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Purely electronic nanometallic ReRAM
Authors:
Yang Lu,
Jung Ho Yoon,
Yanhao Dong,
I-Wei Chen
Abstract:
Resistance switching random access memory (ReRAM), with the ability to repeatedly modulate electrical resistance, has been highlighted as a feasible high-density memory with the potential to replace negative-AND (NAND) flash memory. Such resistance modulation usually involves ion migration and filament formation, which usually lead to relatively low device reliability and yield. Resistance switchi…
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Resistance switching random access memory (ReRAM), with the ability to repeatedly modulate electrical resistance, has been highlighted as a feasible high-density memory with the potential to replace negative-AND (NAND) flash memory. Such resistance modulation usually involves ion migration and filament formation, which usually lead to relatively low device reliability and yield. Resistance switching can also come from an entirely electronic origin, as in nanometallic memory, by electron trapping and detrapping. Recent research has revealed additional merits of its mechanism, which entails smart, atomic-sized floating gates that can be easily engineered in amorphous Si, oxides, and nitrides. This article addresses the basic ideas of nanometallic ReRAM, which may also be a contender for analogue computing and non-von Neumann-type computation.
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Submitted 9 April, 2018;
originally announced April 2018.
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Optical properties of iron-based superconductor LiFeAs single crystal
Authors:
Byeong Hun Min,
Jong Beom Hong,
Jae Hyun Yoon,
Takuya Iizuka,
Shin-ichi Kimura,
Yunkyu Bang,
Yong Seung Kwon
Abstract:
We have measured the reflectivity spectra of the iron based superconductor LiFeAs (Tc = 17.6 K) in the temperature range from 4 to 300 K. In the superconducting state (T < Tc), the clear opening of the optical absorption gap was observed below 25 cm-1, indicating an isotropic full gap formation. In the normal state (T > Tc), the optical conductivity spectra display a typical metallic behavior with…
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We have measured the reflectivity spectra of the iron based superconductor LiFeAs (Tc = 17.6 K) in the temperature range from 4 to 300 K. In the superconducting state (T < Tc), the clear opening of the optical absorption gap was observed below 25 cm-1, indicating an isotropic full gap formation. In the normal state (T > Tc), the optical conductivity spectra display a typical metallic behavior with the Drude type spectra at low frequencies, but we found that the introduction of the two Drude components best fits the data, indicating the multiband nature of this superconductor. A theoretical analysis of the low temperature data (T=4K < Tc) also suggests that two superconducting gaps best fit the data and their values were estimated as Δ1 = 1.59 meV and Δ2 = 3.15 meV, respectively. Using the Ferrell-Glover-Tinkham (FGT) sum rule and dielectric function ε1(ω), the superconducting plasma frequency (ωps) is consistently estimated to be 6,665 cm-1, implying that about 59 % of the free carriers in the normal state condenses into the SC condensate. To investigate the various interband transition processes (for ω > 200 cm-1), we have also performed the local-density approximation (LDA) band calculation and calculated the optical spectra of the interband transitions. The theoretical results provided a qualitative agreement with the experimental data below 4000 cm-1
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Submitted 1 July, 2013; v1 submitted 4 January, 2013;
originally announced January 2013.
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Small anisotropy of the lower critical field and $s_\pm$-wave two-gap feature in single crystal LiFeAs
Authors:
Yoo Jang Song,
Jin Soo Ghim,
Jae Hyun Yoon,
Kyu Joon Lee,
Myung Hwa Jung,
Hyo-Seok Ji,
Ji Hoon Shim,
Yong Seung Kwon
Abstract:
The in- and out-of-plane lower critical fields and magnetic penetration depths for LiFeAs were examined. The anisotropy ratio $γ_{H_{c1}}(0)$ is smaller than the expected theoretical value, and increased slightly with increasing temperature from 0.6$T_c$ to $T_c$. This small degree of anisotropy was numerically confirmed by considering electron correlation effect. The temperature dependence of the…
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The in- and out-of-plane lower critical fields and magnetic penetration depths for LiFeAs were examined. The anisotropy ratio $γ_{H_{c1}}(0)$ is smaller than the expected theoretical value, and increased slightly with increasing temperature from 0.6$T_c$ to $T_c$. This small degree of anisotropy was numerically confirmed by considering electron correlation effect. The temperature dependence of the penetration depths followed a power law($\sim$$T^n$) below 0.3$T_c$, with $n$$>$3.5 for both $λ_{ab}$ and $λ_c$. Based on theoretical studies of iron-based superconductors, these results suggest that the superconductivity of LiFeAs can be represented by an extended $s_\pm$-wave due to weak impurity scattering effect. And the magnitudes of the two gaps were also evaluted by fitting the superfluid density for both the in- and out-of-plane to the two-gap model. The estimated values for the two gaps are consistent with the results of angle resolved photoemission spectroscopy and specific heat experiments.
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Submitted 13 April, 2011; v1 submitted 28 July, 2010;
originally announced July 2010.