Impact of Plastic Deformation and Shear Band Formation on the Boson Heat Capacity Peak of a Bulk Metallic Glass Yu. P. Mitrofanov, 1,2,* M. Peterlechner, 1 S. V. Divinski, 1 and G. Wilde 1,3 1 Institute of Materials Physics, University of Münster, 10 Wilhelm-Klemm Strasse, Münster 48149, Germany 2 Department of Solid State Physics, State Technical University, 14 Moscow Avenue, Voronezh 394026, Russia 3 Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, People’s Republic of China (Received 8 November 2013; published 4 April 2014) The effect of annealing on the low-temperature heat capacity of a bulk Pd 38.5 Ni 40 P 21.5 metallic glass is investigated for as-quenched and deformed (rolled) states. Although the boson heat capacity peak increases with increasing strain, it relaxes faster and to a lower level compared to that of the as-quenched state after annealing treatments both below and above the glass transition temperature T g . The glass is found to retain a certain “memory” on the room-temperature plastic deformation even after annealing above T g . Indications for two counteracting processes that might be related to different types of shear bands are observed. DOI: 10.1103/PhysRevLett.112.135901 PACS numbers: 65.60.+a, 63.50.Lm Glasses in general show an anomaly in their vibrational spectrum in the terra Hertz region that is commonly referred to as the “boson peak” contribution. This enhance- ment of the local vibrational density of states that lead to additional scattering of phonons and thus to enhanced damping and the so-called phonon broadening is a general feature of glasses, irrespective of the dominant type of the interatomic or intermolecular binding energy and is thus also observed for the class of metallic glasses. Despite controversial discussions, it now seems accepted that the boson peak originates from quasilocalized transverse vibrational modes associated with “defective” soft local structures in a topologically disordered material (glass) [1,2], and thus occurs also in metallic glasses [3]. In addition, it also seems accepted that the anomalies in the vibrational density of states are also reflected in a heat capacity C p contribution in excess of the Debye heat capacity, which in the temperature dependence of C p =T 3 yields an excess peak at temperatures of about 5–40 K for all glasses [4]. Based on experimental data, atomistic simulations and semiempirical models, different views concerning an atomistic description of the origin of the localized soft modes have been advanced. Yet, the origin of the low-frequency excited states remains unclear despite numerous experimental and theoretical investigations. These excited states are described in terms of soft anharmonic potentials [5], fluctuating density [6] or/and force constants [7], strings of atoms [8], or interstitialcy-like “defects” [9]. While it is not the intention or purpose of the present Letter to distinguish between such models, it is emphasized that without regard of the specific atomic configuration invoked, the different model approaches can be viewed as being in line with a mesoscopically heterogeneous spatial distribution of regions that contribute an excess vibrational density of states. While the origin and configurations of such regions in macroscopically homogeneous glasses after careful aging in a uniform and homogeneous temperature field is debatable, one can also start from a different viewpoint and use the boson-peak behavior, in the present case represented by the excess heat capacity at temperatures in the range of 5–40 K, for analyzing mesoscopically heterogeneous glasses with spatial regions of different specific volume and fictive temperature [10] to elucidate the specific property changes of these regions. In the present work, thus, low-temperature heat capacity mea- surements have been performed on Pd 40 Ni 40 P 20 glasses that were subjected to different well-controlled thermomechan- ical processing histories. In particular, glassy samples that had been deformed plastically included the deformation- induced, mesoscopic features that are called “shear bands” that result from flow localization and shear softening of glasses and that are several nanometers thickness and macroscopic in length. There is no accepted viewpoint on the nature of shear bands and related phenomena. The structure of shear bands is known [11–14] to be different from that of the unde- formed matrix and the shear bands formation influences the physical properties [14,15]. It should naturally be expected that the inhomogeneous deformation leads to the formation of some areas with a different (either more disordered or more ordered) structure in comparison with the matrix [11–13]. Such areas must effectively change the dynamics of the glass on the whole. The shear bands are very thin, about 10–20 nm [11,12,16]; i.e., the relative volume occupied by one shear band is very low. Consequently, an observable contribution to changes of the dynamic behavior is expected at a high density of the shear bands, i.e., at high degrees of deformation. PRL 112, 135901 (2014) PHYSICAL REVIEW LETTERS week ending 4 APRIL 2014 0031-9007=14=112(13)=135901(5) 135901-1 © 2014 American Physical Society