Showing 1–50 of 62 results for author: Qian, J

The evolution of pairing correlation with $3d_{z^{2}}$ electron filling in a bilayer two-orbital model for La$_3$Ni$_2$O$_7$

Authors: Y. F. Chen, Y. Shen, X. J. Qian, G. M. Zhang, M. P. Qin

Abstract: The discovery of high-${T_c}$ superconductivity in pressurized bilayer nickelate La$_3$Ni$_2$O$_7$ presents a new arena for exploring unconventional pairing mechanisms. A pivotal yet unresolved issue is the specific role of the $3d_{z^{2}}$ orbital of Ni. While its inter-layer super-exchange antiferromagnetic coupling is widely considered crucial for superconductivity, the role of its itinerancy r… ▽ More The discovery of high-${T_c}$ superconductivity in pressurized bilayer nickelate La$_3$Ni$_2$O$_7$ presents a new arena for exploring unconventional pairing mechanisms. A pivotal yet unresolved issue is the specific role of the $3d_{z^{2}}$ orbital of Ni. While its inter-layer super-exchange antiferromagnetic coupling is widely considered crucial for superconductivity, the role of its itinerancy remains undetermined. Early studies showed that the superconductivity is accompanied by the emergence of a small Fermi pocket of the $3d_{z^{2}}$ orbitals. However, recent experiments show controversial results on the role of the $3d_{z^{2}}$ Fermi pocket on superconductivity. Motivated by these experimental results, we investigate an effective bilayer two-orbital model for La$_3$Ni$_2$O$_7$ using density-matrix renormalization group (DMRG) on a minimal one-dimensional geometry. By systematically varying the $3d_{z^{2}}$ orbital filling from $1/12$ doping to half-filling, we observe a pronounced suppression of superconducting correlations near half-filling. Our results demonstrate the itinerancy of $3d_{z^{2}}$ orbital is favorable for the pairing in the bilayer two-orbital model for La$_3$Ni$_2$O$_7$. Moreover, we observe that the pairing correlation is enhanced in regions where charge fluctuations are large, suggesting a competition between charge order and superconductivity in the model. △ Less

Submitted 25 May, 2026; originally announced May 2026.

Comments: 10 pages, 11 figures

Altermagnets Enable Gate-Switchable Helical and Chiral Topological Transport with Spin-Valley-Momentum-Locked Dual Protection

Authors: Xianzhang Chen, Jiayong Zhang, Bowen Hao, Jiahui Qian, Ziye Zhu, Igor Zutic, Zhenyu Zhang, Tong Zhou

Abstract: We establish a unified, symmetry-driven framework that combines the alternating spin splitting of altermagnets with valley topology to realize and electrically interconvert helical and chiral topological phases within a single material platform. We first demonstrate a magnetic analogue of the quantum spin Hall effect in altermagnets, hosting helical spin-valley-momentum-locked (SVML) edge states c… ▽ More We establish a unified, symmetry-driven framework that combines the alternating spin splitting of altermagnets with valley topology to realize and electrically interconvert helical and chiral topological phases within a single material platform. We first demonstrate a magnetic analogue of the quantum spin Hall effect in altermagnets, hosting helical spin-valley-momentum-locked (SVML) edge states characterized by a composite spin-valley Chern number Csv = 2. Large-scale quantum transport simulations show these SVML edge states exhibit fully quantized spin conductance robust against nonmagnetic and long-range magnetic disorder, reflecting their dual topological protection, while remaining vulnerable to short-range magnetic disorder. Exploiting that the counterpropagating SVML modes are linked by crystal rotation symmetry, we introduce a gate-tunable sublattice-staggered potential that selectively gaps one valley and converts the helical state into a chiral quantum anomalous Hall phase with Csv = 1, robust against all disorder types. Reversing the potential switches the transmitted spin-valley polarization. Our first-principles calculations identify monolayer V2STeO and VO families as realistic platforms supporting both helical and chiral topological phases and their electrical switching. These results establish altermagnets as electrically programmable platforms for robust topological devices across charge, spin, and valley. △ Less

Submitted 6 March, 2026; originally announced March 2026.

Comments: 7 pages, 4 figures

Tuneable ion selectivity in vermiculite membranes intercalated with unexchangeable ions

Authors: Zhuang Liu, Yumei Tan, Jianhao Qian, Min Cao, Eli Hoenig, Guowei Yang, Fengchao Wang, Francois M. Peeters, Yi-Chao Zou, Liang-Yin Chu, Marcelo Lozada-Hidalgo

Abstract: Membranes selective to ions of the same charge are increasingly sought for wastewater processing and valuable element recovery. However, while narrow channels are known to be essential, other membrane parameters remain difficult to identify and control. Here we show that Zr$^{4+}$, Sn$^{4+}$, Ir$^{4+}$, and La$^{3+}$ ions intercalated into vermiculite laminate membranes become effectively unexchan… ▽ More Membranes selective to ions of the same charge are increasingly sought for wastewater processing and valuable element recovery. However, while narrow channels are known to be essential, other membrane parameters remain difficult to identify and control. Here we show that Zr$^{4+}$, Sn$^{4+}$, Ir$^{4+}$, and La$^{3+}$ ions intercalated into vermiculite laminate membranes become effectively unexchangeable, creating stable channels, one to two water layers wide, that exhibit robust and tuneable ion selectivity. Ion permeability in these membranes spans five orders of magnitude, following a trend dictated by the ions' Gibbs free energy of hydration. Unexpectedly, different intercalated ions lead to two distinct monovalent ion selectivity sequences, despite producing channels of identical width. The selectivity instead correlates with the membranes' stiffness and the entropy of hydration of the intercalated ions. These results introduce a new ion selectivity mechanism driven by entropic and mechanical effects, beyond classical size and charge exclusion. △ Less

Submitted 4 November, 2025; v1 submitted 27 October, 2025; originally announced October 2025.

Journal ref: Nature Communications 17, 25 (2026)

Unidirectional perfect absorption induced by chiral coupling in spin-momentum locked waveguide magnonics

Authors: Jie Qian, Qi Hong, Zi-Yuan Wang, Wen-Xin Wu, Yihao Yang, C. -M. Hu, J. Q. You, Yi-Pu Wang

Abstract: Chiral coupling opens new avenues for controlling and exploiting light-matter interactions. We demonstrate that chiral coupling can be utilized to achieve unidirectional perfect absorption. In our experiments, chiral magnon-photon coupling is realized by coupling the magnon modes in yttrium iron garnet (YIG) spheres with spin-momentum-locked waveguide modes supported by spoof surface plasmon polar… ▽ More Chiral coupling opens new avenues for controlling and exploiting light-matter interactions. We demonstrate that chiral coupling can be utilized to achieve unidirectional perfect absorption. In our experiments, chiral magnon-photon coupling is realized by coupling the magnon modes in yttrium iron garnet (YIG) spheres with spin-momentum-locked waveguide modes supported by spoof surface plasmon polaritons (SSPPs). These photon modes exhibit transverse spin, with the spin direction determined by the propagation direction. Due to the intrinsic spin properties of the magnon mode, it exclusively couples with microwaves traveling in one direction, effectively suppressing the reflection channel. Under the critical coupling condition, transmission is also eliminated, resulting in unidirectional perfect absorption. By incorporating additional YIG spheres, bidirectional and multi-frequency perfect absorption can be achieved. Our work introduces a novel platform for exploring and harnessing chiral light-matter interactions within spin-momentum locked devices, offering a paradigm for unidirectional signal processing and energy harvesting technologies. △ Less

Submitted 22 July, 2025; originally announced July 2025.

Comments: 9 pages, 4 figures

Unconventional Spin-Orbit Torques from Sputtered MoTe2 Films

Authors: Shuchen Li, Jonathan Gibbons, Stasiu Chyczewski, Zetai Liu, Hsu-Chih Ni, Jiangchao Qian, Jian-Min Zuo, Jun-Fei Zheng, Wenjuan Zhu, Axel Hoffmann

Abstract: Materials with strong spin-orbit coupling and low crystalline symmetry are promising for generating large unconventional spin-orbit torques (SOTs), such as in-plane field-like (FL) torques and out-of-plane damping-like (DL) torques, which can effectively manipulate and deterministically switch an out-of-plane magnetization without the need for additional external in-plane magnetic fields. Here, we… ▽ More Materials with strong spin-orbit coupling and low crystalline symmetry are promising for generating large unconventional spin-orbit torques (SOTs), such as in-plane field-like (FL) torques and out-of-plane damping-like (DL) torques, which can effectively manipulate and deterministically switch an out-of-plane magnetization without the need for additional external in-plane magnetic fields. Here, we report SOTs generated by magnetron-sputtered 1T' MoTe2/Permalloy (Py; Ni80Fe20)/MgO heterostructures using both spin-torque ferromagnetic resonance (ST-FMR) and second harmonic Hall measurements. We observed unconventional FL and DL torques in our samples due to spins polarized normal to the interface of MoTe2 and Py layers, and studied the influence of crystallographic order and MoTe2 layer thickness on the SOTs. By comparing the Raman spectra of 1T' MoTe2 samples prepared in different ways, we found a tensile strain in sputtered MoTe2 films, which might further enhance the generation of unconventional torques by reducing the symmetry of 1T' MoTe2. △ Less

Submitted 8 July, 2024; originally announced July 2024.

