Speaker:  Dr. Vasily S. Minkov, Max Planck Institute for Chemistry, Mainz, Germany

Hosts: Sergey Bud'ko / Paul Canfield

Title:  Towards room-temperature superconductivity: Experimental evidence

Abstract:  Superconductivity – the complete loss of electrical resistance – is one of the most remarkable phenomena in condensed matter physics. Since its discovery in mercury in 1911, it was long regarded as an exclusively very low-temperature phenomenon. The development of the Bardeen-Cooper-Schrieffer theory, together with subsequent theoretical advances, demonstrated that no fundamental upper limit exists for the superconducting critical temperature (T_c). These insights suggest that room-temperature superconductivity is, in principle, achievable.

A major breakthrough came in 2015 with the pioneering work of Mikhail Eremets and collaborators, who discovered superconductivity in highly compressed hydrogen sulfide (H₃S) with a record T_c of 203 K at approximately 150 GPa. This result provided the first experimental confirmation of high-T_c conventional superconductivity in hydrides and sparked an intense surge of theoretical and experimental activity in the field.

Subsequent studies identified additional metal hydrides – particularly the so-called “superhydrides” such as LaH₁₀ and YH₉ – that exhibit T_c values approaching 250 K. These discoveries pushed the field closer than ever to achieving room-temperature superconductivity. More recently, attention has shifted from binary to ternary hydride systems, which introduce additional chemical degrees of freedom and hold the potential for even higher T_c values, while simultaneously presenting greater challenges for synthesis and characterization.

Despite formidable experimental constrains – including the synthesize and characterization of micrometer-scale samples in diamond anvil cells at multimegabar pressures – superconductivity in these compounds has been confirmed using multiple complementary techniques. Four-probe electrical transport measurements remain the benchmark for detecting resistive transitions, while advanced magnetic probes such as SQUID magnetometry, nuclear resonant scattering, double-modulation AC susceptibility, and nitrogen-vacancy-center magnetometry enable direct detection of magnetic field screening, flux expulsion and trapping. More recently, electron tunneling spectroscopy has been extended to megabar pressures, providing direct spectroscopic evidence of superconductivity in hydrogen-rich materials.

In this talk, we review the development of conventional high-temperature superconductivity in hydrides, with particular emphasis of the contributions of Mikhail Eremets and his group. We also present our recent experimental progress in the search of room-temperature hydride superconductors, including the development of new measurement techniques for extreme-pressure environments and emerging indications of “hot” superconductivity in carbon-based materials.

Bio:  Vasily Minkov is an expert in static high-pressure experiments using diamond anvil cells (DAC). Earlier in his career, he studied structure-property relationship in molecular crystals composed of small organic molecules at hydrostatic pressures up to 10 GPa. In 2016, he joined the laboratory led by Mikhail Eremets, where he gained extensive experience working with a leading high-pressure scientist. Since then, his research has focused on developing high-pressure apparatus, the chemical synthesis of novel compounds, and the adaptation of experimental techniques for extreme-pressure conditions in DACs.
While in Mainz, Vasily and the team discovered record high-temperature superconductivity in hydrogen-rich compounds LaH10 and YH9, with Tc  250 K.
He played a key role in the development of a miniature non-magnetic DAC for studies of superconductivity in magnetic fields up to 65 Tesla and advanced
SQUID magnetometry techniques for probing magnetic field screening, flux expulsion, and flux trapping in hydrides. His contributions also include the first
direct measurements of the superconducting gap in H3S and D3S by electron tunneling spectroscopy and the development of the Universal diamond edge Raman pressure scale extending to 500 GPa.
More recently, he and the team discovered possible high-temperature superconductivity in graphite intercalated with metal–ammonia solutions and Libased metal alloys, exhibiting Tc up to 350 K at atmospheric pressure.