arXiv subjects

M. Jarrell

Publications and source records attributed to M. Jarrell.

At least 37 records · Page 2Linked to original sources

arXiv2014

Electronic Structure and Spectra of CuO

We report the electronic structure of monoclinic CuO as obtained from first principles calculations utilizing density functional theory plus effective Coulomb interaction (DFT + U) method. In contrast to standard DFT calculations taking into account electronic correlations in DFT + U gave antiferromagnetic insulator with energy gap and magnetic moment values in good agreement with experimental data. The electronic states around the Fermi level are formed by partially filled Cu 3$d_{x^2-y^2}$ orbitals with significant admixture of O 2$p$ states. Theoretical spectra are calculated using DFT + U electronic structure method and their comparison with experimental photoemission and optical spectra show very good agreement.

cond-mat.str-el↗

arXiv2013

Mean-field embedding of the dual fermion approach for correlated electron systems

To reduce the rapidly growing computational cost of the dual fermion lattice calculation with increasing system size, we introduce two embedding schemes. One is the real fermion embedding, and the other is the dual fermion embedding. Our numerical tests show that the real fermion and dual fermion embedding approaches converge to essentially the same result. The application on the Anderson disorder and Hubbard models shows that these embedding algorithms converge more quickly with system size as compared to the conventional dual fermion method, for the calculation of both single-particle and two-particle quantities.

cond-mat.str-el↗

arXiv2013

Re-examining the electronic structure of germanium: A first-principle study

We report results from an efficient, robust, ab-initio method for self-consistent calculations of electronic and structural properties of Ge. Our non-relativistic calculations employed a generalized gradient approximation (GGA) potential and the linear combination of atomic orbitals (LCAO) formalism. The distinctive feature of our computations stem from the use of Bagayoko-Zhao-Williams-Ekuma-Franklin (BZW-EF) method. Our results are in agreement with experimental ones where the latter are available. In particular, our theoretical, indirect band gap of 0.65 eV, at the experimental lattice constant of 5.66 Å, is in excellent agreement with experiment. Our predicted, equilibrium lattice constant is 5.63 Å, with a corresponding indirect band gap of 0.65 eV and a bulk modulus of 80 GPa. We also calculated the effective masses in various directions with respect to the $Γ$ point.

cond-mat.mtrl-sci↗

arXiv2013

Phase Stability in the Two dimensional Anisotropic Boson Hubbard Hamiltonian

The two dimensional square lattice hard-core boson Hubbard model with near neighbor interactions has a `checkerboard' charge density wave insulating phase at half-filling and sufficiently large intersite repulsion. When doped, rather than forming a supersolid phase in which long range charge density wave correlations coexist with a condensation of superfluid defects, the system instead phase separates. However, it is known that there are other lattice geometries and interaction patterns for which such coexistence takes place. In this paper we explore the possibility that anisotropic hopping or anisotropic near neighbor repulsion might similarly stabilize the square lattice supersolid. By considering the charge density wave structure factor and superfluid density for different ratios of interaction strength and hybridization in the $\hat x$ and $\hat y$ directions, we conclude that phase separation still occurs.

cond-mat.str-el↗

arXiv2012

Physical Properties of $Ba_2 Mn_2 Sb_2 O$ Single Crystals

We report both experimental and theoretical investigations of the physical properties of Ba$_\mathrm{2}$Mn$_\mathrm{2}$Sb$_\mathrm{2}$O single crystals. This material exhibits a hexagonal structure with lattice constants: a = 4.7029(15) Å and c = 19.9401(27) Å, as obtained from powder X-ray diffraction measurements, and in agreement with structural optimization through density functional theory (DFT) calculations. The magnetic susceptibility and specific heat show anomalies at T$_\mathrm{N}$ = 60 K, consistent with antiferromagnetic ordering. However, the magnitude of T$_\mathrm{N}$ is significantly smaller than the Curie-Weiss temperature ($\mid$$\mathrm{Θ_{CW}}$$\mid$ $\approx$ 560 K), suggesting a magnetic system of reduced dimensionality. The temperature dependence of both the in-plane and out-of-plane resistivity changes from an activated at $T$ $>$ T$_\mathrm{x}$ $\sim$ 200 K to a logarithmic at $T$ $<$ T$_\mathrm{x}$. Correspondingly, the magnetic susceptibility displays a bump at T$_\mathrm{x}$. DFT calculations at the DFT + U level support the experimental observation of an antiferromagnetic ground state.

