gu,
Xu Yang,
Dandan Guan,
Shiyong Wang,
Yaoyi Li,
Canhua Liu,
Jianlin Luo,
Zhu-An Xu,
Hao Zheng,
Liang Fu,
Jin-Feng Jia
Abstract:
Since the early days of Bardeen-Cooper-Schrieffer theory, it has been predicted that a sufficiently large supercurrent can close the energy gap in a superconductor and creates gapless Bogoliubov quasiparticles through the Doppler shift of quasiparticle energy due to the Cooper pair momentum. In this gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal state F…
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Since the early days of Bardeen-Cooper-Schrieffer theory, it has been predicted that a sufficiently large supercurrent can close the energy gap in a superconductor and creates gapless Bogoliubov quasiparticles through the Doppler shift of quasiparticle energy due to the Cooper pair momentum. In this gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal state Fermi surface, while its remaining part is still gapped. The finite density of states of field-induced quasiparticles, known as the Volovik effect, has been observed in tunneling and specific heat measurements on d- and s-wave superconductors. However, the segmented Fermi surface of a finite-momentum state carrying a supercurrent has never been detected directly. Here we use quasiparticle interference (QPI) technique to image field-controlled Fermi surface of Bi$_2$Te$_3$ thin films proximitized by the superconductor NbSe$_2$. By applying a small in-plane magnetic field, a screening supercurrent is induced which leads to finite-momentum pairing on topological surface states of Bi$_2$Te$_3$. Our measurements and analysis reveal the strong impact of finite Cooper pair momentum on the quasiparticle spectrum, and thus pave the way for STM study of pair density wave and FFLO states in unconventional superconductors.
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Submitted 5 October, 2020;
originally announced October 2020.
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Experimental Detection of the Quantum Phases of a Three-Dimensional Topological Insulator on a Spin Quantum Simulator
Authors:
Tao Xin,
Yishan Li,
Yu-ang Fan,
Xuanran Zhu,
Yingjie Zhang,
Xinfang Nie,
Jun Li,
Qihang Liu,
Dawei Lu
Abstract:
The detection of topological phases of matter becomes a central issue in recent years. Conventionally, the realization of a specific topological phase in condensed matter physics relies on probing the underlying surface band dispersion or quantum transport signature of a real material, which may be imperfect or even absent. On the other hand, quantum simulation offers an alternative approach to di…
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The detection of topological phases of matter becomes a central issue in recent years. Conventionally, the realization of a specific topological phase in condensed matter physics relies on probing the underlying surface band dispersion or quantum transport signature of a real material, which may be imperfect or even absent. On the other hand, quantum simulation offers an alternative approach to directly measure the topological invariant on a universal quantum computer. However, experimentally demonstrating high-dimensional topological phases remains a challenge due to the technical limitations of current experimental platforms. Here, we investigate the three-dimensional topological insulators in the AIII (chiral unitary) symmetry class which yet lack experimental realization. Using the nuclear magnetic resonance system, we experimentally demonstrate their topological properties, where a dynamical quenching approach is adopted and the dynamical bulk-boundary correspondence in the momentum space is observed. As a result, the topological invariants are measured with high precision on the band-inversion surface, exhibiting robustness to the decoherence effect. Our work paves the way towards the quantum simulation of topological phases of matter in higher dimensions and more complex systems through controllable quantum phases transitions.
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Submitted 14 January, 2020;
originally announced January 2020.
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Ultrafast hot carrier dynamics of ZrTe$_5$ from time-resolved optical reflectivity
Authors:
Xiu Zhang,
Hai-Ying Song,
X. C. Nie,
Shi-Bing Liu,
Yang Wang,
Cong-Ying Jiang,
Shi-Zhong Zhao,
Genfu Chen,
Jian-Qiao Meng,
Yu-Xia Duan,
H. Y. Liu
Abstract:
We investigate the hot carrier dynamics of ZrTe$_5$ by ultrafast time-resolved optical reflectivity. Our results reveal a phonon-mediated across-gap recombination, consistent with its temperature-dependent gap nature as observed previously by photoemission. In addition, two distinct relaxations with a kink feature right after initial photoexcitation are well resolved, suggesting the complexity of…
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We investigate the hot carrier dynamics of ZrTe$_5$ by ultrafast time-resolved optical reflectivity. Our results reveal a phonon-mediated across-gap recombination, consistent with its temperature-dependent gap nature as observed previously by photoemission. In addition, two distinct relaxations with a kink feature right after initial photoexcitation are well resolved, suggesting the complexity of electron thermalization process. Our findings indicate that correlated many-body effects play important role for the transient dynamics of ZrTe$_5$.