Unraveling the origin of antiferromagnetic coupling at YIG/permalloy interface

Authors: Jiangchao Qian, Yi Li, Zhihao Jiang, Robert Busch, Hsu-Chih Ni, Tzu-Hsiang Lo, Axel Hoffmann, André Schleife, Jian-Min Zuo

Abstract: We investigate the structural and electronic origin of antiferromagnetic (AFM) coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in samples prepared with surface ion milling, indicative of antiferromagnetic exchange coupling at the YIG/Py interface. Using atomic resolution scanning transmission… ▽ More We investigate the structural and electronic origin of antiferromagnetic (AFM) coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in samples prepared with surface ion milling, indicative of antiferromagnetic exchange coupling at the YIG/Py interface. Using atomic resolution scanning transmission electron microscopy (STEM), we found that AFM coupling appears at the YIG/Py interface of the tetrahedral YIG surface formed with ion milling. The STEM measurements suggest that the interfacial AFM coupling is predominantly driven by an oxygen-mediated super-exchange coupling mechanism, which is confirmed by the density functional theory (DFT) calculations to be energetically favorable. Thus, the combined experimental and theoretical results reveal the critical role of interfacial atomic structure in determining the type magnetic coupling in a YIG/ferromagnet heterostructure, and prove that the interfacial structure can be experimentally tuned by surface ion-milling. △ Less

Submitted 11 September, 2024; v1 submitted 22 February, 2024; originally announced February 2024.

Tunable Magnon-Photon Coupling by Magnon Band Gap in a Layered Hybrid Perovskite Antiferromagnet

Authors: Yi Li, Timothy Draher, Andrew H. Comstock, Yuzan Xiong, Md Azimul Haque, Elham Easy, Jiang-Chao Qian, Tomas Polakovic, John E. Pearson, Ralu Divan, Jian-Min Zuo, Xian Zhang, Ulrich Welp, Wai-Kwong Kwok, Axel Hoffmann, Joseph M. Luther, Matthew C. Beard, Dali Sun, Wei Zhang, Valentine Novosad

Abstract: Tunability of coherent coupling between fundamental excitations is an important prerequisite for expanding their functionality in hybrid quantum systems. In hybrid magnonics, the dipolar interaction between magnon and photon usually persists and cannot be switched off. Here, we demonstrate this capability by coupling a superconducting resonator to a layered hybrid perovskite antiferromagnet, which… ▽ More Tunability of coherent coupling between fundamental excitations is an important prerequisite for expanding their functionality in hybrid quantum systems. In hybrid magnonics, the dipolar interaction between magnon and photon usually persists and cannot be switched off. Here, we demonstrate this capability by coupling a superconducting resonator to a layered hybrid perovskite antiferromagnet, which exhibits a magnon band gap due to its intrinsic Dzyaloshinskii-Moriya interaction. The pronounced temperature sensitivity of the magnon band gap location allows us to set the photon mode within the gap and to disable magnon-photon hybridization. When the resonator mode falls into the magnon band gap, the resonator damping rate increases due to the nonzero coupling to the detuned magnon mode. This phenomena can be used to quantify the magnon band gap using an analytical model. Our work brings new opportunities in controlling coherent information processing with quantum properties in complex magnetic materials. △ Less

Submitted 26 July, 2023; originally announced July 2023.

Comments: 8 pages, 4 figures

Enhanced Strong Coupling between Spin Ensemble and non-Hermitian Topological Edge States

Authors: Jie Qian, Jie Li, Shi-Yao Zhu, J. Q. You, Yi-Pu Wang

Abstract: Light-matter interaction is crucial to both understanding fundamental phenomena and developing versatile applications. Strong coupling, robustness, and controllability are the three most important aspects in realizing light-matter interactions. Topological and non-Hermitian photonics, have provided frameworks for robustness and extensive control freedom, respectively. How to engineer the propertie… ▽ More Light-matter interaction is crucial to both understanding fundamental phenomena and developing versatile applications. Strong coupling, robustness, and controllability are the three most important aspects in realizing light-matter interactions. Topological and non-Hermitian photonics, have provided frameworks for robustness and extensive control freedom, respectively. How to engineer the properties of the edge state such as photonic density of state, scattering parameters by using non-Hermitian engineering while ensuring topological protection has not been fully studied. Here we construct a parity-time-symmetric dimerized photonic lattice and generate complex-valued edge states via spontaneous PT-symmetry breaking. The enhanced strong coupling between the topological photonic edge mode and magnon mode in a ferromagnetic spin ensemble is demonstrated. Our research reveals the subtle non-Hermitian topological edge states and provides strategies for realizing and engineering topological light-matter interactions. △ Less

Submitted 8 July, 2023; originally announced July 2023.

Comments: 6 pages, 4 figures

Gd-Based Solvated Shells for Defect Passivation of CsPbBr$_3$ Nanoplatelets Enabling Efficient Color-Saturated Blue Electroluminescence

Authors: Haoran Wang, Jingyu Qian, Jiayun Sun, Tong Su, Shiming Lei, Xiaoyu Zhang, Wallace C. H. Choy, Xiao Wei Sun, Kai Wang, Weiwei Zhao

Abstract: Reduced-dimensional CsPbBr$_3$ nanoplatelets (NPLs) are promising candidates for color-saturated blue emitters, yet their electroluminescence performance is hampered by non-radiative recombination, which is associated with bromine vacancies. Here, we show that a post-synthetic treatment of CsPbBr$_3$ NPLs with GdBr$_3$-dimethylformamide (DMF) can effectively eliminate defects while preserving the… ▽ More Reduced-dimensional CsPbBr$_3$ nanoplatelets (NPLs) are promising candidates for color-saturated blue emitters, yet their electroluminescence performance is hampered by non-radiative recombination, which is associated with bromine vacancies. Here, we show that a post-synthetic treatment of CsPbBr$_3$ NPLs with GdBr$_3$-dimethylformamide (DMF) can effectively eliminate defects while preserving the color. According to a combined experimental and theoretical study, Gd$^{3+}$ ions are less reactive with NPLs as a result of compact interaction between them and DMF, and this stable Gd$^{3+}$-DMF solvation structure makes Brions more available and allows them to move more freely. Consequently, defects are rapidly passivated and photoluminescence quantum yield increases dramatically (from 35 to ~100%), while the surface ligand density and emission color remain unchanged. The result is a remarkable electroluminescence efficiency of 2.4% (at 464 nm), one of the highest in pure blue perovskite NPL light-emitting diodes. It is noteworthy that the conductive NPL film shows a high photoluminescence quantum yield of 80%, demonstrating NPLs' significant electroluminescence potential with further device structure design. △ Less

Submitted 23 June, 2023; originally announced June 2023.

Slave spin theory of magnetic states in Hubbard model

Authors: Jiasheng Qian, Zhiguang Liao, Rong Yu

Abstract: Magnetic properties of Hubbard model have been studied extensively. A theoretical description of these states, however, is not straight forward within conventional mean-field approach due to the electron correlation effects. Here we provide a slave spin theory of the magnetic states in the single band Hubbard model. By introducing an additional decomposition of the on-site Coulomb interaction in t… ▽ More Magnetic properties of Hubbard model have been studied extensively. A theoretical description of these states, however, is not straight forward within conventional mean-field approach due to the electron correlation effects. Here we provide a slave spin theory of the magnetic states in the single band Hubbard model. By introducing an additional decomposition of the on-site Coulomb interaction in the magnetic channel in both the slave spin and the fermionic spinon sectors, we show a magnetic solution with renormalized quasiparticle spectral weight can be stabilized at both half-filling and finite doping. By comparing the energies of antiferromagnetic and ferromagnetic states, we provide a ground-state phase diagram for generic electron filling. We further discuss possible generalization of the slave-spin method. △ Less

Submitted 7 May, 2023; originally announced May 2023.

Comments: 7 pages, 4 figures

Integrating Magnons for Quantum Information

Authors: Zhihao Jiang, Jinho Lim, Yi Li, Wolfgang Pfaff, Tzu-Hsiang Lo, Jiangchao Qian, André Schleife, Jian-Min Zuo, Valentine Novosad, Axel Hoffmann

Abstract: Magnons, the quanta of collective spin excitations in magnetically ordered materials, have distinct properties that make them uniquely appealing for quantum information applications. They can have ultra-small wavelengths down to the nanometer scale even at microwave frequencies. They can provide coupling to a diverse set of other quantum excitations, and their inherently gyrotropic dynamics forms… ▽ More Magnons, the quanta of collective spin excitations in magnetically ordered materials, have distinct properties that make them uniquely appealing for quantum information applications. They can have ultra-small wavelengths down to the nanometer scale even at microwave frequencies. They can provide coupling to a diverse set of other quantum excitations, and their inherently gyrotropic dynamics forms the basis for pronounced non-reciprocities. In this article we discuss what the current research challenges are for integrating magnetic materials into quantum information systems and provide a perspective on how to address them. △ Less

Submitted 4 May, 2023; originally announced May 2023.

Kekulé Moiré Superlattices

Authors: Yusen Ye, Jimin Qian, Xiao-Wei Zhang, Chong Wang, Di Xiao, Ting Cao

Abstract: Moiré superlattices from stacks of van der Waals materials offer an exciting arena in the fields of condensed matter physics and materials science. Typically, these moiré superlattices consist of materials with identical or similar structures, and the long moiré period arises from a small twist angle or lattice mismatch. In this article, we discuss that long moiré period appears in a new moiré sys… ▽ More Moiré superlattices from stacks of van der Waals materials offer an exciting arena in the fields of condensed matter physics and materials science. Typically, these moiré superlattices consist of materials with identical or similar structures, and the long moiré period arises from a small twist angle or lattice mismatch. In this article, we discuss that long moiré period appears in a new moiré system by stacking two dissimilar van der Waals layers with large lattice mismatch, resulting in couplings between moiré bands from remote valleys in the momentum space. In this system, the first layer is reconstructed using a $\sqrt{3}$ by $\sqrt{3}$ supercell that resembles the Kekulé distortion in graphene, and such reconstruction becomes nearly commensurate with the second layer. This Kekulé moiré superlattice is realized in heterostructures of transition metal dichalcogenides and metal phosphorus trichalcogenides such as MoTe$_2$/MnPSe$_3$. By first-principles calculations, we demonstrate that the antiferromagnetic MnPSe$_3$ strongly couples the otherwise degenerate Kramers' valleys of MoTe$_2$, resulting in valley pseudospin textures that depend on Néel vector direction, stacking geometry, and external fields. With one hole per moiré supercell, we predict that the system can become a Chern insulator, of which the topology is tunable by external fields. △ Less

Submitted 14 March, 2023; originally announced March 2023.

