arXiv subjects

J. Y. Lin

Publications and source records attributed to J. Y. Lin.

12 recordsLinked to original sources

arXiv2025

Successive magnetic transitions and multiferroicity in layered honeycomb BiCrTeO$_{6}$

Low-dimensional magnetic systems based on honeycomb lattices provide a promising platform for exploring exotic quantum phenomena that emerge from the intricate interplay of competing spin, orbital, lattice, and dipolar degrees of freedom. Here, we present a comprehensive study of the layered honeycomb lattice antiferromagnet BiCrTeO$_6$ using magnetization, specific heat, muon spin--relaxation ($\mu$SR) spectroscopy, dielectric, pyrocurrent, and high-resolution synchrotron X-ray diffraction (SXRD) measurements. Our results reveal an array of intriguing and strongly correlated phenomena, including two successive antiferromagnetic transitions at $T_{\rm N1}\approx16$ K and $T_{\rm N2}\approx11$ K, a pronounced magnetodielectric coupling effect, and ferroelectric order at $T_{\rm N2}$. Consequently, this compound emerges as a new spin-driven multiferroic system. The SXRD analysis reveals a magnetoelastic-coupling-induced structural phase transition at $T_{\rm N2}$, characterized by a symmetry lowering from P$\bar{3}$1c (163) to P31c (159), which likely triggers the onset of ferroelectricity. In addition to its low-temperature multiferroic behavior, the system exhibits dielectric relaxor characteristics at higher temperatures within the paramagnetic region ($T<50$ K), which is intrinsically linked to the antisite disorder of Cr and Te atoms.

cond-mat.str-el↗

arXiv2020

Unidirectional ripplopolaron charge transport in a three-terminal microchannel device

We study the transport of surface electrons on superfluid helium through a microchannel structure in which the charge flow splits into two branches, one flowing straight and one turned at 90 degrees. According to Ohm law, an equal number of charges should flow into each branch. However, when the electrons are dressed by surface excitations (ripplons) to form polaron-like particles with sufficiently large effective mass, all the charge follows the straight path due to momentum conservation. This surface-wave induced transport is analogous to the motion of electrons coupled to surface acoustic waves in semiconductor 2DEGs.

cond-mat.mes-hall↗

arXiv2020

Observation of Optical Gain in Er-Doped GaN Epilayers

Rare-earth based lasing action in GaN semiconductor at the telecommunication wavelength of 1.5 micron has been demonstrated at room temperature. We have reported the stimulated emission under the above bandgap excitation from Er doped GaN epilayers prepared by metal-organic chemical vapor deposition. Using the variable stripe technique, the observation of the stimulated emission has been demonstrated through characteristic features of threshold behavior of emission intensity as functions of pump intensity, excitation length, and spectral linewidth narrowing. Using the variable stripe setup, the optical gain up to 75 cm-1 has been obtained in the GaN:Er epilayers. The near infrared lasing from GaN semiconductor opens up new possibilities for extended functionalities and integration capabilities for optoelectronic devices.

physics.app-ph↗

arXiv2018

Transport properties of a quasi-1D Wigner Solid on liquid helium confined in a microchannel with periodic potential

We present transport measurements in a quasi-1D system of surface electrons on liquid helium confined in a 101-$μ$m long and 5-$μ$m wide microchannel where an electrostatic potential with periodicity of $1$-$μ$m along the channel is introduced. In particular, we investigate the influence of such a potential on the nonlinear transport of quasi-1D Wigner Solid (WS) by varying the amplitude of the periodic potential in a wide range. At zero and small values of amplitude, quasi-1D WS in microchannel shows expected features such as the Bragg-Cherenkov scattering of ripplons and reentrant melting. As the amplitude of potential increases, the above features are strongly suppressed. This behavior suggests loss of the long-range positional order in the electron system, which is reminiscent of the re-entrant melting behaviour due to the lateral confinement of WS in the channel.

