arXiv subjects

D. Vandervelde

Publications and source records attributed to D. Vandervelde.

4 recordsLinked to original sources

arXiv2012

Penetration depth study of LaOs$_4$Sb$_{12}$: Multiband s-wave superconductivity

We measured the magnetic penetration depth $λ(T)$ in single crystals of LaOs$_{4}$Sb$_{12}$ ($T_c$=0.74 K) down to 85 mK using a tunnel diode oscillator technique. The observed low-temperature exponential dependence indicates a s-wave gap. Fitting the low temperature data to BCS s-wave expression gives the zero temperature gap value $Δ(0)= (1.34 \pm 0.07) k_B T_c$ which is significantly smaller than the BCS value of 1.76$k_B T_c$. In addition, the normalized superfluid density $ρ(T)$ shows an unusually long suppression near $T_c$, and are best fit by a two-band s-wave model.

cond-mat.supr-con↗

arXiv2006

S-wave/spin-triplet order in superconductors without inversion symmetry: Li$_2$Pd$_3$B and Li$_2$Pt$_3$B

We investigate the order parameter of noncentrosymmetric superconductors Li$_2$Pd$_3$B and Li$_2$Pt$_3$B via the behavior of the penetration depth $λ(T)$. The low-temperature penetration depth shows BCS-like behavior in Li$_2$Pd$_3$B, while in Li$_2$Pt$_3$B it follows a linear temperature dependence. We propose that broken inversion symmetry and the accompanying antisymmetric spin-orbit coupling, which admix spin-singlet and spin-triplet pairing, are responsible for this behavior. The triplet contribution is weak in Li$_2$Pd$_3$B, leading to a wholly open but anisotropic gap. The significantly larger spin-orbit coupling in Li$_2$Pt$_3$B allows the spin-triplet component to be larger in Li$_2$Pt$_3$B, producing line nodes in the energy gap as evidenced by the linear temperature dependence of $λ(T)$. The experimental data are in quantitative agreement with theory.

cond-mat.supr-con↗

arXiv2005

A Penetration Depth Study on Li2Pd3B and Li2Pt3B

In this paper we present a penetration depth study on the newly discovered superconductors Li$_2$Pd$_3$B and Li$_2$Pt$_3$B. Surprisingly, the low-temperature penetration depth $f(T)$ demonstrates distinct behavior in these two isostructural compounds. In Li$_2$Pd$_3$B, $f(T)$ follows an exponential decay and can be nicely fitted by a two-gap BCS superconducting model with a small gap $δ_1=3.2$K and a large gap $δ_2=11.5$K. However, linear temperature dependence of $f(T)$ is observed in Li$_2$Pt$_3$B below 0.3$T_c$, giving evidence of line nodes in the energy gap.

cond-mat.supr-con↗

arXiv2004

Evolution of superconducting order in Pr(Os$_{1-x}$Ru$_{x}$)$_{4}$Sb$_{12}$

We report measurements of the magnetic penetration depth $λ$ in single crystals of Pr(Os$_{1-x}$Ru$_{x}$)$_{4}$Sb$_{12}$ down to 0.1 K. Both $λ$ and superfluid density $ρ_{s}$ exhibit an exponential behavior for the $x$$\geq$0.4 samples, going from weak ($x$=0.4,0.6), to moderate, coupling ($x$=0.8). For the $x$$\leq$0.2 samples, both $λ$ and $ρ_{s}$ vary as $T^{2}$ at low temperatures, but $ρ_{s}$ is s-wave-like at intermediate to high temperatures. Our data are consistent with a three-phase scenario, where a fully-gapped phase at $T_{c1}$ undergoes two transitions: first to an unconventional phase at $T_{c2}$$\lesssim$$T_{c1}$, then to a nodal low-$T$ phase at $T_{c3}$$<$$T_{c2}$, for small values of $x$.

cond-mat.supr-con↗