arXiv subjects

C. L. Huang

Publications and source records attributed to C. L. Huang.

10 recordsLinked to original sources

arXiv2025

Complex magnetic phases and thermodynamics of CuB_2O_4

The copper metaborate CuB_2O_4(CBO) has been studied within the parametric space of magnetic field (B) and temperature (T), showing a series of distinct phases, including commensurate and incommensurate magnetic orders, as well as magnetic soliton phases. However, no single study has simultaneously demonstrated all these phases. moreover, the existence of additional phases below 2 K or above 2 T for B perpenducular to c has been scarcely explored. This work presents the first comprehensive construction of the complex B-T phase diagram for T = 0.1 to 25 K and B = 0 to 9 T (B perpenducular to c), utilizing thermodynamic probes, magnetic measurements, and neutron scattering on a single batch of CBO crystals. Our findings elucidate new magnetic phases and regimes. First-principles calculations help to gain a deeper understanding of this complex phase diagram. The emergence of various phases within such a narrow B and T regime is attributed to two primary mechanisms: the delicate competition between ferromagnetic and antiferromagnetic interactions, and the weak exchange and superexchange interactions within and between the Cu(A) and Cu(B) sublattices. This competition also leads to a magnetically frustrated ground state at absolute zero where the total magnetic entropy release from high to low temperatures is only 0.76 Rln2, lower than Rln2 expected for copper spin 1/2. Using CBO as a model system, the present work elucidates the intricate mechanisms underlying the formation of complex magnetic phases.

cond-mat.str-el↗

arXiv2020

SYMBA: An end-to-end VLBI synthetic data generation pipeline

Realistic synthetic observations of theoretical source models are essential for our understanding of real observational data. In using synthetic data, one can verify the extent to which source parameters can be recovered and evaluate how various data corruption effects can be calibrated. These studies are important when proposing observations of new sources, in the characterization of the capabilities of new or upgraded instruments, and when verifying model-based theoretical predictions in a comparison with observational data. We present the SYnthetic Measurement creator for long Baseline Arrays (SYMBA), a novel synthetic data generation pipeline for Very Long Baseline Interferometry (VLBI) observations. SYMBA takes into account several realistic atmospheric, instrumental, and calibration effects. We used SYMBA to create synthetic observations for the Event Horizon Telescope (EHT), a mm VLBI array, which has recently captured the first image of a black hole shadow. After testing SYMBA with simple source and corruption models, we study the importance of including all corruption and calibration effects. Based on two example general relativistic magnetohydrodynamics (GRMHD) model images of M87, we performed case studies to assess the attainable image quality with the current and future EHT array for different weather conditions. The results show that the effects of atmospheric and instrumental corruptions on the measured visibilities are significant. Despite these effects, we demonstrate how the overall structure of the input models can be recovered robustly after performing calibration steps. With the planned addition of new stations to the EHT array, images could be reconstructed with higher angular resolution and dynamic range. In our case study, these improvements allowed for a distinction between a thermal and a non-thermal GRMHD model based on salient features in reconstructed images.

astro-ph.IM↗

arXiv2019

Complex Transport and Magnetism in Inhomogeneous Mixed Valence Ce$_3$Ir$_4$Ge$_{13}$

We report the discovery of Ce$_3$Ir$_4$Ge$_{13}$, a new Remeika phase compound with a complex array of structural, electronic, and magnetic properties. Our single crystal x-ray diffraction measurements show that Ce$_3$Ir$_4$Ge$_{13}$ forms in the tetragonally distorted $I4_1/amd$ space group. The electrical resistivity is almost temperature independent over three decades in temperature, from 0.4 K to 400 K, while the Hall coefficient measurements are consistent with a low-carrier semimetal. Magnetic susceptibility measurements reveal an effective moment of $μ^{\text{exp}}_{\text{eff}} = 1.87 μ_B$/Ce, suggesting that this material has a mixture of magnetic Ce$^{3+}$ and non-magnetic Ce$^{4+}$. Upon cooling, Ce$_3$Ir$_4$Ge$_{13}$ first enters a short range magnetically ordered state below $T_{\text{SRO}}=10$ K, marked by a deviation from Curie-Weiss behavior in susceptibility and a broad field-independent heat capacity anomaly. At lower temperatures, we observe a second, sharper peak in the heat capacity at $T^* = 1.7$ K, concurrent with a splitting of the field-cooled and zero-field-cooled susceptibilities. A small resistivity drop at $T^*$ suggests a loss of spin disorder scattering consistent with a magnetic ordering or spin freezing transition. Ce$_3$Ir$_4$Ge$_{13}$ is therefore a rare example of an inhomogeneous mixed valence compound with a complex array of thermodynamic and transport properties.

cond-mat.str-el↗

arXiv2010

Colossal Electroresistance and Colossal Magnetoresistance in Spinel Multiferroic CdCr2S4

Colossal magnetoresistance (CMR) and electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition (MIT) in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive (CMC), colossal electrocapacitive (CEC), CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.

