Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSuperconducting tunneling spectroscopy of spin-orbit coupling and orbital depairing in Nb:SrTiO$_3$
203
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We have examined the intrinsic spin-orbit coupling (SOC) and orbital depairing in thin films of Nb-doped SrTiO$_3$ by superconducting tunneling spectroscopy. The orbital depairing is geometrically suppressed in the two-dimensional limit, enabling a quantitative evaluation of the Fermi level spin-orbit scattering using Makis theory. The response of the superconducting gap under in-plane magnetic fields demonstrates short spin-orbit scattering times $tau_{so} leq 1.1$ ps. Analysis of the orbital depairing indicates that the heavy electron band contributes significantly to pairing. These results suggest that the intrinsic spin-orbit scattering time in SrTiO$_3$ is comparable to those associated with Rashba effects in SrTiO$_3$ interfacial conducting layers and can be considered significant in all forms of superconductivity in SrTiO$_3$.
rate research
Read More
The combination of Rashba spin-orbit coupling and electron correlations can induce unusual phenomena in the metallic interface between SrTiO$_3$ and LaAlO$_3$. We consider effects of Rashba spin-orbit coupling at this interface in the context of the recent observation of anisotropic magnetism. Firstly, we show how Rashba spin-orbit coupling in a system near a band-edge can account for the observed magnetic anisotropy. Secondly, we investigate the coupling between in-plane magnetic-moment anisotropy and nematicity in the form of an orbital imbalance between d$_{xz}$ / d$_{yz}$ orbitals. We estimate this coupling to be substantial in the low electron density regime. Such an orbital ordering can affect magneto transport.
Whereas there exists considerable evidence for the conversion of singlet Cooper pairs into triplet Cooper pairs in the presence of inhomogeneous magnetic fields, recent theoretical proposals have suggested an alternative way to exert control over triplet generation: intrinsic spin-orbit coupling in a homogeneous ferromagnet coupled to a superconductor. Here, we proximity-couple Nb to an asymmetric Pt/Co/Pt trilayer, which acts as an effective spin-orbit coupled ferromagnet owing to structural inversion asymmetry. Unconventional modulation of the superconducting critical temperature as a function of in-plane and out-of- plane applied magnetic fields suggests the presence of triplets that can be controlled by the magnetic orientation of a single homogeneous ferromagnet. Our studies demonstrate for the first time an active role of spin-orbit coupling in controlling the triplets -- an important step towards the realization of novel superconducting spintronic devices.
We measure the gate voltage ($V_g$) dependence of the superconducting properties and the spin-orbit interaction in the (111)-oriented LaAlO$_3$/SrTiO$_3$ interface. Superconductivity is observed in a dome-shaped region in the carrier density-temperature phase diagram with the maxima of superconducting transition temperature $T_c$ and the upper critical fields lying at the same $V_g$. The spin-orbit interaction determined from the superconducting parameters and confirmed by weak-antilocalization measurements follows the same gate voltage dependence as $T_c$. The correlation between the superconductivity and spin-orbit interaction as well as the enhancement of the parallel upper critical field, well beyond the Chandrasekhar-Clogston limit suggest that superconductivity and the spin-orbit interaction are linked in a nontrivial fashion. We propose possible scenarios to explain this unconventional behavior.
It is shown that in a structure consisting of a superconducting ring-shaped electrode overlapped by a normal metal contact through a thin oxide barrier, measurements of the tunnel current in magnetic field can probe persistent currents in the ring. The effect manifests itself as periodic oscillations of the tunnel current through the junction at a fixed bias voltage as function of perpendicular magnetic field. The magnitude of oscillations depends on bias point. It reaches maximum at energy eV which is close to the superconducting gap and decreases with increase of temperature. The period of oscillations dF in units of magnetic flux is equal neither to h/e nor to h/2e, but significantly exceeds these values for larger loop circumferences. The phenomenon is explained by formation of metastable states with large vorticity. The pairing potential and the superconducting density of states are periodically modulated by the persistent currents at sub-critical values resulting in corresponding variations of the measured tunnel current.
We use both Eilenberger-Usadel and Ginzburg-Landau (GL) theory to calculate the superfluids temperature-dependent kinetic inductance for all currents up to the depairing current in thin and narrow superconducting films. The calculations apply to BCS weak-coupling superconductors with isotropic gaps and transport mean-free paths much less than the BCS coherence length. The kinetic inductance is calculated for the response to a small alternating current when the film is carrying a dc bias current. In the slow-experiment/fast-relaxation limit, in which the superconducting order parameter quasistatically follows the time-dependent current, the kinetic inductance diverges as the bias current approaches the depairing value. However, in the fast-experiment/slow-relaxiation limit, in which the the superconducting order parameter remains fixed at a value corresponding to the dc bias current, the kinetic inductance rises to a finite value at the depairing current. We then use time-dependent GL theory to calculate the kinetic impedance of the superfluid, which includes not only the kinetic reactance but also the kinetic resistance of the superfluid arising from dissipation due to order-parameter relaxation. The kinetic resistance is largest for angular frequencies $omega$ obeying $omega tau_s > 1$, where $tau_s$ is the order-parameter relaxation time, and for bias currents close to the depairing current. We also include the normal fluids contribution to dissipation in deriving an expression for the total kinetic impedance. The Appendices contain many details about the temperature-dependent behavior of superconductors carrying current up to the depairing value.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
