Showing 1–22 of 22 results for author: Mu, H

Diamond membranes: platform for photonic and opto-mechanical applications

Authors: Hsin-Hui Huang, Gediminas Seniutinas, Haoran Mu, Nguyen Hoai An Le, Eulalia Puig Vilardell, Vijayakumar Anand, Jitraporn Vongsvivut, Tomas Katkus, Meguya Ryu, Junko Morikawa, Saulius Juodkazis

Abstract: Diamond 1 - 10 micrometers thick membranes are platform for photonic, quantum and opto-mechanic devices with applications across UV-IR spectral ranges. IR characterization of diamond gratings in reflection and transmission showed a change of the IR absorbance dichroism between positive and negative when the grating period was 1-2 wavelengths (free space) including inside the region of the intrinsi… ▽ More Diamond 1 - 10 micrometers thick membranes are platform for photonic, quantum and opto-mechanic devices with applications across UV-IR spectral ranges. IR characterization of diamond gratings in reflection and transmission showed a change of the IR absorbance dichroism between positive and negative when the grating period was 1-2 wavelengths (free space) including inside the region of the intrinsic diamond absorbance. Femtosecond laser cutting of micrometers-wide and mm-long structures are demonstrated by steps of carbonization > 0.4 J/cm2/pulse (1030 nm/200 fs) and oxidation of diamond membranes. Light intensity distribution inside form-birefringent diamond structure was modeled for a scaled-down structure and wavelength to reveal characteristic interference patterns for different polarizations. △ Less

Submitted 11 May, 2026; originally announced May 2026.

Comments: 13 pages and 7 figures (main text)

Olivine annealed up to 1500 C: changes traced by polarised IR reflectance and magnetization

Authors: Daniel Smith, Donatas Narbutis, Hsin-Hui Huang, Philipp Zanon, Michael Boschen, Jitraporn Vongsvivut, Dominique Appadoo, Soon Hock Ng, Haoran Mu, Tomas Katkus, Nguyen Hoai An Le, Dan Kapsaskis, Andy I. R. Herries, Vijayakumar Anand, Meguya Ryu, Junko Morikawa, Saulius Juodkazis

Abstract: Spectral analysis at the infrared (IR) spectral range is introduced with assignment of synthetic red-green-blue (RGB) colours defined by adjustable wavelength and bandwidth. The RGB bands were selected at the phase-specific absorbance A or reflectance R bands of olivine and related materials, which can be formed via high temperature annealing (HTA) of natural minerals up to 1500 C. Natural olivine… ▽ More Spectral analysis at the infrared (IR) spectral range is introduced with assignment of synthetic red-green-blue (RGB) colours defined by adjustable wavelength and bandwidth. The RGB bands were selected at the phase-specific absorbance A or reflectance R bands of olivine and related materials, which can be formed via high temperature annealing (HTA) of natural minerals up to 1500 C. Natural olivines were collected from quarry at volcanic site in Mortlake, Victoria, Australia and spectrally characterised during IR-THz spectroscopy beamtime experiments at Australian Synchrotron. Phase changes in HTA natural olivines were traced by correlation of optical IR 4-polarisation spectroscopy, X-ray energy dispersive spectroscopy and magnetisation. After HTA, olivine samples were magnetized via precipitation of Fe-rich oxides. △ Less

Submitted 28 March, 2026; originally announced April 2026.

Comments: 10 pages, 8 figures (main text)

Nanoscale Surface Analysis of High Entropy Alloy

Authors: Hsin-Hui Huang, Meguya Ryu, Yoshiaki Nishijima, Haoran Mu, Mohit Kumar, Nguyen Hoai An Le, Adrian Cernescu, Jitraporn Vongsvivut, Andrew Siao Ming Ang, Lina Grineviciute, Challapalli Subrahmanyam, Junko Morikawa, Saulius Juodkazis

Abstract: Nanoscale surface analysis of 1 micrometer thick high entropy alloys (HEAs) was carried out using nano-IR for hyperspectral imaging and single point spectroscopy in the 700-1700 1/cm spectral range. Nano-IR is based on the detection of scattered light from an oscillating metal coated nano-tip in one of the arms of the Fourier transform infrared spectrometer and has a resolution defined by the tip… ▽ More Nanoscale surface analysis of 1 micrometer thick high entropy alloys (HEAs) was carried out using nano-IR for hyperspectral imaging and single point spectroscopy in the 700-1700 1/cm spectral range. Nano-IR is based on the detection of scattered light from an oscillating metal coated nano-tip in one of the arms of the Fourier transform infrared spectrometer and has a resolution defined by the tip radius of the probe, 20 nm, regardless of the excitation wavelength. HEA CuPdAgPtAu showed an absorption and reflection increase at 900-1100 1/cm band, which is consistent with Drude-Lorenz modeling of permittivity, however, could also signify oxide formation as tested by X-ray photoelectron spectroscopy of CuPdAgPtAu and CrFeCoNiCuMo. Realization of polarization analysis for nano-IR nano-spectroscopy in the plane perpendicular to the sample's surface is discussed and modeled. The currently available modality of surface analysis with the excitation-detection mode of the p-pol. antenna can be extended to full 3D analysis of the orientational dependencies of local absorbance and refractive index. △ Less

Submitted 27 March, 2026; originally announced March 2026.

