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Lithium Ion Batteries Operated at $-100\,^{\circ}\!$C
Jianli Gai, Jirong Yang, Wei Yang, Quan Li, Xiaodong Wu, and Hong Li
Chin. Phys. Lett.    2023, 40 (8): 086101 .   DOI: 10.1088/0256-307X/40/8/086101
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Enabling lithium-ion batteries (LIBs) to operate in a wider temperature range, e.g., as low or high as possible or capable of both, is an urgent need and shared goal. Here we report, for the first time, a low-temperature electrolyte consisting of traditional ethylene carbonate, methyl acetate, butyronitrile solvents, and 1 M LiPF$_{6}$ salt, attributed to its very low freezing point ($T_{\rm f} = -126.3\,^{\circ}\!$C) and high ion conductivity at extremely low temperatures (0.21 mS/cm at $-100\,^{\circ}\!$C), successfully extends the service temperature of a practical 9.6 Ah LIB down to $-100\,^{\circ}\!$C (49.6% capacity retention compared to that at room temperature), which is the lowest temperature reported for practical cells so far as we know, and is lower than the lowest natural temperature ($-89.2\,^{\circ}\!$C) recorded on earth. Meanwhile, the high-temperature performance of lithium-ion batteries is not affected. The capacity retention is 88.2% and 83.4% after 800 cycles at 25$\,^{\circ}\!$C and 45$\,^{\circ}\!$C, respectively. The progress also makes LIB a proper power supplier for space vehicles in astronautic explorations.
Chiral Dirac Fermion in a Collinear Antiferromagnet
Ao Zhang, Ke Deng, Jieming Sheng, Pengfei Liu, Shiv Kumar, Kenya Shimada, Zhicheng Jiang, Zhengtai Liu, Dawei Shen, Jiayu Li, Jun Ren, Le Wang, Liang Zhou, Yoshihisa Ishikawa, Takashi Ohhara, Qiang Zhang, Garry McIntyre, Dehong Yu, Enke Liu, Liusuo Wu, Chaoyu Chen, and Qihang Liu
Chin. Phys. Lett.    2023, 40 (12): 126101 .   DOI: 10.1088/0256-307X/40/12/126101
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In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral “Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden $SU(2)$ symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb$_{3}$S$_{6}$. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions. Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb$_{3}$S$_{6}$, paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.
Magnetic-Field-Induced Sign Changes of Thermal Expansion in DyCrO$_{4}$
Jin-Cheng He, Zhao Pan, Dan Su, Xu-Dong Shen, Jie Zhang, Da-Biao Lu, Hao-Ting Zhao, Jun-Zhuang Cong, En-Ke Liu, You-Wen Long, and Young Sun
Chin. Phys. Lett.    2023, 40 (6): 066501 .   DOI: 10.1088/0256-307X/40/6/066501
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The anharmonicity of lattice vibration is mainly responsible for the coefficient of thermal expansion (CTE) of materials. External stimuli, such as magnetic and electric fields, thus cannot effectively change the CTE, much less the sign variation from positive to negative or vice versa. In this study, we report significant magnetic field effects on the CTE of zircon- and scheelite-type DyCrO$_{4}$ prepared at ambient and high pressures, respectively. At zero field, the zircon-type DyCrO$_{4}$ exhibits a negative CTE below the ferromagnetic-order temperature of 23 K. With increasing field up to $\ge $1.0 T, however, the sign of the CTE changes from negative to positive. In the scheelite phase, magnetic field can change the initially positive CTE to be negative with a field up to 2.0 T, and then a reentrant positive CTE is induced by enhanced fields $\ge $3.5 T. Both zircon and scheelite phases exhibit considerable magnetostrictive effects with the absolute values as high as $\sim$ $800$ ppm at 2 K and 10 T. The strong spin–lattice coupling is discussed to understand the unprecedented sign changes of the CTE caused by applying magnetic fields. The current DyCrO$_{4}$ provides the first example of field-induced sign change of thermal expansion, opening up a way to readily control the thermal expansion beyond the conventional chemical substitution.
