arXiv subjects

A. Rosch

Publications and source records attributed to A. Rosch.

At least 73 records · Page 4Linked to original sources

arXiv2004

Relaxation of Hot Quasiparticles in a d-Wave Superconductor

Motivated by recent pump-probe experiments we consider the processes by which "hot" quasiparticles produced near the antinodes of a d-wave superconductor can relax. We show that in a large region of momentum space processes which break Cooper pairs are forbidden by energy and momentum conservation. Equilibration then occurs by scattering with thermal quasiparticles: Umklapp scattering is exponentially suppressed at low temperatures, but small-angle scattering leads to power-law behavior. By solving the Boltzmann equation analytically we make detailed predictions for the temperature and intensity dependence of these processes, which we compare with experiment.

cond-mat.supr-con↗

arXiv2004

Nonequilibrium Transport through a Kondo Dot: Decoherence Effects

We investigate the effects of voltage induced spin-relaxation in a quantum dot in the Kondo regime. Using nonequilibrium perturbation theory, we determine the joint effect of self-energy and vertex corrections to the conduction electron T-matrix in the limit of transport voltage much larger than temperature. The logarithmic divergences, developing near the different chemical potentials of the leads, are found to be cut off by spin-relaxation rates, implying that the nonequilibrium Kondo-problem remains at weak coupling as long as voltage is much larger than the Kondo temperature.

cond-mat.str-el↗

arXiv2003

Nonequilibrium Transport through a Kondo Dot in a Magnetic Field: Perturbation Theory

Using nonequilibrium perturbation theory, we investigate the nonlinear transport through a quantum dot in the Kondo regime in the presence of a magnetic field. We calculate the leading logarithmic corrections to the local magnetization and the differential conductance, which are characteristic of the Kondo effect out of equilibrium. By solving a quantum Boltzmann equation, we determine the nonequilibrium magnetization on the dot and show that the application of both a finite bias voltage and a magnetic field induces a novel structure of logarithmic corrections not present in equilibrium. These corrections lead to more pronounced features in the conductance, and their form calls for a modification of the perturbative renormalization group.

cond-mat.str-el↗

arXiv2003

Spectral function of the Kondo model in high magnetic fields

Using a recently developed perturbative renormalization group (RG) scheme, we calculate analytically the spectral function of a Kondo impurity for either large frequencies w or large magnetic field B and arbitrary frequencies. For large w >> max[B,T_K] the spectral function decays as 1/ln^2[ w/T_K ] with prefactors which depend on the magnetization. The spin-resolved spectral function displays a pronounced peak at w=B with a characteristic asymmetry. In a detailed comparison with results from numerical renormalization group (NRG) and bare perturbation theory in next-to-leading logarithmic order, we show that our perturbative RG scheme is controlled by the small parameter 1/ln[ max(w,B)/T_K]. Furthermore, we assess the ability of the NRG to resolve structures at finite frequencies.

cond-mat.str-el↗

arXiv2003

Pseudogaps in the t-J model: Extended DMFT study

We investigate the highly incoherent regime of hole-doped 2d Mott-Hubbard insulators at moderately small doping and temperatures T>=0.1J, where J is the exchange coupling. Within an extended dynamical mean-field theory of the t-J model and a generalized non-crossing approximation we calculate the single-particle spectral function, the dynamical susceptibility, and thermodynamic and transport quantities. Short-ranged antiferromagnetic fluctuations lead to strongly incoherent single-particle dynamics, large entropy and large electrical resistivity. At low doping a pseudogap is found to open up both in the single-particle and the spin excitation spectra leading to a decrease in entropy and resistivity. The Hall coefficient changes sign to positive values upon lowering the doping level and increases inversely proportional to doping.

cond-mat.str-el↗

arXiv2003

Non-Equilibrium Transport through a Kondo-Dot in a Magnetic Field: Perturbation Theory and Poor Man's Scaling

We consider electron transport through a quantum dot described by the Kondo model in the regime of large transport voltage V in the presence of a magnetic field B with max(V,B) >> T_K. The electric current I and the local magnetization M are found to be universal functions of V/T_K and B/T_K, where T_K is the equilibrium Kondo temperature. We present a generalization of the perturbative renormalization group to frequency dependent coupling functions, as necessitated by the structure of bare perturbation theory. We calculate I and M within a poor man's scaling approach and find excellent agreement with experiment.

