arXiv subjects

Mark Jarrell

Publications and source records attributed to Mark Jarrell.

62 records · Page 4Linked to original sources

arXiv1996

Magneto-Resistance in the Two-Channel Anderson Lattice

The paramagnetic phase of the two channel Anderson Lattice model in the Kondo limit is investigated in infinite spatial dimensions using the non-crossing approximation. The resistivity exhibits a Kondo upturn with decreasing $T$, followed by a slow decrease to a finite value at $T=0$. The decrease reflects lattice coherence effects in concert with particle-hole symmetry breaking. The magneto-resistance obeys an approximate scaling relation, decreasing towards coherent Fermi liquid behavior with increasing field. The magnetic field induces a Drude peak in the optical conductivity.

cond-mat↗

arXiv1996

Gap States in Dilute Magnetic Alloy Superconductors

We study states in the superconducting gap induced by magnetic impurities using self-consistent quantum Monte Carlo with maximum entropy and formally exact analytic continuation methods. The magnetic impurity susceptibility has different characteristics for $T_{0} \alt T_{c0}$ and $T_{0} \agt T_{c0}$ ($T_{0}$: Kondo temperature, $T_{c0}$: superconducting transition temperature) due to the crossover between a doublet and a singlet ground state. We systematically study the location and the weight of the gap states and the gap parameter as a function of $T_{0}/T_{c0}$ and the concentration of the impurities.

cond-mat↗

arXiv1996

The anharmonic electron-phonon problem

The anharmonic electron-phonon problem is solved in the infinite-dimensional limit using quantum Monte Carlo simulation. Charge-density-wave order is seen to remain at half filling even though the anharmonicity removes the particle-hole symmetry (and hence the nesting instability) of the model. Superconductivity is strongly favored away from half filling (relative to the charge-density-wave order) but the anharmonicity does not enhance transition temperatures over the maximal values found in the harmonic limit.

cond-mat↗

arXiv1996

Two-Channel Kondo Lattice: An Incoherent Metal

The two-channel Kondo lattice model is examined with a Quantum Monte Carlo simulation in the limit of infinite dimensions. We find non-fermi-liquid behavior at low temperatures including a finite low-temperature single-particle scattering rate, the lack of a fermi edge and Drude weight. However, the low-energy density of electronic states is finite. Thus, we identify this system as an incoherent metal. We discuss the relevance of our results for concentrated heavy fermion metals with non-Fermi-Liquid behavior.

cond-mat↗

arXiv1995

Competition between electron-phonon attraction and weak Coulomb repulsion

The Holstein-Hubbard model is examined in the limit of infinite dimensions. Conventional folklore states that charge-density-wave (CDW) order is more strongly affected by Coulomb repulsion than superconducting order because of the pseudopotential effect. We find that both incommensurate CDW and superconducting phases are stabilized by the Coulomb repulsion, but, surprisingly, the commensurate CDW transition temperature is more robust than the superconducting transition temperature. This puzzling feature is resolved by a detailed analysis of perturbation theory.

cond-mat↗

arXiv1994

Magnetic phase diagram of the Hubbard model

The competition between commensurate and incommensurate spin-density-wave phases in the infinite-dimensional single-band Hubbard model is examined with quantum Monte Carlo simulation and strong and weak coupling approximations. Quantum fluctuations modify the weak-coupling phase diagram by factors of order unity and produce remarkable agreement with the quantum Monte Carlo data, but strong-coupling theories (that map onto effective Falicov-Kimball models) display pathological behavior. The single-band model can be used to describe much of the experimental data in Cr and its dilute alloys with V and Mn.

cond-mat↗

arXiv1994

Iterated perturbation theory for the attractive Holstein and Hubbard models

A strictly truncated (weak-coupling) perturbation theory is applied to the attractive Holstein and Hubbard models in infinite dimensions. These results are qualified by comparison with essentially exact Monte Carlo results. The second order iterated perturbation theory is shown to be quite accurate in calculating transition temperatures for retarded interactions, but is not as accurate for the self energy or the irreducible vertex functions themselves. Iterated perturbation theory is carried out thru fourth order for the Hubbard model. The self energy is quite accurately reproduced by the theory, but the vertex functions are not. Anomalous behavior occurs near half filling because the iterated perturbation theory is not a conserving approximation. (REPLACED WITH UUENCODED FIGURES AT THE END. THE TEXT IS UNCHANGED)

cond-mat↗

arXiv1994

Simulation of the electron-phonon interaction in infinite dimensions

The electron-phonon interaction corresponding to the Holstein model (with Coulomb repulsion) is simulated in infinite dimensions using a novel quantum Monte Carlo algorithm. The thermodynamic phase diagram includes commensurate charge-density-wave phases, incommensurate charge-density-wave phases, and superconductivity. The crossover from a weak-coupling picture (where pairs both form and condense at $T_c$) to a strong-coupling picture (where preformed pairs condense at $T_c$) is illustrated with the onset of a double-well structure in the effective phonon potential.

cond-mat↗