Comments: 13 pages 7 figures (main text)

High Entropy Alloy under Shock Compression: Optical-Pump X-Ray-Probe

Authors: Hsin Hui Huang, Meguya Ryu, Shuji Kamegaki, Dominyka Stonyte, Tadas Malinauskas, Yoshiaki Nishijima, Rosalie Hocking, Nguyen Hoai An Le, Tomas Katkus, Haoran Mu, Soon Hock Ng, Samuel Pinches, Andrew S. M. Ang, Vygantas Mizeikis, Nadia Zatsepin, Kohei Miyanishi, Toshinori Yabuuchi, Hirotaka Nakamura, Alexis Amouretti, Norimasa Ozaki, Tommaso Vinci, Arturas Vailionis, Eugene G. Gamaly, Damien G. Hicks, Junko Morikawa , et al. (1 additional authors not shown)

Abstract: High entropy alloys (HEAs) are multi-principal-element alloys designed for tailorable mechanical performance and have been attracting significant engineering interest, yet their fundamental behaviour under extreme dynamic conditions, such as shock loading, remains unexplored. Here, we report laser-shock experiments on two different types of 1-micrometers-thick HEA microfilms, CuPdAgPtAu and CrFeCo… ▽ More High entropy alloys (HEAs) are multi-principal-element alloys designed for tailorable mechanical performance and have been attracting significant engineering interest, yet their fundamental behaviour under extreme dynamic conditions, such as shock loading, remains unexplored. Here, we report laser-shock experiments on two different types of 1-micrometers-thick HEA microfilms, CuPdAgPtAu and CrFeCoNiCuMo, on 25-micrometers-thick black-Kapton ablator driven by a high intensity laser pulse (532 nm, 5 ns, 16 J, 0.5-mm diameter focal spot) and probed by an X-ray free electron laser (XFEL) pulse (12 keV, 7 fs). Time-resolved X-ray diffraction (XRD) shows the formation of a transient phase with a lattice compression up to 5.1% of the CuPdAgPtAu HEA along the (111) plane; this transient compressed phase existed for 0.3 ns. The impedance matching Hugoniot analysis estimated a shock pressure of 55 +/- 6 GPa in the HEA film, while Au- and Fe-based equations of state (EoS) modelling predict 80 GPa (0.8 MBar) at the free HEA surface. The free HEA surface reached maximum velocities of ~ 5 km/s as recorded from in situ monitoring with the velocity interferometry system for any reflector (VISAR) imaging. These initial HEA results show the suitability of HEA sample preparation and XFEL-based XRD characterisation under extreme shock loading, and are promising for experimental determination of the EoS of this emerging class of materials (beamtime proposal No.: 2024A8503 for a 6-hour preliminary experiment). △ Less

Submitted 22 March, 2026; originally announced March 2026.

Comments: 15 pages, 9 figures (in the main text)

Multiple quantum spin Hall states and topological current divider in Twisted Bilayer WSe$_2$

Authors: Hao He, Zhao Gong, Shuai Li, Jian-Jun Liu, Hui-Ying Mu, Xing-Tao An

Abstract: It has been demonstrated that topological quantum spin Hall (QSH) state exist in twisted bilayers of transition metal dichalcogenides. However, a comprehensive theoretical characterization of the topological edge states remains a topic of interest and an unresolved issue. Here, the topological transport properties of the twisted WSe$_2$ bilayers are investigated. Beyond the conventional single QSH… ▽ More It has been demonstrated that topological quantum spin Hall (QSH) state exist in twisted bilayers of transition metal dichalcogenides. However, a comprehensive theoretical characterization of the topological edge states remains a topic of interest and an unresolved issue. Here, the topological transport properties of the twisted WSe$_2$ bilayers are investigated. Beyond the conventional single QSH, we identify emergent double and quartuple quantum spin Hall states, hosting two and four pairs of counter-propagating helical edge channels respectively. Furthermore, the charge carriers in these edge states are not localized at edge but rather the high potential point of the moire superlattice boundary, undergoing interlayer transitions and propagating forward continuously. We term these edge states as moire edge states. These edge states can survive in non-magnetic disorder, with the robustness of double QSH states surpassing that of single QSH states. At a twisting angle of 2.45$^\circ$, the transition between the single and double QSH states can be achieved by adjusting the gate on the surface. Based on this, we propose a five-terminal device to as a topological current devider. Our findings provide support for the development of dissipationless spintronics. △ Less

Submitted 7 August, 2025; originally announced August 2025.

