arXiv subjects

Danqing Liu

Publications and source records attributed to Danqing Liu.

11 recordsLinked to original sources

arXiv2026

Reactive polar mesogenic self-assembly approach enables domain-programmable polymer ferroelectrics

Ferroelectric polymers combine switchable polarization with the processability of soft materials, but their development has been dominated by poly(vinylidene fluoride) and related fluoropolymers, whose crystalline polar phases restrict mechanical compliance and domain design with spatial precision. Here we establish a generic design principle for creating intrinsically flexible ferroelectric liquid-crystal polymers through reactive polar mesogenic self-assembly. The approach creates polyfluoroalkyl-free polymer films in which robust ferroelectric order arises from liquid-crystalline molecular organization rather than crystalline phase formation. By transferring ferroelectric order from fluid mesogenic states into polymer networks, the resulting materials combine mechanical adaptability with programmable polar architectures. Especially, the photoalignment technology enables these polar states to be organized into pixelated domain architectures. This work establishes a design space towards soft ferroelectric polymers that integrate molecularly programmed polar order, mechanical tunability and environmentally conscious chemistry, expanding the design space of adaptive materials for flexible electronics, wearable systems and soft robotics.

cond-mat.soft↗

arXiv2026

High-quality Nano-patterning of Oxide Interfaces Using Transferred Gold Mask

Complex oxide interfaces, such as $\mathrm{SrTiO_3}$ and $\mathrm{KTaO_3}$ based heterostructures, host rich correlated phenomena with strong potential for advanced device applications. However, these interfaces are extremely susceptible to contamination and defect formation during nanofabrication, which often compromises device performance. Here, we present a solvent-free method for patterning oxide interfaces by employing high-resolution transferable thin metal masks in conjunction with oxygen-enriched $\mathrm{Ar^+}$ ion milling, which enables a clean and well-controlled nanofabrication process. Transport measurements demonstrate that the fabricated devices preserve their intrinsic properties, including high carrier mobilities, with negligible degradation compared to the pristine interfaces. This technique offers a convenient and robust route for engineering high-performance oxide electronic devices with precisely tailored transport characteristics.

cond-mat.mtrl-sci↗

arXiv2026

Reconfigurable Oxide Nanoelectronics by Tip-induced Electron Delocalization

Reconfigurable oxide nanoelectronics, enabled by conductive atomic force microscope (cAFM) lithography, have established complex oxide interfaces as a promising platform for quantum engineering that harnesses emergent phenomena for advanced functionalities. However, this cAFM nanofabrication process can only occur in the air, with simultaneous device decay described under the "water-cycle" writing mechanism. These restrictions pose ongoing challenges for device optimization in the quantum regime at mK temperatures. Here, we demonstrate a "waterless" cAFM lithography approach that is compatible with vacuum and cryogenic environments. Through oxygen vacancy engineering at the LaAlO$_3$/SrTiO$_3$ interface, we have achieved nonvolatile and reconfigurable cAFM control of nanoscale interfacial polaron-electron liquid transition at mK temperatures with an ultrafine line resolution of 0.85 nm. Supported by first-principles calculations and drift-diffusion modeling, we show that tip-controlled oxygen vacancy electromigration plays a key role. This advancement bridges reconfigurable device fabrication and concurrent characterization in situ at mK temperatures, and establishes a versatile Hubbard toolbox for engineering programmable quantum phases in correlated oxides.

cond-mat.mes-hall↗

arXiv2025

Time-Reversal Symmetry Protected Transport at Correlated Oxide Interfaces

Time-reversal symmetry (TRS) protection is core to topological physics, yet its role in correlated oxides-typically non-topological-remains underexplored. This limit hampers the potential in engineering exotic quantum states by fusing TRS protection and the rich emergent phenomena in the oxide platform. Here, we report evidence of a TRS-protected subband at oxygen vacancy-free LaAlO3/SrTiO3 interfaces. This subband causes a low-field quantum oscillation with anomalous characters: exceptionally light electron mass, aperiodicity, and susceptibility to magnetic fields. All findings align with a Rashba model in which TRS-protected transport occurs along quasi-1D ferroelastic domain walls, which possess a Dirac band topology and a giant Rashba spin-orbit coupling, two orders stronger than the 2D interface. Our results deepen the understanding of SrTiO3-based electron systems, unveiling an appealing new platform for quantum engineering.

