SEARCH · Searcharxiv

Results for “cond-mat.str-el”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources

arXiv2010

An ab-initio evaluation of the local effective interactions in the $\rm Na_{x} Co O_2$ familly

We used quantum chemical ab initio methods to determine the effective parameters of Hubbard and $t-J$ models for the $\rm Na_{x}CoO_2$ compounds (x=0 and 0.5). As for the superconducting compound we found the $a_{1g}$ cobalt orbitals above the $e_g^\prime$ ones by a few hundreds of meV due to the $e_g^\prime$--$e_g$ hybridization of the cobalt $3d$ orbitals. The correlation strength was found to increase with the sodium content $x$ while the in-plane AFM coupling decreases. The less correlated system was found to be the pure $CoO_2$, however it is still strongly correlated and very close to the Mott transition. Indeed we found $U/t\sim 15$, which is the critical value for the Mott transition in a triangular lattice. Finally, one finds the magnetic exchanges in the $\rm CoO_2$ layers, strongly dependant of the weak local structural distortions.

cond-mat.str-el↗

arXiv2008

Superconducting Gap and Pseudogap in Sm(O$_{1-x}$F$_x$)FeAs Layered Superconductor from Photoemission Spectroscopy

High resolution photoemission measurements have been carried out on non-superconducting SmOFeAs parent compound and superconducting Sm(O$_{1-x}$F$_x$)FeAs (x=0.12, and 0.15) compounds. The momentum-integrated spectra exhibit a clear Fermi cutoff that shows little leading-edge shift in the superconducting state which suggests the Fermi surface sheet(s) around the $Γ$ point may not be gapped in this multiband superconductors. A robust feature at 13 meV is identified in all these samples. Spectral weight suppression near E$_F$ with decreasing temperature is observed in both undoped and doped samples that points to a possible existence of a pseudogap in these Fe-based compounds.

cond-mat.supr-con↗

arXiv2008

Effect of disorder on the interacting Fermi gases in a one-dimensional optical lattice

Interacting two-component Fermi gases loaded in a one-dimensional (1D) lattice and subjected to an harmonic trapping potential exhibit interesting compound phases in which fluid regions coexist with local Mott-insulator and/or band-insulator regions. Motivated by experiments on cold atoms inside disordered optical lattices, we present a theoretical study of the effects of a correlated random potential on these ground-state phases. We employ a lattice version of density-functional theory within the local-density approximation to determine the density distribution of fermions in these phases. The exchange-correlation potential is obtained from the Lieb-Wu exact solution of Fermi-Hubbard model. On-site disorder (with and without Gaussian correlations) and harmonic trap are treated as external potentials. We find that disorder has two main effects: (i) it destroys the local insulating regions if it is sufficiently strong compared with the on-site atom-atom repulsion, and (ii) it induces an anomaly in the inverse compressibility at low density from quenching of percolation. For sufficiently large disorder correlation length the enhancement in the inverse compressibility diminishes.

cond-mat.dis-nn↗

arXiv2009

Theory of superconducting and nonsuperconducting stripe phases in the hole-doped superconductor Ca{2-x}Na{x}CuO{2}Cl{2} (x=1/8,1/16)

Based on the newly developed real-space spin-parallel pairing and superconducting theory, we explore a simple explanation for the observed checkerboard patterns in hole-doped Ca{2-x}Na{x}CuO{2}Cl{2} cuprate superconductor. At a hole concentration x=1/8=0.125, the analytical results show that there exists a phase competition between non-superconducting 4a*4b (a=b) checkerboard phase and 8a*2c superconducting vortex phase, where a, b and c are the lattice constants of the superconductor. At a lower hole concentration x=1/16=0.0625, it is revealed that the metastable 4\sqrt{2}a*4\sqrt{2}a checkerboard phase can reorganize itself into a more stable octahedron phase with the 4a*4a checkerboard symmetry.

cond-mat.str-el↗

arXiv2012

First Order Phase Transition in Quantum Paraelectrics

We discuss the nature of pressure induced phase transitions in standard Quantum Paraelectrics near quantum critical point. From a microscopic theory we first show that near the critical point the transition temperature $T_c(p)$ varies as $ (1-p/p_c)^ξ$ with $ξ={1/2}$. Within the Landau scheme, it is shown that for $ξ\leq 1$, a condition satisfied by most quantum paraelectrics the transition is inevitably first order in nature. The present analysis is valid for non-polar impurity induced transitions in these materials and is supported by some recent experiment.

