Coexisting localized and itinerant gapless excitations in a quantum spin liquid candidate 1T-TaS $_2$ Coexisting localized and itinerant gapless excitations in a quantum spin liquid candidate 1T-TaS$_2$

H. Murayama, Yuki Sato, Xiangzhuo Xing +6 more

To reveal the nature of elementary excitations in a quantum spin liquid (QSL), we measured low temperature thermal conductivity and specific heat of 1T-TaS $_2$ , a QSL candidate material with frustrated triangular lattice of spin-1/2. The nonzero temperature linear specific heat coefficient $γ$ and the finite residual linear term of the thermal conductivity in the zero temperature limit $κ_0/T=κ/T(T\rightarrow 0)$ are clearly resolved. This demonstrates the presence of highly mobile gapless excitations, which is consistent with fractionalized spinon excitations that form a Fermi surface. Remarkably, an external magnetic field strongly suppresses $γ$ , whereas it enhances $κ_0/T$ . This unusual contrasting behavior in the field dependence of specific heat and thermal conductivity can be accounted for by the presence of two types of gapless excitations with itinerant and localized characters, as recently predicted theoretically (I. Kimchi et al., arXiv:1803.00013 (2018)). This unique feature of 1T-TaS $_2$ provides new insights into the influence of quenched disorder on the QSL.To reveal the nature of elementary excitations in a quantum spin liquid (QSL), we measured low temperature thermal conductivity and specific heat of 1T-TaS$_2$, a QSL candidate material with frustrated triangular lattice of spin-1/2. The nonzero temperature linear specific heat coefficient $γ$ and the finite residual linear term of the thermal conductivity in the zero temperature limit $κ_0/T=κ/T(T\rightarrow 0)$ are clearly resolved. This demonstrates the presence of highly mobile gapless excitations, which is consistent with fractionalized spinon excitations that form a Fermi surface. Remarkably, an external magnetic field strongly suppresses $γ$, whereas it enhances $κ_0/T$. This unusual contrasting behavior in the field dependence of specific heat and thermal conductivity can be accounted for by the presence of two types of gapless excitations with itinerant and localized characters, as recently predicted theoretically (I. Kimchi et al., arXiv:1803.00013 (2018)). This unique feature of 1T-TaS$_2$ provides new insights into the influence of quenched disorder on the QSL.

arXiv:1803.06100Mar 16, 201812 citations

Imaging spinons in a 2D gapless quantum spin liquid

Michael F. Crommie

Bulletin of the American Physical SocietyMar 2, 20200 citations

Dynamical dimer structure factor of the triangular $S=1/2$ Heisenberg antiferromagnetDynamical dimer structure factor of the triangular $S=1/2$ Heisenberg antiferromagnet

Markus Drescher, Laurens Vanderstraeten, Roderich Moessner +2 more

The dynamical dimer structure factor is an observable probing spin-singlet excitations of quantum magnets distinct from those commonly studied by the spin structure factor. We report the dimer response for the extended spin- $1/2$ antiferromagnetic Heisenberg model on the triangular lattice using large-scale GPU-accelerated matrix-product-state simulations. We investigate the ordered phases with $120^\circ$ coplanar, collinear stripe, and tetrahedral spin order, as well as candidate quantum spin-liquid (QSL) regimes, comprising an expected gapless $U(1)$ Dirac QSL and a chiral QSL at finite spin-scalar-chirality coupling. In the ordered phases, we find low-energy modes below the onset of the two-magnon continuum illustrating avoided quasiparticle decay. Within the candidate gapless QSL, we observe absolute dispersion minima at momenta of half the Brillouin zone corners, $X\equiv K/2$ , in agreement with field-theory predictions that singlet monopole excitations of the $U(1)$ Dirac spin liquid become gapless at these points. Thus, the high-resolution dynamical dimer response provides support for a $U(1)$ Dirac QSL with singlet monopole excitations.The dynamical dimer structure factor is an observable probing spin-singlet excitations of quantum magnets distinct from those commonly studied by the spin structure factor. We report the dimer response for the extended spin-$1/2$ antiferromagnetic Heisenberg model on the triangular lattice using large-scale GPU-accelerated matrix-product-state simulations. We investigate the ordered phases with $120^\circ$ coplanar, collinear stripe, and tetrahedral spin order, as well as candidate quantum spin-liquid (QSL) regimes, comprising an expected gapless $U(1)$ Dirac QSL and a chiral QSL at finite spin-scalar-chirality coupling. In the ordered phases, we find low-energy modes below the onset of the two-magnon continuum illustrating avoided quasiparticle decay. Within the candidate gapless QSL, we observe absolute dispersion minima at momenta of half the Brillouin zone corners, $X\equiv K/2$, in agreement with field-theory predictions that singlet monopole excitations of the $U(1)$ Dirac spin liquid become gapless at these points. Thus, the high-resolution dynamical dimer response provides support for a $U(1)$ Dirac QSL with singlet monopole excitations.