Universality of the {\bf q}=1/2 Orbital Magnetism in the Pseudogap Phase of the High-$T_c$ superconductor $\rm YBa_{2}Cu_{3}O_{6+x}$

Authors: Dalila Bounoua, Yvan Sidis, Martin Boehm, Paul Steffens, Toshinao Loew, Lin Shan Guo, Jun Qian, Xin Yao, Philippe Bourges

Abstract: Several decades of debate have centered around the nature of the enigmatic pseudo-gap state in high temperature superconducting copper oxides. Recently, we reported polarized neutron diffraction measurements that suggested the existence of a magnetic texture bound to the pseudo-gap phase [Bounoua, {\it et al}. Communications Physics 5, 268 (2022)]. Such a magnetic texture is likely to involve the… ▽ More Several decades of debate have centered around the nature of the enigmatic pseudo-gap state in high temperature superconducting copper oxides. Recently, we reported polarized neutron diffraction measurements that suggested the existence of a magnetic texture bound to the pseudo-gap phase [Bounoua, {\it et al}. Communications Physics 5, 268 (2022)]. Such a magnetic texture is likely to involve the spontaneous appearance of loop currents within the CuO$_2$ unit cells, which give birth to complex correlated patterns. In the underdoped ${\rm YBa_{2}Cu_{3}O_{6.6}}$, the magnetic structure factor of such an orbital magnetic texture gives rise to two distinct magnetic responses at {\bf q}=0 and {\bf q}=1/2. As this pattern alters the lattice translation invariance, such a state of matter could contribute to an instability of the Fermi surface. Here, we report polarized neutron scattering measurements on a nearly optimally doped high quality single crystal of ${\rm YBa_{2}Cu_{3}O_{6.9}}$ that exhibits the same {\bf q}=1/2 magnetism and a weakly overdoped ${\rm YBa_{2}Cu_{3}O_{7}}$ sample where this signal is no longer sizeable. The in-plane and out-of-plane magnetic neutron scattering intensities in ${\rm YBa_{2}Cu_{3}O_{6.9}}$ (at {\bf q}=1/2) and ${\rm YBa_{2}Cu_{3}O_{6.85}}$ (at {\bf q}=0), reported previously, display the same temperature dependent hallmarks. The magnitudes of both {\bf q}=0 and {\bf q}=1/2 magnetic signals further exhibit the same trends upon doping in ${\rm YBa_{2}Cu_{3}O_{6+x}}$, confirming that they are likely intertwined. △ Less

Submitted 26 November, 2023; v1 submitted 3 February, 2023; originally announced February 2023.

Comments: supplemental information + 6 figures

Journal ref: Phys. Rev. B 108, 214408 (2023)

Coexistence of ferromagnetism and superconductivity at KTaO$_3$ heterointerfaces

Authors: Zhongfeng Ning, Jiahui Qian, Yixin Liu, Fan Chen, Mingzhu Zhang, Liwei Deng, Xinli Yuan, Qingqin Ge, Hua Jin, Guanqun Zhang, Wei Peng, Shan Qiao, Gang Mu, Yan Chen, Wei Li

Abstract: The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the experimental observation of two-dimensional long-range ferromagnetic orde… ▽ More The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the experimental observation of two-dimensional long-range ferromagnetic order in the KTaO$_3$ heterointerface superconductor, showing the coexistence of superconductivity and ferromagnetism. Remarkably, our direct current superconducting quantum interference device measurements reveal an in-plane magnetization hysteresis loop persisting above room temperature. Moreover, the first-principles calculations and X-ray magnetic circular dichroism measurements provide decisive insights into the origin of the observed robust ferromagnetism, attributing it to oxygen vacancies that localize electrons in nearby Ta 5$d$ states. Our findings not only suggest KTaO$_3$ heterointerfaces as time-reversal symmetry breaking superconductors, but also inject fresh momentum into the exploration of the intricate interplay between superconductivity and magnetism, enhanced by the strong spin-orbit coupling inherent to the heavy Ta in 5$d$ orbitals of KTaO$_3$ heterointerfaces. △ Less

Submitted 30 May, 2024; v1 submitted 3 February, 2023; originally announced February 2023.

Comments: 9 pages, 5 figures

Journal ref: Nano Letters 24, 7134 (2024)

Imaging Stacking-Dependent Surface Plasmon Polaritons in Trilayer Graphene

Authors: Yilong Luan, Jun Qian, Minsung Kim, Kai-Ming Ho, Yi Shi, Yun Li, Cai-Zhuang Wang, Michael C. Tringides, Zhe Fei

Abstract: We report a nano-infrared (IR) imaging study of trilayer graphene (TLG) with both ABA (Bernal) and ABC (rhombohedral) stacking orders using the scattering-type scanning near-field optical microscope (s-SNOM). With s-SNOM operating in the mid-IR region, we mapped in real space the surface plasmon polaritons (SPPs) of ABA-TLG and ABC-TLG, which are tunable with electrical gating. Through quantitativ… ▽ More We report a nano-infrared (IR) imaging study of trilayer graphene (TLG) with both ABA (Bernal) and ABC (rhombohedral) stacking orders using the scattering-type scanning near-field optical microscope (s-SNOM). With s-SNOM operating in the mid-IR region, we mapped in real space the surface plasmon polaritons (SPPs) of ABA-TLG and ABC-TLG, which are tunable with electrical gating. Through quantitative modeling of the plasmonic imaging data, we found that the plasmon wavelength of ABA-TLG is significantly larger than that of ABC-TLG, resulting in a sizable impedance mismatch and hence a strong plasmon reflection at the ABA/ABC lateral junction. Further analysis indicates that the different plasmonic responses of the two types of TLG are directly linked to their electronic structures and carrier properties. Our work uncovers the physics behind the stacking-dependent plasmonic responses of TLG and sheds light on future applications of TLG and the ABA/ABC junctions in IR plasmonics and planar nano-optics. △ Less

Submitted 26 January, 2023; originally announced January 2023.

Comments: 11 pages

Journal ref: Phys. Rev. Applied 18, 024052 (2022)

The collective motion of self-propelled particles affected by the spatial-dependent noise

Authors: Jia-xin Qian, Yan-qing Lu

Abstract: We study the collective motion of self-propelled particles affected by the spatial-dependent noise based on the Vicsek rules. Only the particles inside the special region will affected by noise. The consideration of the spatial-dependent noise is closer to reality because of the complexity of the environment. Interestingly, we find that there exists an optimal amplitude of noise to adjust the aver… ▽ More We study the collective motion of self-propelled particles affected by the spatial-dependent noise based on the Vicsek rules. Only the particles inside the special region will affected by noise. The consideration of the spatial-dependent noise is closer to reality because of the complexity of the environment. Interestingly, we find that there exists an optimal amplitude of noise to adjust the average motional direction of the system. Particular orientation of the noisy region makes the motional direction of the system parallel to the orientation of the noisy region. The adjustment of the motional direction of the system also depends on the shape, the proportion and the spatial distribution of the noisy region. Our findings may inspire the capture of the key features of collective motion underlying various phenomena. △ Less

Submitted 27 November, 2022; originally announced November 2022.

Comments: 12 pages, 6 figures, 39 references

Antisymmetric Seebeck effect in a tilted Weyl semimetal

Authors: Bingyan Jiang, Jiaji Zhao, Jiangyuan Qian, Shen Zhang, XiaoBin Qiang, Lujunyu Wang, Ran Bi, Juewen Fan, Hai-Zhou Lu, Enke Liu, Xiaosong Wu

Abstract: Tilting the Weyl cone breaks the Lorentz invariance and enriches the Weyl physics. Here, we report the observation of a magnetic-field-antisymmetric Seebeck effect in a tilted Weyl semimetal, Co$_3$Sn$_2$S$_2$. Moreover, it is found that the Seebeck effect and the Nernst effect are antisymmetric in both the in-plane magnetic field and the magnetization. We attribute these exotic effects to the one… ▽ More Tilting the Weyl cone breaks the Lorentz invariance and enriches the Weyl physics. Here, we report the observation of a magnetic-field-antisymmetric Seebeck effect in a tilted Weyl semimetal, Co$_3$Sn$_2$S$_2$. Moreover, it is found that the Seebeck effect and the Nernst effect are antisymmetric in both the in-plane magnetic field and the magnetization. We attribute these exotic effects to the one-dimensional chiral anomaly and phase space correction due to the Berry curvature. The observation is further reproduced by a theoretical calculation, taking into account the orbital magnetization. △ Less

Submitted 31 July, 2022; originally announced August 2022.

Comments: 14 pages, 3 figures

Journal ref: Phys. Rev. Lett. 129, 056601 (2022)

Structural and Magnetic Properties of Pt/Co/Mn-Based Multilayers

Authors: Martin Lonsky, Myoung-Woo Yoo, Yi-Siou Huang, Jiangchao Qian, Jian-Min Zuo, Axel Hoffmann

Abstract: Magnetic multilayers are a rich class of materials systems with numerous highly tunable physical parameters that determine both their magnetic and electronic properties. Here we present a comprehensive experimental study of a novel system, Pt/Co/Mn, which extends the group of Pt/Co/X ($\mathrm{X}=$ metal) multilayers that have been investigated thus far. We demonstrate that an increasing Co layer… ▽ More Magnetic multilayers are a rich class of materials systems with numerous highly tunable physical parameters that determine both their magnetic and electronic properties. Here we present a comprehensive experimental study of a novel system, Pt/Co/Mn, which extends the group of Pt/Co/X ($\mathrm{X}=$ metal) multilayers that have been investigated thus far. We demonstrate that an increasing Co layer thickness changes the magnetic anisotropy from out-of-plane to in-plane, whereas the deposition of thicker Mn layers leads to a decrease in the saturation magnetization. Temperature-dependent magnetometry measurements reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces being responsible for the observed Mn thickness dependence of the magnetization reversal. Moreover, magneto-optical imaging experiments indicate systematic changes in magnetic domain patterns as a function of the Co and Mn layer thickness, suggesting the existence of bubble-like domains -- potentially even magnetic skyrmions -- in the case of sufficiently thick Mn layers, which are expected to contribute to a sizeable Dzyaloshinskii-Moriya interaction in the multilayer stacks. We identify Pt/Co/Mn as a highly complex multilayer system with strong potential for further fundamental studies and possible applications. △ Less

Submitted 20 March, 2022; v1 submitted 18 March, 2022; originally announced March 2022.

