arXiv subjects

Yuntian Li

Publications and source records attributed to Yuntian Li.

7 recordsLinked to original sources

arXiv2026

Slow spin-lattice relaxation dynamics in YbVO4 revealed by extended thermal impedance spectroscopy from AC susceptibility and AC magnetocaloric measurements

Alternating (AC) magnetic fields can induce not only an alternating magnetization in materials, but also an alternating temperature via the magnetocaloric effect. The latter effect is typically neglected when performing AC susceptibility measurements, but consideration of both effects on an equal footing is necessary in order to reliably distinguish between internal and external causes of magnetic response and accurately extract quantitative information about relaxation processes. In order to address this, we have developed a method to measure the AC magnetocaloric effect that is compatible with AC susceptibility measurements, and also a framework to analyze these data in combination. We demonstrate the efficacy of this approach using YbVO4, a material for which strong single-ion anisotropy leads to slow spin-lattice relaxation at low temperatures via a phonon bottleneck effect. We report AC magnetic susceptibility and AC magnetocaloric effect measurements for this material as a function of field and frequency at a temperature of 3 K. We analyze the data using a discretized thermal model, and extract the field-dependence of the intrinsic spin-lattice relaxation rate. This demonstration experiment illustrates a general approach to quantitatively address multiple measured quantities in driven systems using a unified thermal circuit analysis. The thermal analysis methods presented in this report can be extended to study other magnetic, dielectric, and elastic materials exhibiting a complex response to an external driving field in the presence of internal and external relaxation, particularly when an energy dissipation process is within an accessible frequency regime.

cond-mat.mtrl-sci↗

arXiv2026

AutoFly: Vision-Language-Action Model for UAV Autonomous Navigation in the Wild

Vision-language navigation (VLN) requires intelligent agents to navigate environments by interpreting linguistic instructions alongside visual observations, serving as a cornerstone task in Embodied AI. Current VLN research for unmanned aerial vehicles (UAVs) relies on detailed, pre-specified instructions to guide the UAV along predetermined routes. However, real-world outdoor exploration typically occurs in unknown environments where detailed navigation instructions are unavailable. Instead, only coarse-grained positional or directional guidance can be provided, requiring UAVs to autonomously navigate through continuous planning and obstacle avoidance. To bridge this gap, we propose AutoFly, an end-to-end Vision-Language-Action (VLA) model for autonomous UAV navigation. AutoFly incorporates a pseudo-depth encoder that derives depth-aware features from RGB inputs to enhance spatial reasoning, coupled with a progressive two-stage training strategy that effectively aligns visual, depth, and linguistic representations with action policies. Moreover, existing VLN datasets have fundamental limitations for real-world autonomous navigation, stemming from their heavy reliance on explicit instruction-following over autonomous decision-making and insufficient real-world data. To address these issues, we construct a novel autonomous navigation dataset that shifts the paradigm from instruction-following to autonomous behavior modeling through: (1) trajectory collection emphasizing continuous obstacle avoidance, autonomous planning, and recognition workflows; (2) comprehensive real-world data integration. Experimental results demonstrate that AutoFly achieves a 3.9% higher success rate compared to state-of-the-art VLA baselines, with consistent performance across simulated and real environments.

cs.RO↗

arXiv2025

Electro-nuclear quantum phase transition in TmVO$_4$

Hyperfine interactions couple nuclear and electronic degrees of freedom. The present work explores how hyperfine coupling within the Tm ions in TmVO$_4$ single crystals affects an electronic ferroquadrupole ordered ground state and its associated field-tuned quantum phase transition. For temperatures below the hyperfine energy scale, the nuclear moments reduce the critical field for the electronic order, resulting in a dramatic back-bending of the phase boundary delineating the ferroquadrupole order. This behavior is well described by a single-ion semiclassical mean-field model. Moreover, analysis of the effective Hamiltonian leads to a prediction of spontaneous nuclear magnetic order mediated by 4$f$ electrons, which in principle persists with the application of orthogonal antisymmetric strain, yielding a proposed electro-nuclear tetracritical point.

cond-mat.str-el↗

arXiv2025

Is Artificial Intelligence Reshaping the Landscape of the International Academic Community of Geosciences?

