arXiv subjects

N. K. Man

Publications and source records attributed to N. K. Man.

3 recordsLinked to original sources

arXiv2026

Evidence for superconductivity at 190 K in a pressure-overdoped cuprate

It is well established that the critical temperature ($T_c$) of cuprate superconductors can be tuned by pressure. For example, compression decouples the hole doping from chemical doping allowing for overdoped samples far beyond what is possible at ambient pressure. In this work, multiple techniques are used to probe the onset of the Meissner effect at $T_c$ as a function of pressure in $\mathrm{Pb_{0.4}Bi_{1.6}Sr_2Ca_2Cu_3O_{10+\delta}}$ (Bi-2223) to 60 GPa in different compression environments. Samples compressed under quasihydrostatic conditions exhibit a distinctive non-monotonic pressure dependence of $T_c$ below 25 GPa, in agreement with previous reports. With further increase in pressure $T_c$ climbs continuously to 190 K at 60 GPa. Evidence for critical temperatures exceeding those reported to date for cuprates at ambient and high pressures, the results may be understood in terms of the proposed second superconducting regime at high hole doping.

cond-mat.supr-con↗

arXiv2026

Fingerprint of $T_c$ advancement in Li-doped Bi-2223 superconductors prepared by cationic molecular mixing within Pechini sol-gel synthesis

Trilayered Bi-2223 superconductor features the highest critical temperature $T_c$ among the bismuth-based cuprate collection and symbolizes an ideal prototype for studying intrinsic superconducting properties. The previous solid-state reaction method substantiated the growth of the high-quality Bi-2223 compounds but was accompanied by excessively laborious time and effort in terms of multiple grinding, pressing, as well as calcining stages, %causing risk of constituent loss, so finding a less tedious synthesis path is imperative. Here, we present an advanced sol-gel synthesis for assembling the multicomponent complexity of Bi1.4Pb0.6Sr2Ca2(Cu1-xLix)3O10 superconductors (Li-doped Bi-2223), with $x$ = 0.0--0.20, utilizing metallic cationic molecular mixing within the chemical Pechini polyesterization route followed by single-step pyrolysis and sintering stages. Although monovalent cations such as Li$^+$ pose limitations in establishing a perplex crosslinking network or chelating mechanism in the Pechini method, they represent a unique probe to elucidate the major chemical process during polymerization. We observe that a 5 molar~\% Li-doped sample pronounces the highest $T_c$ = 111.4 K among the series of samples, as confirmed by both ac susceptibility and dc resistivity measurements, and is equivalent to the value obtained by our preceding solid state fabrication. In addition, we showcase a rare observation of layer-by-layer crystalline phase growth under microstructure probe. Through analyzing the reliable ac susceptibility data at low magnetic fields in a wide range of frequency, we provide the quantum flux formation and flux creep mechanism by Anderson-M\"uller's model and Cole-Cole plot.

cond-mat.supr-con↗

arXiv2024

Signature of T$_\textrm{c}$ above 111 K in Li-doped (Bi,Pb)-2223 superconductors: synergistic nature of hole concentration, coherence length and Josephson interlayer coupling

Understanding the bottleneck to drive higher critical transition temperature $T_\textrm{c}$ plays a pivotal role in the underlying study of superconductors. We systematically investigate the effect of Li$^+$ substitution for Cu$^{2+}$ cations on the $T_\textrm{c}$, hole concentration, coherence length and interlayer coupling, and microstructure in Li-doped Bi$_{1.6}$Pb$_{0.4}$Sr$_2$Ca$_2$Cu$_3$O$_{10 + \delta}$ or (Bi,Pb)-2223 compound. Remarkably, we demonstrate by utilizing a long-time sintering accompanied by a multiple recurrent intermediate stages of calcining and pressing within our renovated solid-state reaction method, the optimal Li-doped (Bi,Pb)-2223 samples achieve the well-enhanced $T_\textrm{c}$ of 111--113.8 K compared with the standard value of 110 K. We evince the superconducting mechanism that the substitution of Li$^{+}$ for Cu$^{2+}$ ions on the CuO$_2$ layers causes augmenting the hole concentrations and promotes the correlation between the overdoped outer and the underdoped inner CuO$_2$ planes, and thus effects improve $T_\textrm{c}$. Following a universal quadratic relation between $T_\textrm{c}$ and hole concentration, a new higher optimal hole concentration is provided. Additionally, by analyzing the Aslamazov-Larkin and Lawrence-Doniach theories on the reliable excess conductivity data near the critical temperature, we observe the strong effect of Li-doping on the system. The coherence length steadily increases versus the Li-doped content, while the Josephson interlayer coupling strength between the CuO$_2$ layers almost remains a constant for the whole series of Li-doping. Our findings establish an insightful roadmap to improve the critical temperature and intrinsic superconducting properties in the Bi-2223 compounds through the doping process.

cond-mat.supr-con↗