Universal phase diagram of disordered bosons from a doped quantum magnet (2009)
Yu, Rong, Haas, Stephan, Roscilde, Tommaso
A quantum particle cannot in general diffuse through a disordered medium because of its wavelike nature, but interacting particles can escape localization by collectively percolating through the...
Fractal dimension and threshold properties in a spatially correlated percolation model (2009)
Yang, Hongting, Zhang, Wen, Bray-Ali, Noah, Haas, Stephan
We consider the effects of spatial correlations in a two-dimensional site percolation model. By generalizing the Newman-Ziff Monte Carlo algorithm to include spatial correlations, percolation...
Fidelity and superconductivity in two-dimensional t-J models (2009)
Rigol, Marcos, Shastry, B. Sriram, Haas, Stephan
We compute the ground-state fidelity and various correlations to gauge the competition between different orders in two-dimensional t-J-type models. Using exact numerical diagonalization techniques,...
Revealing Novel Quantum Phases in Quantum Antiferromagnets on Random Lattices (2009)
Yu, Rong, Haas, Stephan, Roscilde, Tommaso
Quantum magnets represent an ideal playground for the controlled realization of novel quantum phases and of quantum phase transitions. The Hamiltonian of the system can be indeed manipulated by...
Plasmonic Excitations in Tight-Binding Nanostructures (2009)
Muniz, Rodrigo A., Haas, Stephan, Levi, A. F. J., Grigorenko, Ilya
We explore the collective electromagnetic response in atomic clusters of various sizes and geometries. Our aim is to understand, and hence to control, their dielectric response, based on a fully...
Scaling of the fidelity susceptibility in a disordered quantum spin chain (2009)
Jacobson, N. Tobias, Garnerone, Silvano, Haas, Stephan, Zanardi, Paolo
The phase diagram of a quantum XY spin chain with Gaussian-distributed random anisotropies and transverse fields is investigated, with focus on the fidelity susceptibility, a recently introduced...
Switching Mechanism in Ferromagnetic Nanorings (2009)
Ferromagnetic rings exhibit many novel physical phenomena with promise for potential applications. Here, we focus on switching processes which are fundamental properties of magnetic systems and are...
Fidelity in topological quantum phases of matter (2009)
Garnerone, Silvano, Abasto, Damian, Haas, Stephan, Zanardi, Paolo
Quantum phase transitions that take place between two distinct topological phases remain an unexplored area for the applicability of the fidelity approach. Here, we apply this method to spin systems...
Yu, Rong, Trinh, Kien T., Moreo, Adriana, Daghofer, Maria, Riera, José A., Haas, Stephan, ...
Multi-orbital Hubbard model Hamiltonians for the undoped parent compounds of the Fe-pnictide superconductors are here investigated using mean-field techniques. For a realistic four-orbital model, our...
An implementation of the fast multiple method (FMM) is performed for magnetic systems with long-ranged dipolar interactions. Expansion in spherical harmonics of the original FMM is replaced by...
Electron-phonon bound states and impurity band formation in quantum wells (2008)
A generalized propagation matrix method is used to study how scattering off local Einstein phonons affects resonant electron transmission through quantum wells. In particular, the parity and the...
Effects of Strong Correlations and Disorder in d-Wave Superconductors (2008)
Rigol, Marcos, Shastry, B. Sriram, Haas, Stephan
We use exact diagonalization techniques to study the interplay between strong correlations, superconductivity, and disorder in a model system. We study an extension of the t-J model by adding an...
Fidelity approach to the disordered quantum XY model (2008)
Garnerone, Silvano, Jacobson, N. Tobias, Haas, Stephan, Zanardi, Paolo
We study the random XY spin chain in a transverse field by analyzing the susceptibility of the ground state fidelity, numerically evaluated through a standard mapping of the model onto quasi-free...
Cassidy, Amy, Grigorenko, Ilya, Haas, Stephan
We investigate theoretically the formation of collective excitations in atomic scale quasi-one dimensional metallic nanostructures. The response of the system is calculated within the linear response...
Optimal control of electromagnetic field using metallic nanoclusters (2008)
Grigorenko, Ilya, Haas, Stephan, Balatsky, Alexander, Levi, A. F. J.
