arXiv subjects

Brian Moritz

Publications and source records attributed to Brian Moritz.

83 records · Page 5Linked to original sources

arXiv2016

Numerical evidence of fluctuating stripes in the normal state of high-Tc cuprate superconductors

Upon doping, Mott insulators often exhibit symmetry breaking where charge carriers and their spins organize into patterns known as stripes. For high-Tc superconducting cuprates, stripes are widely suspected to exist in a fluctuating form. Here, we use numerically exact determinant quantum Monte Carlo calculations to demonstrate dynamical stripe correlations in the three-band Hubbard model, which represents the local electronic structure of the Cu-O plane. Our results, which are robust to varying parameters, cluster size, and boundary condition, strongly support the interpretation of a variety of experimental observations in terms of the physics of fluctuating stripes, including the hourglass magnetic dispersion and the Yamada plot of incommensurability vs. doping. These findings provide a novel perspective on the intertwined orders emerging from the cuprates' normal state.

cond-mat.str-el↗

arXiv2016

All-Optical Materials Design of Chiral Edge Modes in Transition-Metal Dichalcogenides

Manipulating materials properties far from equilibrium recently garnered significant attention, with experimental emphasis on transient melting, enhancement, or induction of electronic order. A more tantalizing aspect of the matter-light interaction regards the possibility to access dynamical steady states with distinct non-equilibrium phase transitions to affect electronic transport. Here, we show that the interplay of crystal symmetry and optical pumping of monolayer transition-metal dichalcogenides (TMDCs) provides a novel avenue to engineer topologically-protected chiral edge modes. In stark contrast to graphene and previously-discussed toy models, the underlying generic mechanism relies on the intrinsic three-band nature of TMDCs near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit a transition from one to two chiral edge modes upon sweeping from red to blue detuning. We develop a strategy to understand non-equilibrium Floquet-Bloch bands and topological transitions directly from ab initio calculations, and illustrate for the example of WS$_2$ that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.

cond-mat.mtrl-sci↗

arXiv2016

Using Nonequilibrium Dynamics to Probe Competing Orders in a Mott-Peierls System

Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. Here we examine one aspect, the nonequilibrium dynamics of a photoexcited Mott-Peierls system, using an effective Peierls-Hubbard model and exact diagonalization. Near a transition where spin and charge become strongly intertwined, we observe anti-phase dynamics and a coupling-strength-dependent suppression or enhancement in the static structure factors. The renormalized bosonic excitations coupled to a particular photoexcited electron can be extracted, which provides an approach for characterizing the underlying bosonic modes. The results from this analysis for different electronic momenta show an uneven softening due to a stronger coupling near $k_F$. This behavior reflects the strong link between the fermionic momenta, the coupling vertices, and ultimately the bosonic susceptibilities when multiple phases compete for the ground state of the system.

cond-mat.str-el↗

arXiv2015

Using RIXS to uncover elementary charge and spin excitations in correlated materials

Despite significant progress in resonant inelastic x-ray scattering (RIXS) experiments on cuprates at the Cu L-edge, a theoretical understanding of the cross-section remains incomplete in terms of elementary excitations and the connection to both charge and spin structure factors. Here we use state-of-the-art, unbiased numerical calculations to study the low energy excitations probed by RIXS in undoped and doped Hubbard model relevant to the cuprates. The results highlight the importance of scattering geometry, in particular both the incident and scattered x-ray photon polarization, and demonstrate that on a qualitative level the RIXS spectral shape in the cross-polarized channel approximates that of the spin dynamical structure factor. However, in the parallel-polarized channel the complexity of the RIXS process beyond a simple two-particle response complicates the analysis, and demonstrates that approximations and expansions which attempt to relate RIXS to less complex correlation functions can not reproduce the full diversity of RIXS spectral features.

cond-mat.str-el↗

arXiv2015

Origin of Strong Dispersion in Hubbard Insulators

Using cluster perturbation theory, we explain the origin of the strongly dispersive feature found at high binding energy in the spectral function of the Hubbard model. By comparing the Hubbard and $t\small{-}J\small{-} 3s$ model spectra, we show that this dispersion does not originate from either coupling to spin fluctuations ($\propto\! J$) or the free hopping ($\propto\! t$). Instead, it should be attributed to a long-range, correlated hopping $\propto\! t^2/U$, which allows an effectively free motion of the hole within the same antiferromagnetic sublattice. This origin explains both the formation of the high energy anomaly in the single-particle spectrum and the sensitivity of the high binding energy dispersion to the next-nearest-neighbor hopping $t^\prime$.