Comments: 10 pages, 9 figures

Evolution from helical to collinear ferromagnetic order of the Eu$^{2+}$ spins in RbEu(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$

Authors: Qianhui Xu, Yi Liu, Sijie Hao, Jiahui Qian, Cheng Su, Chin-Wei Wang, Thomas Hansen, Zhendong Fu, Yixi Su, Wei Li, Guang-Han Cao, Yinguo Xiao, Wentao Jin

Abstract: The ground-state magnetic structures of the Eu$^{2+}$ spins in recently discovered RbEu(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$ superconductors have been investigated by neutron powder diffraction measurements. It is found that as the superconductivity gets suppressed with the increase of Ni doping, the magnetic propagation vector of the Eu sublattice diminishes, corresponding to the decrease of the rot… ▽ More The ground-state magnetic structures of the Eu$^{2+}$ spins in recently discovered RbEu(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$ superconductors have been investigated by neutron powder diffraction measurements. It is found that as the superconductivity gets suppressed with the increase of Ni doping, the magnetic propagation vector of the Eu sublattice diminishes, corresponding to the decrease of the rotation angle between the moments in neighboring Eu layers. The ferromagnetic Eu layers are helically modulated along the $\mathit{c}$ axis with an incommensurate magnetic propagation vector in both the ferromagnetic superconductor RbEu(Fe$_{0.95}$Ni$_{0.05}$)$_{4}$As$_{4}$ and the superconducting ferromagnet RbEu(Fe$_{0.93}$Ni$_{0.07}$)$_{4}$As$_{4}$. Such a helical structure transforms into a purely collinear ferromagnetic structure for non-superconducting RbEu(Fe$_{0.91}$Ni$_{0.09}$)$_{4}$As$_{4}$, with all the Eu$^{2+}$ spins lying along the tetragonal (1 1 0) direction. The evolution from helical to collinear ferromagnetic order of the Eu$^{2+}$ spins with increasing Ni doping is supported by first-principles calculations. The variation of the rotation angle between adjacent Eu$^{2+}$ layers can be well explained by considering the change of magnetic exchange couplings mediated by the indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. △ Less

Submitted 16 January, 2022; originally announced January 2022.

Comments: 9 pages, 6 figures, accepted for publication in Physical Review Research

Journal ref: Phys. Rev. Research 4, 013077 (2022)

Observation of magnon cross-Kerr effect in cavity magnonics

Authors: Wei-Jiang Wu, Da Xu, Jie Qian, Jie Li, Yi-Pu Wang, J. Q. You

Abstract: When there is a certain amount of field inhomogeneity, the biased ferrimagnetic crystal will exhibit the higher-order magnetostatic (HMS) mode in addition to the uniform-precession Kittel mode. In cavity magnonics, we show both experimentally and theoretically the cross-Kerr-type interaction between the Kittel mode and HMS mode. When the Kittel mode is driven to generate a certain number of excita… ▽ More When there is a certain amount of field inhomogeneity, the biased ferrimagnetic crystal will exhibit the higher-order magnetostatic (HMS) mode in addition to the uniform-precession Kittel mode. In cavity magnonics, we show both experimentally and theoretically the cross-Kerr-type interaction between the Kittel mode and HMS mode. When the Kittel mode is driven to generate a certain number of excitations, the HMS mode displays a corresponding frequency shift and vice versa. The cross-Kerr effect is caused by an exchange interaction between these two spin-wave modes. Utilizing the cross-Kerr effect, we realize and integrate a multi-mode cavity magnonic system with only one yttrium iron garnet (YIG) sphere. Our results will bring new methods to magnetization dynamics studies and pave a way for novel cavity magnonic devices by including the magnetostatic mode-mode interaction as an operational degree of freedom. △ Less

Submitted 27 December, 2021; originally announced December 2021.

Comments: 9 pages, 5 figures

Z$_2$ nontrivial topology of rare-earth binary oxide superconductor

Authors: Jiahui Qian, Zongqi Shen, Xinyuan Wei, Wei Li

Abstract: Recently, superconductivity has been discovered in rock-salt structured binary lanthanum monoxide LaO through state-of-the-art oxide thin-film epitaxy. In this work, we reveal that the normal state of superconducting LaO is a $Z_2$ nontrivial topological metal, where the Dirac point protected by the crystal symmetry is located around the Fermi energy. By analysing the orbital characteristics, we s… ▽ More Recently, superconductivity has been discovered in rock-salt structured binary lanthanum monoxide LaO through state-of-the-art oxide thin-film epitaxy. In this work, we reveal that the normal state of superconducting LaO is a $Z_2$ nontrivial topological metal, where the Dirac point protected by the crystal symmetry is located around the Fermi energy. By analysing the orbital characteristics, we show that the nature of the topological band structure of LaO originates from the intra-atomic transition from the outer shell La 5$d$ to the inner shell 4$f$ orbitals driven by the strong octahedral crystal-field. Furthermore, the appearance of novel surface states unambiguously demonstrates the topological signature of LaO superconductor. Our theoretical findings not only shed new light into the understanding of the exotic quantum behaviors in LaO superconductor with intimate correlation between 4$f$ and 5$d$ orbitals in La, but also provide an exciting platform to explore the interplay between nontrivial topology and superconductivity. △ Less

Submitted 19 January, 2022; v1 submitted 23 August, 2021; originally announced August 2021.

Comments: 6 pages, 4 figures, 1 table

Journal ref: Phys. Rev. B 105, L020508 (2022)

Self-propelling Microdroplets Generated and Sustained by Liquid-liquid Phase Separation in Confined Spaces

Authors: Xuehua Zhang, Jae Bem You, Gilmar F. Arends, Jiasheng Qian, Yibo Chen, Detlef Lohse, John M. Shaw

Abstract: Flow transport in confined spaces is ubiquitous in technological processes, ranging from separation and purification of pharmaceutical ingredients by microporous membranes and drug delivery in biomedical treatment to chemical and biomass conversion in catalyst-packed reactors and carbon dioxide sequestration. In this work, we suggest a distinct pathway for enhanced liquid transport in a confined s… ▽ More Flow transport in confined spaces is ubiquitous in technological processes, ranging from separation and purification of pharmaceutical ingredients by microporous membranes and drug delivery in biomedical treatment to chemical and biomass conversion in catalyst-packed reactors and carbon dioxide sequestration. In this work, we suggest a distinct pathway for enhanced liquid transport in a confined space via self-propelling microdroplets. These microdroplets can form spontaneously from localized liquid-liquid phase separation as a ternary mixture is diluted by a diffusing poor solvent. High speed images reveal how the microdroplets grow, break up and propel rapidly along the solid surface, with a maximal velocity up to ~160 um/s, in response to a sharp concentration gradient resulting from phase separation. The microdroplet self-propulsion induces a replenishing flow between the walls of the confined space towards the location of phase separation, which in turn drives the mixture out of equilibrium and leads to a repeating cascade of events. Our findings on the complex and rich phenomena of self-propelling droplets suggest an effective approach to enhanced flow motion of multicomponent liquid mixtures within confined spaces for time effective separation and smart transport processes. △ Less

Submitted 28 December, 2020; originally announced December 2020.

Comments: This is the authors' submitted version of the manuscript

Muon Spin Relaxation and fluctuating magnetism in the pseudogap phase of YBa$_{2}$Cu$_{3}$O$_{y}$

Authors: Zihao Zhu, Jian Zhang, Zhaofeng Ding, Cheng Tan, Changsheng Chen, Qiong Wu, Yanxing Yang, Oscar O. Bernal, Pei-Chun Ho, Gerald D. Morris, Akihiro Koda, Adrian D. Hillier, Stephen P. Cottrell, Peter J. Baker, Pabitra K. Biswas, Jun Qian, Xin Yao, Douglas E. MacLaughlin, Lei Shu

Abstract: We report results of a muon spin relaxation study of slow magnetic fluctuations in the pseudogap phase of underdoped single-crystalline YBa$_{2}$Cu$_{3}$O$_{y}$, $y = 6.77$ and 6.83. The dependence of the dynamic muon spin relaxation rate on applied magnetic field yields the rms magnitude~$B\mathrm{_{loc}^{rms}}$ and correlation time~$τ_c$ of fluctuating local fields at muon sites. The observed re… ▽ More We report results of a muon spin relaxation study of slow magnetic fluctuations in the pseudogap phase of underdoped single-crystalline YBa$_{2}$Cu$_{3}$O$_{y}$, $y = 6.77$ and 6.83. The dependence of the dynamic muon spin relaxation rate on applied magnetic field yields the rms magnitude~$B\mathrm{_{loc}^{rms}}$ and correlation time~$τ_c$ of fluctuating local fields at muon sites. The observed relaxation rates do not decrease with decreasing temperature~$T$ below the pseudogap onset at $T^\ast$, as would be expected for a conventional magnetic transition; both $B\mathrm{_{loc}^{rms}}$ and $τ_c$ are roughly constant in the pseudogap phase down to the superconducting transition. Corresponding NMR relaxation rates are estimated to be too small to be observable. Our results put strong constraints on theories of the anomalous pseudogap magnetism in YBa$_{2}$Cu$_{3}$O$_{y}$. △ Less

Submitted 31 July, 2020; originally announced August 2020.

