arXiv subjects

Chi Sun

Publications and source records attributed to Chi Sun.

At least 19 recordsLinked to original sources

arXiv2026

Turning Zeeman splitting into switchable charge polarization in a double quantum dot

A magnetic field that acts identically on two quantum dots is not expected to move charge between them. Nevertheless, we show that a uniform Zeeman field can strongly reconfigure and even reverse the single-electron charge polarization of an asymmetric open double quantum dot. Using a symmetry-preserving Green's-function equation-of-motion approach, we identify regimes where the preferred dot occupation reverses while the system remains in the single-electron charge sector. Two distinct mechanisms produce this behavior. Unequal gate levels produce different occupation responses because the Zeeman-shifted resonances lie at different positions relative to the reservoir chemical potential, whereas unequal onsite interactions distinguish the dots through their many-body addition spectra. Coulomb blockade stabilizes the single-electron sector, causing the reservoir-mediated response to appear as spatial charge redistribution rather than a change in total occupation. Our results establish a mechanism for magnetic control of charge polarization at fixed electrostatic detuning.

cond-mat.mes-hall↗

arXiv2026

Interfacial orbital transmission, conversion, and mechanical torque in metals

Interfacial orbital transport remains far less understood than its bulk counterpart despite its central role in orbitronic experiments. Here, we theoretically investigate the transmission and conversion of orbital angular momentum across a metallic interface using a model Hamiltonian incorporating crystal-field effects. We show that an injected orbital dipole moment undergoes pronounced oscillations driven by the crystal field and generates characteristic quadrupole moments determined by the orbital orientation relative to the interface. Unlike spin precession, the dipole relaxes toward a finite value away from the interface. We further quantify interfacial orbital memory loss and demonstrate that orbital absorption produces a sizable mechanical torque obtained from the orbital continuity equation.

cond-mat.mes-hall↗

arXiv2025

Multipolar orbital relaxation of the $t_{2g}$ states

Using a nonperturbative approach, the relaxation rate of orbital dipolar and quadrupolar moments is computed analytically for the t2g states. In the presence of short-range impurities and in the absence of spin-orbit coupling, the orbital relaxation emerges from the competition between momentum scattering and the effect of the crystal field. In the case of weak disorder, the orbital relaxation time is proportional to the momentum scattering time: each scattering event contributes to destroying the orbital moment. In the case of strong disorder, the effect of the crystal field is averaged out, and the orbital relaxation time is inversely proportional to the momentum scattering. We finally find that the dipolar and quadrupolar orbital moments are coupled by the crystal field, resulting in a complex dynamical behavior upon orbital injection.

cond-mat.mes-hall↗

arXiv2025

Mutual enhancement of altermagnetism and ferroelectricity

We consider theoretically the possibility of coexisting ferroelectric and metallic altermagnetic order, which has recently been predicted in insulating and semiconducting systems via ab initio calculations. Solving self-consistently a mean-field Hubbard model, accounting also for the energy cost of distorting the lattice to produce an electric polarization, our results show that metallic altermagnetism and ferroelectricity suppress or enhance each other depending on the doping level of the system. Close to half-filling, the system can lower its energy by becoming altermagnetic, but at the expense of losing the electric polarization. Away from half-filling, the coexistence of ferroelectricity and altermagnetism is much more robust toward an increase in the energy cost associated with the deformation of the lattice. Therefore, our results suggest that filling fractions corresponding to doping relatively far away from half-filling constitute the most promising regime to look for coexistent ferroelectricity and metallic altermagnetism with mutual enhancement. Moreover, we propose a way to electrically tune altermagnetism between nodal and nodeless phases as well as achieving coexistence of a nodal and nodeless phase for the two spin species.

cond-mat.mtrl-sci↗

arXiv2025

MIRAGE: Multimodal Intention Recognition and Admittance-Guided Enhancement in VR-based Multi-object Teleoperation

