skip to main content

Title: Ground-state phase diagram of the t-t-J model

We report results of large-scale ground-state density matrix renormalization group (DMRG) calculations on t-t-J cylinders with circumferences 6 and 8. We determine a rough phase diagram that appears to approximate the two-dimensional (2D) system. While for many properties, positive and negativetvalues (t/t=±0.2) appear to correspond to electron- and hole-doped cuprate systems, respectively, the behavior of superconductivity itself shows an inconsistency between the model and the materials. Thet<0(hole-doped) region shows antiferromagnetism limited to very low doping, stripes more generally, and the familiar Fermi surface of the hole-doped cuprates. However, we findt<0strongly suppresses superconductivity. Thet>0(electron-doped) region shows the expected circular Fermi pocket of holes around the(π,π)point and a broad low-doped region of coexisting antiferromagnetism and d-wave pairing with a triplet p component at wavevector(π,π)induced by the antiferromagnetism and d-wave pairing. The pairing for the electron low-doped system witht>0is strong and unambiguous in the DMRG simulations. At larger doping another broad region with stripes in addition to weaker d-wave pairing and striped p-wave pairing appears. In a small doping region nearx=0.08fort0.2, we find an unconventional type of stripe involving unpaired holes located predominantly on chains spaced three lattice spacings apart. The undoped more » two-leg ladder regions in between mimic the short-ranged spin correlations seen in two-leg Heisenberg ladders.

« less
; ;
Award ID(s):
Publication Date:
Journal Name:
Proceedings of the National Academy of Sciences
Page Range or eLocation-ID:
Article No. e2109978118
Proceedings of the National Academy of Sciences
Sponsoring Org:
National Science Foundation
More Like this
  1. In the physics of condensed matter, quantum critical phenomena and unconventional superconductivity are two major themes. In electron-doped cuprates, the low critical field (HC2) allows one to study the putative quantum critical point (QCP) at low temperature and to understand its connection to the long-standing problem of the origin of the high-TCsuperconductivity. Here we present measurements of the low-temperature normal-state thermopower (S) of the electron-doped cuprate superconductor La2−xCexCuO4(LCCO) fromx= 0.11–0.19. We observe quantum criticalS/Tversusln(1/T)behavior over an unexpectedly wide doping rangex= 0.15–0.17 above the QCP (x= 0.14), with a slope that scales monotonically with the superconducting transition temperature (TCwith H = 0). The presence of quantum criticality over a wide doping range provides a window on the criticality. The thermopower behavior also suggests that the critical fluctuations are linked withTC. Above the superconductivity dome, atx= 0.19, a conventional Fermi-liquidSTbehavior is found forT40 K.

  2. We present exact results that give insight into how interactions lead to transport and superconductivity in a flat band where the electrons have no kinetic energy. We obtain bounds for the optical spectral weight for flat-band superconductors that lead to upper bounds for the superfluid stiffness and the two-dimensional (2D)Tc. We focus on on-site attraction|U|on the Lieb lattice with trivial flat bands and on the π-flux model with topological flat bands. For trivial flat bands, the low-energy optical spectral weightD̃lowñ|U|Ω/2withñ=minn,2n, where n is the flat-band density and Ω is the Marzari–Vanderbilt spread of the Wannier functions (WFs). We also obtain a lower bound involving the quantum metric. For topological flat bands, with an obstruction to localized WFs respecting all symmetries, we again obtain an upper bound forD̃lowlinear in|U|. We discuss the insights obtained from our bounds by comparing them with mean-field and quantum Monte Carlo results.

  3. The explicit breaking of the axial symmetry by quantum fluctuations gives rise to the so-called axial anomaly. This phenomenon is solely responsible for the decay of the neutral pion π0into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of theπ0 γγprocess. The differential cross sections for π0photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yieldingΓ(π0 γγ)=7.798±0.056(stat.)±0.109(syst.) eV, where stat. denotes the statistical uncertainty and syst. the systematic uncertainty. We combined the results of this and an earlier experiment to generate a weighted average ofΓ(π0 γγ)=7.802±0.052(stat.)±0.105(syst.) eV. Our final result has a total uncertainty of 1.50% and confirms the prediction based on the chiral anomaly in quantum chromodynamics.

  4. Abstract

    We develop a Newtonian model of a deep tidal disruption event (TDE), for which the pericenter distance of the star,rp, is well within the tidal radius of the black hole,rt, i.e., whenβrt/rp≫ 1. We find that shocks form forβ≳ 3, but they are weak (with Mach numbers ∼1) for allβ, and that they reach the center of the star prior to the time of maximum adiabatic compression forβ≳ 10. The maximum density and temperature reached during the TDE follow much shallower relations withβthan the previously predictedρmaxβ3andTmaxβ2scalings. Belowβ≃ 10, this shallower dependence occurs because the pressure gradient is dynamically significant before the pressure is comparable to the ram pressure of the free-falling gas, while aboveβ≃ 10, we find that shocks prematurely halt the compression and yield the scalingsρmaxβ1.62andTmaxβ1.12. We find excellent agreement between our results and high-resolution simulations. Our results demonstrate that, in the Newtonian limit, the compression experienced by the star is completely independent of the mass of the black hole. We discuss our results in the context of existing (affine) models, polytropic versus non-polytropic stars, and general relativistic effects, which become important when the pericenter ofmore »the star nears the direct capture radius, atβ∼ 12.5 (2.7) for a solar-like star disrupted by a 106M(107M) supermassive black hole.

    « less
  5. We use neutron scattering to show that ferromagnetism and antiferromagnetism coexist in the low T state of the pyrochlore quantum magnetYb2Ti2O7. While magnetic Bragg peaks evidence long-range static ferromagnetic order, inelastic scattering shows that short-range correlated antiferromagnetism is also present. Small-angle neutron scattering provides direct evidence for mesoscale magnetic structure that we associate with metastable antiferromagnetism. Classical Monte Carlo simulations based on exchange interactions inferred from111-oriented high-field spin wave measurements confirm that antiferromagnetism is metastable within the otherwise ferromagnetic ground state. The apparent lack of coherent spin wave excitations and strong sensitivity to quenched disorder characterizingYb2Ti2O7is a consequence of this multiphase magnetism.