The recent observation [A. Oosawa et al., J. Phys. Condens. Matter 11, 265 (1999)] of the field-induced Neel ordering in spin-gap magnetic compound TlCuCl3 is interpreted as a Bose-Einstein condensation magnons. A Hartree-Fock-type calculation based on this picture shown to describe temperature dependence magnetization well.

The layered compound $\alpha$-RuCl$_3$ is composed of a honeycomb lattice magnetic Ru$^{3+}$ ions with the $4d^5$ electronic state. We have investigated properties via magnetization and specific heat measurements using single crystals. It was observed that undergoes structural phase transition at $T_{t}\,{\simeq}\,150$ K accompanied by fairly large hysteresis. This expected to be similar in closely related CrCl$_3$. magnetizations susceptibilities are strongly anisotropic, which mainly arise...

We report the results of magnetization and specific heat measurements on Ba$_3$CoSb$_2$O$_9$, in which magnetic Co$^{2+}$ ion has a fictitious spin-1/2, show evidence that spin-1/2 Heisenberg antiferromagnet regular triangular lattice is actually realized Ba$_3$CoSb$_2$O$_9$. found entire curve including one-third quantum plateau excellent agreement with theoretical calculations at quantitative level.

Half-integer thermal quantum Hall conductance has recently been reported for the two-dimensional honeycomb material α-RuCl3 We found that half-integer plateau appears even a magnetic field with no out-of-plane components. The measured field-angular variation of quantized same sign structure as topological Chern number pure Kitaev spin liquid. This observation suggests non-Abelian order associated fractionalization local moments persists in presence non-Kitaev interactions α-RuCl3.

We have performed high-field magnetization and electronic spin resonance (ESR) measurements on Ba3CoSb2O9 single crystals, which approximates the two-dimensional (2D) S=1/2 triangular-lattice Heisenberg antiferromagnet. For an applied magnetic field H parallel to ab plane, entire curve including plateau at one-third of saturation (Ms) is in excellent agreement with results theoretical calculations except a small step anomaly near (3/5)Ms, indicative theoretically undiscovered quantum phase...

The Kitaev quantum spin liquid displays the fractionalization of spins into Majorana fermions. emergent edge current is predicted to manifest itself in form a finite thermal Hall effect, feature commonly discussed topological superconductors. Here we report on conductivity $\kappa_{xy}$ measurements $\alpha$-RuCl$_3$, candidate magnet with two-dimensional honeycomb lattice. In spin-liquid (Kitaev paramagnetic) state below temperature characterized by interaction $J_K/k_B \sim 80$ K, positive...

Thermal signatures of fractionalized excitations are a fingerprint quantum spin liquids (QSLs). In the $J_{eff}=1/2$ honeycomb magnet $\alpha$-RuCl$_3$, QSL state emerges upon applying an in-plane magnetic field $H_{||}$ greater than critical $H_{C2} \approx$ 7 T along a-axis, where thermal Hall conductivity ($k_{XY}/T$) was reported to take on half-quantized value $k_{HQ}/T$. This finding discussed as signature emergent Majorana edge mode predicted for Kitaev QSL. The $H_{||}$- and...

The magnetic phase transitions of ${\mathrm{Cs}}_{2}{\mathrm{CuBr}}_{4},$ which may be described as a spin-$\frac{1}{2}$ quasi-two-dimensional frustrated antiferromagnet, were investigated by means magnetization and specific heat measurements. ${\mathrm{Cs}}_{2}{\mathrm{CuBr}}_{4}$ undergoes ordering at N\'eel temperature ${T}_{\mathrm{N}}=1.4\mathrm{K}$ zero field. curve has plateau approximately one-third the saturation for field H parallel to b c axes, while no was observed...

We report magnetocaloric and magnetic-torque evidence that in ${\mathrm{Cs}}_{2}{\mathrm{CuBr}}_{4}$---a geometrically frustrated Heisenberg $S=\frac{1}{2}$ triangular-lattice antiferromagnet---quantum fluctuations stabilize a series of spin states at simple increasing fractions the saturation magnetization ${M}_{s}$. Only first these states---at $M=\frac{1}{3}{M}_{s}$---has been theoretically predicted. discuss how higher fraction quantum might arise propose model arrangements. argue...

A spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) is a prototypical frustrated quantum magnet, which exhibits remarkable many-body effects that arise from the synergy between spin frustration and fluctuation. The ground-state properties of TLHAF are theoretically well understood. However, theoretical consensus regarding magnetic excitations limited. experimental study in TLHAFs has also been Here we show structure Ba3CoSb2O9 investigated by inelastic neutron scattering....

