Showing 1–50 of 109 results for author: Ye, D

200 mm Wafer-Scale Monolithic 3D Integration of Atomic Layer-Deposited Oxide Semiconductors

Authors: Chang Niu, Linjia Long, Luqi Zheng, Shuting Du, Jian-Yu Lin, Kisoo Nam, Zehao Lin, Chang Liu, Juanjuan Lu, Haiyan Wang, Haitong Li, Peide D. Ye

Abstract: Monolithic 3D (M3D) integration offers a pathway to overcome the scaling limits of conventional silicon complementary metal-oxide-semiconductor (CMOS) technology by extending dense vertical stacking of multifunctional logic and memory devices. Here, we demonstrate wafer-scale M3D integration of three tiers of atomic-layer-deposited (ALD) indium oxide (InOx)-based devices (>100,000 fabricated), inc… ▽ More Monolithic 3D (M3D) integration offers a pathway to overcome the scaling limits of conventional silicon complementary metal-oxide-semiconductor (CMOS) technology by extending dense vertical stacking of multifunctional logic and memory devices. Here, we demonstrate wafer-scale M3D integration of three tiers of atomic-layer-deposited (ALD) indium oxide (InOx)-based devices (>100,000 fabricated), including ferroelectric, enhancement-mode, and depletion-mode field-effect transistors, on 200 mm silicon wafers. We achieve threshold voltage standard deviation as low as 0.04 V, average electron mobility up to 91.6 cm2V-1s-1, and fully functional cross-tier circuits. A four-tier 3D computing-in-memory (CIM) accelerator targeting large language model workloads is developed using a custom InOx process design kit, delivering 1.4x to 2.9x speedup and comparable energy-delay product improvements over 2D baselines. These results establish ALD InOx M3D integration as a scalable and CMOS-compatible platform for next-generation artificial intelligence hardware and advanced electronics. △ Less

Submitted 10 August, 2026; originally announced August 2026.

Size-Dependent Band-Tail Localization in Oxide Semiconductors Revealed by Direct Density-of-States Mapping

Authors: Chang Niu, Kisoo Nam, Aravindh Shankar, Jian-Yu Lin, Sanjeev Khare, Sumi Lee, Pramey Upadhyaya, Peide D. Ye

Abstract: Disorder-induced localization is expected to become increasingly important as amorphous oxide semiconductor transistors are scaled toward low-dimensional channels, yet the electronic states responsible for this transport regime remain difficult to resolve experimentally. Here, we use a lock-in-based electric-field penetration technique to directly map the effective density of states (DOS) in In-ba… ▽ More Disorder-induced localization is expected to become increasingly important as amorphous oxide semiconductor transistors are scaled toward low-dimensional channels, yet the electronic states responsible for this transport regime remain difficult to resolve experimentally. Here, we use a lock-in-based electric-field penetration technique to directly map the effective density of states (DOS) in In-based oxide semiconductor thin-film transistors (TFTs). The extracted quantum capacitance, carrier density, and chemical potential reveal a disorder-dominated transport regime in which band-tail states are not merely passive traps, but become screening-active and partially transport-active. Geometry-dependent DOS mapping shows an exponential suppression of the effective DOS with channel length, demonstrating size-dependent band-tail localization and providing a microscopic origin for a distinct localization-induced threshold-voltage roll-off mechanism. Temperature-dependent measurements show that the disorder-dominated DOS is strongly suppressed at low temperatures, while extended diffusive states remain nearly unchanged, confirming the localization origin. By tuning film thickness, O2 annealing, and In/Ga/Zn composition, we further demonstrate systematic suppression of disorder and effective-DOS localization. This work establishes direct DOS mapping as a device-level probe of localization physics and provides a pathway for engineering disorder in low-dimensional oxide semiconductor electronics. △ Less

Submitted 10 August, 2026; originally announced August 2026.

Comments: 30 pages

Terahertz field-driven nonlinear Hall effect and other second order transport phenomena in two-dimensional tellurene

Authors: M. D. Moldavskaya, L. E. Golub, E. Mönch, Chang Niu, Peide D. Ye, J. Wunderlich, S. D. Ganichev

Abstract: We study terahertz field-driven second-order nonlinear electron transport phenomena, including the nonlinear Hall effect (NLHE), in two-dimensional tellurene flakes. The dc current excited by linearly polarized terahertz (THz) radiation in Hall bar samples is investigated in directions both along and perpendicular to the $c$-axis of tellurene. As expected for second-order transport phenomena, the… ▽ More We study terahertz field-driven second-order nonlinear electron transport phenomena, including the nonlinear Hall effect (NLHE), in two-dimensional tellurene flakes. The dc current excited by linearly polarized terahertz (THz) radiation in Hall bar samples is investigated in directions both along and perpendicular to the $c$-axis of tellurene. As expected for second-order transport phenomena, the current scales as the square of the in-plane electric field of the radiation $\bf E$, and depends on its orientation. The current results from a combination of three contributions, including the NLHE, the Nonlinear Longitudinal (NLL) and Nonlinear Diagonal (NLD) currents. We established the equivalence between NLH, NLL, and NLD transport currents and Linear photogalvanic effect (LPGE) contributions induced by the absorption of linearly polarized and unpolarized THz radiation. All contributions can be controlled by a gate voltage and have opposite signs for electron and hole conductivity. The magnitude of the current increases drastically when the samples are cooled from room temperature to 4.2 K. It also increases with decreasing radiation frequency. These results are well described by the developed phenomenological and microscopic theories. We show that the THz radiation-induced electric current originates from microscopic mechanisms such as skew scattering, side jump, and the Berry curvature dipole. △ Less

Submitted 10 July, 2026; originally announced July 2026.

Comments: 13 pages, 9 figures

Surface lone-pair polarization probed by quantum-geometric transport in tellurium

Authors: Nathanael N. Batista, Wendel S. Paz, Manuel Suárez-Rodríguez, Pierpaolo Fontana, Victor Velasco, Marcus V. O. Moutinho, Chang Niu, Peide D. Ye, Marco Gobbi, Fèlix Casanova, Luis E. Hueso, Caio Lewenkopf, Marcello B. Silva Neto

Abstract: Stereochemically active lone pairs are ubiquitous microscopic sources of polarity in molecules and solids, but their collective behavior in crystals is often hidden by symmetry or confined to surfaces. Here we show that quantum-geometry transport provides a sensitive probe of surface lone-pair polarization in trigonal tellurium. This surface polarization appears microscopically as an inversion-odd… ▽ More Stereochemically active lone pairs are ubiquitous microscopic sources of polarity in molecules and solids, but their collective behavior in crystals is often hidden by symmetry or confined to surfaces. Here we show that quantum-geometry transport provides a sensitive probe of surface lone-pair polarization in trigonal tellurium. This surface polarization appears microscopically as an inversion-odd dipolar component of the crystal potential, which shifts the center of mass of Bloch wavepackets and produces quantum-geometric corrections to their velocity. We describe this lone-pair polar texture through a minimal three-component lattice model, and we show that the resulting linear and nonlinear transport coefficients probe, respectively, the second and first moments of the net polarization field. Because rectified voltages in tellurium flakes are directly proportional to the surface lone-pair polarization, our results provide a microscopic route to understanding and engineering polarization-driven, quantum-geometric electronic devices based on tellurium allotropes. △ Less

Submitted 29 May, 2026; originally announced May 2026.

Comments: Main 7 pages and 6 figures, Suppl Info 12 pages and 1 figure

Polar unidirectional magnetotransport in $p-$type tellurene from quantum geometry

Authors: Claudio Iacovelli, Pierpaolo Fontana, Victor Velasco, Chang Niu, Peide D. Ye, Marcus V. O. Moutinho, Caio Lewenkopf, Marcello B. Silva Neto

Abstract: Unidirectional magnetoresistance, or electric magnetochiral anisotropy (eMChA), is a nonlinear magnetotransport phenomenon that arises in noncentrosymmetric conductors , where changes in resistance $R(B)$ are: (i) chiral, $ΔR(B)/R(0)=2\,χ\, {\bf I}\cdot{\bf B}$, or (ii) polar, $ΔR(B)/R(0)=2\,γ\, {\bf I}\cdot({\bf P}\times{\bf B})$, with eMChA coefficients $χ$ and $γ$. In [Phys. Rev. Lett. 135, 106… ▽ More Unidirectional magnetoresistance, or electric magnetochiral anisotropy (eMChA), is a nonlinear magnetotransport phenomenon that arises in noncentrosymmetric conductors , where changes in resistance $R(B)$ are: (i) chiral, $ΔR(B)/R(0)=2\,χ\, {\bf I}\cdot{\bf B}$, or (ii) polar, $ΔR(B)/R(0)=2\,γ\, {\bf I}\cdot({\bf P}\times{\bf B})$, with eMChA coefficients $χ$ and $γ$. In [Phys. Rev. Lett. 135, 106602 (2025)], we showed that the eMChA in the conduction band of tellurene is polar ($χ=0$, $γ\neq 0$) and emerges from the quantum metric dipole due to its Weyl node and from the lone pair polarization ${\bf P}$. Here, we extend our work to the valence band of tellurene, where the eMChA is usually said to be chiral ($χ\neq 0, γ= 0$). We show that also a polar coefficient $γ\neq 0$ emerges naturally through a downfolding procedure, in which remote Weyl-node containing bands induce momentum-space gradients of the quantum metric in the low-energy levels, activating finite metric dipoles. Combining semiclassical Boltzmann transport with a ${\bf k}\cdot{\bf p}$ description of tellurene, our numerical calculations agree quantitatively with doping ($μ$) dependent second-harmonic measurements of the longitudinal voltage $V^{2ω}_\parallel(μ)$ in perpendicular field. The combined chiral and polar characters ($χ\neq0, γ\neq 0)$ of the eMChA in tellurene also explains the shift in the angular ($φ$) dependence of $V^{2ω}_\parallel(φ)$ for in plane fields. Our results demonstrate that the polar eMChA can arise in topologically trivial bands through multiband effects and establishes tellurene as a platform for quantum-geometric rectification in both electron and hole regimes. △ Less

Submitted 14 February, 2026; originally announced February 2026.

Comments: 21 pages, 10 figures

Chirality Driven Ratchet Currents in Two-Dimensional Tellurene with an Asymmetric Grating

Authors: M. D. Moldavskaya, L. E. Golub, Chang Niu, Peide D. Ye, S. D. Ganichev

Abstract: The emergence of the terahertz (THz) ratchet effect is a rapidly expanding field of research that utilizes broken spatial symmetry in low-dimensional materials to rectify alternating current (AC) induced by THz fields into direct current (DC). This mechanism is highly promising for next-generation, room-temperature terahertz applications, particularly in high-speed, sensitive detection and imaging… ▽ More The emergence of the terahertz (THz) ratchet effect is a rapidly expanding field of research that utilizes broken spatial symmetry in low-dimensional materials to rectify alternating current (AC) induced by THz fields into direct current (DC). This mechanism is highly promising for next-generation, room-temperature terahertz applications, particularly in high-speed, sensitive detection and imaging. In this work, we explore a ratchet effect generated in two dimensional tellurene, a novel promising semiconductor material consisting of helical atomic chains, creating a structure with inherent chirality. As a key result, the DC circular ratchet current flowing in the chiral axis direction $c$ is determined by the helicity of the radiation and can be reversed by switching the helicity from right to left handed. The circular ratchet effect excited by THz laser radiation is demonstrated for room temperature. The effect is demonstrated at various gate voltages when the Fermi level lies in vicinity of the Weyl point in the conduction band, in the band gap, and in the valence band with almost parabolic energy dispersion. The results are described by the developed microscopic theory based on the Boltzmann kinetic equation approach. △ Less

Submitted 6 February, 2026; originally announced February 2026.

