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C. H. Lin

Publications and source records attributed to C. H. Lin.

11 recordsLinked to original sources
arXiv2017

Bolometric arrays and infrared sensitivity of VO2 films with varying stoichiometry

Here we propose a linear microbolometric array based on VOx thin films. The linear microbolometric array is fabricated by using micromachining technology, and its thermo-sensitive VOx thin film has excellent infrared response spectrum and TCR characteristics. Nano-scale VOx thin films deposited on SiO2/Si substrates were obtained by e-beam vapor deposition. The VOx films were then annealed at temperatures between 300 to 500 C with various deposition duration time. The crystal structures and microstructures were examined by XRD, SEM and ESCA. These films showed a predominant phase of rhombohedral VO2 and the crystallinity of the VO2 increased as the annealing temperature increased. Integrated with CMOS circuit, an experimentally prototypical monolithic linear microbolometric array is designed and fabricated. The testing results of the experimental linear array show that the responsivity of linear array can approach 18KV/W and is potential for infrared image systems.

cond-mat.mes-hall↗
arXiv2016

29Si nuclear magnetic resonance study of URu2Si2 under pressure

We report 29Si nuclear magnetic resonance measurements of single crystals and aligned powders of URu2Si2 under pressure in the hidden order and paramagnetic phases. We find that the Knight shift decreases with applied pressure, consistent with previous measurements of the static magnetic susceptibility. Previous measurements of the spin lattice relaxation time revealed a partial suppression of the density of states below 30 K. This suppression persists under pressure, and the onset temperature is mildly enhanced.

cond-mat.str-el↗
arXiv2015

Evolution of hyperfine parameters across a quantum critical point in CeRhIn$_5$

We report Nuclear Magnetic Resonance (NMR) data for both the In(1) and In(2) sites in the heavy fermion material CeRhIn$_5$ under hydrostatic pressure. The Knight shift data reveal a suppression of the hyperfine coupling to the In(1) site as a function of pressure, and the electric field gradient, $ν_{αα}$, at the In(2) site exhibits a change of slope, $dν_{αα}/dP$, at $P_{c1} = 1.75$ GPa. These changes to these coupling constants reflect alterations to the electronic structure at the quantum critical point.

cond-mat.str-el↗
arXiv2015

NMR evidence for inhomogeneous nematic fluctuations in BaFe$_2$(As$_{1-x}$P$_x$)$_2$

We present evidence for nuclear spin-lattice relaxation driven by glassy nematic fluctuations in isovalent P-doped BaFe$_2$As$_2$ single crystals. Both the $^{75}$As and $^{31}$P sites exhibit stretched-exponential relaxation similar to the electron-doped systems. By comparing the hyperfine fields and the relaxation rates at these sites we find that the As relaxation cannot be explained solely in terms of magnetic spin fluctuations. We demonstrate that nematic fluctuations couple to the As nuclear quadrupolar moment and can explain the excess relaxation. These results suggest that glassy nematic dynamics are a universal phenomenon in the iron-based superconductors.

cond-mat.str-el↗
arXiv2015

NMR Evidence of anisotropic Kondo liquid behavior in CeIrIn$_5$

We report detailed Knight shift measurements of the two indium sites in the heavy fermion compound CeIrIn$_5$ as a function of temperature and field orientation. We find that the Knight shift anomaly is orientation-dependent, with a crossover temperature $T^*$ that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce 4f states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.

cond-mat.str-el↗
arXiv2013

Coexistence of cluster spin glass and superconductivity in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ for $0.060 \leq x \leq 0.071$

We present 75As nuclear magnetic resonance data from measurements of a series of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ crystals with $0.00 \leq x \leq 0.075$ that reveals the coexistence of frozen antiferromagnetic domains and superconductivity for $0.060 \leq x \leq 0.071$. Although bulk probes reveal no long range antiferromagnetic order beyond $x = 0.06$, we find that the local spin dynamics reveal no qualitative change across this transition. The characteristic domain sizes vary by more than an order of magnitude, reaching a maximum variation at $x = 0.06$. This inhomogeneous glassy dynamics may be an intrinsic response to the competition between superconductivity and antiferromagnetism in this system.

cond-mat.str-el↗
arXiv2013

Nuclear magnetic resonance as a probe of electronic states of Bi2Se3

We present magnetotransport and Bi-209 nuclear magnetic resonance (NMR) data on a series of single crystals of Bi2Se3, Bi2Te2Se and Cu_xBi2Se3 with varying carrier concentrations. The Knight shift of the bulk nuclei is strongly correlated with the carrier concentration via a hyperfine coupling of 27 ueV, which may have important consequences for scattering of the protected surface states. Surprisingly we find that the NMR linewidths and the spin lattice relaxation rate appear to be dominated by the presence of localized spins, which may be related to the presence of Se vacancies.

cond-mat.mtrl-sci↗
arXiv2010

Commensurate Antiferromagnetism in CePt2In7, a Nearly Two-Dimensional Heavy Fermion System

CePt$_2$In$_7$ is a new heavy fermion system with a structure similar to the CeMIn$_5$ system but with greater two-dimensional character. We report the synthesis and characterization of phase pure polycrystalline material, which reveals an antiferromagnetic transition at $T_N = 5.2$ K. Nuclear Quadrupolar Resonance (NQR) studies indicate that the antiferromagnetism is commensurate and exhibits strong antiferromagnetic fluctuations in the paramagnetic state.

cond-mat.str-el↗
arXiv2008

Sodium Trimer Ordering on NaxCoO2 Surface

Sodium ion ordering on in situ cleaved NaxCoO2 (x=0.84) surface has been studied by ultra high vacuum scanning tunneling microscopy (UHV-STM) at room temperature. Three main phases, with p(3x3), (root 7 x root 7), and (2 root 3 x 2 root 3) hexagonal unit cells and surface Na concentration of 1/3, 3/7, 1/2, respectively, were identified. One surprising finding is that Na trimers act as the basic building blocks that order in long range. The stability of Na trimers is attributed to the increased Na coordination with oxygen as indicated by ab initio calculations, and possibly at finite temperature by configuration entropy.

cond-mat.mtrl-sci↗
arXiv2006

Phase separation and nanostructuring in the thermoelectric material PbTe1-xSx

The average and local structures of the (PbTe)1-x(PbS)x system of thermoelectric materials has been studied using the Rietveld and atomic pair distribution function (PDF) methods. Samples with 0:25 < x are macroscopically phase separated. Phase separation was suppressed in a quenched x = 0:5 sample which, nonetheless, exhibited a partial spinodal decomposition. The promising thermoelectric material with x = 0:16 showed intermediate behavior. Combining TEM and bulk scattering data suggests that the sample is a mixture of PbTe rich material and a partially spinodally decomposed phase similar to the quenched 50% sample. This results in a nano-meter scale inhomogeneous material that accounts for its very low thermal conductivity.

cond-mat.mtrl-sci↗