The dielectric properties of metallic nanoclusters in the presence of an applied electromagnetic field are investigated using non-local linear response theory. In the quantum limit we find a...
Subarea law of entanglement in nodal fermionic systems (2008)
Ding, Letian, Bray-Ali, Noah, Yu, Rong, Haas, Stephan
We investigate the subarea law scaling properties of the block entropy in bipartite fermionic systems which do not have a finite Fermi surface. It is found that in gapped regimes the leading subarea...
Chiral d-wave superconductivity in the heavy-fermion compound CeIrIn_5 (2007)
Maki, Kazumi, Raghavan, Aditya, Haas, Stephan
Recent thermal conductivity measurements in the heavy-fermion compound CeIrIn_5 indicate that its superconducting order parameter is very different from CeCoIn_5. Here we show that these experiments...
Zhang, Wen, Singh, Rohit, Bray-Ali, Noah, Haas, Stephan
The magnetic properties of single-domain nanoparticles with different geometric shapes, crystalline anisotropies and lattice structures are investigated. A recently proposed scaling approach is shown...
Entanglement Entropy in the Two-Dimensional Random Transverse Field Ising Model (2007)
Yu, Rong, Saleur, Hubert, Haas, Stephan
The scaling behavior of the entanglement entropy in the two-dimensional random transverse field Ising model is studied numerically through the strong disordered renormalization group method. We find...
Quantum glass phases in the disordered Bose-Hubbard model (2007)
Sengupta, Pinaki, Haas, Stephan
The phase diagram of the Bose-Hubbard model in the presence of off-diagonal disorder is determined using Quantum Monte Carlo simulations. A sequence of quantum glass phases intervene at the interface...
Yu, Rong, Roscilde, Tommaso, Haas, Stephan
Site dilution of spin-gapped antiferromagnets leads to localized free moments, which can order antiferromagnetically in two and higher dimensions. Here we show how a weak magnetic field drives this...
Bottom-up approach to high-temperature superconductivity (2006)
Won, Hyekung, Haas, Stephan, Maki, Kazumi
Since the discovery of high-temperature superconductivity in the cuprates a theoretical understanding of their phase diagram has remained one of the major outstanding problems in condensed matter...
Small $T_1^{-1}$ coherence peak near $T_c$ in unconventional superconductors (2006)
It is usually believed that a coherence peak just below T$_{c}$ in the nuclear spin lattice relaxation rate T$_{1}^{-1}$ in superconducting materials is a signature of conventional s-wave pairing. In...
Electromagnetic response of broken-symmetry nano-scale clusters (2006)
Grigorenko, Ilya, Haas, Stephan, Levi, A. F. J.
A microscopic, non-local response theory is developed to model the interaction of electromagnetic radiation with inhomogeneous nano-scale clusters. The breakdown of classical continuum-field Mie...
Quantum phase transition in spin systems studied through entanglement estimators (2006)
Fubini, Andrea, Haas, Stephan, Roscilde, Tommaso, Tognetti, Valerio, Verrucchi, Paola
Entanglement represents a pure quantum effect involving two or more particles. Spin systems are good candidates for studying this effect and its relation with other collective phenomena ruled by...
Mott glass in site-diluted S=1 antiferromagnets with single-ion anisotropy (2006)
Roscilde, Tommaso, Haas, Stephan
The interplay between site dilution and quantum fluctuations in S=1 Heisenberg antiferromagnets on the square lattice is investigated using quantum Monte Carlo simulations. Quantum fluctuations are...
Disorder-enhanced phase coherence in trapped bosons on optical lattices (2006)
Sengupta, Pinaki, Raghavan, Aditya, Haas, Stephan
The consequences of disorder on interacting bosons trapped in optical lattices are investigated by quantum Monte Carlo simulations. At small to moderate strengths of potential disorder a unique...
Scaling Behavior of Entanglement in Two- and Three-Dimensional Free Fermions (2006)
Li, Weifei, Ding, Letian, Yu, Rong, Roscilde, Tommaso, Haas, Stephan
Exactly solving a spinless fermionic system in two and three dimensions, we investigate the scaling behavior of the block entropy in critical and non-critical phases. The scaling of the block entropy...