Comments: 7+3 pages, 6+6 figures

Breakdown of Ohm's Law by Disorders in Low-Dimensional Transistors

Authors: Chang Niu, Adam Charnas, Jian-Yu Lin, Linjia Long, Zehao Lin, Zhuocheng Zhang, Peide D. Ye

Abstract: Ohm's law provides a fundamental framework for understanding charge transport in conductors and underpins the concept of electrical scaling that has enabled the continuous advancement of modern CMOS technologies. As transistors are scaled to even smaller dimensions, device channels inevitably enter low-dimensional regimes to achieve higher performance. Low-dimensional materials such as atomically… ▽ More Ohm's law provides a fundamental framework for understanding charge transport in conductors and underpins the concept of electrical scaling that has enabled the continuous advancement of modern CMOS technologies. As transistors are scaled to even smaller dimensions, device channels inevitably enter low-dimensional regimes to achieve higher performance. Low-dimensional materials such as atomically thin oxide semiconductors, 2D van der Waals semiconductors, and 1D carbon nanotubes, have thus emerged as key candidates for extending Moore's law. Here, we reveal the fundamental distinction between three-dimensional and low-dimensional conductors arising from disorder-induced electron localization, which leads to the breakdown of Ohm's law and lateral linear scaling. We develop a quantitative model that captures the role of the disordered region, a unique characteristic intrinsically to low-dimensional transistors. Furthermore, the disorder-induced localization framework consistently explains experimental observations in atomically thin In2O3 field-effect transistors across variations in channel length, temperature, thickness, and post-annealing conditions. This work establishes a unified physical picture for understanding and optimizing disorder-driven electronic transport in low-dimensional transistors. △ Less

Submitted 3 January, 2026; originally announced January 2026.

Gate-Tunable Giant Negative Magnetoresistance in Tellurene Driven by Quantum Geometry

Authors: Marcello B. Silva Neto, Chang Niu, Marcus V. O. Moutinho, Pierpaolo Fontana, Claudio Iacovelli, Victor Velasco, Caio Lewenkopf, Peide D. Ye

Abstract: Negative magnetoresistance in conventional two-dimensional electron gases is a well-known phenomenon, but its origin in complex and topological materials, especially those endowed with quantum geometry, remains largely elusive. Here, we report the discovery of a giant negative magnetoresistance, reaching a remarkable $- 90\%$ of the resistance at zero magnetic field, $R_0$, in $n$-type tellurene f… ▽ More Negative magnetoresistance in conventional two-dimensional electron gases is a well-known phenomenon, but its origin in complex and topological materials, especially those endowed with quantum geometry, remains largely elusive. Here, we report the discovery of a giant negative magnetoresistance, reaching a remarkable $- 90\%$ of the resistance at zero magnetic field, $R_0$, in $n$-type tellurene films. This record-breaking effect persists over a wide magnetic field range (measured up to $35$ T) at cryogenic temperatures and is suppressed when the chemical potential shifts away from the Weyl node in the conduction band, strongly suggesting a quantum geometric origin. We propose two novel mechanisms for this phenomenon: a quantum geometric enhancement of diffusion and a magnetoelectric spin interaction that locks the spin of a Weyl fermion, in cyclotron motion under crossed electric $\boldsymbol{\cal E}$ and magnetic ${\bf B}$ fields, to its guiding-center drift, $(\boldsymbol{\cal E}\times{\bf B})\cdotσ$. We show that the time integral of the velocity auto-correlations promoted by the quantum metric between the spin-split conduction bands enhance diffusion, thereby reducing the resistance. This mechanism is experimentally confirmed by its unique magnetoelectric dependence, $ΔR_{zz}(\boldsymbol{\cal E},{\bf B})/R_0=-β_{g}(\boldsymbol{\cal E}\times{\bf B})^2$, with $β_{g}$ determined by the quantum metric. Our findings establish a new, quantum geometric and non-Markovian memory effect in magnetotransport, paving the way for controlling electronic transport in complex and topological matter. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Comments: 28 pages, 6 figures in the Main Text + 15 pages, 3 figures of Supplementary Information

Journal ref: Nat. Commun. 17, 5783 (2026)

Non-reciprocal Magnetoresistances in Chiral Tellurium

Authors: Shuchen Li, Chang Niu, Peide D. Ye, Axel Hoffmann

Abstract: Materials with broken fundamental symmetries, such as chiral crystals, provide a rich playground for exploring unconventional spin-dependent transport phenomena. The interplay between a material's chirality, strong spin-orbit coupling, and charge currents can lead to complex non-reciprocal effects, where electrical resistance depends on the direction of current and magnetic fields. In this study,… ▽ More Materials with broken fundamental symmetries, such as chiral crystals, provide a rich playground for exploring unconventional spin-dependent transport phenomena. The interplay between a material's chirality, strong spin-orbit coupling, and charge currents can lead to complex non-reciprocal effects, where electrical resistance depends on the direction of current and magnetic fields. In this study, we systematically investigate the angular dependencies of magnetoresistance in single-crystalline chiral Tellurium (Te). We observe distinct non-reciprocal magnetoresistances for magnetic fields applied along three orthogonal directions: parallel to the current along the chiral axis (z), in the sample plane but perpendicular to the current (y), and out of the sample plane (x). Through detailed analysis of the chirality- and thickness-dependence of the signals, we successfully disentangle multiple coexisting mechanisms. We conclude that the Edelstein effect, arising from the chiral structure's radial spin texture, is responsible for the non-reciprocity along the z-axis. In contrast, the chirality-independent signal along the y-axis is attributed to the Nernst effect, and the non-reciprocity along the x-axis may originate from intrinsic orbital magnetizations. These findings elucidate the complex interplay of spin, orbital, and thermal effects in Te, providing a complete picture of its non-reciprocal transport properties. △ Less

Submitted 18 December, 2025; v1 submitted 5 December, 2025; originally announced December 2025.

A Global Spacetime Optimization Approach to the Real-Space Time-Dependent Schrödinger Equation

Authors: Enze Hou, Yuzhi Liu, Linxuan Zhang, Difa Ye, Lei Wang, Han Wang

Abstract: The time-dependent Schrödinger equation (TDSE) in real space is fundamental to understanding the dynamics of many-electron quantum systems, with applications ranging from quantum chemistry to condensed matter physics and materials science. However, solving the TDSE for complex fermionic systems remains a significant challenge, particularly due to the need to capture the time-evolving many-body cor… ▽ More The time-dependent Schrödinger equation (TDSE) in real space is fundamental to understanding the dynamics of many-electron quantum systems, with applications ranging from quantum chemistry to condensed matter physics and materials science. However, solving the TDSE for complex fermionic systems remains a significant challenge, particularly due to the need to capture the time-evolving many-body correlations, while the antisymmetric nature of fermionic wavefunctions complicates the function space in which these solutions must be represented. We propose a general-purpose neural network framework for solving the real-space TDSE, Fermionic Antisymmetric Spatio-Temporal Network, which treats time as an explicit input alongside spatial coordinates, enabling a unified spatiotemporal representation of complex, antisymmetric wavefunctions for fermionic systems. This approach formulates the TDSE as a global optimization problem, avoiding step-by-step propagation and supporting highly parallelizable training. The method is demonstrated on five benchmark problems, achieving excellent agreement with reference solutions across all cases. These results demonstrate the method's accuracy and flexibility within the bound-state manifold across various dimensions and interaction regimes. While the current localized Ansatz inherently restricts the description of extensive ionization and continuum states, the method demonstrates the capability to stably simulate coherent multi-electron dynamics over extended time windows. Our framework offers a highly expressive alternative to traditional basis-dependent or mean-field methods, opening new possibilities for ab initio simulations of time-dependent quantum systems, with applications in quantum dynamics, molecular control, and ultrafast spectroscopy. △ Less

Submitted 27 March, 2026; v1 submitted 17 November, 2025; originally announced November 2025.

Comments: 26 pages, 7 figures

Cascade of Even-Denominator Fractional Quantum Hall States in Mixed-Stacked Multilayer Graphene

Authors: Yating Sha, Kai Liu, Chenxin Jiang, Dan Ye, Shuhan Liu, Zhongxun Guo, Jingjing Gao, Ming Tian, Neng Wan, Kenji Watanabe, Takashi Taniguchi, Bingbing Tong, Guangtong Liu, Li Lu, Yuanbo Zhang, Zhiwen Shi, Zixiang Hu, Guorui Chen

Abstract: The fractional quantum Hall effect (FQHE), particularly at half-filling of Landau levels, provides a unique window into topological phases hosting non-Abelian excitations. However, experimental platforms simultaneously offering large energy gaps, delicate tunability, and robust non-Abelian signatures remain scarce. Here, we report the observation of a cascade of even-denominator FQH states at fill… ▽ More The fractional quantum Hall effect (FQHE), particularly at half-filling of Landau levels, provides a unique window into topological phases hosting non-Abelian excitations. However, experimental platforms simultaneously offering large energy gaps, delicate tunability, and robust non-Abelian signatures remain scarce. Here, we report the observation of a cascade of even-denominator FQH states at filling factors $ν$ = ${-5/2}$, ${-7/2}$, ${-9/2}$, ${-11/2}$, and ${-13/2}$, alongside numerous odd-denominator states in mixed-stacked pentalayer graphene, a previously unexplored system characterized by intertwined quadratic and cubic band dispersions. These even-denominator states, representing the highest filling half-filled states reported so far in the zeroth Landau level (ZLL), emerge from two distinct intra-ZLL and exhibit unprecedented displacement field tunability driven by LL crossings in the hybridized multiband structure. At half fillings, continuous quasiparticle phase transitions between paired FQH states, magnetic Bloch states, and composite Fermi liquids are clearly identified upon tuning external fields. Numerical calculations, revealing characteristic sixfold ground-state degeneracy and chiral graviton spectral analysis, suggest the observed even-denominator FQH states belong to the non-Abelian Moore-Read type. These results establish mixed-stacked multilayer graphene as a rich and versatile crystalline platform for exploring tunable correlated topological phases. △ Less

Submitted 28 July, 2025; originally announced July 2025.

Lithography defined semiconductor moires with anomalous in-gap quantum Hall states

Authors: Wei Pan, D. Bruce Burckel, Catalin D. Spataru, Keshab R. Sapkota, Aaron J. Muhowski, Samuel D. Hawkins, John F. Klem, Layla S. Smith, Doyle A. Temple, Zachery A. Enderson, Zhigang Jiang, Komalavalli Thirunavukkuarasu, Li Xiang, Mykhaylo Ozerov, Dmitry Smirnov, Chang Niu, Peide D. Ye, Praveen Pai, Fan Zhang

Abstract: Quantum materials and phenomena have attracted great interest for their potential applications in next-generation microelectronics and quantum-information technologies. In one especially interesting class of quantum materials, moire superlattices (MSL) formed by twisted bilayers of 2D materials, a wide range of novel phenomena are observed. However, there exist daunting challenges such as reproduc… ▽ More Quantum materials and phenomena have attracted great interest for their potential applications in next-generation microelectronics and quantum-information technologies. In one especially interesting class of quantum materials, moire superlattices (MSL) formed by twisted bilayers of 2D materials, a wide range of novel phenomena are observed. However, there exist daunting challenges such as reproducibility and scalability of utilizing 2D MSLs for microelectronics and quantum technologies due to their exfoliate-tear-stack method. Here, we propose lithography defined semiconductor moires superlattices, in which three fundamental parameters, electron-electron interaction, spin-orbit coupling, and band topology, are designable. We experimentally investigate quantum transport properties in a moire specimen made in an InAs quantum well. Strong anomalous in-gap states are observed within the same integer quantum Hall state. Our work opens up new horizons for studying 2D quantum-materials phenomena in semiconductors featuring superior industry-level quality and state-of-the-art technologies, and they may potentially enable new quantum information and microelectronics technologies. △ Less

Submitted 6 June, 2025; originally announced June 2025.

