arXiv subjects

Shaobo Liu

Publications and source records attributed to Shaobo Liu.

32 records · Page 2Linked to original sources

arXiv2024

Three-dimensional hidden phase probed by in-plane magnetotransport in kagome metal CsV$_3$Sb$_5$ thin flakes

Transition metal compounds with kagome structure have been found to exhibit a variety of exotic structural, electronic, and magnetic orders. These orders are competing with energies very close to each other, resulting in complex phase transitions. Some of the phases are easily observable, such as the charge density wave (CDW) and the superconducting phase, while others are more challenging to identify and characterize. Here we present magneto-transport evidence of a new phase below ~35 K in the kagome topological metal CsV$_3$Sb$_5$ (CVS) thin flakes between the CDW and the superconducting transition temperatures. This phase is characterized by six-fold rotational symmetry in the in-plane magnetoresistance (MR) and is connected to the orbital current order in CVS. Furthermore, the phase is characterized by a large in-plane negative magnetoresistance, which suggests the existence of a three-dimensional, magnetic field-tunable orbital current ordered phase. Our results highlight the potential of magneto-transport to reveal the interactions between exotic quantum states of matter and to uncover the symmetry of such hidden phases.

cond-mat.str-el↗

arXiv2024

Application Of Vision-Language Models For Assessing Osteoarthritis Disease Severity

Osteoarthritis (OA) poses a global health challenge, demanding precise diagnostic methods. Current radiographic assessments are time consuming and prone to variability, prompting the need for automated solutions. The existing deep learning models for OA assessment are unimodal single task systems and they don't incorporate relevant text information such as patient demographics, disease history, or physician reports. This study investigates employing Vision Language Processing (VLP) models to predict OA severity using Xray images and corresponding reports. Our method leverages Xray images of the knee and diverse report templates generated from tabular OA scoring values to train a CLIP (Contrastive Language Image PreTraining) style VLP model. Furthermore, we incorporate additional contrasting captions to enforce the model to discriminate between positive and negative reports. Results demonstrate the efficacy of these models in learning text image representations and their contextual relationships, showcase potential advancement in OA assessment, and establish a foundation for specialized vision language models in medical contexts.

cs.CV↗

arXiv2022

Linear nonsaturating magnetoresistance in kagome superconductor CsV3Sb5 thin flakes

Linear nonsaturating magnetoresistance (LMR) represents a class of anomalous resistivity response to external magnetic field that has been observed in a variety of materials including but not limited to topological semi-metals, high-Tc superconductors and materials with charge/spin density wave (CDW/SDW) orders. Here we report the observation of LMR in layered kagome superconductor and CDW material CsV3Sb5 thin flakes, as well as the dimensional crossover and temperature (T) crossover of such LMR. Specifically, in ultrathin CsV3Sb5 crystals, the magnetoresistance (MR) exhibits a crossover from LMR at low T to quadratic B dependence above the CDW transition temperature; the MR also exhibits a crossover from LMR to sublinear MR for sample thickness at around ~20 nm at low T. We discuss several possible origins of the LMR and attribute the effect to two-dimensional (2D) CDW fluctuations. Our results may provide a new perspective for understanding the interactions between competing orders in kagome superconductors.

cond-mat.supr-con↗

arXiv2021

Cu doping effects on the electronic structure of Fe1-xCuxSe

Using angle-resolved photoemission spectroscopy (ARPES), we studied the evolution of the electronic structure of Fe1-xCuxSe from x = 0 to 0.10. We found that the Cu dopant introduces extra electron carriers. The hole bands near the gamma point are observed to steadily shift downward with increasing doping and completely sink down below the Fermi level (EF) for x > 0.05. Meanwhile, the electron pocket near the M point becomes larger but loses the spectral weight near EF. We also observed that effective mass of the electron band near the M point increases with doping. Our result explains why superconductivity disappears and metal insulator transition (MIT) like behavior occurs upon Cu doping in terms of electronic structure, and provide insight into emergent magnetic fluctuation in Fe1-xCuxSe.

cond-mat.supr-con↗

arXiv2021

Magnetic-Field-Induced Spin Nematicity in FeSe1-xSx and FeSe1-yTey Superconductor Systems

The angular-dependent magnetoresistance (AMR) of the ab plane is measured on the single crystals of FeSe1-xSx (x = 0, 0.07, 0.13 and 1) and FeSe1-yTey (y = 0.06, 0.61 and 1) at various temperatures under fields up to 9 T. A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR, and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature Tsn. This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe1-xSx and FeSe1-yTey systems, no matter whether the sample shows an electronic nematic order at Ts < Tsn, or an antiferromagnetic order at TN < Tsn, or neither order. Importantly, we find that the isoelectronic substitution with sulfur does not suppress but even enhances the characteristic Tsn of the induced spin nematicity in FeSe1-xSx samples. This contrasts sharply with their rapidly suppressed Ts, the transition temperature of the spontaneous electronic nematicity. Furthermore, we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe1-xSx and FeSe1-yTey samples.

