New details in the phase diagram of $\lambda\textnormal{-}(\textnormal{BETS})_2\textnormal{Ga}\textnormal{Cl}_4$ made by advancing the art of RF penetration depth measurements in pulsed fields using a tunnel diode oscillator

We report improvements to the Tunnel Diode Oscillator method of measuring the penetration depth of a superconductor at RF frequencies above 100 MHz. Optimizations to the circuit for high frequency and pulsed fields are briefly discussed as well as a digital demodulation technique for rendering the oscillation frequency with accuracy suitably better than the stability of the oscillator itself. Using a 390 MHz oscillator, we measured the penetration depth of $\lambda\textnormal{-}(\textnormal{BETS})_2\textnormal{Ga}\textnormal{Cl}_4$ with the magnetic field oriented parallel to the conducting planes of the sample using fields up to 21\,T and temperatures from 400\,mK to 5.5\,K. Our new data crunching techniques have allowed us to resolve two phase transitions between the superconducting and normal states as well as a third transition that appears at low temperature as an enhancement to the upper critical field. We explore the properties of the phase diagram in two samples.