Roscilde, Tommaso, Haas, Stephan
We investigate the field-induced insulator-to-superfluid transition of bosonic quasiparticles in $S=1/2$ weakly-coupled dimer antiferromagnets. In presence of realistic disorder due to site dilution...
Yu, Rong, Roscilde, Tommaso, Haas, Stephan
We investigate quantum phase transitions in the spin-1/2 Heisenberg antiferromagnet on square lattices with inhomogeneous bond dilution. It is shown that quantum fluctuations can be continuously...
Quantum localization in bilayer Heisenberg antiferromagnets with site dilution (2005)
Roscilde, Tommaso, Haas, Stephan
The field-induced antiferromagnetic ordering in systems of weakly coupled S=1/2 dimers at zero temperature can be described as a Bose-Einstein condensation of triplet quasiparticles (singlet...
Bose-Glass Phases in Disordered Quantum Magnets (2005)
Nohadani, Omid, Wessel, Stefan, Haas, Stephan
In disordered spin systems with antiferromagnetic Heisenberg exchange, transitions into and out of a magnetic-field-induced ordered phase pass through a unique regime. Using quantum Monte Carlo...
Entanglement and factorized ground states in two-dimensional quantum antiferromagnets (2004)
Roscilde, Tommaso, Verrucchi, Paola, Fubini, Andrea, Haas, Stephan, Tognetti, Valerio
Making use of exact results and quantum Monte Carlo data for the entanglement of formation, we show that the ground state of anisotropic two-dimensional S=1/2 antiferromagnets in a uniform field...
Entanglement in quantum critical spin systems (2004)
Roscilde, Tommaso, Verrucchi, Paola, Fubini, Andrea, Haas, Stephan, Tognetti, Valerio
We study the field dependence of the entanglement of formation in anisotropic S=1/2 antiferromagnetic chains and two-leg ladders displaying a T=0 field-driven quantum phase transition. The analysis...
Quantum Phase Transitions in Coupled Dimer Compounds (2004)
Nohadani, Omid, Wessel, Stefan, Haas, Stephan
We study the critical properties in cubic systems of antiferromagnetically coupled spin dimers near magnetic-field induced quantum phase transitions. The quantum critical points in the...
Quantum percolation in two-dimensional antiferromagnets (2004)
Yu, Rong, Roscilde, Tommaso, Haas, Stephan
The interplay of geometric randomness and strong quantum fluctuations is an exciting topic in quantum many-body physics, leading to the emergence of novel quantum phases in strongly correlated...
High-Tc Cuprate Superconductivity in a Nutshell (2004)
Won, Hyekyung, Haas, Stephan, Parker, David, Maki, Kazumi
Since the discovery of high-Tc cuprate superconductivity in 1986 many new experimental techniques and theoretical concepts have been developed. In particular it was shown that the BCS theory of...
Perspectives on Nodal Superconductors (2004)
Maki, Kazumi, Haas, Stephan, Parker, David, Won, Hyekyung
In the last few years the gap symmetries of many new superconductors,including Sr$_2$RuO$_4$, CeCoIn$_5$, $\kappa$-(ET)$_{2}$Cu(NCS)$_{2}$, YNi$_{2}$B$_{2}$C and PrOs$_{4}$Sb$_{12}$, have been...
Anisotropic superconductivity in PrOs4Sb12 (2004)
Parker, David, Maki, Kazumi, Haas, Stephan
Recently the superconducting gap functions of the skutterudite PrOs$_4$Sb$_{12}$ have been proposed [K. Maki et al, Europhys. Lett. {\bf 68}, 720 (2004)]. The superconductivity is spin-triplet and...
Triplet superconductivity in the skutterudite PrOs_4Sb_12 (2004)
Maki, Kazumi, Haas, Stephan, Parker, David, Won, Hyekyung, Izawa, K., Matsuda, Y.
There is mounting evidence for triplet superconductivity in the recently discovered skutterudite compound PrOs_4Sb_12. In this work, we propose nodal order parameters for the A- and B-phases of this...
Studying quantum spin systems through entanglement estimators (2004)
Roscilde, Tommaso, Verrucchi, Paola, Fubini, Andrea, Haas, Stephan, Tognetti, Valerio
We study the field dependence of the entanglement of formation in anisotropic S=1/2 antiferromagnetic chains displaying a T=0 field-driven quantum phase transition. The analysis is carried out via...