Comments: published by Nano Letters

Towards scientific machine learning for granular material simulations -- challenges and opportunities

Authors: Marc Fransen, Andreas Fürst, Deepak Tunuguntla, Daniel N. Wilke, Benedikt Alkin, Daniel Barreto, Johannes Brandstetter, Miguel Angel Cabrera, Xinyan Fan, Mengwu Guo, Bram Kieskamp, Krishna Kumar, John Morrissey, Jonathan Nuttall, Jin Ooi, Luisa Orozco, Stefanos-Aldo Papanicolopulos, Tongming Qu, Dingena Schott, Takayuki Shuku, WaiChing Sun, Thomas Weinhart, Dongwei Ye, Hongyang Cheng

Abstract: Micro-scale mechanisms, such as inter-particle and particle-fluid interactions, govern the behaviour of granular systems. While particle-scale simulations provide detailed insights into these interactions, their computational cost is often prohibitive. Attended by researchers from both the granular materials (GM) and machine learning (ML) communities, a recent Lorentz Center Workshop on "Machine L… ▽ More Micro-scale mechanisms, such as inter-particle and particle-fluid interactions, govern the behaviour of granular systems. While particle-scale simulations provide detailed insights into these interactions, their computational cost is often prohibitive. Attended by researchers from both the granular materials (GM) and machine learning (ML) communities, a recent Lorentz Center Workshop on "Machine Learning for Discrete Granular Media" brought the ML community up to date with GM challenges. This position paper emerged from the workshop discussions. We define granular materials and identify seven key challenges that characterise their distinctive behaviour across various scales and regimes, ranging from gas-like to fluid-like and solid-like. Addressing these challenges is essential for developing robust and efficient digital twins for granular systems in various industrial applications. To showcase the potential of ML to the GM community, we present classical and emerging machine/deep learning techniques that have been, or could be, applied to granular materials. We reviewed sequence-based learning models for path-dependent constitutive behaviour, followed by encoder-decoder type models for representing high-dimensional data. We then explore graph neural networks and recent advances in neural operator learning. Lastly, we discuss model-order reduction and probabilistic learning techniques for high-dimensional parameterised systems, which are crucial for quantifying uncertainties arising from physics-based and data-driven models. We present a workflow aimed at unifying data structures and modelling pipelines and guiding readers through the selection, training, and deployment of ML surrogates for granular material simulations. Finally, we illustrate the workflow's practical use with two representative examples, focusing on granular materials in solid-like and fluid-like regimes. △ Less

Submitted 1 April, 2025; originally announced April 2025.

Comments: 35 pages, 17 figures

Quantum geometry and the electric magnetochiral anisotropy in noncentrosymmetric polar media

Authors: Pierpaolo Fontana, Victor Velasco, Chang Niu, Peide D. Ye, Pedro V. Lopes, Kaio E. M. de Souza, Marcus V. O. Moutinho, Caio Lewenkopf, Marcello B. Silva Neto

Abstract: The electric magnetochiral anisotropy is a nonreciprocal phenomenon accessible via second harmonic transport in noncentrosymmetric, time-reversal invariant materials, in which the rectification of current, ${\bf I}$, can be controlled by an external magnetic field, ${\bf B}$. Quantum geometry, which characterizes the topology of Bloch electrons in a Hilbert space, provides a powerful description o… ▽ More The electric magnetochiral anisotropy is a nonreciprocal phenomenon accessible via second harmonic transport in noncentrosymmetric, time-reversal invariant materials, in which the rectification of current, ${\bf I}$, can be controlled by an external magnetic field, ${\bf B}$. Quantum geometry, which characterizes the topology of Bloch electrons in a Hilbert space, provides a powerful description of the nonlinear dynamics in topological materials. Here, we demonstrate that the electric magnetochiral anisotropy in noncentrosymmetric polar media owes its existence to the quantum metric, arising from the spin-orbit coupling, and to large Born effective charges. In this context, the reciprocal magnetoresistance $β{\bf B}^2$ is modified to $R( I,P,B)=R_0[1+βB^2 + γ^{\pm}{\bf I}\cdot({\bf P}\times{\bf B})]$, where the chirality dependent $γ^{\pm}$ is determined by the quantum metric dipole and the polarization ${\bf P}$. We predict a universal scaling $γ^{\pm}(V)\sim V^{-5/2}$ which we verified by phase sensitive, second harmonic transport measurements on hydrothermally grown 2D tellurium films under applied gate voltage, $V$. The control of rectification by varying ${\bf I}$, ${\bf P}$, ${\bf B}$, and $V$, demonstrated in this work, opens up new avenues for the building of ultra-scaled CMOS circuits. △ Less

Submitted 13 February, 2025; originally announced February 2025.

Comments: 6 pages, 4 figures + 10 pages, 4 figures of Supplemental Material

Journal ref: Phys. Rev. Lett. 135, 106602 (2025)

Ultralow Voltage Operation of p- and n-FETs Enabled by Self-Formed Gate Dielectric and Metal Contacts on 2D Tellurium

Authors: Chang Niu, Linjia Long, Yizhi Zhang, Zehao Lin, Pukun Tan, Jian-Yu Lin, Wenzhuo Wu, Haiyan Wang, Peide D. Ye

Abstract: The ongoing demand for more energy-efficient, high-performance electronics is driving the exploration of innovative materials and device architectures, where interfaces play a crucial role due to the continuous downscaling of device dimensions. Tellurium (Te), in its two-dimensional (2D) form, offers significant potential due to its high carrier mobility and ambipolar characteristics, with the car… ▽ More The ongoing demand for more energy-efficient, high-performance electronics is driving the exploration of innovative materials and device architectures, where interfaces play a crucial role due to the continuous downscaling of device dimensions. Tellurium (Te), in its two-dimensional (2D) form, offers significant potential due to its high carrier mobility and ambipolar characteristics, with the carrier type easily tunable via surface modulation. In this study, we leverage atomically controlled material transformations in 2D Te to create intimate junctions, enabling near-ideal field-effect transistors (FETs) for both n-type and p-type operation. A NiTex-Te contact provides highly transparent interfaces, resulting in low contact resistance, while the TiOx-Te gate dielectric forms an ultraclean interface with a capacitance equivalent to 0.88 nm equivalent oxide thickness (EOT), where the quantum capacitance of Te is observed. Subthreshold slopes (SS) approach the Boltzmann limit, with a record-low SS of 3.5 mV/dec achieved at 10 K. Furthermore, we demonstrate 2D Te-based complementary metal-oxide-semiconductor (CMOS) inverters operating at an ultralow voltage of 0.08 V with a voltage gain of 7.1 V/V. This work presents a promising approach to forming intimate dielectric/semiconductor and metal/semiconductor junctions for next-generation low-power electronic devices. △ Less

Submitted 5 December, 2024; originally announced December 2024.

Comments: 27 pages, 5 figures

Experimental Investigation of Variations in Polycrystalline Hf0.5Zr0.5O2 (HZO)-based MFIM

Authors: Tae Ryong Kim, Revanth Koduru, Zehao Lin, Peide. D. Ye, Sumeet Kumar Gupta

Abstract: Device-to-device variations in ferroelectric (FE) hafnium oxide (HfO2)-based devices pose a crucial challenge that limits the otherwise promising capabilities of this technology. Although previous simulation-based studies have identified polarization (P) domain nucleation and polycrystallinity as key contributors to variations in HfO2, experimental validation remains limited. Here, we experimental… ▽ More Device-to-device variations in ferroelectric (FE) hafnium oxide (HfO2)-based devices pose a crucial challenge that limits the otherwise promising capabilities of this technology. Although previous simulation-based studies have identified polarization (P) domain nucleation and polycrystallinity as key contributors to variations in HfO2, experimental validation remains limited. Here, we experimentally investigate variations in remanent polarization (PR) of Hf0.5Zr0.5O2 (HZO)-based metal-ferroelectric-insulator-metal (MFIM) capacitors across different set voltages (VSET) and FE thicknesses (TFE). Our measurements reveal a non-monotonic behavior of the standard deviation of PR with VSET peaking around coercive voltage (VC), which is consistent with previous simulation-based predictions. In the low- and high-VSET regions, PR variations are primarily dictated by saturation polarization (PS) variations, mainly originating from charge trap effects at the interface between the FE-dielectric (DE) layer and the polycrystallinity of FE. On the other hand, in the mid-VSET region peak, the PR variations are attributed to the VC variation, which comes from a combined effect of multi-domain (MD) P switching and polycrystallinity. Notably, sharp P switching associated with domain nucleation amplifies the variations, resulting in a peak of PR variations in this VSET range. Further, we observe that as HZO thickness (TFE) is scaled, the non-monotonicity in variations with VSET is reduced, primarily due to reduced domain nucleation and smaller grain sizes. We experimentally establish a strong correlation of PR with PS in the low- and high-VSET regions and with VC in the mid-VSET region across various TFE. Finally, our experimental findings are corroborated with simulations using a 3D phase-field model. △ Less

Submitted 27 March, 2025; v1 submitted 7 November, 2024; originally announced November 2024.

Comments: 7 pages, 8 figures

Terahertz radiation driven nonlinear transport phenomena in two-dimensional tellurene

Authors: Erwin Mönch, Mariya D. Moldavskaya, Leonid E. Golub, Vasily V. Bel'kov, Jörg Wunderlich, Dieter Weiss, Joanna Gumenjuk-Sichevska, Chang Niu, Peide D. Ye, Sergey D. Ganichev

Abstract: Nonlinear electron transport induced by polarized terahertz radiation is studied in two-dimensional tellurene at room temperature. A direct current, quadratic in the radiation's electric field, is observed. Contributions sensitive to radiation helicity, polarization orientation as well as polarization independent current are found. We show that these contributions can be modified by the magnitude… ▽ More Nonlinear electron transport induced by polarized terahertz radiation is studied in two-dimensional tellurene at room temperature. A direct current, quadratic in the radiation's electric field, is observed. Contributions sensitive to radiation helicity, polarization orientation as well as polarization independent current are found. We show that these contributions can be modified by the magnitude of the external gate potential. We demonstrate that this terahertz-driven electric current arises from the Berry curvature dipole and the side-jump microscopic mechanisms.Nonlinear electron transport induced by polarized terahertz radiation is studied in two-dimensional tellurene at room temperature. A direct current, quadratic in the radiation's electric field, is observed. Contributions sensitive to radiation helicity, polarization orientation as well as polarization independent current are found. We show that these contributions can be modified by the magnitude of the external gate potential. We demonstrate that this terahertz-driven electric current arises from the Berry curvature dipole and the side-jump microscopic mechanisms. △ Less

Submitted 23 October, 2024; originally announced October 2024.