Journal ref: Phys. Rev. B 103, 134426 (2021)

Formaldehyde sensing by Co3O4 hollow spheres at room temperature

Authors: Yang Cao, Jingyu Qian, Yong Yang, Yongguang Tu

Abstract: Formaldehyde is a ubiquitous and high toxicity gas. It is an essential task to efficient detect owing to their toxicity and diffusion. In this work, we studied on the detection of trace amount of formaldehyde based on hollow Co3O4 nanostructure. It is found that Co3O4 hollow spheres with different structures shows distinct sensing performance towards formaldehyde at room temperature, the response… ▽ More Formaldehyde is a ubiquitous and high toxicity gas. It is an essential task to efficient detect owing to their toxicity and diffusion. In this work, we studied on the detection of trace amount of formaldehyde based on hollow Co3O4 nanostructure. It is found that Co3O4 hollow spheres with different structures shows distinct sensing performance towards formaldehyde at room temperature, the response value of nanosheet modified Co3O4 towards 100 ppm formaldehyde will reach 35 in 18 second, and the nanoparticle modified Co3O4 hollow sphere will reach 2.1 in 18 second, 17 in 300 second. The nanosheet modified and nanoparticle modified Co3O4 hollow sphere will reach 4 and 20 in 10 second towards 100 ppm formaldehyde at room temperature. As room temperature, the sensors do not response towards NH3, CO, etc. The sensing mechanism was proposed based on the theoretical and experimental results. The Co3O4 sensor shows that potential utility in CH2O quick sensing at room temperature. △ Less

Submitted 11 February, 2024; v1 submitted 5 June, 2020; originally announced June 2020.

Comments: The work are added for contents of novelty

Strongly confined atomic localization by Rydberg coherent population trapping

Authors: Teodora Kirova, Ning Jia, Seyyed Hossein Asadpour, Jing Qian, Gediminas Juzeliunas, Hamid Reza Hamedi

Abstract: In this letter we investigate the possibility to attain strongly confined atomic localization using interacting Rydberg atoms in a Coherent Population Trapping (CPT) ladder configuration, where a standing-wave (SW) is used as a coupling field in the second leg of the ladder. Depending on the degree of compensation of the Rydberg level energy shift induced by the van der Waals (vdW) interaction, by… ▽ More In this letter we investigate the possibility to attain strongly confined atomic localization using interacting Rydberg atoms in a Coherent Population Trapping (CPT) ladder configuration, where a standing-wave (SW) is used as a coupling field in the second leg of the ladder. Depending on the degree of compensation of the Rydberg level energy shift induced by the van der Waals (vdW) interaction, by the coupling field detuning, we distinguish between two antiblockade regimes, i.e. a partial antiblockade (PA) and a full antiblockade (FA). While a periodic pattern of tightly localized regions can be achieved for both regimes, the PA allows much faster converge of spatial confinement yielding a high resolution Rydberg state-selective superlocalization regime for higher-lying Rydberg levels. In comparison, for lower-lying Rydberg levels the PA leads to an anomalous change of spectra linewidth, confirming the importance of using a stable uppermost state to achieve a superlocalization regime. △ Less

Submitted 23 June, 2020; originally announced June 2020.

Comments: 4 pages, 4 figures

Periodically-driven facilitated high-efficiency dissipative entanglement with Rydberg atoms

Authors: Rui Li, Dongmin Yu, Shi-Lei Su, Jing Qian

Abstract: A time-dependent periodical field can be utilized to efficiently modify the Rabi coupling of system, exhibiting nontrivial dynamics. We propose a scheme to show that this feature can be applied for speeding up the formation of dissipative steady entanglement based on Rydberg anti-blockade mechanism in a simplified configuration, fundamentally stemming from a frequency match between the external-fi… ▽ More A time-dependent periodical field can be utilized to efficiently modify the Rabi coupling of system, exhibiting nontrivial dynamics. We propose a scheme to show that this feature can be applied for speeding up the formation of dissipative steady entanglement based on Rydberg anti-blockade mechanism in a simplified configuration, fundamentally stemming from a frequency match between the external-field modulation frequency and the systematic characteristic frequency. In the presence of an optimal modulation frequency that is exactly equal to the central frequency of driving field, it enables a sufficient residence time of the two-excitation Rydberg state for an irreversible spontaneous decay onto the target state, leading to an accelerated high-fidelity steady entanglement ~0.98, with a shorter formation time <400μs. We show that, a global maximal fidelity benefits from a consistence of microwave-field coupling and spontaneous decay strengths, by which the scheme promises a robust insensitivity to the initial population distributions. This simple approach to facilitate the generation of dissipative entangled two-qubit states by using periodic drivings may guide a new experimental direction in Rydberg quantum technology and quantum information. △ Less

Submitted 22 March, 2020; v1 submitted 9 November, 2019; originally announced November 2019.

Comments: 9 pages, 7 figures, accepted by Physical Review A

Journal ref: Phys. Rev. A 101, 042328 (2020)

Deterministic facilitated excitation of the weakly-driven atom in heteronuclear Rydberg atom pairs beyond antiblockade

Authors: Han Wang, Dongmin Yu, Rui Li, Jing Qian

Abstract: Due to the intrinsic strong blockaded interaction shifting the energy level of Rydberg state, the steady Rydberg probability may be substantially restrained to a low level, especially for atoms suffering from weak drivings. We report an exotic excitation facilitation using strong blockaded energy shifting the double excitation state, leading to the weakly-driven atom deterministically excited by a… ▽ More Due to the intrinsic strong blockaded interaction shifting the energy level of Rydberg state, the steady Rydberg probability may be substantially restrained to a low level, especially for atoms suffering from weak drivings. We report an exotic excitation facilitation using strong blockaded energy shifting the double excitation state, leading to the weakly-driven atom deterministically excited by a significantly improved fraction even at far off-resonant regimes. This phenomenon is attributed to the effective induction of a reduced detuning to the weakly-driven atom by optimizing parameters of an auxiliary strongly-driven atom, arising a modified large probability preserved for a broadening range of detunings. The influence from breaking blockade condition on the excitation probability is also discussed. In contrast to previous approaches, our excitation facilitation mechanism does not rely on antiblockade effect to the compensation of Rydberg energy, serving as a fresh way to a deterministic single-atom excitation of the target atom in a pair of heteronuclear Rydberg atoms, where a strong interatomic interaction is required. △ Less

Submitted 31 July, 2019; originally announced July 2019.

Comments: 8 pages, 4 figures, accepted by Journal of the Optical Society of America B

Switchable dynamic Rydberg-dressed excitation via a cascaded double electromagnetically induced transparency

Authors: Yichun Gao, Yinghui Ren, Dongmin Yu, Jing Qian

Abstract: Dynamic control of atomic dressing to the highly-excited Rydberg state in multi-level systems has special appeals owing to the development of flexible and precise measurement. In this study we develop an experimentally-accessible proposal to robustly control the dressing probability via a three-step cascaded excitation with double electromagnetically induced transparency (EIT) technique. The syste… ▽ More Dynamic control of atomic dressing to the highly-excited Rydberg state in multi-level systems has special appeals owing to the development of flexible and precise measurement. In this study we develop an experimentally-accessible proposal to robustly control the dressing probability via a three-step cascaded excitation with double electromagnetically induced transparency (EIT) technique. The system can function as an optical switch where the third addressing laser serving as the control knob can switchably engineer the dressing probability with time. Differing from a conventional two-photon EIT, this novel scheme facilitates the maximal dressing probability determined by a relative strength between two coupling fields, entirely relaxing the absolute values for strong lasers. The collective feature caused by the interactions of a few atoms is also studied leading to an enhanced dressing probability as well as a reduced response time. Our work offers the opportunity to a coherent dynamic control of Rydberg excitation and to realize sizable Rydberg-Rydberg interactions in weakly-driven quantum systems. △ Less

Submitted 13 May, 2019; originally announced May 2019.

Comments: 10 pages, 6 figures

Journal ref: Phys. Rev. A 100, 033823 (2019)

Low-frequency dielectric response of a periodic array of charged spheres in an electrolyte solution: The simple cubic lattice

Authors: Chang-Yu Hou, Jiang Qian, Denise E. Freed

Abstract: We study the low-frequency dielectric response of highly charged spheres arranged in a cubic lattice and immersed in an electrolyte solution. We focus on the influence of the out-of-phase current in the regime where the ionic charge is neutral. We consider the case where the charged spheres have no surface conductance and no frequency-dependent surface capacitance. Hence, the frequency dispersion… ▽ More We study the low-frequency dielectric response of highly charged spheres arranged in a cubic lattice and immersed in an electrolyte solution. We focus on the influence of the out-of-phase current in the regime where the ionic charge is neutral. We consider the case where the charged spheres have no surface conductance and no frequency-dependent surface capacitance. Hence, the frequency dispersion of the dielectric constant is dominated by the effect of neutral currents outside the electric double layer. In the thin double-layer limit, we use Fixman's boundary condition at the outer surface of the double layer to capture interaction between the electric field and the flow of the ions. For periodic conditions, we combine the methods developed by Lord Rayleigh for understanding the electric conduction across rectangularly arranged obstacles and by Korringa, Kohn and Rostoker for the electronic band structure computation. When the charged spheres occupy a very small volume fraction, smaller than one percent, our solution becomes consistent with the Maxwell Garnett mixing formula together with the single-particle polarization response, as expected, because inter-particle interactions become less prominent in the dilute limit. By contrast, the inter-particle interaction greatly alters the dielectric response even when charged spheres occupy only two percent of the volume. We found that the characteristic frequency shifts to a higher value compared to that derived from the single-particle polarization response. At the same time, the low-frequency dielectric enhancement, a signature of charged spheres immersed in an electrolyte, becomes less prominent for the periodic array of charged spheres. Our results imply that the signature of the dielectric response of a system consisting of densely packed charged spheres immersed in an electrolyte can differ drastically from a dilute suspension. △ Less

Submitted 30 November, 2018; originally announced December 2018.