Scalable, universal and conformal direct electrodes microprinting for high-performance van der Waals-integrated two-dimensional electronics and flexible applications

Authors: Nan Cui, Tinghe Yun, Bohan Wei, Yang Li, Wenzhi Yu, Denghui Yan, Lianbi Li, Haoran Mu, Weiqiang Chen, Guangyu Zhang, Shenghuang Lin

Abstract: Two-dimensional (2D) materials with extraordinary electrical properties, hold promising for large-scale, flexible electronics. However, their device performance could be hindered due to the excessive defects introduced via traditional electrode integration processes. Transfer printing techniques have been developed for van der Waals contacts integration, while existing techniques encounter limitat… ▽ More Two-dimensional (2D) materials with extraordinary electrical properties, hold promising for large-scale, flexible electronics. However, their device performance could be hindered due to the excessive defects introduced via traditional electrode integration processes. Transfer printing techniques have been developed for van der Waals contacts integration, while existing techniques encounter limitations in achieving conformal electrode transfer and compatibility with flexible devices. Here we introduce a highly conformal microprinting technique utilizing polypropylene carbonate (PPC)/Polyvinyl alcohol (PVA) copolymer, which enables successful transfer of wafer-scale, micropatterned electrodes onto diverse substrates, including those with complex geometries. This technique, implemented with 2D transition metal dichalcogenides (TMDCs), yields 2D field-effect transistors with near-ideal ohmic contacts, and a record-high carrier mobility up to 334 cm2 V-1 s-1 for a WSe2 device. Furthermore, we fabricated transistor arrays on MoS2 thin film, which show uniform device performance. We also present the flexible MoS2 transistors that not only achieve a high electron mobility of up to 111 cm2 V-1 s-1 but also exhibit outstanding mechanical robustness. Our findings represent a significant leap forward in the fabrication of flexible 2D electronics, paving the way for numerous emerging technologies. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Ultrathin Ga$_2$O$_3$ Tunneling Contact for 2D Transition-metal Dichalcogenides Transistor

Authors: Yun Li, Tinghe Yun, Bohan Wei, Haoran Mu, Luojun Du, Nan Cui, Guangyu Zhang, Shenghuang Lin

Abstract: The development of two-dimensional (2D) transition metal dichalcogenides (TMDs) based transistors has been constrained by high contact resistance and inadequate current delivery, primarily stemming from metal-induced gap states and Fermi level pinning. Research into addressing these challenges is essential for the advancing 2D transistors from laboratory experiments to industrial-grade production.… ▽ More The development of two-dimensional (2D) transition metal dichalcogenides (TMDs) based transistors has been constrained by high contact resistance and inadequate current delivery, primarily stemming from metal-induced gap states and Fermi level pinning. Research into addressing these challenges is essential for the advancing 2D transistors from laboratory experiments to industrial-grade production. In this work, we present amorphous Ga$_2$O$_3$ as a novel tunneling contact layer for multilayer WS2-based field-effect transistors (FETs) to enhance electrical performance. The addition of this innovative tunneling layer avoid Schottky barrier forming while finally change into a tunneling barrier with the barrier height to just 3.7 meV, near-ideal ohmic contacts. This approach effectively reduces contact resistance to only 2.38 k$Ω\,μ$m and specific contact resistivity as low as $3 \times 10^{-5}$ $Ω$cm$^2$. A record-high electron mobility of 296 cm$^2$ V$^{-1}$ s$^{-1}$ and ON-OFF ratio over 106 are realized for WS$_2$ transistor at room temperature. Compared to other tunneling materials, ultrathin Ga$_2$O$_3$ layer offers scalability, cost-efficient production and broad substrate compatibility, making it well-suited for seamless integration with industrial wafer-scale electronics. A robust device performance remains highly consistent in a large-scale transistor array fabricated on $1.5\times 1.5$ cm$^2$ chips, with the average mobility closing to 200 cm$^2$ V$^{-1}$ s$^{-1}$. These findings establish a new benchmark for contact performance in 2D transistors and prove the potential of tunneling contact engineering in advancing high-performance, scalable 29 pelectronics with promising applications in quantum computing and communication. △ Less

Submitted 19 February, 2025; originally announced February 2025.

Comments: 29 pages, 5figures

Inverse Design of Nonlinear Mechanics of Bio-inspired Materials Through Interface Engineering and Bayesian Optimization

Authors: Wei Zhang, Mingjian Tang, Haoxuan Mu, Xingzi Yang, Xiaowei Zeng, Rui Tuo, Wei, Chen, Wei Gao

