Anharmonicity, vibrational instability, and the Boson peak in glasses

Abstract

We show that a vibrational instability of the spectrum of weakly interacting quasi-local harmonic modes creates the maximum in the inelastic scattering intensity in glasses, the Boson peak. The instability, limited by anharmonicity, causes a complete reconstruction of the vibrational density of states (DOS) below some frequency ωc, proportional to the strength of interaction. The DOS of the new harmonic modes is independent of the actual value of the anharmonicity. It is a universal function of frequency depending on a single parameter -the Boson peak frequency, ω b which is a function of interaction strength. The excess of the DOS over the Debye value is ∝ ω 4 at low frequencies and linear in ω in the interval ω b ≪ ω ≪ ωc. Our results are in an excellent agreement with recent experimental studies.

Vibrations and relaxations in a soft sphere glass: boson peak and structure factors

“…The harmonic spectrum in this new stable configuration exhibits a BP with a universal shape as it is observed in experiment. In particular the shape of the BP is independent of the actual magnitude of the anharmonicity [20].…”

Pauli-limiting effects in the upper critical fields of a clean LiFeAs single crystal

“…Based on the experimental studies of the well-known two band superconductor MgB 2 , the multi-band effects are expected to result in either quite linear or even upward curvature in the H c2 (T) curves near T c . 10 Moreover, the anisotropy ratio γ H = H c2 increase down to lowest temperatures and γ H is ~ 2 -4 near T c and reduces toward 1 at low temperatures possibly due to the band warping effects. [15][16][17][18][19] On the other hand, experimental evidence for the spin-paramagnetic effects are also accumulating in the Fe-based superconductors.…”

Synthesis and characterization of excess magnesium MgB2 superconductor under inert carbon environment

“…Any attempts to increase the superconducting transition temperature [6][7][8][9] have not achieved success yet [10][11][12], due to its typical phonon coupling mechanism [13][14][15][16][17][18]. But the other critical parameters like critical current density, and upper critical field can be enhanced remarkably by nano-particle doping [19][20][21][22][23][24][25][26]. Moreover, the mechanical properties of MgB 2 superconductor also vary depending upon the dopant as well as on the synthesis route.…”