Hydrodynamics of a Multi-Component Bosonic Superfluid
Fan Zhang and Lan Yin
Chin. Phys. Lett.    2023, 40 (6): 066701 .   DOI: 10.1088/0256-307X/40/6/066701
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We obtain the superfluid hydrodynamic equations of a multi-component Bose gas with short-ranged interactions at zero temperature under the local equilibrium assumption and show that the quantum pressure is generally present in the nonuniform case. Our approach can be extended to systems with long-range interactions such as dipole-dipole interactions by treating the Hartree energy properly. For a highly symmetric superfluid, we obtain the excitation spectrum and show that except for the density phonon, all other excitations are all degenerate. The implication of our results is discussed.
High-Temperature Superconductivity in Doped Boron Clathrates
Liang Ma, Lingrui Wang, Yifang Yuan, Haizhong Guo, and Hongbo Wang
Chin. Phys. Lett.    2023, 40 (8): 086201 .   DOI: 10.1088/0256-307X/40/8/086201
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The recent discoveries of near-room-temperature superconductivity in clathrate hydrides present compelling evidence for the reliability of theory-orientated conventional superconductivity. Nevertheless, the harsh pressure conditions required to maintain such high $T_{\rm c}$ limit their practical applications. To address this challenge, we conducted extensive first-principles calculations to investigate the doping effect of the recently synthesized LaB$_{8}$ clathrate, intending to design high-temperature superconductors at ambient pressure. Our results demonstrate that these clathrates are highly promising for high-temperature superconductivity owing to the coexistence of rigid boron covalent networks and the tunable density of states at the Fermi level. Remarkably, the predicted $T_{\rm c}$ of BaB$_{8}$ could reach 62 K at ambient pressure, suggesting a significant improvement over the calculated $T_{\rm c}$ of 14 K in LaB$_{8}$. Moreover, further calculations of the formation enthalpies suggest that BaB$_{8}$ could be potentially synthesized under high-temperature and high-pressure conditions. These findings highlight the potential of doped boron clathrates as promising superconductors and provide valuable insights into the design of light-element clathrate superconductors.
Realization of $^{87}$Rb Bose–Einstein Condensates in Higher Bands of a Hexagonal Boron-Nitride Optical Lattice
Jin-Yu Liu, Xiao-Qiong Wang, and Zhi-Fang Xu
Chin. Phys. Lett.    2023, 40 (8): 086701 .   DOI: 10.1088/0256-307X/40/8/086701
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Ultracold neutral atoms in higher bands of an optical lattice provide a natural avenue to emulate orbital physics in solid state materials. Here, we report the realization of $^{87}$Rb Bose–Einstein condensates in the fourth and seventh Bloch bands of a hexagonal boron-nitride optical lattice, exhibiting remarkably long coherence time through active cooling. Using band mapping spectroscopy, we observe that atoms condensed at the energy minimum of $\varGamma$ point ($K_{1}$ and $K_{2}$ points) in the fourth (seventh) band as sharp Bragg peaks. The lifetime for the condensate in the fourth (seventh) band is about 57.6 (4.8) ms, and the phase coherence of atoms in the fourth band persists for a long time larger than 110 ms. Our work thus offers great promise for studying unconventional bosonic superfluidity of neutral atoms in higher bands of optical lattices.
Synthesis of Chemically Sharp Interface in NdNiO$_{3}$/SrTiO$_{3}$ Heterostructures
Yueying Li, Xiangbin Cai, Wenjie Sun, Jiangfeng Yang, Wei Guo, Zhengbin Gu, Ye Zhu, and Yuefeng Nie
Chin. Phys. Lett.    2023, 40 (7): 076801 .   DOI: 10.1088/0256-307X/40/7/076801
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The nickel-based superconductivity provides a fascinating new platform to explore high-$T_{\rm c}$ superconductivity. As the infinite-layer nickelates are obtained by removing the apical oxygens from the precursor perovskite phase, the crystalline quality of the perovskite phase is crucial in synthesizing high quality superconducting nickelates. Especially, cation-related defects, such as the Ruddlesden–Popper-type (RP-type) faults, are unlikely to disappear after the topotactic reduction process and should be avoided during the growth of the perovskite phase. Herein, using reactive molecular beam epitaxy, we report the atomic-scale engineering of the interface structure and demonstrate its impact in reducing crystalline defects in Nd-based nickelate/SrTiO$_{3}$ heterostructures. A simultaneous deposition of stoichiometric Nd and Ni directly on SrTiO$_{3}$ substrates results in prominent Nd vacancies and Ti diffusion at the interface and RP-type defects in nickelate films. In contrast, inserting an extra [NdO] monolayer before the simultaneous deposition of Nd and Ni forms a sharp interface and greatly eliminates RP-type defects in nickelate films. A possible explanation related to the polar discontinuity is also discussed. Our results provide an effective method to synthesize high-quality precursor perovskite phase for the investigation of the novel superconductivity in nickelates.
