arXiv subjects

Chang Niu

Publications and source records attributed to Chang Niu.

At least 19 recordsLinked to original sources

arXiv2026

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

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.

cond-mat.mes-hall↗

arXiv2026

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

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.

physics.app-ph↗

arXiv2026

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

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.

cond-mat.mes-hall↗

arXiv2026

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

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.

cond-mat.mes-hall↗

arXiv2026

Seed Layer Engineering for Effective Charge Transfer Doping of MoS$_2$ Transistors

Integrating two-dimensional semiconductors such as MoS$_2$ with dielectric materials remains a central challenge for their use in future logic technologies. While seed layers are typically introduced to promote dielectric nucleation and adhesion, we show that they also critically govern charge-transfer doping and, in turn, transistor performance. Back-gated monolayer MoS$_2$ transistors passivated on their top-surface with a Ta-seed/HfO$_x$ dielectric stack were fabricated and characterized electrically and physically using Raman, photoluminescence, and X-ray photoelectron spectroscopies. Threshold voltage and on-current varied strongly with Ta-seed thickness and deposition conditions, and these changes correlated with signatures observed across all spectroscopic probes. The results reveal that the seed layer both introduces disorder into the MoS$_2$ channel and modifies the interfacial charge environment controlling charge transfer between HfO$_x$ and MoS$_2$. Optical spectroscopy shows that on-current tracks seed-induced disorder, whereas X-ray photoelectron spectroscopy indicates that threshold voltage correlates with shifts in the local electrostatic environment associated with interfacial charge transfer. Better performance was obtained with ultrathin 0.2 nm Ta seed layers deposited under oxygen-poor conditions, which limit deposition-induced damage while facilitating charge transfer. These findings identify seed-layer engineering as a key strategy for controlling disorder and interfacial doping in MoS$_2$ devices and establish multimodal spectroscopy as a practical during-fabrication approach for process development and monitoring.

cond-mat.mtrl-sci↗

arXiv2026

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

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, $\Delta R(B)/R(0)=2\,\chi\, {\bf I}\cdot{\bf B}$, or (ii) polar, $\Delta R(B)/R(0)=2\,\gamma\, {\bf I}\cdot({\bf P}\times{\bf B})$, with eMChA coefficients $\chi$ and $\gamma$. In [Phys. Rev. Lett. 135, 106602 (2025)], we showed that the eMChA in the conduction band of tellurene is polar ($\chi=0$, $\gamma\neq 0$) 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 ($\chi \neq 0, \gamma = 0$). We show that also a polar coefficient $\gamma \neq 0$ 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 ($\mu$) dependent second-harmonic measurements of the longitudinal voltage $V^{2\omega}_\parallel(\mu)$ in perpendicular field. The combined chiral and polar characters ($\chi\neq0, \gamma\neq 0)$ of the eMChA in tellurene also explains the shift in the angular ($\phi$) dependence of $V^{2\omega}_\parallel(\phi)$ 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.

cond-mat.mes-hall↗

arXiv2026

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

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.

cond-mat.mes-hall↗

arXiv2026

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

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.

cond-mat.mes-hall↗

arXiv2025

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

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, $(\boldsymbol{\cal E}\times{\bf B})\cdot\sigma$. 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, $\Delta R_{zz}(\boldsymbol{\cal E},{\bf B})/R_0=-\beta_{g}(\boldsymbol{\cal E}\times{\bf B})^2$, with $\beta_{g}$ 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.

cond-mat.mes-hall↗

arXiv2025

Non-reciprocal Magnetoresistances in Chiral Tellurium

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.

cond-mat.mtrl-sci↗

arXiv2025

Giant octupole moment in magnetic multilayers

Multipole moments serve as order parameters for characterizing higher-order magnetic effects in momentum space, providing a framework to describe diverse magnetic responses by extending the concept of magnetism. In this letter, we introduce a methodology to quantitatively determine the multipole moment contributions in anomalous Hall effect through angle-dependent anomalous Hall current, with explicit incorporation of discrete crystal symmetries. Our technique uniquely enables the investigation of octupole contribution in non-periodic systems, particularly at interfaces and surfaces. Typically, in (Ag$_{2}$Fe$_{5}$)$_{n}$ multilayers with quantum-well-engineered $k$-point selectivity, we observe an octupole-dominated anomalous Hall effect in conventional ferromagnetic materials, through first-principles calculations. These results fundamentally challenge the existing theoretical understanding of the anomalous Hall effect, showing that even the conventional contribution arises not only from the dipole moment (net magnetization). Furthermore, we establish practical control over the octupole contribution through two distinct approaches: interface engineering and magnetic ordering reconfiguration, opening new possibilities for manipulating higher-order transport effects.

