Topological Phase Transitions in States with Low and High Density of 2D Vortical Pairs Induced by Magnetic Field in Gapless Quantum Spin Liquid with Structural Disorder

Measurements of the magnetization temperature dependences of La0.15Sm0.85MnO3+δ in the temperature range 4.2 - 100 K revealed a threshold magnetization feature near the temperature Td 50 K, associated with the existence of a small pseudogap Δe in the electron spectrum, which is characteristic of a weak Mott dielectric. An increase in the strength H of the external magnetic field leads to suppression of the dielectric pseudogap Δe, an increase in the density of states of free charge/ spin carriers at EF, and transformation of the charge/spin density waves fragments. A quantization of the pairs spectrum of the low-energy magnetic excitations of a Z2 quantum spin liquid in the form of spinon-gauge field composite quasiparticles was found in the temperature range 4.2 - 12 K. Formation of a continuous spectrum of the quantum spin liquid excitations in the regime of “weak magnetic fields” Н = 100 Oe, 350 Oe, 1 kOe is explained within the framework of the Landau quantization models of the spectrum of composite quasiparticles with fractional values of the factor ν filling of three overlapping Landau zones.. In the regime of a “strong external magnetic field” H = 3.5 kOe, the new quantum oscillations of the temperature dependences of the magnetization of an incompressible spinon liquid were founded in the form of three narrow steps (plateaus) corresponding to the complete filling of non-overlapping Landau zones with integer values of the filling factor by spinons.

Download Full-text

Magnetic field-induced intermediate quantum spin liquid with a spinon Fermi surface

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1821406116 ◽

2019 ◽

Vol 116 (25) ◽

pp. 12199-12203 ◽

Cited By ~ 18

Author(s):

Niravkumar D. Patel ◽

Nandini Trivedi

Keyword(s):

Magnetic Field ◽

Fermi Surface ◽

Intermediate Phase ◽

Quantum Spin ◽

Spin Liquid ◽

Spin Correlations ◽

Density Matrix Renormalization ◽

Static Spin ◽

Kitaev Model ◽

Quantum Spin Liquid

The Kitaev model with an applied magnetic field in the H∥[111] direction shows two transitions: from a nonabelian gapped quantum spin liquid (QSL) to a gapless QSL at Hc1≃0.2K and a second transition at a higher field Hc2≃0.35K to a gapped partially polarized phase, where K is the strength of the Kitaev exchange interaction. We identify the intermediate phase to be a gapless U(1) QSL and determine the spin structure function S(k) and the Fermi surface ϵFS(k) of the gapless spinons using the density matrix renormalization group (DMRG) method for large honeycomb clusters. Further calculations of static spin-spin correlations, magnetization, spin susceptibility, and finite temperature-specific heat and entropy corroborate the gapped and gapless nature of the different field-dependent phases. In the intermediate phase, the spin-spin correlations decay as a power law with distance, indicative of a gapless phase.

Download Full-text

Two-dimensional electron crystal in magnetic field. Topological phase transitions and stability region.

Solid State Communications ◽

10.1016/0038-1098(80)90372-5 ◽

1980 ◽

Vol 36 (6) ◽

pp. 485-492 ◽

Cited By ~ 15

Author(s):

Yu.E. Lozovik ◽

S.M. Apenko ◽

A.V. Klyuchnik

Keyword(s):

Magnetic Field ◽

Phase Transitions ◽

Stability Region ◽

Topological Phase ◽

Two Dimensional ◽

Dimensional Electron ◽

Topological Phase Transitions ◽

Electron Crystal

Download Full-text

Topological phase transition of two-dimensional topological polaritons

International Journal of Modern Physics B ◽

10.1142/s0217979217500709 ◽

2017 ◽

Vol 31 (11) ◽

pp. 1750070

Author(s):

Zimeng Chi ◽

Xiaoyong Guo ◽

Zaijun Wang

Keyword(s):

Phase Transitions ◽

Energy Gap ◽

Tight Binding ◽

Quantum Spin ◽

Generic Model ◽

Topological Phase ◽

Two Dimensional ◽

Strongly Coupled ◽

Bulk Energy ◽

Topological Phase Transitions

Topological phase transitions of a two-dimensional topologically nontrivial polaritonic system are studied. A generic model of semiconductor excitons strongly coupled with tailored photonic modes is considered. We introduce a pseudospin operator, measuring the polariton polarization between photonic-like and excitonic-like. The associated pseudospin spectrum and pseudospin Chern numbers are calculated. It is shown that the pseudospin Chern number phase diagram exhibits certain features resembling the topological phase of quantum-spin-Hall-like. Moreover, a series of topological phase transitions may occur with the closing of the bulk energy gap or the pseudospin spectrum gap. In a tight-binding form, the edge-mode simulation is done numerically to confirm the analytically results.