cond-mat.mes-hall↗

arXiv2018

Room-temperature lasing action in GaN quantum wells in the infrared 1.5 micron region

Large-scale optoelectronics integration is strongly limited by the lack of efficient light sources, which could be integrated with the silicon complementary metal-oxide-semiconductor (CMOS) technology. Persistent efforts continue to achieve efficient light emission from silicon in the extending the silicon technology into fully integrated optoelectronic circuits. Here, we report the realization of room-temperature stimulated emission in the technologically crucial 1.5 micron wavelength range from Er-doped GaN multiple-quantum wells on silicon and sapphire. Employing the well-acknowledged variable stripe technique, we have demonstrated an optical gain up to 170 cm-1 in the multiple-quantum well structures. The observation of the stimulated emission is accompanied by the characteristic threshold behavior of emission intensity as a function of pump fluence, spectral linewidth narrowing and excitation length. The demonstration of room-temperature lasing at the minimum loss window of optical fibers and in the eye-safe wavelength region of 1.5 micron are highly sought-after for use in many applications including defense, industrial processing, communication, medicine, spectroscopy and imaging. As the synthesis of Er-doped GaN epitaxial layers on silicon and sapphire has been successfully demonstrated, the results laid the foundation for achieving hybrid GaN-Si lasers providing a new pathway towards full photonic integration for silicon optoelectronics.

physics.app-ph↗

arXiv2016

Photoluminescence quantum efficiency of Er optical centers in GaN epilayers

We report the quantum efficiency of photoluminescence processes of Er optical centers as well as the thermal quenching mechanism in GaN epilayers prepared by metal-organic chemical vapor deposition. High resolution infrared spectroscopy and temperature dependence measurements of photoluminescence intensity from Er ions in GaN under resonant excitation excitations were performed. Data provide a picture of the thermal quenching processes and activation energy levels. By comparing the photoluminescence from Er ions in the epilayer with a reference sample of Er-doped SiO2, we find that the fraction of Er ions that emits photon at 1.54 micron upon a resonant optical excitation is approximately 68%. This result presents a significant step in the realization of GaN:Er epilayers as an optical gain medium at 1.54 micron.

cond-mat.mtrl-sci↗

arXiv2015

Antisite disorder driven spontaneous exchange bias effect in La2-xSrxCoMnO6 (0<x<1)

Doping at the rare-earth site by divalent alkaline-earth ions in perovskite lattice has witnessed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report an antisite disorder driven spontaneous exchange bias effect as a result of hole carrier (Sr2+) doping in La2-xSrxCoMnO6 (0 < x < 1) double perovskites. X-ray diffraction and Raman spectroscopy have evidenced an increase in disorder with the increase of Sr content up to x = 0.5 and thereby decreases from x = 0.5 to 1. X-ray absorption spectroscopy has revealed that only Co is present in mixed valent Co2+ and Co3+ states with Sr doping to compensate the charge neutrality. Magnetotransport is strongly correlated with the increase of antisite disorder. The antisite disorder at the B-site interrupts the long-range ferromagnetic order by introducing various magnetic interactions and instigates reentrant glassy dynamics, phase separation and canted type antiferromagnetic behavior with the decrease of temperature. This leads to novel magnetic microstructure with unidirectional anisotropy that causes spontaneous exchange bias effect that can be tuned with the amount of antisite disorder.

cond-mat.str-el↗

arXiv2015

Excitation Mechanisms of Er Optical Centers in GaN Epilayers

We report direct evidence of two mechanisms responsible for the excitation of optically active Er3+ ions in GaN epilayers grown by metal-organic chemical vapor deposition. These mechanisms, resonant excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, lead to narrow emission lines from isolated and the defect-related Er centers. However, these centers have different photoluminescence spectra, decay dynamics, and excitation cross sections. The isolated Er optical center, which can be excited by either mechanism, has the same decay dynamics, but possesses a much higher cross-section under band-to-band excitation. In contrast, the defect-related Er center can only be excited through band-to-band excitation but has the largest cross-section. These results explain the difficulty in achieving gain in Er doped GaN and indicate new approaches for realization of optical amplification, and possibly lasing, at room temperature.