Anisotropy-induced ordering in the quantum J1-J2 antiferromagnet (2004)
Roscilde, Tommaso, Feiguin, Adrian, Chernyshev, Alexander L., Liu, Shiu, Haas, Stephan
We study the effect of spin anisotropies on a frustrated quantum antiferromagnet using the J_1-J_2^{XXZ} model on the square lattice. The T=0 and finite-T phase diagrams of this model are obtained...
Adaptive Design of Excitonic Absorption in Broken-Symmetry Quantum Wells (2004)
Thalken, Jason, Li, Weifei, Haas, Stephan, Levi, A. F. J.
Adaptive quantum design is used to identify broken-symmetry quantum well potential profiles with optical response properties superior to previous ad-hoc solutions. This technique performs an unbiased...
Anatomy of Gossamer Superconductivity (2003)
Haas, Stephan, Maki, Kazumi, Dahm, Thomas, Thalmeier, Peter
There are many systems in which two order parameters compete with each other. Of particular interest are systems in which these order parameters are both unconventional. In this contribution, we...
Adaptive quantum design of atomic clusters (2003)
Thalken, Jason, Chen, Yu, Levi, A. F. J., Haas, Stephan
Adaptive quantum design identifies the best broken-symmetry configurations of atoms and molecules that enable a desired target function response. In this work, numerical optimization is used to...
Aperiodic nano-photonic design (2003)
Gheorma, Ioan L., Haas, Stephan, Levi, A. F. J.
The photon scattering properties of aperiodic nano-scale dielectric structures can be tailored to closely match a desired response by using adaptive algorithms for device design. We show that broken...
Quasiparticle spectrum of the hybrid s+g-wave superconductors YNi_2B_2C and LuNi_2B_2C (2003)
Maki, Kazumi, Won, Hyekyung, Haas, Stephan
Recent experiments on single crystals of YNi$_2$B$_2$C have revealed the presence of point nodes in the superconducting energy gap Delta(k} at k = (1,0,0), (0,1,0), (-1,0,0), and (0,-1,0). In this...
Universal scaling at field-induced magnetic phase transitions (2003)
Nohadani, Omid, Wessel, Stefan, Normand, Bruce, Haas, Stephan
We study field-induced magnetic order in cubic lattices of dimers with antiferromagnetic Heisenberg interactions. The thermal critical exponents at the quantum phase transition from a spin liquid to...
Possible Fulde-Ferrell-Larkin-Ovchinnikov State in CeCoIn_5 (2003)
Won, Hyekyung, Maki, Kazumi, Haas, Stephan, Oeschler, Niels, Weickert, Franziska, Gegenwart, Philipp
Angular dependent magnetothermal conductivity experiments on CeCoIn_5 indicate that this compound is a d-wave superconductor. In this study, the low-temperature behavior of the upper critical field...
Adaptive design of nano-scale dielectric structures for photonics (2003)
Chen, Yu, Yu, Rong, Li, Weifei, Nohadani, Omid, Haas, Stephan, Levi, A. F. J.
Using adaptive algorithms, the design of nano-scale dielectric structures for photonic applications is explored. Widths of dielectric layers in a linear array are adjusted to match target responses...
Theory of c-axis Josephson tunneling in d-wave superconductors (2003)
The temperature and angular dependence of the c-axis Josephson current and the superfluid density in layered d-wave superconductors are studied within the framework of an extended Ambegaokar-Baratoff...
Quantum Antiferromagnetism in Quasicrystals (2002)
Wessel, Stefan, Jagannathan, Anuradha, Haas, Stephan
The antiferromagnetic Heisenberg model is studied on a two-dimensional bipartite quasiperiodic lattice. The distribution of local staggered magnetic moments is determined on finite square...
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Redistribution of Spectral Weight in Spin-1/2-Doped Haldane Chains (2001)
We study the evolution of the dynamical spin structure factor in a spin-1 antiferromagnetic Heisenberg chain which is randomly doped with spin-1/2 moments. Using stochastic series expansion Quantum...
