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Effect of quenched disorder on a quantum spin liquid state of triangular-lattice antiferromagnet 1T-TaS$_2$ | H. Murayama
; Y. Sato
; T. Taniguchi
; R. Kurihara
; X. Z. Xing
; W. Huang
; S. Kasahara
; Y. Kasahara
; I. Kimchi
; M. Yoshida
; Y. Iwasa
; Y. Mizukami
; T. Shibauchi
; M. Konczykowski
; Y. Matsuda
; | Date: |
2 Sep 2019 | Abstract: | A quantum spin liquid (QSL) is an exotic state of matter characterized by
quantum entanglement and the absence of any broken symmetry. A long-standing
open problem, which is a key for fundamental understanding the mysterious QSL
states, is how the quantum fluctuations respond to randomness due to quenched
disorder. Transition metal dichalcogenide 1T-TaS$_2$ is a candidate material
that hosts a QSL ground state with spin-1/2 on the two-dimensional perfect
triangular lattice. Here, we performed systematic studies of low-temperature
heat capacity and thermal conductivity on pure, Se-substituted and electron
irradiated crystals of 1T-TaS$_2$. In pure 1T-TaS$_2$, the linear temperature
term of the heat capacity $gamma T$ and the finite residual linear term of the
thermal conductivity in the zero-temperature limit
$kappa_{0}/Tequivkappa/T(T
ightarrow0)$ are clearly resolved, consistent
with the presence of gapless spinons with a Fermi surface. Moreover, while the
strong magnetic field slightly enhances $kappa_0/T$, it strongly suppresses
$gamma$. These unusual contrasting responses to magnetic field imply the
coexistence of two types of gapless excitations with itinerant and localized
characters. Introduction of additional weak random exchange disorder in
1T-Ta(S$_{1-x}$Se$_x$)$_2$ leads to vanishing of $kappa_0/T$, indicating that
the itinerant gapless excitations are sensitive to the disorder. On the other
hand, in both pure and Se-substituted systems, the magnetic contribution of the
heat capacity obeys a universal scaling relation, which is consistent with a
theory that assumes the presence of localized orphan spins forming random
singlets. Electron irradiation in pure 1T-TaS$_2$ largely enhances $gamma$ and
changes the scaling function dramatically, suggesting a possible new state of
spin liquid. | Source: | arXiv, 1909.0583 | Services: | Forum | Review | PDF | Favorites |
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