Phonon Focusing Effect in an Atomic Level Triangular Structure
Jian-Hui Jiang, Shuang Lu, and Jie Chen
Chin. Phys. Lett.    2023, 40 (9): 096301 .   DOI: 10.1088/0256-307X/40/9/096301
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The rise of artificial microstructures has made it possible to modulate propagation of various kinds of waves, such as light, sound and heat. Among them, the focusing effect is a modulation function of particular interest. We propose an atomic level triangular structure to realize the phonon focusing effect in single-layer graphene. In the positive incident direction, our phonon wave packet simulation results confirm that multiple features related to the phonon focusing effect can be controlled by adjusting the height of the triangular structure. More interestingly, a completed different focusing pattern and an enhanced energy transmission coefficient are found in the reverse incident direction. The detailed mode conversion physics is discussed based on the Fourier transform analysis on the spatial distribution of the phonon wave packet. Our study provides physical insights to achieving phonon focusing effect by designing atomic level microstructures.
Resonant Charge Transport Assisted by the Molecular Vibration in Single-Molecule Junction from Time-Domain ab initio Nonadiabatic Molecular Dynamics Simulations
Yunzhe Tian, Qijing Zheng, and Jin Zhao
Chin. Phys. Lett.    2023, 40 (12): 126301 .   DOI: 10.1088/0256-307X/40/12/126301
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Using ab initio nonadiabatic molecular dynamics simulation, we study the time-dependent charge transport dynamics in a single-molecule junction formed by gold (Au) electrodes and a single benzene-1,4-dithiol (BDT) molecule. Two different types of charge transport channels are found in the simulation. One is the routine non-resonant charge transfer path, which occurs in several picoseconds. The other is activated when the electronic state of the electrodes and that of the molecule get close in energy, which is referred to as the resonant charge transport. More strikingly, the resonant charge transfer occurs in an ultrafast manner within 100 fs, which notably increases the conductance of the device. Further analysis shows that the resonant charge transport is directly assisted by the $B_{2}$ and $A_{1}$ molecular vibration modes. Our study provides atomic insights into the time-dependent charge transport dynamics in single-molecule junctions, which is important for designing highly efficient single-molecule devices.
Anomalous Thermal Transport across the Superionic Transition in Ice
Rong Qiu, Qiyu Zeng, Han Wang, Dongdong Kang, Xiaoxiang Yu, and Jiayu Dai
Chin. Phys. Lett.    2023, 40 (11): 116301 .   DOI: 10.1088/0256-307X/40/11/116301
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Superionic ices with highly mobile protons within stable oxygen sub-lattices occupy an important proportion of the phase diagram of ice and widely exist in the interior of icy giants and throughout the Universe. Understanding the thermal transport in superionic ice is vital for the thermal evolution of icy planets. However, it is highly challenging due to the extreme thermodynamic conditions and dynamical nature of protons, beyond the capability of the traditional lattice dynamics and empirical potential molecular dynamics approaches. By utilizing the deep potential molecular dynamics approach, we investigate the thermal conductivity of ice-VII and superionic ice-VII$''$ along the isobar of $P = 30$ GPa. A non-monotonic trend of thermal conductivity with elevated temperature is observed. Through heat flux decomposition and trajectory-based spectra analysis, we show that the thermally activated proton diffusion in ice-VII and superionic ice-VII$''$ contribute significantly to heat convection, while the broadening in vibrational energy peaks and significant softening of transverse acoustic branches lead to a reduction in heat conduction. The competition between proton diffusion and phonon scattering results in anomalous thermal transport across the superionic transition in ice. This work unravels the important role of proton diffusion in the thermal transport of high-pressure ice. Our approach provides new insights into modeling the thermal transport and atomistic dynamics in superionic materials.