Comments: 15 pages, 4 figures

Journal ref: Phys. Rev. E 99, 032604 (2019)

Anomalous excitation enhancement with Rydberg-dressed atoms

Authors: Xiaoqian Chai, Lu Zhang, Dandan Ma, Luyao Yan, Huihan Bao, Jing Qian

Abstract: We develop the research achievement of recent work [M. Gärttner, et.al., Phys. Rev. Letts. 113, 233002 (2014)], in which an anomalous excitation enhancement is observed in a three-level Rydberg-atom ensemble with many-body coherence. In our novel theoretical analysis, this effect is ascribed to the existence of a quasi-dark state as well as its avoided crossings to nearby Rydberg-dressed states. M… ▽ More We develop the research achievement of recent work [M. Gärttner, et.al., Phys. Rev. Letts. 113, 233002 (2014)], in which an anomalous excitation enhancement is observed in a three-level Rydberg-atom ensemble with many-body coherence. In our novel theoretical analysis, this effect is ascribed to the existence of a quasi-dark state as well as its avoided crossings to nearby Rydberg-dressed states. Moreover, we show that with an appropriate control of the optical detuning to the intermediate state, the enhancement can evoke a direct facilitation to atom-light coupling that even breaks through the conventional $\sqrt{N}$ limit of strong-blockaded ensembles. As a consequence, the intensity of the probe laser for intermediate transition can be reduced considerably, increasing the feasibility of experiments with Rydberg-dressed atoms. △ Less

Submitted 27 October, 2017; originally announced October 2017.

Comments: 8 pages, 6 figures, PRA in press

Robust quantum switch with Rydberg excitations

Authors: Jing Qian

Abstract: We develop an approach to realize a quantum switch for Rydberg excitation in atoms with $Y$-typed level configuration. We find that the steady population on two different Rydberg states can be reversibly exchanged in a controllable way by properly tuning the Rydberg-Rydberg interaction. Moreover, our numerical simulations verify that the switching scheme is robust against spontaneous decay, enviro… ▽ More We develop an approach to realize a quantum switch for Rydberg excitation in atoms with $Y$-typed level configuration. We find that the steady population on two different Rydberg states can be reversibly exchanged in a controllable way by properly tuning the Rydberg-Rydberg interaction. Moreover, our numerical simulations verify that the switching scheme is robust against spontaneous decay, environmental disturbance, as well as the duration of operation on the interaction, and also a high switching efficiency is quite attainable, which makes it have potential applications in quantum information processing and other Rydberg-based quantum technologies. △ Less

Submitted 13 September, 2017; originally announced September 2017.

Comments: Accepted by scientific reports

Deterministic entanglement generation between a pair of atoms on different Rydberg states via chirped adiabatic passage

Authors: Jing Qian, Weiping Zhang

Abstract: We develop a scheme for deterministic generation of an entangled state between two atoms on different Rydberg states via a chirped adiabatic passage, which directly connects the initial ground and target entangled states and also does not request the normally needed blockade effect. The occupancy of intermediate states suffers from a strong reduction via two pulses with proper time-dependent detun… ▽ More We develop a scheme for deterministic generation of an entangled state between two atoms on different Rydberg states via a chirped adiabatic passage, which directly connects the initial ground and target entangled states and also does not request the normally needed blockade effect. The occupancy of intermediate states suffers from a strong reduction via two pulses with proper time-dependent detunings and the electromagnetically induced transparency condition. By solving the analytical expressions of eigenvalues and eigenstates of a two-atom system, we investigate the optimal parameters for guaranteeing the adiabatic condition. We present a detailed study for the effect of pulse duration, changing rate, different Rydberg interactions on the fidelity of the prepared entangled state with experimentally feasible parameters, which reveals a good agreement between the analytic and full numerical results. △ Less

Submitted 14 February, 2017; originally announced February 2017.

Comments: 15 pages, 6 figures, JPB in press

Plasmonic complex fluids of nematiclike and helicoidal self-assemblies of gold nanorods with a negative order parameter

Authors: Qingkun Liu, Bohdan Senyuk, Jianwei Tang, Taewoo Lee, Jun Qian, Sailing He, Ivan I. Smalyukh

Abstract: We describe a soft matter system of self-organized oblate micelles and plasmonic gold nanorods that exhibit a negative orientational order parameter. Because of anisotropic surface anchoring interactions, colloidal gold nanorods tend to align perpendicular to the director describing the average orientation of normals to the discoidal micelles. Helicoidal structures of highly concentrated nanorods… ▽ More We describe a soft matter system of self-organized oblate micelles and plasmonic gold nanorods that exhibit a negative orientational order parameter. Because of anisotropic surface anchoring interactions, colloidal gold nanorods tend to align perpendicular to the director describing the average orientation of normals to the discoidal micelles. Helicoidal structures of highly concentrated nanorods with a negative order parameter are realized by adding a chiral additive and are further controlled by means of confinement and mechanical stress. Polarization-sensitive absorption, scattering, and two-photon luminescence are used to characterize orientations and spatial distributions of nanorods. Self-alignment and effective-medium optical properties of these hybrid inorganic-organic complex fluids match predictions of a simple model based on anisotropic surface anchoring interactions of nanorods with the structured host medium. △ Less

Submitted 27 December, 2016; originally announced December 2016.

Journal ref: Phys. Rev. Lett. 109, 088301 (2012)

Resonance-enhanced collective effect in a triangle arrangement of Rydberg atoms with anisotropic interactions

Authors: Jing Qian

Abstract: We investigate the collective excitation effect in a scheme where three identical Rydberg atoms are arranged in an equilateral triangular lattice. By using a static electric field polarizing the atomic dipoles, the dipole-dipole interactions between two Rydberg atoms are essentially anisotropic and can even disappear in the several special resonance cases. For that fact, we observe collectively en… ▽ More We investigate the collective excitation effect in a scheme where three identical Rydberg atoms are arranged in an equilateral triangular lattice. By using a static electric field polarizing the atomic dipoles, the dipole-dipole interactions between two Rydberg atoms are essentially anisotropic and can even disappear in the several special resonance cases. For that fact, we observe collectively enhanced excitation probability of single Rydberg atom in resonant areas in the case of strong blockade, and that of double or triple Rydberg atoms in the case of partial blockade. To give more evidences for this collective excitation enhancement, we study the two-body quantum correlation between three Rydberg atoms, as well as the dependence of the blockade radius on the length of triangle sides, which present a good agreement with the excitation properties. △ Less

Submitted 7 July, 2016; originally announced July 2016.

Comments: accepted by josab

Dielectric Enhancement from Non-Insulating Particles with Ideally Polarized Interfaces and Zero $ζ$-Potential I: Exact Solution

Authors: Jiang Qian, Pabitra N. Sen

Abstract: We solve exactly the dielectric response of a non-insulating sphere of radius $a$ suspended in symmetric, univalent electrolyte solution, with ideally-polarizable interface but without significant $ζ$-potential. We then use this solution to derive the dielectric response of a dilute random suspension of such spheres, with volume fraction $f\ll1$, within the Maxwell-Garnett Effective Medium Approxi… ▽ More We solve exactly the dielectric response of a non-insulating sphere of radius $a$ suspended in symmetric, univalent electrolyte solution, with ideally-polarizable interface but without significant $ζ$-potential. We then use this solution to derive the dielectric response of a dilute random suspension of such spheres, with volume fraction $f\ll1$, within the Maxwell-Garnett Effective Medium Approximation. Surprisingly, we discover a huge dielectric enhancement in this bare essential model of dielectric responses of solids in electrolyte solution: at low frequency $ωτ_D \ll (λ/a) / (σ_w / σ_s+1/2)$, the real part of the effective dielectric constant of the mixture is $1-(3f/2)+(9f/4)(a/λ)$. Here $σ_{w/s}$ is the conductivity of the electrolyte solution/solids, $λ$ is the Debye screening length in the solution, $τ_D=λ^2/D$ is the standard time scale of diffusion and $D$ is the ion diffusion coefficient. As $λ$ is of the order nm even for dilute electrolyte solution, even for sub-mm spheres and low volume fraction $f=0.05$ the huge geometric factor $a/λ$ implies an over $10^4$-fold enhancement. Furthermore, we show that this enhancement produces a significant low frequency ($ωτ_D\ll1$) phase shift $\tanθ= \mathrm{Re}~ ε(ω) / \mathrm{Im} ~ε(ω)$ in a simple impedance measurement of the mixture, which is usually negligible in pure electrolyte solution. The phase shift has a scale-invariant maximum $\tanθ_{\mathrm{max}}=(9/4)f/(2σ_w/σ_s+1)$ at $ω_{\mathrm{max}}=(2D/λa)/(2σ_w/σ_s+1)$. We provide a physical picture of the enhancement from an accumulation of charges in a thin Externally Induced Double Layer (EIDL) due to the blocking boundary conditions on interfaces. △ Less

Submitted 23 October, 2016; v1 submitted 17 May, 2016; originally announced May 2016.

Comments: 22 pages, 1 figure, replaced mislabeled figure

Nonlinear optomechanics with gain and loss: amplifying higher-order sideband and group delay

Authors: Y. Jiao, H. Lü, J. Qian, Y. Li, H. Jing

Abstract: We study the nonlinear optomechanically-induced transparency (OMIT) with gain and loss. We find that (i) for a single active cavity, significant enhancement can be achieved for the higher-order sidebands, including the transmission rate and the group delay; (ii) for active- passive-coupled cavities, hundreds of microsecond of optical delay or advance are attainable for the nonlinear sideband pulse… ▽ More We study the nonlinear optomechanically-induced transparency (OMIT) with gain and loss. We find that (i) for a single active cavity, significant enhancement can be achieved for the higher-order sidebands, including the transmission rate and the group delay; (ii) for active- passive-coupled cavities, hundreds of microsecond of optical delay or advance are attainable for the nonlinear sideband pulses in the parity-time-symmetric regime. The active higher-order OMIT effects, as firstly revealed here, open up the way to make a low-power optomechaical amplifier, which can amplify both the strength and group delay of not only the probe light but also its higher-order sidebands. △ Less

Submitted 7 August, 2016; v1 submitted 17 February, 2016; originally announced February 2016.