Effective human-robot interaction (HRI) in multi-object teleoperation tasks faces significant challenges due to perceptual ambiguities in virtual reality (VR) environments and the limitations of single-modality intention recognition. This paper proposes a shared control framework that combines a virtual admittance (VA) model with a Multimodal-CNN-based Human Intention Perception Network (MMIPN) to enhance teleoperation performance and user experience. The VA model employs artificial potential fields to guide operators toward target objects by adjusting admittance force and optimizing motion trajectories. MMIPN processes multimodal inputs, including gaze movement, robot motions, and environmental context, to estimate human grasping intentions, helping to overcome depth perception challenges in VR. Our user study evaluated four conditions across two factors, and the results showed that MMIPN significantly improved grasp success rates, while the VA model enhanced movement efficiency by reducing path lengths. Gaze data emerged as the most crucial input modality. These findings demonstrate the effectiveness of combining multimodal cues with implicit guidance in VR-based teleoperation, providing a robust solution for multi-object grasping tasks and enabling more natural interactions across various applications in the future.

cs.RO↗

arXiv2024

Josephson transistor and robust supercurrent enhancement with spin-split superconductors

We theoretically investigate the supercurrent flow in a Josephson junction consisting of two spin-split superconductors combined by a normal metal weak link. The normal metal may be driven out of equilibrium, thus modifying the electron and hole occupation and consequently the supercurrent through the system. Considering first an equilibrium normal metal, we find that increasing the spin-splitting field can enhance the supercurrent strongly for long junctions at low temperatures. In contrast to previous work, this is a much larger enhancement (over 100%) and it is achieved for both parallel and antiparallel spin-splitting field configurations, making the effect robust. On the other hand, when a gate voltage is applied to drive the system out of equilibrium, we demonstrate a more efficient $\pi$-transition of the supercurrent in terms of a lower transition voltage by tuning the spin-splitting. Moreover, we find the application of temperature bias strongly suppresses the supercurrent, resulting in very sharp supercurrent jumps as outputs.

cond-mat.supr-con↗

arXiv2024

Voltage-tunable spin supercurrent nonreciprocity reaching 100% efficiency

The superconducting version of a diode effect has been the subject of extensive research in the past few years. So far, the focus has almost exclusively been on charge transport, but a natural question is whether it is possible to obtain nonreciprocal spin transport without dissipation. Here, we demonstrate that it is possible to generate electrically tunable nonreciprocal spin transport carried by a supercurrent using superconductor/ferromagnet multilayers. The nonreciprocal spin supercurrent reaches an ideal efficiency of 100%, meaning that the spin-polarization of the critical current is finite in one flow direction whereas it vanishes in the other direction. We explain the underlying physics generating this phenomenon. This result provides a way to integrate nonreciprocal supercurrents with spin-polarization, offering new functionality in quantum technologies based on Josephson junctions.

cond-mat.supr-con↗

arXiv2024

Strong-coupling approach to temperature dependence of competing orders of superconductivity: Possible time-reversal symmetry breaking and nontrivial topology

We use strong-coupling Eliashberg theory to study the competition of separate superconducting orders at low temperatures. Specifically, we study magnon-mediated superconductivity in a trilayer heterostructure with a thin normal metal between two antiferromagnetic insulators. Spin-triplet $p$-wave, spin-triplet $f$-wave, and spin-singlet $d$-wave superconducting gaps have been predicted to occur close to the critical temperature for the superconducting instability. The gap symmetry with the largest critical temperature depends on parameters in the model. We confirm that the same gap symmetries appear at any temperature below the critical temperature. Furthermore, we show that the temperature can affect the competition between the different superconducting orders. In addition, we consider time-reversal-symmetry-breaking, complex linear combinations of candidate pairings, such as chiral $p$-, $f$-, and $d$-wave gaps, as well as $p_x+if_y$-wave gaps. We find indications that some of these time-reversal-symmetry-breaking, nodeless gaps offer a greater condensation energy than the time-reversal symmetric gaps. This indicates that superconducting states with spontaneously broken time-reversal symmetry and nontrivial topology may be preferred in this system.

cond-mat.supr-con↗

arXiv2023

Supercurrent-induced spin switching via indirect exchange interaction

Localized spins of single atoms adsorbed on surfaces have been proposed as building blocks for spintronics and quantum computation devices. However, identifying a way to achieve current-induced switching of spins with very low dissipation is an outstanding challenge with regard to practical applications. Here, we show that the indirect exchange interaction between spin impurities can be controlled by a dissipationless supercurrent. All that is required is a conventional superconductor and two spin impurities placed on its surface. No triplet Cooper pairs or exotic material choices are needed. This finding provides a new and accessible way to achieve the long-standing goal of supercurrent-induced spin switching.