cond-mat.str-el↗

arXiv2012

Dual Fermion Method for Disordered Electronic Systems

While the coherent potential approximation (CPA) is the prevalent method for the study of disordered electronic systems, it fails to capture non-local correlations and Anderson localization. To incorporate such effects, we extend the dual fermion approach to disordered non-interacting systems using the replica method. Results for single- and two- particle quantities show good agreement with cluster extensions of the CPA; moreover, weak localization is captured. As a natural extension of the CPA, our method presents an alternative to the existing cluster theories. It can be used in various applications, including the study of disordered interacting systems, or for the description of non-local effects in electronic structure calculations.

cond-mat.str-el↗

arXiv2012

First Principle Local Density Approximation Description of the Electronic Properties of Ferroelectric Sodium Nitrite

The electronic structure of the ferroelectric crystal, NaNO$_2$, is studied by means of first-principles, local density calculations. Our ab-initio, non-relativistic calculations employed a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Following the Bagayoko, Zhao, Williams, method, as enhanced by Ekuma, and Franklin (BZW-EF), we solved self-consistently both the Kohn-Sham equation and the equation giving the ground state charge density in terms of the wave functions of the occupied states. We found an indirect band gap of 2.83 eV, from W to R. Our calculated direct gaps are 2.90, 2.98, 3.02, 3.22, and 3.51 eV at R, W, X, Γ, and T, respectively. The band structure and density of states show high localization, typical of a molecular solid. The partial density of states shows that the valence bands are formed only by complex anionic states. These results are in excellent agreement with experiment. So are the calculated densities of states. Our calculated electron effective masses of 1.18, 0.63, and 0.73 mo in the Γ-X, Γ-R, and Γ-W directions, respectively, show the highly anisotropic nature of this material.

cond-mat.mtrl-sci↗

arXiv2012

Electronic, structural, and elastic properties of metal nitrides XN (X = Sc, Y): A first principle study

We utilized a simple, robust, first principle method, based on basis set optimization with the BZW-EF method, to study the electronic and related properties of transition metal mono-nitrides: ScN and YN. We solved the KS system of equations self-consistently within the linear combination of atomic orbitals (LCAO) formalism. It is shown that the band gap and low energy conduction bands, as well as elastic and structural properties, can be calculated with a reasonable accuracy when the LCAO formalism is used to obtain an optimal basis. Our calculated, indirect electronic band gap (E$^\mathrm{Γ-X}_g$) is 0.79 (LDA) and 0.88 eV (GGA) for ScN. In the case of YN, we predict an indirect band gap (E$^\mathrm{Γ-X}_g$) of 1.09 (LDA) and 1.15 eV (GGA). We also calculated the equilibrium lattice constants, the bulk moduli (B$_{o}$), effective masses, and elastic constants for both systems. Our calculated values are in excellent agreement with experimental ones where the latter are available.

cond-mat.mtrl-sci↗

arXiv2012

First principle electronic, structural, elastic, and optical properties of strontium titanate

We report self-consistent ab-initio electronic, structural, elastic, and optical properties of cubic SrTiO$_{3}$ perovskite. Our non-relativistic calculations employed a generalized gradient approximation (GGA) potential and the linear combination of atomic orbitals (LCAO) formalism. The distinctive feature of our computations stem from solving self-consistently the system of equations describing the GGA, using the Bagayoko-Zhao-Williams (BZW) method. Our results are in agreement with experimental ones where the later are available. In particular, our theoretical, indirect band gap of 3.24 eV, at the experimental lattice constant of 3.91 Å, is in excellent agreement with experiment. Our predicted, equilibrium lattice constant is 3.92 Å, with a corresponding indirect band gap of 3.21 eV and bulk modulus of 183 GPa.