cond-mat.str-el↗

arXiv2002

Pseudogaps in an Incoherent Metal

How are the properties of a metal changed by strong inelastic scattering? We investigate this question within the two-dimensional t-J model using extended dynamical mean field theory and a generalized non-crossing approximation. Short-ranged antiferromagnetic fluctuations lead to a strongly incoherent single particle dynamics, large entropy and resistance. Close to the Mott transition at low hole doping a pseudogap opens, accompanied by a drop in resistivity and an increase in the Hall constant for both lower temperatures and doping levels. The behavior obtained bears surprising similarity to properties of the cuprates.

cond-mat.str-el↗

arXiv2002

Optical Conductivity and Pseudo-Momentum Conservation in Anisotropic Fermi Liquids

Umklapp scattering determines the conductivity of clean metals. In typical quasi one-dimensional Fermi liquids with an open Fermi surface, certain pseudo-momenta do not decay by 2-particle collisions even in situations where Umklapp scattering relaxes the momentum of the quasi particles efficiently. Due to this approximate conservation of pseudo-momentum, a certain fraction of the electrical current decays very slowly and a well-pronounced low-frequency peak emerges in the optical conductivity. We develop simple criteria to determine under what conditions approximate pseudo-momentum conservation is relevant and calculate within in Fermi liquid theory the weights of the corresponding low-frequency peaks and the temperature dependence of the various relevant decay rates. Based on these considerations, we obtain a qualitative picture of the frequency and temperature dependence of the optical conductivity of an anisotropic Fermi liquid.

cond-mat.str-el↗

arXiv2001

Some remarks about pseudo gap behavior of nearly antiferromagnetic metals

In the antiferromagnetically ordered phase of a metal, gaps open on parts of the Fermi surface if the Fermi volume is sufficiently large. We discuss simple qualitative and heuristic arguments under what conditions precursor effects, i.e. pseudo gaps, are expected in the paramagnetic phase of a metal close to an antiferromagnetic quantum phase transition. At least for weak interactions, we do not expect the formation of pseudo gaps in a three dimensional material. According to our arguments, the upper critical dimension d_c for the formation of pseudo gaps is d_c=2. However, at the present stage we cannot rule out a higher upper critical dimension, 2 < d_c <= 3. We also discuss briefly the role of statistical interactions in pseudo gap phases.

cond-mat.str-el↗

arXiv2001

Mesoscopic effects in tunneling between parallel quantum wires

We consider a phase-coherent system of two parallel quantum wires that are coupled via a tunneling barrier of finite length. The usual perturbative treatment of tunneling fails in this case, even in the diffusive limit, once the length L of the coupling region exceeds a characteristic length scale L_t set by tunneling. Exact solution of the scattering problem posed by the extended tunneling barrier allows us to compute tunneling conductances as a function of applied voltage and magnetic field. We take into account charging effects in the quantum wires due to applied voltages and find that these are important for 1D-to-1D tunneling transport.

cond-mat.mes-hall↗

arXiv2001

The Kondo effect in quantum dots at high voltage: Universality and scaling

We examine the properties of a dc-biased quantum dot in the Coulomb blockade regime. For voltages V large compared to the Kondo temperature T_K, the physics is governed by the scales V and gamma, where gamma ~ V/ln^2(V/T_K) is the non-equilibrium decoherence rate induced by the voltage-driven current. Based on scaling arguments, self-consistent perturbation theory and perturbative renormalization group, we argue that due to the large gamma, the system can be described by renormalized perturbation theory for ln(V/T_K) >> 1. However, in certain variants of the Kondo problem, two-channel Kondo physics is induced by a large voltage V.

cond-mat.mes-hall↗

arXiv2001

Transport in a classical model of an one-dimensional Mott insulator: Influence of conservation laws

We study numerically how conservation laws affect the optical conductivity sigma(w) of a slightly doped one-dimensional Mott insulator. We investigate a regime where the average distance between charge excitations is large compared to their thermal de Broglie wave length and a classical description is possible. Due to conservation laws, the dc-conductivity is infinite and the Drude weight D is finite even at finite temperatures. Our numerical results test and confirm exact theoretical predictions for D both for integrable and non-integrable models. Small deviations from integrability induce slowly decaying modes and, consequently, low-frequency peaks in sigma(w) which can be described by a memory matrix approach.