We have investigated the sample dependence of half-integer thermal Hall effect in $\alpha$-RuCl$_3$ under a magnetic field tilted 45 degree from $c$ axis to $a$ axis. find that with largest longitudinal conductivity ($\kappa_{xx}$) shows quantized expected Kitaev model. On other hand, was not observed samples smaller $\kappa_{xx}$. suggest suppressing scattering effects on phonon conduction, which broaden field-induced gap protecting chiral edge current Majorana fermions, is important observe effect.

The excitations in the Kitaev spin liquid (KSL) can be described by Majorana fermions, which have characteristic field dependence of bulk gap and topological edge modes. In high-field state layered honeycomb magnet <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mi>α</a:mi><a:mtext>−</a:mtext><a:msub><a:mrow><a:mi>RuCl</a:mi></a:mrow><a:mrow><a:mn>3</a:mn></a:mrow></a:msub></a:mrow></a:math>, experimental results supporting these features been reported...

The field-induced quantum-disordered state of layered honeycomb magnet α-RuCl

The temperature and field variations of the magnetization have been measured for which has a singlet ground state with an excitation gap. It is found that undergoes three-dimensional ordering in magnetic fields. phase boundaries between paramagnetic ordered states are determined . these directions coincide when normalized by g-factor. gap at zero re-evaluated as

The magnetic susceptibility and high-field magnetization process of NH 4 CuCl 3 with double chains have been measured using single crystals. No anomaly indicative the three-dimensional ordering is observed in data above 1.7 K. It found, by measurement down to 0.5 K, that contrast KCuCl TlCuCl , has a gapless ground state at zero field. curve two plateaus one-quarter three-quarters saturation magnetization, irrespective external field direction. origin attributed not anisotropy, but quantum...

High-field magnetization processes of S =1/2 double spin chain systems KCuCl 3 and TlCuCl have been measured up to 39 T at 4.2 1.7 K for both 1.0 0.5 using single crystals. A transition from a singlet ground state with an excitation gap gapless magnetic finite susceptibility occurs H c ∼20 6 , respectively. The critical field depends on the external direction due anisotropy g -factor. Δ is evaluated as Δ/ k B =31.1 7.5 . Although antiferromagnetic interactions in are stronger than those...

Neutron elastic scattering experiments have been performed on the spin gap system TlCuCl$_3$ in magnetic fields parallel to $b$-axis. The Bragg peaks which indicate field-induced N\'{e}el ordering were observed for field higher than $H_{\rm g}\approx 5.5$ T at $Q=(h, 0, l)$ with odd $l$ $a^*-c^*$ plane. structure ordered phase was determined. temperature and dependence of peak intensities boundary obtained discussed connection a recent theory describes as Bose-Einstein condensation magnons.

The Kitaev quantum spin liquid on a honeycomb lattice has received much interest in magnetism, mainly because of the possibility emergence novel excitations called Majorana quasiparticles. quest is under way to realize this exotic state actual materials. One promising materials layered material RuCl${}_{3}$, for which signatures quasiparticles have been reported. Here, authors investigate magnetic thermal conductivity RuCl${}_{3}$ along with bulk thermodynamic measurements. They find that...

Despite extensive investigations, a topological state that hosts Majorana edge modes in the magnetic field-induced quantum disordered of Kitaev candidate material $\alpha$-RuCl$_3$ has been hotly debated. To gain more insight into this issue, we measured thermal Hall conductivity $\kappa_{xy}$ various samples grown by Bridgman method. The results show half-integer effect is intimately related to magnitude longitudinal and N\'{e}el temperature at zero field, both which are sample dependent....

We report the results of low-temperature thermal and magnetic measurements on Ba$_3$CoNb$_2$O$_9$ powder, described as a uniform triangular-lattice antiferromagnet (TLAF) with fictitious spin-1/2. is found to undergo two-step antiferromagnetic transitions at $T_{\rm N1}=1.39~{\rm K}$ N2}=1.13~{\rm K}$. As field increased, both N1}$ N2}$ monotonically decrease. The vs temperature phase diagram indicates that exchange interactions are nearly Heisenberg type weak easy-axis anisotropy...

The magnetic structure of the double perovskite compound Sr$_2$CuTeO$_6$ was determined from neutron powder diffraction data. This material is magnetically described as an $S\,{=}\,1/2$ quasi-two-dimensional square-lattice Heisenberg model with antiferromagnetic nearest-neighbor and next-nearest-neighbor interactions. undergoes a phase transition at $T_{\rm N}\,{\simeq}\,29\,$ K. spin below N}$ N\'{e}el on square lattice, which means that interaction ($J_1$) stronger than ($J_2$), in...

The layered honeycomb magnet α-RuCl3 has been suggested to exhibit a field-induced quantum spin liquid state, in which the reported large thermal Hall effect close half-quantized value still remains subject of debate. Recently, oscillatory structures magnetothermal conductivity were and interpreted as oscillations charge-neutral particles. To investigate origin these structures, we performed comprehensive measurement in-plane κ(H) down low temperature (100 mK), well magnetization M, for...