Suppression of tunneling two-level systems in ultrastable glasses of indomethacin

Paper and ArXiv.

Coverage in PNAS (Commentary) (international)

UCC UAM , notiweb madri+d , Revista Española de Física (Spanish)

Glasses are disordered solids usually obtained by supercooling a liquid bypassing crystallization. A remarkable feature of glasses is that, independently of their nature and composition, they exhibit universal properties in the low-temperature range. Of interest here, the specific heat is characterized by a linear term below 1 K, ascribed to quantum tunneling between two states of similar energy. We have investigated if this ubiquitous behavior also applies to so-called “ultrastable glasses,” directly synthesized from the vapor phase into low-energy positions of the potential-energy landscape. Interestingly, we find a full suppression of the linear term in the specific heat, which questions the current view of the popular tunneling model and sheds light on the microscopic origin of two-level systems in glasses.

Magnetic field-induced dissipation-free state in superconducting nanostructures.

 ArXiV (to come) and paper. Coverage in MadridI+D, in UAM UCC and in 2Physics.

A superconductor in a magnetic field acquires a finite electrical resistance caused by vortex motion. A quest to immobilize vortices and recover zero resistance at high fields made intense studies of vortex pinning one of the mainstreams of superconducting research. Yet, the decades of efforts resulted in a realization that even promising nanostructures, utilizing vortex matching, cannot withstand high vortex density at large magnetic fields. Here, we report a giant reentrance of vortex pinning induced by increasing magnetic field in a W-based nanowire and a TiN-perforated film densely populated with vortices. We find an extended range of zero resistance with vortex motion arrested by self-induced collective traps. The latter emerge due to order parameter suppression by vortices confined in narrow constrictions by surface superconductivity. Our findings show that geometric restrictions can radically change magnetic properties of superconductors and reverse detrimental effects of magnetic field.

Two-Level Systems and Boson Peak Remain Stable in 110-Million-Year-Old Amber Glass

Paper  and  ArXiV .

Coverage in Nature Materials , Physics (APS) , Chemical & Engineering News (ACS)  (international)

UCC UAM , notiweb madri+d , Blogs Investigacion y Ciencia , El Mundo – Cantabria , La Vanguardia – Madrid , Revista Española de Física (Spanish)   

Amber has been appreciated by mankind for its color and natural beauty since the Neolithic era. However, amber can also be a gemstone for physics and chemistry research on glasses. In this work, we have measured the specific heat of 110 million-year-old Spanish amber to temperatures below 0.1 K, and show that the two most prominent and ubiquitous features of glasses at low temperatures, namely the presence of tunneling two-level systems and the so-called boson peak, persist essentially unchanged in highly stabilized glasses, contrary to what was usually envisaged during last forty years. Therefore, these controversial features of all non-crystalline solids at low temperatures are shown to be indeed robust and intrinsic properties which also remain “fossilized” in 110-million-year aged glasses of Spanish amber, as insects or other bioinclusions do. We expect that amber will serve in the near future as an extremely enlightening model glass to study many other puzzles involved in the physics of the glass state.