cond-mat.mes-hall↗

arXiv2025

Sub-kHz single-frequency pulsed semiconductor laser based on NPRO injection locking

We report a single-frequency, narrow-linewidth semiconductor pulsed laser based on pump current modulation and optical injection locking technique. A monolithic non-planar ring oscillator laser is employed as the seed source to guarantee the single-frequency narrow-linewidth performance. Simultaneously, pulse operation is achieved by directly modulating the pump current of the semiconductor laser. The single-frequency pulsed laser (SFPL) has achieved a pulse repetition rate of 50 kHz-1 MHz, a pulse duration ranging from 120 ns to a quasi-continuous state, and a peak power of 160 mW. Moreover, the SFPL has reached a pulsed laser linewidth as narrow as 905 Hz, optical spectrum signal-to-noise ratio of better than 65 dB at a center wavelength of 1064.45 nm. Such extremely narrow-linewidth, repetition-rate and pulse-width tunable SFPL has great potential for applications in coherent LIDAR, metrology, remote sensing, and nonlinear frequency conversion.

physics.optics↗

arXiv2025

Comprehensive Investigation of Fundamental Mode Profiles in Monolithic Nonplanar Ring Oscillators

Nonplanar ring oscillators (NPROs) are building blocks for high-performance single-frequency lasers and ring-laser gyroscopes that have profoundly improved the state-of-the-art laser technologies, fundamental research and precision measurements. However, a comprehensive investigation of fundamental mode profiles in monolithic NPROs has been a missing part even though they will affect the performance of the lasers or ring-laser gyroscopes. Here, we present a comprehensive finite-element modeling of the output beam profiles of monolithic NPROs by combining ABCD transmission matrix and generalized Huygens-Fresnel integral. We theoretically investigate the effects of geometric parameters of monolithic NPROs on their output mode profiles. In particular, we focus on the thermal effect inside the monolithic NPRO and calculate the equivalent focal-length of the thermal-lens by using a ray-tracing-method. Furthermore, we experimentally characterize the output laser beam profile, reconstruct the beam profile at the A-facet of the monolithic NPRO, and compare the experimental results with the simulation, thereby validating the accuracy and reliability of our model. The investigation may facilitate monolithic NPRO design and subsequently improve the performances of NPRO lasers and gyroscopes in the future.

physics.optics↗

arXiv2025

A Milli-Kelvin Atomic Force Microscope Made of Glass

Milli-Kelvin atomic force microscopy (mK-AFM) presents an ongoing experimental challenge due to the intense vibrations in a cryogen-free dilution refrigerator and the low cooling power available at mK temperatures. A viable approach is to make the system exceptionally rigid and thermally insulating to decouple external vibrations and isolate heat dissipation from the piezo elements. Here, we present a low-cost and large scan-range mK-AFM that operates below 100 mK. All the essential parts of our mK-AFM, including the scanners, tip assembly, and microscope body, are custom-made of fused silica glass by taking advantage of its high specific modulus, extremely low thermal expansion coefficient, and excellent thermal insulation properties. We carefully balance the scan range (25 ${\mu}$m $\times$ 25 ${\mu}$m), heat dissipation, and stiffness of the system to reach optimal performance at mK temperatures.

