Low temperature thermodynamics of $S_{\mathrm{eff}}=1/2$ triangular lattice quantum spin liquid candidate TlYbS$_2$

Bishnu P. Belbase; Arjun Unnikrishnan; Piyush Chhallare; Mohan B. Neupane; Eun Sang Choi; Sebastian Erdmann; Muhammad U. Akbar; Mamoun Hemmida; H. -A. Krug von Nidda; Philipp Gegenwart; Arnab Banerjee

arXiv · 2609.11881

Low temperature thermodynamics of $S_{\mathrm{eff}}=1/2$ triangular lattice quantum spin liquid candidate TlYbS$_2$

Bishnu P. Belbase·Arjun Unnikrishnan·Piyush Chhallare·Mohan B. Neupane·Eun Sang Choi·Sebastian Erdmann·Muhammad U. Akbar·Mamoun Hemmida·H. -A. Krug von Nidda·Philipp Gegenwart·Arnab Banerjee

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Abstract

Geometrically frustrated triangular-lattice antiferromagnets exhibit a delicate competition between magnetic order and quantum spin liquid (QSL) behavior, with the Yb-based delafossite family $A$Yb$X_2$ providing a structurally clean platform for exploring this physics. Here, we report a comprehensive study of single-crystal TlYbS$_2$ using DC magnetization, AC susceptibility, electron spin resonance (ESR), and specific heat measurements extending from room temperature to the millikelvin regime. Single-crystal X-ray diffraction confirms a trigonal $R\bar{3}m$ structure comprising well-separated triangular layers of Yb$^{3+}$ ions with no detectable site disorder. At zero field, a weak thermodynamic anomaly is observed near $530$ mK, which may indicate the onset of a weakly ordered state similar to that reported in KYbSe$_2$. Below $300$ mK, the zero-field magnetic specific heat follows $C_{\rm m}\propto T^{1.8}$, close to a quadratic temperature dependence, in contrast to the linear temperature dependence reported for the sister compound TlYbSe$_2$, which has been described in terms of the interplay between spinons and thermally excited gauge-flux excitations. Magnetization and ESR measurements establish pronounced easy-plane magnetic anisotropy, with $g_\perp/g_\parallel \approx 6.9$. The anomaly near $530$ mK exhibits a strongly anisotropic response to magnetic field. For $H\perp c$, it remains visible up to approximately $2$ T and continuously evolves toward a field-induced ordered phase above approximately $2.5$ T, followed by a sequence of field-induced phases that includes a $1/3$ magnetization plateau between approximately $5$ and $8$ T and full polarization near $17$ T. In contrast, for $H\parallel c$, the anomaly weakens and is suppressed near $3$ T, consistent with the recently reported confinement--deconfinement transition from an ordered state to a field-induced QSL.

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Bishnu P. Belbase, Arjun Unnikrishnan, Piyush Chhallare, Mohan B. Neupane, Eun Sang Choi, Sebastian Erdmann, Muhammad U. Akbar, Mamoun Hemmida, H. -A. Krug von Nidda, Philipp Gegenwart, Arnab Banerjee. 2026-09-10. Low temperature thermodynamics of $S_{\mathrm{eff}}=1/2$ triangular lattice quantum spin liquid candidate TlYbS$_2$. https://arxiv.org/abs/2609.11881

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