Superfluid density and carrier concentration across a superconducting dome: The case of strontium titanate

Abstract

We present a study of the lower critical field, Hc1, of SrTi1−xNbxO3 as a function of carrier concentration with the aim of quantifying the superfluid density. At low carrier concentration (i.e. the underdoped side), superfluid density and the carrier concentration in the normal state are equal within experimental margin. A significant deviation between the two numbers starts at optimal doping and gradually increases with doping. The inverse of the penetration depth and the critical temperature follow parallel evolutions as in the case of cuprate superconductors. In the overdoped regime, the zero-temperature superfluid density becomes much lower than the normal-state carrier density before vanishing all together. We show that the density mismatch and the clean-to-dirty crossover are concomitant. Our results imply that the discrepancy between normal and superconducting densities is expected whenever the superconducting gap becomes small enough to put the system in the dirty limit. A quantitative test of the dirty BCS theory is not straightforward, due to he multiplicity of the bands in superconducting strontium titanate.

Chiral domain walls of Mn3Sn and their memory

“…The device was fabricated using electron beam lithography and 250 V argon ions to define the mesa. Supplementary Figure 1 shows an array of ten sensors each 5 × 5µm 2 square with a 100 µm interval between two neighboring sensors [26]. Attaching the device to the surface of the sample, the local magnetic field was determined by measuring the Hall resistivity of the sensor using an AC current source and a lock-in amplifier.…”

“…The second observation is the existence of a transverse magnetic response in the same narrow field window. Employing micron-size Hall sensors in close proximity with the sample [25,26], we monitored the local magnetic field at the surface and found in the same field window a finite off-diagonal magnetization: a finite magnetization oriented perpendicular to the orientation of the applied magnetic field. We will argue below that a satisfactory explanation of both these observations is provided by a specific spin texture inside the domain walls.…”

Metallicity and Superconductivity in Doped Strontium Titanate

“…To take a closer look, the ratios n s /n H and π∆τ / reported in Ref [109] are plotted in Figure 5d. At the lowest doping, n s matches n H as expected.…”

“…However, recent tunneling studies detect a single superconducting gap [117] and microwave measurements [133] see a single energy scale for the superfluid condensate. A future challenge is to reconcile these experimental results with the temperature dependence of H c1 [109] in a quantitative way.…”

Millikelvin-compatible apparatus for studies of quantum materials under uniaxial stress

“…For example, in strontium titanate, which is a low critical temperature (Tc) superconductor, questions about our fundamental understanding of electron lattice coupling and ways to enhance Tc are at the forefront of the modern quest to understand quantum phase transitions. [1]- [7] In high temperature superconductors, pressure and strain may be the keys to potentially even higher temperature superconductivity. [8] For example, recent observations of the high-pressure-induced (compressive strain) record-breaking superconductivity in sulfur hydride at about 200 K are a vivid demonstration that strain and pressure effects are a promising control parameter to make significant advances in tuning superconducting transitions.…”