cond-mat.supr-con↗

arXiv2021

Unusual normal and superconducting state properties observed in hydrothermal Fe1-xSe flakes

The electronic and superconducting properties of Fe1-xSe single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T. The results contrast sharply with those previously reported for nematically ordered FeSe by chemical-vapor-transport (CVT) growth. No signature of the electronic nematicity, but an evident metal-to-nonmetal crossover with increasing temperature, is detected in the normal state of the present hydrothermal samples. Interestingly, a higher superconducting critical temperature Tc of 13.2 K is observed compared to a suppressed Tc of 9 K in the presence of the nematicity in the CVT FeSe. Moreover, the upper critical field in the zero-temperature limit is found to be isotropic with respect to the field direction and to reach a higher value of ~42 T, which breaks the Pauli limit by a factor of 1.8.

cond-mat.supr-con↗

arXiv2021

Anisotropic superconducting properties of Kagome metal CsV3Sb5

We systematically measure the superconducting (SC) and mixed state properties of high-quality CsV3Sb5 single crystals with Tc ~ 3.5 K. We find that the upper critical field Hc2(T) exhibits a large anisotropic ratio of Hc2^(ab)/Hc2^(c) ~ 9 at zero temperature and fitting its temperature dependence requires a minimum two-band effective model. Moreover, the ratio of the lower critical field, Hc1^(ab)/Hc1^(c), is also found to be larger than 1, which indicates that the in-plane energy dispersion is strongly renormalized near Fermi energy. Both Hc1(T) and SC diamagnetic signal are found to change little initially below Tc ~ 3.5 K and then to increase abruptly upon cooling to a characteristic temperature of ~2.8 K. Furthermore, we identify a two-fold anisotropy of in-plane angular-dependent magnetoresistance in the mixed state. Interestingly, we find that, below the same characteristic T ~ 2.8 K, the orientation of this two-fold anisotropy displays a peculiar twist by an angle of 60o characteristic of the Kagome geometry. Our results suggest an intriguing superconducting state emerging in the complex environment of Kagome lattice, which, at least, is partially driven by electron-electron correlation.

cond-mat.supr-con↗

arXiv2020

Disentangle-based Continual Graph Representation Learning

Graph embedding (GE) methods embed nodes (and/or edges) in graph into a low-dimensional semantic space, and have shown its effectiveness in modeling multi-relational data. However, existing GE models are not practical in real-world applications since it overlooked the streaming nature of incoming data. To address this issue, we study the problem of continual graph representation learning which aims to continually train a GE model on new data to learn incessantly emerging multi-relational data while avoiding catastrophically forgetting old learned knowledge. Moreover, we propose a disentangle-based continual graph representation learning (DiCGRL) framework inspired by the human's ability to learn procedural knowledge. The experimental results show that DiCGRL could effectively alleviate the catastrophic forgetting problem and outperform state-of-the-art continual learning models.

cs.LG↗

arXiv2020

Electronic phase diagram of iron chalcogenide superconductors FeSe1-xSx and FeSe1-yTey

Here we establish a combined electronic phase diagram of isoelectronic FeSe1-xSx (0.19 > x > 0.0) and FeSe1-yTey (0.04 < y < 1.0) single crystals. The FeSe1-yTey crystals with y = 0.04 - 0.30 are grown by a hydrothermal ion-deintercalation (HID) method. Based on combined experiments of the specific heat, electrical transport, and angle-resolved photoemission spectroscopy, no signature of the tetragonal-symmetry-broken transition to orthorhombic (nematic) phase is observed in the HID FeSe1-yTey samples, as compared with the FeSe1-xSx samples showing this transition at Ts. A ubiquitous dip-like temperature dependence of the Hall coefficient is observed around a characteristic temperature T* in the tetragonal regimes, which is well above the superconducting transition. More importantly, we find that the superconducting transition temperature Tc is positively correlated with the Hall-dip temperature T* across the FeSe1-xSx and FeSe1-yTey systems, suggesting that the tetragonal background is a fundamental host for the superconductivity.

cond-mat.supr-con↗

arXiv2018

Exploiting Contextual Information via Dynamic Memory Network for Event Detection

The task of event detection involves identifying and categorizing event triggers. Contextual information has been shown effective on the task. However, existing methods which utilize contextual information only process the context once. We argue that the context can be better exploited by processing the context multiple times, allowing the model to perform complex reasoning and to generate better context representation, thus improving the overall performance. Meanwhile, dynamic memory network (DMN) has demonstrated promising capability in capturing contextual information and has been applied successfully to various tasks. In light of the multi-hop mechanism of the DMN to model the context, we propose the trigger detection dynamic memory network (TD-DMN) to tackle the event detection problem. We performed a five-fold cross-validation on the ACE-2005 dataset and experimental results show that the multi-hop mechanism does improve the performance and the proposed model achieves best $F_1$ score compared to the state-of-the-art methods.

