Isotope effect in superconducting n-doped SrTiO₃.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Strontium titanate (SrTiO3) is a material exhibiting superconductivity when doped.
• The influence of oxygen isotopes on superconducting properties is a key area of research.
• Understanding the mechanisms behind superconductivity in SrTiO3 can provide insights into novel electronic phenomena.

Purpose of the Study:

• To investigate the effect of oxygen isotope substitution (16O vs. 18O) on the superconducting critical temperature (Tc) in doped SrTiO3.
• To examine the impact of this substitution on the magnetic critical field (Hc2).
• To explore the underlying mechanisms responsible for the observed superconductivity and isotope effects.

Main Methods:

• Synthesis of doped SrTiO3 samples with natural (16O) and enriched (18O) oxygen isotopes.
• Measurement of superconducting critical temperature (Tc) using electrical resistivity.
• Determination of the magnetic critical field (Hc2) through magnetic susceptibility measurements.

Main Results:

• A significant (~50%) enhancement of the superconducting critical temperature (Tc) was observed upon substitution of 16O with 18O.
• The magnetic critical field (Hc2) increased by approximately a factor of 2 with the heavier oxygen isotope.
• The observed isotope effect was unusually large and opposite in sign compared to conventional superconductors.

Conclusions:

• The substantial oxygen isotope effect strongly suggests a significant role of electron-phonon coupling in the superconductivity of doped SrTiO3.
• The findings support recent models attributing superconductivity to strong coupling with ferroelectric soft modes in SrTiO3.
• This research highlights the potential for isotope engineering to tune and enhance superconducting properties in oxide materials.