Route to Stabilize Cubic Gauche Polynitrogen to Ambient Conditions via Surface Saturation by Hydrogen
Guo Chen, Caoping Niu, Wenming Xia, Jie Zhang, Zhi Zeng, and Xianlong Wang
Chin. Phys. Lett.    2023, 40 (8): 086102 .   DOI: 10.1088/0256-307X/40/8/086102
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Cubic gauche polynitrogen (cg-N) is an attractive high-energy density material. However, high-pressure synthesized cg-N will decompose at low pressure and cannot exist under ambient conditions. Here, the stabilities of cg-N surfaces with and without saturations at different pressures and temperatures are systematically investigated based on first-principles calculations and molecular dynamics simulations. Pristine surfaces at 0 GPa are very brittle and will decompose at 300 K, especially (110) surface will collapse completely just after structural relaxation, whereas the decompositions of surfaces can be suppressed by applying pressure, indicating that surface instability causes the cg-N decomposition at low pressure. Due to the saturation of dangling bonds and transferring electrons to the surfaces, saturation with H can stabilize surfaces under ambient conditions, while it is impossible for OH saturation to occur solely from obtaining electrons from surfaces. This suggests that polynitrogen is more stable in an acidic environment or when the surface is saturated with less electronegative adsorbates.
Two-Dimensional Thermal Regulation Based on Non-Hermitian Skin Effect
Qiang-Kai-Lai Huang, Yun-Kai Liu, Pei-Chao Cao, Xue-Feng Zhu, and Ying Li
Chin. Phys. Lett.    2023, 40 (10): 106601 .   DOI: 10.1088/0256-307X/40/10/106601
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The non-Hermitian skin effect has been applied in multiple fields. However, there are relatively few models in the field of thermal diffusion that utilize the non-Hermitian skin effect for achieving thermal regulation. Here, we propose two non-Hermitian Su–Schrieffer–Heeger (SSH) models for thermal regulation: one capable of achieving edge states, and the other capable of achieving corner states within the thermal field. By analyzing the energy band structures and the generalized Brillouin zone, we predict the appearance of the non-Hermitian skin effect in these two models. Furthermore, we analyze the time-dependent evolution results and assess the robustness of the models. The results indicate that the localized thermal effects of the models align with our predictions. In a word, this work presents two models based on the non-Hermitian skin effect for regulating the thermal field, injecting vitality into the design of non-Hermitian thermal diffusion systems.
Atomic Valley Filter Effect Induced by an Individual Flower Defect in Graphene
Yu Zhang, Rong Liu, Lili Zhou, Can Zhang, Guoyuan Yang, Yeliang Wang, and Lin He
Chin. Phys. Lett.    2023, 40 (9): 096801 .   DOI: 10.1088/0256-307X/40/9/096801
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Owing to the bipartite nature of honeycomb lattice, the electrons in graphene host valley degree of freedom, which gives rise to a rich set of unique physical phenomena including chiral tunneling, Klein paradox, and quantum Hall ferromagnetism. Atomic defects in graphene can efficiently break the local sublattice symmetry, and hence, have significant effects on the valley-based electronic behaviors. Here we demonstrate that an individual flower defect in graphene has the ability of valley filter at the atomic scale. With the combination of scanning tunneling microscopy and Landau level measurements, we observe two valley-polarized density-of-states peaks near the outside of the flower defects, implying the symmetry breaking of the $K$ and $K'$ valleys in graphene. Moreover, the electrons in the $K$ valley can highly penetrate inside the flower defects. In contrast, the electrons in the $K'$ valley cannot directly penetrate, instead, they should be assisted by the valley switch from the $K'$ to K. Our results demonstrate that an individual flower defect in graphene can be regarded as a nanoscale valley filter, providing insight into the practical valleytronics.
Ambipolar Doping of Monolayer FeSe by Interface Engineering
Fang-Jun Cheng, Yi-Min Zhang, Jia-Qi Fan, Can-Li Song, Xu-Cun Ma, and Qi-Kun Xue
Chin. Phys. Lett.    2023, 40 (8): 086801 .   DOI: 10.1088/0256-307X/40/8/086801
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We report on ambipolar modulation doping of monolayer FeSe epitaxial films grown by molecular beam epitaxy and in situ spectroscopic measurements via a cryogenic scanning tunneling microscopy. It is found that hole doping kills superconductivity in monolayer FeSe films on metallic Ir(001) substrates, whereas electron doping from polycrystalline IrO$_2$/SrTiO$_3$ substrate enhances significantly the superconductivity with an energy gap of 10.3 meV. By exploring substrate-dependent superconductivity, we elucidate the essential impact of substrate work functions on the superconductivity of monolayer FeSe films. Our results therefore offer a valuable reference guide for further enhancement of the transition temperature $T_{\rm c}$ in FeSe-based superconductors by interface engineering.