Comments: 6 pages and 5 figures

First Demonstration of HZO/beta-Ga2O3 Ferroelectric FinFET with Improved Memory Window

Authors: Seohyeon Park, Jaewook Yoo, Hyeojun Song, Hongseung Lee, Seongbin Lim, Soyeon Kim, Minah Park, Bongjoong Kim, Keun Heo, Peide D. Ye, Hagyoul Bae

Abstract: We have experimentally demonstrated the effectiveness of beta-gallium oxide (beta-Ga2O3) ferroelectric fin field-effect transistors (Fe-FinFETs) for the first time. Atomic layer deposited (ALD) hafnium zirconium oxide (HZO) is used as the ferroelectric layer. The HZO/beta-Ga2O3 Fe-FinFETs have wider counterclockwise hysteresis loops in the transfer characteristics than that of conventional planar… ▽ More We have experimentally demonstrated the effectiveness of beta-gallium oxide (beta-Ga2O3) ferroelectric fin field-effect transistors (Fe-FinFETs) for the first time. Atomic layer deposited (ALD) hafnium zirconium oxide (HZO) is used as the ferroelectric layer. The HZO/beta-Ga2O3 Fe-FinFETs have wider counterclockwise hysteresis loops in the transfer characteristics than that of conventional planar FET, achieving record-high memory window (MW) of 13.9 V in a single HZO layer. When normalized to the actual channel width, FinFETs show an improved ION/IOFF ratio of 2.3x10^7 and a subthreshold swing value of 110 mV/dec. The enhanced characteristics are attributed to the low-interface state density (Dit), showing good interface properties between the beta-Ga2O3 and HZO layer. The enhanced polarization due to larger electric fields across the entire ferroelectric layer in FinFETs is validated using Sentaurus TCAD. After 5x10^6 program/erase (PGM/ERS) cycles, the MW was maintained at 9.2 V, and the retention time was measured up to 3x10^4 s with low degradation. Therefore, the ultrawide bandgap (UWBG) Fe-FinFET was shown to be one of the promising candidates for high-density non-volatile memory devices. △ Less

Submitted 25 July, 2024; originally announced July 2024.

Comments: 14 pages, 5 figures

The fractional quantum Hall nematics on the first Landau level in a tilted field

Authors: Dan Ye, Chen-Xin Jiang, Zi-Xiang Hu

Abstract: We investigated the behavior of fractional quantum Hall (FQH) states in a two-dimensional electron system with layer thickness and an in-plane magnetic field. Our comparisons across various filling factors within the first Landau level revealed a crucial observation. A slight in-plane magnetic field specifically enhances the nematic order of the $ν= 7/3$ FQH state. For this particular filling, thr… ▽ More We investigated the behavior of fractional quantum Hall (FQH) states in a two-dimensional electron system with layer thickness and an in-plane magnetic field. Our comparisons across various filling factors within the first Landau level revealed a crucial observation. A slight in-plane magnetic field specifically enhances the nematic order of the $ν= 7/3$ FQH state. For this particular filling, through calculating the energy gap, the Ising nematic order parameter, the pair-correlation function, and the static structure factor, we observed that as the in-plane magnetic field increases, the system first enters into an anisotropic FQH phase without closing the spectrum gap, then the FQH nematic (FQHN) phase after neutral gap closing. The system eventually enters a gapless one-dimensional charge density wave (CDW) phase for a large in-plane field. We thus provide a full phase diagram of the $ν= 7/3$ state in a tilted magnetic field, demonstrating the existence of the FQHN, which aligns with recent resonant inelastic light scattering (RILS) experimental observations. △ Less

Submitted 23 March, 2024; originally announced March 2024.

Comments: 9 pages, 11 figures

Hydrogen-induced tunable remanent polarization in a perovskite nickelate

Authors: Yifan Yuan, Michele Kotiuga, Tae Joon Park, Yuanyuan Ni, Arnob Saha, Hua Zhou, Jerzy T. Sadowski, Abdullah Al-Mahboob, Haoming Yu, Kai Du, Minning Zhu, Sunbin Deng, Ravindra S. Bisht, Xiao Lyu, Chung-Tse Michael Wu, Peide D. Ye, Abhronil Sengupta, Sang-Wook Cheong, Xiaoshan Xu, Karin M. Rabe, Shriram Ramanathan

Abstract: Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential ca… ▽ More Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential capacitance in thin film capacitors. The space-charge polarization caused by long-range movement and trapping of protons dominates when the electric field exceeds the threshold value. First-principles calculations suggest the polarization originates from the polar structure created by H doping. We find that polarization decays within ~1 second which is an interesting temporal regime for neuromorphic computing hardware design, and we implement the transient characteristics in a neural network to demonstrate unsupervised learning. These discoveries open new avenues for designing novel ferroelectric materials and electrets using light-ion doping. △ Less

Submitted 20 November, 2023; originally announced November 2023.

Comments: 13 pages, 5 figures

Tunable Circular Photogalvanic and Photovoltaic Effect in 2D Tellurium with Different Chirality

Authors: Chang Niu, Shouyuan Huang, Neil Ghosh, Pukun Tan, Mingyi Wang, Wenzhuo Wu, Xianfan Xu, Peide D. Ye

Abstract: Chirality arises from the asymmetry of matters, where two counterparts are the mirror image of each other. The interaction between circular-polarization light and quantum materials is enhanced in chiral space groups due to the structural chirality. Tellurium (Te) possesses the simplest chiral crystal structure, with Te atoms covalently bonded into a spiral atomic chain (left- or right-handed) with… ▽ More Chirality arises from the asymmetry of matters, where two counterparts are the mirror image of each other. The interaction between circular-polarization light and quantum materials is enhanced in chiral space groups due to the structural chirality. Tellurium (Te) possesses the simplest chiral crystal structure, with Te atoms covalently bonded into a spiral atomic chain (left- or right-handed) with a periodicity of three. Here, we investigate the tunable circular photo-electric responses in 2D Te field-effect transistor with different chirality, including the longitudinal circular photogalvanic effect induced by the radial spin texture (electron-spin polarization parallel to the electron momentum direction) and the circular photovoltaic induced by the chiral crystal structure (helical Te atomic chains). Our work demonstrates the controllable manipulation of the chirality degree of freedom in materials. △ Less

Submitted 12 September, 2023; originally announced September 2023.

Comments: 30 pages

Journal ref: Nano Letters 23, no. 8 (2023): 3599-3606

Quantum Algebra of Chern-Simons Matrix Model and Large $N$ Limit

Authors: Sen Hu, Si Li, Dongheng Ye, Yehao Zhou

Abstract: In this paper we study the algebra of quantum observables of the Chern-Simons matrix model which was originally proposed by Susskind and Polychronakos to describe electrons in fractional quantum Hall effects. We establish the commutation relations for its generators and study the large $N$ limit of its representation. We show that the large $N$ limit algebra is isomorphic to the uniform in $N$ alg… ▽ More In this paper we study the algebra of quantum observables of the Chern-Simons matrix model which was originally proposed by Susskind and Polychronakos to describe electrons in fractional quantum Hall effects. We establish the commutation relations for its generators and study the large $N$ limit of its representation. We show that the large $N$ limit algebra is isomorphic to the uniform in $N$ algebra studied by Costello, which is isomorphic to the deformed double current algebra studied by Guay. Under appropriate scaling limit, we show that the large $N$ limit algebra degenerates to a Lie algebra which admits a surjective map to the affine Lie algebra of $\mathfrak{u}(p)$. This leads to a complete proof of the large $N$ emergence of the $\mathfrak{u}(p)$ current algebra as proposed by Dorey, Tong and Turner. This also suggests a rigorous derivation of edge excitation of a fractional quantum Hall droplet. △ Less

Submitted 30 July, 2024; v1 submitted 27 August, 2023; originally announced August 2023.

Comments: 45+15 pages. Comments are welcome

MSC Class: 81T32; 81S08; 81V70; 81R60

Journal ref: Ann. Henri Poincaré (2025)

Discovery of Stable Hybrid Organic-inorganic Double Perovskites for High-performance Solar Cells via Machine-learning Algorithms and Crystal Graph Convolution Neural Network Method

Authors: Linkang Zhan, Danfeng Ye, Xinjian Qiu, Yan Cen

Abstract: Hybrid peroskite solar cells are newly emergent high-performance photovoltaic devices, which suffer from disadvantages such as toxic elements, short-term stabilities, and so on. Searching for alternative perovskites with high photovoltaic performances and thermally stabilities is urgent in this field. In this work, stimulated by the recently proposed materials-genome initiative project, firstly we… ▽ More Hybrid peroskite solar cells are newly emergent high-performance photovoltaic devices, which suffer from disadvantages such as toxic elements, short-term stabilities, and so on. Searching for alternative perovskites with high photovoltaic performances and thermally stabilities is urgent in this field. In this work, stimulated by the recently proposed materials-genome initiative project, firstly we build classical machine-learning algorithms for the models of formation energies, bangdaps and Deybe temperatures for hybrid organic-inorganic double perovskites, then we choose the high-precision models to screen a large scale of double-perovskite chemical space, to filter out good pervoskite candidates for solar cells. We also analyze features of importances for the the three target properties to reveal the underlying mechanisms and discover the typical characteristics of high-performances double perovskites. Secondly we adopt the Crystal graph convolution neural network (CGCNN), to build precise model for bandgaps of perovskites for further filtering. Finally we use the ab-initio method to verify the results predicted by the CGCNN method, and find that, six out of twenty randomly chosen (CH3)2NH2-based HOIDP candidates possess finite bandgaps, and especially, (CH3)2NH2AuSbCl6 and (CH3)2NH2CsPdF6 possess the bandgaps of 0.633 eV and 0.504 eV, which are appropriate for photovoltaic applications. Our work not only provides a large scale of potential high-performance double-perovskite candidates for futural experimental or theoretical verification, but also showcases the effective and powerful prediction of the combined ML and CGCNN method proposed for the first time here. △ Less

Submitted 1 August, 2023; originally announced August 2023.

Electrostatic moiré potential from twisted-hBN layers

Authors: Dong Seob Kim, Roy C. Dominguez, Rigo Mayorga-Luna, Dingyi Ye, Jacob Embley, Tixuan Tan, Yue Ni, Zhida Liu, Mitchell Ford, Frank Y. Gao, Saba Arash, Kenji Watanabe, Takashi Taniguchi, Suenne Kim, Chih-Kang Shih, Keji Lai, Wang Yao, Li Yang, Xiaoqin Li, Yoichi Miyahara

Abstract: Moiré superlattices formed by vertically stacking van der Waals layers host a rich variety of correlated electronic phases and function as novel photonic materials. The moiré potential of the superlattice, however, is fixed by the interlayer coupling of the stacked functional layers (e.g. graphene) and dependent on carrier types (e.g. electrons or holes) and valleys (e.g. Γ vs. K). In contrast, tw… ▽ More Moiré superlattices formed by vertically stacking van der Waals layers host a rich variety of correlated electronic phases and function as novel photonic materials. The moiré potential of the superlattice, however, is fixed by the interlayer coupling of the stacked functional layers (e.g. graphene) and dependent on carrier types (e.g. electrons or holes) and valleys (e.g. Γ vs. K). In contrast, twisted hexagonal boron nitride (hBN) layers are predicted to impose a periodic electrostatic potential that may be used to engineer the properties of an adjacent functional thin layer. Here, we show that this potential is described by a simple theory of electric polarization originating from the interfacial charge redistribution, validated by its dependence on supercell sizes and distance from the twisted interfaces. We demonstrate that the potential depth and profile can be further controlled by assembling a double moiré structure. When the twist angles are similar at the two interfaces, the potential is deepened by adding the potential from the two twisted interfaces, reaching ~ 400 meV. When the twist angles are dissimilar at the two interfaces, multi-level polarization states are observed. As an example of controlling a functional layer, we demonstrate how the electrostatic potential from a twisted hBN substrate impedes exciton diffusion in a semiconductor monolayer. These findings suggest exciting opportunities for engineering properties of an adjacent functional layer using the surface potential of a twisted hBN substrate. △ Less

Submitted 13 June, 2023; originally announced June 2023.