Through bibliometric analysis and topic modeling, we find that artificial intelligence (AI) is positively transforming geosciences research, with a notable increase in AI-related scientific output in recent years. We are encouraged to observe that earth scientists from developing countries have gained better visibility in the recent AI for Science (AI4S) paradigm and that AI is also improving the landscape of international collaboration in geoscience-related research.

cs.DL↗

arXiv2025

Realization of discretized response in rare-earth vanadates accessed by AC susceptibility and magnetocaloric methods

This report presents a new technique to probe the quantitative dynamical response of the magnetic field induced heating/cooling process in rare-earth vanadium materials. The approach combines AC susceptibility and AC caloric measurements to reveal the intrinsic timescale associated with the magnetic relaxation process of rare-earth ions at low temperatures. Utilizing the well-known crystal field effect in YbVO4, we prove and demonstrate a discretized thermal analysis through a common spin-lattice relaxation phenomenon. The demonstration experiment presented in this study provides a general approach to quantitatively address multiple measured quantities in one unified discretized thermal circuit analysis. It can be extended to study other magnetic, dielectric, and elastic materials exhibiting a complex response to an external driving field in the presence of intrinsic interactions and fluctuations, particularly when an energy dissipation process is within an accessible frequency regime.

cond-mat.mtrl-sci↗

arXiv2024

Role of magnetic ions in the thermal Hall effect of the paramagnetic insulator TmVO$_{4}$

In a growing number of materials, phonons have been found to generate a thermal Hall effect, but the underlying mechanism remains unclear. Inspired by previous studies that revealed the importance of Tb$^{3+}$ ions in generating the thermal Hall effect in a family of pyrochlores, we investigated the role of Tm$^{3+}$ ions in TmVO$_{4}$, a paramagnetic insulator with a different crystal structure. We observe a negative thermal Hall conductivity in TmVO$_{4}$ with a magnitude such that the Hall angle, $|κ_{xy}$/$κ_{xx}|$, is approximately 1 x 10$^{-3}$ at $H$ = 15 T and $T$ = 20 K, typical for a phonon-generated thermal Hall effect. In contrast to the negligible $κ_{xy}$ found in the nonmagnetic pyrochlore analog (where the Tb$^{3+}$ ions are replaced with Y$^{3+}$), we observe a negative $κ_{xy}$ in YVO$_{4}$ with a Hall angle of magnitude comparable to that of TmVO$_{4}$. This shows that the Tm$^{3+}$ ions are not essential for the thermal Hall effect in this family of materials. Interestingly, at an intermediate Y concentration of $x$ = 0.3 in Tm$_{1-x}$Y$_{x}$VO$_{4}$, $κ_{xy}$ was found to have a positive sign, pointing to the importance of impurities in the thermal Hall effect of phonons.

cond-mat.mtrl-sci↗

arXiv2024

Disorder-induced local strain distribution in Y-substituted TmVO4

We report an investigation of the effect of substitution of Y for Tm in $Tm_{1-x}Y_xVO4$ via low-temperature heat capacity measurements, with the yttrium content $x$ varying from $0$ to $0.997$. Because the Tm ions support a local quadrupolar (nematic) moment, they act as reporters of the local strain state in the material, with the splitting of the ion's non-Kramers crystal field groundstate proportional to the quadrature sum of the in-plane tetragonal symmetry-breaking transverse and longitudinal strains experienced by each ion individually. Analysis of the heat capacity therefore provides detailed insights into the distribution of local strains that arise as a consequence of the chemical substitution. These local strains suppress long-range quadrupole order for $x>0.22$, and result in a broad Schottky-like feature for higher concentrations. Heat capacity data are compared to expectations for a distribution of uncorrelated (random) strains. For dilute Tm concentrations, the heat capacity cannot be accounted for by randomly distributed strains, demonstrating the presence of significant strain correlations between sites. For intermediate Tm concentrations, these correlations must still exist, but the data cannot be distinguished from that which would be obtained from a 2D Gaussian distribution. The cross-over between these limits is discussed in terms of the interplay of key length scales in the substituted material. The central result of this work, that local strains arising from chemical substitution are not uncorrelated, has implications for the range of validity of theoretical models based on random effective fields that are used to describe such chemically substituted materials, particularly when electronic nematic correlations are present.

cond-mat.str-el↗