arXiv subjects

I. Hetel

Publications and source records attributed to I. Hetel.

5 recordsLinked to original sources

arXiv2010

Anomalously Sharp Superconducting Transitions in Overdoped $La_{2-x}Sr_{x}CuO_{4}$ Films

We present measurements of $ab$-plane resistivity $ρ_{ab}(T)$ and superfluid density [$\propto λ^{-2}$, $λ$ = magnetic penetration depth] in $La_{2-x}Sr_{x}CuO_{4}$ films. As Sr concentration $x$ exceeds about 0.22, the superconducting transition sharpens dramatically, becoming as narrow as 200 mK near the super-to-normal metal quantum critical point. At the same time, $ρ_{ab}(T)$, $λ^{-2}(T)$, and transition temperature $T_c$ decrease, and upward curvature develops in $λ^{-2}(T)$. Given the sharp transitions, we interpret these results in the context of a homogeneous d-wave superconducting state, with elastic scattering that is enhanced relative to underdoped LSCO due to weaker electron correlations. This interpretation conflicts with the viewpoint that the overdoped state is inhomogeneous due to phase separation into superconducting and normal metal regions.

cond-mat.supr-con↗

arXiv2010

Superconductor-to-Metal Quantum Phase Transition in Overdoped $La_{2-x}Sr_xCuO_4$

We investigate $T_c$ and magnetic penetration depth $λ(T)$ near the superconductor-metal quantum phase transition in overdoped $La_{2-x}Sr_{x}CuO_{4}$ films. Both $T_c$ and superfluid density $n_s$, $\propto λ^{-2}$, decrease with overdoping. They obey the scaling relation $T_c \propto [λ^{-2}(0)]^α$ with $α\approx 1/2$. We discuss this result in the frameworks of disordered d-wave superconductors and of scaling near quantum critical points. Our result, and the linear scaling ($α\approx 1$) found for the more anisotropic $Tl_2Ba_2CuO_{6+δ}$, can both be understood in terms of quantum critical scaling, with different dimensionalities for fluctuations.

cond-mat.supr-con↗

arXiv2006

Search for Cooper-pair Fluctuations in Severely Underdoped YBCO Films

The preformed-pairs theory of pseudogap physics in high-$T_C$ superconductors predicts a nonanalytic $T$-dependence for the $ab$-plane superfluid fraction, $ρ_S$, at low temperatures in underdoped cuprates. We report high-precision measurements of $ρ_S(T)$ on severely underdoped YBa$_2$Cu$_3$O$_{6+x}$ and Y$_{0.8}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{6+x}$ films. At low $T$, $ρ_S$ looks more like $1 - T^2$ than $1 - T^{3/2}$, in disagreement with theory.

cond-mat.supr-con↗

arXiv2004

Field-dependent diamagnetic transition in magnetic superconductor $Sm_{1.85} Ce_{0.15} Cu O_{4-y}$

The magnetic penetration depth of single crystal $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ was measured down to 0.4 K in dc fields up to 7 kOe. For insulating $\rm{Sm_2CuO_4}$, Sm$^{3+}$ spins order at the Néel temperature, $T_N = 6$ K, independent of the applied field. Superconducting $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ ($T_c \approx 23$ K) shows a sharp increase in diamagnetic screening below $T^{\ast}(H)$ which varied from 4.0 K ($H = 0$) to 0.5 K ($H =$ 7 kOe) for a field along the c-axis. If the field was aligned parallel to the conducting planes, $T^{\ast}$ remained unchanged. The unusual field dependence of $T^{\ast}$ indicates a spin freezing transition that dramatically increases the superfluid density.

cond-mat.supr-con↗

arXiv2003

Fourfold oscillations and anomalous magnetic irreversibility of magnetoresistance in the non-metallic regime of Pr1.85Ce0.15CuO4

Using magnetoresistance measurements as a function of applied magnetic field and its direction of application, we present sharp angular-dependent magnetoresistance oscillations for the electron-doped cuprates in their low-temperature non-metallic regime. The presence of irreversibility in the magnetoresistance measurements and the related strong anisotropy of the field dependence for different in-plane magnetic field orientations indicate that magnetic domains play an important role for the determination of electronic properties. These domains are likely related to the stripe phase reported previously in hole-doped cuprates.

cond-mat.supr-con↗