Comments: Final version, accepted by New J. Phys

Journal ref: New J. Phys. 18 (2016) 083034

Dynamical phases in a one-dimensional chain of Heterospecies Rydberg atoms with next-nearest neighbor interactions

Authors: Jing Qian, Lu Zhang, Jingjing Zhai, Weiping Zhang

Abstract: We theoretically investigate the dynamical phase diagram of a one-dimensional chain of laser-excited two-species Rydberg atoms. The existence of a variety of unique dynamical phases in the experimentally-achievable parameter region is predicted under the mean-field approximation, and the change of those phases when the effect of the next-nearest neighbor interaction is included is further discusse… ▽ More We theoretically investigate the dynamical phase diagram of a one-dimensional chain of laser-excited two-species Rydberg atoms. The existence of a variety of unique dynamical phases in the experimentally-achievable parameter region is predicted under the mean-field approximation, and the change of those phases when the effect of the next-nearest neighbor interaction is included is further discussed. In particular we find the competition of the strong Rydberg-Rydberg interactions and the optical excitation imbalance can lead to the presence of complex multiple chaotic phases, which are highly sensitive to the initial Rydberg-state population and the strength of the next-nearest neighbor interactions. △ Less

Submitted 15 November, 2015; originally announced November 2015.

Comments: 8 pages, 6 figures, accepted by Physical Review A

Universal Dielectric Enhancement from Externally Induced Double Layer Without $ζ$-Potential

Authors: Jiang Qian, Pabitra N Sen

Abstract: Motivated by recent experiments showing over $10^4$-fold increase in induced polarization from electrochemically inert, conducting materials in dilute saline solutions, we theoretically demonstrate a new mechanism for dielectric enhancement, in the absence of $ζ-$potentials at interfaces between non-insulating particles and an electrolyte solution. We further show that the magnitude of such enhanc… ▽ More Motivated by recent experiments showing over $10^4$-fold increase in induced polarization from electrochemically inert, conducting materials in dilute saline solutions, we theoretically demonstrate a new mechanism for dielectric enhancement, in the absence of $ζ-$potentials at interfaces between non-insulating particles and an electrolyte solution. We further show that the magnitude of such enhancement obeys universal scaling laws, independent of the particle's electrical properties and valid across particle shapes: for a dilute suspension of identical, but arbitrarily shaped particles of a linear dimension $a$ and volume fraction $f$, as $ω\to0$ the effective real dielectric constant of the mixture is enhanced from that of water by a factor $1+f~(P_r+(a/λ)P_i)$, and the frequency-dependent phase shift of its impedance has a scale-invariant maximum $f\,\mathsfΘ$ if particles are much more conductive than the solution. Here $λ$ is the solution's Debye length and $P_r$, $P_i$, $\mathsfΘ$ are dimensionless numbers determined solely by the particles' shape. Even for a very dilute electrolyte solution (e.g. $10^{-3}$ molar), sub-mm sized particles, at volume fraction $f=0.1$, can give a $10^4$-fold dielectric enhancement, producing an easily observable phase shift maximum in a simple impedance measurement.We also derive frequency cutoffs as conditions for observing these enhancements, showing that insulating particles produce no enhancement without $ζ$-potential.To prove these results for particles of arbitrary shapes, we develop a physical picture where an externally induced double layer (EIDL), in contrast to the Guoy-Chapman double layer on interfaces with significant $ζ$-potentials, dominates the low-frequency dynamics and produces dielectric enhancement. △ Less

Submitted 10 April, 2016; v1 submitted 22 October, 2015; originally announced October 2015.

Comments: 32 pages, no figures, added correction of a typo in the second half of Eq. 10

Efficiency limitation for realizing an atom-molecule adiabatic transfer based on a chainwise system

Authors: Jingjing Zhai, Lu Zhang, Keye Zhang, Jing Qian, Weiping Zhang

Abstract: In a recent work we have developed a robust chainwise atom-molecule adiabatic passage scheme to produce ultracold ground-state molecules via photo-associating free atoms [J. Qian {\it et.al.} Phys. Rev. A 81 013632 (2010)]. With the help of intermediate auxiliary levels, the pump laser intensity requested in the atomic photo-association process can be greatly reduced. In the present work, we exten… ▽ More In a recent work we have developed a robust chainwise atom-molecule adiabatic passage scheme to produce ultracold ground-state molecules via photo-associating free atoms [J. Qian {\it et.al.} Phys. Rev. A 81 013632 (2010)]. With the help of intermediate auxiliary levels, the pump laser intensity requested in the atomic photo-association process can be greatly reduced. In the present work, we extend the scheme to a more generalized (2$n$+1)-level system and investigate the efficiency limitation for it. As the increase of intermediate levels and auxiliary lasers, the atom-molecule adiabatic passage would be gradually closed, leading to a poor transfer efficiency. For the purpose of enhancing the efficiency, we present various optimization approaches to the laser parameters, involving order number $n$, relative strength ratio and absolute strength. We show there can remain a limit on the population transfer efficiency given by a three-level $Λ$ system. In addition, we illustrate the importance of selecting an appropriate number of intermediate levels for maintaining a highly efficient transfer under mild experimental conditions. △ Less

Submitted 27 August, 2015; originally announced August 2015.

Comments: 9 pages, 6 figures, accepted by josab

Cyclotron Dynamics of a Kondo Singlet in a Spin-Orbit-Coupled Alkaline-Earth Atomic Gas

Authors: Bo-Nan Jiang, Hao Lv, Wen-LiWang, Juan Du, Jun Qian, Yu-Zhu Wang

Abstract: We propose a scheme to investigate the interplay between Kondo-exchange interaction and quantum spin Hall effect with ultracold fermionic alkaline-earth atoms trapped in two-dimensional optical lattices using ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling regime, though the loop trajectory of the mobile atom disappears, collective dynamics of an atom pair in two clo… ▽ More We propose a scheme to investigate the interplay between Kondo-exchange interaction and quantum spin Hall effect with ultracold fermionic alkaline-earth atoms trapped in two-dimensional optical lattices using ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling regime, though the loop trajectory of the mobile atom disappears, collective dynamics of an atom pair in two clock states can exhibit an unexpected spin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall effect of the Kondo singlet. We demonstrate that the collective cyclotron dynamics of the spin-zero Kondo singlet is governed by an effective Harper-Hofstadter model in addition to second-order diagonal tunneling. △ Less

Submitted 15 February, 2015; originally announced February 2015.

Journal ref: Phys. Rev. A 90,053631(2014)

Chirped Multi-photon adiabatic passage for a four-level ladder-type Rydberg excitation

Authors: Jing Qian, Jingjing Zhai, Lu Zhang, Weiping Zhang

Abstract: We develop a multi-photon adiabatic passage to realize a highly efficient Rydberg excitation in a four-level ladder-type atomic system. The adiabatic passage is based on the existence of a novel quasi-dark state in the cascade excitation system where the frequencies of the lasers are appropriately chirped with time. We also investigate the influence of the interatomic Rydberg interaction on the pa… ▽ More We develop a multi-photon adiabatic passage to realize a highly efficient Rydberg excitation in a four-level ladder-type atomic system. The adiabatic passage is based on the existence of a novel quasi-dark state in the cascade excitation system where the frequencies of the lasers are appropriately chirped with time. We also investigate the influence of the interatomic Rydberg interaction on the passage and extend its application to the preparation of anti-blockade Rydberg atom pairs in the Rydberg blockade regime. △ Less

Submitted 6 January, 2015; originally announced January 2015.

Comments: 7 pages, 5 figures, to appear in Physical Review A

Interacting heavy fermions in a disordered optical lattice

Authors: Bo-Nan Jiang, Jun Qian, Wen-Li Wang, Juan Du, Yu-Zhu Wang

Abstract: We have theoretically studied the effect of disorder on ultracold alkaline-earth atoms governed by the Kondo lattice model in an optical lattice via simplified double-well model and hybridization mean-field theory. Disorder-induced narrowing and even complete closure of hybridization gap have been predicted and the compressibility of the system has also been investigated for metallic and Kondo ins… ▽ More We have theoretically studied the effect of disorder on ultracold alkaline-earth atoms governed by the Kondo lattice model in an optical lattice via simplified double-well model and hybridization mean-field theory. Disorder-induced narrowing and even complete closure of hybridization gap have been predicted and the compressibility of the system has also been investigated for metallic and Kondo insulator phases in the presence of the disordered potential. To make connection to the experimental situation, we have numerically solved the disordered Kondo lattice model with an external harmonic trap and shown both the melting of Kondo insulator plateau and an compressibility anomaly at low-density. △ Less

Submitted 9 December, 2014; v1 submitted 26 December, 2013; originally announced December 2013.

Journal ref: Eur. Phys. J. D, 68 12 (2014) 361

Exchange bias up to room temperature in the antiferromagnetic bulk hexagonal Mn3Ge

Authors: Jin- Feng Qian, Ajaya K. Nayak, Guido Kreiner, Walter Schnelle, Claudia Felser

Abstract: This work reports an exchange bias (EB) effect up to room temperature in the binary intermetallic bulk compound Mn3.04Ge0.96. The sample annealed at 700 K crystallizes in a tetragonal structure with ferromagnetic ordering, whereas, the sample annealed at 1073 K crystallizes in a hexagonal structure with antiferromagnetic ordering. The hexagonal Mn3.04Ge0.96 sample exhibits an EB of around 70 mT at… ▽ More This work reports an exchange bias (EB) effect up to room temperature in the binary intermetallic bulk compound Mn3.04Ge0.96. The sample annealed at 700 K crystallizes in a tetragonal structure with ferromagnetic ordering, whereas, the sample annealed at 1073 K crystallizes in a hexagonal structure with antiferromagnetic ordering. The hexagonal Mn3.04Ge0.96 sample exhibits an EB of around 70 mT at 2 K that continues with a non-zero value up to room temperature. The exchange anisotropy is proposed to be originating from the exchange interaction between the triangular antiferromagnetic host and the embedded ferrimagnetic like clusters. The ferrimagnetic clusters develop when excess Mn atoms occupy empty Ge sites in the original triangular antiferromagnet structure of Mn3Ge. △ Less

Submitted 13 November, 2013; originally announced November 2013.