cond-mat.mes-hall↗

arXiv2023

CALM: Contrastive Cross-modal Speaking Style Modeling for Expressive Text-to-Speech Synthesis

To further improve the speaking styles of synthesized speeches, current text-to-speech (TTS) synthesis systems commonly employ reference speeches to stylize their outputs instead of just the input texts. These reference speeches are obtained by manual selection which is resource-consuming, or selected by semantic features. However, semantic features contain not only style-related information, but also style irrelevant information. The information irrelevant to speaking style in the text could interfere the reference audio selection and result in improper speaking styles. To improve the reference selection, we propose Contrastive Acoustic-Linguistic Module (CALM) to extract the Style-related Text Feature (STF) from the text. CALM optimizes the correlation between the speaking style embedding and the extracted STF with contrastive learning. Thus, a certain number of the most appropriate reference speeches for the input text are selected by retrieving the speeches with the top STF similarities. Then the style embeddings are weighted summarized according to their STF similarities and used to stylize the synthesized speech of TTS. Experiment results demonstrate the effectiveness of our proposed approach, with both objective evaluations and subjective evaluations on the speaking styles of the synthesized speeches outperform a baseline approach with semantic-feature-based reference selection.

cs.SD↗

arXiv2023

Spin pumping from a ferromagnetic insulator into an altermagnet

A class of antiferromagnets with spin-polarized electron bands, yet zero net magnetization, called altermagnets is attracting increasing attention due to their potential use in spintronics. Here, we study spin injection into an altermagnet via spin pumping from a ferromagnetic insulator. We find that the spin pumping behaves qualitatively different depending on how the altermagnet is crystallographically oriented relative the interface to the ferromagnetic insulator. The altermagnetic state can enhance or suppress spin pumping, which we explain in terms of spin-split altermagnetic band structure and the spin-flip probability for the incident modes. Including the effect of interfacial Rashba spin-orbit coupling, we find that the spin-pumping effect is in general magnified, but that it can display a non-monotonic behavior as a function of the spin-orbit coupling strength. We show that there exists an optimal value of the spin-orbit coupling strength which causes an order of magnitude increase in the pumped spin current, even for the crystallographic orientation of the altermagnet which suppresses the spin pumping.

cond-mat.mes-hall↗

arXiv2023

Stability of superconducting gap symmetries arising from antiferromagnetic magnons

We consider a planar heterostructure consisting of a normal metal in proximity to an antiferromagnetic insulator, with an interlayer exchange coupling between the metal and the insulator. The coupling to the two sublattices of the antiferromagnetic insulator is allowed to be asymmetric. An effective electron-electron interaction in the normal metal, mediated by antiferromagnetic magnons in the insulator, is derived to second order in the interlayer exchange coupling. Particular emphasis is placed on including analytically derived expressions for the effective interactions including Umklapp processes in the solutions to the superconducting gap equation. The gap equation is first solved at the critical temperature as an eigenvalue problem by linearizing the gap equation. The eigenvectors yield information on the symmetry of the superconducting gap at the onset of superconductivity, and we derive a phase diagram for the order parameter in this case. In the various regimes of the phase diagram, we find $p$-wave, $f$-wave, and $d$-wave superconductivity, with $p$-wave superconductivity in the dominant part of the phase diagram. Umklapp processes, that come into play with increasing size of the Fermi surface, yield $f$- and $d$-wave symmetries as the preferred symmetries when band filling approaches half filling. To investigate the stability of this order parameter symmetry as the temperature is lowered, we also consider the nonlinear gap equation at zero temperature. We conclude that the phase diagram and the symmetries of the superconducting order parameter essentially are left intact as the temperature is lowered to zero temperature.

cond-mat.supr-con↗

arXiv2023

Andreev reflection in altermagnets

Recent works have predicted materials featuring bands with a large spin-splitting distinct from ferromagnetic and relativistically spin-orbit coupled systems. Materials displaying this property are known as altermagnets and feature a spin-polarized band structure reminiscent of a $d$-wave superconducting order parameter. We here consider the contact between an altermagnet and a superconductor and determine how the altermagnetism affects the fundamental process of Andreev reflection. We show that the resulting charge conductance depends strongly on the interfacial orientation of the altermagnet relative to the superconductor, displaying features similar to normal metals or ferromagnets. The zero-bias conductance peak present at the interface in the $d$-wave case are robust toward the presence of an altermagnetic interaction. Moreover, the spin conductance strongly depends on the orientation of the altermagnet relative the interface. These results show how the anisotropic altermagnetic state can be probed by conductance spectroscopy and how it offers voltage control over charge and spin currents that are modulated due to superconductivity.

