The specific heat and upper critical field of amorphous - electronic and vibrational excitations

Abstract

The specific heat C of amorphous films was investigated between 0.3 K and 7 K in the superconducting state as well as in the normal state using a modified AC method. The analysis of the data allows one to determine the electronic density of states at the Fermi energy , the density of states of low-energy excitations and the Debye temperature . The concentration dependence of shows a pronounced minimum at x = 60 at.% in comparison to the free-electron model, in agreement with specific heat and UPS measurements and theoretical calculations published recently. The specific heat of the low-energy excitations is of the same order of magnitude as data available from the literature, and shows a linear temperature dependence. increases with copper concentration and the values agree with those published recently. In addition, the critical magnetic field of the same films was measured. The analysis of these data which should be valid for strongly disordered superconductors yields values of which are about 20% higher than those determined by specific heat measurements. Arguments are given as to why values taken from critical field measurements might be too high. Finally, the specific heat of an amorphous film was measured. was found to be 30% below the free-electron model value, in contrast to results published previously by Rieger and Baumann who found to be in accordance with the free-electron model.

Electronic transport properties of amorphous and quasicrystals TMxAl100−x alloys

“…Changes in the broad minima can be understood as affected by an improvement of the SPO, characteristic for electronic stabilized amorphous metals. Broad minima at E F were confirmed additionally by measurements of the electronic density of states [14], by specific heat measurements at low-temperature [15], as well as by the electronic susceptibility [16]. Changes of the sharp minima are interpreted as affected by an evolvement of angular correlation, evident in the case of Al 70.5 Pd 21 Mn 8.5 and Al 62.5 Cu 25 Fe 12.5 , where the influence of local angular order is related to s [8][9][10].…”

“…), which get more pronounced by annealing and are related to local angular correlation (AC) described by the irrational number s = 2(cos36°) [8][9][10]. 15 Al 85 versus temperature, representative for the other binary alloys. After deposition the sample was annealed at different temperatures T ann up to 350 K. After each step the sample was cooled down to liquid 4 He and q(T) and S(T) were again measured.…”

Thin film microcalorimeter for heat capacity measurements in high magnetic fields

“…Many studies of specific heat in high magnetic fields have been reported for bulk samples, but measurements of thin films have been limited in temperature range or field. [1][2][3][4] These techniques are therefore useful only for samples which have a response to magnetic fields at relatively low temperature.…”