cond-mat.str-el↗

arXiv2008

Quantum oscillations of ortho-II YBa_2Cu_3O_6.5

Motivated by quantum oscillations observed in highly ordered ortho-II YBa_2Cu_3O_6.5, we study the Fermi surface topology of d-density wave (ddw) or antiferromagnetic (AF) ordering in the presence of the ortho-II potential. We find that the electron pocket is unaffected by the presence of the ortho-II potential. This further strengthens the proposal that quantum oscillations observed in ortho-II-free YBa_2Cu_4O_8 arise from an electron pocket. On the other hand, the hole pocket topology is sensitive to the ortho-II potential. We show there exist generically three distinct quantum oscillations associated with one electron-like and two hole-like Fermi pockets. We compare our results to the quantum oscillations observed in experiments. We discuss possible ways to distinguish between ddw and antiferromagnetic orders in a potential single-layer ortho-II material.

cond-mat.supr-con↗

arXiv2008

Crossover from one-dimensional copper-oxygen chains to two-dimensional ladders charge transport in (La,Y)y(Sr,Ca)14-yCu24O41

The charge transport in the copper-oxygen chain/ladder layers of (La,Y)y(Sr,Ca)14-yCu24O41 is investigated along two crystallographic directions in the temperature range from 50 K to 700 K and for doping levels from y ~= 6 (number of holes nh < 1) to y = 0 (number of holes nh = 6). A crossover from a one-dimensional hopping transport along the chains for y >= 3 to a quasi-two-dimensional charge conduction in the ladder planes for y <~ 2 is observed. This is attributed to a partial hole transfer from chains to ladders when the hole doping exceeds nh ~= 4 and approaches fully doped value n_h = 6. For y <~ 2 a weak dielectric relaxation at radio-frequencies and a microwave mode are detected, which might be recognized as signatures of a charge-density wave phase developed at short length scales in the ladders planes.

cond-mat.str-el↗

arXiv2008

Screening of magnetic moments in PuAm alloy : LDA+DMFT study

The puzzling absence of Pu magnetic moments in a PuAm environment is explored using the self-consistent Dynamical Mean Field Theory (DMFT) calculations in combination with the Local Density Approximation. We argue that delta-Pu -Am alloys provide an ideal test bed for investigating the screening of moments from the single impurity limit to the dense limit. Several important effects can be studied: volume expansion, shift of the bare Pu on-site f energy level, and the reduction of the hybridization cloud resulting from the collective character of the Kondo effect in the Anderson lattice. These effects compensate each other and result in a coherence scale, which is independent of alloy composition, and is around 800K. We emphasize the role of the DMFT self-consistency condition, and multiplet splittings in Pu and Am atoms, in order to capture the correct value of the coherence scale in the alloy.

cond-mat.str-el↗

arXiv2010

Solvable Limit for SU(N) Kondo Model

We study a single channel one dimensional Kondo Model where the impurity spin is replaced by an su(n) spin. Using Abelian bosonization and canonical transformation we explicitly show that this system has an exactly solvable point. The calculation also shows that there are $n$ collective excitation modes in the system, one charged and $n-1$ neutral spin excitation modes.

cond-mat.mes-hall↗

arXiv2009

Anyons from fermions with conventional two-body interactions

Emergent anyons are the key elements of the topological quantum computation and topological quantum memory. We study a two-component fermion model with conventional two-body interaction in an open boundary condition and show that several subsets in the low-lying excitations obey the same fusion rules as those of the toric code model. Those string-like non-local excitations in a given subset obey mutual semionic statistics. We show how to peel off one of such subset from other degenerate subsets and manipulate anyons in cold dipolar Fermi atoms or cold dipolar fermionic heteronuclear molecules in optical lattices by means of the established techniques.

cond-mat.other↗

arXiv2009

Exact Ground State Energy of Hubbard Rings in the Atomic Limit

Using a straightforward extension of the analysis of Lieb and Wu, we derive a simple analytic form for the ground state energy of a one-dimensional Hubbard ring in the atomic limit. This result is valid for an \textit{arbitrary} number of lattice sites $L$ and electrons $N \leq L$. Furthermore, our analysis, including an application of the theory of stochastic matrices, provides insight into the degeneracy and spin properties of the ground states in the atomic limit. We give numerical results which illustrate how the atomic limit is approached.