cond-mat.supr-con↗

arXiv2022

Spin-pumping from a ferromagnetic insulator to an unconventional superconductor with interfacial Andreev bound-states

Spin-pumping from a ferromagnetic insulator into a high-$T_c$ superconductor with a $d$-wave superconducting order parameter has recently been experimentally observed. Such unconventional superconducting order is known to produce interfacial bound-states for certain crystallographic orientations. Here, we present a methodology which can be used to study spin-pumping into unconventional superconductors, including the role of interfacial bound-states. As an example, we determine how the crystallographic orientation of the $d$-wave order parameter relative the interface changes the spin-pumping effect. We find that the spin-pumping effect is slightly enhanced at low temperatures for orientations hosting interfacial bound-states compared to other superconducting states. However, the spin-pumping effect does not show a coherence peak close to $T_c$ for such orientations, and instead remains smaller than the normal state value for all $T$. For orientations not hosting interfacial bound-states, we find that the pumped spin current can be increased to several times the normal-state spin current at frequencies that are small compared to the superconducting gap. Our results show that the spin-pumping dependency on frequency and temperature changes qualitatively depending on the crystallographic orientation of unconventional superconducting order parameters relative the interface.

cond-mat.supr-con↗

arXiv2019

GlossBERT: BERT for Word Sense Disambiguation with Gloss Knowledge

Word Sense Disambiguation (WSD) aims to find the exact sense of an ambiguous word in a particular context. Traditional supervised methods rarely take into consideration the lexical resources like WordNet, which are widely utilized in knowledge-based methods. Recent studies have shown the effectiveness of incorporating gloss (sense definition) into neural networks for WSD. However, compared with traditional word expert supervised methods, they have not achieved much improvement. In this paper, we focus on how to better leverage gloss knowledge in a supervised neural WSD system. We construct context-gloss pairs and propose three BERT-based models for WSD. We fine-tune the pre-trained BERT model on SemCor3.0 training corpus and the experimental results on several English all-words WSD benchmark datasets show that our approach outperforms the state-of-the-art systems.

cs.CL↗

arXiv2019

How to Fine-Tune BERT for Text Classification?

Language model pre-training has proven to be useful in learning universal language representations. As a state-of-the-art language model pre-training model, BERT (Bidirectional Encoder Representations from Transformers) has achieved amazing results in many language understanding tasks. In this paper, we conduct exhaustive experiments to investigate different fine-tuning methods of BERT on text classification task and provide a general solution for BERT fine-tuning. Finally, the proposed solution obtains new state-of-the-art results on eight widely-studied text classification datasets.

cs.CL↗

arXiv2019

Utilizing BERT for Aspect-Based Sentiment Analysis via Constructing Auxiliary Sentence

Aspect-based sentiment analysis (ABSA), which aims to identify fine-grained opinion polarity towards a specific aspect, is a challenging subtask of sentiment analysis (SA). In this paper, we construct an auxiliary sentence from the aspect and convert ABSA to a sentence-pair classification task, such as question answering (QA) and natural language inference (NLI). We fine-tune the pre-trained model from BERT and achieve new state-of-the-art results on SentiHood and SemEval-2014 Task 4 datasets.

cs.CL↗

arXiv2019

VCWE: Visual Character-Enhanced Word Embeddings

Chinese is a logographic writing system, and the shape of Chinese characters contain rich syntactic and semantic information. In this paper, we propose a model to learn Chinese word embeddings via three-level composition: (1) a convolutional neural network to extract the intra-character compositionality from the visual shape of a character; (2) a recurrent neural network with self-attention to compose character representation into word embeddings; (3) the Skip-Gram framework to capture non-compositionality directly from the contextual information. Evaluations demonstrate the superior performance of our model on four tasks: word similarity, sentiment analysis, named entity recognition and part-of-speech tagging.

cs.CL↗