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Submitted 25 October, 2018;
originally announced October 2018.
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STM and DFT studies of CO2 adsorption on Cu(100)-O surface
Authors:
Steven J. Tjung,
Qiang Zhang,
Jacob J. Repicky,
Simuck F. Yuk,
Xiaowa Nie,
Nancy M. Santagata,
Aravind Asthagiri,
Jay A. Gupta
Abstract:
We characterized CO2 adsorption and diffusion on the missing row reconstructed Cu(100)-O surface using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations with dispersion. We deposited CO2 molecules in situ at 5K, which allowed us to unambiguously identify individual CO2 molecules and their adsorption sites. Based on a comparison of experimental an…
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We characterized CO2 adsorption and diffusion on the missing row reconstructed Cu(100)-O surface using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations with dispersion. We deposited CO2 molecules in situ at 5K, which allowed us to unambiguously identify individual CO2 molecules and their adsorption sites. Based on a comparison of experimental and DFT-generated STM images, we find that the CO2 molecules sit in between the O atoms in the missing row reconstructed Cu(100)-O surface. The CO2 molecules are easily perturbed by the STM tip under typical imaging conditions, suggesting that the molecules are weakly bound to the surface. The calculated adsorption energy, vibrational modes, and diffusion barriers of the CO2 molecules also indicate weak adsorption, in qualitative agreement with the experiments. A comparison of tunneling spectroscopy and DFT-calculated density of states shows that the primary change near the Fermi level is associated with changes to the surface states with negligible contribution from the CO2 molecular states.
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Submitted 7 June, 2018;
originally announced June 2018.
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Photoinduced two-step insulator-metal transition in Ti4O7 by ultrafast time-resolved optical reflectivity
Authors:
X. C. Nie,
Hai-Ying Song,
Xiu Zhang,
Shi-Bing Liu,
Fan Li,
Lili Yue,
Jian-Qiao Meng,
Yu-Xia Duan,
H. Y. Liu
Abstract:
We report on systematic investigation of hot carrier dynamics in Ti4O7 by ultrafast time-resolved optical reflectivity. We find the transient indication for its two-step insulator-metal (I-M) transition, in which two phase transitions occur from long-range order bipolaron low-temperature insulating (LI) phase to disordered bipolaron high-temperature insulating (HI) phase at Tc1 and to free carrier…
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We report on systematic investigation of hot carrier dynamics in Ti4O7 by ultrafast time-resolved optical reflectivity. We find the transient indication for its two-step insulator-metal (I-M) transition, in which two phase transitions occur from long-range order bipolaron low-temperature insulating (LI) phase to disordered bipolaron high-temperature insulating (HI) phase at Tc1 and to free carrier metallic (M) phase at Tc2. Our results reveal that photoexcitation can effectively lower down both Tc1 and Tc2 with pump fluence increasing, allowing a light-control of I-M transition. We address a phase diagram that provides a framework for the photoinduced I-M transition and helps the potential use of Ti4O7 for photoelectric and thermoelectric devices.
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Submitted 17 May, 2018;
originally announced May 2018.
