Abstract:An explanation for the glass-like anomaly observed in the low-temperature specific heat of incommensurate phases is proposed. The key point of this explanation is the proper account for the phason damping when computing the thermodynamic magnitudes. The low-temperature specific heat of the incommensurate phases is discussed within three possible scenarios for the phason dynamics: no phason gap, static phason gap and a phason gap of dynamical origin. Existing NMR and inelastic scattering data indicate that thes… Show more
“…Accounting for this q = 0 phason damping or pinning in the heat capacity calculation produces upturns in C P / T 3 similar to that observed in Fig. 4b 30 . Hence, the thermodynamic properties are consistent with the presence of phasons in fresnoite.Fig.…”
Section: Resultssupporting
confidence: 68%
“…The acoustic phonons and phasons have measured line widths that are instrument resolution limited, so we cannot resolve differences in lifetime broadening directly. The known damping of long wavelength phasons 30 should not change this estimate of the thermal conductivity, however, since the density of states at long wavelengths is very small (Fig. 5).…”
Section: Resultsmentioning
confidence: 97%
“…While at high temperatures the heat capacity is well described by phonon theory, below 3 K there is a clear upturn in C P / T 3 rather than the constant expected from the Debye T 3 law. This is a known feature of the heat capacity of incommensurate structures, and has been explained in terms of phason damping or possibly a small gap from phason pinning at long wavelengths ( q = 0) 30 . Unlike acoustic phonons, phasons are always overdamped at long wavelengths because a uniform sliding of the modulation phase has viscosity 30 .…”
Section: Resultsmentioning
confidence: 97%
“…This is a known feature of the heat capacity of incommensurate structures, and has been explained in terms of phason damping or possibly a small gap from phason pinning at long wavelengths ( q = 0) 30 . Unlike acoustic phonons, phasons are always overdamped at long wavelengths because a uniform sliding of the modulation phase has viscosity 30 . Accounting for this q = 0 phason damping or pinning in the heat capacity calculation produces upturns in C P / T 3 similar to that observed in Fig.…”
Controlling the thermal energy of lattice vibrations separately from electrons is vital to many applications including electronic devices and thermoelectric energy conversion. To remove heat without shorting electrical connections, heat must be carried in the lattice of electrical insulators. Phonons are limited to the speed of sound, which, compared to the speed of electronic processes, puts a fundamental constraint on thermal management. Here we report a supersonic channel for the propagation of lattice energy in the technologically promising piezoelectric mineral fresnoite (Ba2TiSi2O8) using neutron scattering. Lattice energy propagates 2.8−4.3 times the speed of sound in the form of phasons, which are caused by an incommensurate modulation in the flexible framework structure of fresnoite. The phasons enhance the thermal conductivity by 20% at room temperature and carry lattice-energy signals at speeds beyond the limits of phonons.
“…Accounting for this q = 0 phason damping or pinning in the heat capacity calculation produces upturns in C P / T 3 similar to that observed in Fig. 4b 30 . Hence, the thermodynamic properties are consistent with the presence of phasons in fresnoite.Fig.…”
Section: Resultssupporting
confidence: 68%
“…The acoustic phonons and phasons have measured line widths that are instrument resolution limited, so we cannot resolve differences in lifetime broadening directly. The known damping of long wavelength phasons 30 should not change this estimate of the thermal conductivity, however, since the density of states at long wavelengths is very small (Fig. 5).…”
Section: Resultsmentioning
confidence: 97%
“…While at high temperatures the heat capacity is well described by phonon theory, below 3 K there is a clear upturn in C P / T 3 rather than the constant expected from the Debye T 3 law. This is a known feature of the heat capacity of incommensurate structures, and has been explained in terms of phason damping or possibly a small gap from phason pinning at long wavelengths ( q = 0) 30 . Unlike acoustic phonons, phasons are always overdamped at long wavelengths because a uniform sliding of the modulation phase has viscosity 30 .…”
Section: Resultsmentioning
confidence: 97%
“…This is a known feature of the heat capacity of incommensurate structures, and has been explained in terms of phason damping or possibly a small gap from phason pinning at long wavelengths ( q = 0) 30 . Unlike acoustic phonons, phasons are always overdamped at long wavelengths because a uniform sliding of the modulation phase has viscosity 30 . Accounting for this q = 0 phason damping or pinning in the heat capacity calculation produces upturns in C P / T 3 similar to that observed in Fig.…”
Controlling the thermal energy of lattice vibrations separately from electrons is vital to many applications including electronic devices and thermoelectric energy conversion. To remove heat without shorting electrical connections, heat must be carried in the lattice of electrical insulators. Phonons are limited to the speed of sound, which, compared to the speed of electronic processes, puts a fundamental constraint on thermal management. Here we report a supersonic channel for the propagation of lattice energy in the technologically promising piezoelectric mineral fresnoite (Ba2TiSi2O8) using neutron scattering. Lattice energy propagates 2.8−4.3 times the speed of sound in the form of phasons, which are caused by an incommensurate modulation in the flexible framework structure of fresnoite. The phasons enhance the thermal conductivity by 20% at room temperature and carry lattice-energy signals at speeds beyond the limits of phonons.
“…Low temperature linear contribution to c p is typical for glasses [17] and modeled by socalled two-level states (TLS) [145,146] in local anharmonic atomic potentials. However, it has been shown [147,148] that any damped vibration in solid contributes to linear c p at very low energies. This contribution is proportional to the damping and inversely proportional to the square of vibration frequency [147].…”
Hard form of carbon obtained by collapsing C 60 fullerene molecules at moderate pressure and temperature was investigated using different imaging techniques at spatial resolutions ranging from angstrom to millimeter. Hierarchical granular morphology has been observed from the atomic up to the sample size length scale, revealing scale independent grain size distribution. The unusual fractal-like structure correlates with unique transport and calorimetric properties of this material. Hard carbon can be considered as a bridge between porous and dense amorphous materials.
Phosphate tungsten and molybenum bronzes represent an outstanding class of materials displaying textbook examples of charge‐density‐wave (CDW) physics among other fundamental properties. Here we report on the existence of a novel structural branch with the general formula [Ba(PO4)2][WmO3m−3] (m=3, 4 and 5) denominated ′layered monophosphate tungsten bronzes′ (L‐MPTB). It results from thick [Ba(PO4)2]4− spacer layers disrupting the cationic metal‐oxide 2D units and enforcing an overall trigonal structure. Their symmetries are preserved down to 1.8 K and the compounds show metallic behaviour with no clear anomaly as a function of temperature. However, their electronic structure displays the characteristic Fermi surface of previous bronzes derived from 5d W states with hidden nesting properties. By analogy with previous bronzes, such a Fermi surface should result into CDW order. Evidence of CDW order was only indirectly observed in the low‐temperature specific heat, giving an exotic context at the crossover between stable 2D metals and CDW order.
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