cond-mat.str-el↗

arXiv2008

Remote hole-doping of Mott insulators on the nanometer scale

At interfaces between polar and nonpolar perovskite oxides, an unusual electron-doping has been previously observed, due to electronic reconstructions. We report on remote hole-doping at an interface composed of only polar layers, revealed by high-resolution hard x-ray core-level photoemission spectroscopy. In LaAlO3/LaVO3/LaAlO3 trilayers, the vanadium valence systematically evolves from the bulk value of V3+ to higher oxidation states with decreasing LaAlO3 cap layer thickness. These results provide a synthetic approach to hole-doping transition metal oxide heterointerfaces without invoking a polar discontinuity.

cond-mat.str-el↗

arXiv2008

Bulk-like d band of SrVO3 under a self-protective cap layer

We have performed a detailed angel-resolved photoemission spectroscopy study of in-situ prepared SrVO3 thin films. Naturally capped by a ``transparent'' protective layer, contributions from surface states centered at ~ -1.5 eV are dramatically reduced, enabling us to study the bulk V 3d states. We have observed a clear band dispersion not only in the coherent quasiparticle part but also in the incoherent part, which are reproduced by dynamical mean-field theory calculations and the spectral weight of the incoherent part is stronger within the Fermi surface.

cond-mat.str-el↗

arXiv2008

A direct transition between a Neel ordered Mott insulator and a $d_{x^2-y^2}$ superconductor on the square lattice

In this paper we study a bandwidth-controlled direct, continuous, phase transition from a Mott insulator, with easy plane Neel order, to a fully gapped $d_{x^2-y^2}$ superconductor with a doubled unit cell on the square lattice, a transition that is forbidden according to the Landau paradigm. This transition is made possible because the vortices of the antiferromagnet are charged and the vortices of the superconductor carry spins. These nontrivial vortex quantum numbers arise because the ordered phases are intimately related to a topological band insulator. We describe the lattice model as well as the effective field theory.

cond-mat.str-el↗

arXiv2008

Origin of large thermopower in LiRh$_2$O$_4$

Motivated by the newly synthesized mixed-valent spinel LiRh$_2$O$_4$ for which a large thermopower is observed in the metallic cubic phase above 230K [Okamoto {\it et al.} (arXiv:0806.2504)], we calculate the Seebeck coefficient by the combination of local density approximation and dynamical mean field theory (LDA+DMFT). The experimental values are well reproduced not only by LDA+DMFT but also by the less involved Boltzmann equation approach. A careful analysis of the latter shows unexpectedly that the origin of the large thermopower shares a common root with a very different oxide: Na$_x$CoO$_2$. We also discuss how it is possible to further increase the powerfactor of LiRh$_2$O$_4$ through doping, which makes the material even more promoising for technological applications.

cond-mat.str-el↗

arXiv2008

Identification of a Marginal Fermi-Liquid in Itinerant Ferromagnet CoS2

We report specific heat, resistivity and susceptibility measurements at different temperatures, magnetic fields, and pressures to provide solid evidence of CoS2 being a marginal Fermi liquid. The presence of a tricritical point in the phase diagram of the system provides an opportunity to test the spin fluctuation theory with a high limit of accuracy. A magnetic field suppresses the amplitude of the spin fluctuations and recovers conventional Fermi liquid behavior, connecting both states continuously.

cond-mat.str-el↗

arXiv2008

Real Space Coulomb Interaction: A Pairing Glue for FeAs Superconductors

In this paper we present a real space pairing glue for the iron-based layered superconductors. It is shown that two static electrons embedded symmetrically into two adjacent Fe plaquettes of the superconductor can be bounded due to the Coulombic interaction. The pairing mechanism favors the existence of the pseudogap in the underdoped FeAs superconductors. A criterion is introduced to distinguish whether or not the pseudogap can open in a material.

cond-mat.str-el↗

arXiv2008

Relativistic BCS Theory in Quasi-(2+1)-Dimensions: Effects of an Inter-layer Transfer in the Honeycomb Lattice Symmetry

Motivated by recent huge interests on graphene sheet and graphite as "relativistic" systems, a BCS superconductivity in a quasi-(2+1)-dimensional relativistic model is investigated. The intra-layer particle dynamics is described by a (2+1)-dimensional Gross-Neveu-type four-body contact interaction model, while inter-layer particle motions will be caused by a hopping term with a transfer parameter $t$. Especially, we examine the effects of non-vanishing $t$, chemical potential $μ$, and a mass parameter $m$ which will give a gap at a conical intersection point of the relativistic band dispersion, in the BCS s-wave (scalar) superconducting gap function $Δ$.

cond-mat.supr-con↗