Self-doping effect in confined copper selenide semiconducting quantum dots for efficient photoelectrocatalytic oxygen evolution

Authors: Jie Ren, Chenya Zhao, Lanshan He, Congcong Wu, Wenting Jia, Shengwen Xu, Daojian Ye, Weiyang Xu, Fujin Huang, Hang Zhou, Chengwu Zou, Ce Hu, Ting Yu, Xingfang Luo, Cailei Yuan

Abstract: Self-doping can not only suppress the photogenerated charge recombination of semiconducting quantum dots by self-introducing trapping states within the bandgap, but also provide high-density catalytic active sites as the consequence of abundant non-saturated bonds associated with the defects. Here, we successfully prepared semiconducting copper selenide (CuSe) confined quantum dots with abundant v… ▽ More Self-doping can not only suppress the photogenerated charge recombination of semiconducting quantum dots by self-introducing trapping states within the bandgap, but also provide high-density catalytic active sites as the consequence of abundant non-saturated bonds associated with the defects. Here, we successfully prepared semiconducting copper selenide (CuSe) confined quantum dots with abundant vacancies and systematically investigated their photoelectrochemical characteristics. Photoluminescence characterizations reveal that the presence of vacancies reduces the emission intensity dramatically, indicating a low recombination rate of photogenerated charge carriers due to the self-introduced trapping states within the bandgap. In addition, the ultra-low charge transfer resistance measured by electrochemical impedance spectroscopy implies the efficient charge transfer of CuSe semiconducting quantum dots-based photoelectrocatalysts, which is guaranteed by the high conductivity of their confined structure as revealed by room-temperature electrical transport measurements. Such high conductivity and low photogenerated charge carriers recombination rate, combined with high-density active sites and confined structure, guaranteeing the remarkable photoelectrocatalytic performance and stability as manifested by photoelectrocatalysis characterizations. This work promotes the development of semiconducting quantum dots-based photoelectrocatalysis and demonstrates CuSe semiconducting quantum confined catalysts as an advanced photoelectrocatalysts for oxygen evolution reaction. △ Less

Submitted 13 April, 2023; originally announced April 2023.

The entanglement entropy of the quantum Hall edge and its geometric contribution

Authors: Dan Ye, Yi Yang, Qi Li, Zi-Xiang Hu

Abstract: Generally speaking, the entanglement entropy (EE) between two subregions of a gapped quantum many-body state is proportional to the area/length of their interface due to the short range quantum correlation. However, the so-called area law is violated logarithmically in a quantum critical phase. Moreover, the subleading correction exists in a long range entangled topological phases. It is referred… ▽ More Generally speaking, the entanglement entropy (EE) between two subregions of a gapped quantum many-body state is proportional to the area/length of their interface due to the short range quantum correlation. However, the so-called area law is violated logarithmically in a quantum critical phase. Moreover, the subleading correction exists in a long range entangled topological phases. It is referred to as topological EE which is related to the quantum dimension of the collective excitation in the bulk. Further more, if a non-smooth sharp angle is in the presence of the subsystem boundary, a universal angle dependent geometric contribution is expected to appear in the subleading correction. In this work, we simultaneously explore the geometric and edge contribution in the integer quantum Hall (IQH) state and its edge reconstruction in a unified bipartite method. Their scaling is found to be consistent with the conformal field theory (CFT) predictions and recent results of the particle number fluctuation calculations. △ Less

Submitted 18 December, 2022; originally announced December 2022.

Comments: 7 pages, 10 figures

Journal ref: Frontiers in Physics 10, 971423 (2022)

A Gate-All-Around Single-Channel In2O3 Nanoribbon FET with Near 20 mA/μm Drain Current

Authors: Zhuocheng Zhang, Zehao Lin, Pai-Ying Liao, Vahid Askarpour, Hongyi Dou, Zhongxia Shang, Adam Charnas, Mengwei Si, Sami Alajlouni, Jinhyun Noh, Ali Shakouri, Haiyan Wang, Mark Lundstrom, Jesse Maassen, Peide D. Ye

Abstract: In this work, we demonstrate atomic-layer-deposited (ALD) single-channel indium oxide (In2O3) gate-all-around (GAA) nanoribbon FETs in a back-end-of-line (BEOL) compatible process. A maximum on-state current (ION) of 19.3 mA/μm (near 20 mA/μm) is achieved in an In2O3 GAA nanoribbon FET with a channel thickness (TIO) of 3.1 nm, channel length (Lch) of 40 nm, channel width (Wch) of 30 nm and dielect… ▽ More In this work, we demonstrate atomic-layer-deposited (ALD) single-channel indium oxide (In2O3) gate-all-around (GAA) nanoribbon FETs in a back-end-of-line (BEOL) compatible process. A maximum on-state current (ION) of 19.3 mA/μm (near 20 mA/μm) is achieved in an In2O3 GAA nanoribbon FET with a channel thickness (TIO) of 3.1 nm, channel length (Lch) of 40 nm, channel width (Wch) of 30 nm and dielectric HfO2 of 5 nm. The record high drain current obtained from an In2O3 FET is about one order of magnitude higher than any conventional single-channel semiconductor FETs. This extraordinary drain current and its related on-state performance demonstrate ALD In2O3 is a promising oxide semiconductor channel with great opportunities in BEOL compatible monolithic 3D integration. △ Less

Submitted 30 April, 2022; originally announced May 2022.

A Nanometer-Thick Oxide Semiconductor Transistor with Ultra-High Drain Current

Authors: Zehao Lin, Mengwei Si, Vahid Askarpour, Chang Niu, Adam Charnas, Zhongxia Shang, Yizhi Zhang, Yaoqiao Hu, Zhuocheng Zhang, Pai-Ying Liao, Kyeongjae Cho, Haiyan Wang, Mark Lundstrom, Jesse Maassen, Peide D. Ye

Abstract: High drive current is a critical performance parameter in semiconductor devices for high-speed, low-power logic applications or high-efficiency, high-power, high-speed radio frequency (RF) analog applications. In this work, we demonstrate an In2O3 transistor grown by atomic layer deposition (ALD) at back-end-of-line (BEOL) compatible temperatures with a record high drain current exceeding 10 A/mm,… ▽ More High drive current is a critical performance parameter in semiconductor devices for high-speed, low-power logic applications or high-efficiency, high-power, high-speed radio frequency (RF) analog applications. In this work, we demonstrate an In2O3 transistor grown by atomic layer deposition (ALD) at back-end-of-line (BEOL) compatible temperatures with a record high drain current exceeding 10 A/mm, the performance of which is 2-3 times better than all known transistors with semiconductor channels. A record high transconductance of 4 S/mm is also achieved among all transistors with a planar structure. It is found that a high carrier density and high electron velocity both contribute to this remarkably high on-state performance in ALD In2O3 transistors, which is made possible by the high-quality oxide/oxide interface, the metal-like charge-neutrality-level (CNL) alignment, and the high band velocities induced by the low density-of-state (DOS). Experimental Hall, I-V and split C-V measurements at room temperature confirm a high carrier density up to 6-7*10^13 /cm2 and a high velocity of about 10^7 cm/s. Ultra-thin oxide semiconductors, with a CNL located deep inside the conduction band, represent a promising new direction for the search of alternative channel materials for high-performance semiconductor devices. △ Less

Submitted 30 April, 2022; originally announced May 2022.

Scaled indium oxide transistors fabricated using atomic layer deposition

Authors: Mengwei Si, Zehao Lin, Zhizhong Chen, Xing Sun, Haiyan Wang, Peide D. Ye

Abstract: In order to continue to improve integrated circuit performance and functionality, scaled transistors with short channel lengths and low thickness are needed. But the further scaling of silicon-based devices and the development of alternative semiconductor channel materials that are compatible with current fabrication processes is challenging. Here we report atomic-layer-deposited indium oxide tran… ▽ More In order to continue to improve integrated circuit performance and functionality, scaled transistors with short channel lengths and low thickness are needed. But the further scaling of silicon-based devices and the development of alternative semiconductor channel materials that are compatible with current fabrication processes is challenging. Here we report atomic-layer-deposited indium oxide transistors with channel lengths down to 8 nm, channel thicknesses down to 0.5 nm and equivalent dielectric oxide thickness down to 0.84 nm. Due to the scaled device dimensions and low contact resistance, the devices exhibit high on-state currents of 3.1 A/mm at a drain voltage of 0.5 V and a transconductance of 1.5 S/mm at a drain voltage 1 V. Our devices are a promising alternative channel material for scaled transistors with back-end-of-line processing compatibility. △ Less

Submitted 5 March, 2022; originally announced March 2022.

Comments: 30 pages, 9 figures. Nat Electron (2022)

Anyonic braiding via quench dynamics in fractional quantum Hall liquids

Authors: Jie Li, Dan Ye, Chen-Xin Jiang, Na Jiang, Xin Wan, Zi-Xiang Hu

Abstract: In a Laughlin fractional quantum Hall state, one- and two-quasihole states can be obtained by diagonalizing the many-body Hamiltonian with a trapping potential or, for larger systems, from the linear combination of the edge Jack polynomials. The quasihole states live entirely in the subspace of the lowest-energy branch in the energy spectrum with a fixed number of orbits, or a hard-wall confinemen… ▽ More In a Laughlin fractional quantum Hall state, one- and two-quasihole states can be obtained by diagonalizing the many-body Hamiltonian with a trapping potential or, for larger systems, from the linear combination of the edge Jack polynomials. The quasihole states live entirely in the subspace of the lowest-energy branch in the energy spectrum with a fixed number of orbits, or a hard-wall confinement. The reduction in the Hilbert space dimension facilitates the study of time evolution of the quasihole states after, say, the removal of the trapping potential. We explore the quench dynamics under a harmonic external potential, which rotates the quasiholes in the droplet, and discuss the effect of long-range interaction and more realistic confinement. Accurate evaluation of the mutual statistics phase of anyons for a wide range of anyon separation can be achieved from the Berry-phase calculation. △ Less

Submitted 21 February, 2022; originally announced February 2022.