cond-mat.str-el↗

arXiv2001

Transport in Quasi One-Dimensional Systems

The interplay of Umklapp scattering from a periodic potential and other scattering processes determine the conductivity of (quasi) one-dimensional metals. We show that the transport at finite temperature is qualitatively and quantitatively strongly influenced by a number of approximate conservation laws. Typically, not the strongest but the second strongest scattering mechanism determines the dc-conductivity. We discuss the optical conductivity both of strongly anisotropic, quasi one-dimensional Fermi liquids and of Luttinger liquids.

cond-mat.str-el↗

arXiv2000

Pressure-induced residual resistivity anomaly in CeCu_5Au

The electrical resistivity of the magnetically ordered CeCu_5Au has been investigated under pressure up to 8.5 GPa. In the magnetically ordered region (p<3.4 GPa) the residual resistivity rho_0 shows a pronounced maximum as a function of pressure. Even in the nonmagnetic region rho_0 decreases monotonically by more than a factor of three. These two effects can be qualitatively explained in terms of the interplay of pressure, magnetism and disorder in a strongly correlated electron system with weak disorder.

cond-mat.str-el↗

arXiv2000

Conductivity of a clean one-dimensional wire

We study the low-temperature low-frequency conductivity sigma of an interacting one dimensional electron system in the presence of a periodic potential. The conductivity is strongly influenced by conservation laws, which, we argue, need be violated by at least two non-commuting Umklapp processes to render sigma finite. The resulting dynamics of the slow modes is studied within a memory matrix approach, and we find exponential increase as the temperature is lowered, sigma = (Delta n)^2 e^{T_0/(N T)} close to commensurate filling M/N, Delta n=n-M/N << 1, and sigma = e^{(T'_0/T)^{2/3}} elsewhere.

cond-mat.str-el↗

arXiv1999

Magnetotransport in nearly antiferromagnetic metals

We present a theory of the magnetotransport in weakly disordered metals close to an antiferromagnetic quantum-critical point. The anisotropic scattering from critical spin fluctuations is strongly influenced by weak but isotropic scattering from small amounts of disorder. This leads to a large regime where the resistivity obeys a scaling form rho=rho_0+Delta rho = rho_0+T^{3/2} f(T/ρ_0,(p-p_c)/rho_0,B/rho_0^{3/2}), where rho_0 is the residual resistivity, B the magnetic field and p-p_c>0 measures the distance from the quantum-critical point on the paramagnetic side of the phase diagram. Orbital effects of the magnetic field are most pronounced in very clean samples for not too low temperatures, where the resistivity for increasing magnetic field crosses over from a linear temperature dependence Delta rho =T*sqrt{rho_0} to a resistivity linear in B and independent of T and rho_0. At higher magnetic fields Delta rho saturates at a value proportional to T^{1.5} or T^2/(p-p_c). Deviations from scaling, the interplay of orbital and spin contributions of the magnetic field and experimental test of the spin-fluctuation model are discussed in detail.

cond-mat.str-el↗

arXiv1999

Disorder effects on transport near AFM quantum phase transitions

We discuss three different scenarios recently proposed to account for the non-Fermi liquid behavior near antiferromagnetic (AFM) quantum critical points in heavy-Fermion systems: (i) scattering of Fermi liquid quasiparticles by strong spin fluctuations near the spin-density-wave instability, (ii) the breakdown of the Kondo effect due to the competition with the RKKY interaction, and (iii) the formation of magnetic regions due to rare configurations of the disorder. Here we focus on the first scenario and show that it explains in some detail the anomalous temperature dependence of the resistivity observed e.g. in CePd_2Si_2, CeNi_2Ge_2 or CeIn_3. The interplay of strongly anisotropic scattering due to critical spin-fluctuations and weak isotropic impurity scattering leads to a regime with a resistivity rho = rho_0 +Delta rho(T), Delta rho(T) =T^{3/2} f(T/rho_0) \propto T sqrt{rho_0} for sufficiently large T and small rho_0.

cond-mat.str-el↗

arXiv1999

Interplay of disorder and spin fluctuations in the resistivity near a quantum critical point

The resistivity in metals near an antiferromagnetic quantum critical point (QCP) is strongly affected by small amounts of disorder. In a quasi-classical treatment, we show that an interplay of strongly anisotropic scattering due to spin fluctuations and isotropic impurity scattering leads to a large regime where the resistivity varies as T^alpha, with an anomalous exponent, alpha, 1 <= alpha <= 1.5, depending on the amount of disorder. I argue that this mechanism explains in some detail the anomalous temperature dependence of the resistivity observed in CePd_2Si_2, CeNi_2Ge_2 and CeIn_3 near the QCP.

cond-mat.str-el↗