Laser scanning confocal microscopy studies were carried out on charged screened colloidal silica microspheres in sedimentation equilibrium in the presence of a tunable external alternating electric field. The external a.c. field controls the averaged dipolar interaction between the silica microspheres. From the equilibrium sedimentation profiles, equations of state were obtained as a function of the dipolar strength and volume fraction. The colloidal fluid at zero field follows the hard-sphere equation of state but with an effective larger hard-sphere diameter. At non-zero fields, the average colloidal fluid isothermal compressibility was obtained as a function of a dipolar strength parameter. We then investigated bond order parameters upon increasing the field, and monitored an orientational order parameter associated with the field dependence of the average orientation of dual-particle bonds. The orientational order parameters were found to be very sensitive measures of anisotropy. The field dependence strongly confirms the use of the point dipolar approximation in this system.

This laboratory experiment allows one to study the effect of temperature in the process of formation of hydrogen bound cyclic dimers of benzoic acid (BA). The implementation of the proposed methodology, which comprises the use of FTIR spectroscopy and quantum chemistry calculations, enables the obtaining of the thermodynamic parameters of the dimerization reaction and their subsequent validation by computational chemistry calculations. Hence, the students are involved in a practical learning scheme focused in the study of a central topic in chemistry, such as hydrogen bonding, with the final purpose being to train chemistry students in applying theoretical-experimental approaches to extract meaningful data and valuable information for explaining experimental observables.

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We present an extension of the phenomenological pseudogap model proposed by Rodríguez-Núñez et al (2005 J. Phys.: Condens. Matter 17 323) which relies on the assumption that the self-energy is given by PGwhere G 0 (k, iω n ) is the one-particle free Green function. Going beyond this mean-field model for the pseudogap we now take into account fluctuations of the pseudogap aswhere G PG (k, iω n ) is the pseudogap one-particle Green function and E G ( k) is the value of the pseudogap parameter. We study the combined effect of α , the second-nearest neighbour in the band structure ( ( k) = −2t[cos(k x ) + cos(k y )] + 4tα cos(k x ) cos(k y )) and the cutoff frequency, ω D , on the superconducting critical temperature, T c , as a function of the number of carriers per site, n. The effect of V /t and ω D /t is to increase the value of T c /t, while α displaces T c,max /t away from half-filling.