physics.ins-det↗

arXiv2024

Frequency-shifted laser feedback interferometry in non-planar ring oscillators

Laser feedback interferometry (LFI) has a wide range of applications such as displacement, distance and velocity measurements. LFI has been realized in many types of lasers but has never been reported in non-planar ring oscillators (NPRO) to the best of our knowledge. Here, we present a new type of LFI based on an NPRO laser. The intrinsic resistance to optical feedback in NPROs is broken under weak magnetic intensity condition, where stable bidirectional lasing is initiated in the ring cavity. The interference signal, i.e., the beat of the bidirectional lasing is with frequency in the range of a few hundred kilohertz, which is mainly determined by the applied magnetic intensity in NPRO. Frequency shifted LFI is thus constructed in NPRO without using acoustic optic modulators as mostly used in conventional LFI. A theoretical model based on two frequency rate equations and Lang-Kobayashi equation is presented to describe the mechanism of LFI in NPRO. In the end, micro-vibrational measurements are demonstrated to prove the potential application, where vibration-detection amplitude limit is sub-picometer, and the detection frequency range from kilohertz to a few hundred kilohertz is achieved. Benefiting from the characteristics of tiny footprint, ruggedized structure, long lifetime and ultralow-noise of NPRO lasers, NPRO-based LFI may find important applications in industry, scientific research,military and aerospace.

physics.optics↗

arXiv2024

LongCite: Enabling LLMs to Generate Fine-grained Citations in Long-context QA

Though current long-context large language models (LLMs) have demonstrated impressive capacities in answering user questions based on extensive text, the lack of citations in their responses makes user verification difficult, leading to concerns about their trustworthiness due to their potential hallucinations. In this work, we aim to enable long-context LLMs to generate responses with fine-grained sentence-level citations, improving their faithfulness and verifiability. We first introduce LongBench-Cite, an automated benchmark for assessing current LLMs' performance in Long-Context Question Answering with Citations (LQAC), revealing considerable room for improvement. To this end, we propose CoF (Coarse to Fine), a novel pipeline that utilizes off-the-shelf LLMs to automatically generate long-context QA instances with precise sentence-level citations, and leverage this pipeline to construct LongCite-45k, a large-scale SFT dataset for LQAC. Finally, we train LongCite-8B and LongCite-9B using the LongCite-45k dataset, successfully enabling their generation of accurate responses and fine-grained sentence-level citations in a single output. The evaluation results on LongBench-Cite show that our trained models achieve state-of-the-art citation quality, surpassing advanced proprietary models including GPT-4o.

cs.CL↗

arXiv2023

Domain wall nature of sketched LaAlO3/SrTiO3 nanowires

The rich electron correlations and highly coherent transport in reconfigurable devices sketched by a conductive atomic force microscope tip at the LaAlO3/SrTiO3 interface have enabled the oxide platform an ideal playground for studying correlated electrons and quantum technological applications. Why these one-dimensional devices possess enhanced properties over the two-dimensional interface, however, has remained elusive. Here we provide evidence that one-dimensional LaAlO3/SrTiO3 nanowires are intrinsically ferroelastic domain walls by nature through thermodynamic study. We have observed spreading resistance anomalies under thermo-stimulus and temperature cycles, with characteristic temperatures matching domain wall polarity. This information is crucial in understanding the novel phenomena including superconductivity and high mobility quantum transport.

cond-mat.mes-hall↗

arXiv2021

Linking Physical Objects to Their Digital Twins via Fiducial Markers Designed for Invisibility to Humans

The ability to label and track physical objects that are assets in digital representations of the world is foundational to many complex systems. Simple, yet powerful methods such as bar- and QR-codes have been highly successful, e.g. in the retail space, but the lack of security, limited information content and impossibility of seamless integration with the environment have prevented a large-scale linking of physical objects to their digital twins. This paper proposes to link digital assets created through BIM with their physical counterparts using fiducial markers with patterns defined by Cholesteric Spherical Reflectors (CSRs), selective retroreflectors produced using liquid crystal self-assembly. The markers leverage the ability of CSRs to encode information that is easily detected and read with computer vision while remaining practically invisible to the human eye. We analyze the potential of a CSR-based infrastructure from the perspective of BIM, critically reviewing the outstanding challenges in applying this new class of functional materials, and we discuss extended opportunities arising in assisting autonomous mobile robots to reliably navigate human-populated environments, as well as in augmented reality.

cond-mat.soft↗