arXiv:2604.24868Apr 9, 20260 citations

Disorder in a two-dimensional quantum spin liquid

D. Hüvonen, Martin Må̊nsson, S. N. Gvasaliya +8 more

Bulletin of the American Physical SocietyFeb 28, 20120 citations

Dynamics of a Quantum Spin Liquid

Johannes Knolle

Springer thesesJan 1, 201640 citations

Gapless Spin Liquids on the Three-Dimensional Hyperkagome Lattice of Na4Ir3O8

Michael J. Lawler, Arun Paramekanti, Yong Baek Kim +1 more

Recent experiments indicate that Na4Ir3O8, a material in which s=1/2 Ir local moments live on a three-dimensional "hyperkagome" lattice of corner-sharing triangles, may have a quantum spin liquid ground state with gapless spin excitations. Using a combination of exact diagonalization, symmetry analysis of fermionic mean field ground states and Gutzwiller projected variational wave functions studies, we propose a quantum spin liquid with spinon Fermi surfaces as a favorable candidate for the ground state of the Heisenberg model on this lattice. We point out implications of this proposal for thermodynamic properties and discuss possible weak instabilities of the spinon Fermi surfaces.Recent experiments indicate that Na4Ir3O8, a material in which s=1/2 Ir local moments live on a three-dimensional "hyperkagome" lattice of corner-sharing triangles, may have a quantum spin liquid ground state with gapless spin excitations. Using a combination of exact diagonalization, symmetry analysis of fermionic mean field ground states and Gutzwiller projected variational wave functions studies, we propose a quantum spin liquid with spinon Fermi surfaces as a favorable candidate for the ground state of the Heisenberg model on this lattice. We point out implications of this proposal for thermodynamic properties and discuss possible weak instabilities of the spinon Fermi surfaces.

arXiv:0806.4395Physical Review LettersNov 3, 2008132 citations

Coexisting localized and itinerant gapless excitations in a quantum spin liquid candidate 1T-TaS

_2

To reveal the nature of elementary excitations in a quantum spin liquid (QSL), we measured low temperature thermal conductivity and specific heat of 1T-TaS

_2

, a QSL candidate material with frustrated triangular lattice of spin-1/2. The nonzero temperature linear specific heat coefficient

γ

and the finite residual linear term of the thermal conductivity in the zero temperature limit

κ_0/T=κ/T(T\rightarrow 0)

are clearly resolved. This demonstrates the presence of highly mobile gapless excitations, which is consistent with fractionalized spinon excitations that form a Fermi surface. Remarkably, an external magnetic field strongly suppresses

γ

, whereas it enhances

κ_0/T

. This unusual contrasting behavior in the field dependence of specific heat and thermal conductivity can be accounted for by the presence of two types of gapless excitations with itinerant and localized characters, as recently predicted theoretically (I. Kimchi et al., arXiv:1803.00013 (2018)). This unique feature of 1T-TaS

_2

provides new insights into the influence of quenched disorder on the QSL.

Dynamical dimer structure factor of the triangular

S=1/2

Heisenberg antiferromagnet

1/2

antiferromagnetic Heisenberg model on the triangular lattice using large-scale GPU-accelerated matrix-product-state simulations. We investigate the ordered phases with

120^\circ

coplanar, collinear stripe, and tetrahedral spin order, as well as candidate quantum spin-liquid (QSL) regimes, comprising an expected gapless

U(1)

Dirac QSL and a chiral QSL at finite spin-scalar-chirality coupling. In the ordered phases, we find low-energy modes below the onset of the two-magnon continuum illustrating avoided quasiparticle decay. Within the candidate gapless QSL, we observe absolute dispersion minima at momenta of half the Brillouin zone corners,

X\equiv K/2

, in agreement with field-theory predictions that singlet monopole excitations of the

U(1)

Dirac spin liquid become gapless at these points. Thus, the high-resolution dynamical dimer response provides support for a

U(1)

Dirac QSL with singlet monopole excitations.