cond-mat.mtrl-sci↗

arXiv2014

Metamagnetic behavior and effect of field cooling on sharp magnetization jumps in multiferroic Y2CoMnO6

We present sharp magnetization jumps and field induced irreversibility in magnetization in multiferroic Y2CoMnO6. Appearance of magnetic relaxation and field sweep rate dependence of magnetization jumps resemble the martensite like scenario and suggests the coexistence of E*-type antiferromagnetic and ferromagnetic phases at low temperatures. In Y2CoMnO6, the critical field required for the sharp jump can be increased or decreased depening on the magnitude and direction of the cooling field; this is remarkably different from manganites or other metamagnetic materials where the critical field increases irrespective of the direction of the field cooling. The cooling field dependence on the sharp magnetization jumps has been described by considering exchange pinning mechanism at the interface, like in exchange bias model.

cond-mat.str-el↗

arXiv2011

Metastable giant moments in Gd-implanted GaN, Si, and sapphire

We report on Gd ion implantation and magnetic characterization of GaN films on sapphire substrates and of bare sapphire and Si substrates to shed light on the mechanism underlying the induced magnetism upon Gd ion implantation. For all three hosts, giant magnetic moments per Gd ion were observed at temperatures of 5 through 300 K. The maximum moment per Gd in GaN was 1800 mu_B, while the moments in Gd-implanted Si and sapphire were only slightly smaller. The apparent induced ferromagnetic response was found to be metastable, disappearing after on the order of 50 days at room temperature, except for the implanted sapphire. We argue that our findings support a defect-based picture of magnetism in Gd-implanted semiconductors and insulators.

cond-mat.mtrl-sci↗

arXiv2006

Carbon-doped ZnO: A New Class of Room Temperature Dilute Magnetic Semiconductor

We report magnetism in carbon doped ZnO. Our first-principles calculations based on density functional theory predicted that carbon substitution for oxygen in ZnO results in a magnetic moment of 1.78 $μ_B$ per carbon. The theoretical prediction was confirmed experimentally. C-doped ZnO films deposited by pulsed laser deposition with various carbon concentrations showed ferromagnetism with Curie temperatures higher than 400 K, and the measured magnetic moment based on the content of carbide in the films ($1.5 - 3.0 μ_B$ per carbon) is in agreement with the theoretical prediction. The magnetism is due to bonding coupling between Zn ions and doped C atoms. Results of magneto-resistance and abnormal Hall effect show that the doped films are $n$-type semiconductors with intrinsic ferromagnetism. The carbon doped ZnO could be a promising room temperature dilute magnetic semiconductor (DMS) and our work demonstrates possiblity of produing DMS with non-metal doping.

cond-mat.mtrl-sci↗

arXiv2005

Comparative analysis of specific heat of YNi2B2C using nodal and two-gap models

The magnetic field dependence of low temperature specific heat in YNi2B2C was measured and analyzed using various pairing order parameters. At zero magnetic field, the two-gap model which has been successfully applied to MgB2 and the point-node model, appear to describe the superconducting gap function of YNi2B2C better than other models based on the isotropic s-wave, the d-wave line nodes, or the s+g wave. The two energy gaps, delta_L=2.67 meV and delta_S=1.19 meV are obtained. The observed nonlinear field dependence of electronic specific heat coefficient, gamma(H)~H0.47, is quantitatively close to gamma(H)~H0.5 expected for nodal superconductivity or can be qualitatively explained using two-gap scenario. Furthermore, the positive curvature in Hc2(T) near Tc is qualitatively similar to that in the other two-gap superconductor MgB2.

cond-mat.supr-con↗