Comments: 9 pages, 9 figures

Tunable Chirality-dependent Nonlinear Electrical Responses in 2D Tellurium

Authors: Chang Niu, Gang Qiu, Yixiu Wang, Pukun Tan, Mingyi Wang, Jie Jian, Haiyan Wang, Wenzhuo Wu, Peide D. Ye

Abstract: Tellurium (Te) is an elemental semiconductor with a simple chiral crystal structure. Te in a two-dimensional (2D) form synthesized by solution-based method shows excellent electrical, optical, and thermal properties. In this work, the chirality of hydrothermally grown 2D Te is identified and analyzed by hot sulfuric acid etching and high-angle tilted high-resolution scanning transmission electron… ▽ More Tellurium (Te) is an elemental semiconductor with a simple chiral crystal structure. Te in a two-dimensional (2D) form synthesized by solution-based method shows excellent electrical, optical, and thermal properties. In this work, the chirality of hydrothermally grown 2D Te is identified and analyzed by hot sulfuric acid etching and high-angle tilted high-resolution scanning transmission electron microscopy. The gate-tunable nonlinear electrical responses, including the nonreciprocal electrical transport in the longitudinal direction and the nonlinear planar Hall effect in the transverse direction, are observed in 2D Te under a magnetic field. Moreover, the nonlinear electrical responses have opposite signs in left- and right-handed 2D Te due to the opposite spin polarizations ensured by the chiral symmetry. The fundamental relationship between the spin-orbit coupling and the crystal symmetry in two enantiomers provides a viable platform for realizing chirality-based electronic devices by introducing the chirality degree of freedom into electron transport. △ Less

Submitted 12 September, 2023; v1 submitted 21 January, 2022; originally announced January 2022.

Comments: 44 pages, Nano Letters (2023)

DyOCl: a rare-earth based two-dimensional van der Waals material with strong magnetic anisotropy

Authors: Congkuan Tian, Feihao Pan, Dehua Ye, Jieming Sheng, Jinchen Wang, Juanjuan Liu, Jiale Huang, Hongxia Zhang, Daye Xu, Jianfei Qin, Lijie Hao, Yuanhua Xia, Hao Li, Xin Tong, Liusuo Wu, Jian-Hao Chen, Shuang Jia, Peng Cheng, Jianhui Yang, Youqu Zheng

Abstract: Comparing with the widely known transitional metal based van der Waals (vdW) materials, rare-earth based ones are rarely explored in the research of intrinsic two-dimensional (2D) magnetism. In this work, we report the physical properties of DyOCl, a rare-earth based vdW magnetic insulator with direct band gap of $\sim 5.72~eV$. The magnetic order of bulk DyOCl is determined by neutron scattering… ▽ More Comparing with the widely known transitional metal based van der Waals (vdW) materials, rare-earth based ones are rarely explored in the research of intrinsic two-dimensional (2D) magnetism. In this work, we report the physical properties of DyOCl, a rare-earth based vdW magnetic insulator with direct band gap of $\sim 5.72~eV$. The magnetic order of bulk DyOCl is determined by neutron scattering as the $A$-type antiferromagnetic structure below the Néel temperature $T_N=10~$K. The large magnetic moment near 10.1 $ μ_{B} $/Dy lies parallel to the $a$-axis with strong uniaxial magnetic anisotropy. At $2~K$, a moderate magnetic field ($\sim 2~T$) applied along the easy axis generates spin-flip transitions and polarizes DyOCl to a ferromagnetic state. Density functional theory calculations reveal an extremely large magnetic anisotropy energy ($-5850~μeV/Dy$) for DyOCl, indicating the great potentials to realize magnetism in 2D limit. Furthermore, the mechanical exfoliation of bulk DyOCl single crystals down to seven layers is demonstrated. Our findings suggest DyOCl is a promising material playground to investigate 2D $f$-electron magnetism and spintronic applications at the nanoscale. △ Less

Submitted 23 December, 2021; originally announced December 2021.

Journal ref: Physical Review B 104.21 (2021): 214410

Ionic control over ferroelectricity in 2D layered van der Waals capacitors

Authors: Sabine M. Neumayer, Mengwei Si, Junkang Li, Pai-Ying Liao, Lei Tao, Andrew O'Hara, Sokrates T. Pantelides, Peide D. Ye, Petro Maksymovych, Nina Balke

Abstract: The van der Waals layered material CuInP2S6 features interesting functional behavior, including the existence of four uniaxial polarization states, polarization reversal against the electric field through Cu ion migration, a negative-capacitance regime, and reversible extraction of Cu ions. At the heart of these characteristics lies the high mobility of Cu ions, which also determines the spontaneo… ▽ More The van der Waals layered material CuInP2S6 features interesting functional behavior, including the existence of four uniaxial polarization states, polarization reversal against the electric field through Cu ion migration, a negative-capacitance regime, and reversible extraction of Cu ions. At the heart of these characteristics lies the high mobility of Cu ions, which also determines the spontaneous polarization. Therefore, Cu migration across the lattice results in unusual ferroelectric behavior. Here, we demonstrate how the interplay of polar and ionic properties provides a path to ionically controlled ferroelectric behavior, achieved by applying selected DC voltage pulses and subsequently probing ferroelectric switching during fast triangular voltage sweeps. Using current measurements and theoretical calculations, we observe that increasing DC pulse duration results in higher ionic currents, the build-up of an internal electric field that shifts polarization loops, and an increase in total switchable polarization by ~50% due to the existence of a high polarization phase which is stabilized by the internal electric field. Apart from tuning ferroelectric behavior by selected square pulses, hysteretic polarization switching can even be entirely deactivated and reactivated, resulting in three-state systems where polarization switching is either inhibited or can be performed in two different directions. △ Less

Submitted 19 January, 2022; v1 submitted 27 September, 2021; originally announced September 2021.

Journal ref: ACS Appl. Mater. Interfaces 2022, 14, 2, 3018-3026

Bilayer Quantum Hall States in an n-type Wide Tellurium Quantum Well

Authors: Chang Niu, Gang Qiu, Yixiu Wang, Mengwei Si, Wenzhuo Wu, Peide D. Ye

Abstract: Tellurium (Te) is a narrow bandgap semiconductor with a unique chiral crystal structure. The topological nature of electrons in the Te conduction band can be studied by realizing n-type doping using atomic layer deposition (ALD) technique on two-dimensional (2D) Te film. In this work, we fabricated and measured the double-gated n-type Te Hall-bar devices, which can operate as two separate or coupl… ▽ More Tellurium (Te) is a narrow bandgap semiconductor with a unique chiral crystal structure. The topological nature of electrons in the Te conduction band can be studied by realizing n-type doping using atomic layer deposition (ALD) technique on two-dimensional (2D) Te film. In this work, we fabricated and measured the double-gated n-type Te Hall-bar devices, which can operate as two separate or coupled electron layers controlled by the top gate and back gate. Profound Shubnikov-de Haas (SdH) oscillations are observed in both top and bottom electron layers. Landau level hybridization between two layers, compound and charge-transferable bilayer quantum Hall states at filling factor 4, 6, and 8 are analyzed. Our work opens the door for the study of Weyl physics in coupled bilayer systems of 2D materials. △ Less

Submitted 18 July, 2021; originally announced July 2021.

Comments: Submitted to Nano Letters

The Critical Role of Charge Balance on the Memory Characteristics of Ferroelectric Field-Effect Transistors

Authors: Mengwei Si, Peide D. Ye

Abstract: Ferroelectric field-effect transistors (Fe-FETs) with ferroelectric hafnium oxide (FE HfO2) as gate insulator are being extensively explored as a promising device candidate for three-dimensional (3D) NAND memory application. FE HfO2 exhibits long retention over 10 years, high endurance over 1012 cycles, high speed with sub-ns polarization switching, and high remnant polarization of 10-30 μC/cm2. H… ▽ More Ferroelectric field-effect transistors (Fe-FETs) with ferroelectric hafnium oxide (FE HfO2) as gate insulator are being extensively explored as a promising device candidate for three-dimensional (3D) NAND memory application. FE HfO2 exhibits long retention over 10 years, high endurance over 1012 cycles, high speed with sub-ns polarization switching, and high remnant polarization of 10-30 μC/cm2. However, the performance of Fe-FETs is known to be much worse than FE HfO2 capacitors, which is not completely understood. In this work, we developed a comprehensive Fe-FET model based on a charge balance framework. The role of charge balance and the impact of leakage-assist-switching mechanism on the memory characteristics of Fe-FETs with M/FE/DE/S (Metal/Ferroelectric/Dielectric/Semiconductor) gate stack is studied. It is found that the FE/DE interface and DE layer instead of FE layer is critical to determine the memory characteristics of Fe-FETs, and experimental Fe-FETs can be well explained by this model, where the discrepancy between FE capacitors and Fe-FETs are successfully understood. △ Less

Submitted 26 May, 2021; originally announced May 2021.

Comments: 6 pages, 3 figures, IEEE TED under review

Thermoelectric Hall conductivity of the fractional quantum Hall systems on a disk

Authors: Zi-Yi Fang, Dan Ye, Yu-Yu Zhang, Zi-Xiang Hu

Abstract: For the fractional quantum Hall states on a finite disc, we study the thermoelectric transport properties under the influence of an edge and its reconstruction. In a recent study on a torus [Phys. Rev. B 101, 241101 (2020)], Sheng and Fu found a universal non-Fermi liquid power-law scaling of the thermoelectric conductivity $α_{xy} \propto T^η$ for the gapless composite Fermi-liquid state. The exp… ▽ More For the fractional quantum Hall states on a finite disc, we study the thermoelectric transport properties under the influence of an edge and its reconstruction. In a recent study on a torus [Phys. Rev. B 101, 241101 (2020)], Sheng and Fu found a universal non-Fermi liquid power-law scaling of the thermoelectric conductivity $α_{xy} \propto T^η$ for the gapless composite Fermi-liquid state. The exponent $η\sim 0.5$ appears an independence of the filling factors and the details of the interactions. In the presence of an edge, we find the properties of the edge spectrum dominants the low-temperature behaviors and breaks the universal scaling law of the thermoelectric conductivity. In order to consider individually the effects of the edge states, the entanglement spectrum in real space is employed and tuned by varying the area of subsystem. In non-Abelian Moore-Read state, the Majorana neutral edge mode is found to have more significant effect than that of the charge mode in the low temperature. △ Less

Submitted 1 February, 2021; originally announced February 2021.

Comments: 6 pages, 5 figures

Journal ref: Phys. Rev. B 103, 235161 (2021)

Why In2O3 Can Make 0.7 nm Atomic Layer Thin Transistors?

Authors: Mengwei Si, Yaoqiao Hu, Zehao Lin, Xing Sun, Adam Charnas, Dongqi Zheng, Xiao Lyu, Haiyan Wang, Kyeongjae Cho, Peide D. Ye

Abstract: In this work, we demonstrate enhancement-mode field-effect transistors by atomic-layer-deposited (ALD) amorphous In2O3 channel with thickness down to 0.7 nm. Thickness is found to be critical on the materials and electron transport of In2O3. Controllable thickness of In2O3 at atomic scale enables the design of sufficient 2D carrier density in the In2O3 channel integrated with the conventional diel… ▽ More In this work, we demonstrate enhancement-mode field-effect transistors by atomic-layer-deposited (ALD) amorphous In2O3 channel with thickness down to 0.7 nm. Thickness is found to be critical on the materials and electron transport of In2O3. Controllable thickness of In2O3 at atomic scale enables the design of sufficient 2D carrier density in the In2O3 channel integrated with the conventional dielectric. The threshold voltage and channel carrier density are found to be considerably tuned by channel thickness. Such phenomenon is understood by the trap neutral level (TNL) model where the Fermi-level tends to align deeply inside the conduction band of In2O3 and can be modulated to the bandgap in atomic layer thin In2O3 due to quantum confinement effect, which is confirmed by density function theory (DFT) calculation. The demonstration of enhancement-mode amorphous In2O3 transistors suggests In2O3 is a competitive channel material for back-end-of-line (BEOL) compatible transistors and monolithic 3D integration applications. △ Less

Submitted 22 December, 2020; originally announced December 2020.