Field-Induced Magnetic Order in Quantum Spin Liquids (2001)
Wessel, Stefan, Olshanii, Maxim, Haas, Stephan
We study magnetic field-induced three-dimensional ordering transitions in low-dimensional quantum spin liquids, such as weakly coupled, antiferromagnetic spin-1/2 Heisenberg dimers and ladders. Using...
Anisotropic s-wave superconductivity in MgB_2 (2001)
It has recently been observed that MgB_2 is a superconductor with a high transition temperature. Here we propose a model of anisotropic s-wave superconductivity which consistently describes the...
Temperature dependence of impurity bound states in d-wave superconductors (2000)
We study the evolution with temperature of quasiparticle bound states around non-magnetic impurities in d-wave superconductors. The associated local density of states has a fourfold symmetry which...
Impurity Bound States and Symmetry of the Superconducting Order Parameter in Sr_2RuO_4 (2000)
Recent experiments on Sr_2RuO_4 have indicated the presence of linear nodes in the superconducting order parameter. Among the possible spin triplet states, 2D p-wave superconductivity with E_u...
Dynamical Properties of Spin-Orbital Chains in a Magnetic Field (2000)
The excitation spectrum of the one-dimensional spin-orbital model in a magnetic field is studied, using a recently developed dynamical density matrix renormalization group technique. The method is...
Quasi-Particle Bound States around Impurities in d-wave Superconductors (2000)
Zn and Ni impurities in the hole-doped high-temperature superconductors are known to have strong effects on thermodynamic and transport properties. A recent scanning tunneling microscope study of...
Paramagnetic Reentrance Effect in NS Proximity Cylinders (2000)
A scenario for the unusual paramagnetic reentrance behavior at ultra-low temperatures in Nb-Ag, Nb-Au, and Nb-Cu cylinders is presented. For the diamagnetic response down to temperatures of the order...
Excitation Spectra and Thermodynamic Response of Segmented Heisenberg Spin Chains (2000)
The spectral and thermodynamic response of segmented quantum spin chains is analyzed using a combination of numerical techniques and finite-size scaling arguments. Various distributions of segment...
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Three-Dimensional Ordering in Weakly Coupled Antiferromagnetic Ladders and Chains (1999)
A theoretical description is presented for low-temperature magnetic-field induced three-dimensional (3D) ordering transitions in strongly anisotropic quantum antiferromagnets, consisting of weakly...
Excitation Spectra of Structurally Dimerized and Spin-Peierls Chains in a Magnetic Field (1999)
The dynamical spin structure factor and the Raman response are calculated for structurally dimerized and spin-Peierls chains in a magnetic field, using exact diagonalization techniques. In both cases...
Magnetic Field Induced Ordering in Quasi-One-Dimensional Quantum Magnets (1999)
Three-dimensional magnetic ordering transitions are studied theoretically in strongly anisotropic quantum magnets. An external magnetic field can drive quasi-one-dimensional subsystems with a spin...
Phase diagram of three-leg ladders at strong coupling along the rungs (1999)
Kagan, Maxim Yu., Haas, Stephan, Rice, T. M.
A phase diagram of the t-J three-leg ladder as a function of hole dopping is derived in the limit where the coupling parameters along the rungs, $t_{\perp}$ and $J_{\perp}$, are taken to be much...
From the Hubbard to the SO(5) Ladder: A Numerical Study (1998)
Duffy, Daniel, Haas, Stephan, Kim, Eugene
The Hubbard Hamiltonian on a two-leg ladder is studied numerically using quantum Monte Carlo and Exact Diagonalization techniques. A rung interaction, $V$, is turned on such that the resulting model...
Generalization of the Luttinger Theorem for Fermionic Ladder Systems (1998)
Gagliardini, Patrick, Haas, Stephan, Rice, T. M.
We apply a generalized version of the Lieb-Schultz-Mattis Theorem to fermionic ladder systems to show the existence of a low-lying excited state (except for some special fillings). This can be...
Spectral Analysis of Correlated One-Dimensional Systems with Impurities (1997)
An averaging procedure is proposed to account for spectral features of correlated one-dimensional systems in the presence of non-magnetic impurities. The dynamical spin structure factor for a...