Regulation of Ionic Bond in Group IIB Transition Metal Iodides
Zhenzhen Xu, Jianfu Li, Yanlei Geng, Zhaobin Zhang, Yang Lv, Chao Zhang, Qinglin Wang, and Xiaoli Wang
Chin. Phys. Lett.    2023, 40 (7): 076201 .   DOI: 10.1088/0256-307X/40/7/076201
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Using a swarm intelligence structure search method combining with first-principles calculations, three new structures of Zn–I and Hg–I compounds are discovered and pressure-composition phase diagrams are determined. An interesting phenomenon is found, that is, the compounds that are stable at 0 GPa in both systems will decompose into their constituent elements under certain pressure, which is contrary to the general intuition that pressure always makes materials more stability and density. A detailed analysis of the decomposition mechanism reveals the increase of formation enthalpy with the increase of pressure due to contributions from both $\Delta U$ and $\Delta [PV]$. Pressure-dependent studies of the $\Delta V$ demonstrate that denser materials tend to be stabilized at higher pressures. Additionally, charge transfer calculations show that external pressure is more effective in regulating the ionic bond of Hg–I, resulting in a lower decomposition pressure for HgI$_{2}$ than for ZnI$_{2}$. These findings have important implications for designs and syntheses of new materials, as they challenge the conventional understanding on how pressure affects stability.
Determination of Thermal Properties of Unsmooth Si Nanowires
Shixian Liu, Alexander A. Barinov, Fei Yin, and Vladimir I. Khvesyuk
Chin. Phys. Lett.    2024, 41 (1): 016301 .   DOI: 10.1088/0256-307X/41/1/016301
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We estimate the thermal properties of unsmooth Si nanowires, considering key factors such as size (diameter), surface texture (roughness) and quantum size effects (phonon states) at different temperatures. For nanowires with a diameter of less than 20 nm, we highlight the importance of quantum size effects in heat capacity calculations, using dispersion relations derived from the modified frequency equation for the elasticity of a rod. The thermal conductivities of nanowires with diameters of 37, 56, and 115 nm are predicted using the Fuchs–Sondheimer model and Soffer's specular parameter. Notably, the roughness parameters are chosen to reflect the technological characteristics of the real surfaces. Our findings reveal that surface texture plays a significant role in thermal conductivity, particularly in the realm of ballistic heat transfer within nanowires. This study provides practical recommendations for developing new thermal management materials.
Profiling Electronic and Phononic Band Structures of Semiconductors at Finite Temperatures: Methods and Applications
Xie Zhang, Jun Kang, and Su-Huai Wei
Chin. Phys. Lett.    2024, 41 (2): 026301 .   DOI: 10.1088/0256-307X/41/2/026301
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Semiconductor devices are often operated at elevated temperatures that are well above zero Kelvin, which is the temperature in most first-principles density functional calculations. Computational approaches to computing and understanding the properties of semiconductors at finite temperatures are thus in critical demand. In this review, we discuss the recent progress in computationally assessing the electronic and phononic band structures of semiconductors at finite temperatures. As an emerging semiconductor with particularly strong temperature-induced renormalization of the electronic and phononic band structures, halide perovskites are used as a representative example to demonstrate how computational advances may help to understand the band structures at elevated temperatures. Finally, we briefly illustrate the remaining computational challenges and outlook promising research directions that may help to guide future research in this field.
