arXiv subjects

Elizabeth M. Carnicom

Publications and source records attributed to Elizabeth M. Carnicom.

5 recordsLinked to original sources

arXiv2018

Superconductivity in the Superhard Boride WB$_{4.2}$

We show that the superhard boride WB$_{4.2}$ is a superconductor with a T$_c$ of 2.05(5) K. Temperature-dependent magnetic susceptibility, electrical resistivity, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ for WB$_{4.2}$ is 2.07(3) mJ mol$^{-1}$ K$^{-2}$ and the ΔC/γT$_c$ = 1.56, which is somewhat higher than what is expected for weakly coupled BCS type superconductors. The H$_{c2}$ vs T plot is linear over a wide temperature range but does show signs of flattening by the lowest temperatures studied and therefore the zero-temperature upper critical field (μ$_0$H$_{c2}$(0)) for WB$_{4.2}$ lies somewhere between the linear extrapolation of μ$_0$H$_{c2}$(T) to 0 K and expectations based on the WHH model.

cond-mat.supr-con↗

arXiv2018

Stabilizing the Tb-based 214 cuprate by partial Pd substitution

Previously known to form only under high pressure synthetic conditions, here we report that the T'-type 214-structure cuprate based on the rare earth atom Tb is stabilized for ambient pressure synthesis through partial substitution of Pd for Cu. The new material is obtained in purest form for mixtures of nominal composition $Tb_{1.96}Cu_{0.80}Pd_{0.20}O_{4}$. The refined formula, in orthorhombic space group Pbca, with a = 5.5117(1) Å, b = 5.5088(1) Å, and c = 11.8818(1) Å, is $Tb_{2}Cu_{0.83}Pd_{0.17}O_{4}$. An incommensurate structural modulation is seen along the a axis by electron diffraction and high resolution imaging. Magnetic susceptibility measurements reveal long range antiferromagnetic ordering at 7.9 K, with a less pronounced feature at 95 K; a magnetic moment reorientation transition is observed to onset at a field of approximately 1.1 Tesla at 3 K. The material is an n-type semiconductor.

cond-mat.supr-con↗

arXiv2018

The Chiral Non-Centrosymmetric Superconductors TaRh$_2$B$_2$ and NbRh$_2$B$_2$

The symmetry of a material's crystal structure has a significant effect on the energy states of its electrons. Inversion symmetry, for example, results in energetically degenerate electron energy bands for electrons with wave vectors $\textit{k}$ and -$\textit{k}$, but, when spatial inversion symmetry is absent, this equivalence is no longer possible. In a non-centrosymmetric superconductor, such inequivalence has an important effect: the standard superconducting state, where electrons with opposite momenta form pairs on the Fermi surface, is not possible. A handful of such materials is known; they display different degrees of influence of this lack of inversion symmetry on their superconducting properties. The effect of crystal structure chirality on the properties and applications of superconductors, on the other hand, is little discussed. Here we report the new isostructural non-centrosymmetric superconductors TaRh$_2$B$_2$ and NbRh$_2$B$_2$, which have a previously unreported crystal structure type. Not only do these materials lack inversion symmetry, but their crystal structure is also chiral; in other words, they can exist in right-handed or left-handed forms. Unlike most superconductors, their upper critical magnetic fields extrapolated to 0 K exceed the Pauli limit, which is often taken as the first indication that a superconducting material is anomalous. We propose that these materials represent a new kind of platform on which the effects of handedness on superconductors and their devices can be tested.

cond-mat.supr-con↗

arXiv2017

Superconductivity in the Nb-Ru-Ge $σ$-Phase

We show that the previously unreported ternary $σ$-phase material Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ is a superconductor with a critical temperature of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant $γ$ for Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ is 91 mJ mol-f.u.$^{-1}$K$^{-2}$ and the specific heat anomaly at the superconducting transition, $Δ$C/$γ$T$_c$, is approximately 1.38. The zero-temperature upper critical field ($μ_0$H$_{c2}$(0)) was estimated to be 2 T by resistance data. Field-dependent magnetization data analysis estimated $μ_0$H$_{c1}$(0) to be 5.5 mT. Thus, the characterization shows Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ to be a type II BCS superconductor. This material appears to be the first reported ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously reported binary Nb-Ru, Nb-Ge, or Ru-Ge $σ$-phases shows that all three elements are necessary to stabilize the material. A $σ$-phase in the Ta-Ru-Ge system was synthesized but did not display superconductivity above 1.7 K, which suggests that electron count cannot govern the superconductivity observed. Preliminary characterization of a possible superconducting $σ$-phase in the Nb-Ru-Ga system is also reported.

cond-mat.supr-con↗

arXiv2017

Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4

The growth and characterization of CePtIn4, stabilized by 10% Zn substitution for In, is reported. The new material is orthorhombic, space group Cmcm (No. 63), with lattice parameters a = 4.51751(4) Å, b = 16.7570(2) Å, and c = 7.36682(8) Å, and the refined crystal composition has 10% of Zn substituted for In, i.e. the crystals are CePt(In3.6Zn0.1)4. Crystals were grown using a self-flux method: only growths containing Zn yielded CePtIn4 crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic temperature-dependent magnetic susceptibilities for single crystals show that Zn-stabilized CePtIn4 orders magnetically at ~1.9 K. High-temperature Curie-Weiss fits indicate an effective moment of ~2.30 muB/ Ce and a directionally averaged Weiss-temperature of approximately - 9 K. Specific heat data shows a peak consistent with the ordering temperature seen in the magnetic susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no superconducting transition down to 0.14 K.

cond-mat.mtrl-sci↗