cond-mat.str-el↗

arXiv2014

Direct spectroscopic evidence for phase competition between the pseudogap and superconductivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$

In the high-temperature ($T_{c}$) cuprate superconductors, increasing evidence suggests that the pseudogap, existing below the pseudogap temperature $T$*, has a distinct broken electronic symmetry from that of superconductivity. Particularly, recent scattering experiments on the underdoped cuprates have suggested that a charge ordering competes with superconductivity. However, no direct link of this physics and the important low-energy excitations has been identified. Here we report an antagonistic singularity at $T_{c}$ in the spectral weight of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ as a compelling evidence for phase competition, which persists up to a high hole concentration $p$ ~ 0.22. Comparison with a theoretical calculation confirms that the singularity is a signature of competition between the order parameters for the pseudogap and superconductivity. The observation of the spectroscopic singularity at finite temperatures over a wide doping range provides new insights into the nature of the competitive interplay between the two intertwined phases and the complex phase diagram near the pseudogap critical point.

cond-mat.supr-con↗

arXiv2014

Real-Space Visualization of Remnant Mott Gap and Magnon Excitations

We demonstrate the ability to visualize real-space dynamics of charge gap and magnon excitations in the Mott phase of the single-band Hubbard model and the remnants of these excitations with hole or electron doping. At short times, the character of magnetic and charge excitations is maintained even for large doping away from the Mott and antiferromagnetic phases. Doping influences both the real-space patterns and long timescales of these excitations with a clear carrier asymmetry attributable to particle-hole symmetry breaking in the underlying model. Further, a rapidly-oscillating charge density wave-like pattern weakens, but persists as a visible demonstration of a sub-leading instability at half-filling which remains upon doping. The results offer an approach to analyzing the behavior of systems where momentum-space is either inaccessible or poorly defined.

cond-mat.str-el↗

arXiv2013

Examining electron-boson coupling using time-resolved spectroscopy

Nonequilibrium pump-probe time domain spectroscopies can become an important tool to disentangle degrees of freedom whose coupling leads to broad structures in the frequency domain. Here, using the time-resolved solution of a model photoexcited electron-phonon system we show that the relaxational dynamics are directly governed by the equilibrium self-energy so that the phonon frequency sets a window for "slow" versus "fast" recovery. The overall temporal structure of this relaxation spectroscopy allows for a reliable and quantitative extraction of the electron-phonon coupling strength without requiring an effective temperature model or making strong assumptions about the underlying bare electronic band dispersion.

cond-mat.other↗

arXiv2010

Nonlocal effects on magnetism in the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As

The magnetic properties of the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As are studied within the dynamical cluster approximation. We use the k-dot-p Hamiltonian to describe the electronic structure of GaAs with spin-orbit coupling and strain effects. We show that nonlocal effects are essential for explaining the experimentally observed transition temperature and saturation magnetization. We also demonstrate that the cluster anisotropy is very strong and induces rotational frustration and a cube-edge direction magnetic anisotropy at low temperature. With this, we explain the temperature-driven spin reorientation in this system.

cond-mat.str-el↗

arXiv2006

Suppression of superconductivity in the Hubbard model by buckling and breathing phonons

We study the effect of buckling and breathing phonons, relevant for cuprate superconductors, on the d-wave superconductivity in the two-dimensional Hubbard model by employing dynamical cluster Monte Carlo calculations. The interplay of electronic correlations and the electron-phonon interaction produces two competing effects, an enhancement of the effective d-wave pairing interaction, which favors d-wave superconductivity, and a strong renormalization of the single-particle propagator, which suppress superconductivity. Due to the later effect we find that buckling and breathing phonons suppress the superconductivity in the region of parameter space relevant for cuprate superconductors.

cond-mat.str-el↗

arXiv2006

Synergistic Polaron Formation in the Hubbard-Holstein Model at Small Doping

We study the effect of dynamical Holstein phonons on the physics of the Hubbard model at small doping using the dynamical cluster approximation on a $2\times2$ cluster. Non-local antiferromagnetic correlations are found to significantly enhance the electron-phonon coupling, resulting in polaron formation for moderate coupling strengths. At finite doping, the electron-phonon coupling is found to strongly enhance the non-local spin correlations, indicating a synergistic interplay between the electron-phonon coupling and antiferromagnetic correlations. Although it enhances the pairing interaction, the electron-phonon coupling is found to decrease the superconducting transition temperature, due to the reduction in the quasiparticle fraction.

cond-mat.str-el↗