Comments: 21 pages, 8 figures

Scaled Atomic-Layer-Deposited Indium Oxide Nanometer Transistors with Maximum Drain Current Exceeding 2 A/mm at Drain Voltage of 0.7 V

Authors: Mengwei Si, Zehao Lin, Adam Charnas, Peide D. Ye

Abstract: In this work, we demonstrate scaled back-end-of-line (BEOL) compatible indium oxide (In2O3) transistors by atomic layer deposition (ALD) with channel thickness (Tch) of 1.0-1.5 nm, channel length (Lch) down to 40 nm, and equivalent oxide thickness (EOT) of 2.1 nm, with record high drain current of 2.0 A/mm at VDS of 0.7 V among all oxide semiconductors. Enhancement-mode In2O3 transistors with ID o… ▽ More In this work, we demonstrate scaled back-end-of-line (BEOL) compatible indium oxide (In2O3) transistors by atomic layer deposition (ALD) with channel thickness (Tch) of 1.0-1.5 nm, channel length (Lch) down to 40 nm, and equivalent oxide thickness (EOT) of 2.1 nm, with record high drain current of 2.0 A/mm at VDS of 0.7 V among all oxide semiconductors. Enhancement-mode In2O3 transistors with ID over 1.0 A/mm at VDS of 1 V are also achieved by controlling the channel thickness down to 1.0 nm at atomic layer scale. Such high current density in a relatively low mobility amorphous oxide semiconductor is understood by the formation of high density 2D channel beyond 4E13 /cm2 at HfO2/In2O3 oxide/oxide interface. △ Less

Submitted 8 December, 2020; originally announced December 2020.

Comments: 14 pages, 6 figures, to be published in IEEE Electron Device Letters

Indium-Tin-Oxide Transistors with One Nanometer Thick Channel and Ferroelectric Gating

Authors: Mengwei Si, Joseph Andler, Xiao Lyu, Chang Niu, Suman Datta, Rakesh Agrawal, Peide D. Ye

Abstract: In this work, we demonstrate high performance indium-tin-oxide (ITO) transistors with the channel thickness down to 1 nm and ferroelectric Hf0.5Zr0.5O2 as gate dielectric. On-current of 0.243 A/mm is achieved on sub-micron gate-length ITO transistors with a channel thickness of 1 nm, while it increases to as high as 1.06 A/mm when the channel thickness increases to 2 nm. A raised source/drain stru… ▽ More In this work, we demonstrate high performance indium-tin-oxide (ITO) transistors with the channel thickness down to 1 nm and ferroelectric Hf0.5Zr0.5O2 as gate dielectric. On-current of 0.243 A/mm is achieved on sub-micron gate-length ITO transistors with a channel thickness of 1 nm, while it increases to as high as 1.06 A/mm when the channel thickness increases to 2 nm. A raised source/drain structure with a thickness of 10 nm is employed, contributing to a low contact resistance of 0.15 Ωmm and a low contact resistivity of 1.1{\times}10-7 Ωcm2. The ITO transistor with a recessed channel and ferroelectric gating demonstrates several advantages over 2D semiconductor transistors and other thin film transistors, including large-area wafer-size nanometer thin film formation, low contact resistance and contact resistivity, atomic thin channel being immunity to short channel effects, large gate modulation of high carrier density by ferroelectric gating, high-quality gate dielectric and passivation formation, and a large bandgap for the low-power back-end-of-line (BEOL) CMOS application. △ Less

Submitted 22 August, 2020; originally announced August 2020.

Comments: 32 pages, 16 figures. To be published in ACS Nano

Journal ref: ACS Nano 2020, 14, 9, 11542-11547

Raman Response and Transport Properties of One-Dimensional van der Waals Tellurium Nanowires

Authors: Jing-Kai Qin, Pai-Ying Liao, Mengwei Si, Shiyuan Gao, Gang Qiu, Jie Jian, Qingxiao Wang, Si-Qi Zhang, Shouyuan Huang, Adam Charnas, Yixiu Wang, Moon J. Kim, Wenzhuo Wu, Xianfan Xu, Hai-Yan Wang, Li Yang, Yoke Khin Yap, Peide D. Ye

Abstract: Tellurium can form nanowires of helical atomic chains. Given their unique one-dimensional van der Waals structure, these nanowires are expected to show remarkably different physical and electronic properties than bulk tellurium. Here we show that few-chain and single-chain van der Waals tellurium nanowires can be isolated using carbon nanotube and boron nitride nanotube encapsulation. With the app… ▽ More Tellurium can form nanowires of helical atomic chains. Given their unique one-dimensional van der Waals structure, these nanowires are expected to show remarkably different physical and electronic properties than bulk tellurium. Here we show that few-chain and single-chain van der Waals tellurium nanowires can be isolated using carbon nanotube and boron nitride nanotube encapsulation. With the approach, the number of atomic chains can be controlled by the inner diameter of the nanotube. The Raman response of the structures suggests that the interaction between a single-atomic tellurium chain and a carbon nanotube is weak, and that the inter-chain interaction becomes stronger as the number of chains increases. Compared with bare tellurium nanowires on SiO2, nanowires encapsulated in boron nitride nanotubes exhibit a dramatically enhanced current-carrying capacity, with a current density of 1.5*10^8 A cm-2, which exceeds that of most semiconducting nanowires. We also use our tellurium nanowires encapsulated in boron nitride nanotubes to create field-effect transistors that have a diameter of only 2 nm. △ Less

Submitted 15 January, 2020; originally announced January 2020.

Comments: 45 pages, 23 figures. Nature Electronics, to be published

Ultrafast Photoinduced Band Splitting and Carrier Dynamics in Chiral Tellurium Nanosheets

Authors: Giriraj Jnawali, Yuan Xiang, Samuel M. Linser, Iraj Abbasian Shojaei, Ruoxing Wang, Gang Qiu, Chao Lian, Bryan M. Wong, Wu Wenzhuo, Peide D. Ye, Yongsheng Leng, Howard E. Jackson, Leigh M. Smith

Abstract: Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and inversion symmetries, resulting in complex band structures with Weyl crossings and unique spin textures. Detailed time-resolved polarized reflectance spectroscopy is used to investigate its band structure and carrier dynamics. The polarized transient spectra reveal optical transitions between the uppermost spin-split H4 a… ▽ More Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and inversion symmetries, resulting in complex band structures with Weyl crossings and unique spin textures. Detailed time-resolved polarized reflectance spectroscopy is used to investigate its band structure and carrier dynamics. The polarized transient spectra reveal optical transitions between the uppermost spin-split H4 and H5 and the degenerate H6 valence bands (VB) and the lowest degenerate H6 conduction band (CB) as well as a higher energy transition at the L-point. Surprisingly, the degeneracy of the H6 CB (a proposed Weyl node) is lifted and the spin-split VB gap is reduced upon photoexcitation before relaxing to equilibrium as the carriers decay. Using ab initio density functional theory (DFT) calculations we conclude that the dynamic band structure is caused by a photoinduced shear strain in the Te film that breaks the screw symmetry of the crystal. The band-edge anisotropy is also reflected in the hot carrier decay rate, which is a factor of two slower along c-axis than perpendicular to it. The majority of photoexcited carriers near the band-edge are seen to recombine within 30 ps while higher lying transitions observed near 1.2 eV appear to have substantially longer lifetimes, potentially due to contributions of intervalley processes in the recombination rate. These new findings shed light on the strong correlation between photoinduced carriers and electronic structure in anisotropic crystals, which opens a potential pathway for designing novel Te-based devices that take advantage of the topological structures as well as strong spin-related properties. △ Less

Submitted 20 July, 2020; v1 submitted 22 October, 2019; originally announced October 2019.

Comments: 42 pages, 13 figures

Gate-tunable Strong Spin-orbit Interaction in Two-dimensional Tellurium Probed by Weak-antilocalization

Authors: Chang Niu, Gang Qiu, Yixiu Wang, Zhuocheng Zhang, Mengwei Si, Wenzhuo Wu, Peide D. Ye

Abstract: Tellurium (Te) has attracted great research interest due to its unique crystal structure since 1970s. However, the conduction band of Te is rarely studied experimentally because of the intrinsic p-type nature of Te crystal. By atomic layer deposited dielectric doping technique, we are able to access the conduction band transport properties of Te in a controlled fashion. In this paper, we report on… ▽ More Tellurium (Te) has attracted great research interest due to its unique crystal structure since 1970s. However, the conduction band of Te is rarely studied experimentally because of the intrinsic p-type nature of Te crystal. By atomic layer deposited dielectric doping technique, we are able to access the conduction band transport properties of Te in a controlled fashion. In this paper, we report on a systematic study of weak-antilocalization (WAL) effect in n-type two-dimensional (2D) Te films. We find that the WAL agrees well with Iordanskii, Lyanda-Geller, and Pikus (ILP) theory. The gate and temperature dependent WAL reveals that Dyakonov-Perel (DP) mechanism is dominant for spin relaxation and phase relaxation is governed by electron-electron (e-e) interaction. Large phase coherence length near 600nm at T=1K is obtained, together with gate tunable spin-orbit interaction (SOI). Transition from weak-localization (WL) to weak-antilocalization (WAL) depending on gate bias is also observed. These results demonstrate that newly developed solution-based synthesized Te films provide a new controllable strong SOI 2D semiconductor with high potential for spintronic applications. △ Less

Submitted 14 September, 2019; originally announced September 2019.

Journal ref: Phys. Rev. B 101, 205414 (2020)

Quantum Hall Effect of Weyl Fermions in Semiconducting n-type Tellurene

Authors: Gang Qiu, Chang Niu, Yixiu Wang, Mengwei Si, Zhuocheng Zhang, Wenzhuo Wu, Peide D. Ye

Abstract: Dirac and Weyl nodal materials can host low-energy relativistic quasiparticles. Under strong magnetic fields, the topological properties of Dirac/Weyl materials can directly manifest through quantum Hall states. However, most Dirac/Weyl nodes generically exist in semimetals without exploitable bandgaps due to their accidental band-crossing origin. Here we report the first experimental observation… ▽ More Dirac and Weyl nodal materials can host low-energy relativistic quasiparticles. Under strong magnetic fields, the topological properties of Dirac/Weyl materials can directly manifest through quantum Hall states. However, most Dirac/Weyl nodes generically exist in semimetals without exploitable bandgaps due to their accidental band-crossing origin. Here we report the first experimental observation of Weyl fermions in a semiconductor. Tellurene, the 2D form of tellurium, possesses chiral crystal structure which induces unconventional Weyl nodes with a hedgehog-like radial spin texture near the conduction band edge. We synthesize high-quality n-type tellurene by a hydrothermal method with subsequent dielectric doping and detect a topologically non-trivial pi Berry phase in quantum Hall sequences. Our work expands the spectrum of Weyl matter into semiconductors and offers a new platform to design novel quantum devices by marrying the advantages of topological materials to versatile semiconductors. △ Less

Submitted 26 April, 2020; v1 submitted 29 August, 2019; originally announced August 2019.