Abstract: In many biological materials such as nacre and bone, the material structure consists of hard grains and soft interfaces, with the interfaces playing a significant role in the material's mechanical behavior. This type of structures has been utilized in the design of various bio-inspired composite materials. Such applications often require the materials to exhibit a specified nonlinear stress-strain… ▽ More In many biological materials such as nacre and bone, the material structure consists of hard grains and soft interfaces, with the interfaces playing a significant role in the material's mechanical behavior. This type of structures has been utilized in the design of various bio-inspired composite materials. Such applications often require the materials to exhibit a specified nonlinear stress-strain relationship. A key challenge lies in identifying appropriate interface properties from an infinite search space to achieve a given target stress-strain curve. This study introduces a Bayesian optimization (BO) framework specifically tailored for the inverse design of interfaces in bio-inspired composites. As a notable advantage, this method is capable of expanding the design space, allowing the discovery of optimal solutions even when the target curve deviates significantly from the initial dataset. Furthermore, our results show that BO can identify distinct interface designs that produce similar target stress-strain responses, yet differ in their deformation and failure mechanisms. These findings highlight the potential of the proposed BO framework to address a wide range of inverse design challenges in nonlinear mechanics problems. △ Less

Submitted 18 December, 2024; originally announced December 2024.

Synergistic Interface Effects in Composite Dielectrics: Insights into Charge Trapping Regulation through Multiscale Modeling

Authors: Haoxiang Zhao, Lixuan An, Daning Zhang, Xiong Yang, Huanmin Yao, Guanjun Zhang, Haibao Mu, Björn Baumeier

Abstract: The rapid development of modern energy applications drives an urgent need to enhance the dielectric strength of energy storage dielectrics for higher power density. Interface design is a promising strategy to regulate the crucial charge transport process determining dielectric strength. However, the targeted exploitation of interface effects on charge transport is limited due to a lack of fundamen… ▽ More The rapid development of modern energy applications drives an urgent need to enhance the dielectric strength of energy storage dielectrics for higher power density. Interface design is a promising strategy to regulate the crucial charge transport process determining dielectric strength. However, the targeted exploitation of interface effects on charge transport is limited due to a lack of fundamental understanding of the underlying mechanisms involving elementary electronic processes and details of the intricate interplay of characteristics of molecular building blocks and the interfacial morphology -- details that cannot fully be resolved with experimental methods. Here we employ a multiscale modeling approach linking the quantum properties of the charge carriers with nano- and mesoscale structural details of complex interfaces. Applied to a prototypical application-proven cellulose-oil composite with interfaces formed between oil, disordered, and crystalline cellulose regions, this approach demonstrates that charges are trapped in the disordered region. Specifically, it unveils this trapping as a synergistic effect of two transport-regulating interface mechanisms: back-transfer to the oil region is suppressed by energetic factors, while forward-transfer to the crystalline cellulose is suppressed by low electronic coupling. The insight into the molecular origins of interface effects via dual-interface regulation offers new development paths for advanced energy materials. △ Less

Submitted 3 November, 2024; originally announced November 2024.

Subharmonic oscillations in the Floquet circuit with the frequency-synthesis dimension

Authors: Bo Lv, Shiyun Xia, Ye Tian, Ting Liu, Hongyang Mu, Zhichao Shen, Sijie Wang, Zheng Zhu, Huibin Tao, Fanyi Meng, Jinhui Shi

Abstract: The period-doubling oscillation emerges with the coexistence between zero and π modes in Floquet topological insulator. Here, utilized the flexibility of the circuit, we construct the Floquet circuit with frequency-synthetic dimension and find the topological-protected deeply-subharmonic oscillations with the period extensively exceeding the doubling-driven period. In the construction framework, t… ▽ More The period-doubling oscillation emerges with the coexistence between zero and π modes in Floquet topological insulator. Here, utilized the flexibility of the circuit, we construct the Floquet circuit with frequency-synthetic dimension and find the topological-protected deeply-subharmonic oscillations with the period extensively exceeding the doubling-driven period. In the construction framework, the periodically-driven mechanism is attained by implementing the circuit-oscillator hierarchy with the stepping-variation resonances in frequency domain. The zero and π modes that arise at the Floquet band in the circuit indicate the anomalous boundary-bulk correspondence. The coexistence of zero and π modes, results in a subharmonic oscillation with the extremely-low frequency on the edge of the Floquet circuit. Furthermore, we explore the Floquet band with the enhanced periodically-driven strength tailored by the component flexibility of the circuit. Our method provides a flexible scheme to study Floquet topological phases, and open a new path for realizing the deeply subwavelength system. △ Less

Submitted 5 August, 2024; v1 submitted 26 June, 2024; originally announced June 2024.