cond-mat.mtrl-sci↗

arXiv2011

Role of the van Hove Singularity in the Quantum Criticality of the Hubbard Model

A quantum critical point (QCP), separating the non-Fermi liquid region from the Fermi liquid, exists in the phase diagram of the 2D Hubbard model [Vidhyadhiraja et. al, Phys. Rev. Lett. 102, 206407 (2009)]. Due to the vanishing of the critical temperature associated with a phase separation transition, the QCP is characterized by a vanishing quasiparticle weight. Near the QCP, the pairing is enhanced since the real part of the bare d-wave p-p susceptibility exhibits algebraic divergence with decreasing temperature, replacing the logarithmic divergence found in a Fermi liquid [Yang et. al, Phys. Rev. Lett. 106, 047004 (2011)]. In this paper we explore the single-particle and transport properties near the QCP. We focus mainly on a van Hove singularity (vHS) coming from the relatively flat dispersion that crosses the Fermi level near the quantum critical filling. The flat part of the dispersion orthogonal to the antinodal direction remains pinned near the Fermi level for a range of doping that increases when we include a negative next-near-neighbor hopping t' in the model. For comparison, we calculate the bare d-wave pairing susceptibility for non-interacting models with the usual two-dimensional tight binding dispersion and a hypothetical quartic dispersion. We find that neither model yields a vHS that completely describes the critical algebraic behavior of the bare d-wave pairing susceptibility. The resistivity, thermal conductivity, thermopower, and the Wiedemann-Franz Law are examined in the Fermi liquid, marginal Fermi liquid, and pseudo-gap doping regions. A negative next-near-neighbor hopping t' increases the doping region with marginal Fermi liquid character. Both T and negative t' are relevant variables for the QCP, and both the transport and the motion of the vHS with filling suggest that they are qualitatively similar in their effect.

cond-mat.str-el↗

arXiv2011

Dual Fermion Dynamical Cluster Approach for Strongly Correlated Systems

We have designed a new multi-scale approach for Strongly Correlated Systems by combining the Dynamical Cluster Approximation (DCA) and the recently introduced dual-fermion formalism. This approach employs an exact mapping from a real lattice to a DCA cluster of linear size Lc embedded in a dual fermion lattice. Short-length-scale physics is addressed by the DCA cluster calculation, while longer-length-scale physics is addressed diagrammatically using dual fermions. The bare and dressed dual Fermionic Green functions scale as O(1/Lc) so perturbation theory on the dual lattice converges very quickly. E.g., the dual Fermion self-energy calculated with simple second order perturbation theory is of order O(1/Lc^3), with third order and three body corrections down by an additional factor of O(1/Lc^2).

cond-mat.str-el↗

arXiv2011

Solving the Parquet Equations for the Hubbard Model beyond Weak Coupling

We find that imposing the crossing symmetry in the iteration process considerably extends the range of convergence for solutions of the parquet equations for the Hubbard model. When the crossing symmetry is not imposed, the convergence of both simple iteration and more complicated continuous loading (homotopy) methods are limited to high temperatures and weak interactions. We modify the algorithm to impose the crossing symmetry without increasing the computational complexity. We also imposed time reversal and a subset of the point group symmetries, but they did not further improve the convergence. We elaborate the details of the latency hiding scheme which can significantly improve the performance in the computational implementation. With these modifications, stable solutions for the parquet equations can be obtained by iteration more quickly even for values of the interaction that are a significant fraction of the bandwidth and for temperatures that are much smaller than the bandwidth. This may represent a crucial step towards the solution of two-particle field theories for correlated electron models.

cond-mat.str-el↗

arXiv2011

Using off-diagonal confinement as a cooling method

In a recent letter [Phys. Rev. Lett. 104, 167201 (2010)] we proposed a new confining method for ultracold atoms on optical lattices, based on off-diagonal confinement (ODC). This method was shown to have distinct advantages over the conventional diagonal confinement (DC) that makes use of a trapping potential, including the existence of pure Mott phases and highly populated condensates. In this paper we show that the ODC method can also lead to temperatures that are smaller than with the conventional DC method, depending on the control parameters. We determine these parameters using exact diagonalizations for the hard-core case, then we extend our results to the soft-core case by performing quantum Monte Carlo (QMC) simulations for both DC and ODC systems at fixed temperatures, and analysing the corresponding entropies. We also propose a method for measuring the entropy in QMC simulations.

cond-mat.quant-gas↗

arXiv2010

Quantum Criticality and Incipient Phase Separation in the Thermodynamic Properties of the Hubbard Model

