11 research outputs found
Higher Berry curvature from matrix product states
The higher Berry curvature was introduced by Kapustin and Spodyneiko as an
extension of the Berry curvature in quantum mechanical systems with finite
degrees of freedom to quantum many-body systems in finite spatial dimensions.
In this paper, we propose an alternative formulation of the higher Berry
curvature using translationally invariant matrix product states. They are the
ground states of a set of gapped Hamiltonians which are evolved adiabatically
through a discretized parameter space. Because matrix product states transform
under a projective representation, evaluating the Berry curvature on a closed
loop through parameter space is not sufficient to fix all the gauge degrees of
freedom. To obtain a gauge-invariant real quantity, the higher-dimensional
Berry curvature is evaluated on small tetrahedra in parameter space. Our
numerical calculations confirm that the higher Berry curvature varies
continuously throughout an adiabatic evolution and becomes quantized over a
closed 3-dimensional parameter space.Comment: Sec. V-B-2, numerical calculation for random J1 J2 adde
Stable Bosonic Topological Edge Modes in the Presence of Many-Body Interactions
Many magnetic materials are predicted to exhibit bosonic topological edge
modes in their excitation spectra, because of the nontrivial topology of their
magnon, triplon or other quasi-particle band structures. However, there is a
discrepancy between theory prediction and experimental observation, which
suggests some underlying mechanism that intrinsically suppresses the expected
experimental signatures, like the thermal Hall current. Many-body interactions
that are not accounted for in the non-interacting quasi-particle picture are
most often identified as the reason for the absence of the topological edge
modes. Here we report stable bosonic edge modes at the boundaries of a ladder
quantum paramagnet with gapped triplon excitations in the presence of the full
many-body interaction. For the first time, we use tensor network methods to
resolve topological edge modes in the time-dependent spin-spin correlations and
the dynamical structure factor, which is directly accessible experimentally. We
further show that these edge modes have anomalously long time coherence,
discuss the topological phase diagram of the model, demonstrate the
fractionalization of its low-lying excitations, and propose potential material
candidates
Discovery of Superconductivity and Electron-Phonon Drag in the Non-Centrosymmetric Semimetal LaRhGe
We present a comprehensive study of the non-centrosymmetric semimetal
LaRhGe. Our transport measurements reveal evidence for electron-hole
compensation at low temperatures, resulting in a large magnetoresistance of
3000% at 1.8 K and 14 T. The carrier concentration is on the order of
, higher than typical semimetals. We predict theoretically
the existence of Weyl nodal lines that are protected
by the tetragonal space group. We discover superconductivity for the first time
in this compound with a of 0.39(1) K and of
2.1(1) mT, with evidence from specific heat and transverse-field muon spin
relaxation (). LaRhGe is a weakly-coupled type-I
superconductor, and we find no evidence for time-reversal symmetry breaking in
our zero-field . We study the electrical transport in the normal
state and find an unusual dependence at low temperature while
Seebeck coefficient and thermal conductivity measurements reveal a peak in the
same temperature range. We conclude that the transport properties of LaRhGe
in its normal state are strongly influenced by electron-phonon interactions.
Furthermore, we examine the temperature dependent Raman spectra of LaRhGe
and find that the lifetime of the lowest energy phonon is dominated by
phonon-electron scattering instead of anharmonic decay
Anisotropic superconductivity in the spin-vortex antiferromagnetic superconductor CaK(Fe0.95Ni0.05)(4)As-4
High critical temperature superconductivity often occurs in systems where an antiferromagnetic order is brought near T=0 K by slightly modifying pressure or doping. CaKFe4As4 is a superconducting, stoichiometric iron-pnictide compound showing optimal superconducting critical temperature with Tc as large as 35 K. Doping with Ni induces a decrease in Tc and the onset of spin-vortex crystal (SVC) antiferromagnetic order, which consists of spins pointing inwards to or outwards from alternating As sites on the diagonals of the in-plane square Fe lattice. Here we study the band structure of CaK(Fe0.95Ni0.05)4As4 (Tc=10 K, TSVC=50 K) using quasiparticle interference with a scanning tunneling microscope and show how the SVC modifies the band structure and induces a fourfold superconducting gap anisotropy
Quantum error mitigation in quantum annealing
Quantum Error Mitigation (QEM) presents a promising near-term approach to
reduce error when estimating expectation values in quantum computing. Here, we
introduce QEM techniques tailored for quantum annealing, using Zero-Noise
Extrapolation (ZNE). We implement ZNE through zero-temperature extrapolation as
well as energy-time rescaling. We conduct experimental investigations into the
quantum critical dynamics of a transverse-field Ising spin chain, demonstrating
the successful mitigation of thermal noise through both of these techniques.
Moreover, we show that energy-time rescaling effectively mitigates control
errors in the coherent regime where the effect of thermal noise is minimal. Our
ZNE results agree with exact calculations of the coherent evolution over a
range of annealing times that exceeds the coherent annealing range by almost an
order of magnitude.Comment: 10 pages, 5 figure
Towards a topological quantum chemistry description of correlated systems: The case of the Hubbard diamond chain
The recently introduced topological quantum chemistry (TQC) framework has provided a description of universal topological properties of all possible band insulators in all space groups based on crystalline unitary symmetries and time reversal. While this formalism filled the gap between the mathematical classification and the practical diagnosis of topological materials, an obvious limitation is that it only applies to weakly interacting systems, which can be described within band theory. It is an open question to which extent this formalism can be generalized to correlated systems that can exhibit symmetry-protected topological phases which are not adiabatically connected to any band insulator. In this work, we address the many facets of this question by considering the specific example of an extended version of a Hubbard diamond chain. This model features a Mott insulator, a trivial insulating phase, and an obstructed atomic limit phase. Here we first discuss the nature of the Mott insulator and determine the phase diagram and topology of the interacting model with infinite density matrix renormalization group calculations, variational Monte Carlo simulations, and with many-body topological invariants. We then proceed by considering a generalization of the TQC formalism to Green's functions combined with the concept of a topological Hamiltonian to identify the topological nature of the phases. Here we use cluster perturbation theory to calculate the Green's functions. The results are benchmarked with the above-determined phase diagram, and we discuss the applicability and limitations of the approach and its possible extensions in the diagnosis of topological phases in materials, in contrast to the use of many-body topological invariants