Comments: 4 pages, 4 figures

Undercooling growth and magnetic characterization of ferromagnetic shape memory alloy Ni2FeGa single crystals

Authors: Jin-Feng Qian, Hong Guo Zhang, Jing Lan Chen, Wen Hong Wang, Guang Heng Wu

Abstract: Ni2FeGa single crystals have been grown in undercooling conditions provided by a glass-purification method. It has been found that trace amounts of gamma phase embededin the single crystalline matrix preferentially orients in the <100> orientation along the growth direction. This gamma phase generates directional residual stress and results in an anisotropic two-way shape memory effect. Large stra… ▽ More Ni2FeGa single crystals have been grown in undercooling conditions provided by a glass-purification method. It has been found that trace amounts of gamma phase embededin the single crystalline matrix preferentially orients in the <100> orientation along the growth direction. This gamma phase generates directional residual stress and results in an anisotropic two-way shape memory effect. Large strains of -2.5% in the [001] and 1.5% in the [010] directions have been observed. This trace gamma phase also improves the ductility of the material and thus the crystals could be plastically deformed at room temperature in the parent phase. The <110> and <111> orientations in Ni2FeGa alloy were identified as the easy and hard magnetization directions, respectively, in the parent phase by using low field M-T measurements. △ Less

Submitted 12 November, 2013; originally announced November 2013.

Comments: 15 pages, 8 figures, accepted by Journal of Crystal Growth

Laser Theory for Optomechanics: Limit Cycles in the Quantum Regime

Authors: Niels Lörch, Jiang Qian, Aashish Clerk, Florian Marquardt, Klemens Hammerer

Abstract: Optomechanical systems can exhibit self-sustained limit cycles where the quantum state of the mechanical resonator possesses nonclassical characteristics such as a strongly negative Wigner density, as was shown recently in a numerical study by Qian et al. [Physical Review Letters, 109, 253601 (2012)]. Here we derive a Fokker-Planck equation describing mechanical limit cycles in the quantum regime… ▽ More Optomechanical systems can exhibit self-sustained limit cycles where the quantum state of the mechanical resonator possesses nonclassical characteristics such as a strongly negative Wigner density, as was shown recently in a numerical study by Qian et al. [Physical Review Letters, 109, 253601 (2012)]. Here we derive a Fokker-Planck equation describing mechanical limit cycles in the quantum regime which correctly reproduces the numerically observed nonclassical features. The derivation starts from the standard optomechanical master equation, and is based on techniques borrowed from the laser theory due to Haake's and Lewenstein. We compare our analytical model with numerical solutions of the master equation based on Monte-Carlo simulations, and find very good agreement over a wide and so far unexplored regime of system parameters. As one main conclusion, we predict negative Wigner functions to be observable even for surprisingly classical parameters, i.e. outside the single-photon strong coupling regime, for strong cavity drive, and rather large limit cycle amplitudes. The general approach taken here provides a natural starting point for further studies of quantum effects in optomechanics. △ Less

Submitted 10 February, 2014; v1 submitted 4 October, 2013; originally announced October 2013.

Comments: 17 pages, 7 figures

Journal ref: Phys. Rev. X 4, 011015 (2014)

Anisotropic deformation of Rydberg blockade sphere in few-atom systems

Authors: Jing Qian, Xing-Dong Zhao, Lu Zhou, Weiping Zhang

Abstract: Rydberg blockade sphere persists an intriguing picture by which a number of collective many-body effects caused by the strong Rydberg-Rydberg interactions can be clearly understood and profoundly investigated. In the present work, we develop a new definition for the effective two-atom blockade radius and show that the original spherically shaped blockade surface would be deformed when the real num… ▽ More Rydberg blockade sphere persists an intriguing picture by which a number of collective many-body effects caused by the strong Rydberg-Rydberg interactions can be clearly understood and profoundly investigated. In the present work, we develop a new definition for the effective two-atom blockade radius and show that the original spherically shaped blockade surface would be deformed when the real number of atoms increases from two to three. This deformation of blockade sphere reveals spatially anisotropic and shrunken properties which strongly depend on the interatomic distance. In addition, we also study the optimal conditions for the Rydberg antiblockade effect and make predictions for improving the antiblockade efficiency in few-atom systems. △ Less

Submitted 2 September, 2013; originally announced September 2013.

Comments: 7 pages, 3 figures, submitted to Physical Review A

Quantum phases of strongly interacting Rydberg atoms in triangular lattices

Authors: Jing Qian, Lu Zhou, Weiping Zhang

Abstract: We present a theoretical study on the system of laser-driven strongly interacting Rydberg atoms trapped in a two-dimensional triangular lattice, in which the dipole-dipole interactions between Rydberg states result in exotic quantum phases. By using the mean-field theory, we investigate the steady state solutions and analyze their dynamical stabilities. We find that in the strong-interaction limit… ▽ More We present a theoretical study on the system of laser-driven strongly interacting Rydberg atoms trapped in a two-dimensional triangular lattice, in which the dipole-dipole interactions between Rydberg states result in exotic quantum phases. By using the mean-field theory, we investigate the steady state solutions and analyze their dynamical stabilities. We find that in the strong-interaction limit, the dynamics of the system is chaotic and exhibits random oscillations under appropriate laser detunings. Lyapunov exponent criterion is introduced to confirm the existence of this chaotic behavior. In addition, we present a full quantum calculation based on a six-atom model, and find that the system exhibits some bi-antiferromagnetic properties in every triangular cell when the one-photon detuning is exactly resonant or blue-shifted. △ Less

Submitted 28 May, 2013; originally announced May 2013.

Comments: 5 pages, 4 figures

Phase Diagram of Rydberg atoms in a nonequilibrium optical lattice

Authors: Jing Qian, Guangjiong Dong, Lu Zhou, Weiping Zhang

Abstract: We study the quantum nonequilibrium dynamics of ultracold three-level atoms trapped in an optical lattice, which are excited to their Rydberg states via a two-photon excitation with nonnegligible spontaneous emission. Rich quantum phases including uniform phase, antiferromagnetic phase and oscillatory phase are identified. We map out the phase diagram and find these phases can be controlled by adj… ▽ More We study the quantum nonequilibrium dynamics of ultracold three-level atoms trapped in an optical lattice, which are excited to their Rydberg states via a two-photon excitation with nonnegligible spontaneous emission. Rich quantum phases including uniform phase, antiferromagnetic phase and oscillatory phase are identified. We map out the phase diagram and find these phases can be controlled by adjusting the ratio of intensity of the pump light to the control light, and that of two-photon detuning to the Rydberg interaction strength. When the two-photon detuning is blue-shifted and the latter ratio is less than 1, bistability exists among the phases. Actually, this ratio controls the Rydberg-blockade and antiblockade effect, thus the phase transition in this system can be considered as a possible approach to study both effects. △ Less

Submitted 26 June, 2012; originally announced June 2012.

Comments: 5 pages,5 figures

Journal ref: Physical Review A 85 065401(2012)

Criticality and Continuity of Explosive Site Percolation in Random Networks

Authors: J. H. Qian, D. D. Han, Y. G. Ma

Abstract: This Letter studies the critical point as well as the discontinuity of a class of explosive site percolation in Erdös and Rényi (ER) random network. The class of the percolation is implemented by introducing a best-of-m rule. Two major results are found: i). For any specific $m$, the critical percolation point scales with the average degree of the network while its exponent associated with $m$ is… ▽ More This Letter studies the critical point as well as the discontinuity of a class of explosive site percolation in Erdös and Rényi (ER) random network. The class of the percolation is implemented by introducing a best-of-m rule. Two major results are found: i). For any specific $m$, the critical percolation point scales with the average degree of the network while its exponent associated with $m$ is bounded by -1 and $\sim-0.5$. ii). Discontinuous percolation could occur on sparse networks if and only if $m$ approaches infinite. These results not only generalize some conclusions of ordinary percolation but also provide new insights to the network robustness. △ Less

Submitted 3 December, 2012; v1 submitted 1 March, 2012; originally announced March 2012.

Comments: 5 pages, 5 figures

Journal ref: Europhys. Lett. (EPL), 100 (2012) 48006

Observation of Multiphoton-induced Fluorescence from Nano Graphene Oxide and Its Applications in In vitro and In vivo Bioimaging

Authors: Jun Qian, Dan Wang, Li Peng, Wang Xi, Fu-Hong Cai, Zhen-Feng Zhu, Hao He, Ming-Lie Hu, Sailing He

Abstract: In the present paper, we observed both two-photon and three-photon induced distinct photoluminescence from GO nanoparticles under fs laser excitation. Conjugated with PEG molecules, GO nanoparticles exhibited high chemical stability, and could effectively label HeLa cells. Imaged with a two-photon scanning microscope, GO nanoparticles were observed to localize in the mitochondria, endoplasmic reti… ▽ More In the present paper, we observed both two-photon and three-photon induced distinct photoluminescence from GO nanoparticles under fs laser excitation. Conjugated with PEG molecules, GO nanoparticles exhibited high chemical stability, and could effectively label HeLa cells. Imaged with a two-photon scanning microscope, GO nanoparticles were observed to localize in the mitochondria, endoplasmic reticulum, Golgi and lysosome of HeLa cells. Furthermore, GO nanoparticles were micro-injected into the brain of a black mouse, and in vivo two-photon luminescence imaging illustrated that GO nanoparticles located at 300 μm depth in the brain could be clearly distinguished. △ Less

Submitted 9 February, 2012; originally announced February 2012.

Comments: submitted to Angew. Chem. Int. Ed. on Jan 25, 2012