Comments: 5 figures for main text; 8 figures for supporting information

A Critical Review of Recent Progress on Negative Capacitance Field-Effect Transistors

Authors: Muhammad A. Alam, Mengwei Si, Peide D. Ye

Abstract: The elegant simplicity of the device concept and the urgent need for a new "transistor" at the twilight of Moore's law have inspired many researchers in industry and academia to explore the physics and technology of negative capacitance field effect transistor (NC-FET). Although hundreds of papers have been published, the validity of quasi-static NC and the frequency-reliability limits of NC-FET a… ▽ More The elegant simplicity of the device concept and the urgent need for a new "transistor" at the twilight of Moore's law have inspired many researchers in industry and academia to explore the physics and technology of negative capacitance field effect transistor (NC-FET). Although hundreds of papers have been published, the validity of quasi-static NC and the frequency-reliability limits of NC-FET are still being debated. The concept of NC - if conclusively demonstrated - will have broad impacts on device physics and technology development. Here, the authors provide a critical review of recent progress on NC-FETs research and some starting points for a coherent discussion. △ Less

Submitted 9 March, 2019; originally announced March 2019.

Comments: 19 pages, 2 figures

Journal ref: Appl. Phys. Lett. 114, 090401 (2019), Guest Editorial

Room Temperature Electrocaloric Effect in Layered Ferroelectric CuInP2S6 for Solid State Refrigeration

Authors: Mengwei Si, Atanu K. Saha, Pai-Ying Liao, Shengjie Gao, Sabine M. Neumayer, Jie Jian, Jingkai Qin, Nina Balke, Haiyan Wang, Petro Maksymovych, Wenzhuo Wu, Sumeet K. Gupta, Peide D. Ye

Abstract: A material with reversible temperature change capability under an external electric field, known as the electrocaloric effect (ECE), has long been considered as a promising solid-state cooling solution. However, electrocaloric (EC) performance of EC materials generally is not sufficiently high for real cooling applications. As a result, exploring EC materials with high performance is of great inte… ▽ More A material with reversible temperature change capability under an external electric field, known as the electrocaloric effect (ECE), has long been considered as a promising solid-state cooling solution. However, electrocaloric (EC) performance of EC materials generally is not sufficiently high for real cooling applications. As a result, exploring EC materials with high performance is of great interest and importance. Here, we report on the ECE of ferroelectric materials with van der Waals layered structure (CuInP2S6 or CIPS in this work in particular). Over 60% polarization charge change is observed within a temperature change of only 10 K at Curie temperature. Large adiabatic temperature change (|ΔT|) of 3.3 K, isothermal entropy change (|ΔS|) of 5.8 J kg-1 K-1 at |ΔE|=142.0 kV cm-1 at 315 K (above and near room temperature) are achieved, with a large EC strength (|ΔT|/|ΔE|) of 29.5 mK cm kV-1. The ECE of CIPS is also investigated theoretically by numerical simulation and a further EC performance projection is provided. △ Less

Submitted 13 September, 2019; v1 submitted 19 January, 2019; originally announced January 2019.

Comments: 32 pages, 10 figures

Journal ref: ACS Nano 2019, 13, 8, 8760-8765

Thermoelectric Performance of 2D Tellurium with Accumulation Contacts

Authors: Gang Qiu, Shouyuan Huang, Mauricio Segovia, Prabhu K. Venuthurumilli, Yixiu Wang, Wenzhuo Wu, Xianfan Xu, Peide D. Ye

Abstract: Tellurium (Te) is an intrinsically p-type doped narrow bandgap semiconductor with excellent electrical conductivity and low thermal conductivity. Bulk trigonal Te has been theoretically predicted and experimentally demonstrated to be an outstanding thermoelectric material with high value of thermoelectric figure-of-merit ZT. In view of the recent progress in developing synthesis route of two-dimen… ▽ More Tellurium (Te) is an intrinsically p-type doped narrow bandgap semiconductor with excellent electrical conductivity and low thermal conductivity. Bulk trigonal Te has been theoretically predicted and experimentally demonstrated to be an outstanding thermoelectric material with high value of thermoelectric figure-of-merit ZT. In view of the recent progress in developing synthesis route of two-dimensional (2D) tellurium thin films as well as the growing trend of exploiting nanostructures as thermoelectric devices, here for the first time we report excellent thermoelectric performance of tellurium nanofilms, with room temperature power factor of 31.7 μWcm-1K-2 and ZT value of 0.63. To further enhance the efficiency of harvesting thermoelectric power in nanofilm devices, thermoelectrical current mapping was performed with a laser as a heating source, and we found high work function metals such as palladium can form rare accumulation-type metal-to-semiconductor contacts to 2D Te, which allows thermoelectrically generated carriers to be collected more efficiently. High-performance thermoelectric 2D Te devices have broad applications as energy harvesting devices or nanoscale Peltier coolers in microsystems. △ Less

Submitted 26 December, 2018; originally announced December 2018.

Comments: manuscript+SI, 30 pages

On the Ferroelectric Polarization Switching of Hafnium Zirconium Oxide in Ferroelectric/Dielectric Stack

Authors: Mengwei Si, Xiao Lyu, Peide D. Ye

Abstract: The ferroelectric polarization switching in ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) in the HZO/Al2O3 ferroelectric/dielectric stack is investigated systematically by capacitance-voltage and polarization-voltage measurements. The thickness of dielectric layer is found to have a determinant impact on the ferroelectric polarization switching of ferroelectric HZO. A suppression of fe… ▽ More The ferroelectric polarization switching in ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) in the HZO/Al2O3 ferroelectric/dielectric stack is investigated systematically by capacitance-voltage and polarization-voltage measurements. The thickness of dielectric layer is found to have a determinant impact on the ferroelectric polarization switching of ferroelectric HZO. A suppression of ferroelectricity is observed with thick dielectric layer. In the gate stacks with thin dielectric layers, a full polarization switching of the ferroelectric layer is found possible by the proposed leakage-current-assist mechanism through the ultrathin dielectric layer. Theoretical simulation results agree well with experimental data. This work clarifies some of the critical parts of the long-standing confusions and debating related to negative capacitance field-effect transistors (NC-FETs) concepts and experiments. △ Less

Submitted 24 June, 2019; v1 submitted 12 December, 2018; originally announced December 2018.

Comments: 32 pages, 10 figures

Journal ref: ACS Appl. Electron. Mater., vol. 1, no. 5, pp. 745-751, 2019

A Ferroelectric Semiconductor Field-Effect Transistor

Authors: Mengwei Si, Atanu K. Saha, Shengjie Gao, Gang Qiu, Jingkai Qin, Yuqin Duan, Jie Jian, Chang Niu, Haiyan Wang, Wenzhuo Wu, Sumeet K. Gupta, Peide D. Ye

Abstract: Ferroelectric field-effect transistors employ a ferroelectric material as a gate insulator, the polarization state of which can be detected using the channel conductance of the device. As a result, the devices are of potential to use in non-volatile memory technology, but suffer from short retention times, which limits their wider application. Here we report a ferroelectric semiconductor field-eff… ▽ More Ferroelectric field-effect transistors employ a ferroelectric material as a gate insulator, the polarization state of which can be detected using the channel conductance of the device. As a result, the devices are of potential to use in non-volatile memory technology, but suffer from short retention times, which limits their wider application. Here we report a ferroelectric semiconductor field-effect transistor in which a two-dimensional ferroelectric semiconductor, indium selenide (α-In2Se3), is used as the channel material in the device. α-In2Se3 was chosen due to its appropriate bandgap, room temperature ferroelectricity, ability to maintain ferroelectricity down to a few atomic layers, and potential for large-area growth. A passivation method based on the atomic-layer deposition of aluminum oxide (Al2O3) was developed to protect and enhance the performance of the transistors. With 15-nm-thick hafnium oxide (HfO2) as a scaled gate dielectric, the resulting devices offer high performance with a large memory window, a high on/off ratio of over 108, a maximum on-current of 862 μA μm-1, and a low supply voltage. △ Less

Submitted 9 January, 2020; v1 submitted 7 December, 2018; originally announced December 2018.

Comments: 44 pages, 16 figures

Journal ref: Nat. Electron. 2, 580-586 (2019)

Imaging Carrier Inhomogeneities in Ambipolar Tellurene Field Effect Transistors

Authors: Samuel Berweger, Gang Qiu, Yixiu Wang, Benjamin Pollard, Kristen L. Genter, Robert Tyrell-Ead, T. Mitch Wallis, Wenzhuo Wu, Peide D. Ye, Pavel Kabos

Abstract: Developing van der Waals (vdW) homojunction devices requires materials with narrow bandgaps and simultaneously high hole and electron mobilities for bipolar transport, as well as methods to image and study spatial variations in carrier type and associated conductivity with nanometer spatial resolution. Here we demonstrate the general capability of near-field scanning microwave microscopy (SMM) to… ▽ More Developing van der Waals (vdW) homojunction devices requires materials with narrow bandgaps and simultaneously high hole and electron mobilities for bipolar transport, as well as methods to image and study spatial variations in carrier type and associated conductivity with nanometer spatial resolution. Here we demonstrate the general capability of near-field scanning microwave microscopy (SMM) to image and study the local carrier type and associated conductivity in operando by studying ambiploar field effect transistors (FETs) of the 1D vdW material tellurium in 2D form. To quantitatively understand electronic variations across the device, we produce nanometer resolved maps of the local carrier equivalence backgate voltage. We show that the global device conductivity minimum determined from transport measurements does not arise from uniform carrier neutrality, but rather from the continued coexistence of p-type regions at the device edge and n-type regions in the interior of our micron-scale devices. This work both underscores and addresses the need to image and understand spatial variations in the electronic properties of nanoscale devices. △ Less

Submitted 3 November, 2018; originally announced November 2018.

Comments: 15 pages, 4 figures

Quantum Transport and Band Structure Evolution under High Magnetic Field in Few-Layer Tellurene

Authors: Gang Qiu, Yixiu Wang, Yifan Nie, Yongping Zheng, Kyeongjae Cho, Wenzhuo Wu, Peide D. Ye

Abstract: Quantum Hall effect (QHE) is a macroscopic manifestation of quantized states which only occurs in confined two-dimensional electron gas (2DEG) systems. Experimentally, QHE is hosted in high mobility 2DEG with large external magnetic field at low temperature. Two-dimensional van der Waals materials, such as graphene and black phosphorus, are considered interesting material systems to study quantum… ▽ More Quantum Hall effect (QHE) is a macroscopic manifestation of quantized states which only occurs in confined two-dimensional electron gas (2DEG) systems. Experimentally, QHE is hosted in high mobility 2DEG with large external magnetic field at low temperature. Two-dimensional van der Waals materials, such as graphene and black phosphorus, are considered interesting material systems to study quantum transport, because it could unveil unique host material properties due to its easy accessibility of monolayer or few-layer thin films at 2D quantum limit. Here for the first time, we report direct observation of QHE in a novel low-dimensional material system: tellurene.High-quality 2D tellurene thin films were acquired from recently reported hydrothermal method with high hole mobility of nearly 3,000 cm2/Vs at low temperatures, which allows the observation of well-developed Shubnikov-de-Haas (SdH) oscillations and QHE. A four-fold degeneracy of Landau levels in SdH oscillations and QHE was revealed. Quantum oscillations were investigated under different gate biases, tilted magnetic fields and various temperatures, and the results manifest the inherent information of the electronic structure of Te. Anomalies in both temperature-dependent oscillation amplitudes and transport characteristics were observed which are ascribed to the interplay between Zeeman effect and spin-orbit coupling as depicted by the density functional theory (DFT) calculations. △ Less

Submitted 21 June, 2018; originally announced June 2018.