Incommensurate Systems as Model Compounds for Disorder Revealing Low-Temperature Glasslike Behavior

Abstract

We show that the specific heat of incommensurately modulated crystals with broken translational periodicity presents similar features at low temperatures to those of amorphous and glass materials. Here we demonstrate that the excess to the constant C_{p}(T)/T^{3} law (or Debye limit) is made up of an upturn below 1 K and of a broad bump at T≈10 K that directly originates from the gapped phase and amplitude modes of the incommensurate structure. We argue that the low-energy dynamics of incommensurate systems constitute a plausible simplification of the landscape of interactions present in glasses, giving rise to their low-temperature anomalies.

Molecular quantum materials: electronic phases and charge dynamics in two-dimensional organic solids

“…From this point of view, the low-frequency Raman mode is interpreted as a Boson peak arising from charge fluctuations between two molecular dimer sites. In analogy to the charge-density wave phenomenology, we speculate that the low-frequency Raman mode (Boson peak) and the dielectric mode in kHz-MHz range represent fingerprints of the same phenomenon [629,630]: the formation of dipole liquid state occurs on the local scale and bears glassy signatures. This interpretation is in accord with previous observations: systems with strong Boson peaks above T g tend to be those with strong liquid character [206,631,632].…”

Discovery of a Low Thermal Conductivity Oxide Guided by Probe Structure Prediction and Machine Learning

“…[ 50 , 51 ] The presence of the boson peak and linear contribution in the heat capacity are characteristic thermal properties of glasses and have been proposed to be a general feature of aperiodic materials as well. [52] The speed of sound ( v s ) for Ba 10 Y 6 Ti 4 O 27 of 2204(45) m s −1 , obtained from Grüneisen parameters (Figure 5 d ) is, like the thermal conductivity, very low for an oxide, approximately half that of known quaternary Ba 6 Y 2 Ti 4 O 17 (4443(21) m s −1 ).…”

A new paradigm for the low-T glassy-like thermal properties of solids

“…In this Letter, we provide more evidence for the case by considering the low-temperature thermal properties of quasicrystals and incommensurate structures. Both anomalous features (BP and linear in T specific heat) have been experimentally observed in quasicrystals [16]. Phenomenological models have been constructed and pinpoint as the origin of these anomalies the dynamics of the phason and amplitude modes [24,25].…”

“…In addition to this questionable confidence and theoretical confusion, the "anomalous" nature of glassy features in solids is in deep crisis [12]. This is because the same allegedly "anomalous" features have been systematically observed in non-disordered systems, atomic and molecular cryocrystals [13][14][15] and in quasicrystals/incommensurate structures [16]. * matteo.baggioli@uam.es † alessio.zaccone@unimi.it…”

“…Recently, the idea that these (not anymore anomalous) features can actually be induced by different physical mechanisms has gained strength, supported by experimental observations [13][14][15][16] and first principles theoretical analyses. Robust theoretical frameworks, which fit harmoniously with several experimental data [17] and observations [13][14][15][16], have proven that a BP anomaly in crystals can be induced by overdamped low-energy modes and (Akhiezer-type) anharmonicity [18,19] and also by the piling up of softly gapped optical-like modes [20,21]. Moreover, it has been shown [22] that low-energy diffusive excitations produce a linear in T contribution to the specific heat, in agreement with the results from random matrix theory [23].…”