Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSignatures of gapless fermionic spinons on a strip of the kagome Heisenberg antiferromagnet
62
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The search for exotic quantum spin liquid states in simple yet realistic spin models remains a central challenge in the field of frustrated quantum magnetism. Here we consider the canonical nearest-neighbor kagome Heisenberg antiferromagnet restricted to a quasi-1D strip consisting entirely of corner-sharing triangles. Using large-scale density matrix renormalization group calculations, we identify in this model an extended gapless quantum phase characterized by central charge $c=2$ and power-law decaying spin and bond-energy correlations which oscillate at tunably incommensurate wave vectors. We argue that this intriguing spin liquid phase can be understood as a marginal instability of a two-band spinon Fermi surface coupled to an emergent U(1) gauge field, an interpretation which we substantiate via bosonization analysis and Monte Carlo calculations on model Gutzwiller variational wave functions. Our results represent one of the first numerical demonstrations of emergent fermionic spinons in a simple SU(2) invariant nearest-neighbor Heisenberg model beyond the strictly 1D (Bethe chain) limit.
rate research
Read More
The $S$ = $frac{1}{2}$ kagome Heisenberg antiferromagnet (KHA) is a leading model hosting a quantum spin liquid (QSL), but the exact nature of its ground state remains a key issue under debate. In the previously well-studied candidate materials, magnetic defects always dominate the low-energy spectrum and hinder the detection of the intrinsic nature. We demonstrate that the new single crystal of YCu$_3$[OH(D)]$_{6.5}$Br$_{2.5}$ is a perfect KHA without evident magnetic defects ($ll$ 0.8%). Through fitting the magnetic susceptibilities of the orientated single crystals, we find the spin system with weak anisotropic interactions and with first-, second-, and third-neighbor couplings, $J_1$ $sim$ 56 K and $J_2$ $sim$ $J_3$ $sim$ 0.1$J_1$, belongs to the continuous family of fully frustrated KHAs. No conventional freezing is observed down to 0.36 K $sim$ 0.006$J_1$, and the raw specific heat exhibits a nearly quadratic temperature dependence below 1 K $sim$ 0.02$J_1$, well consistent with a gapless (spin gap $leq$ 0.025$J_1$) Dirac QSL.
The nature of the ground state of the spin $S=1/2$ Heisenberg antiferromagnet on the kagome lattice with breathing anisotropy (i.e., with different superexchange couplings $J_{vartriangle}$ and $J_{triangledown}$ within elementary up- and down-pointing triangles) is investigated within the framework of Gutzwiller projected fermionic wave functions and Monte Carlo methods. We analyze the stability of the U(1) Dirac spin liquid with respect to the presence of fermionic pairing that leads to a gapped $mathbb{Z}_{2}$ spin liquid. For several values of the ratio $J_{triangledown}/J_{vartriangle}$, the size scaling of the energy gain due to the pairing fields and the variational parameters are reported. Our results show that the energy gain of the gapped spin liquid with respect to the gapless state either vanishes for large enough system size or scales to zero in the thermodynamic limit. Similarly, the optimized pairing amplitudes (responsible for opening the spin gap) are shown to vanish in the thermodynamic limit. Our outcome is corroborated by the application of one and two Lanczos steps to the gapless and gapped wave functions, for which no energy gain of the gapped state is detected when improving the quality of the variational states. Finally, we discuss the competition with the simplex $mathbb{Z}_{2}$ resonating-valence-bond spin liquid, valence-bond crystal, and nematic states in the strongly anisotropic regime, i.e., $J_{triangledown} ll J_{vartriangle}$.
We develop a theory for the thermal Hall coefficient in a spin-$frac{1}{2}$ system on a strip of Kagome lattice, where a chiral spin-interaction term is present. To this end, we model the Kagome strip as a three-leg $XXZ$ spin-ladder, and use Bosonization to derive a low-energy theory for the spinons in this system. Introducing further a Dzyaloshinskii-Moriya interaction ($D$) and a tunable magnetic field ($B$), we identify three distinct $B$-dependent quantum phases: a valence-bond crystal (VBC), a metallic spin liquid (MSL) and a chiral spin liquid (CSL). In the presence of a temperature difference $Delta T$ between the top and the bottom edges of the strip, we evaluate the net heat current $J_h$ along the strip, and consequently the thermal Hall conductivity $kappa_{xy}$. We find that the VBC-MSL-CSL transitions are accompanied by a pronounced qualitative change in the behavior of $kappa_{xy}$ as a function of $B$. In particular, analogously to the quantum Hall effect, $kappa_{xy}$ in the CSL phase exhibits a quantized plateau centered around a commensurate value of the spinon filling factor $ u_spropto B/D$.
A preponderance of evidence suggests that the ground state of the nearest-neighbor $S = 1/2$ antiferromagnetic Heisenberg model on the kagome lattice is a gapless spin liquid. Many candidate materials for the realization of this model possess in addition a Dzyaloshinskii-Moriya (DM) interaction. We study this system by tensor-network methods and deduce that a weak but finite DM interaction is required to destabilize the gapless spin-liquid state. The critical magnitude, $D_c/J simeq 0.012(2)$, lies well below the DM strength proposed in the kagome material herbertsmithite, indicating a need to reassess the apparent spin-liquid behavior reported in this system.
In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimental studies [Hiroi et al.,2001]. It has been suggested that the magnetic properties of this material are described by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. We report on investigations of the Sp(N) symmetric generalisation of this model in the large N limit. We obtain a detailed description of the dependence of possible ground states on the anisotropy and on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with and without long range order and a decoupled chain phase emerges.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