cond-mat.mes-hall↗

arXiv2025

Tunable interplay of orbital and spin magnetization in trigonal tellurium

Orbital effects, despite their fundamental significance and potential to engender novel physical phenomena and enable new applications, have long been underexplored compared to their spin counterparts. Recently, surging interest in the orbital degree of freedom has led to the discovery of a plethora of orbital-related effects, underscoring the need for a deeper understanding of their roles in quantum materials. Here, we report systematic experimental evidence consistent with orbital magnetization and spontaneous rotational symmetry breaking in trigonal Tellurium, an elemental semiconductor with a unique helical crystal structure that serves as a natural platform for investigating orbital effects. Detailed angular dependent linear and nonlinear magnetotransport measurements, supported by symmetry-guided Boltzmann transport analysis, support the interpretation of coexistence of current-induced spin polarization and orbital magnetization. With the goal of disentangling the interplay between spin and orbital degrees of freedom through electrostatic gating, this work establishes a general framework for understanding orbital magnetization in chiral crystals and beyond, paving the way for its utilization in orbitronics and spintronics.

cond-mat.mtrl-sci↗

arXiv2025

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

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.

cond-mat.mes-hall↗

arXiv2025

Quantum geometry and the electric magnetochiral anisotropy in noncentrosymmetric polar media

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 $\beta{\bf B}^2$ is modified to $R( I,P,B)=R_0[1+\beta B^2 + \gamma^{\pm}{\bf I}\cdot({\bf P}\times{\bf B})]$, where the chirality dependent $\gamma^{\pm}$ is determined by the quantum metric dipole and the polarization ${\bf P}$. We predict a universal scaling $\gamma^{\pm}(V)\sim V^{-5/2}$ 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.

cond-mat.mes-hall↗

arXiv2025

Superior probabilistic computing using operationally stable probabilistic-bit constructed by manganite nanowire

Probabilistic computing has emerged as a viable approach to treat optimization problems. To achieve superior computing performance, the key aspect during computation is massive sampling and tuning on the probability states of each probabilistic bit (p-bit), demanding its high stability under extensive operations. Here, we demonstrate a p-bit constructed by manganite nanowire that shows exceptionally high stability. The p-bit contains an electronic domain that fluctuates between metallic (low resistance) and insulating (high resistance) states near its transition temperature. The probability for the two states can be directly controlled by nano-ampere electrical current. Under extensive operations, the standard error of its probability values is less than 1.3%. Simulations show that our operationally stable p-bit plays the key role to achieve correct inference in Bayesian network by strongly suppressing the relative error, displaying the potential for superior computing performance. Our p-bit also serves as high quality random number generator without extra data-processing, beneficial for cryptographic applications.

physics.app-ph↗

arXiv2025

A self-learning magnetic Hopfield neural network with intrinsic gradient descent adaption

Physical neural networks using physical materials and devices to mimic synapses and neurons offer an energy-efficient way to implement artificial neural networks. Yet, training physical neural networks are difficult and heavily relies on external computing resources. An emerging concept to solve this issue is called physical self-learning that uses intrinsic physical parameters as trainable weights. Under external inputs (i.e. training data), training is achieved by the natural evolution of physical parameters that intrinsically adapt modern learning rules via autonomous physical process, eliminating the requirements on external computation resources.Here, we demonstrate a real spintronic system that mimics Hopfield neural networks (HNN) and unsupervised learning is intrinsically performed via the evolution of physical process. Using magnetic texture defined conductance matrix as trainable weights, we illustrate that under external voltage inputs, the conductance matrix naturally evolves and adapts Oja's learning algorithm in a gradient descent manner. The self-learning HNN is scalable and can achieve associative memories on patterns with high similarities. The fast spin dynamics and reconfigurability of magnetic textures offer an advantageous platform towards efficient autonomous training directly in materials.

cond-mat.dis-nn↗

arXiv2024

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

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.

physics.app-ph↗

arXiv2024

Terahertz radiation driven nonlinear transport phenomena in two-dimensional tellurene

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.

cond-mat.mes-hall↗