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Study of pseudogap and superconducting quasiparticle dynamics in $\rm{Bi_2Sr_2CaCu_2O_{8+δ}}$ by time-resolved optical reflectivity
Authors:
X. C. Nie,
Hai-Ying Song,
Xiu Zhang,
Shi-Bing Liu,
Yang Wang,
Qiang Gao,
Lin Zhao,
X. J. Zhou,
Jian-Qiao Meng,
Yu-Xia Duan,
H. Y. Liu
Abstract:
The relation between pseudogap (PG) and superconducting (SC) gap, whether PG is a precursor of SC or they coexist or compete, is a long-standing controversy in cuprate high-temperature supercondutors. Here, we report ultrafast time-resolved optical reflectivity investigation of the dynamic densities and relaxations of PG and SC quasiparticles (QPs) in the underdoped $\rm{Bi_2Sr_2CaCu_2O_{8+δ}}$ (…
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The relation between pseudogap (PG) and superconducting (SC) gap, whether PG is a precursor of SC or they coexist or compete, is a long-standing controversy in cuprate high-temperature supercondutors. Here, we report ultrafast time-resolved optical reflectivity investigation of the dynamic densities and relaxations of PG and SC quasiparticles (QPs) in the underdoped $\rm{Bi_2Sr_2CaCu_2O_{8+δ}}$ ($T_c$ = 82 K) single crystals. We find evidence of two distinct PG components in the positive reflectivity changes in the PG state, characterized by relaxation timescales of $τ_{fast}$ $\approx$ 0.2 ps and $τ_{slow}$ $\approx$ 2 ps with abrupt changes in both amplitudes $A_{fast}$ and $A_{slow}$ at the PG-opening temperature $T^*$. The former presents no obvious change at $T_c$ and coexists with the SC QP. The latter's amplitude starts decreasing at the SC phase fluctuation $T_p$ and vanishes at $T_c$ followed by a negative amplitude signifying the emergence of the SC QP, therefore suggesting a competition with superconductivity.
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Submitted 13 February, 2020; v1 submitted 28 March, 2018;
originally announced March 2018.
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Transient transition from free carrier metallic state to exciton insulating state in GaAs by ultrafast photoexcitation
Authors:
X. C. Nie,
H. Y. Liu,
Xiu Zhang,
Peng Gu,
Hai-Ying Song,
Fan Li,
Jian-Qiao Meng,
Yu-Xia Duin,
Shi-Bing Liu
Abstract:
We present systematic studies of the transient dynamics of GaAs by ultrafast time-resolved optical reflectivity. In photo excited non-equilibrium states, we found a sign reverse in transient reflectivity spectra $ΔR/R$ (t $>$ 0), from positive around room temperature to negative at cryogenic temperatures. The former corresponds to a transient free carrier metallic state, while the latter is attrib…
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We present systematic studies of the transient dynamics of GaAs by ultrafast time-resolved optical reflectivity. In photo excited non-equilibrium states, we found a sign reverse in transient reflectivity spectra $ΔR/R$ (t $>$ 0), from positive around room temperature to negative at cryogenic temperatures. The former corresponds to a transient free carrier metallic state, while the latter is attributed to an exciton insulating state, in which the transient electronic properties is mostly dominated by excitons, resulting in a transient metal-insulator transition (MIT). Two transition temperatures (T$_1$ and T$_2$) are well identified by analysing the intensity change of the time-resolved optical spectra. We found that photoexcited MIT starts emerging at T$_1$ as high as $\sim$ 230 K, in terms of a negative dip feature at 0.4 ps, and becomes stabilized below T$_2$ associated with a negative constant after 40 ps in spectra. Our results address a phase diagram that provides a framework for MIT through temperature and photoexcitation, and shed light on the understanding of light-semiconductor interaction and exciton physics.
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Submitted 23 May, 2017;
originally announced May 2017.
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Nano watermill driven by the revolving charge
Authors:
Xiaoyan Zhou,
Jianlong Kou,
Xuechuan Nie,
Fengmin Wu,
Yang Liu,
Hangjun Lu
Abstract:
Using molecular dynamics simulations, we propose a novel nanoscale watermill for unidirectional transport of water molecules through a curved single-walled carbon nanotube (SWNT). In this nanoscale system, a revolving charge is introduced to drive water chain confined inside the SWNT, which is served as nano waterwheel and nano engine. A resonance-like phenomenon is found that the revolving freque…
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Using molecular dynamics simulations, we propose a novel nanoscale watermill for unidirectional transport of water molecules through a curved single-walled carbon nanotube (SWNT). In this nanoscale system, a revolving charge is introduced to drive water chain confined inside the SWNT, which is served as nano waterwheel and nano engine. A resonance-like phenomenon is found that the revolving frequency of the charge plays a key role in pumping water chain. The water flux across the SWNT increases with respect to the revolving frequency of the external charge and reaches the maximum when the frequency is 4 THz. Correspondingly, the number of the hydrogen bonds of water chain inside the SWNT decreases dramatically with the frequency ranging from 4 THz to 25 THz. The mechanism behind the resonant phenomenon has been investigated systematically. Our findings are helpful for designing nanoscale fluidic devices and energy converters.
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Submitted 12 February, 2015;
originally announced February 2015.