Local Rotational Jamming and Multi-Stage Hyperuniformities in an Active Spinner System
Rui Liu, Jianxiao Gong, Mingcheng Yang, and Ke Chen
Chin. Phys. Lett.    2023, 40 (12): 126402 .   DOI: 10.1088/0256-307X/40/12/126402
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An active system consisting of many self-spinning dimers is simulated, and a distinct local rotational jamming transition is observed as the density increases. In the low density regime, the system stays in an absorbing state, in which each dimer rotates independently subject to the applied torque; while in the high density regime, a fraction of the dimers become rotationally jammed into local clusters, and the system exhibits microphase-separation like two-phase morphologies. For high enough densities, the system becomes completely jammed in both rotational and translational degrees of freedom. Such a simple system is found to exhibit rich and multiscale disordered hyperuniformities among the above phases: the absorbing state shows a critical hyperuniformity of the strongest class and subcritically preserves the vanishing density fluctuation scaling up to some length scale; the locally jammed state shows a two-phase hyperuniformity conversely beyond some length scale with respect to the phase cluster sizes; the totally jammed state appears to be a monomer crystal, but intrinsically loses large-scale hyperuniformity. These results are inspiring for designing novel phase-separation and disordered hyperuniform systems through dynamical organization.
Unlocking the Potential of Two-Dimensional Janus Superlattices: Directly Visualizing Phonon Transitions
Yingzhou Liu, Jincheng Yue, Yinong Liu, Lei-Lei Nian, and Shiqian Hu
Chin. Phys. Lett.    2023, 40 (8): 086301 .   DOI: 10.1088/0256-307X/40/8/086301
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Recent research has focused on using Anderson's localization concept to modulate coherent phonon transport by introducing disorder into periodic structures. However, designing and identifying the disorder's strength remain challenging, and visual evidence characterizing phonon localization is lacking. Here, we investigate the effect of disorder on coherent phonon transport in a two-dimensional Janus MoSSe/WSSe superlattice with a defined disorder strength. Using non-equilibrium molecular dynamics, we demonstrate that strong disorder can lead to strong phonon localization, as evidenced by smaller thermal conductivity and significantly different dependence on defect ratio in strongly disordered structures. Furthermore, we propose a novel defect engineering method to determine whether phonon localization occurs. Our work provides a unique platform for modulating coherent phonon transport and presents visual evidence of the phonon transition from localization to nonlocalization. These findings will contribute to development of phonon transport and even phononics, which are essential for thermoelectric and phononic applications.
Phonon Thermal Transport at Interfaces of a Graphene/Vertically Aligned Carbon Nanotubes/Hexagonal Boron Nitride Sandwiched Heterostructure
Menglin Li, Muhammad Asif Shakoori, Ruipeng Wang, and Haipeng Li
Chin. Phys. Lett.    2024, 41 (1): 016302 .   DOI: 10.1088/0256-307X/41/1/016302
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Molecular dynamics simulation is used to calculate the interfacial thermal resistance of a graphene/carbon nanotubes/hexagonal boron nitride (Gr/CNTs/hBN) sandwiched heterostructure, in which vertically aligned carbon nanotube (VACNT) arrays are covalently bonded to graphene and hexagonal boron nitride layers. We find that the interfacial thermal resistance (ITR) of the Gr/VACNT/hBN sandwiched heterostructure is one to two orders of magnitude smaller than the ITR of a Gr/hBN van der Waals heterostructure with the same plane size. It is observed that covalent bonding effectively enhances the phonon coupling between Gr and hBN layers, resulting in an increase in the overlap factor of phonon density of states between Gr and hBN, thus reducing the ITR of Gr and hBN. In addition, the chirality, size (diameter and length), and packing density of sandwich-layer VACNTs have an important influence on the ITR of the heterostructure. Under the same CNT diameter and length, the ITR of the sandwiched heterostructure with armchair-shaped VACNTs is higher than that of the sandwiched heterostructure with zigzag-shaped VACNTs due to the different chemical bonding of chiral CNTs with Gr and hBN. When the armchair-shaped CNT diameter increases or the length decreases, the ITR of the sandwiched heterostructure tends to decrease. Moreover, the increase in the VACNT packing density also leads to a continuous decrease in the ITR of the sandwiched heterostructure, attributed to the extremely high intrinsic thermal conductivity of CNTs and the increase of out-of-plane heat transfer channels. This work may be helpful for understanding the mechanism for ITR in multilayer vertical heterostructures, and provides theoretical guidance for a new strategy to regulate the interlayer thermal resistance of heterostructures by optimizing the design of sandwich layer thermal interface materials.