Comments: 31 pages, 10 figures

Layer-dependent transport properties in the Moiré of strained homobilayer transition metal dichalcogenides

Authors: Chao-Jie Ren, Zhao Gong, Hui-Ying Mu, Xing-Tao An, Wang Yao, Jian-Jun Liu

Abstract: Bilayer moiré structures have attracted significant attention recently due to their spatially modulated layer degrees of freedom. However, the layer-dependent transport mechanism in the moiré structures is still a problem to be explored. Here we investigate the layer-dependent transport properties regulated by the strain, the interlayer bias and the number of moiré periods in a strained moiré homo… ▽ More Bilayer moiré structures have attracted significant attention recently due to their spatially modulated layer degrees of freedom. However, the layer-dependent transport mechanism in the moiré structures is still a problem to be explored. Here we investigate the layer-dependent transport properties regulated by the strain, the interlayer bias and the number of moiré periods in a strained moiré homobilayer TMDs nanoribbon based on low-energy efficient models. The charge carriers can pass perfectly through the scattering region with the moiré potential. While, it is noted that the overall transmission coefficient is mainly contributed from either intralayer or interlayer transmissions. The transition of transport mechanism between intralayer and interlayer transmissions can be achieved by adjusting the strain. The intralayer transmissions are suppressed and one of the interlayer transmissions can be selected by a vertical external electric field, which can cause a controllable layer polarization. Moreover, the staggered intralayer and interlayer minigaps are formed as the number of moiré periods increases in the scattering region due to the overlap of the wave functions in two adjacent moiré periods. Our finding points to an opportunity to realize layer functionalities by the strain and electric field. △ Less

Submitted 28 February, 2024; v1 submitted 28 September, 2023; originally announced September 2023.

Comments: 10 pages, 6 figures

Journal ref: Physical Review B109,075424(2024)

Spin-polarized transport properties in magnetic moiré superlattices

Authors: Zhao Gong, Qing-Qing Zhang, Hui-Ying Mu, Xing-Tao An, Jian-Jun Liu

Abstract: Since the discovery of the fascinating properties in magic-angle graphene, the exploration of moiré systems in other two-dimensional materials has garnered significant attention and given rise to a field known as 'moiré physics'. Within this realm, magnetic van der Waals heterostructure and the magnetic proximity effect in moiré superlattices have also become subjects of great interest. However, t… ▽ More Since the discovery of the fascinating properties in magic-angle graphene, the exploration of moiré systems in other two-dimensional materials has garnered significant attention and given rise to a field known as 'moiré physics'. Within this realm, magnetic van der Waals heterostructure and the magnetic proximity effect in moiré superlattices have also become subjects of great interest. However, the spin-polarized transport property in this moiré structures is still a problem to be explored. Here, we investigate the spin-polarized transport properties in a moiré superlattices formed by a two-dimensional ferromagnet CrI_3 stacked on a monolayer BAs, where the spin degeneracy is lifted because of the magnetic proximity effect associated with the moiré superlattices. We find that the conductance exhibits spin-resolved miniband transport properties at a small twist angle because of the periodic moiré superlattices. When the incident energy is in the spin-resolved minigaps, the available states are spin polarized, thus providing a spin-polarized current from the superlattice. Moreover, only a finite number of moiré period is required to obtain a net spin polarization of 100\%. In addition, the interlayer distance of the heterojunction is also moiré modifiable, so a perpendicular electric field can be applied to modulate the intensity and direction of the spin polarization. Our finding points to an opportunity to realize spin functionalities in magnetic moiré superlattices. △ Less

Submitted 14 December, 2023; v1 submitted 28 August, 2023; originally announced August 2023.

Comments: 7 pages, 5 figures

Journal ref: Phys. Rev. B 109, 045301 (2024)

Temperature dependent anisotropy and two-band superconductivity revealed by lower critical field in organic superconductor $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br

Authors: Huijing Mu, Jin Si, Qingui Yang, Ying Xiang, Haipeng Yang, Hai-Hu Wen

Abstract: Resistivity and magnetization have been measured at different temperatures and magnetic fields in organic superconductors $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. The lower critical field and upper critical field are determined, which allow to depict a complete phase diagram. Through the comparison between the upper critical fields with magnetic field perpendicular and parallel to the conducting ac-… ▽ More Resistivity and magnetization have been measured at different temperatures and magnetic fields in organic superconductors $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. The lower critical field and upper critical field are determined, which allow to depict a complete phase diagram. Through the comparison between the upper critical fields with magnetic field perpendicular and parallel to the conducting ac-planes, and the scaling of the in-plane resistivity with field along different directions, we found that the anisotropy $Γ$ is strongly temperature dependent. It is found that $Γ$ is quite large (above 20) near $T_{c}$, which satisfies the 2D model, but approaches a small value in the low-temperature region. The 2D-Tinkham model can also be used to fit the data at high temperatures. This is explained as a crossover from the orbital depairing mechanism in high-temperature and low-field region to the paramagnetic depairing mechanism in the high-field and low-temperature region. The temperature dependence of lower critical field $H_{c1} (T)$ shows a concave shape in wide temperature region. It is found that neither a single $d$-wave nor a single $s$-wave gap can fit the $H_{c1} (T)$, however a two-gap model containing an $s$-wave and a $d$-wave can fit the data rather well, suggesting two-band superconductivity and an unconventional pairing mechanism in this organic superconductor. △ Less

Submitted 6 February, 2023; originally announced February 2023.