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Resolving singular forces in cavity flow: Multiscale modeling from atoms to millimeters
Authors:
Xiaobo Nie,
Mark. O. Robbins,
Shiyi Chen
Abstract:
A multiscale approach for fluid flow is developed that retains an atomistic description in key regions. The method is applied to a classic problem where all scales contribute: The force on a moving wall bounding a fluid-filled cavity. Continuum equations predict an infinite force due to stress singularities. Following the stress over more than six decades in length in systems with characteristic…
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A multiscale approach for fluid flow is developed that retains an atomistic description in key regions. The method is applied to a classic problem where all scales contribute: The force on a moving wall bounding a fluid-filled cavity. Continuum equations predict an infinite force due to stress singularities. Following the stress over more than six decades in length in systems with characteristic scales of millimeters and milliseconds allows us to resolve the singularities and determine the force for the first time. The speedup over pure atomistic calculations is more than fourteen orders of magnitude. We find a universal dependence on the macroscopic Reynolds number, and large atomistic effects that depend on wall velocity and interactions.
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Submitted 9 August, 2005;
originally announced August 2005.
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Dynamics of Freely Cooling Granular Gases
Authors:
Xiaobo Nie,
Eli Ben-Naim,
Shiyi Chen
Abstract:
We study dynamics of freely cooling granular gases in two-dimensions using large-scale molecular dynamics simulations. We find that for dilute systems the typical kinetic energy decays algebraically with time, E(t) ~ t^{-1}, in the long time limit. Asymptotically, velocity statistics are characterized by a universal Gaussian distribution, in contrast with the exponential high-energy tails charac…
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We study dynamics of freely cooling granular gases in two-dimensions using large-scale molecular dynamics simulations. We find that for dilute systems the typical kinetic energy decays algebraically with time, E(t) ~ t^{-1}, in the long time limit. Asymptotically, velocity statistics are characterized by a universal Gaussian distribution, in contrast with the exponential high-energy tails characterizing the early homogeneous regime. We show that in the late clustering regime particles move coherently as typical local velocity fluctuations, Delta v, are small compared with the typical velocity, Delta v/v ~ t^{-1/4}. Furthermore, locally averaged shear modes dominate over acoustic modes. The small thermal velocity fluctuations suggest that the system can be heuristically described by Burgers-like equations.
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Submitted 17 September, 2002;
originally announced September 2002.
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Dynamics of Vibrated Granular Monolayers
Authors:
X. Nie,
E. Ben-Naim,
S. Y. Chen
Abstract:
We study statistical properties of vibrated granular monolayers using molecular dynamics simulations. We show that at high excitation strengths, the system is in a gas state, particle motion is isotropic, and the velocity distributions are Gaussian. As the vibration strength is lowered the system's dimensionality is reduced from three to two. Below a critical excitation strength, a gas-cluster p…
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We study statistical properties of vibrated granular monolayers using molecular dynamics simulations. We show that at high excitation strengths, the system is in a gas state, particle motion is isotropic, and the velocity distributions are Gaussian. As the vibration strength is lowered the system's dimensionality is reduced from three to two. Below a critical excitation strength, a gas-cluster phase occurs, and the velocity distribution becomes bimodal. In this phase, the system consists of clusters of immobile particles arranged in close-packed hexagonal arrays, and gas particles whose energy equals the first excited state of an isolated particle on a vibrated plate.
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Submitted 23 October, 1999;
originally announced October 1999.
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Clustering Kinetics of Granular Media in Three Dimensions
Authors:
Shiyi Chen,
Yuefan Deng,
Xiaobo Nie,
Yuhai Tu
Abstract:
Three-dimensional molecular dynamics simulations of dissipative particles (~ 10^6) are carried out for studying the clustering kinetics of granular media during cooling. The inter-connected high particle density regions are identified, showing tube-like structures. The energy decay rates as functions of the particle density and the restitution coefficient are obtained. It is found that the proba…
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Three-dimensional molecular dynamics simulations of dissipative particles (~ 10^6) are carried out for studying the clustering kinetics of granular media during cooling. The inter-connected high particle density regions are identified, showing tube-like structures. The energy decay rates as functions of the particle density and the restitution coefficient are obtained. It is found that the probability density function of the particle density obeys an exponential distribution at late stages. Both the fluctuation of density and the mean cluster size of the particle density have power law relations against time during the inelastic coalescing process.
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Submitted 21 April, 1998;
originally announced April 1998.