Dr. Cristian Rodriguez-Tinoco1,2

Talk: "Exploring the Limits of the Glassy State: Transformation Kinetics and Low-Temperature Anomalies in Ultrastable Glasses"

Co-workers: J. Rodriguez-Viejo1, 2, M. Gonzalez-Silveira1, 2, M.A. Ramos3, 4

1Departamento de Física, Facultad de Ciencias, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain
2Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Bellaterra, 08193, Barcelona, Spain
3Departamento de Física de la Materia Condensada, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, 28049, Madrid, Spain
4Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, 28049, Madrid, Spain

The glassy state remains a profound mystery in condensed matter physics, particularly regarding the existence of an "ideal glass." While conventional glasses require millennia of aging to reach stable thermodynamic states, vapor-deposited ultrastable glasses (UGs) achieve these states in hours. Prepared via physical vapor deposition (PVD), UGs utilize enhanced surface mobility to reach low enthalpies and high kinetic stabilities, challenging our understanding of the glass transition. This talk explores UG transformation kinetics and their unconventional behaviour at cryogenic temperatures.

A central theme in glass research is the transition from the ultrastable glass into a supercooled liquid. Unlike the homogeneous softening of conventional glasses, UGs transform non-homogeneously. In thin films, transformation occurs via propagation fronts originating at surfaces. In thicker, bulk-like films (over one micron) or capped systems, the transition occurs through a bulk process resembling nucleation and growth, driven by intrinsic dynamic fluctuations. We also discuss low-temperature properties that probe the universality of glass physics. Standard glasses typically exhibit a "boson peak" and a linear specific heat term below 1 K, explained by the Standard Tunnelling Model. However, certain UGs, like indomethacin or TPD, show a depletion of these tunnelling states and lack this universal linear coefficient. Other fundamental properties of vapour deposited glasses include a particular molecular orientation and strong anisotropy, which strongly impact properties such as thermal transport or even low temperature properties of the glass. These findings refine theoretical models and suggest new avenues for organic electronics with tailored stabilitye.

Acknowledgements: This work was supported by Grant MAT2016-79759-R and PID2020-117409RB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and the “María de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M), as well as by the Autonomous Community of Madrid through program S2018/NMT-4321 (NANOMAGCOST-CM).