Journal ref: Chinese Physics Letters 40, 067401 (2023)

Valley-resolved Fano resonance in monolayer transition metal dichalcogenides nanoribbons with attached stubs

Authors: Hui-Ying Mu, Nie-Wei Wang, Ying-Na Du, Xing-Tao An, Jian-Jun Liu

Abstract: Valley degree of freedom besides spin is a promising candidate as a carrier of information. Spintronics has come a long way and spin modulation can be realized by quantum interference and spin-orbit coupling effect. However, the control of valley degree of freedom using quantum interference is still a problem to be explored. Here we discover a mechanism of producing valley polarization in a monola… ▽ More Valley degree of freedom besides spin is a promising candidate as a carrier of information. Spintronics has come a long way and spin modulation can be realized by quantum interference and spin-orbit coupling effect. However, the control of valley degree of freedom using quantum interference is still a problem to be explored. Here we discover a mechanism of producing valley polarization in a monolayer transition metal dichalcogenides nanoribbon with attached stubs, in which valley-resolved Fano resonance are formed due to the quantum interference of intervalley backscattering. When the quantum interference occurs between the localized states at the edge of the stubs and the continuous channels in the nanoribbon, the transmission dips of Fano effect is valley-polarized. As the number of stubs increases, the valley-polarized transmission dips will split and valley-resolved minigaps are formed by Fano resonance with intervalley backscattering in stub superlattice. When the electron incident energy is in these valley-resolved gaps of the superlattice, even with several stubs, the transmission can have a significant valley polarization. Our finding points to an opportunity to realize valley functionalities by quantum interference. △ Less

Submitted 14 March, 2022; v1 submitted 5 November, 2021; originally announced November 2021.

Comments: 8 pages, 6 figures

Journal ref: Phys. Rev. B 105, 115305 (2022)

Kekule Lattice in Graphdiyne: Coexistence of Phononic and Electronic Higher-Order Band Topology

Authors: Haimen Mu, Bing Liu, Tianyi Hu, Z. F. Wang

Abstract: The topological physics has been extensively studied in different kinds of bosonic and fermionic systems, ranging from artificial structures to natural materials. However, the coexistence of topological phonon and electron in one single material is seldom reported. Recently, graphdiyne is proposed to be a two-dimensional (2D) electronic second-order topological insulator (SOTI). In this work, base… ▽ More The topological physics has been extensively studied in different kinds of bosonic and fermionic systems, ranging from artificial structures to natural materials. However, the coexistence of topological phonon and electron in one single material is seldom reported. Recently, graphdiyne is proposed to be a two-dimensional (2D) electronic second-order topological insulator (SOTI). In this work, based on density-functional tight-binding calculations, we found that graphdiyne is equivalent to the Kekule lattice, also realizing a 2D phononic SOTI in both out-of-plane and in-plane modes. Depending on edge terminations, the characterized topological corner states can be either inside or outside the bulk gap, which are tunable by local corner potential. Most remarkably, a unique selectivity of space and symmetry is revealed in electron-phonon coupling between the localized phononic and electronic topological corner states. Our results not only demonstrate the phononic higher-order band topology in a real carbon material, but also provide an opportunity to investigate the interplay between phononic and electronic higher-order topological states. △ Less

Submitted 22 October, 2021; originally announced October 2021.

Comments: 5 pages, 4 figures

Higher-Order Topology in Monolayer FeSe

Authors: Gan Zhao, Haimen Mu, Huimin Zhang, Z. F. Wang

Abstract: Generally, the topological corner state in two-dimensional second-order topological insulator (2D SOTI) is equivalent to the well-known domain wall state, originated from the mass-inversion between two adjacent edges with phase shift of pi. In this work, go beyond this conventional physical picture, we report a fractional mass-kink induced 2D SOTI in monolayer FeSe with canted checkerboard antifer… ▽ More Generally, the topological corner state in two-dimensional second-order topological insulator (2D SOTI) is equivalent to the well-known domain wall state, originated from the mass-inversion between two adjacent edges with phase shift of pi. In this work, go beyond this conventional physical picture, we report a fractional mass-kink induced 2D SOTI in monolayer FeSe with canted checkerboard antiferromagnetic (AFM) order by analytic model and first-principles calculations. The canted spin associated in-plane Zeeman field can gap out the quantum spin Hall edge state of FeSe, forming a fractional mass-kink with phase shift of pi/2 at the rectangular corner, and generating an in-gap topological corner state with fractional charge of e/4. Moreover, the topological corner state is robust to local perturbation, existing in both naturally and non-naturally cleaved corners, regardless of the edge orientation. Our results not only demonstrate a material system to realize the unique 2D AFM SOTI, but also pave a new way to design the higher-order topological states from fractional mass-kink with arbitrary phase shift, which are expected to draw immediate experimental attention. △ Less

Submitted 13 July, 2021; originally announced July 2021.