Self-Oscillated Growth Formation of Standing Ultrathin Nanosheets out of Uniform Ge/Si Superlattice Nanowires
Xin Gan, Junyang An, Junzhuan Wang, Zongguang Liu, Jun Xu, Yi Shi, Kunji Chen, and Linwei Yu
Chin. Phys. Lett.    2023, 40 (6): 066101 .   DOI: 10.1088/0256-307X/40/6/066101
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Self-oscillation is an intriguing and omnipresent phenomenon that governs a broad range of growth dynamics and formation of nanoscale periodic and delicate heterostructures. A self-oscillating growth phenomenon of catalyst droplets, consuming surface-coating a-Si/a-Ge bilayer, is exploited to accomplish a high-frequency alternating growth of ultrathin crystalline Si and Ge (c-Si/c-Ge) nano-slates, with Ge-rich layer thickness of 14–19 nm, embedded within a superlattice nanowire structure, with pre-known position and uniform channel diameter. A subsequent selective etching of the Ge-rich segments leaves a chain of ultrafine standing c-Si nanosheets down to $\sim$ $6$ nm thick, without the use of any expensive high-resolution lithography and growth modulation control. A ternary-phase-competition model has been established to explain the underlying formation mechanism of this nanoscale self-oscillating growth dynamics. It is also suggested that these ultrathin nanosheets could help to produce ultrathin fin-channels for advanced electronics, or provide size-specified trapping sites to capture and position hetero nanoparticle for high-precision labelling or light emission.
A Possible Quantum Spin Liquid Phase in the Kitaev–Hubbard Model
Shaojun Dong, Hao Zhang, Chao Wang, Meng Zhang, Yong-Jian Han, and Lixin He
Chin. Phys. Lett.    2023, 40 (12): 126403 .   DOI: 10.1088/0256-307X/40/12/126403
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The quantum spin liquid (QSL) state of Kitaev-like materials, such as iridium oxides $A_2$IrO$_3$ and $\alpha$-RuCl$_3$, has been explored in depth. The half-filled Kitaev–Hubbard model with bond-dependent hopping terms is used to describe the Kitaev-like materials, which is calculated using the state-of-the-art fermionic projected entangled pair states method. We find a QSL phase near the Mott insulator transition, which has a strong first-order transition to the semi-metal phase with the decrease of Hubbard $U$. We suggest that a promising approach to finding QSL states is by finding iridium oxides that are near the Mott insulator transition.
Tunable Memory and Activity of Quincke Particles in Micellar Fluid
Yang Yang, Meng Fei Zhang, Lailai Zhu, and Tian Hui Zhang
Chin. Phys. Lett.    2023, 40 (12): 126401 .   DOI: 10.1088/0256-307X/40/12/126401
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Memory can remarkably modify the collective behavior of active particles. We show that, in a micellar fluid, Quincke particles driven by a square-wave electric field exhibit a frequency-dependent memory. Upon increasing the frequency, a memory of directions emerges, whereas the activity of particles decreases. As the activity is dominated by interaction, Quincke particles aggregate and form dense clusters, in which the memory of the direction is further enhanced due to the stronger electric interactions. The density-dependent memory and activity result in dynamic heterogeneity in flocking and offer a new opportunity for research of collective motions.
Heteronuclear Magnetisms with Ultracold Spinor Bosonic Gases in Optical Lattices
Yongqiang Li, Chengkun Xing, Ming Gong, Guangcan Guo, and Jianmin Yuan
Chin. Phys. Lett.    2024, 41 (2): 026701 .   DOI: 10.1088/0256-307X/41/2/026701
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Motivated by recent realizations of spin-1 NaRb mixtures in the experiments [Phys. Rev. Lett. 114, 255301 (2015); Phys. Rev. Lett. 128, 223201 (2022)], we investigate heteronuclear magnetism in the Mott-insulating regime. Different from the identical mixtures where the boson statistics only admits even parity states from angular momentum composition, for heteronuclear atoms in principle all angular momentum states are allowed, which can give rise to new magnetic phases. While various magnetic phases can be developed over these degenerate spaces, the concrete symmetry breaking phases depend on not only the degree of degeneracy but also the competitions from many-body interactions. We unveil these rich phases using the bosonic dynamical mean-field theory approach. These phases are characterized by various orders, including spontaneous magnetization order, spin magnitude order, singlet pairing order, and nematic order, which may coexist specially in the regime with odd parity. Finally we address the possible parameter regimes for observing these spin-ordered Mott phases.
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