arXiv subjects

Malcolm P. Kennett

Publications and source records attributed to Malcolm P. Kennett.

39 records · Page 3Linked to original sources

arXiv2001

Diluted Magnetic Semiconductors in the Low Carrier Density Regime

This paper, based on a presentation at the Spintronics 2001 conference, provides a review of our studies on II-VI and III-V Mn-doped Diluted Magnetic Semiconductors. We use simple models appropriate for the low carrier density (insulating) regime, although we believe that some of the unusual features of the magnetization curves should qualitatively be present at larger dopings (metallic regime) as well. Positional disorder of the magnetic impurities inside the host semiconductor is shown to have observable consequences for the shape of the magnetization curve. Below the critical temperature the magnetization is spatially inhomogeneous, leading to very unusual temperature dependence of the average magnetization as well as specific heat. Disorder is also found to enhance the ferromagnetic transition temperature. Unusual spin and charge transport is implied.

cond-mat.mtrl-sci↗

arXiv2001

Aging dynamics of quantum spin glasses of rotors

We study the long time dynamics of quantum spin glasses of rotors using the non-equilibrium Schwinger-Keldysh formalism. These models are known to have a quantum phase transition from a paramagnetic to a spin glass phase, which we approach by looking at the divergence of the spin relaxation rate at the transition point. In the aging regime, we determine the dynamical equations governing the time evolution of the spin response and correlation functions, and show that all terms in the equations that arise solely from quantum effects are irrelevant at long times under time reparametrization group (RpG) transformations. At long times, quantum effects enter only through the renormalization of the parameters in the dynamical equations for the classical counterpart of the rotor model. Consequently, quantum effects only modify the out of equilibrium fluctuation dissipation relation (OEFDR), i.e. the ratio X between the temperature and the effective temperature, but not the form of the classical OEFDR.

cond-mat.dis-nn↗

arXiv2000

Time reparametrization group and the long time behaviour in quantum glassy systems

We study the long time dynamics of a quantum version of the Sherrington-Kirkpatrick model. Time reparametrizations of the dynamical equations have a parallel with renormalization group transformations, and within this language the long time behaviour of this model is controlled by a reparametrization group (R$_p$G) fixed point of the classical dynamics. The irrelevance of the quantum terms in the dynamical equations in the aging regime explains the classical nature of the violation of the fluctuation-dissipation theorem.

cond-mat.dis-nn↗