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Ekkehard Lange

Publications and source records attributed to Ekkehard Lange.

6 recordsLinked to original sources
arXiv2000

Impact of magnetic frustration on the Mott transition within a slave-boson mean-field theory

We investigate the paramagnetic-metal-to-antiferromagnetic-metal and antiferromagnetic-metal-to- antiferromagnetic-insulator transitions using a slave-boson mean-field theory. To this effect, we discuss the ground state of the half-filled Hubbard model as a function of t'/t and correlation strength U, where t and t' are the hopping amplitudes between nearest and next-nearest neighbors, respectively. The metal-insulator transition at a critical U_{MIT} is of second order for small levels of magnetic frustration, t'/t<0.06, and of first order for large ones, t'/t>0.06. The insulator is always antiferromagnetically ordered, while the metal exhibits a second-order transition from a paramagnetic to an antiferromagnetic state up to t'/t=0.14, as U is increased. We also contrast these findings with what we obtain in Hartree-Fock approximation.

cond-mat.str-el↗
arXiv1999

Magnetooptical sum rules close to the Mott transition

We derive new sum rules for the real and imaginary parts of the frequency-dependent Hall constant and Hall conductivity. As an example, we discuss their relevance to the doped Mott insulator that we describe within the dynamical mean-field theory of strongly correlated electron systems.

cond-mat.str-el↗
arXiv1998

Magnetotransport in the doped Mott insulator

We investigate the Hall effect and the magnetoresistance of strongly correlated electron systems using the dynamical mean-field theory. We treat the low- and high-temperature limits analytically and explore some aspects of the intermediate-temperature regime numerically. We observe that a bipartite-lattice condition is responsible for the high-temperature result $σ_{xy}\sim 1/T^2$ obtained by various authors, whereas the general behavior is $σ_{xy}\sim 1/T$, as for the longitudinal conductivity. We find that Kohler's rule is neither obeyed at high nor at intermediate temperatures.

cond-mat.str-el↗
arXiv1996

Memory function approach to the Hall constant in strongly correlated electron systems: Part II

The anomalous frequency and doping dependence of the Hall constant in the normal state of high-T_c superconductors are investigated within models of strongly correlated electron systems. In Mori theory, the transition of the Hall constant from infinite to zero frequency is described by a memory function. It naturally introduces a second time scale, that, within the t-J model, is identified with the spinon relaxation time of Anderson. This provides us with a phenomenological understanding of the interplay between the frequency and temperature dependence of the Hall constant for frequencies below the Mott-Hubbard gap. Within the single-band Hubbard model in the limit $U\gg t$, the memory function is calculated via its moments and shown to project out the high-energy scale U. This causes the Hall constant to decrease by a factor $(1+δ)/2$ ($δ$: doping), when the frequency is lowered from infinity to values within the Mott-Hubbard gap. Finally, it is outlined, how the Hall constant may be calculated in the low frequency regime.

cond-mat.supr-con↗
arXiv1996

Memory function approach to the Hall constant in strongly correlated electron systems

The anomalous properties of the Hall constant in the normal state of high-$T_c$ superconductors are investigated within the single-band Hubbard model. We argue that the Mori theory is the appropriate formalism to address the Hall constant, since it aims directly at resistivities rather than conductivities. More specifically, the frequency dependent Hall constant decomposes into its infinite frequency limit and a memory function contribution. As a first step, both terms are calculated perturbatively in $U$ and on an infinite dimensional lattice, where $U$ is the correlation strength. If we allow $U$ to be of the order of twice the bare band width, the memory function contribution causes the Hall constant to change sign as a function of doping and to decrease as a function of temperature.

cond-mat↗