cs.CL↗

arXiv2018

Spatial and Spectral Features Fusion for EEG Classification during Motor Imagery in BCI

Brain computer interface (BCI) is the only way for some special patients to communicate with the outside world and provide a direct control channel between brain and the external devices. As a non-invasive interface, the scalp electroencephalography (EEG) has a significant potential to be a major input signal for future BCI systems. Traditional methods only focus on a particular feature in the EEG signal, which limits the practical applications of EEG-based BCI. In this paper, we propose a algorithm for EEG classification with the ability to fuse multiple features. First, use the common spatial pattern (CSP) as the spatial feature and use wavelet coefficient as the spectral feature. Second, fuse these features with a fusion algorithm in orchestrate way to improve the accuracy of classification. Our algorithms are applied to the dataset IVa from BCI complete \uppercase\expandafter{\romannumeral3}. By analyzing the experimental results, it is possible to conclude that we can speculate that our algorithm perform better than traditional methods.

q-bio.QM↗

arXiv2018

Electronic phase separation in iron selenide (Li, Fe)OHFeSe superconductor system

The phenomenon of phase separation into antiferromagnetic (AFM) and superconducting (SC) or normal-state regions has great implication for the origin of high-temperature (high-Tc) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the Tc of (Li, Fe)OHFeSe superconductor is questioned. Here we report a systematic study on a series of (Li, Fe)OHFeSe single crystal samples with Tc up to ~41 K. We observe an evident drop in the static magnetization at Tafm ~125 K, in some of the SC (Tc < ~38 K, cell parameter c < ~9.27 Å) and non-SC samples. We verify that this AFM signal is intrinsic to (Li, Fe)OHFeSe. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal (below Tafm) or SC (below Tc) state in (Li, Fe)OHFeSe. We explain such coexistence by electronic phase separation, similar to that in high-Tc cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of (Li, Fe)OHFeSe, particularly it is never observed in the SC samples of Tc > ~38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. It is suggested that the microscopic static phase separation reaches vanishing point in high-Tc (Li, Fe)OHFeSe, by the occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as Tafm reported previously for a (Li, Fe)OHFeSe (Tc ~42 K) single crystal. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-Tc superconductivity.

cond-mat.supr-con↗

arXiv2017

Superconducting (Li, Fe)OHFeSe film of high quality and high critical parameters

The superconducting film of (Li1-xFex)OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22 deg, in terms of the FWHM (full-width-at-half-maximum) of x-ray rocking curve, and an excellent out-of-plane orientation by x-ray phi-scan. Its bulk superconducting transition temperature (Tc) of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field (Hc2) is estimated to be 79.5 T and 443 T, respectively, for the magnetic field perpendicular and parallel to the ab plane. Moreover, a large critical current density (Jc) of a value over 0.5 MA/cm2 is achieved at ~20 K. Such a (Li1-xFex)OHFeSe film is therefore not only important to the fundamental research for understanding the high-Tc mechanism, but also promising in the field of high-Tc superconductivity application, especially in high-performance electronic devices and large scientific facilities such as superconducting accelerator.

cond-mat.supr-con↗

arXiv2017

Doping Mn into (Li1-xFex)OHFe1-ySe superconducting crystals via ion-exchange and ion-release/introduction syntheses

We report the success in introducing Mn into (Li1-xFex)OHFe1-ySe superconducting crystals by applying two different hydrothermal routes, ion exchange (1-Step) and ion release/introduction (2-Step). The micro-region x-ray diffraction and energy dispersive x-ray spectroscopy analyses indicate that the Mn has been doped into the lattice, and its content in the 1-Step fabricated sample is higher than that in the 2-Step one. Magnetic susceptibility and electric transport properties reveal that Mn doping influences little on the superconducting transition, regardless of 1-Step or 2-Step routes. By contrast, the characteristic temperature, T*, where the negative Hall coefficient reaches its minimum, is significantly reduced by Mn doping. This implies that the reduction of the hole carriers contribution is obviously modified, and hence the hole band might have no direct relationship with the superconductivity in (Li1-xFex)OHFe1-ySe superconductors. Our present hydrothermal methods of ion exchange and ion release/introduction provide an efficient way for elements substitution/doping into (Li1-xFex)OHFe1-ySe superconductors, which will promote the in-depth investigations on the role of multiple electron and hole bands and their interplay with the high-temperature superconductivity in the FeSe-based superconductors.

cond-mat.supr-con↗