Lightly Doped t-J Three-Leg Ladders - an Analog for the Underdoped Cuprates (1997)
Rice, T. M., Haas, Stephan, Sigrist, Manfred, Zhang, Fu-Chun
The three-leg ladder has one odd-parity and two even-parity channels. At low doping these behave quite differently. Numerical calculations for a t-J model show that the initial phase upon hole doping...
Extended Gapless Regions in Disordered d_{x^2-y^2}-Wave Superconductors (1997)
Haas, Stephan, Balatsky, A. V., Sigrist, Manfred, Rice, T. M.
A generalization of the Abrikosov-Gorkov equations for non-magnetic impurities in unconventional superconductors is proposed, including higher harmonics in the expansion of the momentum dependent gap...
Duffy, Daniel, Nazarenko, Alexander, Haas, Stephan, Moreo, Adriana, Riera, Jose, Dagotto, Elbio
Quantum Monte Carlo (QMC) and Maximum Entropy (ME) techniques are used to study the spectral function $A({\bf p},\omega)$ of the one band Hubbard model in strong coupling including a...
Spectral Functions of One-dimensional Models of Correlated Electrons (1996)
Favand, Julien, Haas, Stephan, Penc, Karlo, Mila, Frederic, Dagotto, Elbio
Using the Ogata-Shiba wave function, the spectral functions of the one-dimensional infinite U Hubbard model are calculated for various concentrations. It is shown that the ``shadow band'' feature due...
Spin and Charge Texture around In-Plane Charge Centers in the CuO_2 planes (1996)
Haas, Stephan, Zhang, Fu-Chun, Mila, Frederic, Rice, T. M.
Recent experiments on La_2Cu_{1-x}Li_xO_4 show that although the doped holes remain localized near the substitutional Li impurities, magnetic order is rapidly suppressed. An examination of the spin...
Frischmuth, Beat, Haas, Stephan, Sierra, German, Rice, T. M.
An effective low-energy description for multi-leg spin-1/2 Heisenberg ladders with an odd number of legs is proposed. Using a newly developed Monte Carlo loop algorithm and exact diagonalization...
Photoemission Spectra in t-J Ladders with Two Legs (1996)
Photoemission spectra for the isotropic two-leg t-J ladder are calculated at various hole-doping levels using exact diagonalization techniques. Low-energy sharp features caused by short-range...
Influence of Hole Doping on Antiferromagnetic Real-Space Approaches for the High-Tc Cuprates (1996)
Nazarenko, Alexander, Haas, Stephan, Riera, Jose, Moreo, Adriana, Dagotto, Elbio
Recently proposed scenarios for the cuprates make extensive use of a ``flat'' quasiparticle (q.p.) dispersion and short-range hole-hole interactions in real-space, both caused by antiferromagnetic...
Predictions for Neutron Scattering and Photoemission Experiments on CuGeO_3 (1995)
Applying numerical techniques to a model recently proposed for the one dimensional spin-Peierls compound CuGeO_3, we calculate dynamical properties that can be directly compared with inelastic...
Nori, Franco, Merlin, Roberto, Haas, Stephan, Sandvik, Anders, Dagotto, Elbio
We calculate the Raman spectrum of the two-dimensional (2D) spin-1/2 Heisenberg antiferromagnet by exact diagonalization and quantum Monte Carlo techniques on clusters of up to 144 sites and, on a...
Shadow Bands in the Cuprates (1994)
Haas, Stephan, Moreo, Adriana, Dagotto, Elbio
A consequence of strong antiferromagnetic correlations in models of high-Tc cuprates is the appearance in photoemission (PES) calculations of considerable more weight above the Fermi momentum ${\rm...
On the Liaison Between Superconductivity and Phase Separation (1994)
Haas, Stephan, Dagotto, Elbio, Nazarenko, Alexander, Riera, Jose
Models of strongly correlated electrons that tend to phase separate are studied including a long-range 1/r repulsive interaction. It is observed that charge-density-wave states become stable as the...
Random Exchange Disorder in the Spin-1/2 XXZ Chain (1993)
Haas, Stephan, Riera, Jose, Dagotto, Elbio
The one-dimensional XXZ model is studied in the presence of disorder in the Heisenberg Exchange Integral. Recent predictions obtained from renormalization group calculations are investigated...
Freiburg (Breisgau), Univ., Med. Fak., Diss., 1976. (Nicht f. d. Austausch.).