cond-mat.str-el↗

arXiv2010

Anomalous pressure effect on the magnetic ordering in multiferroic BiMnO3

We report the magnetic field dependent dc magnetization and the pressure-dependent (pmax ~ 16 kbar) ac susceptibilities Xp(T) on both powder and bulk multiferroic BiMnO3 samples, synthesized in different batches under high pressure. A clear ferromagnetic (FM) transition is observed at TC ~ 100 K, and increases with magnetic field. The magnetic hysteresis behavior is similar to that of a soft ferromagnet. Ac susceptibility data indicate that both the FM peak and its temperature (TC) decrease simultaneously with increasing pressure. Interestingly, above a certain pressure (9 ~ 11 kbar), another peak appears at Tp ~ 93 K, which also decreases with increasing pressure, with both these peaks persisting over some intermediate pressure range (9 ~ 13 kbar). The FM peak disappears with further application of pressure; however, the second peak survives until present pressure limit (pmax ~ 16 kbar). These features are considered to originate from the complex interplay of the magnetic and orbital structure of BiMnO3 being affected by pressure.

cond-mat.str-el↗

arXiv2010

Multiple magnetic transitions in multiferroic BiMnO3

The magnetic phase variations under hydrostatic pressure on multiferroic BiMnO3 have been examined by the dc magnetization [Mg(T)], magnetic hysteresis [Ueff(H)], and ac susceptibility [X'g(T)]. Three magnetic transitions, manifested as kinks I, II, and III on the Mg(T)], curves, were identified at 8.7 and 9.4 kbar. With increasing pressure, transition temperatures of kink I and kink II TkI and TkII tend to decrease, but the temperature of kink III TkIII showed more complex variation. Under increasing magnetic field, TkI and TkII increase; however, TkIII decreases. Combining [Mg(T)] curves with Ueff(H) and X'g(T), more detailed properties of these three kinks would be shown as follows. Kink I is a long-range soft ferromagnetic transition which occurs at TkI 100 K under ambient pressure but is suppressed completely at 11.9 kbar. Kink II emerges at 8.7 kbar along with TkII 93 K which is also long-range soft ferromagnetic but canted in nature. Kink III, a canted antiferromagnetic transition, appears at TkIII 72.5 K along with kink II also at 8.7 kbar. The proposed phase diagrams at ambient pressure, 9.4 and 11.9 kbar show the different magnetic features of BiMnO3. These findings are believed to result from the variations in crystal structure influenced by the external pressure. These results also indicate the common complicated

cond-mat.str-el↗

arXiv2007

Experimental evidence for a two-gap structure of superconducting NbSe_2: a specific heat study in external magnetic fields

To resolve the discrepancies of the superconducting order parameter in quasi-two-dimensional NbSe_2, comprehensive specific-heat measurements have been carried out. By analyzing both the zero-field and mixed-state data with magnetic fields perpendicular to and parallel to the c axis of the crystal and using the two-gap model, we conclude that (1) more than one energy scale of the order parameter is required for superconducting NbSe_2 due to the thermodynamic consistency; (2)delta_L=1.26 meV and delta_S=0.73 meV are obtained; (3) N_S(0)/N(0)=11%~20%; (4) The observation of the kink in gamma(H) curve suggests that the two-gap scenario is more favorable than the anisotropic s-wave model to describe the gap structure of NbSe_2; and (5)delta_S is more isotropic and has a three-dimensional-like feature and is located either on the Se or the bonding Nb Fermi sheets.

cond-mat.supr-con↗

arXiv2005

Anomalous Magnetic and Thermal Behavior in Some RMn2O5 Oxides

The RMn2O5 (R=Pr, Nd, Sm, and Eu) oxides showing magnetoelectric (ME) behavior have been prepared in polycrystalline form by a standard citrate route. The lattice parameters, obtained from the powder XRD analysis, follow the rare-earth contraction indicating the trivalent character of the R ions. Cusp-like anomalies in the magnetic susceptibility curve and sharp peaks in the specific heat were reported at the corresponding temperatures in RMn2O5 (R=Pr, Nd, Sm, and Eu) indicating the magnetic or electric ordering transitions.

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↗

arXiv2005

Evidence of nodal superconductivity in Na_0.35CoO2-1.3H_2O: a specific heat study

Comprehensive low-temperature specific heat data C(T,H) of Na_0.35CoO2-1.3H_2O with temperature T down to 0.6 K and the magnetic field H up to 8 T are presented. For the normal state, the values of gamma_n=13.94 mJ/mol K2, and Debye temperature 362 K are reported. At zero field, a very sharp superconducting anomaly was observed at Tc=4.5 K with DeltaC/gamma_nTc=1.45. The superconducting volume fraction is estimated to be 47.4 % based on the consideration of entropy balance at Tc for the second-order superconducting phase transition. In the superconducting state, the electronic contribution C_es at H=0 can be well described by the model of the line nodal order parameter. In low H, gamma(H) H^1/2 which is also a manifestation of the line nodes. The behaviors of both Tc(H) and gamma(H) suggest the anisotropy of Hc2 or possible crossovers or transitions occurring in the mixed state.

cond-mat.supr-con↗