Comments: 13 pages, 3 figures

Field-induced metal-to-insulator transition and colossal anisotropic magnetoresistance in a nearly Dirac material EuMnSb$_2$

Authors: Z. L. Sun, A. F. Wang, H. M. Mu, H. H. Wang, Z. F. Wang, T. Wu, Z. Y. Wang, X. Y. Zhou, X. H. Chen

Abstract: How to realize applicably appreciated functionalities based on the coupling between charge and spin degrees of freedom is still a challenge in the field of spintronics. For example, anisotropic magnetoresistance (AMR) effect is utilized to read out the information stored by various magnetic structures, which usually originates from atomic spin-orbit coupling (SOC). However, the application of AMR… ▽ More How to realize applicably appreciated functionalities based on the coupling between charge and spin degrees of freedom is still a challenge in the field of spintronics. For example, anisotropic magnetoresistance (AMR) effect is utilized to read out the information stored by various magnetic structures, which usually originates from atomic spin-orbit coupling (SOC). However, the application of AMR in antiferromagnet-based spintronics is still hindered by rather small AMR value. Here, we discover a colossal AMR effect during the field-induced metal-to-insulator transition (MIT) in a nearly Dirac material EuMnSb$_2$ with an antiferromagnetic order of Eu$^{2+}$ moments. The colossal AMR reaches to an unprecedented value of 1.84$\times$10$^6$% at 2 K, which is four orders of magnitude larger than previously reported values in antiferromagnets. Based on density functional theory calculations, a Dirac-like band structure, which is strongly dependent on SOC, is confirmed around Y point and dominates the overall transport properties in the present sample with predominant electron-type carriers. Moreover, it is also revealed that the indirect band gap around Fermi level is dependent on the magnetic structure of Eu$^{2+}$ moments, which leads to the field-induced MIT and plays a key role on the colossal AMR effect. Finally, our present work suggests that the similar antiferromagnetic topological materials as EuMnSb$_2$, in which Dirac-like fermions is strongly modulated by SOC and antiferromagnetism, would be a fertile ground to explore applicably appreciated AMR effect. △ Less

Submitted 19 April, 2021; originally announced April 2021.

Valley polarization and valleyresistance in monolayer transition metal dichalcogenides superlattice

Authors: Hui-Ying Mu, Yi-Tong Yao, Jie-Ru Li, Guo-Cai Liu, Chao He, Ying-Jie Sun, Guang Yang, Xing-Tao An, Yong-Zhe Zhang, Jian-Jun Liu

Abstract: Manipulating the valley degree of freedom to encode information for potential valleytronic devices has ignited a new direction in solid-state physics. A significant, fundamental challenge in the field of valleytronics is how to generate and regulate valley-polarized currents by practical ways. Here, we discover a new mechanism of producing valley polarization in a monolayer transition metal dichal… ▽ More Manipulating the valley degree of freedom to encode information for potential valleytronic devices has ignited a new direction in solid-state physics. A significant, fundamental challenge in the field of valleytronics is how to generate and regulate valley-polarized currents by practical ways. Here, we discover a new mechanism of producing valley polarization in a monolayer transition metal dichalcogenides superlattice, in which valley-resolved gaps are formed at the supercell Brillouin zone boundaries and centers due to the intervalley scattering. When the energy of the incident electron is in the gaps, the available states are valley polarized, thus providing a valley-polarized current from the superlattice. We show that the direction and strength of the valley polarization may further be tuned by varying the potential applied the superlattice. The transmission can have a net valley polarization of 55% for a 4-period heterojunction. Moreover, such two valley filters in series may function as an electrostatically controlled giant valleyresistance device, representing a zero magnetic field counterpart to the familiar giant magnetoresistance device. △ Less

Submitted 9 January, 2020; v1 submitted 7 January, 2020; originally announced January 2020.

Comments: 14 pages, 4 figures

Journal ref: J. Phys. Chem. Lett. 11, 3882 (2020)

Critical Current Survival in YBCO Superconducting Layer of the Delaminated Coated Conductor

Authors: Feng Feng, Qishu Fu, Timing Qu, Chen Gu, Yubin Yue, Hui Mu, Xiangsong Zhang, Hongyuan Lu, Linli Wang, Siwei Chen, Pingfa Feng

Abstract: High temperature superconducting coated conductor (CC) could be practically applied in electric equipment due to its favorable mechanical properties and the critical current performance of YBCO superconducting layer. It is well known that CC could be easily delaminated because of its poor stress tolerance in thickness direction, i.e. along the c-axis of YBCO. Commonly, a stack including YBCO layer… ▽ More High temperature superconducting coated conductor (CC) could be practically applied in electric equipment due to its favorable mechanical properties and the critical current performance of YBCO superconducting layer. It is well known that CC could be easily delaminated because of its poor stress tolerance in thickness direction, i.e. along the c-axis of YBCO. Commonly, a stack including YBCO layer and silver stabilizer could be obtained after the delamination. It would be interesting to investigate the superconducting properties of the delaminated stack, since it could also be considered as a new type of CC with the silver stabilizer as the buffer layer, which is quite different from the oxide buffer layers in the traditional CC and might lead to new applications. In this study, a CC sample was delaminated by liquid nitrogen immersing. A Hall probe scanning system was employed to measure the critical current (IC) distribution of the original sample and the obtained stack. It was found that IC could be partially preserved after the delamination. Dense and crack-free morphologies of the delaminated surfaces were observed by scanning electron microscopy, and the potential application of the obtained stack in superconducting joint technology was discussed. △ Less

Submitted 27 December, 2016; originally announced December 2016.