Download Full-text

Short-ranged interaction effects on Z2 topological phase transitions: The perturbative mean-field method

International Journal of Modern Physics B ◽

10.1142/s0217979215300054 ◽

2015 ◽

Vol 29 (06) ◽

pp. 1530005 ◽

Cited By ~ 1

Author(s):

Hsin-Hua Lai ◽

Hsiang-Hsuan Hung

Keyword(s):

Phase Transitions ◽

Analytical Approach ◽

Mean Field ◽

Field Approximation ◽

Quantum Spin ◽

Mean Field Approximation ◽

Topological Phase ◽

Self Consistent ◽

The Mean ◽

Topological Phase Transitions

Time-reversal symmetric topological insulator (TI) is a novel state of matter that a bulk-insulating state carries dissipationless spin transport along the surfaces, embedded by the Z2 topological invariant. In the noninteracting limit, this exotic state has been intensively studied and explored with realistic systems, such as HgTe/(Hg, Cd)Te quantum wells. On the other hand, electronic correlation plays a significant role in many solid-state systems, which further influences topological properties and triggers topological phase transitions. Yet an interacting TI is still an elusive subject and most related analyses rely on the mean-field approximation and numerical simulations. Among the approaches, the mean-field approximation fails to predict the topological phase transition, in particular at intermediate interaction strength without spontaneously breaking symmetry. In this paper, we develop an analytical approach based on a combined perturbative and self-consistent mean-field treatment of interactions that is capable of capturing topological phase transitions beyond either method when used independently. As an illustration of the method, we study the effects of short-ranged interactions on the Z2 TI phase, also known as the quantum spin Hall (QSH) phase, in three generalized versions of the Kane–Mele (KM) model at half-filling on the honeycomb lattice. The results are in excellent agreement with quantum Monte Carlo (QMC) calculations on the same model and cannot be reproduced by either a perturbative treatment or a self-consistent mean-field treatment of the interactions. Our analytical approach helps to clarify how the symmetries of the one-body terms of the Hamiltonian determine whether interactions tend to stabilize or destabilize a topological phase. Moreover, our method should be applicable to a wide class of models where topological transitions due to interactions are in principle possible, but are not correctly predicted by either perturbative or self-consistent treatments.

Download Full-text

Identification of a Kitaev quantum spin liquid by magnetic field angle dependence

Nature Communications ◽

10.1038/s41467-021-27943-9 ◽

2022 ◽

Vol 13 (1) ◽

Author(s):

Kyusung Hwang ◽

Ara Go ◽

Ji Heon Seong ◽

Takasada Shibauchi ◽

Eun-Gook Moon

Keyword(s):

Magnetic Field ◽

Quantum Spin ◽

Majorana Fermion ◽

Spin Liquid ◽

Majorana Fermions ◽

Angle Dependence ◽

Topological Quantum ◽

Quantum Science ◽

Quantum Spin Liquid ◽

Critical Lines

AbstractQuantum spin liquids realize massive entanglement and fractional quasiparticles from localized spins, proposed as an avenue for quantum science and technology. In particular, topological quantum computations are suggested in the non-abelian phase of Kitaev quantum spin liquid with Majorana fermions, and detection of Majorana fermions is one of the most outstanding problems in modern condensed matter physics. Here, we propose a concrete way to identify the non-abelian Kitaev quantum spin liquid by magnetic field angle dependence. Topologically protected critical lines exist on a plane of magnetic field angles, and their shapes are determined by microscopic spin interactions. A chirality operator plays a key role in demonstrating microscopic dependences of the critical lines. We also show that the chirality operator can be used to evaluate topological properties of the non-abelian Kitaev quantum spin liquid without relying on Majorana fermion descriptions. Experimental criteria for the non-abelian spin liquid state are provided for future experiments.

Download Full-text