Transport measurements on the cuprates suggest the presence of a quantum critical point hiding underneath the superconducting dome near optimal hole doping. We provide numerical evidence in support of this scenario via a dynamical cluster quantum Monte Carlo study of the extended two-dimensional Hubbard model. Single particle quantities, such as the spectral function, the quasiparticle weight and the entropy, display a crossover between two distinct ground states: a Fermi liquid at low filling and a non-Fermi liquid with a pseudogap at high filling. Both states are found to cross over to a marginal Fermi-liquid state at higher temperatures. For finite next-nearest-neighbor hopping t' we find a classical critical point at temperature T_c. This classical critical point is found to be associated with a phase separation transition between a compressible Mott gas and an incompressible Mott liquid corresponding to the Fermi liquid and the pseudogap state, respectively. Since the critical temperature T_c extrapolates to zero as t' vanishes, we conclude that a quantum critical point connects the Fermi-liquid to the pseudogap region, and that the marginal-Fermi-liquid behavior in its vicinity is the analogous of the supercritical region in the liquid-gas transition.

cond-mat.str-el↗

arXiv2010

A dynamical mean-field approximation study of a tight-binding model for Ga$_{1-x}$Mn$_{x}$As

The magneto-optical properties of the ferromagnetic semiconductor Ga$_{1-x}$Mn$_{x}$As are studied within the dynamical mean-field approximation (DMFA). A material-specific multiband $sp^{3}$ tight-binding Hamiltonian is employed for the dispersion of the GaAs host. The calculated density of states shows an impurity band and a distorted valence band for large and moderate values of magnetic coupling, respectively. Upon using the more realistic band structure, the ferromagnetic transition temperature is significantly closer to the experimental results than the previous predictions of $k\cdot p$ models. The optical conductivity shows a Drude-like peak at low frequencies which is suppressed by increasing of the magnetic coupling.

cond-mat.str-el↗

arXiv2010

The effect of spin-orbit interaction and attractive Coulomb potential on the magnetic properties of Ga$_{1-x}$Mn$_{x}$As

We employ the dynamical mean-field approximation to study the magnetic properties of a model relevant for the dilute magnetic semiconductors. Our model includes the spin-orbit coupling on the hole bands, the exchange interaction, and the attractive Coulomb potential between the negatively charged magnetic ions and the itinerant holes. The inclusion of the Coulomb potential significantly renormalizes the exchange coupling and enhances the ferromagnetic transition temperature for a wide range of couplings. We also explore the effect of the spin-orbit interaction by using two different values of the ratio of the effective masses of the heavy and light holes. We show that in the regime of small $J_{c}$-$V$ the spin-orbit interaction enhances $T_{c}$, while for large enough values of $J_{c}$-$V$ magnetic frustration reduces $T_c$ to values comparable to the previously calculated strong coupling limit.

cond-mat.str-el↗

arXiv2010

Quantum Criticality Due to Incipient Phase Separation in the Two-dimensional Hubbard Model

We investigate the two-dimensional Hubbard model with next-nearest-neighbor hopping, t', using the dynamical cluster approximation. We confirm the existence of a first-order phase-separation transition terminating at a second-order critical point at filling n_c(t') and temperature T_ps(t'). We find that as t' approaches zero, T_ps(t') vanishes and n_c(t') approaches the filling associated with the quantum critical point separating the Fermi liquid from the pseudogap phase. We propose that the quantum critical point under the superconducting dome is the zero-temperature limit of the line of second-order critical points.

cond-mat.str-el↗

arXiv2010

Cluster solver for dynamical mean-field theory with linear scaling in inverse temperature

Dynamical mean field theory and its cluster extensions provide a very useful approach for examining phase transitions in model Hamiltonians, and, in combination with electronic structure theory, constitute powerful methods to treat strongly correlated materials. The key advantage to the technique is that, unlike competing real space methods, the sign problem is well controlled in the Hirsch-Fye (HF) quantum Monte Carlo used as an exact cluster solver. However, an important computational bottleneck remains; the HF method scales as the cube of the inverse temperature, $β$. This often makes simulations at low temperatures extremely challenging. We present here a new method based on determinant quantum Monte Carlo which scales linearly in $β$, and demonstrate that the sign problem is identical to HF.

cond-mat.str-el↗