Comments: 4 pages, 5 figures

Black Phosphorus-Polymer Composites for Pulsed Lasers

Authors: Haoran Mu, Shenghuang Lin, Zhongchi Wang, Si Xiao, Pengfei Li, Yao Chen, Han Zhang, Haifeng Bao, Shu Ping Lau, Chunxu Pan, Dianyuan Fan, Qiaoliang Bao

Abstract: Black phosphorus is a very promising material for telecommunication due to its direct bandgap and strong resonant absorption in near-infrared wavelength range. However, ultrafast nonlinear photonic applications relying on the ultrafast photo-carrier dynamics as well as optical nonlinearity in black phosphorus remain unexplored. In this work, we investigate nonlinear optical properties of solution… ▽ More Black phosphorus is a very promising material for telecommunication due to its direct bandgap and strong resonant absorption in near-infrared wavelength range. However, ultrafast nonlinear photonic applications relying on the ultrafast photo-carrier dynamics as well as optical nonlinearity in black phosphorus remain unexplored. In this work, we investigate nonlinear optical properties of solution exfoliated BP and demonstrate the usage of BP as a new saturable absorber for high energy pulse generation in fiber laser. In order to avoid the oxidization and degradation of BP, we encapsulated BP by polymer matrix which is optically transparent in the spectrum range of interest to form a composite. Two fabrication approaches were demonstrated to produce BP-polymer composite films which were further incorporated into fiber laser cavity as nonlinear media. BP shows very fast carrier dynamics and BP-polymer composite has a modulation depth of 10.6%. A highly stable Q-switched pulse generation was achieved and the single pulse energy of ~194 nJ was demonstrated. The ease of handling of such black phosphorus-polymer composite thin films affords new opportunities for wider applications such as optical sensing, signal processing and light modulation. △ Less

Submitted 23 June, 2015; originally announced June 2015.

Comments: 18 pages, 4 figures

Spin Current and Current-Induced Spin Transfer Torque in Ferromagnet-Quantum Dot-Ferromagnet Coupled Systems

Authors: Hai-Feng Mu, Gang Su, Qing-Rong Zheng

Abstract: Based on Keldysh's nonequilibrium Green function method, the spin-dependent transport properties in a ferromagnet-quantum dot (QD)-ferromagnet coupled system are investigated. It is shown the spin current shows quite different characteristics from its electrical counterpart, and by changing the relative orientation of both magnetizations, it can change its magnitude even sign. The current-induce… ▽ More Based on Keldysh's nonequilibrium Green function method, the spin-dependent transport properties in a ferromagnet-quantum dot (QD)-ferromagnet coupled system are investigated. It is shown the spin current shows quite different characteristics from its electrical counterpart, and by changing the relative orientation of both magnetizations, it can change its magnitude even sign. The current-induced spin transfer torque (CISTT) is uncovered to be greatly enhanced when the bias voltage meets with the discrete levels of the QD at resonant positions. The relationship between the CISTT, the electrical current and the spin current is also addressed. △ Less

Submitted 9 March, 2006; originally announced March 2006.

Comments: 21 pages, 8 figures

Journal ref: Phys. Rev. B 73, 054414 (2006)

Spin-Polarized Transport in Ferromagnet-Marginal Fermi Liquid Systems

Authors: Hai-Feng Mu, Gang Su, Qing-Rong Zheng, Biao Jin

Abstract: Spin-polarized transport through a marginal Fermi liquid (MFL) which is connected to two noncollinear ferromagnets via tunnel junctions is discussed in terms of the nonequilibrium Green function approach. It is found that the current-voltage characteristics deviate obviously from the ohmic behavior, and the tunnel current increases slightly with temperature, in contrast to those of the system wi… ▽ More Spin-polarized transport through a marginal Fermi liquid (MFL) which is connected to two noncollinear ferromagnets via tunnel junctions is discussed in terms of the nonequilibrium Green function approach. It is found that the current-voltage characteristics deviate obviously from the ohmic behavior, and the tunnel current increases slightly with temperature, in contrast to those of the system with a Fermi liquid. The tunnel magnetoresistance (TMR) is observed to decay exponentially with increasing the bias voltage, and to decrease slowly with increasing temperature. With increasing the coupling constant of the MFL, the current is shown to increase linearly, while the TMR is found to decay slowly. The spin-valve effect is observed. △ Less

Submitted 5 September, 2005; originally announced September 2005.

Comments: 5 pages, 6 figures, Phys. Rev. B 71, 064412 (2005)

Journal ref: Phys. Rev. B 71, 064412 (2005)